Ultrasonic joining method and ultrasonic joining device in vacuum

The present invention relates to a method and a bonding apparatus for surface-activating the objects to be bonded and ultrasonically bonding them in a vacuum.

Conventionally, ultrasonic bonding has only used a method of bonding gold bonding projections in the atmosphere. By using gold, there is no oxide film and a stable bonding surface can be maintained, so bonding can be performed in the atmosphere. Products applying this method have been developed in the field of wire bonding in the semiconductor field and recently in the field of flip chips.

Further, in Patent Document 1, 10^-5A technique called normal temperature bonding, in which the metal bonding surface is sputter-etched with an Ar ion gun in a high vacuum below Torr, the oxide film and organic layer on the surface are removed, and the metals are directly bonded at room temperature, has been disclosed. There is. Usually 10^-8~10^-5It is a research-level device called Torr, which has a high vacuum and is difficult to use in mass production called an ion gun.

Further, Patent Document 2 describes a method of adsorbing OH groups on the bonding surface of the wafer surface with oxygen plasma to activate the surface and heat bonding.

<patcit num="1"><text>JP-A-54-124853</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 3-91227</text></patcit>

<p> Conventionally, ultrasonic bonding has only used a method of bonding gold bonding projections in the atmosphere. This is because the use of gold does not have an oxide film and a stable bonding surface can be maintained, so that bonding can be performed in the atmosphere, and bonding other than gold is difficult. In addition, when joining by ultrasonic vibration in the atmosphere, micro bubbles and residuals remain at the joining interface, creating gaps, so only about 50% can be joined. Further, in ultrasonic bonding, protrusions such as minute bumps can be bonded, but large surfaces cannot be bonded to each other. This is because it is virtually impossible in terms of energy to match the costumes. Further, when a part of the joining is started and a certain part is not joined, slipping at the interface does not occur, so that ultrasonic vibration joining in a substantially large area is impossible.</p><p> Further, in Patent Document 1, the surface activation bonding technique does not leave bubbles or residues, but requires a high vacuum process to prevent reattachment using an ion gun or the like, which is an expensive and complicated device. In addition, since it is at room temperature, a high load of 300 MPa is indispensable, which hinders mass production. In addition, there is a problem that it cannot be applied to other than metal.</p><p> Further, in Patent Document 2, OH groups are adsorbed and wafers are surface-bonded by hydrogen bonds, but heating at a high temperature is required.</p><p> Particles that become small dust are present on the bonding surface of a plurality of objects to be bonded that are in close contact with each other, and in the methods of Patent Documents 1 and 2, when the particles are bonded as a solid layer at a low temperature, there are gaps around the particles. Is formed, and it becomes a large void and is not joined. Especially in the case of laminating wafers, a normal wafer has 10 or more particles having a size of 0.2 μm or more. This is the value already found in the off-the-shelf catalog. Therefore, when the wafers are actually bonded to each other with a low-temperature solid layer, voids having a size of about 10 mm remain in several places. It is practically impossible to remove this because most cleaning methods are impossible and particles adhere to the wafer when it is handled after cleaning.</p><p> Therefore, the present invention has been made in view of the above circumstances, and the joint surfaces of a plurality of objects to be joined having surface shapes that are in close contact with each other are surface-activated by energy waves and then joined with a solid layer. It is an object of the present invention to provide a method and a joining apparatus for joining one or more particles on the joining surface with a voidless with a pressing force of 300 Mpa or less.</p>

