WO2008004395A1

WO2008004395A1 - Laser processing method

Info

Publication number: WO2008004395A1
Application number: PCT/JP2007/061476
Authority: WO
Inventors: Tetsuya Osajima
Original assignee: Hamamatsu Photonics K.K.
Priority date: 2006-07-03
Filing date: 2007-06-06
Publication date: 2008-01-10
Also published as: TW200809941A; JP2008012542A; KR20090030301A; CN101484269A

Abstract

In the case of forming a plurality of rows of modified regions, in the thickness direction of a processing object, along a line to be cut, a first modified region closest to a first surface and a second modified region closest to a second surface are accurately formed. In a laser processing method, laser beams are applied by having a light collecting point inside the processing object (1), and the modified regions (M1-M6) to be starting points of cutting are formed, in the thickness direction of the processing object (1), along the line (5) to be cut on the processing object (1). Among the modified regions (M1-M6), the modified region (M6) closest to a rear surface (21) is formed by having the position of the rear surface (21) as reference, and the modified region (M1) closest to the front surface (11a) is formed by having the position of the front surface (11a) as reference. Thus, even when the thickness of the processing object (1) varies, shift of the position of the modified region (M6) and that of the position of the modified region (M1) due to changes of the thickness of the processing object (1) are suppressed.

Description

Specification

Laser processing method

Technical field

The present invention relates to a laser calorie method for cutting a plate-like workpiece along a planned cutting line.

Background art

[0002] As a conventional laser processing method, by aligning a condensing point inside a plate-like workpiece and irradiating laser light, it becomes a starting point for cutting along the planned cutting line of the workpiece. There is known a method for forming a plurality of modified regions in the thickness direction of a workpiece (for example, see Patent Document 1). In such a laser processing method, the position of the first surface where the laser light is incident on the object to be processed is detected, and the position of the condensing point of the laser light is controlled in accordance with this detection signal, whereby the object to be processed is detected. It is common to form each modified region at the position of the first surface force at a predetermined distance inside the object.

Patent Document 1: Japanese Patent Laid-Open No. 2005-150537

Disclosure of the invention

Problems to be solved by the invention

[0003] Incidentally, when a plurality of modified regions are formed in the thickness direction of the workpiece and the workpiece is cut, the modified region closest to the first surface and the first surface facing the first surface are arranged. The position where the modified region is closest to the surface of 2 is required to have particularly high accuracy in terms of the quality of the cut surface. This is because if these modified regions are not accurately formed at the positions of the first surface and the second surface force at predetermined distances, for example, cutting in the thickness direction of the workpiece is performed. This is because a so-called skirt phenomenon may occur in which the edge of the surface is greatly disengaged from the planned cutting line force.

[0004] However, in the laser cage method as described above, the modified region is formed in a plurality of rows in the thickness direction of the object to be processed on the basis of only the position of the first surface. When the thickness of an object varies among multiple workpieces due to differences in grinding lots, for example, or when a part of the workpiece becomes thicker or thinner (that is, the workpiece to be processed) When the thickness of the object changes), there is a possibility that the modified region closest to the second surface cannot be accurately formed at the position of the second surface force at a predetermined distance.

[0005] Therefore, the present invention provides the first modified region closest to the first surface and the first modified region in the case where a plurality of modified regions are formed in the thickness direction of the workpiece along the planned cutting line. It is an object of the present invention to provide a laser processing method capable of accurately forming the second modified region closest to the second surface.

Means for solving the problem

[0006] In order to achieve the above object, a laser processing method according to the present invention is designed to cut a cutting target line by irradiating a laser beam with a focusing point inside a plate-like processing target. Is a laser calorie method in which a plurality of modified regions that are the starting points of cutting are formed in the thickness direction, and is modified with reference to the position of the first surface where the laser beam is incident on the workpiece. Of the modified regions, the step of forming the first modified region closest to the first surface in the quality region and the position of the second surface facing the first surface in the workpiece are defined. Forming a second modified region closest to the second surface.

[0007] According to this laser processing method, the first modified region closest to the first surface in the modified region is formed with reference to the position of the first surface, and the second modified region in the modified region. A second modified region closest to the surface is formed with reference to the position of the second surface. As described above, since the positions of both the first surface and the second surface are used as a reference, even if the thickness of the workpiece is changed, the first surface of the modified region is changed to the first surface. The position of the first modified region closest to the second surface and the position of the second modified region closest to the second surface can be prevented from shifting due to a change in the thickness of the workpiece. That is, when forming a plurality of modified regions along the planned cutting line in the thickness direction of the workpiece, the first modified region closest to the first surface and the first closest to the second surface It becomes possible to accurately form the second modified region. As a result, the high quality of the cut surface can be maintained. In addition, each modified region causes multiphoton absorption and other light absorption inside the workpiece by irradiating the laser beam with the focusing point on the inside of the workpiece. It is formed.

[0008] Here, in the step of forming the first modified region, the first position information related to the position of the first surface is obtained by detecting the reflected light reflected by the first surface, The first Based on the positional information, in the step of forming the first modified region inside the first surface force by a predetermined distance and forming the second modified region, the reflected light reflected by the second surface Second position information on the position of the second surface is acquired by detecting the second surface force, and based on the second position information, the second surface force is also moved inward by a predetermined distance from the second modified region. May form.

