Wafer processing methods

Abstract

[Problem] To perform laser processing on a wafer using appropriate processing conditions corresponding to the thickness variation of the wafer. [Solution] A wafer processing method is provided, comprising the following steps: a holding step, in which the wafer is attracted and held by a work chuck that is transmissive to a laser beam; and a laser beam irradiation step, in which a laser beam is irradiated along a plurality of predetermined dicing lines, the laser beam irradiation step comprising the following steps: an appropriate condition selection step, in which, while processing along at least one predetermined dicing line, the processing conditions are changed in stages from processing conditions that do not penetrate the wafer to processing conditions that penetrate the wafer, thereby selecting the processing conditions when the photodetector unit detects the laser beam penetrating the wafer as appropriate processing conditions; and a dicing step, in which the processing conditions selected in the appropriate condition selection step are used to irradiate the laser beam along the other predetermined dicing lines, thereby dicing the wafer into a plurality of device wafers.

Description

Technical Field

[0001] This invention relates to a wafer processing method for dividing a wafer into a plurality of device wafers by irradiating a pulsed laser beam having a wavelength that can be absorbed by the wafer along predetermined dicing lines. Prior Technology

[0002] In the semiconductor device wafer manufacturing process, in order to thin the semiconductor device wafer, there are cases where the back side of the wafer is ground by a grinding device before the individual wafers of which a plurality of devices are formed on the front side (hereinafter referred to as wafers) are individually wafered (see, for example, Patent Document 1).

[0003] After grinding, the wafer, which has been thinned to a predetermined finished thickness, is diced into multiple semiconductor device wafers. For example, a laser processing apparatus is used to dic the wafer. To dice the wafer, dicing tape is first attached to the back side of the wafer, and then the back side is held in place by a work chuck through the dicing tape.

[0004] Next, a laser beam with a wavelength that can be absorbed by the wafer is irradiated along the predetermined dicing line of the wafer to form a processing trench that runs from the front to the back of the wafer (i.e., a full dicing), thereby dividing the wafer into a plurality of semiconductor device wafers (see, for example, Patent Document 2).

[0005] When performing laser processing like this, the laser beam output and processing feed speed are determined in advance based on the type of wafer through test cutting. Therefore, the same processing conditions are applied to wafers of the same type.

[0006] However, when comparing wafers manufactured in different lots, for example, there may be slight variations in wafer thickness due to manufacturing inconsistencies in the devices, variations in the thickness of the finished product after grinding, etc.

[0007] Therefore, if laser beams are used for ablation under predetermined processing conditions, defects may occur due to variations in wafer thickness. Specifically, in relatively thick wafers, the following situation may occur: incompletely cut areas may be created throughout the wafer.

[0008] Furthermore, in thinner wafers, the following situation may occur: after the wafer has been cut, the dicing tape melts due to excessive heating by the laser beam, and the molten residue adheres to the work chuck. The molten residue reduces the flatness of the work chuck's holding surface and may further clog the suction holes on the holding surface. Previous technical documents Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2009-90389 Patent Document 2: Japanese Patent Application Publication No. 2018-125448 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] The present invention was made in view of the aforementioned problems, and its purpose is to perform laser processing on the wafer with appropriate processing conditions corresponding to the thickness variation of the wafer when the wafer is cut by ablation. The means to solve the problem

[0012] According to one aspect of the present invention, a wafer processing method is provided, wherein a device is formed on the front side of the wafer in each of a plurality of regions divided by a plurality of predetermined dividing lines arranged in a lattice pattern. The wafer processing method comprises irradiating a pulsed laser beam having a wavelength absorbed by the wafer along each predetermined dividing line to divide the wafer into a plurality of device wafers. In the tape adhesion step, the central portion of the tape is adhered to the back side of the wafer, which is opposite to the front side, and one side of the annular frame is adhered to the outer periphery of the tape. Following the tape adhesion step, the wafer is held in place by a work chuck that is transmissive to the laser beam, using the tape for attraction and holding. In the laser beam irradiation step, after the holding step, the processing position is changed by moving the focal point of the laser beam relative to the worktable in a predetermined direction, while the laser beam is irradiated along the plurality of predetermined dividing lines. The laser beam irradiation process includes the following steps: In the appropriate condition selection step, when processing along at least one predetermined dicing line, the processing conditions are changed in stages from processing conditions that do not penetrate the wafer to processing conditions that penetrate the wafer, until a photodetector unit positioned opposite the wafer to the worktable detects the laser beam penetrating the wafer. The processing conditions at which the photodetector unit detects the laser beam penetrating the wafer are selected as appropriate processing conditions; and The slicing step uses processing conditions selected in the appropriate conditions selection step to irradiate the laser beam along other slicing predetermined lines different from the at least one slicing predetermined line, thereby slicing the wafer into the plurality of device wafers.