<p> The means for both the joining method and the joining device according to the present invention for solving the above problems will be collectively described below. In order to solve the above problems, the joining method and the joining device according to the present invention are a method of joining a plurality of objects to be joined, in which the objects to be joined are contact-pressurized in a vacuum chamber under reduced pressure. (Claim 1) A joining device for joining a plurality of objects to be joined, which comprises a vacuum chamber and an ultrasonic vibration head and a head elevating shaft in the vacuum chamber. It is composed of a joining device, which is provided with a stage and a head, is held by a head and a stage in a vacuum chamber under reduced pressure, and the objects to be joined which are arranged to face each other are contact-pressurized and ultrasonic vibration is applied to join them. (Claim 19) The ultrasonic vibration referred to here means vibration whose frequency is not in the ultrasonic region and includes vibrations having a frequency lower than that, which contributes to bonding. The ultrasonic vibration is generally preferably in the ultrasonic vibration band of 20 khz to 200 Khz, but particularly in longitudinal vibration, a frequency of several hz to 20 khz, which is a lower frequency than that, is also effective and is included in the present invention. Conventionally, when bonding is performed by ultrasonic vibration in the atmosphere, bubbles remain at the bonding interface and gaps are created, so that only about 50% can be bonded. However, by joining in a vacuum, the joining area is increased without bubbles. As a result, the strength can be increased and the electrical resistance value can be decreased. Further, from the method of surface-activating the bonding surface of the object to be joined by an energy wave such as an atomic beam, an ion beam or plasma, the two objects to be joined are contact-pressurized, and ultrasonic vibration is applied to join them in a solid layer. Become. (Claims 2 and 20) Further, the joint surface of the object to be joined is surface-activated by an energy wave such as an atomic beam, an ion beam or plasma, and then the two objects to be joined are contacted. It consists of a joining device that presses and applies ultrasonic vibration to join in a solid layer. (Claims 2 and 20) Atoms on the bonded surface are activated by etching the bonded surface of the object to be bonded with an energy wave before bonding to remove deposits such as oxide films and organic substances on the surface. Atoms on the bonded surface are activated by etching the bonded surface of the object to be bonded with an energy wave before bonding to remove deposits such as oxide films and organic substances on the surface. The energy wave indicates an ion beam, an atomic beam, a plasma, or the like. The surface activation treatment by an energy wave refers to a treatment in which the bonding interface is activated by an atomic beam, an ion beam, or plasma to facilitate bonding. The joining principle by surface activation can be thought of as follows. In a substance such as a metal, the organic matter on the surface and the deposits such as an oxide film are etched and removed to form a dangling bond of an active metal atom on the surface, whereby the other dangling bonds are bonded to each other. Also, Si or glass, SiO₂In the case of oxides containing ceramics, the bonding surface is activated by OH groups by hydrophilic treatment with oxygen or nitrogen plasma, and the other OH groups are bonded to each other. In the case of plasma, in addition to decompression plasma, there is also atmospheric pressure plasma that can be processed under atmospheric pressure, which can be easily handled. According to these bonding principles, the present invention is to increase the bonding strength at a lower temperature by bonding after surface activation by an energy wave. Further, as shown in Patent Document 2, there is also a method in which OH groups are adsorbed on the bonding surface by oxygen plasma to activate the surface. With this method, even if it is exposed to the atmosphere once, it can be joined in the atmosphere or in a vacuum thereafter. Subsequently, if the surface activated state is maintained in a vacuum and the surface is joined by ultrasonic vibration, there are no deposits and the surface is activated. What could not be joined by itself can be joined. For example, with ultrasonic waves, only gold could be bonded in the atmosphere. In addition, since the surface activation method can only join the parts that come into contact with each other at the time of joining, it is difficult to join a hard metal at 100%, and only a soft metal such as gold or copper can be substantially joined. In addition, even vacuum chambers that oxidize quickly, such as Al, could not be joined. However, in the present invention, Al, Si, ceramic, SIO2, glass, oxide and the like can be bonded.</p><p> Further, the method comprises a method of joining with a pressing force of 300 Mpa or less at the time of joining. (Claim 3) Further, the present invention comprises an apparatus for joining with a pressing force of 300 Mpa or less at the time of joining. (Claim 21) The bonding load can be reduced to about 100 to 150 MPa, which is less than half that of the conventional surface-activated bonding, which is a practical level. In addition, it is possible to join even hard metals such as Ni, which have been difficult to join in the past. Table 1 shows the data of the case where the gold bump is bonded at room temperature and the case where the gold bump is ultrasonically bonded as shown in Patent Document 1 as an example in which the bonding load can be reduced. When joining gold metal protrusions, as shown in Table 1, they cannot be joined unless they are crushed with a high pressing force of about 300Mpa at room temperature. When this bump is on the surface of a semiconductor circuit, it generally causes damage depending on the circuit at 200Mpa or more. The conditions in Table 1 are the case where a semiconductor chip using gold bumps, which are 50 μm square and have a height of 20 μm and the bump height variation is 1 μm, is ultrasonically bonded onto a gold thin film substrate and at room temperature. It is the data when it is done. In the case of room temperature joining, it was possible to join for the first time at 80 g / bump, but when ultrasonic waves were applied, it was possible to join with a load of 40 g / bump or more. Therefore, it can be seen that it is necessary to crush a bump of 1 μm or more as a bump crushing allowance.</p><p><tables num="1"><img file="JP2005294824A_D0001.tif" /></tables> Further, the objects to be joined are a plurality of objects to be joined having a surface shape in which the objects to be joined are in close contact with each other, and the method comprises a method in which one or more particles are placed on the surface of the joint and a joining device. (Claims 4 and 22) Particles that become small dust are present on the bonding surface of a plurality of objects to be joined having a surface shape that is in close contact with each other, and if the particles are joined as a solid layer at a low temperature, gaps are formed around the particles. It becomes a large void and is not joined. To remove this, ultrasonic waves are applied at the time of joining, so that the stress is concentrated on the particle portion, so that it can be crushed or buried in the base material. Ultrasound is used to crush and / or bury particles, as surfaces cannot be bonded to each other by surface activation, but the bonding force is bonded by surface activation.</p><p> Further, the material to be bonded is composed of a wafer and a bonding device. (Claims 5 and 23) Especially in the bonding of wafers to each other, a normal wafer has 10 or more particles having a size of 0.2 μm or more, which is a value given in a ready-made catalog. Therefore, when the wafers are actually bonded to each other with a low-temperature solid layer, voids having a size of about 10 mm remain in several places, so this method is particularly effective.</p><p> Further, it comprises a method and a joining device in which the cleaning step by the energy wave and the joining step by ultrasonic vibration are performed in the same chamber. (Claims 6 and 24) Since it is possible to join immediately after cleaning by performing in the same chamber, it is possible to join before reattachment or activation declines. Further, since the handling of the object to be joined becomes unnecessary, it is possible to prevent the adhesion of particles and the like.</p><p> Further, it comprises a method of contacting while irradiating the energy wave and a joining device. (Claims 7 and 25) If joining is performed while irradiating an energy wave, the surface is in a state of being cleaned and activated until just before contact, so that joining is easier. In particular, activation needs to be bonded before the dangling bond disappears, and some materials disappear in a short time. For example, diamond is particularly short, so it has the potential to be joined by this method. The bonding device according to claim 6, wherein the ultrasonic vibration head serves as a plasma electrode and performs plasma cleaning while holding the object to be bonded. It is possible to use the horn portion as a plasma electrode, for example, to perform plasma cleaning while mechanically chucking and holding the object to be joined, and to superimpose the two objects to be joined and apply ultrasonic vibration to join them.</p><p> It also comprises a method in which the energy wave is plasma and a joining device. In addition, compared to conventional room temperature bonding, which cannot be bonded if there is even a small amount of reattachment, ultrasonic vibration is also used, so it is similar to room temperature bonding.^-8~10^-5There is no need for a high vacuum like Torr, and it is a simple 10^-2Since it is possible to use a low vacuum of about Torr, a simple plasma can be used instead of an ion beam or atomic beam that is not suitable for mass production. Since it is possible with a simple device, it is possible to reduce the cost and simplification of equipment, and it is suitable for mass production.</p><p> Further, the method comprises a method in which the energy wave is atmospheric pressure plasma and a joining device. (Claims 8 and 26) If the plasma is atmospheric pressure plasma, it can be easily used in the atmosphere. It is also suitable for chemical treatments such as adhesion of OH groups and nitrogen substitution.</p><p> Further, the method comprises a method in which the energy wave is decompression plasma and a joining device. (Claims 9 and 27) If the plasma is a reduced pressure plasma, the etching force is strong and impurities can be efficiently removed.</p><p> Further, at least one of the objects to be bonded is a semiconductor, and the bonded surfaces of the objects to be bonded are dry-cleaned under reduced pressure with plasma consisting of an alternating power source that switches to both + and-electric fields, and then the cleaned bonded surfaces are brought to room temperature. It consists of a joining method and a joining device. (Claims 10 and 28) When at least one of the objects to be joined is a semiconductor, when + ions or-electrons collide with the circuit surface of the semiconductor, the circuit, especially the gate oxide film, is charged-up damaged. Become. In order to avoid this, + ions and-electrons can be alternately collided to neutralize the charge before it is charged. By doing so, it becomes possible to avoid charge-up damage. It also comprises a method and a joining device in which the alternating power supply is switched evenly from 1: 5. Charge-up damage can be reduced if the ratio of alternating switches is more equal than 1: 5. Also 1: It is more preferable if it is more even than 2. Further, the alternating power supply comprises a method in which Vdc is a value and a + region is 20% to 40%, and a joining device. In addition, since Ar and oxygen plasma become + ions, the electrode holding the object to be joined must have a-electric field in order to accelerate and collide with the cleaning surface for etching. Therefore, the Vdc value is preferably-. Further, it comprises a method of plasma including an alternating power source capable of adjusting the Vdc value and a joining device. If +-is made too even, the chances of + ions colliding will decrease and the cleaning capacity will decrease. Also-causes electronic charge-up damage. Therefore, by making it possible to adjust the optimum Vdc value for each application, it is possible to exert the optimum cleaning ability without causing charge-up damage, which is effective. Further, it comprises a method in which the alternating power source is RF plasma and a joining device. By using RF plasma consisting of alternating current as an alternating power source, it is possible to easily switch the electric field between + and-alternately. Further, the ratio of + and-can be easily adjusted by adjusting the Vdc value. Further, the alternating power source includes a method in which plasma is composed of pulse waves and a joining device. A pulse wave can be used as an alternating power source. If it is a pulse wave, it can rise and fall sharply, and the cleaning ability is also improved. It also consists of a method and a joining device in which the pulse wave is a plasma consisting of an alternating power source whose + region time and-region time can be adjusted. In addition to adjusting the Vdc value, the + -ratio and collision time can be managed by adjusting the pulse width and interval, so it is possible to set more finely than the AC RF, making it easier to find the optimum value. Fig. 4 shows the RF plasma power supply diagram, and Fig. 5 shows the pulse wave plasma power supply diagram. Not only adjusting the dc value, but also adjusting the pulse width and interval can manage the + -ratio and collision time, so it is possible to set more finely than the AC RF, and it is easy to find the optimum value. Fig. 4 shows the RF plasma power supply diagram, and Fig. 5 shows the pulse wave plasma power supply diagram. Not only adjusting the dc value, but also adjusting the pulse width and interval can manage the + -ratio and collision time, so it is possible to set more finely than the AC RF, and it is easy to find the optimum value. Fig. 4 shows the RF plasma power supply diagram, and Fig. 5 shows the pulse wave plasma power supply diagram.