Laser beam machining method

The present invention relates to a laser processing method used for cutting an object to be processed, which is formed by providing a laminated portion on the surface of a substrate.

In recent years, Al for semiconductor devices₂O₃Highly accurate processing objects with various laminated structures, such as those in which a semiconductor operating layer such as GaN is crystal-grown on a substrate, and those in which another glass substrate is laminated on a glass substrate for a liquid crystal display device. Cutting technology is required.

Conventionally, a blade dicing method or a diamond scribe method is generally used for cutting an object to be processed having such a laminated structure.

The blade dicing method is a method of cutting an object to be processed by cutting it with a diamond blade or the like (see, for example, Patent Document 1). On the other hand, in the diamond scribe method, a scribe line is provided on the surface of the object to be processed by a diamond point tool, and a knife edge is pressed against the back surface of the object to be processed along the scribe line to break and cut the object to be processed. This is a method (see, for example, Patent Document 2).<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2003-197561</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 62-296579</text></patcit>

<p> However, in the blade dicing method, for example, when the object to be processed is for the liquid crystal display device described above, a gap is provided between the glass substrate and another glass substrate. There is a risk of shavings and lubricating cleaning water getting in.</p><p> In the diamond scribe method, the object to be processed is Al.₂O₃When a substrate with high hardness such as a substrate is held, or when the object to be processed is a glass substrate bonded to each other, a scribe line is provided not only on the front surface of the object to be processed but also on the back surface. This must be done, and the misalignment of the scribe lines provided on the front surface and the back surface may cause cutting defects.</p><p> Therefore, the present invention has been made in view of such circumstances, and a laser processing method capable of solving the above-mentioned problems and cutting an object to be processed having various laminated structures with high accuracy is provided. The purpose is to provide.</p>

<p> In order to achieve the above object, the laser processing method according to the present invention aligns a condensing point inside one of the substrates in a processed object having a plurality of substrates bonded so as to provide a gap. By irradiating the laser beam with a laser beam, a modified region is formed inside the one substrate, and by aligning a condensing point with the inside of the other substrate among the substrates and irradiating the laser beam, the other substrate is irradiated. A process of forming a modified region inside and forming a cutting starting point region inside a predetermined distance from the laser beam incident surface of the workpiece along the planned cutting line of the workpiece by these modified regions, and a machining target. By applying stress to the object, the object to be processed is cut along the planned cutting line with the cutting origin region as the starting point of cutting, and a plurality of functional elements having a plurality of substrates bonded so as to provide a gap are obtained. It comprises steps and at least one of the substrates is a silicon substrate.</p><p> According to this laser machining method, the machining target is cut by a modification region formed inside one substrate and another substrate among a plurality of substrates bonded so as to provide a gap in the machining object. It is possible to form a cutting origin region along the desired cutting schedule line to be cut. Therefore, with the cutting starting point region as the starting point of cutting, it is possible to cut a work target having a plurality of substrates bonded so as to provide a gap by dividing it with a relatively small force, and the work target has various laminated structures. It is possible to cut an object with high precision.</p><p> The laminated portion provided on the surface of the substrate refers to a laminated portion deposited on the surface of the substrate, bonded to the surface of the substrate, attached to the surface of the substrate, or the like, and is a different material with respect to the substrate. It does not matter whether it is the same material or the same material. The laminated portion provided on the surface of the substrate includes one provided in close contact with the substrate, one provided with a gap from the substrate, and the like. Examples include a semiconductor operating layer formed by crystal growth on a substrate, another glass substrate bonded on a glass substrate, and the like, and the laminated portion includes a layer in which a plurality of different materials are formed. Further, the inside of the substrate means that the inside of the substrate also includes the surface of the substrate on which the laminated portion is provided. The focusing point is a point where the laser beam is focused. Further, the cutting starting point region means a region that becomes a cutting starting point when the workpiece is cut. Therefore, the cutting starting point region is a planned cutting portion of the object to be machined. The cutting origin region may be formed by continuously forming the modified region, or may be formed by intermittently forming the modified region.</p>

<p> According to the laser processing method according to the present invention, it is possible to cut an object to be processed having various laminated structures with high accuracy.</p>

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the laser processing method according to the present embodiment, a modified region by multiphoton absorption is formed inside the object to be processed. Therefore, this laser processing method, particularly multiphoton absorption, will be described first.

Material absorption bandgap E_GWhen the photon energy hν is smaller than that, it becomes optically transparent. Therefore, the condition for absorption in the material is hν&gt; E_GIs. However, even if it is optically transparent, if the intensity of the laser beam is made very large, nhν&gt; E_GAbsorption occurs in the material under the condition of (n = 2,3,4, ...). This phenomenon is called multiphoton absorption. In the case of a pulse wave, the intensity of the laser beam is the peak power density (W / cm) of the focusing point of the laser beam.²), For example, the peak power density is 1 × 10.⁸(W / cm²) Multiphoton absorption occurs under the above conditions. The peak power density is obtained by (energy per pulse of laser light at the focusing point) ÷ (beam spot cross-sectional area of laser light × pulse width). In the case of continuous waves, the intensity of the laser beam is the electric field intensity (W / cm) at the focusing point of the laser beam.²).

The principle of laser processing according to the present embodiment utilizing such multiphoton absorption will be described with reference to FIGS. 1 to 6. FIG. 1 is a plan view of the machining object 1 during laser machining, FIG. 2 is a cross-sectional view of the machining object 1 shown in FIG. 1 along the line II-II, and FIG. 3 is a machining target after laser machining. It is a plan view of the object 1, FIG. 4 is a cross-sectional view of the workpiece 1 shown in FIG. 3 along the IV-IV line, and FIG. 5 is a cross section of the workpiece 1 shown in FIG. 3 along the VV line. FIG. 6 is a plan view of the cut object 1 to be machined.