[0013] Preferably, the appropriate condition selection step includes the following: as the predetermined direction moves relative to each other, the average output is set to high output in stages, thereby changing the processing conditions from processing conditions that have never penetrated the wafer to processing conditions that have penetrated the wafer.

[0014] Furthermore, preferably, the appropriate condition selection step includes the following: as the relative movement in the predetermined direction occurs, the processing feed rate is set to a low speed in stages, thereby changing the processing conditions from processing conditions that have never penetrated the wafer to processing conditions that have penetrated the wafer.

[0015] Furthermore, preferably, the wafer processing method further includes a re-irradiation step, wherein the aforementioned re-irradiation step is to irradiate the non-penetrated area formed during the period from when the photodetector unit detects the laser beam penetrating the wafer in the appropriate condition selection step with the laser beam again.

[0016] Furthermore, preferably, the wafer processing method further includes a tape expansion step, which is performed after the laser beam irradiation step to expand the tape. Invention Effects

[0017] In the wafer processing method of the present invention, when processing along at least one predetermined dicing line, the processing conditions are changed in stages from processing conditions that do not penetrate the wafer to processing conditions that penetrate the wafer, until the photodetector unit detects the laser beam penetrating the wafer, thereby selecting the processing conditions when the photodetector unit detects the laser beam penetrating the wafer as appropriate processing conditions (appropriate condition selection step).

[0018] Therefore, since appropriate processing conditions corresponding to the thickness of the wafer can be selected, laser processing can be performed under the selected processing conditions to prevent the generation of unpenetrated areas in the whole wafer or the adhesion of molten residue to the work jig. Simple Explanation of the Diagram

[0019] Figure 1 is a flowchart of the wafer fabrication process. Figure 2(A) is a three-dimensional view of the wafer, and Figure 2(B) is a three-dimensional view of the wafer unit. Figure 3 is a three-dimensional view of the laser processing device. Figure 4 is a side view of the worktable, etc. Figure 5(A) shows the laser processing performed with the first average output, Figure 5(B) shows the laser processing performed with the second average output, and Figure 5(C) shows the situation where the laser beam has penetrated the wafer. Figure 6 is a three-dimensional view of a plurality of device wafers, etc. Figure 7(A) is a flowchart of the wafer processing method of the first modified example, and Figure 7(B) is a flowchart of the wafer processing method of the second modified example. Figure 8(A) is a partial cross-sectional side view of the expansion device, etc., and Figure 8(B) is a diagram showing the tape expansion steps. Figure 9(A) shows the laser processing at the first processing feed rate, Figure 9(B) shows the laser processing at the second processing feed rate, and Figure 9(C) shows the laser beam penetrating the wafer. Implementation

[0020] Forms used to implement inventions

[0021] Referring to the accompanying drawings, one embodiment of the present invention will be described. FIG1 is a flowchart of a processing method for a wafer 11 (refer to FIG2(A)) according to the first embodiment. In the first embodiment, the following steps are performed sequentially: tape adhesion step S10, holding step S20, appropriate condition selection step S32, dicing step S34, and re-irradiation step S40.

[0022] Furthermore, in this specification, the appropriate condition selection step S32 and the slicing step S34 are sometimes combined and referred to as the laser beam irradiation step S30. First, the wafer 11 to be laser-processed will be described.

[0023] Figure 2(A) is a perspective view of wafer 11. Wafer 11 is mainly formed of semiconductor materials such as silicon and has a circular plate shape. A circuit layer (not shown) is formed on the front side 11a of wafer 11. The aforementioned circuit layer includes an insulating layer formed of a low-dielectric-constant interlayer insulating film material (so-called Low-k material) and a metallization layer.

[0024] On the front side 11a of the wafer 11, a plurality of straight dicing lines (cut lines) 13 are set in a grid pattern. In each of the plurality of rectangular regions divided by the plurality of dicing lines 13, a device 15 such as an IC (Integrated Circuit) is formed.

[0025] Furthermore, the back side 11b of the wafer 11, which is opposite to the front side 11a, has been ground, and the wafer 11 has been thinned to a generally uniform predetermined finished thickness (e.g., a predetermined thickness of less than 50 μm).

[0026] When performing laser processing on wafer 11, wafer unit 21 is first formed (see Figure 2(B)). Figure 2(B) is a perspective view of wafer unit 21.

[0027] When fabricating wafer cell 21, the central part of a cutting tape (tape) 17 with a diameter larger than that of wafer 11 is attached to the back side 11b, and one side of a ring-shaped frame 19 with an opening larger than that of wafer 11 is attached to the outer periphery of the cutting tape 17 (tape attachment step S10).

[0028] The cutting tape 17 is generally transparent and has a laminated structure of a substrate layer and an adhesive layer (paste layer). The substrate layer is formed of resins such as polyolefins and polyesters, and the adhesive layer is composed of uncured adhesive resins such as thermosetting resins and UV-curing resins.

