TWI874687B - Laser processing equipment - Google Patents

Abstract

[Topic] Provide a laser processing device that can stabilize the processing force and improve the processing force even if there is a slight deviation between the center of the pattern of adjusting the spatial optical phase modulator and the optical path of the laser light. [Solution] The laser light irradiation unit of the laser processing device includes: a laser oscillator that emits laser light; a spatial optical phase modulator that adjusts the phase of the laser light emitted from the laser oscillator; a condenser that focuses the laser light whose phase has been adjusted by the spatial optical phase modulator and locates the focal point inside the object to be processed; and a control unit that adjusts the spatial optical phase modulator. The control unit includes a memory unit, the memory unit stores an adjustment pattern table, and the adjustment pattern table has a plurality of adjustment patterns for adjusting the spatial optical phase modulator corresponding to the depth position of the focal point of the laser light.

Description

Laser processing equipment

The present invention relates to a laser processing device which positions the focal point of laser light of a wavelength penetrating a workpiece held on a workpiece at the inside of the workpiece to irradiate the workpiece and form a modified layer.

A wafer having a plurality of devices such as ICs and LSIs formed thereon by dividing it by a plurality of intersecting predetermined dividing lines can be divided into individual device chips by a laser processing device, and each divided device chip can be applied to electrical devices such as mobile phones and personal computers.

The laser processing device includes a workpiece holding a workpiece, a laser irradiation unit for positioning a focal point of a laser beam having a wavelength penetrating the workpiece held on the workpiece to the inside of the workpiece for irradiation to form a modified layer and cracks extending from the modified layer, and a feeding mechanism for feeding the workpiece and the laser irradiation unit relative to each other, and can position a focal point inside the wafer corresponding to a predetermined splitting line to form a modified layer that becomes a starting point for splitting at an appropriate position, and apply an external force to split the wafer into individual device chips (see, for example, Patent Document 1). Prior Art Documents Patent Documents

Patent document 1: Japanese Patent No. 3408805

According to the technology described in the above-mentioned patent document 1, when the thickness of the wafer is relatively thin, for example, about 50 μm to 150 μm, the focal point of the laser beam can be positioned at an appropriate position inside the wafer, and a modified layer and cracks extending from the modified layer can be appropriately formed. However, if the thickness of the wafer increases, for example, when the thickness exceeds 300 μm, the refractive index of the material constituting the wafer (for example, about 3.5 in the case of silicon) will be affected, and there will be the following problems: the aberration will increase, and the focal point of the laser beam will not be concentrated at one point, and an appropriate modified layer cannot be formed.

Invention Problems to be Solved

In order to deal with the above-mentioned problem, the following method is considered: a spatial optical phase modulator (LCOS, etc.) is arranged between the laser oscillator and the condenser constituting the laser light irradiation unit, and the spherical aberration is corrected by the spatial optical phase modulator as a whole, so that the focal point of the laser light is concentrated at a point inside the wafer. However, it is not easy to accurately adjust the center of the pattern of the spatial optical phase modulator and the optical path of the laser light. If there is a deviation between the center of the pattern of the spatial optical phase modulator and the optical path of the laser light, the following problems will occur: the focal point cannot be concentrated as expected, the processing force is reduced, and the processing of the laser processing device cannot be carried out stably. This problem can be solved by weakening the intensity of the correction of spherical aberration performed by the spatial light phase modulator. As a result, even if there is a slight deviation between the center of the pattern of the spatial light phase modulator and the optical path of the laser light, a certain degree of processing force can still be ensured. However, there will be the following problem: as a result of weakening the correction of spherical aberration as mentioned above, the processing force will be sacrificed.

