Single crystal cutting method

Single crystal cutting method

<p>100. . . Single slit radiation device</p><p>101. . . H-plane antenna</p><p>102. . . Slot string</p><p>103. . . Homogenization mechanism</p><p>104. . . Single slot</p><p>200. . . Reflector</p><p>201. . . Supersaturated absorber</p><p>202. . . Reflector</p><p>300. . . Laser oscillator</p><p>301. . . Collection optics</p><p>302. . . Process reaction chamber</p><p>303. . . Terminal Optics</p><p>304. . . nozzle</p>

Figure 1 is a conceptual diagram of an in-phase single-slit radiation device using an H-plane antenna with a uniformization mechanism.

Figure 2 is a conceptual diagram of a femtosecond excimer laser oscillator.

Figure 3 is a schematic configuration diagram of a laser processing machine using a femtosecond excimer laser oscillator.

Fig. 4 is a diagram illustrating the ideal cutting plane orientation for cutting a single crystal wafer by the method of the present invention.

[Technical Field to which the Invention belongs]

The present invention relates to a method for cutting a single crystal by using a laser to minimize the cutting loss and effectively use the method for cutting a single crystal.

[Background technique]

Single crystal wafers represented by silicon (Si) and gallium arsenide (GaAs) are made by cutting single crystal rods made by the up-draw method (CZ method) or the float method (FZ method) into thin slices. It is round. Therefore, the thickness of the wafers that are sliced into thin slices should be as thin as possible, and the width of the cutting loss caused by cutting is reduced, and it is expected that more wafers can be manufactured from a single crystal rod. . In other words, this is a well-known problem in the past, such as reducing the thickness of the wafer and reducing the loss in the wafer process, which can avoid the waste of raw materials and reduce the manufacturing cost.

For example, as a device for cutting a silicon single crystal rod into a silicon wafer, a cutting device formed by a wire saw and an inner peripheral blade is generally the most commonly used. However, when using these devices to cut out silicon wafers, there must be a cut-off gap, so cutting loss of the raw material will occur. Even with a wire saw with relatively small cutting loss, each wafer still cannot avoid a loss of about 200μm. In addition, cutting with wire saws or inner peripheral blades will leave a damaged layer on the cut surface after satin cutting. Therefore, in order to remove this damaged layer, polishing, etching and other processes must be performed. Even so, it will still cause loss of raw materials. Moreover, for mechanical processing like this, if the wafer is sliced too thin from the raw material single crystal rod, it is easy to cause the wafer to crack during the processing, so it is still necessary to cut the wafer thickly until the end After the components are fabricated, the wafer back must be polished or polished to process the wafer to the desired thickness. Therefore, a considerable part of the expensive single crystalline material is simply discarded in vain.

On the other hand, the cutting of single crystal rods has also been considered by laser processing, which is widely used in welding or cutting operations in other fields. Generally speaking, compared with traditional mechanical processing, laser processing has the advantages of higher precision, more precise processing, and less waste of raw materials. However, problems such as melting caused by heat in laser processing can cause deterioration of the periphery of the cut part and leave processing traces. Therefore, it is difficult for laser processing to be applied to the required processing accuracy below the μm level.

In order to solve this problem, the development of ultrashort pulse lasers suitable for cutting semiconductor single crystals is continuing. If an ultrashort pulse with a pulse length of about tens of femtoseconds is used for processing, the excitation time will be at the same level as the buffer time of atomic vibration, and the bond between atoms can be cut without heating. Therefore, the melting caused by heat will be different, and there will be no deterioration or remaining processing marks in the peripheral part, and it is possible to perform high-precision processing only on the irradiated part. Furthermore, if a short-wavelength laser like an excimer laser is used, the photon energy can exceed the energy necessary for cutting off the bonding of atoms, so high quantum accuracy can be obtained for high-speed and high-efficiency processing. At the same time, since the laser compressed into an ultra-short pulse will expand the maximum energy of the pulse to a great extent, it can become a more effective processing with non-linear optical effects such as 2-photon absorption.

However, with such ultrashort pulse laser cutting method, there is a problem that the atomic substance removed by the laser cutting will re-attach to the processed side wall, etc., the cut surface cannot be flat, and the processed shape will be deteriorated. . For this reason, even if laser cutting methods such as excimer lasers are directly applied to the cutting of single crystals such as silicon, the advantages of such laser cutting that can be processed at high speed and high efficiency cannot be used. Mechanical processing, that is, wire saw or inner peripheral edge processing, cannot improve the yield of single crystal cutting.

