Laser processing method

Abstract

This invention provides a laser processing method that, even when tiny bubbles are generated in water causing scattering of the irradiated laser light, does not damage the devices formed on the front side of the wafer, nor does it degrade the quality of the individual segmented devices. The laser processing method includes the following steps: a light-scattering shielding film stacking step, where a light-scattering shielding film is stacked on the upper surface of the wafer to shield the scattered laser light; a holding step, where the lower surface of the wafer is held using a chuck stage; a laser processing step, where a water layer is formed on the upper surface of the wafer, and laser light is irradiated onto the area of ​​the wafer to be processed while the chuck stage is moved relative to a laser irradiation unit; and a light-scattering shielding film removal step, where the light-scattering shielding film is removed from the wafer after the laser processing step.

Description

Technical Field

[0001] This invention relates to a laser processing method using a laser processing apparatus. Background Technology

[0002] A wafer with multiple devices such as ICs and LSIs formed on its front side by multiple intersecting pre-defined dividing lines is divided into individual device chips by a laser processing device. The resulting device chips are used in electronic devices such as mobile phones, personal computers, and lighting equipment.

[0003] It is known in the past that, before processing by irradiating the wafer with a wavelength that is absorbent to the wafer held by the holding unit, a liquid resin is coated on the front side of the wafer to prevent molten material (debris) generated during laser irradiation from adhering to the device (see, for example, Patent Document 1).

[0004] In addition, the applicant has proposed a laser processing apparatus of the following type, which is configured to include at least: a holding unit for holding a wafer; a water layer forming unit for forming a water layer on the upper surface of the wafer held by the holding unit; a laser beam irradiation unit for irradiating the wafer with a laser beam of a wavelength that is absorbent to the wafer to process the wafer; and a processing feed mechanism for feeding the holding unit and the laser beam irradiation unit relative to each other (see, for example, Patent Document 2).

[0005] According to the technical proof described in the aforementioned Patent Document 2, by immersing the wafer in water, it is possible to prevent debris generated during laser processing from adhering to the upper surface of the wafer, and by irradiating the water with laser light, micro-bubbles (cavitation) are generated, which have the effect of scraping out debris that hinders the laser processing from the processing tank. In addition, it also has the effect of improving the bending strength of each segmented device chip.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2004-188475

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-069465

[0008] However, when processing a wafer by forming a water layer on its upper surface as described above and irradiating it with laser light of a wavelength that is absorbent to the wafer, the cavitation causes a portion of the laser light to scatter. As a result, a portion of the laser light irradiates areas outside the desired processing location (e.g., a pre-defined dividing line), thus degrading the quality of the device. Summary of the Invention

[0009] Therefore, the object of the present invention is to provide a laser processing method that, even if tiny bubbles are generated in water and the irradiated laser light is scattered, will not damage the devices formed on the front side of the wafer, and will not reduce the quality of the individual segmented devices.

[0010] According to the present invention, a laser processing method is provided, wherein the laser processing method comprises the following steps: a light-scattering shielding film stacking step, wherein a light-scattering shielding film is stacked on the upper surface side of a wafer, the light-scattering shielding film shielding the scattered light of a laser beam; a holding step, wherein the lower surface side of the wafer is held using a chuck stage; a laser processing step, wherein a water layer is formed on the upper surface side of the wafer, and a laser beam is irradiated onto the area of ​​the wafer to be processed while the chuck stage is moved relative to a laser beam irradiation unit; and a light-scattering shielding film removal step, wherein the light-scattering shielding film is removed from the wafer after the laser processing step has been completed.

[0011] Preferably, in the light-scattering shielding film stacking process, the light-scattering shielding film is stacked by vapor deposition or sputtering of at least one of Si, Ge, or Al. When the light-scattering shielding film is stacked by vapor deposition or sputtering of at least one of Si, Ge, or Al in the light-scattering shielding film stacking process, it is preferable to remove the light-scattering shielding film from the wafer by grinding in the light-scattering shielding film removal process.

[0012] Preferably, in the light-scattering shielding film lamination process, the light-scattering shielding film is laminated by coating or pressing with resin. When the light-scattering shielding film is laminated by coating or pressing with resin in the light-scattering shielding film lamination process, it is preferable to remove the light-scattering shielding film from the wafer using a solvent in the light-scattering shielding film removal process.

[0013] In this light-scattering shielding film stacking process, a resin film can be coated on the upper surface of the wafer before the light-scattering shielding film is stacked by evaporation or sputtering.

