Method for dividing stacked wafers
By forming cutting grooves of predetermined depths and using laser ablation to form dividing grooves, the method addresses crack formation and thickness limitations in laminated wafer division, ensuring effective cutting of both wafers.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- DISCO CORP
- Filing Date
- 2022-09-01
- Publication Date
- 2026-05-26
Smart Images
Figure 0007865832000001 
Figure 0007865832000002 
Figure 0007865832000003
Abstract
Description
Technical Field
[0001] The present invention relates to a method for dividing a laminated wafer in which a first wafer and a second wafer are attached via an adhesive layer into individual device chips.
Background Art
[0002] In recent years, there are cases where a laminated wafer in which a plurality of wafers are laminated is divided into a plurality of chips. For example, after forming a laminated wafer by joining the surface sides of a first wafer having a plurality of photodiodes on the surface side and a second wafer having a wiring layer on the surface side, thinning by grinding is performed, and the thinned laminated wafer is divided into a plurality of device chips by cutting.
[0003] By the way, when dividing a laminated wafer, when the first wafer and the second wafer are formed of different materials, generally, a first cutting blade suitable for cutting the first wafer is used to cut the first wafer, and a second cutting blade suitable for cutting the second wafer is used to cut the second wafer.
[0004] However, when an adhesive such as resin is used for joining the first wafer and the second wafer, the adhesive layer (hereinafter, adhesive layer) functions as a cushion, and cracks may be formed in the vicinity of the joining region of the first wafer and the second wafer. For example, when cutting the first wafer, if a cutting groove having a depth equal to or greater than a predetermined depth that does not reach the adhesive layer is formed, cracks extending to the adhesive layer are formed at the bottom of the cutting groove.
[0005] If cracks formed during cutting remain in the device chip, it causes chipping of the device chip and a decrease in strength. Therefore, it is desirable to reduce the amount of cracks. In order to solve this problem, it is conceivable to apply a technique (for example, Patent Document 1) in which a cutting groove shallower than a predetermined depth is formed in the first wafer, and then an ablation process is performed by irradiating a laser beam to the bottom of the shallow cutting groove.
[0006] In this way, by forming cutting grooves shallower than a predetermined depth, crack formation can be suppressed, and by removing the remaining cut area of the first wafer located below the cutting grooves shallower than the predetermined depth, as well as the adhesive layer, through ablation processing, it may be possible to form a dividing groove leading to the second wafer.
[0007] However, in order to cut the second wafer with the second cutting blade after the formation of this divided groove, the cutting edge thickness of the second cutting blade must be smaller than the width of the laser-processed groove formed by the ablation process. In reality, it is difficult to cut only the second wafer with a second cutting blade that has a cutting edge thickness smaller than the width of the laser-processed groove. [Prior art documents] [Patent Documents]
[0008] [Patent Document 1] Japanese Patent Publication No. 2018-67646 [Overview of the Initiative] [Problems that the invention aims to solve]
[0009] The present invention has been made in view of the aforementioned problems, and aims to reduce the amount of cracks formed when forming cutting grooves in the first wafer when dividing a stacked wafer, and to prevent the cutting thickness of the second cutting blade used when cutting the second wafer from being limited by the width of the laser processing groove. [Means for solving the problem]
[0010] According to one aspect of the present invention, a method for dividing a laminated wafer into individual device chips, wherein a second wafer is attached to the back surface of a first wafer via an adhesive layer, and each region of the first wafer is demarcated by a plurality of intersecting division lines set on the surface of the first wafer, the first wafer having devices in each region, the method comprising: a first cutting groove forming step in which, with the first wafer placed on the second wafer, the lower end of a first cutting blade is positioned between the front surface and the back surface of the first wafer, and the first wafer is cut with the first cutting blade along each division line to form a first cutting groove of a predetermined depth that does not reach the back surface and reduces the amount of cracks formed at the bottom; and after the first cutting groove forming step, the first A method for splitting a laminated wafer is provided, comprising: a division groove forming step of irradiating the first wafer and the adhesive layer along the first cutting groove with a pulsed laser beam having a wavelength absorbed by the wafer to ablate the first wafer and the adhesive layer to cut the first wafer and the adhesive layer along each planned division line to form a division groove leading to the second wafer; and a blade splitting step of, after the division groove forming step, positioning the second wafer on the first wafer, positioning the lower end of the second cutting blade to reach the division groove, and cutting the linear region of the second wafer corresponding to each planned division line in the thickness direction of the laminated wafer with the second cutting blade to split the laminated wafer.
