JP4732063B2 - Laser processing method - Google Patents

Description

  The present invention relates to a laser processing method used for cutting a plate-like workpiece.

  As a method of cutting a workpiece by laser processing, there is a method described in Non-Patent Document 1 below. This laser processing method described in Non-Patent Document 1 cuts a silicon wafer, uses a wavelength in the vicinity of 1 μm through which silicon passes, and condenses the inside of the wafer to continuously form a modified layer. It is a method of cutting using it as a trigger.

Also known is a laser processing method that cuts a workpiece by irradiating the workpiece with an ultra-short pulse laser, forming a machining start point, generating a crack with a heat source, and further propagating along a planned cutting line. (For example, refer to Patent Document 1).
JP 2003-154517 A Kazuhisa Arai, “Laser dicing on semiconductor wafers”, Journal of Abrasive Technology, Vol. 47, no. 5, 2003 MAY. 229-231

  When a modified region is formed inside a plate-shaped workpiece whose surface for processing laser light is an uneven surface using the laser processing method as described above, the position of the condensing point of the processing laser light May not follow the uneven surface, and damage may occur on the incident surface. If the workpiece is cut while such damage remains, the cutting accuracy is lowered and the quality of the workpiece obtained by cutting the workpiece is lowered. Hereinafter, the case where damage occurs on the incident surface will be described in detail with reference to FIG.

  FIG. 19 is a cross-sectional view of a plate-like workpiece 101 whose incident surface r100 of the processing laser beam 100L is an uneven surface. The incident surface r100 has a convex region surface r101 and a concave region surface r102, and the planned cutting line 105 of the workpiece 101 extends over the convex region surface r101 and the concave region surface r102. In this case, when the processing laser beam 100L is irradiated along the planned cutting line 105 with the focusing point 100P of the processing laser beam 100L aligned with the inside of the processing target object 101, the processing target 101 is scheduled to be cut. A modified region 107 along the line 105 is formed.

  The processing laser beam 100 </ b> L is collected by the processing objective lens 130 held by the actuator 132. By operating this actuator 132, the position of the condensing point 100P can be moved in the thickness direction of the workpiece 101. Further, the condensing point 100P is controlled to be a fixed position by a controller 139 connected to the actuator 132. However, since the step r103 in the thickness direction of the workpiece 101 is provided between the convex region surface r101 and the concave region surface r102, the condensing point 100P is condensed when passing through the step r103. There are cases where the position of the point 100P cannot follow the step r103. At this time, damage DM occurs on the concave region surface r102 in the vicinity of the step r103.

  Accordingly, the present invention has been made in view of such circumstances, and a laser processing method that enables high-precision cutting of a plate-like processing target object whose processing laser light incident surface is an uneven surface. The purpose is to provide.

  In order to solve the above-described problem, the laser processing method of the present invention is adapted to synthesize a focused laser beam inside a plate-like workpiece and irradiate a laser beam for processing along the line to be cut of the workpiece. A modified region that is a starting point of cutting inside the workpiece, the incident surface of the processing laser beam on the workpiece is an uneven surface, and the planned cutting line is the incident surface. A first step of forming a first modified region along a predetermined cutting line on the inner side by a predetermined distance from the concave region surface and a predetermined distance from the convex region surface in the case of extending over the concave region surface and the convex region surface; And a second step of forming a second modified region along the line to be cut.

  In the laser processing method of the present invention, the first and second modified regions are formed in separate steps inside the object to be processed on the concave region surface and the convex region surface of the incident surface, respectively. For this reason, when the planned cutting line extends over the concave area surface and the convex area surface of the incident surface, damage to the incident surface caused by irradiation of the processing laser light is reduced in the vicinity between the concave area surface and the convex area surface. it can. Therefore, according to the laser processing method of the present invention, it is possible to cut a plate-like processing target object whose incident surface of the processing laser beam is an uneven surface with high accuracy.

  The predetermined distance between the concave region surface and the first modified region and the predetermined distance between the convex region surface and the second modified region may be the same or different from each other. The order in which the first step and the second step are performed is not particularly limited. For example, the second step may be performed after the first step, or the first step may be performed after the second step. Further, the first step and the second step may be performed simultaneously.

  Further, in the first step, when the processing laser beam is irradiated along the portion on the concave region surface in the planned cutting line, the processing laser beam condensing point is located on the inner side by a predetermined distance from the concave region surface. In this way, it is preferable to fix the irradiation conditions of the processing laser light when changing the irradiation conditions of the processing laser light and irradiating the processing laser light along the portion on the convex region surface in the planned cutting line.

  Thus, in the first step, a modified region that follows the displacement of the incident surface in the thickness direction of the workpiece can be formed inside the concave region surface, and the modified region can also be modified inside the convex region surface. A quality region can be formed.

  In the second step, the processing laser light is pulse-oscillated along the portion on the convex region surface in the planned cutting line, and the processing laser light is continuously oscillated along the portion on the concave region surface in the planned cutting line. It is preferable to make it.