[Revelation of Invention]

Here, the main purpose of the present invention is to provide a cutting method for cutting a single crystal using laser processing, and a cutting method for cutting a single crystal to obtain a good cut surface and minimize the cutting loss. .

In order to solve the above-mentioned problems, the single crystal cutting method of the present invention is characterized by continuously supplying gas molecules or radicals containing gas molecules that react with the single crystal constituent atoms to become stable gas molecules to the cutting part. In the vicinity, it is a method of cutting the single silicon crystal by irradiating an ultra-short pulse laser on the cutting part.

In this way, an ultrashort pulse laser is irradiated to the cut part, and at the same time, gas molecules or radicals containing gas molecules that react with the single crystal constituent atoms to become stable gas molecules or radicals are supplied to the vicinity of the cut part, because it can be The atomic material produced by the cutting process is discharged as a stable gas atom, so this single crystal cutting method can eliminate the atomic material removed by the cutting method of the ultrashort pulse laser again. It adheres to the processed side wall, etc., and the cut surface cannot be flat, and the processed shape is deteriorated.

In this case, the aforementioned ultrashort pulse laser system is the most ideal excimer laser.

In this way, if an excimer laser is used, it is possible to cut the single crystal around the cut portion without deterioration due to melting or leaving traces of processing. Furthermore, since the photon energy can exceed the energy necessary for cutting off the bonding of atoms, high quantum accuracy can be obtained and high-speed and high-efficiency processing can be performed.

In this case, the mode-synchronized Q-switch laser is the most ideal for the aforementioned ultrashort pulse laser.

In this way, if the ultrashort pulse laser is a mode-synchronized Q-switched laser, even when the ultrashort pulse is formed, the ultrashort pulse can be obtained as a continuous excitation state by low energy supply. Reduce energy consumption in single crystal cutting.

In this case, the aforementioned free radical can be defined as a free hydrocarbon group.

In this way, if it is a free hydrocarbon group, it can be easily used as a free radical by the catalyst, which is easy to use, and can efficiently remove the generated atomic substance during cutting.

In this case, it is most desirable that the concentration of the aforementioned free hydrocarbon group in the gas is set at 10% or less.

In this way, by supplying the radicals in a state where the concentration of the free hydrocarbon radicals in the gas is diluted to 10% or less, the life of the radicals can be prolonged as much as possible. If it is set at 0.1~5%, it is more ideal.

In this case, the aforementioned single crystal system can be defined as a single crystal of silicon. In this way, if the single crystal wafer is silicon used in semiconductors, since it is the most widely used semiconductor, the effect of reducing manufacturing costs is very large.

In this case, the cutting loss width can be set to 5μm or less.

In this way, since the cutting method of the present invention can cut a single crystal with high precision and produce a good cut surface by laser processing, the cutting loss width can be reduced compared with the past. Shrunk to a minimum.

In this case, the single crystal wafer can be cut from the aforementioned single crystal so that the thickness of the single crystal wafer (μm)/the diameter of the single crystal wafer (mm)3.

In this way, since the cutting method of the present invention can cut the single crystal with high precision and produce a good cut surface by laser processing, the thickness of the single crystal wafer (μm) can be cut. /Single crystal wafer diameter (mm) 3 such an extremely thin wafer.

In this case, from the aforementioned single crystal, the main surface is relative to the [100] axis of the single crystal, so as to have an angle α in the [011] direction (0°&lt;α&lt;90°) and in the [01-1] direction β angle (0°&lt;β&lt;90°), the surface with the inclination angle toward the [01-1] direction or the [101] direction γ angle (0°γ&lt;45°) or the surface becomes equivalent It is ideal to cut the single crystal wafer by the surface.

This is because, in recent years, a method of forming a good insulator without depending on the surface orientation of the silicon wafer has been developed (refer to 2000 Symposium on VLSI Technology, Honolulu, Hawaii, June13th-15th, 2000 "Advantage of Radica1 Oxidation for Improving Reliability of Ultra-Thin Gate OXide"), so it is not necessary to limit the wafer surface orientation for semiconductor wafer components to the previous [100] surface. Therefore, if the single crystal wafer is cut from the single crystal in order to achieve the above-mentioned plane orientation, the main surface of the wafer becomes inclined from all the [110] planes that become the cleavage plane. Therefore, even if the wafer is thinly cut, the wafer is not easily broken. Therefore, with this cutting method, if the wafer with such a surface is cut, not only the loss during cutting is reduced, but the finished thin wafer is not easy to break, and it is fully equipped with components. Practicality in engineering. In addition, since the cutting method of the present invention does not have the plane orientation dependence of the single crystal, even if such a plane is cut, the atomic order can be flattened.