Accordingly, the purpose of the present invention is to provide a laser processing device that can stabilize and improve the processing force even if there is a slight deviation between the center of the pattern of the spatial optical phase modulator and the optical path of the laser beam. Means for solving the problem

According to the present invention, a laser processing device can be provided, the aforementioned laser processing device has: a worktable for holding a workpiece; a laser light irradiation unit for positioning the focal point of the laser light of a wavelength having a penetrating property for the workpiece held on the worktable inside the workpiece to irradiate the laser light and form a modified layer; and a feeding mechanism for processing and feeding the worktable and the laser light irradiation unit relative to each other. The laser light irradiation unit includes: a laser oscillator for emitting laser light; a spatial light phase modulator for adjusting the phase of the laser light emitted from the laser oscillator; a condenser for focusing the laser light whose phase is adjusted by the spatial light phase modulator and positioning the focal point inside the workpiece; and a control unit for adjusting the spatial light phase modulator. The control unit has a memory section storing an adjustment pattern table, which is a table for adjusting the spatial optical phase modulator to form the following areas: a central area with relatively small aberration and strong correction in the focal point of the laser light incident on the workpiece and refracted, and a peripheral residual area with relatively large aberration and weak correction.

Preferably, the central area of the strong correction is the 20% to 30% area on the central side of the laser light generated by the oscillation of the laser oscillator, and the area of the weak correction is the remaining peripheral area surrounding the central area. Preferably, the adjustment pattern table has an adjustment pattern for performing a plurality of adjustments on the spatial optical phase modulator corresponding to the depth position of the focal point of the laser light positioned inside the workpiece, and the adjustment pattern is selected corresponding to the focal point depth position specified by the operator. Effect of the invention

According to the present invention, even if a deviation occurs between the center of the pattern of the spatial optical phase modulator and the optical path of the laser beam, the processing force can still be stabilized and improved.

The form used to implement the invention

Hereinafter, the laser processing device according to the embodiment of the present invention will be described in detail with reference to the attached drawings.

FIG. 1 shows a wafer 10 prepared as a workpiece to be processed by the present embodiment, and a protective tape T, and a state where the protective tape T is applied on the front surface 10a of the wafer 10. The wafer 10 is, for example, a silicon wafer having a thickness of 700 μm, and is divided by a plurality of intersecting predetermined dividing lines 14, and a plurality of devices 12 are formed on the front surface 10a. The protective tape T is a resin tape having an adhesive layer, and is attached to the front surface 10a side of the wafer 10 to form a whole.

FIG2 shows a laser processing device 2 of this embodiment. The laser processing device 2 includes a base 3, a holding unit 4 for holding a workpiece, a laser beam irradiation unit 6, a photographing unit 7, a moving mechanism 30 for moving the holding unit 4 and a control unit as a feeding mechanism for feeding the holding unit 4 and the laser beam irradiation unit 6 relative to each other.

The holding unit 4 includes a rectangular X-axis movable plate 21 mounted on the base 3 so as to be movable in the X-axis direction indicated by an arrow X in the figure, a rectangular Y-axis movable plate 22 mounted on the X-axis movable plate 21 so as to be movable in the Y-axis direction indicated by an arrow Y in the figure, a cylindrical support 23 fixed to the upper surface of the Y-axis movable plate 22, and a rectangular cover plate 26 fixed to the upper end of the support 23. A circular work clamp 25 extending upward through a long hole is provided on the cover plate 26, and the work clamp 25 is configured to be rotatable by a rotation drive mechanism not shown in the figure. The holding surface (adsorption chuck) 25a defined by the X-axis coordinate and the Y-axis coordinate constituting the upper surface of the work chuck 25 is formed of a porous material and has air permeability, and is connected to a suction component (not shown) through a flow path passing through the inside of the support 23.