[0009] Further, in the step of forming the first modified region, the first position information related to the position of the first surface is acquired by detecting the reflected light reflected by the first surface, Based on the first position information, in the step of forming the first modified region inside the first surface force by a predetermined distance and forming the second modified region, the first position information and Based on the thickness information related to the thickness of the workpiece, the second modified region may be formed on the inner side by a predetermined distance of the second surface force.

[0010] Further, in the step of forming the second modified region, second position information relating to the position of the second surface is acquired by detecting reflected light reflected by the second surface, and Based on the second position information, the second surface area is formed in the second modified area inward by a predetermined distance, and in the step of forming the first modified area, the second position information and Based on the thickness information of the workpiece, the first modified region may be formed inside the first surface force by a predetermined distance.

[0011] In some cases, the workpiece includes a semiconductor substrate, and the modified region includes a melt processing region.

[0012] It is preferable that the method further includes a step of cutting the object to be processed along a planned cutting line using the modified region as a starting point of cutting. As a result, the workpiece can be accurately cut along the planned cutting line.

The invention's effect

[0013] According to the present invention, in the case where a plurality of modified regions are formed in the thickness direction of the workpiece along the planned cutting line, the first modified region closest to the first surface, and the first The second modified region closest to the surface of 2 can be accurately formed.

Brief Description of Drawings

[0014] FIG. 1 is a plan view of an object to be processed in a laser cage by the laser carriage device according to the present embodiment. It is.

FIG. 2 is a cross-sectional view taken along line II-II of the cache object shown in FIG.

FIG. 3 is a plan view of an object to be processed after laser processing by the laser processing apparatus according to the present embodiment.

FIG. 4 is a cross-sectional view taken along line IV-IV of the cache object shown in FIG.

FIG. 5 is a cross-sectional view taken along line VV of the cache object shown in FIG.

FIG. 6 is a plan view of a processing object cut by the laser processing apparatus according to the present embodiment.

FIG. 7 is a graph showing the relationship between electric field strength and crack spot size in the laser processing apparatus according to the present embodiment.

8] A sectional view of the object to be processed in the first step of the laser processing apparatus according to the present embodiment.

9] A sectional view of the object to be processed in the second step of the laser processing apparatus according to the present embodiment.

[10] FIG. 10 is a cross-sectional view of the object to be processed in the third step of the laser processing apparatus according to the present embodiment.

FIG. 11] A sectional view of the object to be processed in the fourth step of the laser processing apparatus according to the present embodiment.

FIG. 12 is a view showing a photograph of a cross section of a part of a silicon wafer cut by the laser carriage device according to the present embodiment.

FIG. 13 is a graph showing the relationship between the wavelength of laser light and the transmittance inside the silicon substrate in the laser processing apparatus according to the present embodiment.

FIG. 14 is a front view showing a workpiece to be processed by the laser processing method according to the first embodiment of the present invention.

FIG. 15 is a partial sectional view taken along line XV—XV in FIG.

16] A flowchart showing the laser processing method according to the first embodiment of the present invention. [17] FIG. 17 is a diagram for explaining calculation of back surface position information and front surface position information in the laser processing method shown in FIG. FIG. 18 is a partial cross-sectional view taken along line XVIII-XVIII in FIG. 14 for illustrating the laser care method shown in FIG.

FIG. 19 is a diagram for explaining calculation of back surface position information and surface position information in the laser processing method according to the second embodiment of the present invention.

FIG. 20 is a partial cross-sectional view taken along line XVIII-XVI II in FIG. 14 in the laser care method using the conventional autofocus function.

FIG. 21 is a schematic configuration diagram showing a laser processing apparatus according to an embodiment of the present invention.

Explanation of symbols

[0015] 31 ··· Work object, 5… Scheduled line, 11a… Front surface (second surface), 21 ··· Back surface (first surface), L… Laser light, LI, L3, L5… Reflected light (reflected light reflected on the first surface), L2, L4, L6 ... Reflected light (reflected light reflected on the second surface), Ml, M2, M3, M4, M5, Μ6 ··· Modified area, P ... Focusing point.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the laser processing method of this 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 the modified region will be described.

[0017] Absorption band gap of material When photon energy h V force S is smaller than EG, it becomes optically transparent. Therefore, the condition for absorption in the material is h v> EG. However, even if it is optically transparent, if the intensity of the laser beam is made very large, the material will be absorbed under the condition of nh v> EG (n = 2, 3, 4,...). 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 (WZcm2) at the condensing point of the laser beam. For example, multiphoton absorption occurs when the peak power density is 1 X 108 (W / cm2) or more. The peak power density is calculated by (energy per pulse of laser beam at the focal point) ÷ (beam spot cross-sectional area of laser beam x pulse width). In the case of a continuous wave, the intensity of the laser beam is determined by the electric field strength (WZcm2) at the focal point of the laser beam.

[0018] The principle of the laser processing method according to the present embodiment using such multiphoton absorption will be described with reference to FIGS. As shown in Figure 1, wafer-like (plate-like) workpiece On the surface 3 of 1, there is a planned cutting line 5 for cutting the workpiece 1. The planned cutting line 5 is a virtual line extending straight. In the laser processing method according to the present embodiment, as shown in FIG. 2, the modified region 7 is irradiated with the laser beam L with the focusing point P aligned inside the workpiece 1 under the condition that multiphoton absorption occurs. Form. The condensing point P is a part where the laser beam 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 laser beam L is moved along the planned cutting line 5 (ie, in the direction of arrow A in FIG. 1) to move the condensing point P along the planned cutting line 5. . 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 the 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. This 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.

