Laser processing device

Abstract

The present invention provides a laser processing apparatus which can stabilize the processing force and improve the processing force even if there is a slight deviation between the optical path of the laser beam and the center of the pattern for adjusting the spatial light phase modulator. The laser beam irradiation unit of the laser processing apparatus includes: a laser oscillator that emits a laser beam; a spatial light phase adjuster that adjusts the phase of the laser beam emitted from the laser oscillator; a condenser that converges the laser beam whose phase has been adjusted by the spatial light phase adjuster and positions the focal point inside the workpiece; and a control unit that adjusts the spatial light phase adjuster. The control unit includes a storage unit that stores an adjustment pattern table having a plurality of adjustment patterns for adjusting the spatial light phase adjuster corresponding to the depth position of the focal point of the laser beam.

Description

Technical Field

[0001] The present invention relates to a laser processing apparatus that forms a modified layer by irradiating a laser beam having a wavelength that is transmissive to a workpiece held by a chuck table with the focal point of the laser beam positioned inside the workpiece. Background Art

[0002] A wafer formed by being divided by a plurality of intersecting division lines into a plurality of devices such as ICs and LSIs is divided into individual device chips by a laser processing apparatus, and the divided device chips are used in electronic devices such as mobile phones and personal computers.

[0003] The laser processing apparatus includes: a chuck table that holds a workpiece; a laser beam irradiation unit that irradiates the workpiece held by the chuck table with the focal point of a laser beam having a wavelength that is transmissive to the workpiece positioned inside the workpiece, thereby forming a modified layer and cracks extending from the modified layer; and a feed mechanism that relatively feeds the chuck table and the laser beam irradiation unit for processing. The laser processing apparatus positions the focal point inside the wafer corresponding to the division line and forms a modified layer as a starting point of division at an appropriate position, and can divide the wafer into individual device chips by applying an external force (for example, refer to Patent Document 1).

[0004] Patent Document 1: Japanese Patent No. 3408805

[0005] According to the technique described in the above Patent Document 1, in the case of a thin thickness of the wafer, 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 to appropriately form a modified layer and cracks extending from the modified layer. However, when the thickness of the wafer increases, for example, when it becomes a thickness exceeding 300 μm, there is a problem that the refractive index of the raw material constituting the wafer (for example, approximately 3.5 in the case of silicon) has an influence, the aberration increases, the focal point of the laser beam no longer converges to a single point, and an appropriate modified layer cannot be formed.

[0006] In order to address the above problems, it is considered to dispose a spatial light phase modulator (such as LCOS) between the laser oscillator and the condenser that constitute the laser beam irradiation unit, and correct spherical aberration as a whole by the spatial light phase modulator to converge the focal point of the laser beam at a point inside the wafer. However, it is not easy to accurately align the center of the pattern of the spatial light phase modulator with the optical path of the laser beam. When there is an offset between the center of the pattern of the spatial light phase modulator and the optical path of the laser beam, the following problems occur: the focal point cannot be converged as intended, the processing force is reduced, and the processing of the laser processing apparatus cannot be stably performed. For this problem, by weakening the intensity of the correction of spherical aberration by the spatial light phase modulator, even if there is a slight offset between the center of the pattern of the spatial light phase modulator and the optical path of the laser beam, a certain degree of processing force can be ensured. However, there is a problem that the processing force is sacrificed as a result of weakening the correction of spherical aberration as described above. Summary of the Invention

[0007] Accordingly, an object of the present invention is to provide a laser processing apparatus that can stabilize the processing force and increase the processing force even if there is a slight offset between the optical path of the laser beam and the center of the pattern of the spatial light phase modulator.

[0008] According to the present invention, there is provided a laser processing apparatus, which includes: a chuck table that holds a workpiece; a laser beam irradiation unit that irradiates the laser beam having a wavelength that is transmissive to the workpiece held by the chuck table, and forms a modified layer by positioning the focal point of the laser beam inside the workpiece; and a feed mechanism that relatively feeds the chuck table and the laser beam irradiation unit for processing. The laser beam irradiation unit includes: a laser oscillator that emits a laser beam; a spatial light phase adjuster that adjusts the phase of the laser beam emitted from the laser oscillator; a condenser that converges the laser beam whose phase has been adjusted by the spatial light phase adjuster and positions the focal point inside the workpiece; and a control unit that adjusts the spatial light phase adjuster. The control unit has a storage unit that stores an adjustment pattern table, and the adjustment pattern table adjusts the spatial light phase adjuster to form a central region with strong correction having relatively small aberration and a peripheral remaining region with weak correction having relatively large aberration at the focal point of the laser beam that enters the workpiece and is refracted.