The moving mechanism 30 includes: an X-axis direction feeding mechanism 31, which is arranged on the base 3 and feeds the holding unit 4 in the X-axis direction; and a Y-axis direction feeding mechanism 32, which feeds the Y-axis direction movable plate 22 in the Y-axis direction. The X-axis direction feeding mechanism 31 converts the rotational motion of the pulse motor 33 into a linear motion through a ball screw 34 and transmits it to the X-axis direction movable plate 21, so that the X-axis direction movable plate 21 moves forward and backward in the X-axis direction along the guide rails 3a, 3a on the base 3. The Y-axis direction feed mechanism 32 converts the rotational motion of the pulse motor 35 into linear motion through the ball screw 36 and transmits it to the Y-axis direction movable plate 22, so that the Y-axis direction movable plate 22 moves forward and backward in the Y-axis direction along the guide rails 21a, 21a on the X-axis direction movable plate 21. Furthermore, although not shown in the figure, the X-axis direction feed mechanism 31, the Y-axis direction feed mechanism 32 and the work clamp 25 are equipped with a position detection component, which can accurately detect the X-axis coordinate, Y-axis coordinate, and circumferential rotation position of the work clamp 25, and transmit the position information to the control unit of the laser processing device 2. Furthermore, the X-axis direction feeding mechanism 31, the Y-axis direction feeding mechanism 32, and the rotation driving mechanism of the work clamp 25 (not shown) can be driven by the indication signal indicated by the control unit according to the position information, so as to position the work clamp 25 to the desired position on the base 3.

As shown in FIG2 , a frame 37 is vertically provided on the side of the moving mechanism 30. The frame 37 includes a vertical wall portion 37a disposed on the base 3 and disposed along the Z axis orthogonal to the X axis direction and the Y axis direction, and a horizontal wall portion 37b extending horizontally from the upper end of the vertical wall portion 37a. The optical system of the laser light irradiation unit 6 is accommodated inside the horizontal wall portion 37b of the frame 37, and a condenser 67 constituting a part of the optical system is disposed on the lower surface of the front end portion of the horizontal wall portion 37b.

The photographing unit 7 is disposed on the lower surface of the front end of the horizontal wall 37b and is spaced apart from the condenser 67 of the laser irradiation unit 6 in the X-axis direction. The photographing unit 7 includes: a normal photographing element (CCD) that photographs with visible light, an infrared light source that irradiates infrared light, and a photographing element (infrared CCD) that can capture infrared light irradiated by the infrared light source and reflected on the work clamp 25 and output an electrical signal corresponding to the infrared light. The image photographed by the photographing unit 7 is transmitted to the control unit and can be displayed on an appropriate display unit (not shown).

The optical system of the laser beam irradiation unit 6 housed in the horizontal wall portion 37b of the laser processing device 2 will be described with reference to FIG. 3 .

The laser irradiation unit 6 comprises: a laser oscillator 61, which emits a laser beam LB0 (in this embodiment, a pulsed laser beam) of a wavelength that is penetrating to the wafer 10 held on the work holder 25; an attenuator 62, which adjusts the laser beam LB0 emitted by the laser oscillator 61 to a desired output; and a spatial optical phase modulator (LCOS, etc.) 63, which adjusts the laser beam LB0 emitted by the attenuator 62 to a desired output. The phase of the output laser beam LB0 is adjusted, and the laser beam LB1 after the phase is adjusted is output; the condenser 67 is equipped with a condenser lens 67a, and the condenser lens 67a condenses the laser beam LB1 whose phase has been adjusted by the spatial optical phase modulator 63 and positions the condensing point inside the wafer 10 on the work clamp 25; and the control unit 100 adjusts the spatial optical phase modulator 63. In addition, the condenser lens 67a is not limited to being composed of one lens, but can also be a combination lens composed of a plurality of lenses.

The control unit 100 is composed of a computer and is electrically connected to the input unit 8 for inputting the control instructions of the operator as needed, and adjusts the operation of the spatial light phase modulator 63. In addition, a memory 110 is provided in the memory of the control unit 100, and the aforementioned memory 110 stores an adjustment pattern table 112 shown in FIG. 3. The adjustment pattern table 112 is composed of the following: a plurality of adjustment patterns 114 are stored, and the aforementioned adjustment pattern 114 is a pattern for adjusting the spatial light phase modulator 63 corresponding to the depth position of the focal point of the laser beam LB1 positioned inside the workpiece. Furthermore, although the control unit 100 in the present embodiment is connected to the above-mentioned laser light irradiation unit 6, the shooting unit 7, the moving mechanism 30, etc. that constitute the laser processing device 2, and is also a control unit that controls each component, it can also be a dedicated control unit separately provided for adjusting the spatial light phase modulator 63.