[0020] In the laser caching method according to this embodiment, the surface 3 of the workpiece 1 is hardly absorbed by the surface 3 of the workpiece 1, so that the surface 3 of the workpiece 1 is not melted.

[0021] If the cutting start region 8 is formed inside the workpiece 1, cracks are likely to occur starting from the cutting start region 8, so that the processing target can be processed with a relatively small force as shown in FIG. Item 1 can be cut. Therefore, it is possible to cut the workpiece 1 that causes unnecessary cracks in the surface 3 of the workpiece 1 with high accuracy.

[0022] The following two types of cutting of the cleaning object 1 starting from the cutting starting region 8 are conceivable. First, after the cutting start region 8 is formed, an artificial force is applied to the processing target 1, so that the processing target 1 is cracked and the processing target 1 is cut from the cutting start region 8. Is the case. This is, for example, cutting when the workpiece 1 is thick. The artificial force is applied, for example, by applying a bending stress or a 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. To generate thermal stress. The other is that by forming the cutting start region 8, it naturally cracks in the cross-sectional direction (thickness direction) of the workpiece 1 starting from the cutting start region 8, resulting in the processing target This is the case where object 1 is cut. This is for example machining vs. When the thickness of the object 1 is small, this can be achieved by forming the cutting start region 8 by the modified region 7 in one row, and when the thickness of the workpiece 1 is large, the thickness direction is increased. This is made possible by forming the cutting start region 8 by the modified regions 7 formed in a plurality of rows. Even in the case of natural cracking, the part where the cutting start region 8 is formed so that the crack does not run on the surface 3 of the portion corresponding to the portion where the cutting start region 8 is not formed at the part to be cut. Since only the part corresponding to 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.

[0023] Now, in the laser processing method according to the present embodiment, the modified region includes the following (1) to (1) to

There is a case of (3).

[0024] (1) When the modified region is a crack region including one or more cracks

The focusing point is set inside the workpiece (for example, piezoelectric material made of glass or LiTa03), and the electric field strength at the focusing point is 1 X 108 (W / cm2) or more and the pulse width is 1 μs or less. Irradiate laser light under conditions. The magnitude of this pulse width is a condition under which a crack region can 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 called 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 × 1012 (WZcm2). The pulse width is preferably lns to 200ns, for example.

Yes. The formation of crack regions by multiphoton absorption is described in, for example, “Glass Substrates Using Solid-State Laser Harmonics” on pages 23-28 of the 45th Laser Thermal Processing Workshop Papers (December 1998). "Internal marking".

The present inventor obtained the relationship between the electric field strength and the crack size 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: 1064nm

Laser beam spot cross section: 3. 14 X 10-8cm2

Oscillation form: Q switch pulse

Repeat frequency: 100kHz

Pulse width: 30ns

Output: Output lmjZ pulse

Laser light quality: TEM00

Polarization characteristics: Linear polarization

(C) Condensing lens

Transmittance for laser light wavelength: 60%

(D) Moving speed of mounting table on which workpiece is mounted: lOOmmZ seconds

[0026] Note that the laser light quality TEMOO means that the light condensing property 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 is the peak power density. Since the laser beam is a pulsed laser beam, the electric field strength is expressed by the peak power density. The vertical axis shows the size of the crack part (crack spot) formed inside the workpiece by 1 pulse of laser light. Crack spots gather to form a crack region. The size of the crack spot is the size of the maximum length of the crack spot shape. The data indicated by the black circles in the graph is when the condenser lens (C) has a magnification of 100 and the numerical aperture (NA) is 0.80. On the other hand, the data indicated by white circles in the graph is for the case where the magnification of the condenser lens (C) is 50 times and the numerical aperture (NA) is 0.55. As the peak power density increases from about 1011 (WZcm2), crack spots are generated inside the cache object and the peak power density increases.

It can be seen that V and crack spots also increase.

[0028] Next, a mechanism of cutting the workpiece by forming a crack region will be described with reference to FIGS. As shown in FIG. 8, under the condition that multiphoton absorption occurs, the condensing point P is aligned inside the workpiece 1 and the laser beam L is irradiated to form a crack region 9 along the planned cutting line. Crack region 9 is a region containing one or more cracks . The crack region 9 thus formed becomes a cutting start region. As shown in FIG. 9, the crack further grows starting from the crack region 9 (that is, starting from the cutting start region), and as shown in FIG. As shown in FIG. 11, when the workpiece 1 is cracked, the workpiece 1 is cut. Cracks that reach the front surface 3 and back surface 21 of the workpiece 1 may grow naturally, and the workpiece 1 is marked with force.

Sometimes it grows by being carotened.