As described above, according to the single crystal cutting method of the present invention, ultra-short pulse laser light is irradiated to cut the bonding of atoms, and at the same time, depending on the processing conditions, the constituent atoms of the processed material and stable gas molecules will be produced. The gas molecules or radicals used are irradiated to prevent reattachment, and the thin silicon wafer that is not easily broken can be cut from the silicon ingot without loss and waste and with good flatness.

[The best embodiment of the invention]

Hereinafter, the aspect of the present invention will be described in detail.

The inventors of the present invention have examined a method that can efficiently use single crystals by cutting thin wafers from single crystals such as silicon in a high-precision and high-efficiency manner. As mentioned above, if the single crystal is cut by an ultrashort pulse laser such as an excimer laser, since the atomic bonds of the single crystal can be cut, it is possible to perform high-precision processing only on the irradiated part. However, laser processing like this has a problem that the removed atomic substance adheres to the processed side wall, etc., so there is a problem that the flatness of the processed surface deteriorates.

Here, the inventors idea of the present invention is that when an ultrashort pulse laser is irradiated to the cutting part to cut the single crystal, it will involve the reaction with the atomic substance removed by the processing to generate a stable gas Molecular gas molecules or radical gas are continuously supplied to the vicinity of the cutting part, and the atomic substances removed during processing are used as stable gas molecules to prevent the removed substances from adhering to the processing surface.

According to the above method, a simple method can prevent the atomic substance removed from the cut surface by laser processing from adhering to the cut surface again. Specifically, when cutting a single crystal of, for example, silicon, a free hydrocarbon group containing an auxiliary gas is supplied to the cut surface, and an excimer laser is irradiated on the cut portion to cut the single crystal. If the Si-Si bond is cut by an ultrashort pulse laser, unnecessary atomic silicon will be released, but such silicon will react with free hydrocarbon groups to become inactive gaseous SiH ₄ . Then, if the gaseous SiH ₄ If it is completely eliminated, it can be cut into a good cut surface with high efficiency.

The present invention is based on such a basic idea and completed after reviewing various conditions.

Hereinafter, the present invention will be further described with reference to the drawings, but the present invention is not limited to these descriptions.

In the present invention, an ultrashort pulse laser is used in order to cut a thin silicon wafer that is not easily broken from a single crystal rod of silicon. The irradiation of the ultrashort pulse laser in this embodiment is performed using a mode-synchronized Q-switched laser by continuous excitation and nonlinear optical elements. The life span of the excimer is generally very short in the nanosecond sequence, for example, the life span of the KrF excimer is 6 nsec. Therefore, in order to operate as an effective Q-switched laser, the length of the resonator is set to approximately 1.5 m or less. As a result, the time required for one shot of the laser can be set to less than 5nsec, so even an excimer laser with a very short lifetime can perform high-efficiency Q-switch operation. In other words, by designing a resonator with the same scan time as the excimer lifetime, it can be used as a Q-switched laser to excite the excimer laser, which is usually not displaceable, with high efficiency.

If the DC pulse excitation type excimer used in the past is made into continuous excitation, it is necessary to supply a billion-watt-level power, otherwise it will not be suitable for the formation of ultra-short pulses. In order to avoid this situation, the Q value of the laser resonator is increased, and a microwave excitation type continuous excitation plasma is used. In order to increase the Q value of the laser resonator, the reflectance of the output mirror is set close to 100%. Thereby, it is possible to reduce the critical point of amplification required for one shot. At the same time, the cross-sectional area of the luminescence is changed from 1mm ² Zoom in to 10mm ² About 1.3MW/cm ² With this extremely high intensity of excitation, a continuous excitation state can be obtained by means of low energy supply. Using the conventional electrode excitation method to make it into a small volume, although the discharge will be unstable or uneven, if the excitation is carried out by microwave, stable and uniform excitation can be produced. In addition, in order to perform microwave excitation with high efficiency, it is necessary to suppress the parking of excitation due to standing waves. According to the in-phase single-slit radiation device with a uniform H-plane antenna as shown in this embodiment, uniform excitation can be performed, and the critical length of laser amplification and high excitation efficiency can be ensured at the same time.