[0014] According to the present invention, when a water layer is formed on the upper surface of a wafer and a laser beam of a wavelength that is absorbent to the wafer is irradiated to process the wafer, even if a portion of the laser beam is scattered by tiny bubbles (cavities) generated in the water layer, damage to the device can be prevented by a light-shielding film formed on the front side of the wafer, thus eliminating the problem of reduced device quality. Attached Figure Description

[0015] Figure 1 This is a three-dimensional view of the laser processing equipment.

[0016] Figure 2 It is Figure 1 An exploded perspective view showing a portion of the laser processing apparatus.

[0017] Figure 3 (a) is installed on Figure 1 The diagram shows a perspective view of the liquid layer former in a laser processing apparatus. Figure 3 (b) is an exploded perspective view showing the liquid layer former.

[0018] Figure 4 This is a schematic diagram illustrating an embodiment of the process for laminating a light-scattering shielding film.

[0019] Figure 5 This is a perspective view showing an embodiment of the holding process.

[0020] Figure 6 (a) is a perspective view showing an embodiment of the laser processing procedure. Figure 6 (b) is Figure 6 A partially enlarged cross-sectional view of the embodiment shown in (a).

[0021] Figure 7 It is Figure 6 The embodiment of the laser processing procedure shown in (b) is further enlarged and shown in a partial enlarged cross-sectional view.

[0022] Figure 8 This is a perspective view illustrating an embodiment of the process for removing the light-scattering shielding film.

[0023] Label Explanation

[0024] 2: Laser processing device; 4: Liquid supply mechanism; 8: Laser beam irradiation unit; 86: Concentrator; 10: Wafer; 12: Device; 14: Segmentation pre-line; 21: Base; 22: Holding unit; 23: Moving mechanism; 231: X-direction feed mechanism (processing feed mechanism); 232: Y-direction feed mechanism; 26: Frame; 261: Vertical wall; 262: Horizontal wall; 30: X-direction movable plate; 31: Y-direction movable plate; 33: Cover plate; 34: Chuck worktable; 35: Adsorption chuck; 40: Liquid layer former; 42: Housing; 421: Upper housing component; 422: Lower housing component; 422e: Slit; 423: 43: Transparent section; 44: Liquid supply section; 45: Liquid supply pump; 50: X-direction moving mechanism; 52: Y-direction moving mechanism; 60: Liquid recovery tank; 60A: Opening; 65: Liquid discharge hole; 70: Liquid recovery path; 90: Alignment unit; 100: Evaporation device; 101: Vacuum chamber; 102: Vacuum pump; 103: Support plate; 104: Crucible; 105: Electron beam generating device; 110: Film forming material (Si); 112: Si molecule; 114: Light scattering shielding film; 130: Polishing device; 135: Polishing wheel; 136: Polishing pad; LB: Laser beam; H: Gap; S: Slurry; W: Water. Detailed Implementation

[0025] Hereinafter, the laser processing method of the present invention will be described in detail with reference to the accompanying drawings.

[0026] exist Figure 1 The figure shows a perspective view of a laser processing apparatus 2 suitable for implementing the laser processing method of this embodiment. The laser processing apparatus 2 includes: a liquid supply mechanism 4 disposed on a base 21, which supplies liquid to a wafer that is a plate-shaped workpiece; a laser beam irradiation unit 8, which irradiates a laser beam of a wavelength that is absorbed by the workpiece; a holding unit 22, which holds the workpiece; a moving mechanism 23, which moves the laser beam irradiation unit 8 and the holding unit 22 relative to each other; and a frame 26, which is composed of a vertical wall portion 261 erected in the Z direction as indicated by the side arrow Z of the moving mechanism 23 on the base 21, and a horizontal wall portion 262 extending horizontally from the upper end of the vertical wall portion 261.

[0027] An optical system (not shown) including a laser oscillator constituting the laser beam irradiation unit 8 is housed inside the horizontal wall portion 262 of the frame 26. A condenser 86 constituting part of the laser beam irradiation unit 8 is disposed on the lower surface side of the front end of the horizontal wall portion 262, and an alignment unit 90 is disposed adjacent to the condenser 86 in the direction indicated by arrow X in the figure.

[0028] The alignment unit 90 is used to photograph the workpiece held by the chuck stage 34 constituting the holding unit 22 to detect the area to be laser-processed, and to align the processing position of the concentrator 86 with that of the workpiece. The alignment unit 90 has a suitable imaging element (CCD) for photographing the upper surface of the workpiece, such as including: an infrared irradiation unit that irradiates infrared light; an optical system that captures the infrared light irradiated by the infrared irradiation unit; and an imaging element (infrared CCD) that outputs an electrical signal corresponding to the infrared light captured by the optical system. In addition, the laser processing apparatus 2 is configured to be completely sealed by a housing or the like (omitted for ease of explanation), so that dust and other contaminants will not enter the interior.

