Laser processing device

Abstract

A laser processing apparatus is provided that prevents debris scattering without degrading productivity and enables appropriate laser processing without laser beam scattering. The laser processing apparatus includes: a concentrator that focuses a laser beam emitted from a laser oscillator onto a workpiece held in a chuck table; and a water column former disposed at the lower end of the concentrator and forming a linear water column on the upper surface of the workpiece. The laser oscillator includes: a first laser oscillator that emits a first laser beam with a short pulse width; and a second laser oscillator that emits a second laser beam with a long pulse width. After the laser beams emitted from the first and second laser oscillators propagate within the linear water column formed by the water column former and irradiate the workpiece, plasma generated within the water column former processes the workpiece.

Description

Technical Field

[0001] The present invention relates to a laser processing apparatus comprising: a chuck stage for holding a plate-shaped workpiece; a laser beam irradiation unit for irradiating the workpiece held on the chuck stage with laser beam to perform processing; and a processing feed mechanism for feeding the chuck stage and the laser beam irradiation unit relative to each other. Background Technology

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

[0003] In addition, laser processing apparatuses can be of the following types: those that irradiate the workpiece with laser light of a wavelength that is absorbent to form a groove as a starting point for segmentation through ablation processing (e.g., see Patent Document 1); those that irradiate the workpiece by positioning a focal point of laser light of a wavelength that is transmissible to the workpiece inside the workpiece, thereby forming a modified layer inside as a starting point for segmentation (e.g., see Patent Document 2); and those that irradiate the workpiece by positioning a focal point of laser light of a wavelength that is transmissible to the workpiece inside the workpiece, thereby forming multiple shield tunnels as the starting point for segmentation, consisting of individual fine holes and amorphous material surrounding the fine holes (e.g., see Patent Document 3). The type of laser processing apparatus used is selected according to the type of workpiece, processing precision, etc.

[0004] Furthermore, in the type of ablation processing on the workpiece, it is possible that debris may fly from the part irradiated by the laser beam and adhere to the device formed on the front side of the workpiece, thereby reducing the quality of the device. Therefore, a solution has been proposed to prevent the adhesion of debris by coating the front side of the wafer with liquid resin before laser processing (for example, see Patent Document 4).

[0005] Patent Document 1: Japanese Patent Application Publication No. 10-305420

[0006] Patent Document 2: Japanese Patent No. 3408805

[0007] Patent Document 3: Japanese Patent Application Publication No. 2014-221483

[0008] Patent Document 4: Japanese Patent Application Publication No. 2004-188475

[0009] As mentioned above, when the workpiece is coated with liquid resin before laser processing, the liquid resin is not reused and is discarded, which is uneconomical. Furthermore, the need for coating and removal processes of the liquid resin results in poor productivity.

[0010] Furthermore, the study investigated the method of irradiating the workpiece with laser light while the wafer was submerged in water, causing debris to float in the water and thus preventing debris from adhering to the front side of the wafer. However, it was also pointed out that the laser light was scattered due to bubbles or cavitation generated in the water, which prevented the desired processing from being carried out. In addition, it was found that the bending strength of the individual device chips was reduced due to the effect of heat. Summary of the Invention

[0011] Therefore, the object of the present invention is to provide a laser processing apparatus that can prevent the scattering of debris without degrading productivity and can perform appropriate laser processing without scattering laser light.

[0012] According to the present invention, a laser processing apparatus is provided, comprising: a chuck stage for holding a plate-shaped workpiece; a laser beam irradiation unit for irradiating the workpiece held by the chuck stage with laser beam to perform processing; and a processing feed mechanism for feeding the chuck stage and the laser beam irradiation unit relative to each other, the laser beam irradiation unit comprising: a laser oscillator for emitting laser beam; a concentrator for focusing the laser beam emitted by the laser oscillator and irradiating the workpiece held by the chuck stage; and a water column former disposed at the lower end of the concentrator and... A linear water column is formed on the upper surface of the workpiece. The laser oscillator includes: a first laser oscillator that emits a first laser beam with a short pulse width; and a second laser oscillator that emits a second laser beam with a long pulse width. After the laser beams emitted from the first laser oscillator and the laser beams emitted from the second laser oscillator are transmitted within the linear water column formed by the water column former and irradiate the workpiece, the plasma generated by the laser beam emitted from the first laser oscillator absorbs the energy of the laser beam emitted from the second laser oscillator and grows, thereby processing the workpiece.