[0009] Preferably, the strongly corrected central region is a region of 20% to 30% on the central side of the laser beam oscillated by the laser oscillator, and the weakly corrected region is the remaining outer peripheral region surrounding the central region. Preferably, the adjustment pattern table has a plurality of adjustment patterns for adjusting the spatial light phase modulator corresponding to the depth position of the focal point of the laser beam located inside the workpiece, and the adjustment pattern is selected corresponding to the focal point depth position designated by the operator.

[0010] According to the present invention, even if the optical path of the laser beam is offset from the center of the pattern for adjusting the spatial light phase modulator, the machining force can be stabilized and the machining force can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a perspective view showing a manner of laying a protective tape on a wafer.

[0012] Figure 2 is a perspective view of a laser processing apparatus.

[0013] Figure 3 is Figure 2 a block diagram of an optical system of a laser beam irradiation unit of the laser processing apparatus shown and an adjustment pattern table.

[0014] Figure 4 (a) to Figure 4 (c) of is a top view showing the shape of a light spot.

[0015] Figure 5 is a partially enlarged cross-sectional view showing a laser processing step.

[0016] Figure 6 is a perspective view showing an embodiment of a grinding step.

[0017] REFERENCE SIGNS LIST

[0018] 2: Laser processing device; 3: Base; 4: Holding unit; 6: Laser beam irradiation unit; 61: Laser oscillator; 62: Attenuator; 63: Spatial light phase modulator; 67: Condenser; 67a: Condensing lens; 10: Wafer; 12: Device; 14: Dicing predetermined line; 18: Modified layer; 18a: First modified layer; 18b: Second modified layer; 18c: Third modified layer; 19: Crack; 21: Movable plate in the X-axis direction; 22: Movable plate in the Y-axis direction; 25: Chuck table; 30: Moving mechanism; 31: Feeding mechanism in the X-axis direction; 32: Feeding mechanism in the Y-axis direction; 50: Grinding device; 51: Chuck table; 52: Grinding unit; 53: Rotating spindle; 54: Grinding wheel mounting base; 55: Grinding wheel; 56: Grinding tool; 100: Control unit; 112: Adjustment pattern table; 114, 114a to 114c: Adjustment pattern; S1 to S3: Light spot; S1a: Central area; S1b: Peripheral area; LB0: Laser beam (before adjustment); LB1: Laser beam (after adjustment). Detailed implementation mode

[0019] Hereinafter, the laser processing device according to the embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0020] In Figure 1 FIG. shows a wafer 10 and a protective tape T prepared as a workpiece to be processed by this embodiment, and shows a method of laying the protective tape T on the front surface 10a of the wafer 10. The wafer 10 is, for example, a silicon wafer with a thickness of 700 μm, and is divided by a plurality of intersecting dicing predetermined lines 14 to form a plurality of devices 12 on the front surface 10a. The protective tape T is a resin tape having an adhesive layer, and is adhered to the front surface 10a side of the wafer 10 to become integrated.

[0021] In Figure 2 FIG. shows the laser processing device 2 of this embodiment. The laser processing device 2 includes: a base 3; a holding unit 4 that holds the workpiece; a laser beam irradiation unit 6; a photographing unit 7; a moving mechanism 30 that is disposed as a feeding mechanism for relatively feeding the holding unit 4 and the laser beam irradiation unit 6 to move the holding unit 4; and a control unit.

[0022] The holding unit 4 includes: a rectangular X-axis movable plate 21 that is movably placed on the base 3 in the X-axis direction indicated by the arrow X in the figure; a rectangular Y-axis movable plate 22 that is movably placed on the X-axis movable plate 21 in the Y-axis direction indicated by the arrow Y in the figure; a cylindrical support column 23 that is fixed to the upper surface of the Y-axis movable plate 22; and a rectangular cover plate 26 that is fixed to the upper end of the support column 23. A circular chuck table 25 extending upward through a long hole is provided on the cover plate 26, and the chuck table 25 is configured to be rotatable by a rotation drive mechanism (not shown). A holding surface 25a defined by the X-axis coordinate and the Y-axis coordinate on the upper surface of the chuck table 25 is formed of a porous material and has air permeability, and is connected to an attracting unit (not shown) through a flow path passing through the inside of the support column 23.