[0029] Reference Figure 1 as well as Figure 2 The laser processing apparatus 2 of this embodiment will be described in more detail. Figure 2 It is shown in Figure 1 The diagram shows a perspective view of the state in which the liquid recovery tank 60, which is part of the liquid supply mechanism 4, is removed from the laser processing apparatus 2 and partially decomposed.

[0030] like Figure 2As shown, the holding unit 22 includes: a rectangular X-direction movable plate 30, which is movably mounted on the base 21 in the X direction as indicated by arrow X; a rectangular Y-direction movable plate 31, which is movably mounted on the X-direction movable plate 30 in the Y direction perpendicular to the X direction as indicated by arrow Y; a cylindrical support column 32, which is fixed to the upper surface of the Y-direction movable plate 31; and a rectangular cover plate 33, which is fixed to the upper end of the support column 32. A chuck worktable 34 extending upward through an elongated hole formed in the cover plate 33 is disposed on the cover plate 33. The chuck worktable 34 holds the plate-shaped workpiece and is configured to be rotatable by a rotary drive unit (not shown). A circular suction chuck 35, which is formed of a porous material with air permeability, is disposed on the chuck worktable 34 and extends substantially horizontally. The suction chuck 35 is connected to an attraction unit (not shown) via a flow path through the support column 32, and four clamps 36 are arranged at intervals around the suction chuck 35. The planes defined by the X and Y directions of the upper surface of the suction chuck 35 substantially constitute a horizontal plane.

[0031] The moving mechanism 23 includes an X-direction moving mechanism 231 and a Y-direction moving mechanism 232. The X-direction moving mechanism 231 converts the rotational motion of the motor 231a into linear motion via the ball screw 231b and transmits it to the X-direction movable plate 30, causing the X-direction movable plate 30 to move forward and backward along the guide rails 27, 27 on the base 21 in the X direction. The Y-direction moving mechanism 232 converts the rotational motion of the motor 232a into linear motion via the ball screw 232b and transmits it to the Y-direction movable plate 31, causing the Y-direction movable plate 31 to move forward and backward along the guide rails 37, 37 on the X-direction movable plate 30 in the Y direction. Furthermore, although the illustrations are omitted, position detection units are respectively installed in the chuck table 34, the X-direction moving mechanism 231, and the Y-direction moving mechanism 232. These units accurately detect the X-direction position, Y-direction position, and circumferential rotation position of the chuck table 34. By driving the X-direction moving mechanism 231, the Y-direction moving mechanism 232, and the rotation drive unit of the chuck table 34 (not shown), the chuck table 34 can be accurately positioned at any position and angle. The X-direction moving mechanism 231 is a machining feed mechanism that moves the holding unit 22 in the machining feed direction, and the Y-direction moving mechanism 232 is an indexing feed unit that moves the holding unit 22 in the indexing feed direction.

[0032] Reference Figure 1 , Figure 2 as well as Figure 3 The liquid supply mechanism 4 will be described below. Figure 1As shown, the liquid supply mechanism 4 includes: a liquid layer former 40 configured as a water layer forming unit, which forms a water layer on the upper surface side of the workpiece; a liquid supply pump 44; a filter 45; a liquid recovery tank 60; a pipe 46a connecting the liquid layer former 40 and the liquid supply pump 44; and a pipe 46b connecting the liquid recovery tank 60 and the filter 45. Furthermore, pipes 46a and 46b are preferably partially or entirely formed of flexible hoses.

[0033] like Figure 3 As shown in (a), the liquid layer former 40 is disposed at the lower end of the concentrator 86. An exploded perspective view of the liquid layer former 40 is shown below. Figure 3 As can be understood in (b), the liquid layer former 40 consists of a housing 42 and a liquid supply part 43 that supplies liquid to the housing 42. The housing 42 is formed in a generally rectangular shape when viewed from above, and consists of an upper housing part 421 and a lower housing part 422.