  When the processing laser light is pulse-oscillated, the modified region can be reliably formed inside the object to be processed as compared with the case where the processing laser light is continuously oscillated. For this reason, in the second step, the processing laser light is pulse-oscillated on the convex region surface, and the processing laser light is continuously oscillated on the concave region surface, thereby along the portion on the convex region surface in the line to be cut. The modified region can be selectively formed.

  When a metal film made of Al or Al-Si is positioned on the planned cutting line, the laser beam for processing is not transmitted and is almost reflected by the metal film. Is not formed. In addition, when laser light is collected on the surface of the metal film, the surface of the metal film may be damaged. In such a case, it is possible to prevent damage to the surface of the metal film by continuously oscillating the processing laser beam.

  ADVANTAGE OF THE INVENTION According to this invention, the laser processing method which enables the highly accurate cutting | disconnection of the plate-shaped workpiece whose incident surface of the processing laser beam is an uneven surface can be provided.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the laser processing method of the present embodiment, a phenomenon called multiphoton absorption is used in order to form a modified region inside the workpiece. Therefore, first, a laser processing method for forming a modified region by multiphoton absorption will be described.

Photon energy hν is smaller than the band gap E _G of absorption of the material becomes transparent. Therefore, a condition under which absorption occurs in the material is hv> E _G. However, even when optically transparent, increasing the intensity of the laser beam very Nhnyu> of _{E G} condition (n = 2,3,4, ···) the intensity of laser light becomes very high. This phenomenon is called multiphoton absorption. In the case of a pulse wave, the intensity of the laser beam is determined by the peak power density (W / cm ² ) at the condensing point of the laser beam. For example, the multiphoton is obtained under conditions where the peak power density is 1 × 10 ⁸ (W / cm ² ) or more. Absorption occurs. The peak power density is determined by (energy per pulse of laser light at the condensing point) / (laser beam cross-sectional area of laser light × pulse width). In the case of a continuous wave, the intensity of the laser beam is determined by the electric field intensity (W / cm ² ) at the condensing point of the laser beam.

  The principle of the laser processing method according to this embodiment using such multiphoton absorption will be described with reference to FIGS. As shown in FIG. 1, there is a planned cutting line 5 for cutting the workpiece 1 on the surface 3 of the wafer-like (plate-like) workpiece 1. The planned cutting line 5 is a virtual line extending linearly. In the laser processing method according to the present embodiment, as shown in FIG. 2, the modified region 7 is formed by irradiating the laser beam L with the focusing point P inside the processing object 1 under the condition that multiphoton absorption occurs. Form. In addition, the condensing point P is a location where the laser light L is condensed. Further, the planned cutting line 5 is not limited to a straight line but may be a curved line, or may be a line actually drawn on the workpiece 1 without being limited to a virtual line.

  Then, the condensing point P is moved along the planned cutting line 5 by relatively moving the laser light L along the planned cutting line 5 (that is, in the direction of arrow A in FIG. 1). Thereby, as shown in FIGS. 3 to 5, the modified region 7 is formed inside the workpiece 1 along the planned cutting line 5, and this modified region 7 becomes the cutting start region 8. Here, the cutting starting point region 8 means a region that becomes a starting point of cutting (cracking) when the workpiece 1 is cut. The cutting starting point region 8 may be formed by continuously forming the modified region 7 or may be formed by intermittently forming the modified region 7.

  The laser processing method according to the present embodiment does not form the modified region 7 by causing the workpiece 1 to generate heat when the workpiece 1 absorbs the laser beam L. The modified region 7 is formed by transmitting the laser beam L through the workpiece 1 and generating multiphoton absorption inside the workpiece 1. Therefore, since the laser beam L is hardly absorbed by the surface 3 of the workpiece 1, the surface 3 of the workpiece 1 is not melted.

  If the cutting start region 8 is formed inside the processing target 1, cracks are likely to occur from the cutting start region 8, so that the processing target 1 is cut with a relatively small force as shown in FIG. 6. be able to. Therefore, it is possible to cut the workpiece 1 with high accuracy without causing unnecessary cracks on the surface 3 of the workpiece 1 that greatly deviate from the planned cutting line 5.

  The following two types of cutting of the workpiece 1 starting from the cutting start region 8 are conceivable. First, after the cutting start region 8 is formed, when the artificial force is applied to the processing target 1, the processing target 1 is broken starting from the cutting start region 8 and the processing target 1 is cut. It is. This is, for example, cutting when the workpiece 1 is thick. The artificial force is applied by, for example, applying bending stress or shear stress to the workpiece 1 along the cutting start region 8 of the workpiece 1 or giving a temperature difference to the workpiece 1. It is to generate thermal stress. The other one forms the cutting start region 8 so that it is naturally cracked from the cutting start region 8 in the cross-sectional direction (thickness direction) of the processing target 1, and as a result, the processing target 1 is formed. This is the case when it is disconnected. This is possible, for example, when the thickness of the workpiece 1 is small, and the cutting start region 8 is formed by one row of the modified region 7, and when the thickness of the workpiece 1 is large. This is made possible by forming the cutting start region 8 by the modified region 7 formed in a plurality of rows in the thickness direction. Even in the case of natural cracking, cracks do not run on the surface 3 of the portion corresponding to the portion where the cutting start region 8 is not formed in the portion to be cut, and the portion where the cutting start region 8 is formed. Since only the corresponding part can be cleaved, the cleaving can be controlled well. In recent years, since the thickness of the workpiece 1 such as a silicon wafer tends to be thin, such a cleaving method with good controllability is very effective.