As shown in FIGS. 1 and 2, the surface 3 of the workpiece 1 has a desired scheduled cutting line 5 on which the workpiece 1 should be cut. The planned cutting line 5 is a virtual line extending in a straight line (a line may be actually drawn on the object 1 to be processed to be the planned cutting line 5). In the laser processing according to the present embodiment, the modified region 7 is formed by irradiating the processed object 1 with the laser beam L by aligning the condensing point P inside the processed object 1 under the condition that multiphoton absorption occurs. The focusing point is a point where the laser beam L is focused.

By moving the laser beam L relatively along the planned cutting line 5 (that is, along the direction of arrow A), the focusing point P is moved along the planned cutting line 5. As a result, as shown in FIGS. 3 to 5, the modified region 7 is formed only inside the workpiece 1 along the scheduled cutting line 5, and the modified region 7 forms the cutting starting region (scheduled cutting portion) 8 Is formed. In the laser machining method according to the present embodiment, the machining target 1 does not generate heat by absorbing the laser beam L to form the modified region 7. The modified region 7 is formed by transmitting the laser beam L through the object to be processed 1 and generating multiphoton absorption inside the object 1 to be processed. Therefore, since the laser beam L is hardly absorbed by the surface 3 of the object to be processed 1, the surface 3 of the object to be processed 1 is not melted.

In cutting the object to be processed 1, if there is a starting point at the cutting point, the object 1 to be processed is cracked from the starting point, so that the object 1 to be processed can be cut with a relatively small force as shown in FIG. Therefore, the machining object 1 can be cut without causing unnecessary cracks on the surface 3 of the machining object 1.

The following two methods can be considered for cutting the workpiece starting from the cutting starting point region. One is a case where an artificial force is applied to a machining object after the cutting starting point region is formed, so that the machining object is cracked starting from the cutting starting region and the machining object is cut. This is, for example, cutting when the thickness of the object to be processed is large. When an artificial force is applied, for example, thermal stress is generated by applying bending stress or shear stress to the machining object along the cutting starting point region of the machining object, or by giving a temperature difference to the machining object. To let them do it. The other is when the cutting starting point region is formed to spontaneously crack in the cross-sectional direction (thickness direction) of the machining object starting from the cutting starting point region, and as a result, the machining object is cut. Is. This is possible, for example, when the thickness of the object to be processed is small, the cutting origin region is formed by one row of modified regions, and when the thickness of the object to be processed is large, the thickness direction This is possible by forming a cutting starting point region by the modified regions formed in a plurality of rows. Even in the case of this spontaneous cracking, the crack does not advance to the surface of the portion corresponding to the portion where the cutting origin region is not formed at the cutting portion, and the portion corresponding to the portion where the cutting origin region is formed. Since only can be divided, the division can be controlled well. In recent years, the thickness of an object to be processed such as a silicon wafer tends to be thin, so such a cutting method with good controllability is very effective.

The modified regions formed by multiphoton absorption in this embodiment include the following (1) to (3).

(1) When the modified region is a crack region containing one or more cracks The object to be processed (for example, glass or LiTaO)₃The electric field strength at the condensing point is 1 × 10 by aligning the condensing point inside the (piezoelectric material consisting of).⁸(W / cm²) Or more and the pulse width is 1 μs or less. The magnitude of this pulse width is a condition in which a crack region can be formed only inside the object to be processed without causing extra damage to the surface of the object to be processed while causing multiphoton absorption. As a result, a phenomenon called optical damage due to multiphoton absorption occurs inside the object to be processed. This optical damage induces thermal strain inside the work piece, which forms a crack region inside the work piece. The upper limit of the electric field strength is, for example, 1 × 10.¹²(W / cm²). The pulse width is preferably 1 ns to 200 ns, for example. The formation of crack regions by multiphoton absorption is described in, for example, "Inside the glass substrate by solid-state laser harmonics" on pages 23 to 28 of the 45th Laser Thermal Processing Workshop Proceedings (December 1998). It is described in "Marking".

The present inventor experimentally determined the relationship between the electric field strength and the size of cracks. The experimental conditions are as follows.

(A) Processed object: Pilex (registered trademark) glass (thickness 700 μm) (B) Laser light source: Semiconductor laser excitation Nd: YAG laser Wavelength: 1064 nm Laser light spot cross-sectional area: 3.14 × 10^-8cm² Oscillation form: Q-switched pulse repetition frequency: 100kHz Pulse width: 30ns Output: Output &lt;1mJ / pulse Laser light quality: TEM₀₀ Polarization characteristics: Linearly polarized light (C) Condensing lens Transmittance to laser light wavelength: 60% (D) Movement speed of the mounting table on which the object to be processed is placed: 100 mm / sec

The laser light quality is TEM.₀₀Means that the light collecting property is high and the light can be collected up to the wavelength of the laser beam.

FIG. 7 is a graph showing the results of the above experiment. The horizontal axis is the peak power density, and since the laser light is a pulsed laser light, the electric field strength is represented by the peak power density. The vertical axis shows the size of the crack portion (crack spot) formed inside the workpiece by the 1-pulse laser beam. Crack spots gather to form a crack area. The size of the crack spot is the size of the portion having the maximum length in the shape of the crack spot. The data indicated by the black circles in the graph is when the magnification of the condensing lens (C) is 100 times and the numerical aperture (NA) is 0.80. On the other hand, the data indicated by white circles in the graph is when the magnification of the condensing lens (C) is 50 times and the numerical aperture (NA) is 0.55. Peak power density is 10¹¹(W / cm²It can be seen that crack spots are generated inside the object to be processed from the degree of), and the crack spots also increase as the peak power density increases.