[0029] However, the dicing tape 17 may also have only a substrate layer. In this case, the wafer unit 21 can be formed by, for example, heat-pressing the dicing tape 17 onto the wafer 11 and the frame 19.

[0030] Next, using Figures 3 and 4, the laser processing apparatus 2 used in the holding step S20 after the tape adhesion step S10 will be explained.

[0031] Figure 3 is a perspective view of the laser processing apparatus 2. Furthermore, in Figure 3, the laser beam irradiation unit 30 and the photodetector mechanism 34 are omitted (see Figure 4). Figure 4 is a side view of the worktable 22, etc. Furthermore, in Figure 4, the shaded lines are omitted for simplicity.

[0032] The X-axis, Y-axis, and Z-axis directions shown in Figures 3 and 4 are mutually orthogonal. For example, the XY plane corresponds to the horizontal plane, and the Z-axis direction corresponds to the vertical direction. The various components of the laser processing device 2 are supported on the base 4.

[0033] A pair of guide rails 6 are fixed along the Y-axis on the upper surface of the base 4. A Y-axis movable plate 8 is slidably mounted on the pair of guide rails 6. A nut (not shown) is provided on the lower surface of the Y-axis movable plate 8.

[0034] A screw shaft 10, which is arranged approximately parallel to the Y-axis, is rotatably connected to the nut portion. The nut portion and the screw shaft 10 constitute a ball screw. A Y-axis drive source 12, such as a pulse motor, is connected to one end of the screw shaft 10.

[0035] As long as the screw shaft 10 is rotated by the Y-axis drive source 12, the Y-axis moving plate 8 will move along the guide rail 6. The guide rail 6, the nut, the screw shaft 10, and the Y-axis drive source 12 constitute the Y-axis moving mechanism.

[0036] A pair of guide rails 14 are fixed along the X-axis direction on the upper surface of the movable plate 8 in the Y-axis direction. A movable worktable 16 is slidably mounted on the pair of guide rails 14. A nut portion (not shown) is provided on the lower surface of the base plate 16c of the movable worktable 16.

[0037] A screw shaft 18, arranged approximately parallel to the X-axis, is rotatably connected to the nut portion. The nut portion and the screw shaft 18 constitute a ball screw. An X-axis drive source 20, such as a pulse motor, is connected to one end of the screw shaft 18.

[0038] As long as the screw shaft 18 is rotated by the X-axis drive source 20, the movable worktable 16 will move along the guide rail 14. The guide rail 14, the nut part, the screw shaft 18, the X-axis drive source 20, etc. constitute the X-axis moving mechanism.

[0039] The movable worktable 16 has a rectangular plate-shaped top plate 16a, a side plate 16b, and a bottom plate 16c. The upper end of the side plate 16b is connected to one end of the top plate 16a in the X-axis direction, and the lower end of the side plate 16b is connected to one end of the bottom plate 16c in the X-axis direction.

[0040] A space 16d is formed by the top plate 16a, the side plate 16b, and the bottom plate 16c, which opens the other end in the X-axis direction and the two ends in the Y-axis direction. A work clamp 22 is provided on the top plate 16a.

[0041] The worktable 22 has a retaining plate 24 in the shape of a circular plate. The retaining plate 24 is formed of a transparent material such as quartz glass and is transmissive to the laser beam L (see Figure 4) described later. The retaining plate 24 includes a generally flat side 24a and another side 24b located on the opposite side of the flat side 24a (see Figure 4).

[0042] A plurality of gas flow paths are formed inside the retaining plate 24. For example, when the retaining plate 24 is viewed from the top surface, the first straight attraction path 24c 1 and the second attraction path 24c 2 are formed to be orthogonal at the center 24c 3 of the surface 24a.

[0043] The first attraction path 24c1 and the second attraction path 24c2 are formed at the same depth in the retaining plate 24 and are connected to each other directly below the center 24c3. On the outer periphery of the surface 24a, a plurality of openings 24d are formed at approximately equal intervals in the circumferential direction of the surface 24a.

[0044] A plurality of openings 24d are formed at both ends of the first attraction path 24c 1, the second attraction path 24c 2, etc. Each opening 24d is formed from one side 24a to a predetermined depth that does not reach the other side 24b, and is interconnected by an outer peripheral attraction path 24e formed at a predetermined depth on the outer periphery of the retaining plate 24.

[0045] An attraction path (not shown) is formed on the outer side of the retaining plate 24 in the radial direction, beyond the opening 24d, and an attraction source (not shown) such as an injector is connected to this attraction path. When the attraction source is activated to generate negative pressure, the negative pressure is transmitted to each opening 24d. In this way, one surface 24a functions as a retaining surface.

[0046] On the outer periphery of the work clamp 22, there is an annular frame suction plate (not shown) with a plurality of suction ports discretely formed along the circumferential direction of the work clamp 22, and the frame 19 can be attracted and held by the frame suction plate.