</p><p> Further, it comprises a method of heating within 180 ° C at the time of joining and a joining device. (Claims 11 and 29) The joining margin is increased by using heating together at the time of joining. In addition, it is possible to join what could not be joined at room temperature in the past. In particular, those having a short activation time reattach quickly, and when used in combination with heating, grain boundary diffusion at the bonding interface becomes easy and bonding becomes easy. Also on the horn side, heating can be used together by providing a heater at the nodal point or by conducting heat conduction to the horn by an external heating means. Since the lead-tin solder is 183 ° C in the conventional low-temperature bonding, it is effective to be able to bond at a temperature lower than that. Further, it is possible and preferable to join at 150 ° C or lower and 100 ° C or lower. Further, it is even better if it is at room temperature. In particular, gold is preferable because it is easy to join at a low temperature.</p><p> Further, the method comprises a method in which the ultrasonic vibration is longitudinal vibration and a joining device. (Claims 12 and 30) Further, the method and a joining device include a method in which the ultrasonic vibration head is a longitudinal vibration type and a vibrator is located above a horn. As a method of applying ultrasonic vibration to surface-bond a large area such as a wafer, lateral vibration is also conceivable, but it requires a considerable amount of energy to perform surface bonding. Since the bonding is performed by the surface activating force this time, it is sufficient that the ultrasonic waves can contribute to the reduction of weight, the crushing of particles, and the burial. However, it is impossible to vibrate including the surface parts joined at the same time by lateral vibration. Therefore, if longitudinal vibration is used, even if bonding is not possible, even if other surface parts are bonded with a small amount of energy, it is effective in reducing the load, crushing particles, and burying them. In addition, although lateral vibration has been used in the past to reduce damage, it can be seen that longitudinal vibration is effective due to problems with joint uniformity and misalignment. However, vertical vibration causes damage, so the point is how to reduce the damage and join with vertical vibration. The solution is to reduce the amplitude to 1 μm or less. By doing so, the impact can be absorbed by the elastic deformation of the object to be joined. For example, a semiconductor chip with a gold bump having a height of 20 μm can absorb an amplitude of 1 μm by elastic deformation of the bump. Further, by attaching an elastic material to the tip of the vibration transmission horn, it is possible to absorb the impact due to the longitudinal vibration. The impact of longitudinal vibration becomes a problem because the operation is like hitting the chip with a mallet from above while creating a gap between the vibration transmission horn and the chip. Therefore, damage can be reduced by absorbing it with an elastic material or bump so that no gap is opened. In joining, since the stress change is transmitted to the joining interface, there is no problem because a new surface appears due to the crushing and movement of particles at the interface and the joining proceeds. As a head structure in an ultrasonic bonding device using these longitudinal vibrations, an efficient oscillator, a vibration transmission horn, and a bonded device including 50% or more longitudinal vibrations shown in FIG. It consists of a method of joining objects in a vertically arranged state. Especially in the case of ultrasonic bonding after surface activation, it is not necessary to break the oxide film at the bonding interface by sliding due to lateral vibration, so if longitudinal vibration is applied to increase the stress at the bonding interface, the bonding load will be increased. It can be dropped and joined. Further, by adopting a vertical vibration head structure, it is possible to use a ceramic material for the horn and incorporate an electrostatic chuck, and since the upper part can be brought into close contact with the oscillator, plasma can be concentrated and generated only in the lower part, which is preferable. It becomes a structure. Further, although it is impossible to cause lateral vibration if the bonding area is large, it can also be applied to surface bonding with a large area, for example, wafer bonding in longitudinal vibration. Further, in lateral vibration, stress is concentrated around the joint surface, but in longitudinal vibration, uniform stress is generated, and uniform bonding is possible over a large area, which is suitable.</p><p> Further, among the holding tools that hold the two objects to be opposed to each other, the two objects are contact-pressurized in the joining mechanism in which a plurality of piezo actuators are in contact with or connected to the object to be joined and the surface of at least one of the holding tools. In this state, the piezo actuator expands and contracts to apply longitudinal vibration to join the piezo actuator. (13) Two holding tools for holding two opposing objects to be pressed, an elevating shaft for moving and pressurizing at least one holding tool in the direction of the pressurizing axis, a plurality of piezo actuators, and a plurality of piezos. A joint in which a plurality of piezo actuators are in contact with or connected to a surface facing the object to be pressed of at least one of the holding tools having a vibration applying means for controlling vibration of the actuator and holding both objects to be pressed facing each other. In the mechanism, from the joining device that applies longitudinal vibration by the expansion and contraction operation of the piezo actuator while both objects to be pressed are contact-pressurized.Become. (Claim 31) The piezo element refers to a piezoelectric element that expands and contracts when a voltage is applied, and is included in the piezoelectric element. Further, the material of the piezoelectric element does not matter. As a method of joining objects to be joined, a method of applying ultrasonic vibration to join them has been conventionally known. The vibration referred to here refers to a vibration including a low frequency to ultrasonic region, and is included in the present invention. In addition, ultrasonic waves are often used for bonding, which is preferable. Further, it is preferable that a large amount of energy can be output by resonating with the holding tool. Further, even in the case of heat bonding or bonding by surface activation, the stress at the bonding interface is increased by applying vibration, so that the bonding load is about half. This is because, in order to join, the unevenness of the minute interface needs to be crushed and brought into close contact with each other, which contributes to the increase in stress due to vibration. Further, in the case of a large area such as a wafer as the object to be bonded, a plurality of piezos are applied to the surface facing the object to be bonded of at least one holding tool, which is a method in which vibration is applied under a large area and a high load. In the joining mechanism in which the actuators are in contact or connected, the above method of joining by applying longitudinal vibration by the expansion / contraction operation of the piezo actuator while the two objects to be joined are contact-pressurized is effective. The method according to Item 16, wherein the number of piezo actuators arranged is 3, and the piezo actuators are arranged at equal intervals on the circumference. Further, the number of piezo actuators arranged is 3, and the piezo actuators are arranged at equal intervals on the circumference to form the joining device described above. As for the arrangement position of the piezo actuator to be the oscillator, for example, if it is arranged at equal intervals on the circumference from the center of the wafer to be joined, the load is evenly applied and the vibration is evenly applied to resonate. It is preferable because it is easy. As a minimum, it is 3 to receive so as not to tilt on the surface. In addition, 3 is preferable for three-dimensional operation. The minimum number is to place three places on the circumference, which is efficient and stable.</p><p> Further, the method comprises a method in which the vibration phases between the plurality of piezo actuators are controlled in a state where the two objects to be joined are contact-pressurized, and the two objects are expanded and contracted so as to sequentially flow in the rotation direction. (Claim 14) A means for controlling the vibration phase between a plurality of piezo actuators is provided, and the vibration phase between the plurality of piezo actuators is controlled in a state where the two objects to be joined are contact-pressurized, and waves are sequentially waved in the rotation direction. It consists of a joining device that expands and contracts to join so that it can flow. (Claim 32) Three-dimensional operation is possible by controlling the vibration phase of the piezo actuators arranged in parallel. In particular, when they are arranged at three locations on the circumference at equal intervals, for example, if a stretching voltage consisting of a sine curve is applied by a vibration applying means and the phase is shifted by 120 °, waves will flow sequentially in the rotation direction3 It is possible to make a dimensional vibration operation. As mentioned above, it is better to apply the operation so that a wave like a wave flows rather than simply the longitudinal vibration, and it is possible to remove the voids generated from the gaps of the interface that are generated even in the air or vacuum that are caught at the time of joining. It is possible by pushing it out. Further, since the concentrated load flows sequentially in the joining, it is also effective for the joining in which the minute irregularities based on the above-mentioned principle are brought into close contact with each other. In particular, compared to uniformly pressurizing the entire surface, it is easier to join with a smaller load by moving while applying a concentrated load to a certain part. The vibration here includes such a three-dimensional continuous operation.