[0023] The moving mechanism 30 has: an X-axis feed mechanism 31 that is disposed on the base 3 and performs machining feed of the holding unit 4 in the X-axis direction; and a Y-axis feed mechanism 32 that performs indexing feed of the Y-axis movable plate 22 in the Y-axis direction. The X-axis feed mechanism 31 converts the rotational motion of the pulse motor 33 into a linear motion by means of a ball screw 34 and transmits it to the X-axis movable plate 21, causing the X-axis movable plate 21 to advance and retreat in the X-axis direction along the guide rails 3a, 3a on the base 3. The Y-axis feed mechanism 32 converts the rotational motion of the pulse motor 35 into a linear motion by means of a ball screw 36 and transmits it to the Y-axis movable plate 22, causing the Y-axis movable plate 22 to advance and retreat in the Y-axis direction along the guide rails 21a, 21a on the X-axis movable plate 21. In addition, although not shown in the figure, position detection units are provided on the X-axis feed mechanism 31, the Y-axis feed mechanism 32, and the chuck table 25 to accurately detect the X-axis coordinate, the Y-axis coordinate, and the circumferential rotational position of the chuck table 25 and send the position information to the control unit of the laser processing device 2. And, according to the instruction signal indicated from the control unit based on this position information, it is possible to drive the X-axis feed mechanism 31, the Y-axis feed mechanism 32, and the rotation drive mechanism of the chuck table 25 (not shown) to position the chuck table 25 at a desired position on the base 3.

[0024] As Figure 2 shown, a frame 37 is erected on the side of the moving mechanism 30. The frame 37 has: a vertical wall portion 37a that is disposed on the base 3 and is disposed along the Z-axis perpendicular to the X-axis direction and the Y-axis direction; and a horizontal wall portion 37b that extends horizontally from the upper end portion of the vertical wall portion 37a. The optical system of the laser beam irradiation unit 6 is housed inside the horizontal wall portion 37b of the frame 37, and a condenser 67 that forms a part of the optical system is disposed on the lower surface of the front end portion of the horizontal wall portion 37b.

[0025] The photographing unit 7 is disposed on the lower surface of the front end portion of the horizontal wall portion 37b and at a position spaced apart from the condenser 67 of the laser light irradiation unit 6 in the X-axis direction. The photographing unit 7 includes a normal photographing element (CCD) that photographs by visible light, an infrared light source that irradiates infrared rays, a photographing element (infrared CCD) that captures the infrared rays irradiated by the infrared light source and reflected on the chuck table 25 and outputs an electric signal corresponding to the infrared rays, and the like. The image photographed by the photographing unit 7 is sent to the control unit and displayed on an appropriate display unit (not shown).

[0026] Refer to Figure 3 The optical system of the laser light irradiation unit 6 housed in the horizontal wall portion 37b of the laser processing apparatus 2 will be described.

[0027] The laser light irradiation unit 6 includes: a laser oscillator 61 that emits a laser beam LB0 having a wavelength that is transmissive to the wafer 10 held by the chuck table 25 (pulsed laser beam in this embodiment); an attenuator 62 that adjusts the laser beam LB0 emitted by the laser oscillator 61 to a desired output; a spatial light phase modulator (LCOS, etc.) 63 that adjusts the phase of the laser beam LB0 whose output has been adjusted by the attenuator 62 and outputs the laser beam LB1 with the adjusted phase; a condenser 67 that is provided with a condenser lens 67a and converges the laser beam LB1 whose phase has been adjusted by the spatial light phase modulator 63 and positions the condensing point inside the wafer 10 on the chuck table 25; and a control unit 100 that adjusts the spatial light phase modulator 63. In addition, the condenser lens 67a is not limited to being composed of one lens, and may also be a set of lenses composed of a plurality of lenses.

[0028] The control unit 100 is composed of a computer, 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 storage unit 110 storing the adjustment pattern table 112 shown in Figure 3 is provided in the memory of the control unit 100. The adjustment pattern table 112 stores a plurality of adjustment patterns 114 for adjusting the spatial light phase modulator 63 corresponding to the depth position D of the condensing point of the laser beam LB1 positioned inside the workpiece. In addition, the control unit 100 in this embodiment is connected to the above-described laser light irradiation unit 6, photographing unit 7, moving mechanism 30, etc. that constitute the laser processing apparatus 2, and also controls each unit, but may also be a dedicated control unit provided separately for adjusting the spatial light phase modulator 63.