  In the laser processing method according to the present embodiment, there are the following cases (1) to (3) as modified regions formed by multiphoton absorption.

(1) In the case where the modified region is a crack region including one or a plurality of cracks, the focusing point is set inside the object to be processed (for example, a piezoelectric material made of glass or LiTaO ₃ ), and the electric field strength at the focusing point is Irradiation with laser light is performed under conditions of 1 × 10 ⁸ (W / cm ² ) or more and a pulse width of 1 μs or less. The magnitude of this pulse width is a condition that allows a crack region to be formed only inside the workpiece without causing extra damage to the surface of the workpiece while causing multiphoton absorption. As a result, a phenomenon of optical damage due to multiphoton absorption occurs inside the workpiece. This optical damage induces thermal strain inside the workpiece, thereby forming a crack region inside the workpiece. The upper limit value of the electric field strength is, for example, 1 × 10 ¹² (W / cm ² ). The pulse width is preferably 1 ns to 200 ns, for example. The formation of the crack region by multiphoton absorption is described in, for example, “Inside of glass substrate by solid-state laser harmonics” on pages 23-28 of the 45th Laser Thermal Processing Research Papers (December 1998). It is described in “Marking”.

  The inventor obtained the relationship between the electric field strength and the size of the cracks by experiment. The experimental conditions are as follows.

(A) Workpiece: Pyrex (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 ⁻⁸ cm ²
Oscillation form: Q switch pulse repetition frequency: 100 kHz
Pulse width: 30ns
Output: Output <1 mJ / pulse laser light quality: TEM ₀₀
Polarization characteristics: Linearly polarized light (C) Condensation lens Transmittance to wavelength of laser beam: 60% (D) Moving speed of mounting table on which workpiece is mounted: 100 mm / second

Note that the laser light quality TEM ₀₀ means that the light condensing performance is high and the light can be condensed up to the wavelength of the laser light.

FIG. 7 is a graph showing the results of the experiment. The horizontal axis represents the peak power density. Since the laser beam is a pulsed laser beam, the electric field strength is represented by the peak power density. The vertical axis represents the size of a crack portion (crack spot) formed inside the workpiece by one pulse of laser light. Crack spots gather to form a crack region. The size of the crack spot is the size of the portion having the maximum length in the shape of the crack spot. Data indicated by black circles in the graph is for the case where the magnification of the condenser lens (C) is 100 times and the numerical aperture (NA) is 0.80. On the other hand, the data indicated by the white circles in the graph is when the magnification of the condenser lens (C) is 50 times and the numerical aperture (NA) is 0.55. From the peak power density of about 10 ¹¹ (W / cm ² ), it can be seen that a crack spot is generated inside the workpiece, and the crack spot increases as the peak power density increases.

  Next, the mechanism of cutting the workpiece by forming the crack region will be described with reference to FIGS. As shown in FIG. 8, under the condition that multiphoton absorption occurs, the converging point P is aligned with the inside of the workpiece 1 and the laser beam L is irradiated to form a crack region 9 along the planned cutting line. The crack region 9 is a region including one or more cracks. The crack region 9 thus formed becomes a cutting start region. As shown in FIG. 9, the crack further grows from the crack region 9 (that is, from the cutting start region), and the crack is formed on the front surface 3 and the back surface 21 of the workpiece 1 as shown in FIG. 10. As shown in FIG. 11, the workpiece 1 is broken and the workpiece 1 is cut. A crack that reaches the front surface 3 and the back surface 21 of the workpiece 1 may grow naturally, or may grow when a force is applied to the workpiece 1.

(2) When the reforming region is a melt processing region The focusing point is set inside the object to be processed (for example, a semiconductor material such as silicon), and the electric field strength at the focusing point is 1 × 10 ⁸ (W / cm ^2). ) Irradiation with laser light is performed under the above conditions with a pulse width of 1 μs or less. As a result, the inside of the workpiece is locally heated by multiphoton absorption. By this heating, a melt processing region is formed inside the workpiece. The melt treatment region is a region once solidified after melting, a region in a molten state, or a region re-solidified from a molten state, and can also be referred to as a phase-changed region or a region in which the crystal structure has changed. The melt treatment region can also be said to be a region in which one structure is changed to another structure in a single crystal structure, an amorphous structure, or a polycrystalline structure. In other words, for example, a region changed from a single crystal structure to an amorphous structure, a region changed from a single crystal structure to a polycrystalline structure, or 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 has, for example, an amorphous silicon structure. The upper limit value of the electric field strength is, for example, 1 × 10 ¹² (W / cm ² ). The pulse width is preferably 1 ns to 200 ns, for example.