Fig. 1 shows the radiation structure of the co-phase single-slit radiation device 100 with a uniform H-plane antenna. The microwave supplied to the H-plane antenna 101 is supplied to the homogenization mechanism 103 through the slot series 102. At this time, by arranging the slot series 102 with a half-wavelength pitch of the inner wavelength of the tube, from the center of the H-plane antenna 101 to both ends, all the microwaves emitted from the slot 102 can be made into the same phase. The microwaves emitted in the same phase from the slot series 102 are homogenized by the homogenization mechanism 103, and then the single slot 104 is used to uniformly emit the microwaves. In addition, depending on the discharge shape, a honing head antenna can also be used to perform uniform microwave discharge.

By introducing the supersaturated absorber into the resonator using this excitation method, a mode-synchronized Q-switched laser can be realized. Since the mode synchronization method is driven mode synchronization, it is easy to obtain ultra-short pulse light close to the Fourier transform critical value (in terms of KrF, about 80fsec). By using this device structure, highly repetitive (repetition frequency is sub Hz), ultrashort pulse (from psec to fsec sequence), high power pulse (GigaW Taylor W class) excimer laser ( High-energy photons).

Figure 2 further shows the detailed device structure. The plasma 204 is excited by a co-phase single-slit radiation method in which an H-plane antenna with a uniformization mechanism is arranged up and down. In addition, after arranging reflectors 200 and 202 (reflectors in this illustration) having complete reflection or close to complete reflection, the supersaturated absorber is introduced into the resonator. By obtaining such a device structure, it is possible to realize an excimer mode synchronous Q-switched laser. In addition, as a reflector, in order to ensure stability, the use of mirrors (XeCl, KrF, ArF laser) is the most ideal, but if there is no high reflectivity mirror, F2 laser by using total reflection prism The mirror can also realize a laser resonator with a high Q value.

Using this laser produced in this way, silicon wafer processing is performed as shown in Figure 3. The shape of the laser beam used in the processing is either a dot or a line. The shape of this light beam can be adjusted by the light-collecting optical system 301 provided after the output of the laser oscillator 300. Laser beam diameter. The width is within about 10 times the wavelength, in other words, when using a KrF laser, it is within 3 μm. Therefore, the machining diameter can be achieved. The width is about 5μm, which can not be wasted during processing. In addition, the lens used in this optical system can utilize high-purity CaF2, etc., which completely control the concentration of heavy metals and the like. In addition, the more the laser beam is collected as close to the final stage (laser output side) as possible, the more damage to the lens and mirror can be reduced, which is beyond doubt. In addition, a terminal optical system 303 is arranged on the secondary side of the workpiece. A high-flatness mirror is installed on the terminal optical system 303, so that the transmitted laser light is incident from a shallow angle and oblique direction, which not only reduces the energy density of the diffusion, but also terminates it by guiding the absorber. In addition, the laser light can also be injected into the water containing the dye solution, etc. to absorb the scattered laser light.

The environment during processing, in other words, inside the process reaction chamber 302, in order to prevent burning caused by oxygen, Ar or N is used ₂ Such inactive high-definition net gas. Here, the cutting method of the present invention is characterized by adding hydrogen gas through the nozzle 304 in order to obtain a flat surface with high-speed processing and atomic order. The hydrogen is radicalized, and the atomic silicon produced by the cutting process is reacted with free hydrocarbon groups, and then used as inactive SiH ₄ By venting the gas, the atomic silicon can be prevented from adhering again, and it can be cut by maintaining a good cut surface.

As the amount of hydrogen supply, for example, when cutting a wafer with a diameter of 300mm, if the processing time per wafer is 5 minutes, the processing speed is 1mm/sec. In this case, the maximum 0.33SLM (Standard Liter per minute). Also, in this case, it is sufficient if there is an average laser output that does not produce an optical loss of about 60W. Will this H ₂ By diluting with Ar, in order to improve the reactivity with atomic Si, a catalyst such as Ni or Pt can be used for radicalization and supply to the processing environment.