Next, in the laser machining according to the present embodiment, the mechanism of cutting the workpiece by forming the crack region will be described with reference to FIGS. 8 to 11. As shown in FIG. 8, under the condition that multiphoton absorption occurs, the condensing point P is aligned with the inside of the work target 1, and the laser light L is irradiated to the work target 1, and a crack region is formed inside along the planned cutting line. Form 9. The crack region 9 is a region containing one or a plurality of cracks. A cutting origin region is formed by the crack region 9. As shown in FIG. 9, the crack grows further starting from the crack region 9 (that is, starting from the cutting starting region), and as shown in FIG. 10, the crack reaches the front surface 3 and the back surface 21 of the workpiece 1. As shown in FIG. 11, when the object to be processed 1 is cracked, the object to be processed 1 is cut. The cracks that reach the front and back surfaces of the object to be processed may grow naturally, or may grow when a force is applied to the object to be processed.

(2) When the modified region is a melt processing region The condensing point is aligned with the inside of the object to be processed (for example, a semiconductor material such as silicon), and the electric field strength at the condensing point is 1 × 10.⁸(W / cm²) Or more and the pulse width is 1 μs or less. As a result, the inside of the object to be processed is locally heated by multiphoton absorption. By this heating, a melt processing region is formed inside the object to be processed. The melting treatment region is a region that is once melted and then resolidified, a region that is just in a molten state, or a region that is in a state of being resolidified from a molten state, and can also be said to be a region in which the phase has changed or a region in which the crystal structure has changed. Further, the melt-treated region can be said to be a region in which one structure is changed to another in a single crystal structure, an amorphous structure, or a polycrystalline structure. That is, for example, it means a region changed from a single crystal structure to an amorphous structure, a region changed from a single crystal structure to a polycrystalline structure, and a region changed from a single crystal structure to a structure including an amorphous structure and a polycrystalline structure. To do. When the object to be processed has a silicon single crystal structure, the melt processing region is, for example, an amorphous silicon structure. The upper limit of the electric field strength is, for example, 1 × 10.¹²(W / cm²). The pulse width is preferably 1 ns to 200 ns, for example.

The present inventor has experimentally confirmed that a melt processing region is formed inside the silicon wafer. The experimental conditions are as follows.

(A) Object to be processed: Silicon wafer (thickness 350 μm, outer diameter 4 inches) (B) Laser light source: Semiconductor laser excitation Nd: YAG laser Wavelength: 1064 nm Laser beam Spot cross-sectional area: 3.14 × 10^-8cm² Oscillation form: Q-switched pulse repetition frequency: 100kHz Pulse width: 30ns Output: 20μJ / pulse Laser light quality: TEM₀₀ Polarization characteristics: Linearly polarized light (C) Condensing lens Magnification: 50 times NA: 0.55 Transmittance to laser light wavelength: 60% (D) Movement speed of the mounting table on which the object to be processed is placed: 100 mm / sec

FIG. 12 is a diagram showing a photograph of a cross section of a part of a silicon wafer cut by laser processing under the above conditions. A melt processing region 13 is formed inside the silicon wafer 11. The size of the melt processing region 13 formed under the above conditions in the thickness direction is about 100 μm.

It will be described that the melt processing region 13 is formed by multiphoton absorption. FIG. 13 is a graph showing the relationship between the wavelength of the laser beam and the transmittance inside the silicon substrate. However, the reflective components on the front surface side and the back surface side of the silicon substrate are removed, and the transmittance is shown only inside. The above relationship was shown for each of the thickness t of the silicon substrate of 50 μm, 100 μm, 200 μm, 500 μm, and 1000 μm.

For example, at 1064 nm, which is the wavelength of the Nd: YAG laser, when the thickness of the silicon substrate is 500 μm or less, it can be seen that 80% or more of the laser light is transmitted inside the silicon substrate. Since the thickness of the silicon wafer 11 shown in FIG. 12 is 350 μm, the melt processing region 13 by multiphoton absorption is formed near the center of the silicon wafer, that is, at a portion of 175 μm from the surface. In this case, the transmittance is 90% or more with reference to a silicon wafer having a thickness of 200 μm, so that the laser beam is hardly absorbed inside the silicon wafer 11 and most of it is transmitted. This does not mean that the laser beam is absorbed inside the silicon wafer 11 and the melt processing region 13 is formed inside the silicon wafer 11 (that is, the melt processing region is formed by normal heating by the laser light). It means that the melt processing region 13 was formed by multiphoton absorption. The formation of the melt processing region by multiphoton absorption can be found in, for example, "Evaluation of Silicon Machining Characteristics by Picosecond Pulsed Laser" on pages 72-73 of the 66th Annual Meeting of the Welding Society (April 2000). Has been described.

The silicon wafer is cut as a result by generating cracks in the cross-sectional direction starting from the cutting starting point region formed by the melting processing region and reaching the front surface and the back surface of the silicon wafer. To. These cracks that reach the front and back surfaces of the silicon wafer may grow naturally, or may grow when a force is applied to the silicon wafer. When cracks naturally grow from the cutting starting point region to the front surface and the back surface of the silicon wafer, cracks grow from the state where the melting treatment region forming the cutting starting point region is melted, and the cutting starting point region. In both cases, cracks grow when the melt-treated region forming the wafer is resolidified from the molten state. However, in both cases, the melt processing region is formed only inside the silicon wafer, and the melt treatment region is formed only inside as shown in FIG. 12 on the cut surface after cutting. When a cutting starting point region is formed inside the work object by the melting treatment region, unnecessary cracking off the cutting starting point region line is unlikely to occur at the time of cutting, so that cutting control becomes easy.