[0013] Preferably, the water column generator includes: a housing having a top wall facing the objective lens constituting the condenser, a bottom wall opposite the top wall and having an ejection hole formed therein, and a side wall surrounding the space formed by the top wall and the bottom wall; and a high-pressure water inlet that introduces high-pressure water into the housing and guides the laser light of the linear water column ejected from the ejection hole formed on the bottom wall to irradiate the workpiece.

[0014] According to the present invention, even if the front side of the wafer is not coated with liquid resin, the adhesion of debris can be prevented, the cost of liquid resin can be reduced, and the time spent coating the upper surface of the workpiece with liquid resin can be saved. Attached Figure Description

[0015] Figure 1 This is a perspective view of the laser processing apparatus according to an embodiment of the present invention.

[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 three-dimensional view of the water column former in the laser processing apparatus. Figure 3 (b) is to Figure 3 The exploded perspective view of the water column generator shown in (a) is shown.

[0018] Figure 4 It is used for installation on Figure 1 A block diagram illustrating the optical system of the laser beam irradiation unit of the laser processing apparatus shown.

[0019] Figure 5 It shows the installation at Figure 1 A partially enlarged cross-sectional view of the water column forming component of the laser processing apparatus shown during processing.

[0020] Figure 6 It schematically shows the pulse widths of the first and second laser beams and a timing diagram of the irradiation timing.

[0021] Figure 7 (a) is shown by Figure 5 The image shown is a partially magnified cross-sectional view of the plasma generated when a laser beam processes a wafer. Figure 7 (b) shows from Figure 7 The result of (a) is a partially enlarged sectional view of the machining groove.

[0022] Label Explanation

[0023] 2: Laser processing device; 4: Liquid supply mechanism; 8: Laser beam irradiation unit; 81: Laser oscillator; 812: First laser oscillator; 814: Second laser oscillator; 82: First 1 / 2 wavelength plate; 84: Second 1 / 2 wavelength plate; 85: Polarizing beam splitter; 86: Condenser; 86a: Objective lens; 10: Wafer; 21: Base; 22: Holding unit; 23: Moving mechanism; 26: Frame; 261: Vertical wall; 262: Horizontal wall; 30: X-direction movable plate; 31: Y-direction movable plate; 34: Chuck stage; 35: Adsorption chuck; 40: Water column former; 42: Housing; 421: Upper component (Top wall); 422: Lower component; 422c: Side wall; 422d: Bottom wall; 423: Ejector hole; 424: Space section; 43: High-pressure water inlet section; 44: Liquid supply pump; 45: Filter; 50: X-direction moving mechanism (machining feed mechanism); 52: Y-direction moving mechanism; 60: Liquid recovery tank; 60A: Opening; 65: Liquid discharge hole; 70: Liquid recovery path; 90: Alignment unit; LB1: First laser beam; LB2: Second laser beam; A: First pulse width; B: Second pulse width; P1: First plasma; P2: Second plasma; W: Liquid (pure water); S: Water column forming area. Detailed Implementation

[0024] Hereinafter, the laser processing apparatus according to embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0025] Figure 1 A perspective view of the laser processing apparatus 2 according to this embodiment is shown. The laser processing apparatus 2 includes: a liquid supply mechanism 4 disposed on a base 21 for supplying liquid to a workpiece (e.g., a silicon wafer 10); a laser beam irradiation unit 8 for irradiating a plate-shaped workpiece with laser beams; a holding unit 22 for holding the workpiece; a moving mechanism 23 for moving the laser beam irradiation unit 8 and the holding unit 22 relative to each other; and a frame 26 consisting of a vertical wall portion 261 and a horizontal wall portion 262. The vertical wall portion 261 is erected on the side of the moving mechanism 23 on the base 21 along the Z direction indicated by arrow Z, and the horizontal wall portion 262 extends horizontally from the upper end of the vertical wall portion 261.