The spatial optical phase modulator 63 is, for example, a structure in which liquid crystal is arranged on a silicon substrate. The liquid crystal is formed by arranging a plurality of pixels (e.g., aluminum electrodes) on the top layer, and the potential of each pixel is independently controlled according to an adjustment pattern 114 selected from an adjustment pattern table 112 shown in FIG. 3 , thereby modulating the wavefront of the laser light LB0 passing through the liquid crystal, that is, the spatial distribution of the phase.

In addition to FIG. 3 , the functions and effects of the spatial light phase modulator 63 of this embodiment will be further described with reference to FIG. 4 . As mentioned above, if the thickness of the wafer 10 becomes larger, the aberration in the light condensing point positioned inside the wafer 10 will become larger due to the influence of the refractive index of the material constituting the wafer 10 (in this embodiment, it is silicon, and it is about 3.5). If the laser light is directly used in this state, the condensing point of the laser light will not be concentrated at one point, and a suitable modified layer will not be formed. In this embodiment, in order to deal with this, the adjustment pattern table 112 stored in the memory 110 of the control unit 100 is referred to, and the adjustment pattern 114 stored corresponding to the desired depth position of the focal point to be formed inside the wafer 10 is selected, and the spatial light phase modulator 63 is adjusted according to the selected adjustment pattern 114. For example, when the desired depth D is 300 μm, the adjustment pattern 114a can be selected by referring to the adjustment pattern table 112, and the spatial light phase modulator 63 is controlled according to the adjustment pattern 114a. The light spot S1 formed as the focal point P at this time is shown in FIG. 4 (a).

As shown in FIG4(a), by appropriately selecting the adjustment pattern 114 from the adjustment pattern table 112 and adjusting the spatial optical phase modulator 63, a strong-corrected central region S1a (indicated by a dotted line) with relatively small aberration and a weak-corrected peripheral region S1b surrounding the central region S1a and with larger aberration than the central region S1a can be formed. Furthermore, the shape of the light spot having the central region and the peripheral region is not limited to the concentric circle shape shown in FIG4(a), and may also be, for example, a square-shaped light spot S2 as shown in FIG4(b) or a triangular-shaped light spot S3 as shown in FIG4(c). Even if the spot S2 formed by focusing the laser beam LB1 is a quadrangular shape as shown in FIG4(b), a strongly corrected central region S2a can be formed on the central side of the spot S2, and a weakly corrected peripheral region S2b can be formed around the central region S2a. Similarly, even if the spot S3 formed by focusing the laser beam LB1 is a triangular shape as shown in FIG4(c), a strongly corrected central region S3a can be formed on the central side, and a weakly corrected peripheral region S3b can be formed around the central region S3a.

Here, the inventors of the present case have repeatedly examined the appropriate ratio between the central area with relatively small aberrations and strong correction, and the peripheral area with relatively large aberrations and weak correction surrounding the central area, and found the following situation: by setting the area of the central area with relatively small aberrations and strong correction to 20%~30% relative to the total area of the spot shape, even if there is a deviation between the center of the adjustment pattern 114 of the spatial optical phase modulator 63 and the optical axis of the laser light LB0 that may be caused by conventional adjustment, laser processing can still be performed while the processing force is stable and the processing force is not sacrificed.

Furthermore, the intensity of correction in the central area S1a of the light spot S1 shown in FIG. 4(a) and the peripheral area S1b surrounding the central area S1a can be set according to the technical concept shown below.