  The inventor has confirmed through experiments that a melt-processed region is formed inside a silicon wafer. The experimental conditions are as follows.

(A) Workpiece: silicon wafer (thickness 350 μm, outer diameter 4 inches)
(B) Laser light source: semiconductor laser excitation Nd: YAG laser wavelength: 1064 nm
Laser light spot cross-sectional area: 3.14 × 10 ⁻⁸ cm ²
Oscillation form: Q switch pulse repetition frequency: 100 kHz
Pulse width: 30ns
Output: 20 μJ / pulse laser light Quality: TEM ₀₀
Polarization characteristics: Linearly polarized light (C) Condensing lens magnification: 50 × N. A. : 0.55
Transmittance with respect to laser light wavelength: 60% (D) Moving speed of mounting table on which workpiece is mounted: 100 mm / second

  FIG. 12 is a view 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 in the thickness direction of the melt processing region 13 formed under the above conditions is about 100 μm.

  The fact that the melt processing region 13 is formed by multiphoton absorption will be described. FIG. 13 is a graph showing the relationship between the wavelength of the laser beam and the transmittance inside the silicon substrate. However, the reflection components on the front side and the back side of the silicon substrate are removed to show the transmittance 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, when the thickness of the silicon substrate is 500 μm or less at the wavelength of the Nd: YAG laser of 1064 nm, it can be seen that the laser light is transmitted by 80% or more 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 11, 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. Therefore, the laser beam is hardly absorbed inside the silicon wafer 11 and almost all is transmitted. This is not because 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 with laser light) It means that the melt processing region 13 is formed by multiphoton absorption. The formation of the melt-processed region by multiphoton absorption is described in, for example, “Evaluation of processing characteristics of silicon by picosecond pulse laser” on pages 72 to 73 of the 66th Annual Meeting of the Japan Welding Society (April 2000). Are listed.

  Note that a silicon wafer is cracked as a result of generating cracks in the cross-sectional direction starting from the cutting start region formed by the melt processing region and reaching the front and back surfaces of the silicon wafer. The The cracks that reach the front and back surfaces of the silicon wafer may grow naturally or may grow by applying force to the silicon wafer. And when a crack naturally grows from the cutting start region to the front and back surfaces of the silicon wafer, the case where the crack grows from a state where the melt treatment region forming the cutting starting region is melted, and the cutting starting region There are both cases where cracks grow when the solidified region is melted from the molten state. However, in either case, the melt processing region is formed only inside the silicon wafer, and the melt processing region is formed only inside the cut surface after cutting as shown in FIG. In this way, when the cutting start region is formed by the melt processing region inside the workpiece, unnecessary cracking off the cutting start region line is unlikely to occur during cleaving, so that cleaving control is facilitated.

(3) When the modified region is a refractive index changing region The focusing point is set inside the object to be processed (for example, glass), and the electric field intensity at the focusing point is 1 × 10 ⁸ (W / cm ² ) or more. Laser light is irradiated under the condition that the pulse width is 1 ns or less. When the pulse width is made extremely short and multiphoton absorption occurs inside the workpiece, the energy due to the multiphoton absorption is not converted into thermal energy, and the ion valence change and crystallization occur inside the workpiece. Alternatively, a permanent structural change such as polarization orientation is induced to form a refractive index change region. The upper limit value of the electric field strength is, for example, 1 × 10 ¹² (W / cm ² ). For example, the pulse width is preferably 1 ns or less, and more preferably 1 ps or less. The formation of the refractive index changing region by multiphoton absorption is described in, for example, “The Femtosecond Laser Irradiation to the Inside of Glass” on pages 105 to 111 of the 42nd Laser Thermal Processing Research Institute Proceedings (November 1997). Photo-induced structure formation ”.

  As described above, the cases of (1) to (3) have been described as the modified regions formed by multiphoton absorption. However, considering the crystal structure of the wafer-like workpiece and its cleavage property, the cutting origin region is described below. If it forms in this way, it will become possible to cut | disconnect a process target object with much smaller force from the cutting | disconnection starting point area | region as a starting point, and still more accurately.

That is, in the case of a substrate made of a single crystal semiconductor having a diamond structure such as silicon, the cutting start region is formed in a direction along the (111) plane (first cleavage plane) or the (110) plane (second cleavage plane). Is preferred. In the case of a substrate made of a zinc-blende-type III-V group compound semiconductor such as GaAs, it is preferable to form the cutting start region in the direction along the (110) plane. Further, in the case of a substrate having a hexagonal crystal structure such as sapphire (Al ₂ O ₃ ), the (1120) plane (A plane) or (1100) plane ( It is preferable to form the cutting start region in a direction along the (M plane).