[0047] However, a portion of the incident light is scattered or reflected in the flow path of the holding plate 24, including the first attraction path 24c1, the second attraction path 24c2, the opening 24d, and the outer peripheral attraction path 24e. Therefore, the flow path of the holding plate 24 is not completely transparent to the laser beam L, but rather has a state of being either translucent or opaque.

[0048] However, the predetermined area other than these flow paths is transparent from one side 24a to the other side 24b. For example, the area that is transparent to the laser beam L from one side 24a to the other side 24b is divided into four parts by the first attraction path 24c 1 and the second attraction path 24c 2, and is located inside the outer peripheral attraction path 24e in the radial direction of the holding plate 24.

[0049] A cylindrical frame 26 made of stainless steel or other metal is provided around the outer periphery of the retaining plate 24. The retaining plate 24 is fixed to the frame 26 by blocking the through opening (not shown) of the frame 26.

[0050] The frame 26 is rotatably supported on the top plate 16a of the movable worktable 16. Furthermore, a through opening (not shown) with approximately the same diameter as the retaining plate 24 is formed in the top plate 16a, through which light shining on one side 24a propagates into the space 16d of the movable worktable 16.

[0051] The cylindrical side of the frame 26 functions as a pulley section 26a. With the frame 26 supported by the top plate 16a, the pulley section 26a is positioned above the top plate 16a. A rotary drive source 28, such as a motor, is provided on the side plate 16b. A pulley 28a is provided on the rotation axis of the rotary drive source 28.

[0052] An endless belt 28b is attached to the pulley section 26a and the pulley 28a. If the pulley 28a is rotated by the rotation drive source 28, the frame 26 will rotate around a rotation axis that is approximately parallel to the Z-axis direction by means of the force transmitted through the endless belt 28b.

[0053] Thus, by controlling the rotation of pulley 28a, the worktable 22 can be rotated at any angle around a rotation axis that is approximately parallel to the Z-axis. As shown in Figure 4, a laser beam irradiation unit 30 is arranged above one side 24a.

[0054] The laser beam irradiation unit 30 has a laser oscillator (not shown), which has a laser medium formed of Nd:YAG, Nd:YVO4, etc. A pulsed laser beam L emitted from the laser oscillator, and then converted into a predetermined wavelength by a wavelength conversion unit (not shown), is incident on the concentrator 32.

[0055] Concentrator 32 has a focusing lens (not shown). Concentrator 32 illuminates a laser beam L toward a surface 24a to focus the light onto a wafer 11 that has been attracted and held by the surface 24a. The wavelength of the main peak of the laser beam L is a wavelength that can be absorbed by the wafer 11 (e.g., 355 nm).

[0056] A light detection mechanism 34 is provided in space 16d. The light detection mechanism 34 has an arm 36 whose long side is arranged along the X-axis direction. A light detection unit 38 is provided at the front end of the arm 36.

[0057] The light detection unit 38 has, for example, a power sensor or power meter, each having a photodiode, as a light receiving element. However, the light detection unit 38 may also be a camera with a light receiving element having a photodiode or the like, and a light-reducing filter that reduces the amount of light taken in by the light receiving element.

[0058] The photodetector unit 38 is configured to sandwich the worktable 22, the wafer 11, etc., between the photodetector 32 and the condenser 32, and is located directly below the condenser 32. Therefore, the laser beam L that has penetrated the wafer 11 and has been transmitted through the cutting tape 17 and the holding plate 24 will be incident on the photodetector unit 38.

[0059] Each component of the laser processing apparatus 2 is controlled by the control unit 40. The control unit 40 is configured by a computer, which includes, for example, a processor (processing device) represented by a CPU (Central Processing Unit), a main memory device such as DRAM (Dynamic Random Access Memory), and an auxiliary memory device such as flash memory.

[0060] The auxiliary memory device stores software containing a predetermined program. By following this software, the processing device and other devices can be operated, thereby realizing the function of the control unit 40.

[0061] Using this laser processing apparatus 2, the process proceeds from the holding step S20 shown in FIG1 to the re-irradiation step S40. First, in the holding step S20, the dicing tape 17 of the wafer cell 21 is placed on one side 24a of the work chuck 22.

[0062] Next, by transmitting negative pressure to the opening 24d, the back side 11b of the wafer 11 is attracted and held through the cutting tape 17 (holding step S20). After holding step S20, an image of the front side 11a is acquired using an imaging unit (not shown) and calibrated.

[0063] Then, the orientation of the worktable 22 is adjusted using a rotary drive source 28, etc., so that the predetermined dividing line 13 along one direction becomes approximately parallel to the X-axis direction. After that, the laser beam irradiation step S30, in which the laser beam L is irradiated along each predetermined dividing line 13, is performed.

[0064] The processing conditions are usually determined in advance according to the thickness and type of the wafer 11. However, if the predetermined processing conditions are used directly, the following situation will occur in a thicker wafer 11: an uncut area will be generated in the whole of the wafer 11, where the wafer 11 is not completely cut off.