[0029] The spatial light phase modulator 63 is formed, for example, by disposing liquid crystal on a silicon substrate. The liquid crystal is formed by a plurality of pixels (such as aluminum electrodes) disposed on the uppermost layer. According to the adjustment pattern 114 selected based on the adjustment pattern table 112 shown in Figure 3 , the potential of each pixel is independently controlled for each pixel, and the spatial distribution of the wavefront, that is, the phase, of the laser beam LB0 passing through the liquid crystal is modulated.

[0030] Based on Figure 3 , with reference to Figure 4 , the functions and actions of the spatial light phase modulator 63 of the present embodiment will be further described. As described above, when the thickness of the wafer 10 increases, due to the influence of the refractive index of the raw material constituting the wafer 10 (silicon in the present embodiment, approximately 3.5), the aberration at the focal point located inside the wafer 10 increases. In such a state, the focal point of the laser beam no longer converges at a single point, and an appropriate modified layer cannot be formed. In the present embodiment, in order to cope with this situation, with reference to the adjustment pattern table 112 stored in the storage unit 110 of the control unit 100, the adjustment pattern 114 stored corresponding to the desired depth position D where it is desired to form a focal point 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, with reference to the above adjustment pattern table 112, the adjustment pattern 114a is selected, and the spatial light phase modulator 63 is controlled according to the adjustment pattern 114a. In Figure 4 , (a) shows the light spot S1 formed at the focal point P at this time.

[0031] As Figure 4 (a) shows, by appropriately selecting the adjustment pattern 114 through the above adjustment pattern table 112 and adjusting the spatial light phase modulator 63, a strongly corrected central region S1a with relatively small aberration (the region shown by the dotted line) and a weakly corrected outer peripheral region S1b surrounding the central region S1a and having a larger aberration than the central region S1a are formed. In addition, the light spot shape having a central region and an outer peripheral region is not limited to the concentric shape shown in Figure 4 (a), and for example, it may also be a quadrilateral light spot S2 shown in Figure 4 (b), or a triangular light spot S3 shown in Figure 4 (c). As Figure 4 (b) shows, when the light spot S2 formed by the convergence of the laser beam LB1 is quadrilateral, a strongly corrected central region S2a is also formed on the central side of the light spot S2, and a weakly corrected outer peripheral region S2b surrounding the central region S2a is formed. Similarly, as Figure 4As shown in (c), when the spot S3 formed by the convergence of the laser beam LB1 is triangular, a strongly corrected central region S3a is also formed on the central side, and a weakly corrected peripheral region S3b surrounding the central region S3a is formed.

[0032] Here, regarding the appropriate ratio between the strongly corrected central region with relatively small aberration and the weakly corrected peripheral region with relatively large aberration surrounding the central region, the researchers of the present application repeatedly conducted research through experiments, simulations, etc. and found that: by setting the area of the strongly corrected central region with relatively small aberration to 20% - 30% of the total area of the spot shape, even if an offset caused by normal adjustment occurs between the center of the adjustment pattern 114 of the spatial light phase modulator 63 and the optical axis of the laser beam LB0, the processing force in laser processing is stable, and laser processing can be implemented without sacrificing the processing force.

[0033] In addition, regarding Figure 4 the intensity of correction in the central region S1a of the spot S1 and the peripheral region S1b surrounding the central region S1a shown in (a) is set according to the technical idea described below.

[0034] As a polynomial approximating the wavefront aberration of an imaging optical system, the Fringe Zernike polynomial (hereinafter referred to as "Zernike polynomial") is known. This Zernike polynomial is conventionally known as a polynomial expressed using polar coordinates (r, θ), where r is the radius of the unit circle and θ is the rotation angle. The 9th term ([Z9]) constituting the Zernike polynomial is as follows:

[0035] [Z9] = 6r 4 - 6r 2 + 1…(1)

[0036] This formula (1) represents spherical aberration. Here, the strongly corrected central region S1a by the above-mentioned spatial light phase modulator 63 is a region corrected by this strong correction so that the aberration at the focus position of the desired depth position D is as close to zero as possible. In contrast, the weakly corrected peripheral region S1b by the spatial light phase modulator 63 is a region calculated and corrected such that the value of the coefficient of the 9th term of the Zernike polynomial is about 0.05 - 0.09, more preferably about 0.07, larger than the correction based on the strong correction.

[0037] The laser processing apparatus 2 of the present embodiment has a structure generally as described above, and its operation and effects will be described below.