  Note that the orientation flat is formed on the substrate along the direction in which the above-described cutting start region is to be formed (for example, the direction along the (111) plane in the single crystal silicon substrate) or the direction perpendicular to the direction in which the cutting start region is to be formed. By using the orientation flat as a reference, it is possible to easily and accurately form the cutting start area along the direction in which the cutting start area is to be formed on the substrate.

  Next, a preferred embodiment of the present invention will be described. FIG. 14 is a plan view schematically showing an example of a processing object in the laser processing method of the present embodiment. 15 is a cross-sectional view taken along the arrow XV-XV in FIG.

  In the present embodiment, the workpiece 1 includes a substrate 4 and a convex portion 4 a provided on the outer periphery of the substrate 4. An example of the substrate 4 is a silicon wafer. The convex portion 4a is made of, for example, silicon oxide or silicon. The processing object 1 has an incident surface r of a laser beam L (processing laser beam). The incident surface r is an uneven surface and includes a concave region surface r2 and a convex region surface r1. The concave area surface r2 may be formed by etching the workpiece 1 such as a silicon wafer. The convex region surface r1 corresponds to, for example, the top surface of the convex portion 4a having a rectangular cross section. The concave region surface r2 corresponds to the bottom surface of a concave portion having a rectangular cross section, for example, located between the convex portions 4a and 4a. A step r3 in the thickness direction of the workpiece 1 is provided between the concave region surface r2 and the convex region surface r1. The height of the step r3 (the height of the convex portion 4a) is, for example, about 16 μm. On the incident surface r, a dicing street is formed in a lattice shape over the concave region surface r2 and the convex region surface r1, and a cutting line 5 is set as a virtual line on the dicing street. Note that the scheduled cutting line 5 is for assuming a cutting location, and the dicing street may not be formed on the workpiece 1. The planned cutting line 5 is composed of, for example, a line parallel to the orientation flat 6 of the substrate 4 and a vertical line. Further, the metal film 4b made of Al or Al—Si may be arranged at three locations on the convex region surface r1. These metal films 4b are formed, for example, when a nail that holds the workpiece 1 such as a silicon wafer blocks light during exposure.

  Next, an example of a laser processing method according to this embodiment for cutting the workpiece 1 configured as described above will be described. 16 (a) and 16 (b) to FIG. 18 (a) and FIG. 18 (b) are cross-sectional views of the object to be processed in each step of the laser processing method of the present embodiment.

(First step)
First, as shown in FIGS. 16 (a) and 16 (b), the laser beam L is applied to the inside of the substrate 4 and the laser beam L is irradiated. A modified region 71 as a starting point is formed inside the substrate 4. The modified region 71 is formed on the inner side by a predetermined distance from the incident surface r in the thickness direction of the workpiece 1. Further, the laser light L is condensed by an objective lens 30 held by an actuator 32 made of, for example, a piezo element. A controller 39 for controlling the actuator 32 is connected to the actuator 32.

  As shown in FIG. 16A, when the laser beam L is irradiated along the portion 51b on the concave region surface r2 in the planned cutting line 5, the condensing point P of the laser light L is the concave region surface r2. The irradiation condition of the laser beam L is changed so as to be located on the inner side of the distance d1. Examples of the irradiation condition of the laser beam L include the position of the objective lens 30 in the thickness direction of the workpiece 1. The position of the objective lens 30 is adjusted by controlling the amount of expansion / contraction of the actuator 32 by the controller 39, and is displaced so as to follow the irregularities and undulations of the concave area surface r2. Thus, the modified region 71b can be formed at a certain position inside the distance d1 from the concave region surface r2 along the portion 51b on the concave region surface r2 in the planned cutting line 5. That is, the modified region 71b is formed inside the concave region surface r2 so as to follow the displacement of the incident surface r in the thickness direction of the workpiece 1.

  On the other hand, as shown in FIG. 16B, when the laser beam L is irradiated along the portion 51a on the convex region surface r1 in the planned cutting line 5, the irradiation condition of the laser beam L is fixed. Specifically, for example, the position of the objective lens 30 in the thickness direction of the workpiece 1 is fixed. At this time, the position of the condensing point P depends on the difference in height between the convex region surface r1 and the concave region surface r2 in the thickness direction of the workpiece 1 (height of the convex portion 4a) ΔH. It is formed below 71b (side away from the convex region surface r1). For example, when considering the outermost light beam of the laser light L collected by the objective lens 30, in principle, the incident angle from the air (refractive index n = 1) to the workpiece 1 is θ, When the refraction angle at the workpiece 1 (refractive index = n ′) is θ ′, if the convex portion 4a and the substrate 4 are made of the same material, {d1 + ΔH · n ′ · (cos θ ′ / The modified region 71a is formed on the lower side by cos θ)}. However, sin θ = n ′ · sin θ ′. Moreover, when the convex part 4a and the board | substrate 4 consist of a mutually different material, it is necessary to further consider the refractive index of each material.