</p><p> Further, the method comprises a method of increasing the pressing force and / or the ultrasonic vibration energy by an increasing curve in the joining process in which the ultrasonic vibration is applied to join. (Claims 15 and 33) Further, a method of increasing the pressing force and / or the ultrasonic vibration energy in proportion to the increase in the joint area is preferable. Considering the joining process microscopically, it is thought that the joining area will gradually increase as the joining progresses due to the small irregularities on the joining surface and the difference in height between multiple joints. Therefore, it is necessary to apply a pressing force and ultrasonic vibration energy proportional to the joining area in the joining process. However, in the initial stage of joining, when ultrasonic vibration energy exceeding the joining area is applied, destruction or damage occurs due to the addition of extra energy to the joining portion or the base material. Also, when considering the transmission of ultrasonic vibration, the vibration is sequentially transmitted from the resonator to the first object to be joined, the second object to be joined, and the stage, but it is added in a situation where constant vibration is given. It is easy to understand that the vibration moves to the lower layer because the frictional force at each transmission interface increases as the pressure increases. Therefore, when a large pressing force is applied from the beginning, the intended slip for joining does not occur between the first and second objects to be joined, and if the base material of the second object to be joined is soft, ultrasonic vibration energy is absorbed. It will not be possible to join. Therefore, in the joining process, it is effective to increase the pressing force and / or the ultrasonic energy for joining, and as a method of controlling these, it is effective to increase the pressing force and / or the ultrasonic energy with an ascending curve. Further, it is preferable to increase the joint area in proportion to the increase. Supplementally, when ultrasonic vibration is applied with a low pressing force at the beginning, joining of a certain area starts. Then, since the first object to be joined is coupled to the second object with a constant force, the amplitude between the first and second objects becomes small, and the amplitude between the resonator and the first object is reduced. Then the slip becomes large. Therefore, when the pressing force is increased, slippage is suppressed as the frictional force between the resonator and the first object to be joined increases, ultrasonic vibration energy is transmitted to the first object to be joined, and the joint area becomes larger. Also, that Since the optimum ultrasonic vibration energy from time to time is applied to the joints in a concentrated manner by pressure control, good joints can be performed without causing extra damage. As the bonding area increases, the bonding force between the first and second objects to be bonded increases and the amplitude decreases, so that the increase in the bonding area can be read by the following method. It has an amplitude detecting means for detecting the amplitude of the first and second objects to be joined, and comprises a method of reading the increase in the joint area by measuring the amplitude between the first and second objects to be joined. Moreover, even if it is not the actual amplitude of the bonding interface, if there is no unstable element, it can be estimated in the following order. It has a means for detecting the amplitude of the object to be joined, and comprises a method of reading the increase in the joint area by measuring the amplitude of the first object to be joined. It also comprises a method of detecting the amplitude of the resonator and reading the increase in the junction area by measuring the amplitude of the resonator. Further, since the amplitude of the oscillator can be estimated from the return current value with respect to the output current applied to the piezo element of the oscillator, the method is to read the increase in the junction area from the return current value with respect to the output current of the oscillator. As a method of always setting the amplitude at the interface to be actually joined to the optimum value for joining, there are a plurality of amplitude detecting means for detecting the amplitude of the first and second objects to be joined, and the first and second It consists of a method of controlling the pressing force and / or the ultrasonic vibration energy so that the amplitude between the objects to be joined becomes an arbitrary constant value. Further, the method includes a means for detecting the amplitude of the object to be joined, and controls the pressing force and / or the ultrasonic vibration energy so that the amplitude of the first object to be joined becomes an arbitrary constant value. This is because the amplitude decreases as the bonding area increases as described above, so if the pressing force and / or the ultrasonic vibration energy is increased so that the amplitude between the first and second objects to be joined is constant, it is always possible. Since a constant amplitude is obtained at the bonding interface, good bonding proceeds. Further, assuming that there is no change in the situation in which the second object to be joined is held on the stage, the same result can be obtained simply by reading the amplitude of the first object to be joined. However, the amplitude of the resonator and the oscillator is affected by the slip between the resonator and the first object to be joined. Adoption is not preferable because it is not fixed. In order to eliminate the damage caused by applying too much ultrasonic energy, and the joining is completed satisfactorily without any damage, the ultrasonic vibration occurs when the pressing force and / or the ultrasonic vibration energy in the previous period reaches a certain target value. Consists of how to stop. Since the pressing force and ultrasonic vibration energy required to join the target joining area are predetermined, the ultrasonic vibration may be stopped when the target value is reached. Conventionally, it is divided into a vertical drive control unit and a load control mechanism unit, and since the pressing force is controlled by the air pressure by the air cylinder, the response is slow, and the vertical movement speed is changed to the speed of the air cylinder from the shock resistance of the air cylinder. Although it was restricted and could not operate at high speed, the joining mechanism has a vertical drive motor and a pressing force detecting means in the vertical driving mechanism of the joining work, and the pressing force control is controlled by the torque of the vertical drive motor. Consists of methods. By adopting this method, it is possible to perform pressurization operation with quick response and high-speed up / down operation.</p><p> Further, the present invention comprises a method and a joining device having an amplitude detecting means, measuring the amplitude of a vibrating object in the joining process of applying the ultrasonic vibration to join, and controlling the ultrasonic vibration energy so as to obtain a target value. .. (Claims 16 and 34) It is important that the amplitude between the first and second objects to be actually joined is set to an arbitrary target value, and the vibration objects to be measured next are described in the preferred order. First, the vibrating object is the first and second objects to be joined, and the method comprises a method of measuring the amplitude between the first and second objects to be joined and controlling the ultrasonic vibration energy so as to obtain a target value. .. Further, assuming that the second object to be bonded is stably adsorbed and held on the stage, the amplitude of the first object to be measured is measured as a vibrating object to be measured without measuring the amplitude of the second object to be bonded. It can be achieved by. Further, assuming that the friction between the first object to be joined and the resonator is stable and the vibration transmission is stable, this can be achieved by measuring the amplitude of the resonator as the vibration object to be measured. Further, in order to eliminate defective products that are damaged by excessive vibration, a method of stopping ultrasonic vibration when the measured amplitude exceeds an arbitrary maximum amplitude value is used. Further, in order to eliminate a defective joint product due to the vibration being too small, a method of stopping the ultrasonic vibration when the measured amplitude does not exceed an arbitrary minimum amplitude value is used. Further, by providing these amplitude detecting means on the recognition means moving table, it is possible to easily move to the measuring place even if there is a difference in size depending on the type of the object to be joined, and one detection means. It is also possible to measure multiple locations by means. Further, since the amplitude detecting means uses a vortex current type, a capacitance type, a light irradiation type, or a sonic type detecting means, a detection means that is two orders of magnitude cheaper can be adopted, and because of its small size, it is a complicated place. But measurement is possible. In the past, a laser Doppler measuring instrument was used to actually capture the movement of a vibrating object at that speed with its resolution, which was vibrating at several tens of kHz, so a very expensive one was required. However, the purpose of this time is whether or not it is the target value of amplitude, and the difference is divided. It is good, and it is not necessary to know what μm and what Hz the actual amplitude is. Therefore, the purpose can be achieved if the conventional vortex current type, capacitance type, light irradiation type, or sonic type detection means having no high-speed response can be used and the average difference between the oscillating high-speed oscillating means can be detected. When this method is particularly suitable, the method comprises a method in which at least one object to be joined is provided with metal protrusions and at least one object to be joined is a semiconductor chip. The lower metal part of the metal protrusion that becomes the electrode of the semiconductor is easily damaged by microcracks due to ultrasonic vibration. Therefore, this method is particularly suitable. In the bonding method and apparatus according to the present invention as described above, in the bonding process of ultrasonically bonding objects to be bonded, an amplitude detecting means is provided, the amplitude of the vibrating object is measured, and the object value is obtained. Since the sonic vibration energy is controlled, a stable target amplitude can be obtained even if disturbances such as slight pressure and deviation of the bonding process, dust, and variation of the friction coefficient due to the surface condition of the object to be bonded are applied, and the target amplitude is stable. Ultrasonic bonding can be achieved. Further, since the amplitude between the first and second objects to be actually joined can be set to an arbitrary target value measured by the amplitude detecting means, a reliable joining state can be obtained. In addition, by catching abnormal vibration, it is possible to prevent defective products from being produced. Further, an inexpensive and compact amplitude detecting means can be adopted. In order to have an amplitude detecting means, measure the amplitude of the vibrating object, and control the ultrasonic vibration energy so as to obtain the target value, a delicate pressing force and a deviation of the bonding process, dust, and the surface of the object to be bonded are used. A stable target amplitude can be obtained even if a disturbance such as a variation in the friction coefficient depending on the state is applied, and a stable ultrasonic bonding can be achieved. Further, since the amplitude between the first and second objects to be actually joined can be set to an arbitrary target value measured by the amplitude detecting means, a reliable joining state can be obtained. In addition, by catching abnormal vibration, it is possible to prevent defective products from being produced. Further, an inexpensive and compact amplitude detecting means can be adopted. In order to have an amplitude detecting means, measure the amplitude of the vibrating object, and control the ultrasonic vibration energy so as to obtain the target value, a delicate pressing force and a deviation of the bonding process, dust, and the surface of the object to be bonded are used. A stable target amplitude can be obtained even if a disturbance such as a variation in the friction coefficient depending on the state is applied, and a stable ultrasonic bonding can be achieved. Further, since the amplitude between the first and second objects to be actually joined can be set to an arbitrary target value measured by the amplitude detecting means, a reliable joining state can be obtained. In addition, by catching abnormal vibration, it is possible to prevent defective products from being produced. Further, an inexpensive and compact amplitude detecting means can be adopted.</p><p> Further, the material to be joined comprises a method and a joining device in which the object to be joined is a semiconductor wafer or chip provided with a plurality of minute bumps. (Claims 17, 18, 35) Further, the object to be joined made by the above method comprises a semiconductor device composed of a semiconductor wafer or a chip provided with a plurality of minute bumps. If the object to be bonded is a semiconductor wafer or chip provided with bumps that serve as electrodes, the bonding portion will be a large number of protrusions, so compared to surface bonding that bonds the entire area at once, ultrasonic bonding will be performed sequentially on each protrusion bump. It is suitable for ultrasonic bonding because it can be advanced.</p>