[0065] Furthermore, in the relatively thin wafer 11, the following situation may occur: after the wafer 11 has been cut, the cutting tape 17 melts, and the molten residue adheres to one side 24a of the holding plate 24. Therefore, in the laser beam irradiation step S30, the appropriate condition selection step S32 is first performed by performing laser processing on at least one predetermined dicing line 13.

[0066] In the appropriate condition selection step S32 of the first embodiment, for example, in a batch of 25 processed wafers 11, the appropriate condition selection step S32 is first performed on the first wafer 11, thereby selecting processing conditions that are more appropriate than the processing conditions determined in advance.

[0067] Furthermore, instead of using one of the plurality of wafers 11 to select appropriate processing conditions as in the first embodiment, the appropriate condition selection step S32 can be performed on each wafer 11 to be laser processed.

[0068] If the appropriate condition selection step S32 is performed on each wafer 11, although the processing time will be longer than that of performing the appropriate condition selection step S32 on only one wafer 11 among a plurality of wafers 11, the processing conditions can be optimized for each wafer 11.

[0069] In the appropriate condition selection step S32 of the first embodiment, the processing feed rate is set to a fixed value, and the average output of the laser beam L is set to high output in stages. This causes the processing conditions to change in stages from processing conditions that do not penetrate the wafer 11 to processing conditions that penetrate, until the photodetector unit 38 detects the laser beam L. The processing conditions are, for example, as shown below.

[0070] Laser medium: Nd:YAG Wavelength: 355nm Average output: 5.0W (at the start of irradiation of wafer 11) Average output change: increases by 0.1W every 0.1 seconds (i.e., 1.0W / second). Repetition frequency: 20kHz Focused beam diameter: 5.0 μm Machining feed rate: 100 mm / s (fixed value)

[0071] Figures 5(A) to 5(C) show the appropriate condition selection step S32 during machining along a predetermined dividing line 13. Furthermore, the direction of the arrow indicates the direction in which the worktable 22 moves, and the length of the arrow corresponds to the magnitude of the machining feed rate.

[0072] In step S32, where appropriate conditions are selected, the focusing point P of the laser beam L is first positioned at one end of a predetermined dividing line 13 along the X-axis. Then, by feeding the moving stage 16, the focusing point P of the laser beam L and the work chuck 22 are moved relative to each other in the X-axis direction (predetermined direction).

[0073] In this way, while changing the processing position, a laser beam L is irradiated along the predetermined dividing line 13 to perform ablation processing. Figure 5(A) is a diagram showing the situation of laser processing with the first average output (about 5.0W).

[0074] Figure 5(B) shows the laser processing at the second average output (approximately 5.1W). The depth of the processing trench 11c formed on the wafer 11 by ablation gradually increases as the average output increases.

[0075] Figure 5(C) shows the situation where laser processing is performed at the third average output (approximately 5.3W) and the laser beam L has penetrated the wafer 11. When the laser beam L penetrates the wafer 11 and the photodetector unit 38 detects the laser beam L, the control unit 40 will memorize the XY coordinates of the condenser 32 at that time point and fix the average output of the laser beam L.

[0076] Then, using a fixed average output, the processing groove 11c is formed to the other end of a predetermined dividing line 13 in the X-axis direction. The control unit 40 selects the average output at the time when the laser beam L is detected by the light detection unit 38 as the average output of the appropriate processing conditions and memorizes it.

[0077] Furthermore, in this specification, the detection of the laser beam L by the photodetector unit 38 is indicated when the power (W) or light intensity of the laser beam L received by the photodetector unit 38 exceeds a predetermined threshold.

[0078] The predetermined threshold is appropriately set for the purpose of processing conditions where the laser beam L accidentally penetrates a locally thinned area of ​​the wafer 11 due to in-plane unevenness caused by thickness, without selecting the time point of penetration in this case.

[0079] Furthermore, the appropriate condition selection step S32 can be performed on a shorter dicing predetermined line 13 located on the outer periphery side of the wafer 11 among a plurality of dicing predetermined lines 13 along one direction, or on a longer dicing predetermined line 13 located on the center side of the wafer 11.

[0080] Although it is preferable to perform the appropriate condition selection step S32 on one predetermined dividing line 13, if the photodetector 38 does not detect the laser beam L on the first predetermined dividing line 13, the appropriate condition selection step S32 can also be performed on a second predetermined dividing line 13 that is different from the first one.

[0081] Thus, the appropriate condition selection step S32 can be performed on two or more predetermined dividing lines 13, but in the first embodiment, the appropriate condition selection step S32 is performed on one predetermined dividing line 13.

[0082] On one predetermined dividing line 13 where appropriate conditions have been selected in step S32, after forming the machining groove 11c to the other end in the X-axis direction, the moving table 16 is indexed and fed by a predetermined length. Next, laser processing is performed on the other predetermined dividing lines 13 adjacent to this predetermined dividing line 13 in the Y-axis direction using the selected processing conditions.