  Thus, in the first step in the present embodiment, the modified region 71b that follows the displacement of the incident surface r in the thickness direction of the workpiece 1 can be formed inside the concave region surface r2. The modified region 71a can also be formed inside the convex region surface r1. In such a case, since the irradiation condition of the laser beam L is fixed when irradiating the laser beam L along the portion 51a on the convex region surface r1 in the planned cutting line 5, the concave region surface r2 and the convex region surface r1 It is possible to reduce the damage of the incident surface r caused by the irradiation of the laser light L in the vicinity of.

  In addition, on the metal film 4b located on the convex region surface r1, it is preferable that the surface of the metal film 4b is not damaged by switching the laser light L from pulse oscillation to continuous oscillation. As a result, the modified region 71a is not formed along the portion on the metal film 4b in the planned cutting line 5.

  Next, as shown in FIGS. 17A and 17B, the modified region 72 and the modified region 73 (first modified region) are formed by the same method as the method of forming the modified region 71. It forms in order toward the incident surface r side. When forming the modified region 72, as shown in FIG. 17A, the modified region 72b is formed along the portion 51b on the concave region surface r2 in the planned cutting line 5, and the planned cutting line 5 is formed. The modified region 72a is formed along the portion 51a on the convex region surface r1. The modified region 72b is formed inside the distance d2 from the recessed region surface r2 in the thickness direction of the workpiece 1. When forming the modified region 73, as shown in FIG. 17B, the modified region 73b is formed along the portion 51b on the concave region surface r2 in the planned cutting line 5, and the planned cutting line 5 is formed. The modified region 73a is formed along the portion 51a on the convex region surface r1. The modified region 73b is formed inside the distance d3 from the recessed region surface r2 in the thickness direction of the workpiece 1.

  In addition, on the metal film 4b located on the convex region surface r1, it is preferable that the surface of the metal film 4b is not damaged by switching the laser light L from pulse oscillation to continuous oscillation. As a result, the modified regions 72a and 73a are not formed along the portion of the cutting line 5 on the metal film 4b.

  In the present embodiment, the three modified regions 71 to 73 are formed in the first step, but the number of the modified regions is not limited to this. For example, only one row of modified regions may be formed, or four or more rows may be formed.

(Second step)
Next, as shown in FIGS. 18 (a) and 18 (b), the laser beam L is irradiated with the focusing point P inside the workpiece 1. As a result, the modified region 74 is formed along the portion 51a on the convex region surface r1 in the planned cutting line 5 on the inner side of the distance d4 from the convex region surface r1. Subsequently, a modified region 75 (second modified region) is formed along the portion 51a on the projected region surface r1 in the planned cutting line 5 on the inner side of the distance d5 from the projected region surface r1. The modified region 75 is formed inside the convex portion 4a, that is, below the convex region surface r1 and above the concave region surface r2. When forming the modified regions 74 and 75, as shown in FIG. 18A, for example, the laser beam L is pulsated along the portion 51a on the convex region surface r1 in the planned cutting line 5, The laser light L is continuously oscillated along the portion 51b on the concave region surface r2 in the planned cutting line 5. When the laser beam L is continuously oscillated, the laser energy becomes low, so that multiphoton absorption does not occur, and it becomes difficult to form a modified region inside the workpiece 1. Further, when the laser beam L is continuously oscillated, the laser energy is low, so the laser energy does not exceed the energy threshold necessary for processing the workpiece 1. For this reason, it is possible to prevent damage to the incident surface r of the workpiece 1.

  In addition, on the metal film 4b located on the convex region surface r1, it is preferable that the surface of the metal film 4b is not damaged by switching the laser light L from pulse oscillation to continuous oscillation. As a result, the modified regions 74 and 75 are not formed along the portion on the metal film 4b in the planned cutting line 5.

  When the laser beam L is pulse-oscillated, the modified region can be reliably formed inside the workpiece 1 as compared with the case where the laser beam L is continuously oscillated. For this reason, the convex region surface r1 pulsates the laser beam L and the concave region surface r2 continuously oscillates the laser beam L, as shown in FIG. The modified regions 74 and 75 can be selectively formed along the portion 51a on r1.

  In the present embodiment, the two modified regions 74 and 75 are formed in the second step, but the number of modified regions is not limited to this. For example, only one row of modified regions may be formed, or three or more rows may be formed. The number of rows in the modified region is preferably set as appropriate according to the height ΔH of the convex portion 4a.

  Further, the modified regions 71 to 75 may be formed of continuously formed modified regions, like the above-described modified region 7, or may be formed intermittently at predetermined intervals. It may consist of regions.

(Cutting process)
After forming the modified regions 71 to 75, an expansion film such as an expanded tape (not shown) is attached to the processing object 1, and the expansion film is expanded by an expanding apparatus (not shown), thereby processing the object. 1 is cut along the planned cutting line 5 and the processed sections are separated from each other. In addition, in a cutting process, you may cut | disconnect the process target object 1 using not only expansion of an expansion film but another stress application means. Further, for example, when a crack starting from the formed modified region extends to the front and back surfaces of the workpiece 1 and the cutting has already been completed, the interval between the processing sections is increased by expanding an expansion film such as an expanded tape. In this way, adjacent processing sections are separated.