[0038] When using Figure 2When the laser processing apparatus 2 shown performs laser processing on the wafer 10, the wafer 10 described according to Figure 1 is carried out from a cassette (not shown), and the wafer 10 is placed on the suction chuck 25a of the chuck table 25 with the back surface 10b side of the wafer 10 facing upward and the protective tape T side facing downward, and the suction unit (not shown) is operated to perform suction and holding.

[0039] Next, the moving mechanism 30 is operated to position the wafer 10 below the imaging unit 7. The imaging unit 7 irradiates infrared rays from the back surface 10b side of the wafer 10, detects the position of the dicing line 14, which is the area to be diced, formed on the front surface 10a, and stores it in the control unit 100 (alignment process).

[0040] After performing this alignment process, the moving mechanism 30 is operated to move the wafer 10 below the condenser 67, align the dicing line 14 with the processing feed direction, that is, the direction along the X-axis, and position the starting position of the processing on the specified dicing line 14 directly below the condenser 67 based on the position information detected by the alignment process.

[0041] Next, the laser beam irradiation unit 6 is operated to position the focal point P at a desired depth D inside the wafer 10, generate a laser beam LB1 having a wavelength that is transmissive to the material (silicon) of the wafer 10, and Figure 5 irradiate it from the back surface 10b of the wafer 10 along the area to be diced, that is, the dicing line 14, as shown, and the moving mechanism 30 is operated to feed the chuck table 25 in the X-axis direction indicated by the arrow X to form the modified layer 18.

[0042] As Figure 5 shown, the modified layer 18 of the present 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. When the laser beam irradiation unit 6 is operated to form the first modified layer 18a, refer to Figure 3The adjustment pattern table 112 of the control unit 100 shown selects the adjustment pattern 114b to adjust the spatial light phase modulator 63, and irradiates the laser beam LB1. Additionally, the depth D of the second modified layer 18b is, for example, 500 μm. When the laser beam irradiation unit 6 operates to form the second modified layer 18b, referring to the adjustment pattern table 112 of the control unit 100, the adjustment pattern 114c is selected to adjust the spatial light phase modulator 63, and the laser beam LB1 is irradiated. Additionally, the depth D of the third modified layer 18c is, for example, 450 μm. When the laser beam irradiation unit 6 operates to form the third modified layer 18c, referring to the adjustment pattern table 112 of the control unit 100, the adjustment pattern 114d is selected to adjust the spatial light phase modulator 63, and the laser beam LB1 is irradiated.

[0043] As described above, when forming the first to third modified layers 18a to 18c with different depths D, the spatial light phase modulator 63 is adjusted according to the desired depth D at which the focal point P is formed, and the light spot S1 is formed. The light spot S1 has a strongly corrected central region S1a with relatively small aberration at the focal point P of the laser beam LB1 refracted upon entering the wafer 10 and a weakly corrected peripheral region S1b with relatively large aberration. By sequentially forming the above-mentioned modified layers, the upper and lower modified layers are connected, and a crack 19 reaching the front surface 10a side is formed.

[0044] If the above-mentioned modified layer 18 and crack 19 are formed along the division predetermined line 14 extending in the specified first direction, the wafer 10 is indexed in the Y-axis direction (the direction perpendicular to the paper surface of Figure 5 ) perpendicular to the X-axis direction at the interval of the division predetermined line 14, and the unprocessed division predetermined line 14 extending in the first direction adjacent in the Y-axis direction is positioned directly below the condenser 67. And, in the same manner as above, the laser beam LB1 is irradiated along the division predetermined line 14 of the wafer 10, and the wafer 10 is processed and fed in the X-axis direction to form the modified layer 18 and the crack 19 inside the wafer 10.

[0045] By repeating the above processing, the laser beam LB1 is irradiated along all the division predetermined lines 14 extending in the first direction to form the modified layer 18 and the crack 19. Next, the wafer 10 is rotated 90 degrees so that the second processed division predetermined line 14 perpendicular to the division predetermined line 14 in the first direction where the modified layer 18 and the crack 19 have already been formed coincides with the X-axis direction. And, in the same manner as above, the focal point P of the laser beam LB1 is positioned inside each division predetermined line 14 extending in the second direction, and the modified layer 18 and the crack 19 are formed along all the division predetermined lines 14 of the wafer 10, thereby completing the laser processing step.

[0046] In addition, the laser processing conditions in the laser processing of the present embodiment are set as follows, for example.