[0083] Since laser processing is performed under selected processing conditions, appropriate processing conditions corresponding to the thickness of wafer 11 can be selected, thus preventing the generation of unpenetrated areas in the whole wafer 11 or the adhesion of molten residue to the work chuck 22.

[0084] In step S32, when appropriate conditions are selected, laser processing is performed on all the predetermined dividing lines 13 along a direction different from the predetermined dividing lines 13 that have already been laser processed, under the selected processing conditions, and then the worktable 22 is rotated 90 degrees.

[0085] Then, laser processing is performed along each predetermined slitting line 13 in other directions orthogonal to one direction, using selected processing conditions. In this way, the wafer 11 is slitted into a plurality of device wafers 23 (see Figure 6) (slitting step S34).

[0086] Figure 6 is a perspective view of the plurality of device wafers 23, etc., after the segmentation step S34. Furthermore, in Figure 6, one device wafer 23 is enlarged for convenience.

[0087] In the first embodiment, after the segmentation step S34, the unpenetrated area 11d of the segmentation predetermined line 13 formed in the appropriate condition selection step S32 (see Figure 5(C)) is irradiated again with a laser beam L (re-irradiation step S40).

[0088] The non-penetrated region 11d is formed in a predetermined dividing line 13 in which appropriate conditions have been selected in step S32, from the start of the irradiation of the laser beam L until the photodetector unit 38 detects that the laser beam L has penetrated the wafer 11.

[0089] In the unpenetrated region 11d, since more than 90% and less than 98% have been removed in the thickness direction of the wafer 11, in the re-irradiation step S40, the average output is adjusted to be high enough to allow ablation processing and low enough to prevent the cutting tape 17 from melting.

[0090] In the first embodiment, since appropriate processing conditions corresponding to the thickness of the wafer 11 can be selected, the generation of unpenetrated areas 11d in the whole wafer 11 or the adhesion of molten residue to the work stand 22 can be prevented.

[0091] Furthermore, by performing laser processing on the remaining 24 wafers 11 under the selected processing conditions, even on the remaining 24 wafers 11, it is possible to prevent the generation of unpenetrated areas 11d in the whole wafer 11 or the adhesion of molten residue to one side 24a.

[0092] Next, a modified example of the first embodiment will be described. Figure 7(A) is a flowchart of the processing method of wafer 11 in the first modified example, and Figure 7(B) is a flowchart of the processing method of wafer 11 in the second modified example.

[0093] In the first variation, the tape expansion step S50 is performed after the re-irradiation step S40 using the expansion device 42 (see Figure 8(A)). In contrast, in the second variation, the tape expansion step S50 is performed after the segmentation step S34 without going through the re-irradiation step S40.

[0094] Figure 8(A) is a partial cross-sectional side view of the expansion device 42, etc. The expansion device 42 has a cylindrical cylinder 44, which has a diameter larger than that of the wafer 11. A plurality of rollers 46 are arranged at approximately equal intervals along the circumference of the upper end of the cylinder 44.

[0095] A circular frame support platform 48 is provided on the outer side of the cylinder 44 in the radial direction. A plurality of clamps 50 are provided on the upper surface of the frame support platform 48, and the plurality of clamps 50 respectively clamp the frame 19 of the wafer unit 21 placed on the frame support platform 48.

[0096] Furthermore, the frame support platform 48 is supported by a plurality of legs 52, which are arranged at approximately equal intervals along the circumference of the frame support platform 48. Each leg 52 can be raised or lowered by a lifting mechanism such as a cylinder.

[0097] In the tape expansion step S50, as shown in FIG8(A), after setting the upper end of the cylinder 44 and the upper surface of the frame support stage 48 to approximately the same height position, the wafer unit 21 after the laser beam irradiates step S30 is placed on the cylinder 44 and the frame support stage 48.

[0098] Next, when the lifting mechanisms are activated to pull down the feet 52, the frame support platform 48 is pulled down relative to the cylinder 44. As a result, as shown in FIG8(B), the cutting tape 17 is expanded radially, and the spacing between the device wafers 23 is increased. FIG8(B) is a diagram showing the tape expansion step S50.

[0099] In the case where the unpenetrated area 11d is not completely penetrated even after the re-irradiation step S40 (first variant of FIG7(A)) or in the case where the re-irradiation step S40 is not performed after the segmentation step S34 (second variant of FIG7(B)), the unpenetrated area 11d can be segmented in the tape expansion step S50.

[0100] In the tape expansion step S50, the wafer 11 can be divided into a plurality of device wafers 23 by dividing the undivided areas in the wafer 11 that have passed through the dicing step S34 and / or the re-irradiation step S40. Furthermore, by increasing the spacing between the device wafers 23, the picking up of the device wafers 23 becomes easier compared to the case where the spacing is not increased.