  As described above, in the laser processing method of the present embodiment, the modified regions 73 and 74 are formed in separate steps in the object 1 on the concave region surface r2 and the convex region surface r1 of the incident surface r, respectively. To do. For this reason, when the planned cutting line 5 extends over the concave region surface r2 and the convex region surface r1 of the incident surface r, the laser beam is near the step r3 provided between the concave region surface r2 and the convex region surface r1. Damage to the incident surface r caused by the irradiation of L can be reduced. Therefore, according to the laser processing method of the present embodiment, it is possible to cut the processing object 1 with high accuracy, where the incident surface r of the laser beam L is an uneven surface.

  In addition, it is also possible to irradiate the incident surface r with the measurement laser beam and determine the position of the step r3 from the reflected light of the measurement laser beam. Specifically, the astigmatism signal or the total light quantity signal of the reflected light is detected by, for example, a four-divided position detection element used in the astigmatism method. The position of the step r3 can be determined at a position where the astigmatism signal of the reflected light becomes zero with respect to the condensing point position of the measurement laser beam or at a position where the total light quantity signal becomes maximum.

  Further, the position of the metal film 4b provided on the convex region surface r1 can also be determined from the difference in the magnitude of the total light amount signal of the reflected light of the measurement laser beam.

  When the position of the step r3 is known, when the laser beam L is moved along the planned cutting line 5, the timing for forming the modified regions 71 to 75 can be determined. For example, in the second step, it is possible to determine the timing at which the laser beam L is pulse-oscillated and the timing at which it is continuously oscillated. In the first step, the timing at which the position of the objective lens 30 is changed in the thickness direction of the workpiece 1 and the timing at which it is fixed can be determined by the actuator 32.

  Further, when the position of the metal film 4b is known, when the laser light L is moved along the scheduled cutting line 5, it is possible to determine the timing at which the laser light L is pulsated or continuously oscillated.

  As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment.

  For example, in the first step, when the modified regions 71b, 72b, and 73b are formed, the irradiation condition of the laser beam L may be fixed in the thickness direction of the workpiece 1.

  Further, when forming the modified regions 71 a, 72 a, 73 a, the irradiation condition of the laser light L may be changed in the thickness direction of the workpiece 1. In this case, the position of the objective lens 30 is adjusted by the amount of expansion / contraction of the actuator 32, and is displaced so as to follow the irregularities and undulations of the convex region surface r1. Therefore, the modified regions 71a, 72b, and 73b are formed on the convex region surface r1 so as to follow the displacement of the incident surface r in the thickness direction of the workpiece 1.

  In the first step, the modified regions 71a, 72a, 73a need not be formed. That is, the modified regions 71b, 72b, 73b may be selectively formed along the portion 51b on the concave region surface r2 in the planned cutting line 5. For that purpose, when irradiating the laser beam L, the pulse oscillation and the continuous oscillation may be selectively switched, the laser beam L may be selectively blocked by a shutter or the like, Oscillation may be selectively stopped.

  Further, if the workpiece 1 can be sufficiently cut by forming one row of modified regions, the modified regions 71 and 72 may not be formed in the first step.

  In the second step, when the modified regions 74 and 75 are selectively formed, the laser light L may be selectively blocked by a shutter or the like, and the oscillation of the laser light L is selectively stopped. It may be allowed. In these cases, the modified region 74 is selectively formed only while the laser beam L is applied to the workpiece 1.

  Further, the modified regions 71 to 75 are not limited to being formed by multiphoton absorption generated inside the workpiece 1. The modified regions 71 to 75 may be formed by causing light absorption equivalent to multiphoton absorption to occur inside the workpiece 1.

  Further, the distance d3 between the concave region surface r2 and the modified region 73 and the distance d5 between the convex region surface r1 and the modified region 75 may be the same or different from each other. Further, the order of forming the modified regions 71 to 75 is not particularly limited. For example, the modified regions 75, 74, 73, 72, 71 may be formed in order from the incident surface r side.

  Further, the position of the step r3 on the incident surface r may be measured in advance by a step meter, for example. Further, the position of the step r3 can be calculated from the design value of the workpiece 1. After the position of the step r3 is known, the scale coordinate of the stage on which the workpiece 1 is placed is taken into the control device for the laser light L, and pulse oscillation and continuous oscillation are selectively switched at the position of the step r3. Alternatively, the laser beam L may be selectively blocked by a shutter or the like, or the oscillation of the laser beam L may be selectively stopped. Further, at the position of the step r3, the irradiation condition of the laser beam L may be switched from the changed state to the fixed state, or the irradiation condition of the laser beam L may be switched from the fixed state to the changed state. .

  In the present embodiment, a silicon semiconductor wafer is used as the workpiece 1, but the material of the semiconductor wafer is not limited to this. Examples of the material of the semiconductor wafer include a group IV element semiconductor other than silicon, a compound semiconductor containing a group IV element such as SiC, a compound semiconductor containing a group III-V element, a compound semiconductor containing a group II-VI element, Examples thereof include semiconductors doped with various dopants (impurities). Further, the workpiece 1 may be an SOI (Silicon-on-Insulator) wafer in which an insulating layer is provided between the semiconductor device and the support substrate.