[0047] Wavelength: 1099 nm

[0048] Average output: 2.6 W

[0049] Repetition frequency: 120 kHz

[0050] Feed rate: 800 mm / second

[0051] The wafer 10 that has undergone laser processing by the above-described laser processing apparatus 2 is transported to Figure 6 the grinding apparatus 50 (only a part is shown) shown in the figure, and the grinding process described below is performed.

[0052] The grinding apparatus 50 includes a chuck table 51 and a grinding unit 52. The chuck table 51 is connected to a suction source (not shown), and a suction negative pressure is provided to the upper surface by the action of this suction source. The chuck table 51 includes a rotation unit and a movement unit (not shown). By the action of this rotation unit, it is configured to be rotatable, and by the action of this movement unit, it moves to the loading / unloading area for loading and unloading the wafer 10 with respect to the chuck table 51 and the grinding area where the grinding process is performed by the grinding unit 52. The grinding unit 52 includes: a main shaft 53 that rotates by a motor (not shown); a grinding wheel mount 54 disposed at the lower end of the main shaft 53; a grinding wheel 55 mounted on the lower surface of the grinding wheel mount 54; and a plurality of grinding tools 56 that are annularly arranged on the lower surface of the grinding wheel 55.

[0053] As Figure 6 shown, the wafer 10 transported to the grinding apparatus 50 is placed on the chuck table 51 positioned in the loading / unloading area with the back surface 10b side facing upward and the protective tape T side facing downward, and is suction-held by the action of this suction source. Next, the chuck table 51 moves to directly below the grinding unit 52, that is, the grinding area, by this movement unit. When viewed from above, the center of the wafer 10 held by the chuck table 51 is positioned at the position through which the annularly arranged grinding tools 56 pass.

[0054] If the wafer 10 is positioned in the grinding area, the chuck table 51 is rotated, for example, at 300 rpm in the direction indicated by arrow R1, and at the same time, the spindle 53 of the grinding unit 52 is rotated, for example, at 6000 rpm in the direction indicated by arrow R2. Then, an unillustrated grinding feed unit is actuated to lower the grinding unit 52 in the direction indicated by arrow R3 to approach the chuck table 51, contact the back surface 10b of the wafer 10 from above, and perform grinding feed at a grinding feed rate of, for example, 1.0 μm / sec. At this time, it is preferable to perform grinding while measuring the thickness of the wafer 10 with an unillustrated measuring instrument. By performing the grinding process in this way, as Figure 6 shown, the wafer 10 is thinned and broken along the dicing line 14 into individual device chips 12'. The wafer 10 that has completed the grinding process is appropriately transferred to the next process or stored in a cassette (not shown).

[0055] According to the present embodiment, even if the optical path of the laser beam LB0 is offset from the center of the pattern of the adjustable spatial light phase modulator 63, the processing force can be stabilized and the processing force can be increased.

[0056] In addition, the above adjustment pattern table 112 is only one example and is not limited to Figure 3 the manner shown.

Claims

1. A laser processing apparatus, wherein, the laser processing apparatus includes: a chuck table for holding a workpiece; a laser beam irradiation unit that irradiates a laser beam having a wavelength that is transmissive to the workpiece held by the chuck table, with the focal point of the laser beam positioned inside the workpiece, thereby forming a modified layer; and a feed mechanism that relatively feeds the chuck table and the laser beam irradiation unit for processing, the laser beam irradiation unit includes: a laser oscillator that emits a laser beam; a spatial light phase adjuster that adjusts the phase of the laser beam emitted from the laser oscillator; a condenser that converges the laser beam whose phase has been adjusted by the spatial light phase adjuster and positions the focal point inside the workpiece; and a control unit that adjusts the spatial light phase adjuster, the control unit has a storage unit storing an adjustment pattern table, the adjustment pattern table adjusts the spatial light phase adjuster to form a strongly corrected central region with relatively small aberration at the focal point of the laser beam incident on the workpiece and refracted, and a weakly corrected peripheral remaining region with relatively large aberration.

2. The laser processing apparatus according to claim 1, wherein, the strongly corrected central region is a region of 20% to 30% on the central side of the laser beam emitted from the laser oscillator, the weakly corrected region is the remaining peripheral region surrounding the central region.

3. The laser processing apparatus according to claim 1, wherein, the adjustment pattern table has a plurality of adjustment patterns for adjusting the spatial light phase adjuster corresponding to the depth position of the focal point of the laser beam positioned inside the workpiece, and the adjustment pattern is selected corresponding to the focal point depth position designated by the operator.

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