[0011] Preferably, the first wafer has a silicon substrate formed of single-crystal silicon, and the second wafer has a glass substrate formed of glass material.
[0012] Preferably, the predetermined depth is 85% to 90% of the thickness of the first wafer from the surface.
[0013] According to another aspect of the present invention, a method for dividing a laminated wafer into individual device chips, wherein a second wafer is attached to the back surface of a first wafer via an adhesive layer, and each region of the first wafer is demarcated by a plurality of intersecting division lines set on the surface of the first wafer, the second wafer having devices in each region, the method comprising: a first cutting groove forming step in which, with the first wafer placed on the second wafer, the lower end of a first cutting blade is positioned between the front and back surfaces of the first wafer, and the first wafer is cut with the first cutting blade along each division line to form a first cutting groove of a predetermined depth that does not reach the back surface and reduces the amount of cracks formed at the bottom; and after the first cutting groove forming step, with the second wafer placed on the first wafer, one surface of the second wafer located on the adhesive layer side and the thickness direction of the second wafer A method for dividing a laminated wafer is provided, comprising: a second cutting groove forming step, in which the lower end of a second cutting blade is positioned between one surface and another surface located on the opposite side, and the second cutting blade is used to cut a linear region of the second wafer corresponding to each planned division line in the thickness direction of the laminated wafer, thereby forming a second cutting groove of a predetermined depth that does not reach the first surface and reduces the amount of cracks formed at the bottom; and a laser division step, in which, after the second cutting groove forming step, the second wafer is placed on the first wafer, and a pulsed laser beam having a wavelength absorbed by the first wafer and the second wafer is irradiated along the second cutting groove to ablate the second wafer, the adhesive layer and the first wafer, thereby cutting the second wafer, the adhesive layer and the first wafer along each planned division line and dividing the laminated wafer.
[0014] Preferably, the predetermined depth of the first cutting groove is 85% to 90% of the thickness of the first wafer from the surface, and the predetermined depth of the second cutting groove is 85% to 90% of the thickness of the second wafer from the other surface. [Effects of the Invention]
[0015] In a method for dividing a stacked wafer according to one aspect of the present invention, the first wafer is cut with a first cutting blade to form a first cutting groove of a predetermined depth that does not reach the back surface of the first wafer and reduces the amount of cracks formed at the bottom (first cutting groove formation step).
[0016] Subsequently, a laser beam is irradiated onto the first cutting groove to ablate the first wafer and the adhesive layer, thereby forming a dividing groove leading to the second wafer (dividing groove formation process). After the dividing groove formation process, the second wafer is placed on top of the first wafer and the second wafer is cut with the second cutting blade to divide the stacked wafer (blade division process).
[0017] Therefore, the amount of cracks formed on the first wafer during the first cutting groove formation process can be reduced, and the second wafer can be cut with the second cutting blade without the blade thickness being limited by the width of the laser-processed groove.
[0018] In another aspect of the present invention, a method for splitting a stacked wafer involves cutting the first wafer with a first cutting blade to form a first cutting groove of a predetermined depth that does not reach the back surface of the first wafer and reduces the amount of cracks formed at the bottom (first cutting groove formation step).
[0019] Subsequently, with the second wafer placed on the first wafer, the second wafer is cut with a second cutting blade to form a second cutting groove of a predetermined depth that does not reach the surface in contact with the adhesive layer and reduces the amount of cracks formed at the bottom of the second wafer (second cutting groove formation step).
[0020] Therefore, the amount of cracks formed on the first wafer in the first cutting groove formation process and the amount of cracks formed on the second wafer in the second cutting groove formation process can be reduced, and the second wafer can be cut with the second cutting blade without the blade thickness of the second cutting blade being limited by the width of the laser processing groove.
[0021] Furthermore, after the second cutting groove forming step, the second wafer, the adhesive layer, and the first wafer are ablated by irradiating the second cutting groove with a laser beam, so that the second wafer, the adhesive layer, and the first wafer can be cut and the stacked wafer can be divided (laser splitting step).