[0034] The upper housing component 421 is divided into two regions 421a and 421b in the Y direction indicated by arrow Y in the figure. The inner region 421a forms a circular opening 421c for inserting the concentrator 86, and the near-front region 421b forms a plate-like portion 421d. In the lower housing component 422, a cylindrical opening 422a, with the same position and shape as the opening 421c when viewed from above, is formed in the region corresponding to the opening 421c of the upper housing component 421. A transparent portion 423 in the shape of a circular plate is provided at the bottom of the opening 422a, sealing the bottom of the opening 422a. The transparent portion 423 has the property of allowing the laser beam LB, described later, to pass through, for example, it is formed of a glass plate. In the lower housing component 422, a liquid flow path 422b is formed in the region opposite to the plate-like portion 421d of the upper housing component 421 for ejecting liquid from the bottom wall 422d of the housing 42. The liquid flow path 422b is a space formed by the plate-shaped portion 421d, side wall 422c, and bottom wall 422d of the upper housing component 421. A slit-shaped nozzle 422e extending in the machining feed direction as shown by arrow X in the figure is formed on the bottom wall 422d of the liquid flow path 422b. A liquid supply port 422f for supplying liquid to the liquid flow path 422b is formed on the side wall connected to the liquid supply portion 43. The lower surface of the transparent portion 423 is formed on the same plane as the slit-shaped nozzle 422e extending in the machining feed direction, and the transparent portion 423 forms part of the bottom wall 422d of the lower housing component 422.

[0035] The liquid supply unit 43 includes: a supply port 43a for supplying water W; a discharge port (not shown) formed opposite to the liquid supply port 422f formed on the housing 42; and a connecting passage (not shown) connecting the supply port 43a and the discharge port. The liquid supply unit 43 is assembled from the Y direction to the side wall of the opening of the liquid supply port 422f on the housing 42, thereby forming a liquid layer former 40. Furthermore, in this embodiment, the water W provided is pure water, but it is not necessarily limited to pure water; any liquid with water as its main component also includes substances with added liquids.

[0036] The liquid layer former 40 has the structure described above, from Figure 1 The water W discharged from the liquid supply pump 44 is supplied to the liquid supply port 422f of the housing 42 via the supply port 43a of the liquid supply section 43, flows in the liquid flow path section 422b of the housing 42, and is discharged to the outside from the spray port 422e formed in the bottom wall 422d. Figure 1 As shown, the liquid layer former 40 mounts the liquid supply unit 43 and the housing 42 to the lower end of the concentrator 86 in a manner along the Y direction in the figure. Thus, the nozzle 422e formed on the bottom wall 422d of the housing 42 is positioned to extend along the X direction, which is the processing feed direction.

[0037] return Figure 1 and Figure 2 The liquid recovery tank 60 is described below. Figure 2 As shown, the liquid recovery tank 60 has an outer frame 61 and two waterproof covers 66.

[0038] The outer frame 61 has: an outer wall 62a extending in the X direction as indicated by arrow X in the figure; an outer wall 62b extending in the Y direction as indicated by arrow Y in the figure; inner walls 63a and 63b arranged parallel to each other at predetermined intervals on the inner sides of the outer walls 62a and 62b; and a bottom wall 64 connecting the lower ends of the outer walls 62a and 62b and the inner walls 63a and 63b. A rectangular liquid recovery path 70 is formed by the outer walls 62a and 62b, the inner walls 63a and 63b, and the bottom wall 64, with its length along the X direction and its width along the Y direction. A vertically penetrating opening is formed on the inner side of the inner walls 63a and 63b constituting the liquid recovery path 70. The bottom wall 64 constituting the liquid recovery path 70 is slightly inclined along the X and Y directions, and a liquid discharge hole 65 is provided at the lowest corner of the liquid recovery path 70 (the corner on the left in the figure). A pipe 46b is connected to the liquid discharge port 65, and the pipe 46b is connected to the filter 45 (see also). Figure 1 In addition, the outer frame 61 is preferably made entirely of a sheet of stainless steel that is corrosion-resistant and rust-resistant.

[0039] The two waterproof covers 66 each have: a gate-shaped fixing metal member 66a; and a corrugated resin cover member 66b with the fixing metal member 66a fixed at both ends. The fixing metal member 66a is formed to span the two inner sidewalls 63a of the outer frame 61, which are arranged opposite each other in the Y direction. One of the fixing metal members 66a of the two waterproof covers 66 is fixed to the inner sidewalls 63b of the outer frame 61, which are arranged opposite each other in the X direction. The liquid recovery pool 60 thus constructed is fixed to the base 21 of the laser processing apparatus 2 by fasteners (not shown). The cover plate 33 of the holding unit 22 is fixed by clamping the two waterproof covers 66 with the fixing metal members 66a. In addition, the end face of the cover member 33 in the X direction is formed with the same gate shape as the fixing metal member 66a, and like the fixing metal member 66a, it spans the inner sidewalls 63a of the outer frame 61 in the Y direction. According to the above structure, when the cover plate 33 moves in the X direction via the X direction moving mechanism 231, the cover plate 33 moves along the inner sidewall 63a of the liquid recovery tank 60.