In this case, in order to extend the life of the free radicals as much as possible, it is most ideal to supply the free radicals in a diluted state below 10%, more preferably between 0.1 and 5%. In addition, if the supply concentration is high, the generation rate of free radicals will decrease, so if the catalyst part is heated at this time, the generation rate can be improved. In addition, if processing is performed at a processing speed of 1mm/sec, the release speed of atomic Si (gaseous) from the processed surface can reach a speed of 1.7m/sec. Therefore, if it is made to spray free hydrocarbon groups near the cut surface, the separated Si can quickly become SiH ₄ It is released out of the wafer. Also, at this time, the reaction product that occurs with 0.17 SLM is SiH ₄ It can be recycled and reused.

In addition, since the wafer cutting process of the present invention is a non-contact cutting method using ultrashort pulse lasers, it can be cut compared with conventional mechanical cutting methods such as wire saws. The wafers that come out are made extremely thin. For example, when cutting a single crystal wafer from a silicon ingot of a semiconductor, the thickness of about 700 to 800 μm is necessary for cutting a wafer with a diameter of 200 mm in the past. However, the single crystal wafer of the present invention It can be made thinner than this. For example, if you want to cut a wafer with a diameter of 200mm, you can cut only a thickness of less than 600μm. Therefore, in contrast to the fact that the cut-off opening becomes smaller, the number of wafers that can be manufactured from a single crystal silicon ingot will greatly increase, and the production cost can be reduced.

In addition, with the wafer cutting process of the present invention, it is possible to flatten the atomic order that does not depend on the orientation of the wafer surface by irradiation of free hydrocarbon groups. Furthermore, as mentioned earlier, in recent years, the method of forming a good insulating film has been developed without depending on the surface orientation of the silicon wafer. It is not necessarily necessary to change the orientation of the wafer surface for semiconductor wafer components. Limited to the previous [100] surface. Therefore, when cutting the wafer in the present invention, if it is made to be inclined from all the [110] planes that can easily split the surface of the wafer, it will be the same as the conventional [100] plane. In contrast to a single crystal circle, the wafer is not easy to crack due to external stress, and a thinner wafer can be produced.

Fig. 4 is a diagram illustrating the ideal cutting plane orientation for cutting a single crystal wafer by the method of the present invention. The arrow symbol (vector) shown by the thick line in Figure 4 shows the plane orientation of the cut single crystal wafer (the direction of the normal to the wafer surface). It has an orientation relative to the [100] axis (X axis) 011direction α angle (0.&lt;α&lt;90°), β angle in the [01-1] direction (0.&lt;β&lt;90°), 01-1] direction or γ angle in the [101] direction (0.γ&lt;45°) the inclination angle.

In other words, a single crystal wafer composed of such a plane orientation has a (011) plane, a (01-1) plane, and a (10-1) plane from the cleavage plane, which are inclined at angles of α, β, and γ. Compared with the (100) surface of the wafer, the mechanical strength against external stress becomes higher, and the wafer can be made that is not easy to break even if it is cut thinner.

In addition, the present invention is not limited to the above-mentioned embodiment. The above-mentioned embodiments are only examples, and devices that have substantially the same structure as the technical idea described in the scope of the patent application of the present invention and can achieve the same effects are all included in the technical scope of the present invention.

For example, in the above embodiment, the gas containing free hydrocarbon groups is supplied to the vicinity of the cut portion, and the surface of the wafer is completely freed from hydrocarbon groups. However, if this is not necessary, even if C12 is used , BC13, NF3 and other added gases can also get the same effect. In addition, the processed single crystal is not limited to Si. For example, GaAs, GaP, InP, various oxide single crystals, quartz and other materials can be processed by appropriately selecting the processed material (H ₂ , CCl ₄ , CH ₃ Br, HCl, etc.) can also be processed in the same way, which is beyond doubt.

Schematic description

Figure 1 is a conceptual diagram of an in-phase single-slit radiation device using an H-plane antenna with a uniformization mechanism.

Figure 2 is a conceptual diagram of a femtosecond excimer laser oscillator.

Figure 3 is a schematic configuration diagram of a laser processing machine using a femtosecond excimer laser oscillator.

Fig. 4 is a diagram illustrating the ideal cutting plane orientation for cutting a single crystal wafer by the method of the present invention.

Symbol description of main components

100. . . Single slit radiation device

101. . . H-plane antenna

102. . . Slot string

103. . . Homogenization mechanism

104. . . Single slot

200. . . Reflector

201. . . Supersaturated absorber

202. . . Reflector

300. . . Laser oscillator

301. . . Collection optics

302. . . Process reaction chamber

303. . . Terminal Optics

304. . . nozzle