As a polynomial for approximating the wavefront aberration of a photographic optical system, the Frits Zernike polynomial (hereinafter referred to as the "Zernike polynomial") is known. The Zernike polynomial is well known as a polynomial expressed using polar coordinates (r‚θ), where r is the radius of a unit circle and θ is the rotation angle. The ninth term ([Z9]) constituting the Zernike polynomial is: [Z9]=6r ⁴ -6r ² +1 …(1), where equation (1) represents spherical aberration. Here, the central area S1a that is strongly corrected by the above-mentioned spatial optical phase modulator 63 is corrected by the strong correction so that the aberration at the focal point position at the desired depth position is as close to zero as possible. In contrast, the peripheral region S1b that is weakly corrected by the spatial optical phase modulator 63 is calculated and corrected in the following manner: the value of the coefficient of the above-mentioned 9th term of the Zernike polynomial increases by about 0.05 to 0.09, and more preferably increases by about 0.07, relative to the correction performed by strong correction.

The laser processing device 2 of this embodiment has a configuration roughly as described above, and its functions and effects will be described below.

When the laser processing device 2 shown in FIG. 2 is used to perform laser processing on the wafer 10, the wafer 10 described in FIG. 1 is moved out from a cassette (not shown), and the back side 10b of the wafer 10 is facing upward and the protective tape T side is facing downward. It is placed on the holding surface (adsorption chuck) 25a of the work clamp 25, and the suction component (not shown) is activated for suction and holding.

Next, the moving mechanism 30 is actuated to position the wafer 10 below the photographing unit 7, and the photographing unit 7 irradiates infrared rays from the back side 10b of the wafer 10 to detect the position of the area to be divided formed on the front side 10a, i.e., the predetermined dividing line 14, and stores it in the control unit 100 (calibration step).

After the calibration step has been implemented, the moving mechanism 30 is actuated to move the wafer 10 to the bottom of the condenser 67, and the predetermined splitting line 14 is aligned with the processing feed direction, that is, along the X-axis direction, and based on the position information detected in the calibration step, the position where processing should start at the predetermined predetermined splitting line 14 is positioned directly below the condenser 67.

Next, the above-mentioned laser light irradiation unit 6 is actuated to generate a laser light LB1 having a wavelength that positions the focal point P at the desired depth D inside the wafer 10 and is penetrating to the material (silicon) of the wafer 10, and as shown in FIG5 , irradiates from the back side 10b of the wafer 10 along the area to be divided, that is, the predetermined dividing line 14, and actuates the moving mechanism 30 to feed the worktable 25 in the X-axis direction indicated by the arrow X to form a modified layer 18.

As shown in Fig. 5, the modified layer 18 of this embodiment is formed by a first modified layer 18a, a second modified layer 18b, and a third modified layer 18c having different depths. The depth D of the first modified layer 18a is, for example, 550 μm, and when the laser light irradiation unit 6 that should form the first modified layer 18a is actuated, the adjustment pattern table 112 of the control unit 100 shown in Fig. 3 is referred to to select the adjustment pattern 114b and adjust the spatial optical phase modulator 63 to irradiate the laser light LB1. Furthermore, when the depth D of the second modified layer 18b is, for example, 500 μm and the laser light irradiation unit 6 is actuated to form the second modified layer 18b, the adjustment pattern table 112 of the control unit 100 is referenced to select the adjustment pattern 114c and adjust the spatial light phase modulator 63 to irradiate the laser light LB1. Furthermore, when the depth D of the third modified layer 18c is, for example, 450 μm and the laser light irradiation unit 6 is actuated to form the third modified layer 18c, the adjustment pattern table 112 of the control unit 100 is referenced to select the adjustment pattern 114d and adjust the spatial light phase modulator 63 to irradiate the laser light LB1.

As mentioned above, when forming the first to third modified layers 18a~18c with different depths D, the spatial optical phase modulator 63 is adjusted in conjunction with the desired depth D of the focal point P to form a light spot S1. The light spot S1 has a central area S1a with a relatively small aberration and a strong correction, and a peripheral area S1b with a relatively large aberration and a weak correction, in the focal point P of the laser light LB1 incident on the wafer 10 and refracted. By sequentially forming the aforementioned modified layers, a crack 19 connecting the upper and lower modified layers and reaching the front side 10a can be formed.