[0101] Next, the second embodiment will be described with reference to Figures 9(A) to 9(C). The second embodiment differs from the first embodiment in the appropriate condition selection step S32. In the appropriate condition selection step S32 of the second embodiment, the machining feed speed is set to a low speed in stages as the focusing point P moves relative to the worktable 22 along the X-axis.

[0102] The lower the processing feed rate is set, the higher the proportion of overlapping areas of the focused spot of the pulsed laser beam L (also known as the overlap ratio, overlap rate, etc.) becomes. Therefore, the processing conditions can be changed from processing conditions where the laser beam L does not penetrate the wafer 11 to processing conditions where the laser beam L penetrates the wafer 11. The processing conditions are as follows, for example.

[0103] Laser medium: Nd:YAG Wavelength: 355nm Average output: 5.0W (fixed value) Repetition frequency: 20kHz Focused beam diameter: 5.0 μm Processing feed rate: 100 mm / s (at the start of irradiation of wafer 11) Changes in machining feed rate: Decrease by 0.2 mm / s (i.e., -2.0 mm / s) every 0.1 seconds.

[0104] Figure 9(A) shows the laser processing at the first processing feed rate (approximately 100 mm / s), and Figure 9(B) shows the laser processing at the second processing feed rate (approximately 98 mm / s).

[0105] Figure 9(C) shows the situation where laser processing is performed at the third processing feed rate (approximately 96 mm / s) and the laser beam L penetrates the wafer 11. Furthermore, in Figures 9(A) to 9(C), the direction of the arrows indicates the direction in which the worktable 22 moves, and the length of the arrows corresponds to the magnitude of the processing feed rate.

[0106] When the laser beam L penetrates the wafer 11 and the photodetector 38 detects the laser beam L, the control unit 40 will memorize the XY coordinates of the condenser 32 at that time point and fix the processing feed rate.

[0107] Then, at a fixed machining feed rate, the machining groove 11c is formed to the other end of the X-axis direction of a predetermined dividing line 13. The control unit 40 selects the machining feed rate at the time when the laser beam L is detected by the light detection unit 38 as the appropriate machining feed rate and memorizes it.

[0108] On a predetermined dividing line 13 where appropriate conditions have been selected in step S32, after the machining groove 11c is formed to the other end in the X-axis direction, the moving worktable 16 is indexed and fed to a predetermined length.

[0109] Next, laser processing is performed on other predetermined dividing lines 13 adjacent to this predetermined dividing line 13 in the Y-axis direction using the selected processing conditions. Similarly, the other predetermined dividing lines 13 are also processed using the processing feed rate selected in the appropriate condition selection step S32.

[0110] In the second embodiment, since appropriate processing conditions corresponding to the thickness of the wafer 11 can also be selected, the generation of unpenetrated areas 11d in the whole wafer 11 or the adhesion of molten residue to the work stand 22 can be prevented.

[0111] Furthermore, in the second embodiment, the appropriate condition selection step S32 can be performed on the first wafer 11 among a batch of 25 processed wafers 11, or the appropriate condition selection step S32 can be performed on each wafer 11 that is subjected to laser processing.

[0112] Furthermore, in the second embodiment, the tape expansion step S50 can also be performed as described in the first and second modifications above. In addition, the structure and method of the above embodiments can be appropriately modified and implemented as long as they do not depart from the purpose of the present invention.

[0113] For example, when the thickness of wafer 11 is less than 50 μm, wafer 11 can be cut by irradiating the aforementioned laser beam L from one end of a predetermined dividing line 13 to the other end once (that is, the focus point P passes through once (i.e., one pass)).

[0114] However, when the thickness of wafer 11 exceeds 50 μm, in order to cut wafer 11, it is sometimes necessary to perform laser processing two or more times (i.e., two or more passes) to make the focus point P pass along a predetermined dividing line 13. Even when it is necessary to perform this laser processing two or more passes, the above-described embodiments and variations can still be applied.

[0115] Specifically, when the wafer 11 is cut by laser processing in N passes (where N is a natural number greater than 2), from the first pass to the (N-1)th pass, laser processing is performed along each predetermined dividing line 13 under processing conditions that are predetermined in advance and correspond to the thickness, type, etc. of the wafer 11.

[0116] Subsequently, during the Nth laser processing pass, the aforementioned appropriate condition selection step S32 is performed on at least one predetermined dividing line 13. For example, the appropriate condition selection step S32 is performed on one predetermined dividing line 13. In this way, processing conditions that are more appropriate than the pre-determined processing conditions are selected.

[0117] Then, the moving worktable 16 is indexed and fed to a predetermined length, and the Nth laser processing is performed on the other predetermined dividing lines 13 adjacent to the one that has been processed in the Y-axis direction, according to the processing conditions selected in step S32.

[0118] Similarly, after performing the Nth laser processing along all the remaining predetermined dividing lines 13 in one direction, with the appropriate processing conditions selected in step S32, the worktable 22 is rotated 90 degrees.