[0026] An optical system constituting a laser beam irradiation unit 8 (described in detail later) is housed inside the horizontal wall portion 262 of the frame 26. This laser beam irradiation unit 8 irradiates laser beams onto the wafer 10 held in the holding unit 22. A concentrator 86, which forms part of the laser beam irradiation unit 8, is disposed on the lower surface side of the front end portion of the horizontal wall portion 262, and an alignment unit 90 is disposed adjacent to the concentrator 86 in the direction indicated by arrow X in the figure.

[0027] The alignment unit 90 is used to detect the position of the wafer 10 to be laser-processed by photographing it held on the chuck stage 34 constituting the holding unit 22. The alignment unit 90 has a visible light imaging element (CCD) for photographing the front of the wafer 10, but depending on the material constituting the wafer 10, it preferably includes: an infrared irradiation member that irradiates infrared light; an optical system that captures the infrared light irradiated by the infrared irradiation member; and an imaging element (infrared CCD) that outputs an electrical signal corresponding to the infrared light captured by the optical system.

[0028] As shown in the figure, the wafer 10 is supported by an annular frame F, for example by an adhesive tape T, and is held in place by an adsorption chuck 35 on the upper surface of the chuck stage 34. Furthermore, for ease of explanation, the laser processing apparatus 2 is configured with an omitted housing or similar covering to prevent dust and other contaminants from entering the interior.

[0029] Reference Figure 1 and Figure 2 The laser processing apparatus 2 of this embodiment will be described in detail. Figure 2 It is shown in Figure 1 A perspective view of the state after 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 2 As 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 in the figure; 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 is disposed on the cover plate 33, which extends upward through an elongated hole formed in the cover plate 33. The chuck worktable 34 is configured to hold a circular workpiece and can be rotated by a rotation drive member (not shown). A circular suction chuck 35 is disposed on the upper surface of the chuck worktable 34, which is formed of a porous material with air permeability and extends substantially horizontally. The suction chuck 35 is connected to an attraction member (not shown) via a flow path passing through the support column 32. Four clamps 36 are arranged at intervals around the suction chuck 35. The clamps 36 hold the frame F of the wafer 10 in place when it is fixed to the chuck stage 34. The planes defined by the X and Y directions substantially constitute a horizontal plane.

[0031] The moving mechanism 23 includes an X-direction moving mechanism 50 and a Y-direction moving mechanism 52. The X-direction moving mechanism 50 converts the rotational motion of the motor 50a into linear motion via the ball screw 50b 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 52 converts the rotational motion of the motor 52a into linear motion via the ball screw 52b 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 components are respectively provided on the chuck table 34, the X-direction moving mechanism 50, and the Y-direction moving mechanism 52. These components accurately detect the X-direction position, Y-direction position, and circumferential rotation position of the chuck table 34, thereby enabling the driving of the X-direction moving mechanism 50, the Y-direction moving mechanism 52, and the rotation drive component of the chuck table 34 (not shown) to accurately position the chuck table 34 at any position and angle. The X-direction moving mechanism 50 is a machining feed mechanism that moves the holding unit 22 along the machining feed direction, and the Y-direction moving mechanism 52 is an indexing feed component that moves the holding unit 22 along the indexing feed direction.

[0032] like Figure 1 As shown, the liquid supply mechanism 4 includes: a water column former 40, which constitutes a water column forming member in this embodiment; a liquid supply pump 44; a filter 45; a liquid recovery tank 60; a pipe 46a connecting the water column 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 water column former 40 is disposed at the lower end of the concentrator 86. An exploded view of the water column former 40 is shown in... Figure 3 As shown in (b). From Figure 3 As can be seen from (b), the water column generator 40 includes a housing 42 and a high-pressure water inlet 43 for introducing high-pressure water into the housing 42. The housing 42 is generally rectangular in shape when viewed from above, and is composed of an upper part 421 that constitutes the top wall of this embodiment and a lower part 422 opposite to the upper part 421.

[0034] like Figure 3As shown in (b), a circular opening 421c is formed on the upper component 421, which extends from the upper surface 421a to the back surface 421b for insertion of the concentrator 86. The lower component 422 has: a bottom wall 422d, which has an ejector hole 423 extending to the lower surface 422b of the lower component 422 in a region opposite to the opening 421c of the upper component 421; and a side wall 422c surrounding the space 424 formed by the lower surface 421b and the bottom wall 422d of the upper component 421. A liquid supply port 422e for supplying liquid to the space 424 is formed on the side wall 422f connected to the high-pressure water inlet 43.