<p> This is a method in which the joint surfaces of a plurality of objects to be joined, which are in close contact with each other, are surface-activated by energy waves and then joined in a solid layer. By contact-pressurizing objects and applying ultrasonic vibration, they can be bonded with a pressing force of 300 Mpa or less, and particles are crushed and / or buried even in a bonded object such as a wafer in which particles are present on the bonding surface, and voidless. Can be joined with.</p><p> Further, even if the bonding surface is oxidized in the atmosphere, it can be bonded by applying ultrasonic waves while maintaining a vacuum after plasma cleaning. This makes it possible to join Al, Si, ceramics, SIO2, glass, oxides, etc., which was difficult to join at low temperatures in the past. In addition, the joining load can be suppressed to less than half as compared with the conventional surface-activated joining, and even a hard metal, which has been difficult to be substantially joined in the past, can be joined. Further, by using longitudinal vibration, it is possible to join a large area such as a wafer.</p>

A preferred embodiment of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows an ultrasonic bonding device in vacuum according to one embodiment of the present invention. In this embodiment, an example is given as an apparatus for joining the upper wafer, which is the first object to be bonded, and the lower wafer, which is the second object to be bonded.

First, the device configuration will be described. A head 7 for holding the upper wafer and a stage 8 for holding the lower wafer are arranged in the vacuum chamber 11, and the head rotates the Z-axis elevating mechanism 2 and the Z-axis elevating mechanism 2 to which the torque-controlled elevating drive motor 1 is connected. It is composed of an alignment moving means in the X, Y, and θ directions and an elevating means in the Z direction by the θ-axis mechanism for moving the head portion and the XY alignment table 6 for moving the head portion in the XY horizontal direction. By feeding back the pressing force at the time of joining detected by the pressure detecting means 4 to the torque control type elevating drive motor 1, position control and pressure control can be switched. The pressure detecting means 4 can also be used to detect contact between objects to be joined. The XY alignment table 6 uses a means that can be used even in a vacuum, but since the Z and θ-axis mechanisms are installed outside the decompression chamber, the head and the outside are movably cut off by the O-ring 5. As the transfer type of the head and the stage and the holding means of the base material, a mechanical chucking method may be used, but it is preferable to provide an electrostatic chuck. In addition, it is equipped with a heater for heating and has two functions of holding means and heating means. As the means for holding the object to be joined of the head and the stage, a mechanical chucking method may be used, but it is preferable to provide an electrostatic chuck. In addition, it is equipped with a heater for heating and also serves as a plasma electrode, and has three functions of holding means, heating means, and plasma generating means.

Since the head part also uses ultrasonic vibration at the time of joining, the head 7 is composed of a horn holding part 24, a horn 25, and an oscillator 26. The vibration generated by the oscillator is transmitted to the horn, and the horn holds the ultrasonic vibration. Transfer to the joint. The horn holding portion comprises means for holding the vibration of the horn or the vibrator so as not to kill it. Since the transmission coefficient at this time is determined by the friction coefficient and pressure of the horn and the object to be joined, it is preferable to control the pressing force in proportion to the joining area as the joining progresses. Further, when joining a large area such as a wafer, it is impossible for a lateral vibration type ultrasonic head to vibrate laterally because the bonding area is large, but if it is a longitudinal vibration type ultrasonic head, it is impossible. Large area surface joining is also possible.

As a depressurizing means, a vacuum pump 17 is connected to an exhaust pipe 15, and an exhaust valve 16 opens and closes and adjusts the flow rate, so that the degree of vacuum can be adjusted. On the suction side, the intake gas switching valve 20 is connected to the intake pipe 18, and the intake valve 19 opens and closes and adjusts the flow rate. As the intake gas, two types of plasma reaction gases can be connected, for example, Ar and oxygen can be connected. The other is connected to the atmosphere or nitrogen for release to the atmosphere. The degree of vacuum and the reaction gas concentration can be adjusted to the optimum values by adjusting the flow rate including the opening and closing of the intake valve 19 and the exhaust valve 16. In addition, automatic feedback can be provided by installing a vacuum pressure sensor in the vacuum chamber.