It is a top view of the processing target object during laser processing by the laser processing method concerning this embodiment. It is sectional drawing along the II-II line of the workpiece shown in FIG. It is a top view of the processing target after laser processing by the laser processing method concerning this embodiment. It is sectional drawing along the IV-IV line of the workpiece shown in FIG. It is sectional drawing along the VV line of the workpiece shown in FIG. It is a top view of the processed object cut | disconnected by the laser processing method which concerns on this embodiment. It is a graph which shows the relationship between the electric field strength and the magnitude | size of a crack spot in the laser processing method which concerns on this embodiment. It is sectional drawing of the processing target object in the crack area | region formation process at the time of cut | disconnecting a processing target object using the laser processing method which concerns on this embodiment. It is sectional drawing of the processing target object in the crack growth process at the time of cut | disconnecting a processing target object using the laser processing method which concerns on this embodiment. It is sectional drawing of the processing target object in the crack growth process at the time of cut | disconnecting a processing target object using the laser processing method which concerns on this embodiment. It is sectional drawing of the processing target object in the cutting process at the time of cut | disconnecting a processing target object using the laser processing method which concerns on this embodiment. It is a figure showing the photograph of the section in the part of silicon wafer cut by the laser processing method concerning this embodiment. It is a graph which shows the relationship between the wavelength of the laser beam and the transmittance | permeability inside a silicon substrate in the laser processing method which concerns on this embodiment. It is a top view which shows typically an example of the processing target object in the laser processing method of this embodiment. It is sectional drawing along the XV-XV arrow in FIG. It is sectional drawing of the process target object in each process of the laser processing method of this embodiment. It is sectional drawing of the process target object in each process of the laser processing method of this embodiment. It is sectional drawing of the process target object in each process of the laser processing method of this embodiment. It is sectional drawing of the plate-shaped to-be-processed object whose incident surface of the laser beam for a process is an uneven surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Work object, 5 ... Planned cutting line, 51a ... Part on convex area surface in planned cutting line, 51b ... Part on concave area surface in planned cutting line, 7 ... Modified area, 73 ... First modification 75, a second modified region, r, an incident surface, r1, a convex region surface of the incident surface, r2, a concave region surface of the incident surface, L, a processing laser beam, and P, a condensing point.

Claims (3)

By aligning a condensing point inside the plate-like object to be processed and irradiating a processing laser beam, a modified region that becomes a starting point of cutting along the scheduled cutting line of the object to be processed is defined as the object to be processed. A laser processing method to be formed inside,
In the case where the processing laser light incident surface in the processing object is a concavo-convex surface, and the planned cutting line extends over the concave region surface and the convex region surface of the incident surface,
A first step of forming a first modified region along the predetermined cutting line on the inner side of the convex region surface and a predetermined distance from the concave region surface ;
A second modified region is selectively formed along the planned cutting line, within a predetermined distance from the convex region surface , between the convex region surface and the concave region surface in the thickness direction of the workpiece. A second step of:
A laser processing method comprising: By aligning a condensing point inside the plate-like object to be processed and irradiating a processing laser beam, a modified region that becomes a starting point of cutting along the scheduled cutting line of the object to be processed is defined as the object to be processed. A laser processing method to be formed inside,
In the case where the processing laser light incident surface in the processing object is a concavo-convex surface, and the planned cutting line extends over the concave region surface and the convex region surface of the incident surface,
A first step of forming a first modified region along the predetermined cutting line inside a predetermined distance from the concave region surface;
A second step of forming a second modified region along the predetermined cutting line inside a predetermined distance from the convex region surface;
Including
In the first step, when irradiating the processing laser light along a portion on the concave region surface in the planned cutting line, the processing laser light is condensed to a predetermined distance inside the concave region surface. When the irradiation condition of the processing laser light is changed so that a point is located and the processing laser light is irradiated along a portion on the convex region surface in the planned cutting line, characterized in that for fixing the irradiation conditions, the laser machining method. By aligning a condensing point inside the plate-like object to be processed and irradiating a processing laser beam, a modified region that becomes a starting point of cutting along the scheduled cutting line of the object to be processed is defined as the object to be processed. A laser processing method to be formed inside,
In the case where the processing laser light incident surface in the processing object is a concavo-convex surface, and the planned cutting line extends over the concave region surface and the convex region surface of the incident surface,
A first step of forming a first modified region along the predetermined cutting line inside a predetermined distance from the concave region surface;
A second step of forming a second modified region along the predetermined cutting line inside a predetermined distance from the convex region surface;
Including
In the second step, the processing laser light is pulse-oscillated along a portion on the convex region surface in the planned cutting line, and the processing laser beam is processed along the portion on the concave region surface in the planned cutting line. characterized in that for continuous wave laser light, the laser processing method.

Images