Brief Description of the Drawings
[0022] [Figure 1] It is a flowchart of a method for splitting a stacked wafer according to the first embodiment. [Figure 2] FIG. 2(A) is a perspective view of the stacked wafer, and FIG. 2(B) is a cross-sectional view of the stacked wafer. [Figure 3] FIG. 3(A) is a perspective view of the first cutting groove forming step, and FIG. 3(B) is a cross-sectional view of the stacked wafer in the first cutting groove forming step. [Figure 4] FIG. 4(A) is a perspective view of the splitting groove forming step, and FIG. 4(B) is a cross-sectional view of the stacked wafer in the splitting groove forming step. [Figure 5] It is a perspective view showing the inversion step. [Figure 6] FIG. 6(A) is a perspective view of the blade splitting step, and FIG. 6(B) is a cross-sectional view of the stacked wafer in the blade splitting step. [Figure 7] It is a flowchart of a method for splitting a stacked wafer according to the second embodiment. [Figure 8] FIG. 8(A) is a perspective view of the second cutting groove forming step, and FIG. 8(B) is a cross-sectional view of the stacked wafer in the second cutting groove forming step. [Figure 9] FIG. 9(A) is a perspective view of the laser splitting step, and FIG. 9(B) is a cross-sectional view of the stacked wafer in the laser splitting step.
Embodiments for Carrying Out the Invention
[0023] Referring to the accompanying drawings, embodiments according to an aspect of the present invention will be described. FIG. 1 is a flowchart of a method for splitting a stacked wafer 11 (see FIG. 2(A), etc.) according to the first embodiment. First, referring to FIGS. 2(A) and 2(B), the stacked wafer 11 will be described.
[0024] Figure 2(A) is a perspective view of the stacked wafer 11, and Figure 2(B) is a cross-sectional view of the stacked wafer 11. The stacked wafer 11 includes a first wafer 21. The first wafer 21 has a disc-shaped silicon substrate formed of single-crystal silicon.
[0025] The first wafer 21 is not limited to silicon, but may have a disc-shaped single-crystal substrate made of other semiconductor materials such as silicon carbide (SiC) or gallium nitride (GaN). Multiple division lines (stories) 23 that are orthogonal to each other (i.e., intersecting at a 90-degree angle) are set on the surface 21a side of the first wafer 21.
[0026] A device 25 is formed in each of the rectangular regions demarcated by multiple division lines 23. The devices 25 include ICs (Integrated Circuits), LEDs (Light Emitting Diodes), MEMS (Micro Electro Mechanical Systems), etc.
[0027] The distance from the front surface 21a to the back surface 21b of the first wafer 21 (i.e., the thickness 21c) is, for example, 200 μm. An adhesive layer 31 is provided over substantially the entire back surface 21b of the first wafer 21. The adhesive layer 31 is formed of, for example, an acrylic, epoxy, or rubber-based adhesive.
[0028] A preferred example of the adhesive layer 31 is an ultraviolet (UV) curing resin, but the adhesive layer 31 may also be a thermosetting resin. The adhesive layer 31 is already cured, and for example, the thickness 31c of the adhesive layer 31 is 40 μm. However, the thickness 31c is not limited to this value.
[0029] The front surface (one side) 41a of a second wafer 41, which has approximately the same diameter as the first wafer 21, is attached to the back surface 21b side of the first wafer 21 via an adhesive layer 31. The second wafer 41 has a glass substrate made of a substantially transparent glass material that transmits light in the visible light band.
[0030] The second wafer 41 in the first embodiment is entirely made of alkali-free glass. However, the glass material is not limited to this and may be made of synthetic quartz glass or the like. The back surface (other surface) 41b of the second wafer 41 is located on the opposite side from the front surface 41a in the thickness direction A1 of the second wafer 41.
[0031] The front surface 41a and the back surface 41b are both substantially flat, and the distance from the front surface 41a to the back surface 41b (i.e., the thickness 41c) is, for example, 300 μm. A first dicing tape 13, which is larger in diameter and circular than the second wafer 41, is attached to the back surface 41b side of the second wafer 41.
[0032] The first dicing tape 13 has a laminated structure in which, for example, a base layer and an adhesive layer are laminated. The base layer is made of, for example, a polyolefin such as polyethylene or polypropylene, or a resin such as polyethylene terephthalate.