(3) When the modified region is the region of change in refractive index The electric field strength at the condensing point is 1 × 10 by aligning the condensing point inside the object to be processed (for example, glass).⁸(W / cm²) Or more and the pulse width is 1 ns or less to irradiate the laser beam. When the pulse width is extremely shortened and multiphoton absorption is caused inside the work object, the energy due to the multi photon absorption is not converted into thermal energy, and the ionic valence changes and crystallizes inside the work object. Alternatively, a permanent structural change such as polarization orientation is induced to form a refractive index change region. The upper limit of the electric field strength is, for example, 1 × 10.¹²(W / cm²). The pulse width is preferably 1 ns or less, more preferably 1 ps or less, for example. The formation of the refractive index change region by multiphoton absorption is described, for example, in "Proceedings of the 42nd Laser Thermal Processing Study Group (November 1997)" on pages 105 to 111, "Inside the glass by femtosecond laser irradiation. Photoinduced structure formation .

The cases (1) to (3) have been described above as the modified region formed by multiphoton absorption. If it is formed as described above, it is possible to cut the object to be machined with even smaller force and with high accuracy starting from the cutting starting point region.

That is, in the case of a substrate made of a diamond-structured single crystal semiconductor such as silicon, a cutting origin region is formed in the direction along the (111) plane (first cleavage plane) and the (110) plane (second cleavage plane). Is preferable. Further, in the case of a substrate made of a group III-V compound semiconductor having a zinc blende type structure such as GaAs, it is preferable to form a cutting origin region in the direction along the (110) plane. In addition, sapphire (Al₂O₃In the case of a substrate having a hexagonal crystal structure such as), the (0001) plane (C plane) is the main plane and the direction is along the (1120) plane (A plane) or the (1100) plane (M plane). It is preferable to form a cutting origin region.

The orientation flat on the substrate along the direction in which the cutting origin region should be formed (for example, the direction along the (111) plane in the single crystal silicon substrate) or the direction orthogonal to the direction in which the cutting origin region should be formed. Then, by using the orientation flat as a reference, it becomes possible to easily and accurately form the cutting origin region along the direction in which the cutting origin region should be formed on the substrate.

Next, the laser processing apparatus used in the above-mentioned laser processing method will be described with reference to FIG. FIG. 14 is a schematic configuration diagram of the laser processing apparatus 100.

The laser processing apparatus 100 includes a laser light source 101 that generates a laser beam L, a laser light source control unit 102 that controls the laser light source 101 to adjust the output of the laser beam L, a pulse width, and the like, and a reflection function of the laser beam L. A dichroic mirror 103 that has a light source L and is arranged so as to change the direction of the optical axis of the laser light L by 90 °, a condensing lens 105 that condenses the laser light L reflected by the dichroic mirror 103, and a condensing lens 105. A mounting table 107 on which the processing object 1 irradiated with the laser beam L focused by the lens 105 is placed, an X-axis stage 109 for moving the mounting table 107 in the X-axis direction, and a mounting table 107 are provided. A Y-axis stage 111 for moving the mounting table 107 in the Y-axis direction orthogonal to the X-axis direction, and a Z-axis stage 113 for moving the mounting table 107 in the Z-axis direction orthogonal to the X-axis and the Y-axis direction. It is provided with a stage control unit 115 that controls the movement of the stages 109,111,113.

The movement of the focusing point P in the X (Y) axis direction is performed by moving the workpiece 1 in the X (Y) axis direction by the X (Y) axis stage 109 (111). Since the Z-axis direction is orthogonal to the surface 3 of the object 1 to be processed, it is the direction of the depth of focus of the laser beam L incident on the object 1 to be processed. Therefore, by moving the Z-axis stage 113 in the Z-axis direction, the condensing point P of the laser beam L can be aligned with the inside of the object 1 to be processed. As a result, for example, when the object to be processed 1 has a multi-layer structure, the condensing point P can be adjusted to a desired position such as the substrate of the object to be processed 1 or the laminated portion on the substrate. it can.

The laser light source 101 is an Nd: YAG laser that generates pulsed laser light. Other lasers that can be used for the laser light source 101, Nd: YVO₄There are lasers, Nd: YLF lasers and titanium sapphire lasers. In the present embodiment, pulsed laser light is used for processing the object 1 to be processed, but continuous wave laser light may be used as long as it can cause multiphoton absorption.

The laser processing apparatus 100 further includes an observation light source 117 that generates visible light for illuminating the processing object 1 mounted on the mounting table 107 with visible light, and the same light as the dichroic mirror 103 and the condensing lens 105. It includes a beam splitter 119 for visible light arranged on the axis. A dichroic mirror 103 is arranged between the beam splitter 119 and the focusing lens 105. The beam splitter 119 has a function of reflecting about half of visible light and transmitting the other half, and is arranged so as to change the direction of the optical axis of visible light by 90 °. Approximately half of the visible light generated from the observation light source 117 is reflected by the beam splitter 119, and this reflected visible light passes through the dichroic mirror 103 and the condensing lens 105, and the line 5 to be cut of the object 1 to be processed, etc. Illuminate surface 3 including. When the object to be processed 1 is placed on the mounting table 107 so that the back surface of the object 1 to be processed is on the side of the condensing lens 105, it goes without saying that the "front surface" here is the "back surface". is there.

The laser processing apparatus 100 further includes a beam splitter 119, a dichroic mirror 103, and an image pickup element 121 and an imaging lens 123 arranged on the same optical axis as the focusing lens 105. As the image sensor 121, for example, there is a CCD camera. The reflected light of the visible light that illuminates the surface 3 including the line 5 to be cut passes through the condensing lens 105, the dichroic mirror 103, and the beam splitter 119, is imaged by the imaging lens 123, and is imaged by the imaging element 121. It becomes the imaging data.