[0035] The high-pressure water inlet 43 has a supply port 43a for supplying liquid W, and forms a water column generator 40 by being assembled from the Y direction onto the side wall of the liquid supply port 422f of the housing 42.

[0036] The water column generator 40 has the structure described above, based on... Figure 1 The liquid W ejected by the liquid supply pump 44 is supplied to the liquid supply port 422e of the housing 42 via the high-pressure water inlet 43, flows through the space 424 of the housing 42 and is ejected from the ejection hole 423 formed on the bottom wall 422d.

[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: a pair of outer side walls 62a extending in the X direction as indicated by arrow X in the figure; a pair of outer side walls 62b extending in the Y direction as indicated by arrow Y in the figure; a pair of inner side walls 63a, 63b arranged parallel to each other at a predetermined interval on the inner sides of the outer side walls 62a, 62b; and a bottom wall 64 connecting the lower ends of the outer side walls 62a, 62b and the inner side walls 63a, 63b. The outer side walls 62a, 62b, inner side walls 63a, 63b, and bottom wall 64 form a rectangular liquid recovery path 70 with its length along the X direction and its width along the Y direction. A vertically penetrating opening is formed on the inner side walls 63a, 63b constituting the liquid recovery path 70. The bottom wall 64 constituting the liquid recovery path 70 has a slight inclination 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). The liquid discharge port 65 is connected to the pipe 46b, and then connected to the filter 45 via the pipe 46b. Furthermore, the outer frame 61 is preferably made entirely of corrosion-resistant and rust-resistant stainless steel sheet.

[0039] The two waterproof covers 66 each have: a fixing fitting 66a, which is gate-shaped; and a corrugated resin cover component 66b, both ends of which are fixed to the fixing fitting 66a. The fixing fitting 66a is sized to span across the two inner sidewalls 63a of the outer frame 61, which are arranged opposite each other in the Y direction. One side of the fixing fitting 66a of the two waterproof covers 66 is fixed to the inner sidewall 63b, which is arranged opposite each other in the X direction of the outer frame 61. 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 installed by being clamped to each other by the fixing fittings 66a of the two waterproof covers 66. In addition, the end face of the cover component 33 in the X direction has the same gate-shaped shape as the fixing fitting 66a, and is sized to span the inner sidewall 63a of the outer frame 61 in the Y direction, just like the fixing fitting 66a. Therefore, after the outer frame 61 of the liquid recovery tank 60 is placed on the base 21, the cover component 33 is installed on the waterproof cover 66. According to the above structure, when the cover 33 moves in the X direction via the X-direction moving mechanism 50, the cover 33 moves along the inner wall 63a of the liquid recovery tank 60. Furthermore, the installation method of the waterproof cover 66 and the cover component 33 is not limited to the steps described above. For example, before installing the two waterproof covers 66 on the inner wall 63b of the outer frame 61, the cover component 33 can be pre-installed, and the waterproof cover 66 and the cover component 33 can be installed together on the outer frame 61 that has already been installed on the base 21.

[0040] return Figure 1 Continuing the explanation, the liquid supply mechanism 4, having the above-described structure, supplies liquid W ejected from the nozzle 44a of the liquid supply pump 44 to the water column former 40 via pipe 46a. The liquid W supplied to the water column former 40 is formed from the liquid in the water column based on… Figure 3 (b) describes the water column generator 40, which sprays downwards from the ejector hole 423 on the bottom wall 422d of the housing 42. The liquid W sprayed from the water column generator 40 flows over the cover plate 33 and the waterproof cover 66 and flows down into the liquid recovery tank 60. The liquid W flowing down into the liquid recovery tank 60 flows through the liquid recovery path 70 and collects in the liquid discharge hole 65 located at the lowest position of the liquid recovery path 70. The liquid W collected in the liquid discharge hole 65 is guided to the filter 45 via the pipe 46b, where the laser processing chips (debris), dust, etc. are removed and returned to the liquid supply pump 44. In this way, the liquid W sprayed by the liquid supply pump 44 circulates within the liquid supply mechanism 4.