[0033] Furthermore, the adhesive layer is formed from an adhesive such as an acrylic, epoxy, or rubber-based adhesive. A suitable example of the adhesive layer is an ultraviolet-curing resin. Note that the first dicing tape 13 is omitted in Figure 2(B).
[0034] The back surface 41b of the second wafer 41 is attached to the center of the first dicing tape 13, and one side 15a of a metal annular frame 15 is attached to the outer periphery of the first dicing tape 13.
[0035] The annular frame 15 has an opening 15b with a larger diameter than the stacked wafer 11. The stacked wafer 11 is supported by the annular frame 15 via the first dicing tape 13 while positioned in the opening 15b. In this way, the processing of the stacked wafer 11 is started with the first wafer 21 positioned on top of the second wafer 41 in the state of a stacked wafer unit 17.
[0036] First, the stacked wafer unit 17 is transported to the cutting device 2, and as shown in Figures 3(A) and 3(B), the first wafer 21 is cut by the cutting device 2 to form a first cutting groove 27 with a predetermined depth 27b that does not reach the back surface 21b (first cutting groove formation step S10).
[0037] The cutting apparatus 2 has a disc-shaped chuck table (not shown) that holds the stacked wafers 11 of the stacked wafer unit 17 by suction. Multiple clamp units (not shown) are provided on the outer circumference of the chuck table, each clamping one surface 15a and the other surface 15c of the annular frame 15.
[0038] The chuck table moves along the X-axis direction of the cutting device 2 by a ball screw type X-axis movement mechanism (not shown). The chuck table is also configured to rotate around a rotation axis located along the Z-axis direction of the cutting device 2.
[0039] A first cutting unit 4 is provided above the chuck table. The first cutting unit 4 is configured to be movable along the Y-axis direction by a ball screw type Y-axis direction movement mechanism (not shown).
[0040] Furthermore, the first cutting unit 4 is configured to be movable along the Z-axis direction by a ball screw type Z-axis direction movement mechanism (not shown). Note that the X-axis, Y-axis, and Z-axis directions are mutually orthogonal.
[0041] The first cutting unit 4 has a cylindrical spindle (not shown) whose longitudinal portion is arranged along the Y-axis. A portion of the spindle is rotatably housed in a spindle housing (not shown). A rotational drive source (not shown), such as a servo motor, is provided near the base end of the spindle.
[0042] The tip of the spindle protrudes from the spindle housing, and a first cutting blade 6 having an annular cutting edge is mounted on the tip of the spindle. A blade cover 8 is fixed to the tip of the spindle housing.
[0043] The blade cover 8 is provided with a pair of cooler nozzles 10 so as to sandwich the first cutting blade 6 in the Y-axis direction. Figure 3(A) shows one of the pair of cooler nozzles 10. The pair of cooler nozzles 10 supply cutting fluid (not shown), such as pure water, to the vicinity of the machining point of the cutting edge.
[0044] A nozzle block (not shown) is provided on the side of the blade cover 8 located on the tip side of the pair of cooler nozzles 10 in the X-axis direction. The nozzle block has a spray nozzle (not shown) located at approximately the same height as the pair of cooler nozzles 10.
[0045] The nozzle block further includes a shower nozzle (not shown) located slightly above the spray nozzle. The spray nozzle and shower nozzle supply cutting fluid, such as pure water, to the outer circumference of the cutting edge.
[0046] A first microscope camera unit (not shown) for imaging subjects with visible light is provided near the spindle housing. The first microscope camera unit includes a focusing lens, a visible light image sensor, a light-emitting element for emitting visible light, and the like.
[0047] Figure 3(A) is a perspective view of the first cutting groove formation process S10, and Figure 3(B) is a cross-sectional view of the stacked wafer 11 in the first cutting groove formation process S10. In the first cutting groove formation process S10, the stacked wafer 11 is first held by suction on the holding surface of the chuck table via the first dicing tape 13, and the annular frame 15 is fixed with each clamp unit.
[0048] Next, alignment is performed using the first microscope camera unit, and the orientation of the chuck table is adjusted so that the planned division line 23, which is aligned in one direction, is approximately parallel to the X-axis direction. Then, the first cutting blade 6, which is rotated at high speed, is positioned on the extension of the planned division line 23.