[0029] (2) When the reforming region is a melt processing region

Condition where 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 X 108 (W / cm2) or more and the pulse width is 1 μs or less. The laser beam is irradiated with. 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 where the crystal structure has changed. The melt-processed region can also be referred to as a region in which one structure is changed to another in a single crystal structure, an amorphous structure, or a polycrystalline structure. In other words, for example, a region changed to a single crystal structural force amorphous structure, a region changed from a single crystal structure to a polycrystalline structure, a region changed to a structure including a single crystal structural force amorphous structure and a polycrystalline structure. means. 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 × 1012 (WZcm2). For example, the pulse width is preferably lns to 200 ns.

[0030] The present inventor has confirmed through experiments that a melt-processed region is formed inside a silicon wafer (semiconductor substrate). 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: 1064nm

Laser beam spot cross section: 3. 14 X 10-8cm2 Oscillation form: Q switch pulse

Repeat frequency: 100kHz

Pulse width: 30ns

Output: 20 JZ pulse

Laser light quality: TEM00

Polarization characteristics: Linear polarization

(C) Condensing lens

Magnification: 50x

N. A .: 0.55

Transmittance for laser light wavelength: 60%

FIG. 12 is a view showing a photograph of a cross section of a part of a silicon wafer cut by a laser cage 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.

[0032] 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 reflection component on the front side and the back side of the silicon substrate is removed, and the transmittance only inside is shown. The above relationship was shown for each of the silicon substrate thicknesses t of 50 μm, 100 μm, 200 μm, 500 μm, and 1000 μm.

[0033] For example, when the thickness of the silicon substrate is 500 m or less at the wavelength of 1064 nm of the Nd: YAG laser, it can be understood 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 m, 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 m from the surface. In this case, the transmittance is 90% or more with reference to a silicon wafer having a thickness of 200 m. Therefore, the laser beam is hardly absorbed inside the silicon wafer 11, and almost all is transmitted. This is because the laser beam is absorbed inside the silicon wafer 11 and the melt treatment region 13 is formed inside the silicon wafer 11 (that is, normal heating by the laser beam). This means that the melt-processed region 13 is formed by multiphoton absorption. The formation of the melt processing region by multiphoton absorption is, for example, “Evaluation of processing characteristics of silicon by picosecond pulse laser” on pages 72 to 73 of the 66th Annual Meeting Summary (April 2000). It is described in.

[0034] It should be noted that the silicon wafer generates a crack by applying a force in the cross-sectional direction starting from the cutting start region formed by the melt processing region, and the crack reaches the front and back surfaces of the silicon wafer. , Resulting in disconnection. The cracks that reach the front and back surfaces of the silicon wafer may grow spontaneously, or they may grow when force is applied to the silicon wafer. Then, if the crack grows naturally on the front and back surfaces of the silicon wafer, the crack grows from the state where the melt processing area forming the cutting origin area is melted, and the cutting origin area In some cases, 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. As described above, when the cutting start region is formed in the workpiece by the melt processing region, unnecessary cracking in which the cutting starting region line force is also not easily generated at the time of cleaving, so that the cleaving control becomes easy. Incidentally, the formation of the melt-processed region may be caused not only by multiphoton absorption but also by other absorption effects.

[0035] (3) When the modified region is a refractive index changing region

A focusing point is set inside the object to be processed (eg, glass), and laser light is irradiated under the condition that the electric field strength at the focusing point is 1 X 108 (W / cm2) or more and the pulse width is Ins or less. If the pulse width is made extremely short and multiphoton absorption occurs inside the target object, the energy due to the multiphoton absorption will not be converted to thermal energy, and the ionic valence will be present inside the workpiece. Permanent structural changes such as change, crystallization or polarization orientation are induced to form a refractive index change region. The upper limit value of the electric field strength is, for example, 1 × 1012 (W / cm2). For example, the Norse width is preferably less than Ins, more preferably less than lps. The formation of the refractive index change region by multiphoton absorption is described in, for example, “Inside Glass by Femtosecond Laser Irradiation” on pages 105-111 of the 42nd Laser Thermal Processing Society Proceedings (November 1997). Described in “Formation of Photo-Induced Structure in Part”.

As described above, the cases of (1) to (3) have been described as the modified regions, but the cutting origin region is determined as follows in consideration of the crystal structure of the wafer-like workpiece and its cleavage property. Once formed, the workpiece can be cut with a smaller force and with higher accuracy, starting from the cutting start region.

[0037] That is, in the case of a substrate having a single crystal semiconductor force of diamond structure such as silicon, the cutting origin region in the direction along the (111) plane (first cleavage plane) or the (110) plane (second cleavage plane) Is preferably formed. In addition, in the case of a substrate having a zinc-blende structure III-V compound semiconductor force such as GaAs, it is preferable to form the cutting start region in the direction along the (110) plane. Furthermore, in the case of a substrate having a hexagonal crystal structure such as sapphire (A1203), the (0001) plane (C plane) is the main plane and the (1120) plane (eight planes) or! (1100) plane ( It is preferable to form the cutting origin region in the direction along the (M-plane) U.

[0038] It should be noted that 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! Is orthogonal to the direction in which the cutting start region is to be formed. If an orientation flat is formed on the substrate along the direction, 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 basis of the orientation flat. become.

[0039] Next, a preferred embodiment of the present invention will be described.