The laser processing apparatus 100 further includes an imaging data processing unit 125 into which imaging data output from the imaging element 121 is input, an overall control unit 127 that controls the entire laser processing apparatus 100, and a monitor 129. The image pickup data processing unit 125 calculates the focus data for focusing the visible light generated by the observation light source 117 on the surface 3 of the processing object 1 based on the image pickup data. Based on this focus data, the stage control unit 115 moves and controls the Z-axis stage 113 so that the focus of visible light is aligned with the surface 3 of the object to be machined. Therefore, the image pickup data processing unit 125 functions as an autofocus unit. Further, the image pickup data processing unit 125 calculates image data such as an enlarged image of the surface 3 based on the image pickup data. This image data is sent to the overall control unit 127, various processes are performed by the overall control unit, and the image data is sent to the monitor 129. As a result, an enlarged image or the like is displayed on the monitor 129.

Data from the stage control unit 115, image data from the imaging data processing unit 125, and the like are input to the overall control unit 127, and the laser light source control unit 102, the observation light source 117, and the stage control unit are also based on these data. By controlling 115, the entire laser processing apparatus 100 is controlled. Therefore, the overall control unit 127 functions as a computer unit.

Next, the laser processing method according to the present embodiment will be described with reference to FIGS. 14 and 15. FIG. 15 is a flowchart for explaining the laser processing method according to the present embodiment. In the present embodiment, the object to be processed 1 has a substrate and a laminated portion provided on the surface of the substrate. Further, the object 1 to be processed is placed on the mounting table 107 of the laser processing apparatus 100 shown in FIG. 14 so that the back surface of the substrate is on the light collecting lens 105 side. That is, the laser beam L is emitted from the back surface side of the substrate of the object 1 to be processed.

First, the light absorption characteristics of the substrate of the object to be processed 1 are measured by a spectrophotometer or the like (not shown). Based on this measurement result, a laser light source 101 that generates laser light L having a transparent wavelength or a wavelength with little absorption is selected with respect to the substrate of the object 1 to be processed (S101). Since the laser beam L is emitted from the back surface side of the substrate, even if the laminated portion provided on the front surface of the substrate has a light-shielding property or an absorptive property to the laser beam. , It does not interfere with laser processing.

Subsequently, the amount of movement of the object to be processed 1 in the Z-axis direction is determined in consideration of the thickness and refractive index of the substrate of the object 1 to be processed, the thickness and material of the laminated portion formed on the surface of the substrate, and the like. (S103). This is because the focusing point P of the laser beam L is aligned with the desired position inside the substrate of the object 1 to be processed, and the focusing point P of the laser beam L located on the back surface of the substrate of the object 1 to be processed. This is the amount of movement of the workpiece 1 in the Z-axis direction based on P. This movement amount is input to the overall control unit 127.

The object 1 to be processed is placed on the mounting table 107 of the laser processing device 100 so that the back surface of the substrate is on the condensing lens 105 side. Then, visible light is generated from the observation light source 117 to illuminate the back surface of the substrate of the object 1 to be processed (S105). The back surface including the illuminated line 5 to be cut is imaged by the image sensor 121. The planned cutting line 5 is a desired virtual line on which the workpiece 1 should be cut. The image pickup data captured by the image sensor 121 is sent to the image pickup data processing unit 125. Based on this image pickup data, the image pickup data processing unit 125 calculates focus data such that the focus of visible light of the observation light source 117 is located on the back surface of the substrate of the object 1 to be processed (S107).

This focus data is sent to the stage control unit 115. The stage control unit 115 moves the Z-axis stage 113 in the Z-axis direction based on the focus data (S109). As a result, the focus of the visible light of the observation light source 117 is located on the back surface of the substrate of the object 1 to be processed. The image pickup data processing unit 125 calculates the enlarged image data of the back surface of the substrate of the processing object 1 including the scheduled cutting line 5 based on the image pickup data. This enlarged image data is sent to the monitor 129 via the overall control unit 127, whereby the enlarged image near the line 5 scheduled to be cut is displayed on the monitor 129.

The movement amount data determined in advance in step S103 is input to the overall control unit 127, and this movement amount data is sent to the stage control unit 115. Based on this movement amount data, the stage control unit 115 moves the processing object 1 in the Z-axis direction by the Z-axis stage 113 to a position where the condensing point P of the laser beam L is inside the substrate of the processing object 1. Let (S111).

Subsequently, the laser light L is generated from the laser light source 101, and the laser light L is irradiated to the planned cutting line 5 on the back surface of the substrate of the processing object 1. Since the condensing point P of the laser beam L is located inside the substrate of the object 1 to be processed, the modified region is formed only inside the substrate of the object 1 to be processed. Then, the X-axis stage 109 and the Y-axis stage 111 are moved along the scheduled cutting line 5, and the cutting starting point region along the scheduled cutting line 5 is processed by the modified region formed along the scheduled cutting line 5. Formed inside object 1 (S113).

As described above, according to the laser processing method according to the present embodiment, the laser beam L is irradiated from the back surface side of the substrate of the object 1 to be processed, and the surface of the substrate is modified by absorbing multiple photons. The quality region can form a cutting origin region along the desired scheduled cutting line 5 where the workpiece 1 should be cut. Then, the position of the modified region formed inside the substrate is adjusted to the position where the condensing point P of the laser beam L is aligned in consideration of the thickness and material of the laminated portion provided on the surface of the substrate. It is controlled by. Therefore, it is possible to cut the workpiece 1 formed by providing the laminated portion on the surface of the substrate by dividing it with a relatively small force, starting from the cutting starting point region formed inside the substrate.