[0040] return Figure 1 Continuing the explanation, the liquid supply mechanism 4 has the above-described structure, so water W discharged from the outlet 44a of the liquid supply pump 44 is supplied to the liquid layer former 40 via pipe 46a. The water W supplied to the liquid layer former 40 is sprayed downward from the nozzle 422e formed on the bottom wall 422d of the housing 42 of the liquid layer former 40. The water W sprayed from the liquid layer former 40 flows over the cover plate 33 or the waterproof cover 66 and flows down into the liquid recovery tank 60. The water W flowing down into the liquid recovery tank 60 flows in the liquid recovery path 70 and collects at the liquid discharge hole 65 located at the lowest position of the liquid recovery path 70. The water W collected in the liquid discharge hole 65 is introduced into the filter 45 via pipe 46b, where the filter 45 removes molten material (debris) or dust and other particles generated by laser processing and returns it to the liquid supply pump 44. In this way, the water W discharged by the liquid supply pump 44 circulates within the liquid supply mechanism 4.

[0041] The laser processing apparatus 2 described above has a structure generally as described above. The laser processing method of this embodiment implemented using the laser processing apparatus 2 will be described below.

[0042] For example, Figure 4As shown on the left side, the workpiece processed in the laser processing method of this embodiment is a silicon wafer 10 with multiple devices 12 formed on the front side 10a by multiple intersecting predetermined dividing lines 14. If the wafer 10 is prepared, it is transported to the vapor deposition apparatus 100 shown in the center of the figure to perform a vapor deposition process in which a light-shielding film 114 is deposited on the upper surface (front side 10a) of the wafer 10 to shield the scattered light of the laser beam LB irradiated in the laser processing step described later. The vapor deposition apparatus 100 has a vacuum chamber 101 whose interior is evacuated by a vacuum pump 102. The vacuum chamber 101 includes: a support plate 103 that supports the wafer 10 on its lower surface and has a heating unit (not shown); and a crucible 104 placed below the support plate 103, which heats the film-forming material 110 by an electron beam B irradiated from an electron beam generating device 105. In this embodiment, the film-forming material 110 is, for example, silicon (Si).

[0043] The wafer 10 is transported to the vapor deposition apparatus 100 with its front side 10a facing downwards and its back side 10b attached to the lower surface of the support plate 103 and held therein. When the vacuum pump 102 is activated, the air in the vacuum chamber 101 is expelled, reducing the pressure in the vacuum chamber 101 to a vacuum. Then, the electron beam generating apparatus 105 is activated, irradiating the film-forming material 110 with an electron beam B, heating it, and releasing Si molecules 112 through evaporation. These molecules are then deposited onto the front side 10a of the wafer 10, forming a light-scattering shielding film 114. Furthermore, the electron beam B emitted from the electron beam generating apparatus 105 is irradiated onto the film-forming material 110 by controlling the trajectory of the electron beam B using a scanning coil (not shown in the figure). The thickness of the light-scattering shielding film 114 formed on the front side 10a of the wafer 10 is, for example, 0.1 μm to 0.5 μm. The thickness of the light-scattering shielding film 114 is such that even if the laser beam LB, described later, is scattered as scattered light due to the water bubble, the device 12 of the wafer 10 will not be damaged, and when the laser beam LB directly irradiates the wafer 10, the desired processing groove is formed by ablation.

[0044] If the light-scattering shielding film 114 is formed on the front side 10a of the wafer 10, the wafer 10 is removed from the evaporation apparatus 100 (see the right side in the diagram), completing the light-scattering shielding film stacking process. Furthermore, the light-scattering shielding film 114 formed by the evaporation apparatus 100 is not limited to Si as described above, but can also be germanium (Ge) or aluminum (Al). Additionally, the specific means of forming the light-scattering shielding film 114 on the front side 10a of the wafer 10 is not limited to the evaporation method described above; the light-scattering shielding film 114 can also be formed by sputtering, a method known as conventional sputtering.