[First embodiment]

As shown in FIGS. 14 and 15, the workpiece 1 includes a silicon wafer 11 and a plurality of functional elements 15, and the surface of the silicon wafer 11 (hereinafter, also simply referred to as “surface”) 11a. The functional element layer 16 is formed in the thickness of about 300 m. The functional element 15 is, for example, a semiconductor operating layer formed by crystal growth, a light receiving element such as a photodiode, a light emitting element such as a laser diode, or a circuit element formed as a circuit. Many are formed in a matrix in the direction parallel to the orientation flat 6 and in the direction perpendicular to it. Such a workpiece 1 is cut along a planned cutting line 5 (see the broken line in FIG. 14) set in a lattice shape so as to pass between the adjacent functional elements 15, and a discrete device or the like that is a microchip. It will be. [0041] When the workpiece 1 is cut, first, a protective tape is applied to the surface of the functional element layer 16, and the functional element layer 16 is protected by the protective tape. Secure the protective tape holding the workpiece 1. Subsequently, the back surface of the workpiece 1 (hereinafter, also simply referred to as “rear surface”) 21 is irradiated with laser light under conditions where multi-photon absorption occurs by aligning the focal point from the inside of the silicon wafer 11 and cutting each cut. A modified region that is the starting point of cutting is formed along the planned line 5 (back-side incident processing). Here, six rows of modified regions are formed in the thickness direction of the workpiece 1 along each planned cutting line 5. Subsequently, the protective tape fixed to the stage is separated with the workpiece 1. Then, an expand tape is applied to the back surface 21 of the silicon wafer 11, and after the protective tape is peeled off from the surface force of the functional element layer 16, the expand tape is expanded. As a result, the processing object 1 is accurately cut for each functional element 15 along the scheduled cutting line 5 using the modified region as a starting point of cutting, and a plurality of semiconductor chips are separated from each other. The modified region may include a crack region in addition to the melt processing region.

[0042] By the way, the thickness of the workpiece 1 varies among a plurality of workpieces 1 due to differences in grinding lots, for example, or a portion of the workpiece 1 is uneven due to unevenness in grinding. It may be thicker or thinner (when the thickness of the workpiece 1 changes). Specifically, in the workpiece 1 with a thickness of 300 m, the thickness may vary by more than ± 10 m between the workpieces 1, and the thickness of a part of one workpiece 1 May vary by more than ± 5 m.

[0043] However, with a general autofocus function, the thickness of the workpiece 1 is considered to be constant, and only the amount of displacement of the back surface 21 that is the laser light incident surface is measured, so that the focal point position of the laser light is measured. Is controlled from the rear surface 21 to a predetermined position. Therefore, conventionally, as shown in FIG. 20, in the modified region M formed, the modified region closest to the surface 1 la is such that the workpiece 1 is thick! May be formed near the back surface 21 without reaching the deep position of the cache object 1 when the object 1 is thin.

Therefore, in the laser processing method of the present embodiment, the back surface (first surface) 21 of the modified regions formed in a plurality of rows in the thickness direction along the line 5 to be cut of the workpiece 1. Closest to The first modified region is formed with reference to the position of the back surface 21, and the second modified region closest to the front surface (second surface) 11a is formed with reference to the position of the front surface 11a. Hereinafter, the formation of the reforming region will be described in more detail.

[0045] [No, Ito Set]

First, with the focus of the reticle image projected on the back surface 21 of the workpiece 1 being focused, for example, the distance measuring laser beam is irradiated and the reflected light of the distance measuring laser beam reflected on the back surface 21 is detected as a voltage value. And memorize the detected voltage value (Sl in Fig. 16).

[0046] [Trace]

Next, the line scheduled to be cut so that the reflected light of the distance measuring laser light irradiated with the distance measuring laser light and reflected by the back surface 21 is detected as a voltage value, and this voltage value maintains the voltage value by the height set. 5 is scanned to obtain the displacement of the back surface 21 along the planned cutting line 5, and the displacement of the back surface 21 is stored as back surface position information (first position information). In other words, it is obtained as the relative distance in the thickness direction from the rear surface 21 to the height 21 back surface position.

[0047] Back surface position information = displacement of back surface 21

= Relative distance in the thickness direction from back 21 to height 21

At this time, at the same time as scanning the distance measuring laser beam, the thickness (thickness information) of the workpiece 1 is optically measured and calculated along the planned cutting line 5 by the thickness measuring device. Specifically, as shown in FIG. 17 (a), along the planned cutting line 5, the reflected light L1 from the back surface 21 and the reflected light L2 that passes through the inside of the workpiece 1 and is reflected by the front surface 11a. Is received by the line sensor 50. Then, the distance from the front surface 11a to the back surface 21, that is, the thickness of the workpiece 1 is calculated based on the light receiving positions of the reflected lights LI and L2 in the line sensor 50 and the refractive index of the workpiece 1 obtained in advance. To do.

[0049] Then, the above-described back surface position information is added to the calculated thickness of the workpiece 1 and stored as surface position information (second position information) along the planned cutting line 5. That is, the surface position information force is obtained as the relative distance in the thickness direction from the front surface 1 la to the height-set 21 back surface position (S2 in FIG. 16).