It should be noted that the laser beam L having a transparent wavelength or a wavelength with little absorption is used to irradiate the laminated portion of the object 1 to be processed with the laser beam L by aligning the condensing point P with the inside of the laminated portion. Also, a cutting starting point region along the planned cutting line 5 may be formed, and in this case, the workpiece 1 can be divided by a smaller force to cut.

Examples of the laser processing method according to the present embodiment will be described with reference to FIGS. 16 to 21.

[Example 1]

FIG. 16 (a) is a diagram showing a case where the modified region 7 is formed in the vicinity of the back surface of the substrate 15 in the processing object 1 according to the first embodiment, and FIG. 16 (b) is a diagram showing the case where the modified region 7 is formed in the vicinity of the back surface of the substrate 15. FIG. It is a figure which shows the case where the modification region 7 was formed in the vicinity of the surface of the substrate 15 in the object 1. The machined objects 1 shown in FIGS. 16 (a) and 16 (b) include those for next-generation high-speed and low-power consumption devices and those for next-generation devices.

The substrate 15 / first laminated portion 17a / second laminated portion 17b for the next-generation high-speed / low power consumption device are Si (500 μm) / SiO, respectively.₂It is (1 μm) / Si (3 μm). On the other hand, the substrate 15 / first laminated portion 17a / second laminated portion 17b for next-generation devices are Si (500 μm) / SrTiO, respectively.₃(Several 100 nm) / GaAs (Several 100 nm) (numbers in parentheses indicate thickness).

As shown in FIG. 16A, when the modified region 7 is located near the back surface 21 of the processed object 1, the processed object 1 is formed along the cutting starting point region formed by the modified region 7. The knife edge 23 is pressed against the surface 3 to break and cut the object 1 to be processed. This is because a large tensile stress among the bending stresses generated by pressing the knife edge 23 acts on the modified region 7, so that the workpiece 1 can be cut with a relatively small force. On the other hand, as shown in FIG. 16 (b), when the modified region 7 is located near the front surface 3 of the workpiece 1, the knife edge 23 is pressed against the back surface 3 of the workpiece 1 for the same reason. It hits and breaks the object to be processed 1 and cuts it.

In addition, "the modified region 7 is located near the back surface 21 of the workpiece 1" means that the modified region 7 constituting the cutting starting point region is the center position (thickness) of the workpiece 1 in the thickness direction. It means that it is formed unevenly from the half position) to the back surface 21 side. That is, it means that the center position of the width of the modified region 7 in the thickness direction of the work object 1 is deviated from the center position in the thickness direction of the work object 1 to the back surface 21 side. It does not mean only when all the parts of the modified region 7 are located on the back surface 21 side with respect to the center position in the thickness direction of the workpiece 1. Similarly, "the modified region 7 is located near the surface 3 of the workpiece 1" means that the modified region 7 constituting the cutting starting point region is the surface 3 from the center position in the thickness direction of the workpiece 1. It means that it is formed unevenly to the side. The above is the same for the formation position of the modified region 7 with respect to the substrate 15.

[Example 2]

FIG. 17 (a) is a diagram showing a case where the modified region 7 is formed in the vicinity of the back surface of the substrate 15 in the processing object 1 according to the second embodiment, and FIG. 17 (b) is a diagram showing the case where the modified region 7 is formed in the vicinity of the back surface of the substrate 15. FIG. It is a figure which shows the case where the modification region 7 was formed in the vicinity of the surface of the substrate 15 in the object 1. The processing object 1 shown in FIGS. 17 (a) and 17 (b) is for a blue LD / LED, and the substrate 15 / laminated portion 17 is Al.₂O₃Laminated functional film (several 100 nm) in which multiple layers of semiconductor crystals such as (500 μm) / GaN are formed, and Al₂O₃In some cases, it is a laminated functional film (several 100 nm) in which multiple layers such as (500 μm) / ZnO are formed (the numbers in parentheses indicate the thickness).

For the same reason as in the case of the work target 1 according to the first embodiment, when the modified region 7 is located near the back surface 21 of the work target 1, as shown in FIG. 17 (a), the work target is processed. The knife edge 23 is pressed against the surface 3 of 1 to break and cut the object 1 to be processed. On the other hand, as shown in FIG. 17B, when the modified region 7 is located near the front surface 3 of the machining object 1, the knife edge 23 is pressed against the back surface 21 of the machining object 1 to be machined. Divide 1 and cut.

[Example 3]

FIG. 18 (a) is a diagram showing a case where the modified region 7 is formed in the vicinity of the surface of the substrate 15 and the laminated portion 17 in the workpiece 1 according to the third embodiment, and FIG. 18 (b) is a diagram showing the case where the modified region 7 is formed. It is a figure which shows the case where the modification region 7 was formed near the back surface of the substrate 15 in the processing object 1 which concerns on Example 3, and FIG. 18 (c) shows the surface of the substrate 15 in processing object 1 which concerns on Example 3. It is a figure which shows the case where the modified region 7 is formed in the vicinity. The processed object 1 shown in FIGS. 18 (a) to 18 (c) is for an infrared photodetector, and the substrate 15 / laminated portion 17 is Al.₂O₃(500 μm) / PbSe (10 μm) and Al₂O₃It may be (500 μm) / HgCdTe (10 μm) (the number in parentheses indicates the thickness).

For the same reason as in the case of the workpiece 1 according to the first embodiment, when the modified region 7 is located near the surface 3 of the workpiece 1 as shown in FIGS. 18 (a) and 18 (c). The knife edge 23 is pressed against the back surface 21 of the object to be processed 1 to break the object 1 to be processed and cut it. On the other hand, as shown in FIG. 18 (b), when the modified region 7 is located near the back surface 21 of the workpiece 1, the knife edge 23 is pressed against the surface 3 of the workpiece 1 to be machined. Divide 1 and cut.