[0045] Next, the wafer 10, which has undergone the light-scattering shielding film stacking process and has been removed from the evaporation apparatus 100, is transferred to the aforementioned laser processing apparatus 2, such as... Figure 5 As shown, the lower surface (back surface 10b) of the wafer 10 is placed on the side of the structure according to... Figure 2 The chuck stage 34 of the holding unit 22 of the laser processing apparatus 2, which is described herein, activates the suction unit (not shown) to perform a holding process. In this embodiment, during the holding process, an annular frame F with an opening Fa capable of receiving the wafer 10 is prepared. The frame F and the wafer 10 are integrated using a protective strap T. When placed on the chuck stage 34, the frame F is fixed and held by a clamp 36.

[0046] If the above-described holding process is performed, a laser processing process is then performed: a water layer is formed on the upper surface of the wafer 10, i.e., the front side 10a, by the liquid layer generator 40 constituting the water layer forming unit, and while the holding unit 22 holding the wafer 10 and the laser beam irradiation unit 8 are moved relative to each other, laser beam LB is irradiated onto the area of ​​the wafer 10 to be processed, i.e., the predetermined dividing line 14. (Refer to...) Figure 1 , Figure 6 , Figure 7 The laser processing procedure will be described in more detail.

[0047] If the chip 10 is held in the suction chuck 35 of the chuck stage 34, then by Figure 1 The moving mechanism 23 shown moves the chuck stage 34 appropriately in the X and Y directions, positioning the wafer 10 on the chuck stage 34 directly below the alignment unit 90. When the wafer 10 is positioned directly below the alignment unit 90, the alignment unit 90 takes an image of the front side 10a of the wafer 10. Then, based on the image of the wafer 10 taken by the alignment unit 90, the position of the predetermined dicing line 14 to be processed on the wafer 10 is detected. Based on this detected position information, the chuck stage 34 is moved, thereby... Figure 6 As shown in (a), the concentrator 86 is positioned above the location on the wafer 10 where processing will begin. Then, the concentrator 86 is moved using a concentrator position adjustment unit (not shown), as follows: Figure 6 As shown in (b), the focusing point is positioned on the front surface 10a of the wafer 10 at the predetermined dividing line 14, which serves as the starting position for laser processing of the wafer 10. Furthermore, as described later, a layer of water W supplied by the liquid supply mechanism 4 is formed between the lower surface of the liquid layer generator 40 and the light-scattering shielding film 114 formed on the front surface 10a of the wafer 10. Therefore, the refractive index of the water W layer is taken into account when positioning the focusing point.

[0048] If the alignment of the concentrator 86 and the wafer 10 is achieved, the necessary and sufficient water W is supplied to the liquid supply mechanism 4, causing the liquid supply pump 44 to operate. Figure 6 (b) It can be understood that when the focusing point is positioned at the front side 10a of the wafer 10, a gap H is formed between the bottom wall 422d of the housing 42 constituting the liquid layer forming device 40 and the lower surface of the transparent portion 423 and the light-scattering shielding film 114 formed on the front side 10a of the wafer 10 (the height of the gap H is, for example, about 0.5 mm to 2.0 mm).

[0049] Water W is supplied from the liquid supply pump 44 to the liquid supply section 43 of the liquid supply mechanism 4. The supplied water W passes through the housing 42 of the liquid layer former 40 and is ejected downwards from the nozzle 422e formed on the bottom wall 422d. The water W ejected from the nozzle 422e is as follows: Figure 6 As shown in (b), a layer of water W is formed, filling the gap H between the bottom wall 422d of the housing 42 and the wafer 10, and between the transparent portion 423 and the wafer 10. The water W flowing through this gap H flows outwards from the chuck stage 34, according to... Figure 1 , Figure 2 The liquid flow in the liquid recovery path 70 of the liquid recovery tank 60 is collected at the liquid discharge hole 65 located at the lowest position of the liquid recovery path 70. The water W collected in the liquid discharge hole 65 is introduced into the filter 45 through the pipe 46b, cleaned by the filter 45, and returned to the liquid supply pump 44 for circulation within the liquid supply mechanism 4.

[0050] The liquid supply mechanism 4 starts to operate. After a specified time (about a few minutes), the gap H between the bottom wall 422d of the housing 42 and the transparent part 423 and the wafer 10 is filled with water W. Thus, a layer of water W without cavitation is formed in the state without laser processing, and the water W is in a stable circulation state in the liquid supply mechanism 4.