[0041] Figure 4 This is a schematic block diagram showing the optical system of the laser beam irradiation unit 8. (See diagram for example.) Figure 4As shown, the laser beam irradiation unit 8 includes: a laser oscillator 81 having a first laser oscillator 812 and a second laser oscillator 814, the first laser oscillator 812 emitting pulsed laser light, i.e., a first laser light LB1 with a short pulse width, and the second laser oscillator 814 emitting pulsed laser light, i.e., a second laser light LB2 with a long pulse width; a half-wavelength plate 82, which imparts a phase difference equivalent to half a wavelength to the incident first laser light LB1 and rotates the linearly polarized light; a half-wavelength plate 84, which imparts a phase difference equivalent to half a wavelength to the incident second laser light LB2 and rotates the linearly polarized light; and a polarization beam splitter 8. 5. The first laser beam LB1, which has passed through the half-wavelength plate 82, is reflected by the S-polarized light and the second laser beam LB2, which has passed through the half-wavelength plate 84, is passed through. The reflected first laser beam LB1 (S-polarized light) and the passed second laser beam LB2 (P-polarized light) are combined to illuminate the same part of the wafer 10, and output as laser beam LB1+LB2. A reflector 87 changes the illumination direction of the laser beam LB1+LB2 output from the polarization beam splitter 85 by 90°. A concentrator 86 focuses the laser beam LB1+LB2 and illuminates the wafer 10 held by the holding unit 22. The first laser oscillator 812 and the second laser oscillator 814, for example, oscillate laser light with wavelengths that are absorbed by the workpiece. Furthermore, although not shown in the figure, the optical system of the laser beam illumination unit 8 may appropriately include attenuators that change the output of each laser beam and reflectors that change the optical path of each laser beam.

[0042] An objective lens 86a is disposed inside the condenser 86. This objective lens 86a focuses the laser beams LB1+LB2 onto the wafer 10. The objective lens 86a is located below the reflector 87 and focuses the laser beams LB1+LB2 reflected by the reflector 87 to irradiate them. A glass component 86b is disposed at the lower end of the condenser 86, and the lower end of the condenser 86 is closed by the glass component 86b. The glass component 86b allows the laser beams LB1+LB2 to pass through and prevents the high-pressure liquid W introduced into the space 424 of the housing 42 from entering the condenser 86. Alternatively, instead of closing the lower end of the condenser 86 with the glass component 86b, the same glass component can be used to close the lower surface of the opening 421c formed on the upper component 421 of the housing 42. In addition, the laser beam irradiation unit 8 has a focusing point position adjustment member (not shown) to adjust the position of the focusing point of the laser beam LB1+LB2 focused by the focusing device 86 in the Z direction.

[0043] The laser processing apparatus 2 of the present invention has a structure generally as described above, and its function will be explained below.

[0044] When laser processing is performed using the laser processing apparatus 2 of this embodiment, such as Figure 1 As shown, for a plate-shaped workpiece supported by an annular frame F by means of adhesive tape T, such as a silicon (Si) wafer 10 with devices formed on its front side, after the wafer 10 is prepared, the wafer 10 is placed on the suction chuck 35 of the chuck stage 34 with the device-formed front side facing up, and the suction member (not shown) is activated and fixed by a clamp 36 or the like.

[0045] After holding the wafer 10 in the chuck 35, the chuck stage 34 is moved appropriately in the X and Y directions by the moving mechanism 23, positioning the wafer 10 on the chuck stage 34 directly below the alignment unit 90. After positioning the wafer 10 directly below the alignment unit 90, the alignment unit 90 takes an image of the wafer 10. Then, based on the image of the wafer 10 taken by the alignment unit 90, the processing position of the wafer 10 is detected by methods such as pattern matching (alignment process). Based on the position information obtained through this alignment process, the chuck stage 34 is moved, thereby positioning the condenser 86 above the processing start position on the wafer 10.

[0046] After aligning the condenser 86 with the wafer 10, the liquid supply mechanism 4 is filled with sufficient liquid W, and the liquid supply pump 44 is activated. The liquid W circulating within the liquid supply mechanism 4 is, for example, pure water.