After the modified layer 18 and the crack 19 are formed along the predetermined dividing line 14 extending in the predetermined first direction, the wafer 10 is indexed and fed in the Y-axis direction (the direction perpendicular to the paper surface of FIG. 5 ) perpendicular to the X-axis direction by the interval of the predetermined dividing line 14, and the unprocessed predetermined dividing line 14 adjacent to the Y-axis direction extending in the first direction is positioned directly below the condenser 67. Then, the laser beam LB1 is irradiated along the predetermined dividing line 14 of the wafer 10 in the same manner as the above-mentioned method, and the wafer 10 is processed and fed in the X-axis direction, and the modified layer 18 and the crack 19 are formed inside the wafer 10.

By repeating the above-mentioned processing, the laser beam LB1 is irradiated along all the predetermined division lines 14 extending in the first direction, thereby forming the modified layer 18 and the crack 19. Next, the wafer 10 is rotated 90 degrees so that the predetermined division lines 14 in the second direction orthogonal to the predetermined division lines 14 in the first direction on which the modified layer 18 and the crack 19 have been formed are aligned in the X-axis direction. Then, the laser beam LB1 is positioned at the focal point P inside each predetermined division line 14 extending in the second direction in the same manner as the above-mentioned method to irradiate, and the modified layer 18 and the crack 19 are formed along all the predetermined division lines 14 of the wafer 10, thereby completing the laser processing step.

Furthermore, the laser processing conditions in the laser processing of this embodiment are set as shown below. Wavelength: 1099nm Average output: 2.6W Repetition frequency: 120kHz Feed speed: 800mm/sec

The wafer 10 that has been laser processed by the laser processing apparatus 2 is transported to a grinding apparatus 50 (only a portion is shown) shown in FIG. 6 and subjected to a grinding process described below.

The grinding device 50 has a worktable 51 and a grinding unit 52. The worktable 51 can be connected to a suction source (not shown), and the suction source can supply a suction negative pressure to the upper surface. The worktable 51 has a rotating assembly and a moving assembly (not shown), and is rotatable by the rotating assembly, and can move between a loading and unloading area and a processing area by the moving assembly. The loading and unloading area is an area where the wafer 10 is loaded and unloaded on the worktable 51, and the processing area is an area where the grinding unit 52 performs grinding processing. The grinding unit 52 includes a main shaft 53 rotated by an electric motor (not shown), a wheel seat 54 disposed at the lower end of the main shaft 53, a grinding wheel 55 mounted on the lower surface of the wheel seat 54, and a plurality of grinding stones 56 disposed in a ring shape on the lower surface of the grinding wheel 55.

As shown in FIG6 , the wafer 10 transported to the grinding device 50 is placed on the work clamp 51 positioned in the loading and unloading area with the back side 10b facing upward and the protective tape T facing downward, and is held by the suction source. Then, the work clamp 51 can be moved to the grinding area directly below the grinding unit 52 by the moving assembly, and the center of the wafer 10 held on the work clamp 51 is positioned to a position where the grinding stone 56 arranged in a ring shape will pass when viewed from above.

After the wafer 10 has been positioned in the grinding processing area, the work chuck 51 is rotated in the direction indicated by the arrow R1 at, for example, 300 rpm, and at the same time, the spindle 53 of the grinding unit 52 is rotated in the direction indicated by the arrow R2 at, for example, 6000 rpm. Then, the grinding feed unit (not shown) is actuated to lower the grinding unit 52 in the direction indicated by the arrow R3 and bring it close to the work chuck 51, so that it contacts the back side 10b of the wafer 10 from above, and is ground and fed at, for example, a grinding feed speed of 1.0 μm/second. At this time, it is preferable to measure the thickness of the wafer 10 by a measuring instrument (not shown) while grinding. By performing the grinding process in this way, as shown in Fig. 6, the wafer 10 can be thinned and broken along the predetermined dividing line 14 to be divided into individual device chips 12'. The wafer 10 that has completed the grinding process can be appropriately transported to the next step or accommodated in a cassette that is not shown in the figure.

According to this embodiment, even if a deviation occurs between the center of the pattern of the spatial optical phase modulator 63 and the optical path of the laser beam LB0, the processing force can still be stabilized and improved.