Alignment mark recognition means consisting of an optical system for alignment is arranged outside the vacuum chamber above the stage standby position and below the head. The number of recognition means should be at least one on the stage and one on the head side, and if you want to recognize a small object such as a chip, the alignment mark has a shape that can read the θ direction component and two marks in one field of view. By arranging them, one recognition means can sufficiently read them, but as in this embodiment, it is better to arrange two large wafers in the radial direction at both ends to read with higher accuracy in the θ direction. It is preferable because it can be done. Further, the recognition means may be provided with means that can move in the horizontal direction or the focal direction so that the alignment mark at an arbitrary position can be read. Further, the recognition means includes, for example, a camera with an optical lens made of visible light or IR (infrared) light. A window made of a material that allows the optical system of the recognition means to pass through, for example, glass, is arranged in the vacuum chamber, and the alignment mark of the object to be joined in the vacuum chamber is recognized through the window. On the object to be joined, for example, alignment marks are provided on the opposing surfaces of the upper wafer and the lower wafer so that they can be recognized with high position accuracy. The alignment mark preferably has a specific shape, but a part of a circuit pattern or the like applied on the wafer may be diverted. In addition, if there is no mark, an outer shape such as an orifra can be used. At the stage standby position, both alignment marks on the upper and lower wafers are read, the stage is moved to the joining position, and the alignment is moved in the X, Y, and θ directions on the head side. In order to reflect the reading result of the standby position at the joint position, the relative movement distance vector between the standby position and the joint position of the stage must be accurate so that the same result is repeatedly obtained. Therefore, a guide having a high-precision repeatability is used, and a linear scale that reads the position recognition on both sides with high precision is arranged. A method to improve the stop position accuracy by feeding back the linear scale to the moving means, and a cylinder-like or bolt with a simple moving means If there is backlash such as a tonut mechanism, the linear scale is read at both stop positions, and the excess or insufficient amount is easily corrected by considering it when moving the head side alignment moving means. Accuracy can be achieved. In addition, in the case of fine alignment with high accuracy at the nano level, after rough positioning, visible light and IR (infrared) are used for both visible light and IR (infrared) in the head side recognition means with the upper and lower wafers close to each other by several μm. By using a recognition means and providing a transmission hole or a transparent material at the alignment mark position of the stage, the alignment mark on both wafers is infrared-transmitted through the stage from the bottom and simultaneously recognized, and X, Y again. , Can be aligned in the θ direction. When the recognition means has a moving means in the focal direction, the upper and lower sides can be recognized individually, but it is preferable to recognize them in close proximity to each other in terms of accuracy. In the case of fine alignment, it is possible to improve the accuracy by repeatedly aligning, and since the θ direction is affected by misalignment, after entering within a certain range, aligning only in the XY direction will improve the accuracy to the nano level. Can be improved. By using a sub-pixel algorithm as an image recognition means, it is possible to obtain recognition accuracy higher than the resolution of infrared rays. In addition, if the alignment is done in close proximity, the amount of Z movement required for joining will be within a minimum of several μm, so backlash and tilt with respect to Z movement can be minimized and high-precision nano-level joining accuracy is achieved. can do. By providing the above, the alignment marks on both wafers can be simultaneously recognized by passing through the stage from the lower part through infrared transmission, and can be aligned again in the X, Y, and θ directions. When the recognition means has the moving means in the focal direction, the upper and lower sides can be recognized individually, but it is preferable to recognize them in close proximity to each other in terms of accuracy. In the case of fine alignment, it is possible to improve the accuracy by repeatedly aligning, and since the θ direction is affected by misalignment, after entering within a certain range, aligning only in the XY direction will improve the accuracy to the nano level. Can be improved. By using a sub-pixel algorithm as an image recognition means, it is possible to obtain recognition accuracy higher than the resolution of infrared rays. In addition, if the alignment is done in close proximity, the amount of Z movement required for joining will be within a minimum of several μm, so backlash and tilt with respect to Z movement can be minimized and high-precision nano-level joining accuracy is achieved. can do. By providing the above, the alignment marks on both wafers can be simultaneously recognized by passing through the stage from the lower part through infrared transmission, and can be aligned again in the X, Y, and θ directions. When the recognition means has a moving means in the focal direction, the upper and lower sides can be recognized individually, but it is preferable to recognize them in close proximity to each other in terms of accuracy. In the case of fine alignment, it is possible to improve the accuracy by repeatedly aligning, and since the θ direction is affected by misalignment, after entering within a certain range, aligning only in the XY direction will improve the accuracy to the nano level. Can be improved. By using a sub-pixel algorithm as an image recognition means, it is possible to obtain recognition accuracy higher than the resolution of infrared rays. In addition, if the alignment is done in close proximity, the amount of Z movement required for joining will be within a minimum of several μm, so backlash and tilt with respect to Z movement can be minimized and high-precision nano-level joining accuracy is achieved. can do.

Next, the operation flow will be explained with reference to Fig. 2. First, as shown in 1, the upper wafer and the lower wafer are held by the stage and the head with the front door of the vacuum chamber open. This can be done manually, but it can also be loaded automatically from the cassette. Next, as shown in 2, the front door is closed and the pressure inside the vacuum chamber is reduced. 10 to remove impurities^-3It is preferable to reduce the pressure below Torr. Subsequently, as shown in 3 and 4, a plasma reaction gas such as Ar is supplied, for example, 10^-2A plasma power supply is applied to the plasma electrode at a constant vacuum degree of about Torr to generate plasma. The generated plasma ions collide with the surface of the wafer held on the power supply side, and the surface is activated by etching the deposits such as the oxide film and the organic substance layer on the surface. It is possible to wash both wafers at the same time, but it is also possible to wash them alternately by switching one matching box. Also to remove reaction gas and etchings after or during cleaning 10^-3It is preferable to reduce the pressure below Torr. In order to remove Ar driven into the joint surface, heating at about 100 to 200 ° C can also be used together. Subsequently, as shown in 5, the alignment marks on the upper and lower wafers are read in vacuum by the recognition means on the head side and the stage side at the stage standby position to recognize the position. Subsequently, as shown in 6, the stage slides to the joint position. The relative movement between the recognized standby position and the sliding joint position at this time is performed with high accuracy using a linear scale. If nano-level high accuracy is required, the process shown in 7 is added. After rough positioning, visible light and IR (infrared) combined recognition means are used for the head side recognition means with the upper wafer and lower wafer close to each other by about several μm, and they are transmitted to the alignment mark position of the stage. By providing holes and a transparent material, it is possible to transmit through the stage from the lower part, simultaneously recognize the alignment marks on both wafers, and align them again in the X, Y, and θ directions. In this case, it is possible to improve the accuracy by repeatedly aligning, and since the θ direction is affected by the misalignment, the accuracy can be improved to the nano level by aligning only in the XY direction after entering within a certain range. .. Subsequently, as shown in 8, the head is lowered, both wafers are brought into contact with each other, and the position control is switched to the pressure control to pressurize. With the contact detected by the pressure detecting means and the height position recognized, the value of the pressure detecting means is fed back to the torque control type elevating drive motor to control the pressure so as to reach the set pressure. Ultrasonic vibration is applied with the initial pressurization applied, and the stress at the bonding interface increases, so that the bonding proceeds with a low load. It is preferable that the pressing force is increased in proportion to the increase in the joint area. In addition, particles that become small dust exist on the bonding surface of the workpieces that have a surface shape that adheres to each other like a wafer, and if they are bonded in a solid layer at low temperature, gaps will be created around the particles, resulting in large voids. It will not be joined. To remove this, apply ultrasonic waves at the time of joining to the particle part. Due to the concentration of stress, it can be crushed or buried in the substrate. Ultrasound is used to crush and / or bury particles, as surfaces cannot be bonded to each other by surface activation, but the bonding force is bonded by surface activation. Since it is in a vacuum, it can be joined without gaps as long as there are no particles. Also, if necessary, heating is applied at the time of joining. Further, in the case of heating after ultrasonic bonding in order to remove residual stress or increase the bonding strength, it is also possible to heat in a state where the accuracy is maintained by contacting at room temperature and then raising the temperature. Subsequently, as shown in 9, the head-side holding means is released and the head is raised. Subsequently, as shown in 10, the stage is returned to the standby position and the inside of the vacuum chamber is released to the atmosphere. Then, as shown in 11, the front door is opened and the joined upper and lower wafers are taken out. It may be done manually, but it is preferable to automatically unload it into the cassette.

In the above embodiment, the wafer is raised as the object to be bonded, but a chip and a substrate may be used. When the bonding area is large such as a wafer, the ultrasonic vibration head structure should also be a longitudinal vibration type, but if the bonding area is small such as a chip, the lateral vibration type as shown in Fig. 3 is the chip. It may be preferable because it causes less mechanical damage to the device. The object to be bonded is not limited to a wafer, a chip, and a substrate, and may be in any form.

The ultrasonic vibration head is placed between the stage standby position and the head position separately from the head, aligned and the upper and lower joints are attached by the head, and then the stage is moved by the ultrasonic vibration head. Pressurization and ultrasonic vibration may be applied from above to join. By doing so, the means for holding the object to be joined by the horn and the plasma electrode function become unnecessary, and the design of the horn becomes easy.

An electrostatic chuck method is desirable as a means for holding the object to be joined, but a mechanical chucking method may also be used. Further, it is preferable to first hold the vacuum suction and hold it in the atmosphere to bring it into close contact, and then mechanically chuck it to improve the adhesion.

In the embodiment, the head side has the alignment moving means and the elevating shaft, and the stage side has the slide shaft. However, the alignment moving means, the elevating shaft, and the slide shaft may be combined in any way on the head side and the stage side. It may be duplicated. Further, even if the head and the stage are not arranged vertically, it does not depend on the arrangement direction such as left-right arrangement or diagonal arrangement.