[0051] like Figure 6 As shown in (b), while water W is stably circulating in the liquid supply mechanism 4, the laser beam irradiation unit 8 is activated while the X-direction feed mechanism 231 constituting the aforementioned moving mechanism 23 is activated, thereby... Figure 6 As shown in (a), the holding unit 22 and the laser irradiation unit 8 are fed in the X direction (the direction perpendicular to the paper shown in the figure) at a predetermined moving speed, and the laser beam LB is irradiated along the predetermined dividing line 14 to form the laser processing groove 16.

[0052] Furthermore, the processing conditions for laser processing performed by the laser processing apparatus 2 described above are set as follows, for example.

[0053] Wavelength: 355nm

[0054] Average output: 6W

[0055] Repetition frequency: 30MHz

[0056] Pulse width: 200 fs

[0057] Machining feed rate: 100 mm / s

[0058] Here, when laser light LB is irradiated onto the front side 10a of the chip 10, as... Figure 7 As shown, a laser beam LB is irradiated onto the wafer 10, thereby creating a cavity C in the water W filling the gap H. Furthermore, a portion of the laser beam LB irradiated from the concentrator 86 encounters the cavity C and is scattered, irradiating a position deviating from the predetermined dicing line 14. However, in this embodiment, a light-shielding film 114 is formed on the front surface 10a of the wafer 10 to shield the scattered light and prevent damage to the wafer 10, thus preventing damage in the device 12. Additionally, as described above, the light-shielding film 114 is set to a thickness such that even if a portion of the laser beam LB encounters the cavity C and the resulting scattered light irradiates the light-shielding film 114, damage to the device 12 can be prevented. However, if the laser beam LB directly irradiates the wafer 10 without encountering the cavity C, ablation occurs, and the desired laser processing groove 16 is formed along the predetermined dicing line 14, thus preventing obstacles in the laser processing step.

[0059] The laser beam irradiation unit 8 is activated, and the rotary drive unit (which rotates the X-direction feed mechanism 231, the Y-direction feed mechanism 232, and the chuck stage 34) is activated, thereby forming a laser processing groove 16 along all the predetermined dividing lines 14 formed on the front side 10a of the wafer 10, and completing the laser processing process.

[0060] Next, the wafer 10, which has undergone laser processing, is removed from the laser processing apparatus 2 and transported to... Figure 8The polishing apparatus 130 shown is only partially shown. The polishing apparatus 130 of this embodiment includes a holding unit (not shown) configured to hold and rotate a wafer 10, and a polishing unit 131 configured to polish the upper surface of the wafer 10 held by the holding unit, and is configured to perform chemical mechanical polishing (CMP). The polishing unit 131 includes: a rotating shaft 133 that rotates in the direction indicated by arrow R1 via a rotating drive unit (not shown); a mounting base 134 formed at the lower end of the rotating shaft 133; and a polishing wheel 135 mounted on the lower surface of the mounting base 134, with a polishing pad 136 disposed on the lower surface of the polishing wheel 135. A connecting passage 137 is formed inside the rotating shaft 133 for providing a slurry S containing various chemical components, fine abrasive particles, etc., provided from a slurry supply unit (not shown).

[0061] The wafer 10 is transported to the polishing apparatus 130, with the light-scattering shielding film 114 side of the transported wafer 10 facing upwards and held in the holding unit, positioning the wafer 10 directly below the polishing unit 131. The polishing wheel 135 is rotated in the direction indicated by arrow R1, and the wafer 10 held by the holding unit is rotated in the direction indicated by arrow R2. Next, the polishing feed mechanism (not shown) is activated, causing the polishing unit 131 to descend in the direction indicated by arrow R3, bringing the polishing pad 136 into contact with the upper surface of the wafer 10 where the light-scattering shielding film 114 is formed. At this time, the slurry supply unit is activated, supplying CMP slurry S suitable for removing the light-scattering shielding film 114 by polishing to the lower surface of the polishing pad 136 and the upper surface of the wafer 10 via the communication path 137 of the rotating shaft 133, performing CMP. The slurry S is selected from, for example, cerium oxide-based slurries, alumina-based slurries, etc., depending on the light-scattering shielding film 114 to be removed. By performing this CMP for a specified time, such as... Figure 8 As shown on the right-hand side, the light-scattering shielding film 114 is removed from the upper surface of the wafer 10, completing the light-scattering shielding film removal process. Furthermore, in the above embodiment, an example of CMP polishing of the upper surface of the wafer 10 is shown; however, the present invention is not limited to this, and the light-scattering shielding film 114 can be removed by mechanical polishing using a slurry that does not contain so-called chemical solutions.