[Example 4]

FIG. 19 is a diagram showing a work target 1 according to the fourth embodiment. The object to be processed 1 shown in FIG. 19 is a multilayer glass, which is formed by laminating two glass substrates as a first laminated portion 17a and a second laminated portion 17b on a glass substrate as a substrate 15. is there. The modified region 7 in each glass substrate is formed on the back surface 21 side of the object to be processed 1. In this case as well, for the same reason as in the case of the workpiece 1 according to the first embodiment, the knife edge 23 is pressed against the surface 3 of the workpiece 1 to break the workpiece 1 and cut it. When the thickness of the laminated portion is thick or the hardness of the laminated portion is high as described above, if a cutting starting point region is also formed inside the laminated portion, the object 1 to be processed can be cut by dividing it with a smaller force. Can be done.

[Example 5]

20 (a) to 21 (b) are diagrams showing the work target 1 according to the fifth embodiment. FIG. 20 (a) is a diagram showing a case where the modified region 7 is formed in the vicinity of the surface of the substrate 15 and the vicinity of the surface of the laminated portion 17 in the workpiece 1 according to the fifth embodiment, and is shown in FIG. 20 (b). FIG. 5 is a diagram showing a case where the modified region 7 is formed in the vicinity of the back surface of the substrate 15 and the vicinity of the back surface of the laminated portion 17 in the processed object 1 according to the fifth embodiment. Further, FIG. 21 (a) is a diagram showing a case where the modified region 7 is formed in the vicinity of the front surface of the substrate 15 and the vicinity of the back surface of the laminated portion 17 in the workpiece 1 according to the fifth embodiment, and is shown in FIG. 21 (a). b) is a diagram showing a case where the modified region 7 is formed in the vicinity of the back surface of the substrate 15 and the vicinity of the front surface of the laminated portion 17 in the workpiece 1 according to the fifth embodiment.

The processed object 1 shown in FIGS. 20 (a) to 21 (b) is for a reflective liquid crystal display device. The substrate 15 is a glass substrate (thickness 1.8 mm, outer diameter 8 inches) on which a common electrode is formed, and the laminated portion 17 is a Si substrate (thickness 500 μm, outer diameter 8 inches) on which a TFT is formed. .. The substrate 15 and the laminated portion 17 are attached to each other by an adhesive 25 with a gap for inserting a liquid crystal.

In the case of FIGS. 20 (a) and 20 (b), a laser beam is irradiated from the back surface 21 side of the object to be processed 1 to form a modified region 7 inside the laminated portion 17, and then the object to be processed is processed. The modified region 7 is formed inside the substrate 15 by irradiating the laser beam from the back surface 21 side of 1. This is because the laser beam has a transparent wavelength or a wavelength with little absorption with respect to both the substrate 15 and the laminated portion 17. Then, for the same reason as in the case of the machined object 1 according to the first embodiment, in the case of FIG. 20 (a), the knife edge 23 is pressed against the back surface 21 of the machined object 1 to break the machined object 1. And disconnect. On the other hand, in the case of FIG. 20 (b), the knife edge 23 is pressed against the surface 3 of the object to be processed 1 to break the object 1 to be processed and cut it.

In this way, if a cutting starting point region is formed between the substrate 15 and the laminated portion 17 by using a laser beam having a transparent wavelength or a wavelength with little absorption for both the substrate 15 and the laminated portion 17, a conventional diamond screen can be formed. It is possible to omit the reversing work of the work object 1 performed by the method, and it is possible to prevent the work object 1 from being destroyed during the reversing work. Further, it is possible to prevent the cutting starting point region formed between the substrate 15 and the laminated portion 17 from being displaced, which enables highly accurate cutting of the machining object 1. Further, since the lubricating cleaning water which is indispensable in the conventional blade dicing method is not required, there is no problem that the lubricating cleaning water gets into the gap between the substrate 15 and the laminated portion 17.

In the case of FIGS. 21 (a) and 21 (b), a laser beam is irradiated from the back surface 21 side of the object to be processed 1 to form a modified region 7 inside the substrate 15, and then the object to be processed 1 is processed. A modified region 7 is formed inside the laminated portion 17 by irradiating a laser beam from the surface 3 side of the above. Then, for the same reason as in the case of the workpiece 1 according to the first embodiment, in the case of FIG. 21 (a), the knife edge 23 is first pressed against the back surface 21 of the workpiece 1 to break the substrate 15. Then, the knife edge 23 is pressed against the surface 3 of the object 1 to be processed to break the laminated portion 17 and cut. On the other hand, in the case of FIG. 21 (b), the knife edge 23 is first pressed against the front surface 3 of the object to be machined 1 to break the substrate 15 and cut, and then the knife edge 23 is pressed against the back surface 21 of the object to be machined 1. Is pressed to break the laminated portion 17 and cut it.

[Example 6]

FIG. 22 is an enlarged cross-sectional view showing a main part of the workpiece 1 according to the sixth embodiment. In this processing object 1, a large number of chip forming regions F are provided on a substrate 15 which is a silicon wafer, and a dicing line region D is formed between adjacent chip forming regions F and F. FIG. 22 shows chip forming. The cross section of the portion where the region F and the dicing line region D are continuous is shown. The line to be cut is set along the dicing line area D.