When plasma cleaning is performed with the stage slid, the electric field environment is similar because the electrode shapes of the head and the stage and the surrounding shapes are similar. Therefore, even if the matching box that automatically adjusts the plasma power supply is not used individually, the electrodes can be switched by one and the head side and the stage side can be cleaned in sequence. By doing so, compactness and cost reduction can be achieved.

Although it is called ultrasonic vibration, the vibration frequency does not have to be in the ultrasonic region. Especially in the longitudinal vibration type, it is sufficiently effective even at low frequencies.

(Second Embodiment) Hereinafter, a desirable second embodiment of the present invention will be described with reference to the drawings. FIG. 6 shows a joining device for joining the opposed objects according to the embodiment of the present invention by applying vibration under reduced pressure after surface activation. In this embodiment, an example is given as an apparatus for joining the upper wafer, which is the first object to be bonded, and the lower wafer, which is the second object to be bonded.

First, the device configuration will be described. A holding tool 25 for holding the upper wafer, which is a part of the head 7, and a stage 8 for holding the lower wafer are arranged in the decompression chamber 11, and the head is a Z-axis lifting mechanism 2 to which a torque-controlled lifting motor 1 is connected. The θ-axis mechanism 3 that rotates the Z-axis elevating mechanism 2 and the XY alignment table 6 that aligns and moves the head portion in the XY horizontal direction comprises an alignment moving means in the X, Y, and θ directions and an elevating means in the Z direction. By feeding back the pressing force at the time of joining detected by the pressure detecting means 4 arranged in the holding tool holding unit 24 to the torque control type elevating drive motor 1, position control and pressure control can be switched. ing. Further, as shown in FIG. 7, the pressure detecting means 4 has three pressure detecting elements 31 arranged at equal intervals on the circumference, and is used for parallel adjustment of the holding tool or the amplitude at the time of vibrate pressurization. Also used for measurement. When used for head load control, the sum of the three is fed back to the servo motor. It can also be used to detect contact between objects to be joined. The XY alignment table 6 uses a means that can be used even in a vacuum, but since the Z and θ-axis mechanisms are installed outside the decompression chamber, the head and the outside are isolated so that they can be moved by an O-ring or bellows 5. As the means for holding the object to be joined of the head and the stage, a mechanical chucking method may be used, but it is preferable to provide an electrostatic chuck. In addition, it is equipped with a heater for heating and also serves as a plasma electrode, and has three functions of holding means, heating means, and plasma generating means.

As shown in FIG. 7, three piezo actuators (piezoelectric elements) 30 are arranged on the circumference of at least one of the holding tools to perform parallel adjustment. In addition, since the head part also uses vibration including the ultrasonic region at the time of joining, the head 7 is composed of the holding tool holding part 24, the holding tool 25, and the vibrator 26, and the vibration by the vibrator is transmitted to the holding tool and vibrates. Is transmitted to the object to be held by the holding tool. As shown in Fig. 7, the piezo actuators 30 that serve as oscillators are arranged in parallel at three locations on the circumference at equal intervals, and the wave motion and amplitude that allow waves to flow by controlling the phase also increase or decrease. It is possible to perform three-dimensional movements such as movements. The holding tool holding portion comprises a holding tool and means for holding the vibrator so as not to kill the vibration. Further, it is preferable to control the pressing force in proportion to the joining area as the joining progresses. Further, when joining a large area such as a wafer, it is impossible to cause lateral vibration with a lateral vibration type vibration head, but a large area is not possible with a longitudinal vibration type vibration head. Surface joining is also possible.

As a depressurizing means, a vacuum pump 17 is connected to an exhaust pipe 15, and an exhaust valve 16 opens and closes and adjusts the flow rate, so that the degree of vacuum can be adjusted. On the suction side, the intake gas switching valve 20 is connected to the intake pipe 18, and the intake valve 19 opens and closes and adjusts the flow rate. As the intake gas, two types of plasma reaction gases can be connected, for example, Ar can be connected to oxygen or oxygen to nitrogen. The other is connected to the atmosphere or nitrogen for release to the atmosphere. The degree of vacuum and the reaction gas concentration can be adjusted to the optimum values by adjusting the flow rate including the opening and closing of the intake valve 19 and the exhaust valve 16. In addition, automatic feedback can be provided by installing a vacuum pressure sensor in the decompression chamber.

Alignment mark recognition means consisting of an optical system for alignment is arranged outside the decompression chamber above the stage standby position and below the head. The number of recognition means should be at least one on the stage and one on the head side, and if you want to recognize a small object such as a chip, the alignment mark has a shape that can read the θ direction component and two marks in one field of view. By arranging them, one recognition means can sufficiently read them, but as in this embodiment, it is better to arrange two large wafers in the radial direction at both ends to read with higher accuracy in the θ direction. It is preferable because it can be done. Further, the recognition means may be provided with means that can move in the horizontal direction or the focal direction so that the alignment mark at an arbitrary position can be read. Further, the recognition means includes, for example, a camera with an optical lens made of visible light or IR (infrared) light. A window made of a material that allows the optical system of the recognition means to pass through, for example, glass, is arranged in the decompression chamber, and the alignment mark of the object to be joined in the decompression chamber is recognized through the window. On the object to be joined, for example, alignment marks are provided on the opposing surfaces of the upper wafer and the lower wafer so that they can be recognized with high position accuracy. The alignment mark preferably has a specific shape, but a part of a circuit pattern or the like applied on the wafer may be diverted. In addition, if there is no mark, an outer shape such as an orifra can be used. In addition, in the case of fine alignment with high accuracy at the nano level, after rough positioning, visible light and IR (infrared) are used for both visible light and IR (infrared) in the head side recognition means with the upper and lower wafers close to each other by about several μm. By using a recognition means and providing a transmission hole or a transparent material at the alignment mark position of the stage, the alignment mark on both wafers is infrared-transmitted through the stage from the bottom and simultaneously recognized, and X, Y again. , Can be aligned in the θ direction. When the recognition means has the moving means in the focal direction, the upper and lower sides can be recognized individually, but it is preferable to recognize them in close proximity to each other in terms of accuracy. For fine alignment It is possible to improve the accuracy by repeatedly aligning, and since the θ direction is affected by the misalignment, the accuracy can be improved to the nano level by aligning only in the XY direction after entering within a certain range. By using a sub-pixel algorithm as an image recognition means, it is possible to obtain recognition accuracy higher than the resolution of infrared rays. In addition, if the alignment is performed in close proximity, the amount of Z movement required for joining will be within a minimum of several μm, so play and tilt with respect to Z movement can be minimized, and highly accurate nano-level alignment accuracy can be achieved. Can be achieved.