[0047] Figure 5 Show along Figure 3 The diagram shows a partially enlarged cross-sectional view of the water column former 40 after the AA is cut, illustrating a laser processing method where a high-pressure liquid W is introduced to form a water column Wp while laser beams LB1+LB2 are irradiated. From Figure 5 It is understood that the water column forming device 40 of the liquid supply mechanism 4 is disposed at the lower end of the condenser 86 and is configured to form a water column forming area S of about 10 mm to 20 mm by the lower surface 422b of the housing 42 constituting the water column forming device 40 and the front surface of the wafer 10 when the condenser point is positioned at the height of the front surface of the wafer 10.

[0048] The liquid supply mechanism 4, having the aforementioned structure, supplies liquid W ejected from the nozzle 44a of the liquid supply pump 44 to the water column generator 40. The liquid W supplied to the water column generator 40 is introduced into the space 424 within the housing 42 via the high-pressure water inlet 43, and ejected downwards from the ejection hole 423 formed in the bottom wall 422d. Figure 5As shown, the liquid W ejected from the ejection hole 423 forms a linear water column Wp in the water column forming region S between the lower surface 422b of the housing 42 and the wafer 10. It then flows over the wafer 10 and out of the chuck stage 34, passing through the liquid recovery path 70 of the liquid recovery tank 60 and collecting in the liquid discharge hole 65 formed in the liquid recovery path 70. The liquid W collected in the liquid discharge hole 65 is guided to the filter 45 via the pipe 46b, purified in the filter 45, and returned to the liquid supply pump 44, thus circulating within the liquid supply mechanism 4. Furthermore, the pressure within the space 424 formed by the liquid W ejected from the liquid supply pump 44 is, for example, 2 MPa to 50 MPa, and the diameter of the linear water column Wp formed from the ejection hole 423 is 20 μm to 150 μm.

[0049] With the liquid W circulating stably in the liquid supply mechanism 4 and forming a water column Wp, the laser beam irradiation unit 8 is activated and the X-direction moving mechanism 50 constituting the moving mechanism 23 is activated, so that the holding unit 22 and the laser beam irradiation unit 8 move relative to each other in the processing feed direction (X direction) from the above-mentioned processing start position at a predetermined moving speed.

[0050] Here, in Figure 5 Based on, refer to Figure 6 , Figure 7 The laser processing implemented by the laser beam irradiation unit 8 of this embodiment will be described in further detail.

[0051] like Figure 5 As shown, the laser beams LB1+LB2 irradiated from the concentrator 86 pass through the space 424 and ejection hole 423 of the water column forming device 40 filled with liquid W, are transmitted within the water column Wp, and irradiate the processing position (predetermined dicing line) of the wafer 10. The laser beams LB1+LB2 are laser beams formed by combining the first laser beam LB1 and the second laser beam LB2 as described above, but as... Figure 6 As shown, the first laser beam LB1 is set to an extremely short pulse width A, and the second laser beam LB2 is set to a pulse width B that is longer than that of the first laser beam LB1. The second laser beam LB2 and the first laser beam LB1 are synchronously irradiated.

[0052] In addition, the laser processing conditions in the laser processing apparatus 2 described above can be implemented, for example, according to the following processing conditions.

[0053] <First Laser Oscillator>

[0054] The wavelengths of the first laser beam are: 355nm, 532nm, and 1064nm.

[0055] Average output: 10W~30W

[0056] Repetition frequency: 1MHz~10MHz

[0057] Pulse width: 50fs~50ps

[0058] <Second Laser Oscillator>

[0059] The wavelengths of the second laser beam are: 355nm, 532nm, and 1064nm.

[0060] Average output: 30W

[0061] Repetition frequency: 1MHz~10MHz

[0062] Pulse width: 50ns

[0063] from Figure 6 and Figure 7 As can be seen from (a), the second laser beam LB2 irradiates the plasma P1 in an induction manner, wherein the plasma P1 is generated near the front side of the wafer 10 by the first laser beam LB1 irradiating the processing position of the wafer 10. In this embodiment, as based on Figure 6 As explained, the first laser beam LB1 is set to an extremely short pulse width, and the second laser beam LB2 is set to a longer pulse width than the first laser beam LB1. Furthermore, the first laser beam LB1 is set to have a high peak power density, and the second laser beam LB2 is set to have a significantly lower peak power density than the first laser beam LB1.