[0049] Then, with the lower end position 6a of the first cutting blade 6 positioned between the front surface 21a and the back surface 21b of the first wafer 21, cutting fluid is supplied to the first cutting blade 6 while the chuck table is moved along the X-axis at a predetermined machining feed rate.
[0050] As a result, the first cutting blade 6 cuts the first wafer 21 along one planned division line 23, forming a first cutting groove 27 of a predetermined depth 27b. In other words, the first cutting groove 27 is not a so-called full-cut groove that cuts the first wafer 21, but rather a so-called half-cut groove that leaves a remaining area without cutting the first wafer 21.
[0051] In particular, the lower end position 6a of the first cutting blade 6 is positioned at a predetermined depth 27b that does not reach the back surface 21b and reduces the amount of cracks formed at the bottom 27a of the first cutting groove 27.
[0052] In the first embodiment, the predetermined depth 27b is a thickness of 85% to 90% of the thickness 21c of the first wafer 21 from the surface 21a. For example, if the thickness 21c is 200 μm, the predetermined depth 27b is 170 μm to 180 μm.
[0053] In the first embodiment, by leaving 10% to 15% of the thickness 21c of the first wafer 21, the cushioning effect of the adhesive layer 31 can be almost eliminated, thereby reducing the amount of cracks extending from the bottom 27a of the first cutting groove 27 to the adhesive layer 31.
[0054] Incidentally, in the first cutting groove formation step S10, it is also conceivable to cut the first wafer 21 with the first cutting blade 6 to form a cutting groove leading to the adhesive layer 31. This may allow for the removal of the cracked area even if a crack is formed in the first wafer 21.
[0055] However, if a cutting groove exceeding a predetermined depth of 27b is formed, the cushioning effect of the adhesive layer 31 during groove formation causes a crack to form on the surface 41a side of the second wafer 41.
[0056] In contrast, it is also possible to reduce the amount of cracks extending from the adhesive layer 31 to the second wafer 41.
[0057] Next, the first cutting unit 4 is moved by a predetermined index amount along the Y-axis direction, and the first cutting blade 6 is positioned on the extension in the X-axis direction of another division line 23 adjacent in the Y-axis direction to the already cut division line 23.
[0058] Then, the first wafer 21 is cut in the same manner along the other planned division lines 23. In this way, the first wafer 21 is cut along each planned division line 23 along one direction. Next, the chuck table is rotated 90 degrees around a predetermined axis of rotation so that one of the planned division lines 23 along the other direction is approximately parallel to the X-axis direction.
[0059] Then, the first wafer 21 is similarly cut along each planned division line 23 in the other direction. This forms a first cutting groove 27 of a predetermined depth 27b along each planned division line 23 of the first wafer 21. The cutting conditions are, for example, as follows:
[0060] Spindle rotation speed: 30,000 rpm Machining feed rate: 20 mm / s Cutting fluid from a pair of cooler nozzles: 1.5 L / min Cutting fluid from spray nozzle: 1.0 L / min Cutting water flow from shower nozzle: 1.0 L / min
[0061] Furthermore, the cutting edge of the first cutting blade 6 has, for example, a blade thickness of 60 μm. This cutting edge has diamond abrasive grains (grit size: #3000) and an electroformed bond that fixes the abrasive grains. The specification of the grit size follows or is equivalent to JIS R6001-2:2017 of the Japanese Industrial Standards (JIS).
[0062] After the first cutting groove formation step S10, as shown in Figures 4(A) and 4(B), a laser beam L is irradiated along each first cutting groove 27 to ablate the first wafer 21 and the adhesive layer 31, thereby cutting the remaining portion of the first wafer 21 and the adhesive layer 31 along each planned division line 23, and forming a division groove 53 leading to the second wafer 41 (division groove formation step S20).
[0063] In the groove formation process S20, a laser processing device 12 is used. The laser processing device 12 has a chuck table (not shown) similar to that of the cutting device 2. A laser irradiation unit 14 is provided above the chuck table. The laser irradiation unit 14 has a laser oscillator (not shown).
[0064] The laser beam L is emitted from the laser oscillator, passes through the focuser 16, and is directed toward the chuck table. The focuser 16 includes a focusing lens (not shown) and is configured to be movable along the Y-axis and Z-axis directions by a Y-axis movement mechanism and a Z-axis movement mechanism (both not shown).