As shown in the figure, an interlayer insulating film (laminated portion) 31 is formed on the substrate 15, and a metal wiring layer 32 is provided on the interlayer insulating film 31 in the chip forming region F of the substrate 15. There is. Further, an interlayer insulating film (laminated portion) 33 is formed on the substrate 15 so as to cover the interlayer insulating film 31 and the metal wiring layer 32, and in the chip forming region F of the substrate 15, metal is formed on the interlayer insulating film 33. A wiring layer 34 is provided. The substrate 15 and the metal wiring layer 32 are electrically connected by a plug 35 penetrating the interlayer insulating film 31. Further, the metal wiring layer 32 and the metal wiring layer 34 are electrically connected by a plug 36 penetrating the interlayer insulating film 33.

The light-collecting point is aligned with the inside of the substrate 15 to irradiate the workpiece 1 configured in this way with a laser beam, and the inside of the substrate 15 is irradiated along the dicing line region D (that is, along the planned cutting line). A modified region 7 is formed in the modified region 7, and a cutting starting region is formed by the modified region 7. Then, by pressing the knife edge 23 against the front surface 3 or the back surface 21 of the machining object 1 along the cutting starting point region, the machining object 1 can be cut with high accuracy.

Like the object 1 to be processed according to the sixth embodiment, SiO is placed on the planned cutting line of the substrate 15.₂Even when the insulating films 31 and 32 made of, SiN, etc. are formed as a laminated portion, it is possible to cut the object 1 to be processed with high accuracy.

Although the embodiments of the present invention have been described in detail above, it goes without saying that the present invention is not limited to the above embodiments.

In the above embodiment, a case where a processing object having a substrate and a laminated portion provided on the surface of the substrate is irradiated with laser light to form a cutting starting point region has been described, but in the present invention, the substrate is After irradiating the laser beam with a laser beam to form a cutting starting point region, a laminated portion may be provided on the surface of the substrate to form an object to be processed.

According to this laser processing method, a cutting origin region is formed inside the substrate before the laminated portion is provided on the surface of the substrate, but the formation of the modified region by multiphoton absorption is local and the substrate is formed. Since the laser beam is hardly absorbed on the surface of the substrate, the surface of the substrate does not melt. Therefore, as in the case where the modified region is not formed inside the substrate, the laminated portion can be provided on the surface of the substrate to form the object to be processed. The object to be processed thus formed can be cut by dividing it with a relatively small force starting from the cutting starting point region formed inside the substrate for the same reason as in the above embodiment.

<figref num="1">It is a top view of the processing object during laser processing by the laser processing method which concerns on this embodiment.</figref><figref num="2">It is sectional drawing along the line II-II of the processing object shown in FIG.</figref><figref num="3">It is a top view of the processing object after laser processing by the laser processing method which concerns on this embodiment.</figref><figref num="4">It is sectional drawing along the IV-IV line of the processing object shown in FIG.</figref><figref num="5">It is sectional drawing along the VV line of the processing object shown in FIG.</figref><figref num="6">It is a top view of the processing object cut by the laser processing method which concerns on this embodiment.</figref><figref num="7">It is a graph which shows the relationship between the electric field strength and the size of a crack spot in the laser processing method which concerns on this embodiment.</figref><figref num="8">It is sectional drawing of the processing object in the 1st process of the laser processing method which concerns on this embodiment.</figref><figref num="9">It is sectional drawing of the processing object in the 2nd step of the laser processing method which concerns on this embodiment.</figref><figref num="10">It is sectional drawing of the processing object in the 3rd process of the laser processing method which concerns on this embodiment.</figref><figref num="11">It is sectional drawing of the processing object in the 4th process of the laser processing method which concerns on this embodiment.</figref><figref num="12">It is a figure showing the photograph of the cross section of a part of the silicon wafer cut by the laser processing method which concerns on this embodiment.</figref><figref num="13">It is a graph which shows the relationship between the wavelength of the laser light and the transmittance inside the silicon substrate in the laser processing method which concerns on this embodiment.</figref><figref num="14">It is a schematic block diagram of the laser processing apparatus which concerns on this embodiment.</figref><figref num="15">It is a flowchart for demonstrating the laser processing method which concerns on this Embodiment.</figref><figref num="16">It is a figure which shows the processing object which concerns on 1st Example, (a) shows the case where the modification region was formed near the back surface of a substrate, and (b) shows the modification region near the front surface of a substrate. The case where it is formed is shown.</figref><figref num="17">It is a figure which shows the processing object which concerns on 2nd Example, (a) shows the case where the modification region was formed near the back surface of a substrate, and (b) shows the modification region near the front surface of a substrate. The case where it is formed is shown.</figref><figref num="18">It is a figure which shows the processing object which concerns on 3rd Example, (a) shows the case where the modification region was formed near the front surface of a substrate, and (b) is near the back surface of a substrate. The case where the modified region is formed is shown, and the case where the modified region is formed near the surface of the substrate is shown in (c).</figref><figref num="19">It is a figure which shows the processing object which concerns on 4th Example.</figref><figref num="20">It is a figure which shows the processing object which concerns on 5th Example, (a) shows the case where the modification region is formed near the surface of a substrate and near the surface of a laminated part, and (b) shows the case of forming a substrate. The case where the modified region is formed in the vicinity of the back surface and the vicinity of the back surface of the laminated portion is shown.</figref><figref num="21">It is a figure which shows the processing object which concerns on 5th Example, (a) shows the case where the modification region is formed near the front surface of a substrate, and near the back surface of a laminated part, and (b) shows the case of the substrate. The case where the modified region is formed in the vicinity of the back surface and the vicinity of the front surface of the laminated portion is shown.</figref><figref num="22">It is an enlarged cross-sectional view which shows the main part of the processing object which concerns on Example 6.</figref>

Code description

1 ... object to be processed, 3 ... front surface, 5 ... planned cutting line, 7 ... modified area, 15 ... substrate, 21 ... back surface, L ... laser light, P ... the focusing point.