[0064] When laser beams LB1+LB2 are irradiated onto the wafer 10 as described above, as Figure 7 As shown in (a), a first plasma P1 is generated on the front side of the wafer 10 by irradiating a first laser beam LB1 with a high peak power density and a short pulse width. Then, a second laser beam LB2 is irradiated towards the first plasma P1 in sync with the first laser beam LB1. As a result, the energy of the second laser beam LB2 is directed to the first plasma P1, causing the first plasma P1 to grow into the second plasma P2. Then, laser beams LB1+LB2 are irradiated along a predetermined dividing line, as shown in (a). Figure 7 As shown in (b), a circular groove is formed by performing isotropic laser processing downwards from the irradiation position, creating a processing groove 100 of the desired depth along a predetermined dividing line. Furthermore, the pressure of the water column Wp causes the bubbles generated by the irradiation of the laser beams LB1+LB2 to burst, and they are rapidly discharged from the processing area of ​​the wafer 10 along with the liquid W that forms the water column Wp, thus not hindering the continuous irradiation of the laser beams.

[0065] Furthermore, even if debris is discharged from the front side of the wafer 10 into the liquid W, it can be rapidly released from the wafer 10 along with the aforementioned bubbles. The liquid W, containing the bubbles and debris, flows over the cover plate 33 and the waterproof cover 66 as described above and is guided to the liquid recovery path 70 of the liquid recovery tank 60. The liquid W guided to the liquid recovery path 70 flows through the liquid recovery path 70 while releasing the bubbles generated by laser processing to the outside, and is discharged from the liquid discharge hole 65 formed at the bottom of the liquid recovery path 70. The liquid W discharged from the liquid discharge hole 65 is guided to the filter 45 via the pipe 46b and is again supplied to the liquid supply pump 44. In this way, by circulating the liquid W in the liquid supply mechanism 4 and by appropriately capturing debris, dust, etc., through the filter 45, the liquid W is maintained in a clean state.

[0066] After performing the aforementioned laser processing on the pre-defined segmentation lines in the first direction, the moving mechanism 23 is activated to position the concentrator 86 at one end of an unprocessed pre-defined segmentation line in the Y direction adjacent to the pre-defined segmentation line in the first direction that has already undergone laser processing, and the same laser processing is performed thereon. Then, after performing this laser processing on all the pre-defined segmentation lines formed along the first direction, the chuck stage 34 is rotated 90 degrees to perform the same laser processing on the pre-defined segmentation lines extending in the unprocessed second direction that are orthogonal to the previously processed pre-defined segmentation lines in the first direction. In this way, laser processing can be performed on all the pre-defined segmentation lines on the wafer 10 to form the processing groove 100 as the starting point for segmentation.

[0067] In this embodiment, as described above, laser beams LB1+LB2 are transmitted within the water column Wp and irradiate the desired irradiation position, and processing is performed using a second plasma P2 grown from the first plasma P1. In contrast, when processing is performed using only a short-pulse-width laser beam like the first laser beam LB1, due to anisotropy in the processing direction, the cross-sectional shape of the processed section is V-shaped, and the processing speed drops sharply when processing is performed from the front along the depth direction. However, when irradiating the laser beam LB1+LB2, which is the result of combining the short-pulse-width first laser beam LB1 and the long-pulse-width second laser beam LB2, as in this embodiment, based on… Figure 7 As explained, it achieves excellent isotropic processing, enabling it to excavate into a circle downwards from the irradiation position without reducing the processing speed, and to form a processing groove 100 of the desired depth along the predetermined dividing line at a good processing speed.

[0068] According to this embodiment, even if the front side of the wafer 10 is not coated with liquid resin, it is possible to prevent debris from adhering to the front side of the wafer 10, thereby reducing the cost of liquid resin and saving the time of coating and removing liquid resin, thus improving productivity.