[0119] Then, along the predetermined dividing lines 13 in other directions orthogonal to one direction, the Nth laser processing pass is performed similarly with the processing conditions selected in step S32. In this way, the wafer 11 can be divided into a plurality of device wafers 23, and the generation of unpenetrated areas in the whole wafer 11 or the adhesion of molten residue to the worktable 22 can be prevented.

[0120] Incidentally, for example, after tape application step S10 and before holding step S20, a protective film (not shown) with water-soluble resin can be uniformly formed on the front side 11a, followed by laser beam irradiation step S30.

[0121] By performing ablation on a protective film that has already been formed, it is possible to prevent the molten material (debris) on the front side 11a of the wafer 11 from adhering to it. Furthermore, the protective film can be washed away and removed along with the debris after the ablation process.

[0122] 2: Laser processing equipment 4:Abutment 6,14: Guide rail 8: Y-axis moving plate 10, 18: Screw shaft 11: Wafer 11a: Front 11b: Back 11c: Processing trench 11d: Unpenetrated area 12: Y-axis drive source 13: Pre-defined dividing line 15: Devices 16: Mobile workbench 16a: Top plate 16b: Side panel 16c: Base Plate 16d: Space 17: Cutting tape 19: Framework 20: X-axis direction drive source 21: Wafer Unit 22: Worktable 23: Device wafers 24: Retention Plate 24a: One side 24b: The Other Side 24c 1: The First Attraction Path 24c 2: The Second Attraction Path 24c 3: Center 24d: Opening 24e: Peripheral Attraction Road 26: Frame 26a: Pulley section 28: Rotary drive source 28a: Pulley 28b: Endless belt 30: Laser beam illumination unit 32: Concentrator 34: Light detection mechanism 36: Arm 38: Light Detection Unit 40: Control Unit 42: Expansion device 44: Cylinder 46: Roller 48: Frame support platform 50: Fixture 52: Feet L: Laser beam P: Focus point S10: Tape application steps S20: Maintain the steps S30: Laser Beam Irradiation Procedure S32: Steps for Selecting Appropriate Conditions S34: Segmentation Steps S40: Re-irradiation procedure S50: Tape Expansion Steps X, Y, Z: Direction

Claims

1. A wafer processing method, wherein a device is formed on each of a plurality of regions on the front side of the wafer, divided by a plurality of predetermined dividing lines arranged in a grid pattern, the wafer processing method comprising irradiating a pulsed laser beam having a wavelength absorbed by the wafer along each predetermined dividing line to divide the wafer into a plurality of device wafers, the wafer processing method being characterized by comprising the following steps: a tape adhesion step, wherein the central portion of a tape is adhered to the back side of the wafer located opposite to the front side, and one side of an annular frame is adhered to the outer periphery of the tape; a holding step, wherein after the tape adhesion step, the wafer is held by means of a work jig that is transmissive to the laser beam, through which the tape is used to attract and hold the wafer; and a laser beam irradiation step, wherein after the holding step, the laser beam is irradiated along the plurality of predetermined dividing lines while changing the processing position by moving the focal point of the laser beam relative to the work jig in a predetermined direction. The laser beam irradiation step includes the following steps: an appropriate condition selection step, in which, while processing along at least one predetermined dicing line, the processing conditions are changed in stages from processing conditions that do not penetrate the wafer to processing conditions that penetrate the wafer, until a photodetector unit positioned opposite the wafer to the worktable detects the laser beam penetrating the wafer, thereby selecting the processing conditions at which the photodetector unit detects the laser beam penetrating the wafer as appropriate processing conditions; and a dicing step, using the processing conditions selected in the appropriate condition selection step, to irradiate the laser beam along other predetermined dicing lines different from the at least one predetermined dicing line, thereby dicing the wafer into the plurality of device wafers.

2. The wafer processing method of claim 1, wherein the appropriate condition selection step includes the following: as the predetermined direction moves relative to each other, the average output is set to high output in stages, thereby changing the processing conditions from processing conditions that do not penetrate the wafer to processing conditions that penetrate the wafer.

3. The wafer processing method of claim 1, wherein the appropriate condition selection step includes the following: as the relative movement in the predetermined direction proceeds, the processing feed rate is set to a low speed in stages, thereby changing the processing conditions from processing conditions that have never penetrated the wafer to processing conditions that have penetrated the wafer.

4. The wafer processing method of any one of claims 1 to 3 further includes a re-irradiation step, wherein the aforementioned re-irradiation step is to irradiate the non-penetrated area formed during the period from when the photodetector unit detects the laser beam penetrating the wafer in the appropriate condition selection step with the laser beam again.

5. The wafer processing method of any one of claims 1 to 3 further includes a tape expansion step, wherein the tape expansion step is performed after the laser beam irradiation step.

6. The wafer processing method of claim 4 further includes a tape expansion step, wherein the tape expansion step is performed after the laser beam irradiation step.

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