Next, the operation flow will be explained with reference to Fig. 8. First, as shown in [1], the upper wafer and the lower wafer to be transfer type are held by the stage and the head with the front door of the decompression chamber opened. This may be done manually, but the wafer may be automatically loaded from the cassette. Next, as shown in [2], the front door is closed to reduce the pressure inside the pressure reducing chamber. 10 to remove impurities^-3It is preferable to reduce the pressure below Torr. Subsequently, a plasma reaction gas such as Ar is supplied, for example, 10^-2A plasma power supply is applied to the plasma electrode at a constant vacuum degree of about Torr to generate plasma. The generated plasma ions collide with the surface of the wafer held on the power supply side, and the surface is activated by etching the deposits such as the oxide film and the organic substance layer on the surface. It is also possible to hydrophilize using oxygen or nitrogen as a reaction gas and surface activate it with an OH group. It is possible to wash both wafers at the same time, but it is also possible to wash them alternately by switching one matching box. Subsequently, as shown in [3], the upper wafer and the lower wafer are brought close to each other by several μm, and visible light and IR (infrared) combined recognition means are used as the recognition means, and the recognition means is transmitted to the alignment mark position of the stage. By providing holes and a transparent material, the alignment marks on both wafers can be simultaneously recognized and aligned in the X, Y, and θ directions through the head through the head from above. In this case, it is possible to improve the accuracy by repeatedly aligning, and since the θ direction is affected by the misalignment, the accuracy can be improved to the nano level by aligning only in the XY direction after entering within a certain range. .. Subsequently, as shown in [4], the stage is raised, both wafers are brought into contact with each other, and the position control is switched to the pressure control to pressurize. With the contact detected by the pressure detecting means and the height position recognized, the value of the pressure detecting means is fed back to the torque control type elevating drive motor to control the pressure so as to reach the set pressure. With the initial pressurization applied, first, the piezo actuator performs parallel adjustment between the upper and lower objects to be joined so that the values of the pressure elements arranged at equal intervals on the circumference become uniform. When high-precision positioning is required, parallel adjustment can be performed in advance before surface activation, and the value can be stored and contacted in the parallel-adjusted state. Next, arbitrary vibration including the above-mentioned three-dimensional operation is applied, and the stress at the bonding interface increases, so that the bonding proceeds with a low load. It is preferable that the pressing force is increased in proportion to the increase in the joint area. Also, like wafers, they are densely packed with each other. Particles that become small dust are present on the bonding surface of the surface-shaped objects to be joined, and if they are bonded as a solid layer at low temperature, gaps will be created around the particles and they will not be bonded as large voids. To remove this, by applying vibration at the time of joining, stress is concentrated on the particle portion, so that it can be crushed or buried in the base material. Further, even in the voids formed by the gaps between the interfaces, vibration is applied to expand and contract them, and by bringing the voids into contact with each other, the already surface-activated interfaces are joined, and voids are reduced. The surfaces cannot be joined by ultrasonic vibration, but the joining force is joined by surface activation, so the vibration is used to crush and / or bury the particles and to bring the voids into contact. Since it is in a vacuum, it can be joined without gaps as long as there are no particles. Also, if necessary, heating is applied at the time of joining. Further, in the case of heating after vibrating bonding in order to remove residual stress or increase the bonding strength, it is also possible to heat in a state where the accuracy is maintained by contacting at room temperature and then raising the temperature. Subsequently, as shown in [6], the stage is returned to the standby position and the inside of the decompression chamber is released to the atmosphere. Then, the front door is opened and the bonded wafer is taken out. It may be done manually, but it is preferable to automatically unload it into the cassette. Since there are particles, they can be joined without gaps as long as there are no particles. Also, if necessary, heating is applied at the time of joining. Further, in the case of heating after vibrating bonding in order to remove residual stress or increase the bonding strength, it is also possible to heat in a state where the accuracy is maintained by contacting at room temperature and then raising the temperature. Subsequently, as shown in [6], the stage is returned to the standby position and the inside of the decompression chamber is released to the atmosphere. Then, the front door is opened and the bonded wafer is taken out. It may be done manually, but it is preferable to automatically unload it into the cassette. Since there are particles, they can be joined without gaps as long as there are no particles. Also, if necessary, heating is applied at the time of joining. Further, in the case of heating after vibrating bonding in order to remove residual stress or increase the bonding strength, it is also possible to heat in a state where the accuracy is maintained by contacting at room temperature and then raising the temperature. Subsequently, as shown in [6], the stage is returned to the standby position and the inside of the decompression chamber is released to the atmosphere. Then, the front door is opened and the bonded wafer is taken out. It may be done manually, but it is preferable to automatically unload it into the cassette.

In the above embodiment, the wafer is raised as the object to be bonded, but a chip and a substrate may be used. As long as it has a large bonding area such as a wafer, the object to be bonded is not limited to a wafer, a chip, or a substrate, and may have any form.

The vibration head is placed between the stage standby position and the head position separately from the head, aligned and the upper and lower joints are attached by the head, then the stage is moved and the vibration head pressurizes from the top. , Vibration may be applied for joining. By doing so, the means for holding the object to be joined by the holding tool and the plasma electrode function become unnecessary, and the design of the holding tool becomes easy.

Further, plasma cleaning may be performed by a separate device, and only bonding may be performed by this device. In that case, the means for moving to the standby position of the stage becomes unnecessary.

An electrostatic chuck method is desirable as a means for holding the object to be joined, but a mechanical chucking method may also be used. Further, it is preferable to first hold the vacuum suction and hold it in the atmosphere to bring it into close contact, and then mechanically chuck it to improve the adhesion.

In the embodiment, the head side has the alignment moving means and the elevating shaft, and the stage side has the slide shaft. However, the alignment moving means, the elevating shaft, and the slide shaft may be combined in any way on the head side and the stage side. It may be duplicated. Further, even if the head and the stage are not arranged vertically, it does not depend on the arrangement direction such as left-right arrangement or diagonal arrangement.

When plasma cleaning is performed with the stage slid, the electric field environment is similar because the electrode shapes of the head and the stage and the surrounding shapes are similar. Therefore, even if the matching box that automatically adjusts the plasma power supply is not used individually, the electrodes can be switched by one and the head side and the stage side can be cleaned in sequence. By doing so, compactness and cost reduction can be achieved.

The vibration frequency does not have to be in the ultrasonic region. Especially in the longitudinal vibration type, it is sufficiently effective even at low frequencies.

In this example, the surface activation by Ar plasma was increased, but plasma was used as a reaction gas using oxygen or nitrogen, and the surface was surface-activated by OH groups by hydrophilization, hydrogen-bonded, and strongly eutectic by heating. A method of combining can also be used. This method is particularly effective for oxides including Si, glass, SIO2, and ceramics.

Although it is brought to the same side as the piezo actuator and arranged, it is preferable to arrange the pressure detecting element on the stage side facing the piezo actuator as shown in FIG. 7 because detection can be performed via the object to be joined. Further, the piezo actuator and the pressure detection arrangement may be reversed. Further, as shown in FIG. 7, by connecting the columns with columns and sealing the columns with an O-ring and arranging the pressure detection element outside the decompression chamber, it is not subject to drift due to temperature changes, so that detection can be performed with high accuracy.

As the timing of parallel adjustment, a value adjusted in advance can be retained. Further, it can be performed more precisely by adjusting the parallel at each contact or correcting at the time of pressurization. Further, when it is necessary to align with high accuracy, it is preferable to perform parallel adjustment before alignment. Further, when the surface is activated and joined, it is necessary to make parallel adjustment before the surface activation treatment.

<figref num="1">Vacuum ultrasonic bonding device configuration diagram</figref><figref num="2">Operation flow diagram</figref><figref num="3">Lateral vibration type head structure diagram</figref><figref num="4">RF plasma power diagram</figref><figref num="5">Pulse wave plasma power supply diagram</figref><figref num="6">Opposed arrangement type joining device configuration diagram</figref><figref num="7">Pressure detection element and piezo actuator layout</figref><figref num="8">Joining operation flow diagram in facing arrangement type joining device</figref>

Code description

1 Torque control type elevating drive motor 2 Z-axis elevating mechanism 3 θ-axis rotating mechanism 4 Pressure detecting means 5 Bellows 6 XY alignment table 7 Head 8 Stage (plasma electrode, heater, holding means) 9 Lower wafer 10 Upper wafer 11 Vacuum chamber 12 Head side wafer recognition camera 13 Stage side wafer recognition camera 14 Glass window 15 Exhaust pipe 16 Exhaust valve 17 Vacuum pump 18 Intake pipe 19 Intake valve 20 Intake gas switching valve 21 Ar22 O223 Atmosphere 24 Horn holding part 25 Horn (plasma electrode, heater, Holding means) 26 Transducer 27 Upper alignment mark 28 Lower alignment mark 29 Slide moving means 30 Piezo actuator 31 Pressure detection element 32 Transfer type holding tool 33 Base material holding tool 34 Transfer type 35 Base material 36 O-ring 37 Support 38 Parallel blister copper adjustment Part 39 Alignment mark recognition camera 40 frame