[0062] According to the above embodiment, when a layer of water W is formed on the upper surface of the wafer 10 and the wafer 10 is processed by irradiating it with a laser beam LB of a wavelength that is absorbent to the wafer 10, even if a portion of the laser beam LB is scattered by a fine bubble (cavitation C) generated in the layer of water W, the light scattering shielding film 114 formed on the front side 10a of the wafer 10 can prevent damage in the device 12, thus eliminating the problem of reduced quality of the device 12.

[0063] In the above embodiments, an example is shown of forming a light-scattering shielding film 114 by depositing any material of Si, Ge, or Al onto the front side 10a of the wafer 10 through evaporation or sputtering in the light-scattering shielding film stacking process; however, the present invention is not limited thereto. For example, an epoxy resin film can be stacked as the light-scattering shielding film 114 by coating or pressing. When this resin is stacked as the light-scattering shielding film 114 and a light-scattering shielding film removal process is subsequently performed, the light-scattering shielding film 114 can be removed using a solvent in which the resin is dissolved or by peeling.

[0064] Furthermore, in the light-scattering shielding film stacking process of the above embodiment, an example is shown where the light-scattering shielding film 114 is directly stacked on the front side 10a of the wafer 10. However, the present invention is not limited to this. In the light-scattering shielding film stacking process, a resin film can be formed on the upper surface (front side 10a) of the wafer 10 before the light-scattering shielding film 114 is stacked by evaporation or sputtering. This resin film can be a resin film such as epoxy as described above, or a water-soluble resin such as polyvinyl alcohol (PVA). Before stacking any substance of Si, Ge, or Al as the light-scattering shielding film 114, a resin film is formed on the front side 10a of the wafer 10 in advance. As a result, when the Si, Ge, Al, etc. film constituting the light-scattering shielding film 114 is removed by grinding in the light-scattering shielding film removal process, the electrodes and the like formed on the device 12 can be protected. In this case, after CMP is performed to remove the Si, Ge, Al, etc. films deposited by evaporation or sputtering, the resin film formed on the front side 10a of the wafer 10 is removed using a solvent corresponding to the resin film. When the resin film is formed using a water-soluble resin, water can be used as the solvent.

[0065] In addition to the embodiments described above, the light-scattering shielding film 114 can also be formed by spin coating of a liquid resin containing powders of carbon, Si, or metal. When the light-scattering shielding film 114 is formed by layering liquid resins containing the powders, the presence of the powders can further suppress scattered light from irradiating the device 12 of the wafer 10.

[0066] As the light-scattering shielding film 114, any material such as gold foil, silver foil, or copper foil can be adhered to the front side 10a of the wafer 10. Alternatively, as the light-scattering shielding film 114, a sheet-like material of graphene (graphite, carbon nanotubes, or fullerenes, etc.) can also be used.

Claims

1. A laser processing method, wherein, This laser processing method has the following steps: In the process of stacking a light-scattering shielding film, a light-scattering shielding film is stacked on the upper surface of the wafer to shield the scattered light of the laser beam. The holding process involves using a chuck stage to hold the wafer on its lower surface. In a laser processing step, a water layer is formed on the upper surface of a wafer, and a laser beam is irradiated onto the area of ​​the wafer to be processed while the chuck stage is moved relative to the laser beam irradiation unit. The laser beam passes through a transparent portion of the laser beam irradiation unit, which is coplanar with the nozzle that supplies water for forming the water layer. The process of removing the light-scattering shielding film involves removing the light-scattering shielding film from the wafer after the laser processing has been completed. The light-scattering shielding film is coated with liquid resin containing powders of carbon, Si, or metal by spin coating, and the thickness of the light-scattering shielding film is 0.1 μm to 0.5 μm.

2. The laser processing method according to claim 1, wherein, In the process of stacking the light-scattering shielding film, the light-scattering shielding film is stacked by vapor deposition or sputtering of at least one of Si, Ge or Al.

3. The laser processing method according to claim 2, wherein, In the process of removing the light-scattering shielding film, the light-scattering shielding film is removed from the wafer by grinding.

4. The laser processing method according to claim 1, wherein, In the process of laminating the light-scattering shielding film, the light-scattering shielding film is laminated by coating or pressing with resin.

5. The laser processing method according to claim 4, wherein, In the process of removing the light-scattering shielding film, the light-scattering shielding film is removed from the wafer by using a solvent.

6. The laser processing method according to claim 2 or 3, wherein, In the process of stacking the light-scattering shielding film, a resin film is coated on the upper surface of the wafer before the light-scattering shielding film is stacked by evaporation or sputtering.

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