[0050] Front surface position information = Back surface position information + thickness of workpiece 1 = Relative distance in the thickness direction from the front surface 11a to the height 21 back surface position [0051] Here, the measurement system of the back surface 21 and the measurement system of the thickness of the cache object 1 are composed of two axes. It has been. Further, the displacement of the back surface 21 and the thickness force of the cover object 1 are acquired in association with the coordinates in the direction along the cutting line 5. Therefore, the measurement system for the back surface 21 and the thickness measurement system for the workpiece 1 are composed of two axes, and the back surface position information and the surface position information are synthesized on the coordinates from the distance D1 between each measurement system. Position information and surface position information are required with high accuracy.

[0052] Alternatively, as shown in FIG. 17 (b), the thickness of the workpiece 1 may be measured by causing the reflected light L3 from the back surface 21 and the reflected light L4 from the front surface 11a to interfere with each other. is there. Even in this case, the measurement system of the back surface 21 and the thickness measurement system of the workpiece 1 are configured with two axes, and the displacement of the back surface 21 and the thickness force of the workpiece 1 are set in the line 5 to be cut. Acquired in association with the coordinates of the direction along. Therefore, the back surface position information and the front surface position information are synthesized on the coordinates from the distance D2 between the respective measurement systems, and the back surface position information and the front surface position information are accurately obtained.

[0053] [Formation of modified region]

Subsequently, as shown in FIG. 18 (a), within the object 1 to be processed, a laser beam is irradiated with the focusing point on the inner side (upper side in the figure) of the surface 11a by m, and along the planned cutting line 5 Scan. Specifically, inside the workpiece 1, the focal point is moved to the position on the rear surface 21 side by 10 m from the surface position information, and laser light is emitted at 0.72 W, and the stored surface position information Is scanned by a position adjusting element (actuator using a piezo element in this embodiment) to scan along the planned cutting line 5 while controlling the focal point position. Thus, a modified region (second modified layer) Ml is formed along the planned cutting line 5 by 10 m from the surface 11a with reference to the surface 11a (S3 in FIG. 16). ). Specifically, a modified region Ml along the planned cutting line 5 is formed at a position on the back surface 21 side by 10 m from the surface position information.

[0054] Subsequently, as shown in FIG. 18 (b), within the object 1 to be processed, a laser beam is irradiated with a focusing point on the inner side (upper side in the drawing) of 25 m from the surface 11a and to be cut. Scan along line 5. Specifically, from the surface position information inside the workpiece 1 Move the condensing point to the position on the back 21 side by 25 μm and output laser light 1. Control the condensing point position by irradiating with 20 W and reproducing the memorized surface position information with the piezo element. Scan along planned cutting line 5. As a result, the modified region M2 is formed along the planned cutting line 5 inward by 25 m from the surface 11a with respect to the surface 11a (S4 in FIG. 16). Specifically, a modified region M2 along the planned cutting line 5 is formed at a position on the back surface 21 side by 25 m from the surface position information.

Subsequently, inside the workpiece 1, the laser beam is irradiated with the focusing point on the inner side (upper side in the drawing) of 35 m from the surface 11 a and scanned along the planned cutting line 5. Specifically, inside the workpiece 1, the focal point is moved to the position on the back 21 side by 35 m from the surface position information, and the laser beam is output. The information is reproduced by the piezo element and scanned along the planned cutting line 5 while controlling the focal point position. Thus, the modified region M3 is formed along the planned cutting line 5 only 35 m from the surface 11a with respect to the surface 11a (S5 in FIG. 16). Specifically, a modified region M3 along the planned cutting line 5 is formed at a position on the back surface 21 side by 35 m from the surface position information.

Subsequently, inside the workpiece 1, the laser beam is irradiated with the focusing point on the inner side (upper side in the drawing) of 45 m from the surface 11 a and scanned along the planned cutting line 5. Specifically, inside the workpiece 1, the focal point is moved to the position on the back 21 side by 45 m from the surface position information, and laser light is output. The information is reproduced by the piezo element and scanned along the planned cutting line 5 while controlling the focal point position. As a result, the modified region M4 is formed along the planned cutting line 5 within 45 m from the surface 11a with respect to the surface 11a (S6 in FIG. 16). Specifically, a modified region M4 along the planned cutting line 5 is formed at a position on the back surface 21 side by 45 m from the surface position information.

[0057] Subsequently, as shown in FIG. 18 (c), inside the object 1 to be processed, a laser beam is irradiated with a focusing point on the inner side (lower side in the drawing) by 25 m from the rear surface 21 and cut. Scan along planned line 5. Specifically, inside the workpiece 1, the laser beam is output by moving the condensing point to the position on the front surface 11a side by 25 μm from the back surface position information. The back side position information stored in memory is reproduced by a piezo element and scanned along the planned cutting line 5 while controlling the focal point position. As a result, the modified region M5 is formed along the planned cutting line 5 within 25 μm from the back surface 21 with respect to the back surface 21 (S7 in FIG. 16). Specifically, a modified region M5 along the planned cutting line 5 is formed at a position on the front surface 11a side by 25 m from the back surface position information.

Finally, inside the workpiece 1, the laser beam is irradiated with the focusing point on the inner side (lower side in the figure) of 15 m from the back surface 21, and scanning is performed along the planned cutting line 5. Specifically, inside the workpiece 1, the focal point is moved to the position on the front surface 11a side by 10 m from the back surface position information, and the laser beam is emitted at 0.68 W, and the back surface stored in memory. The position information is reproduced by the piezo element, and scanning is performed along the planned cutting line 5 while controlling the focal point position. As a result, a modified region (second modified layer) M6 is formed along the planned cutting line 5 on the inner side by 15 / z m from the rear surface 21 with respect to the rear surface 21 (S8 in FIG. 16). Specifically, a modified region M6 along the planned cutting line 5 is formed at a position on the front surface 11a side by 15 / zm from the back surface position information.