Furthermore, the above-mentioned adjustment pattern table 112 is only an embodiment and is not limited to the form shown in FIG. 3 .

2: Laser processing device 3: Base 3a, 21a: Guide rail 4: Holding unit 6: Laser beam irradiation unit 7: Shooting unit 8: Input assembly 10: Wafer 10a: Front side 10b: Back side 12: Device 12': Device wafer 14: Predetermined splitting line 18: Modified layer 18a: First modified layer 18b: Second modified layer 18c: Third modified layer 19: Crack 21: X-axis movable plate 22: Y-axis movable plate 23: Support column 25, 51: Work chuck 25a: Holding surface (adsorption chuck) 26: Cover plate 30: Moving mechanism 31: X-axis feed mechanism 32: Y-axis feed mechanism 33,35: Pulse motor 34,36: Ball screw 37: Frame 37a: Vertical wall 37b: Horizontal wall 50: Grinding device 52: Grinding unit 53: Spindle 54: Wheel seat 55: Grinding wheel 56: Grinding stone 61: Laser oscillator 62: Attenuator 63: Spatial light phase modulator 67: Condenser 67a: Condenser lens 100: Control unit 110: Memory unit 112: Adjustment pattern table 114,114a,114b,114c,114d: Adjustment pattern D: Depth LB0: Laser beam (before adjustment) LB1: Laser beam (after adjustment) P: Focus point R1,R2,R3,X,Y,Z: Arrows S1,S2,S3: Light spot S1a,S2a,S3a: Central area S1b,S2b,S3b: Peripheral area T: Protective tape

FIG1 is a perspective view showing a state of laying protective tape on a wafer. FIG2 is a perspective view of a laser processing device. FIG3 is a block diagram of an optical system of a laser light irradiation unit of the laser processing device shown in FIG2, and an adjustment pattern table. FIG4(a) to (c) are plan views showing the shape of a light spot. FIG5 is a partially enlarged cross-sectional view showing a laser processing step. FIG6 is a perspective view showing an implementation state of a grinding step.

6: Laser irradiation unit

8: Input components

10: Wafer

25: Workbench

61: Laser Oscillator

62: Attenuator

63: Spatial optical phase modulator

67: Concentrator

67a: Focusing lens

100: Control unit

110: Memory Department

112: Adjust pattern table

114,114a,114b,114c,114d:Adjust pattern

D: Depth

LB0: Laser beam (before adjustment)

LB1: Laser beam (after adjustment)

T: Protective tape

Claims (3)

A laser processing device comprises: a worktable for holding a workpiece; a laser light irradiation unit for positioning a focal point of a laser light of a wavelength penetrating the workpiece held on the worktable inside the workpiece to irradiate the laser light and form a modified layer; and a feeding mechanism for feeding the worktable and the laser light irradiation unit relative to each other. The laser light irradiation unit comprises: a laser oscillator for emitting laser light; a spatial light phase modulator for adjusting the phase of the laser light emitted from the laser oscillator; a condenser for focusing the laser light whose phase is adjusted by the spatial light phase modulator and positioning the focal point inside the workpiece; and a control unit for adjusting the spatial light phase modulator. The control unit has a memory section storing an adjustment pattern table, wherein the adjustment pattern table is a table for adjusting the spatial optical phase modulator to form the following areas: a central area with relatively small aberration and strong correction in the focal point of the laser light incident on the workpiece and refracted, and a peripheral residual area with relatively large aberration and weak correction. The laser processing device of claim 1, wherein the central area of strong correction is the area 20-30% of the central side of the laser light emitted from the laser oscillator, and the area of weak correction is the remaining peripheral area surrounding the central area. A laser processing device as claimed in claim 1, wherein the adjustment pattern table has a plurality of adjustment patterns for adjusting the spatial optical phase modulator corresponding to the depth position of the focal point of the laser light positioned inside the object to be processed, and the adjustment pattern is selected corresponding to the focal point depth position specified by an operator.