[0069] Furthermore, the first laser beam LB1 propagates within the water column Wp formed by the water column former 40 and irradiates the wafer 10, thereby generating the first plasma P1. At this time, the first plasma P1 is generated within the layer of liquid W flowing down into the water column Wp, thus suppressing excessive expansion and mitigating the thermal effects. Then, the second laser beam LB2 is absorbed by the first plasma P1 generated by the short-pulse-width first laser beam LB1, thereby generating the second plasma within the layer of liquid W flowing down into the water column Wp for processing. Compared to the case where laser processing is performed using only the second pulse laser beam LB, the thermal impact around the predetermined dicing lines of the wafer 10 is limited, improving the bending strength when dicing the wafer 10 into individual device chips. That is, by combining the first laser beam LB1 and the second laser beam LB2 and transmitting them within the water column Wp as in this embodiment, laser beam LB1+LB2 is irradiated onto the workpiece. Compared to the case where laser processing is performed by irradiating either the first laser beam LB1 or the second laser beam LB2 alone, superior laser processing can be achieved.

[0070] According to the present invention, various modifications are possible without being limited to the embodiments described above. For example, the above embodiments were described assuming that the second laser beam LB2 is a pulsed laser beam, but the present invention is not limited thereto. The second laser beam LB2 can be any laser beam that illuminates with a width longer than the pulse width of the first laser beam LB2, and therefore can also be a continuous wave (CW). That is, the "second laser beam with a long pulse width" of the present invention also includes a laser beam that is a continuous wave (CW).

[0071] In the above embodiment, the second laser beam LB2 is emitted synchronously with the first laser beam LB1, such as... Figure 6 As shown, the second laser beam LB2 is described as being emitted from the first laser oscillator 812 and the second laser oscillator 814 simultaneously with the first laser beam LB1, but the invention is not limited thereto. For example, there is also a case where the second laser beam LB2 is emitted after the first laser beam LB1 has been irradiated, but before the first plasma P1 generated by the first laser beam LB1 is extinguished. In this way, as long as the second laser beam LB2 is emitted from the second laser oscillator 814 after the first laser beam LB1 has been irradiated and before the first plasma P1 is extinguished, the same effect as described above can be achieved.

Claims

1. A laser processing apparatus, comprising: A chuck table that holds a plate-shaped workpiece. A laser beam irradiation unit that irradiates the workpiece held on the chuck table with laser beams to perform machining; and The machining feed mechanism feeds the chuck table and the laser beam irradiation unit relative to each other. The laser beam irradiation unit includes: A laser oscillator that emits laser beams; A concentrator that focuses the laser beam emitted from the laser oscillator and directs it onto the workpiece held by the chuck table; and A water column former is disposed at the lower end of the concentrator and forms a linear water column on the upper surface of the workpiece. The laser oscillator includes: A first laser oscillator, which emits a first laser beam with a short pulse width and a wavelength that is absorbed by the workpiece; and The second laser oscillator emits a second laser beam with a long pulse width and a wavelength that is absorbed by the workpiece. Laser beams emitted from the first and second laser oscillators propagate within a linear water column formed by the water column generator and irradiate the workpiece. The plasma generated on the surface of the workpiece and within the linear water column by the laser beams emitted from the first laser oscillator absorbs the energy of the laser beams emitted from the second laser oscillator and grows, thereby processing the workpiece. A space is formed in the water column generator to introduce high-pressure liquid and spray the liquid onto the workpiece. A liquid supply mechanism in the space is used to supply the liquid to the workpiece by a liquid supply pump. The liquid supplied to the workpiece is then recovered and filtered. The liquid purified by the filtration is then returned to the space of the water column generator by the liquid supply pump and circulated within the liquid supply mechanism, so that the pressure in the space where the liquid is introduced is 2 MPa to 50 MPa.

2. The laser processing apparatus according to claim 1, wherein, The water column generator includes: A housing constituting the space, the housing comprising at least a top wall facing the objective lens constituting the condenser, a bottom wall opposite the top wall and having an ejector hole formed thereon, and side walls surrounding the space formed by the top wall and the bottom wall; and The high-pressure water inlet section introduces high-pressure water into the space within the housing. The laser beam, guided to a linear column of water ejected from the nozzle formed on the bottom wall, irradiates the workpiece.

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