Here, among the modified regions Ml to M6 formed in a plurality of rows in the thickness direction inside the workpiece 1, the modified regions M5 and M6 are modified to form a half cut on the upper surface. This area is called the so-called half-cut SD. This half-cut ensures separation by expanding the expanded tape, so half-cut SD is a very important factor. Of the modified regions M1 to M6 formed in a plurality of rows, the modified region Ml closest to the surface 11a is a modified region that particularly affects the quality of the cut surface after cutting. Called. Quality SD is for cutting the functional element layer 16 with high accuracy, and is a very important factor for maintaining the quality when the workpiece 1 is cut.

Therefore, in the present embodiment, as described above, the modified regions M5 and M6 are scheduled to be cut inside the workpiece 1 by a predetermined distance from the back surface 21 with respect to the back surface 21 as a reference. And the modified region Ml is formed along the planned cutting line 5 inwardly from the surface 11a by a predetermined distance with respect to the surface 11a. Thus, since the positions of both the back surface 21 and the front surface 11a are used as a reference, even if the thickness of the cache object 1 is reduced. Even if it changes, the position of the modified regions M5 and M6 and the position of the modified region M6 can be prevented from shifting due to the change in the thickness of the workpiece 1. Therefore, according to the present embodiment, when multiple modified regions are formed in the thickness direction of the workpiece 1 along the planned cutting line 5, the modified regions M6 and modified regions closest to the back surface 21 are formed. It is possible to accurately form the adjacent modified region M5 and the modified region Ml closest to the surface 11a.

Furthermore, in this embodiment, since the modified regions M5 and M6 are formed with high accuracy, the following effects are obtained. That is, since the modified regions M5 and M6 are too close to the back surface 21, the half-cut meandering and quality deterioration are suppressed. Furthermore, since the modified regions M5 and M6 are too far from the back surface 21, the elongation of cracks generated from the modified regions M5 and M6 becomes insufficient, and it is possible to prevent the half cut from being formed well.

[0062] Further, as described above, the modified region Ml is formed with high accuracy, and therefore the following effects are obtained. That is, since the modified region Ml is too close to the surface 11a, the irradiated laser beam protrudes from the workpiece 1 and a hole is made in the surface 11a, so that the bending strength of the workpiece 1 is weakened. Suppress. Furthermore, since the modified region Ml is too far away from the surface 11a, the end of the surface 1 la side is greatly disengaged from the planned cutting line 5 at the cut surface, thereby preventing the occurrence of a scouring phenomenon. In the present embodiment, the functional element 15 is formed on the surface 11a, which is the surface opposite to the surface on which laser light is incident, for back-side incident processing, and thus the above effect of preventing the occurrence of the skirt phenomenon. Is particularly prominent.

[0063] Further, according to the present embodiment, it is possible to correct the shift of the position of the modified region due to the thickness variation or unevenness of the workpiece 1, and the distance from the front surface 11a and the back surface 21 can be corrected. It is possible to perform multi-stage processing that optimizes the quality of the modified region that depends on the distance of the material, and optimizes the quality of the cut surface after cutting.

[0064] Although the thickness of the workpiece 1 may be measured with a contact-type thickness measuring instrument, in this case, there is a foreign object between the workpiece 1 and the stage, When affixed to the expanded tape, air may be mixed between the expanded tape and the workpiece 1, and the position of the workpiece 1 that is in contact with the expanded tape does not necessarily indicate the thickness of the workpiece 1. Must not. Therefore, in this embodiment, a measuring instrument using a transmission type laser is used. Therefore, the thickness of the workpiece 1 is accurately measured.

Incidentally, in the present embodiment, as described above, the modified regions M2, M3, and M4 are formed based on the surface 11a, but the modified region M is not limited to the present embodiment. 2, M3 and M4 may be formed with reference to the back surface 21.

[Second Embodiment]

Next, a laser processing method according to the second embodiment of the present invention will be described. The laser processing method according to the second embodiment is different from the laser processing method according to the first embodiment in that an autofocus function is used as shown in FIG. 19 without measuring the thickness of the workpiece 1. This is the point at which the reflected light L5 on the back surface 21 and the reflected light L6 on the front surface 11a were detected using the optical system in this case.

[0067] Specifically, in the laser processing method according to the present embodiment, the reflected light L5 reflected by the back surface 21 and the reflected light L6 transmitted through the workpiece 1 and reflected by the surface 11a are detected, respectively, and the surface 11a By directly acquiring the displacement of the back surface and the displacement of the back surface 21, the back surface position information and the front surface position information can be obtained directly.

[0068] Back side position information = displacement of back side 21

= Relative distance in the thickness direction from back 21 to height 21

[0069] Surface position information = displacement of surface 11a

= Relative distance in the thickness direction from the front surface 11a to the height 21 back surface position

[0070] Thus, even in the laser processing method of the present embodiment, the same effect as the above embodiment, that is, even if the thickness of the cache object 1 varies and changes, the modified region This has the effect of suppressing the displacement of the positions of M5 and M6 and the position of the modified region M6 due to the change in the thickness of the workpiece 1. As a result, when multiple modified regions are formed in the thickness direction of the workpiece 1 along the planned cutting line 5, the modified region M6 and the modified region M6 closest to the back surface 21 are formed. The adjacent modified region M5 and the modified region Ml closest to the surface 11a can be formed with high accuracy.

Next, a laser processing apparatus according to an embodiment of the present invention will be described.

[0072] As shown in FIG. 21, the laser carriage device 100 is configured to change the direction of the optical axis of the laser beam L by 90 ° and the laser light source 101 that pulsates the laser beam (processing laser beam) L. Placed A dichroic mirror 103 and a condensing lens 105 for condensing the laser beam L. In addition, the laser carriage device 100 includes a mounting table 107 for mounting the workpiece 1 to be irradiated with the laser beam L condensed by the condensing lens 105, and a mounting table 107 for X, Y, Ζ A stage 111 for moving in the axial direction, a laser light source control unit 102 for controlling the laser light source 101 to adjust the output and pulse width of the laser light L, and a stage control unit 115 for controlling the movement of the stage 111 And prepare for.

[0073] According to this laser carriage device 100, the laser light L emitted from the laser light source 101 is changed in its optical axis by 90 ° by the dichroic mirror 103, and processed on the mounting table 107 by the condenser lens 105. It is condensed inside the object 1. At the same time, the stage 111 is moved, and the workpiece 1 is moved relative to the laser beam L along the planned cutting line 5. As a result, a modified region is formed on the workpiece 1 along the planned cutting line 5.

Note that the laser cache device 100 is not limited to this embodiment, and the laser light L from the laser light source 101 may be guided to the condensing lens 105 without using the dichroic mirror 103. The laser beam L may be moved as long as the laser beam L can be moved relative to the workpiece 1. Particularly in the axial direction, it is possible to change the focal position of the laser light L by moving the position of the condensing lens 105 instead of moving the mounting table 107.

[0075] The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

[0076] For example, in the above embodiment, the displacement of the force surface 1 la, which is a so-called trace carriage that scans the laser light after measuring the displacement or the like of the surface 11a of the workpiece 1 to form a modified region. , Etc., can be measured at the same time to form a modified region.

[0077] Further, a single laser light source may be used for irradiation of the distance measuring laser light that passes through the workpiece and the distance measuring laser light that is reflected without being transmitted. You can change the wavelength and irradiate.

[0078] In the above-described embodiment, the back surface incident processing in which laser light is incident from the back surface 21 side facing the front surface 11a on which the functional element 15 is formed is used. Of course, it is good even for the incident processing.

[0079] In addition, as the object to be processed, the case object 1 including the silicon wafer 11 is used. A material having crystallinity such as a material or a sapphire may be used.

Industrial applicability

[0080] According to the present invention, in the case where a plurality of modified regions are formed in the thickness direction of the workpiece along the planned cutting line, the first modified region closest to the first surface, and the first The second modified region closest to the surface of 2 can be accurately formed.

Claims

The scope of the claims

[1] By aligning the condensing point inside the plate-like workpiece and irradiating the laser beam, the modified region that is the starting point of cutting is processed along the planned cutting line of the workpiece. A laser processing method for forming a plurality of rows in the thickness direction of an object,

Forming a first modified region closest to the first surface in the modified region with reference to a position of a first surface on which laser light is incident on the workpiece, and the processed object Forming a second modified region closest to the second surface in the modified region with reference to the position of the second surface facing the first surface. A laser processing method.

[2] In the step of forming the first modified region, first position information relating to the position of the first surface is obtained by detecting reflected light reflected by the first surface; Based on the first position information, the first modified region is formed inward by a predetermined distance from the first surface,

In the step of forming the second modified region, second position information relating to the position of the second surface is obtained by detecting reflected light reflected by the second surface, and the second modified region is obtained. 2. The laser processing method according to claim 1, wherein the second modified region is formed inward by a predetermined distance from the second surface based on the position information.

[3] In the step of forming the first modified region, first position information relating to the position of the first surface is obtained by detecting reflected light reflected by the first surface; Based on the first position information, the first modified region is formed inward by a predetermined distance from the first surface,

In the step of forming the second modified region, based on the first position information and the thickness information related to the thickness of the workpiece, the second modified region is formed inward by a predetermined distance from the second surface. 2. The laser processing method according to claim 1, wherein the second modified region is formed.

[4] For the step of forming the second modified region, the second position information on the position of the second surface is obtained by detecting the reflected light reflected by the second surface. Based on the second position information, the second revision is made inward by a predetermined distance from the second surface. Forming a quality region,

In the step of forming the first modified region, based on the second position information and the thickness information related to the thickness of the workpiece, the first modified region is inward from the first surface by a predetermined distance. 2. The laser processing method according to claim 1, wherein the first modified region is formed.

5. The laser processing method according to claim 1, wherein the object to be processed includes a semiconductor substrate, and the modified region includes a melt processing region.

6. The laser processing method according to claim 1, further comprising a step of cutting the object to be processed along the scheduled cutting line using the modified region as a starting point for cutting.