[0065] The optical axis of the focusing lens is positioned approximately parallel to the Z-axis direction. The laser beam L emitted from the focusing device 16 is pulsed, with a power peak that repeats at a predetermined repetition frequency, and has a predetermined wavelength that is absorbed by the first wafer 21.
[0066] In the groove formation process S20, first, a water-soluble resin film 51 is formed on the surface 21a side of the first wafer 21 using a spinner coating and cleaning device (not shown). The water-soluble resin film 51 is formed by applying a liquid resin almost uniformly to the surface 21a side and then drying it.
[0067] The liquid resin to be applied includes water-soluble resins such as polyvinyl alcohol and polyethylene glycol, light absorbers such as ferulic acid and dihydroxybenzophenone, additives, and other materials. After the formation of the water-soluble resin film 51, the laminated wafer unit 17 is transported to the laser processing apparatus 12.
[0068] Then, the orientation of the chuck table is adjusted so that the planned division line 23 along one direction is approximately parallel to the X-axis direction. Next, with the focusing point of the laser beam L positioned at the height of the bottom 27a of the first cutting groove 27, the chuck table is fed along the X-axis direction at a predetermined machining feed rate.
[0069] Figure 4(A) is a perspective view of the groove formation process S20, and Figure 4(B) is a cross-sectional view of the laminated wafer 11 during the groove formation process S20. In the groove formation process S20, the laser beam L is irradiated so that the focal point of the laser beam L moves along the planned division line 23 multiple times.
[0070] Specifically, after moving the focusing point from one end to the other along the X-axis direction on the planned division line 23 (i.e., the first pass of laser processing), the focusing point is moved in the opposite direction to the first pass, from the other end to the other end along the X-axis direction on the same planned division line 23 (i.e., the second pass of laser processing). In the same manner, a total of 10 passes of laser processing are performed.
[0071] By irradiating with the laser beam L, the remaining portion of the first wafer 21 (i.e., the region from the bottom 27a of the first cutting groove 27 to the back surface 21b) and the portion of the adhesive layer 31 located below the said remaining portion are removed by ablation.
[0072] Since the spot diameter of the laser beam L is smaller than the cutting thickness of the first cutting blade 6, the laser-processed groove 29 formed on the first wafer 21 by ablation processing and the laser-processed groove 33 formed on the adhesive layer 31 by ablation processing are both narrower than the first cutting groove 27.
[0073] In the first embodiment, the first cutting groove 27 and the laser-processed grooves 29 and 33 are collectively referred to as the dividing groove 53. After forming the dividing grooves 53 along each planned dividing line 23, the debris (not shown) generated by the laser processing is removed together with the water-soluble resin film 51 using a spinner coating and cleaning device, and the surface 21a side is cleaned.
[0074] The laser processing conditions are, for example, as follows:
[0075] Laser beam wavelength: 355nm Average output of laser beam: 10W Laser beam repetition frequency: 100kHz Laser beam spot diameter: 35 μm Machining feed rate: 400 mm / s Number of passes: 10 passes
[0076] After the groove formation process S20, the first wafer 21 and the second wafer 41 are inverted so that the second wafer 41 is exposed (inversion process S30). Figure 5 is a perspective view showing the inversion process S30.
[0077] Specifically, first, the laminated wafer unit 17 is removed from the laser processing apparatus 12. Then, a circular second dicing tape 63 made of resin is attached to the surface 21a of the first wafer 21 and the other surface 15c of the annular frame 15. Next, the first dicing tape 13 is peeled off from the back surface 41b of the second wafer 41 and one surface 15a of the annular frame 15.
[0078] For example, the first dicing tape 13 is irradiated with ultraviolet light to reduce the adhesive strength of the adhesive layer of the first dicing tape 13, and then the first dicing tape 13 is peeled off to form an inverted stacked wafer unit 37.
[0079] The second dicing tape 63 has a laminated structure in which a base layer and an adhesive layer are laminated, similar to the first dicing tape 13. However, the second dicing tape 63 may not have an adhesive layer and may consist only of a base layer, and this base layer may be attached to the first wafer 21 by heat compression bonding.
[0080] After the inversion process S30, the inverted stacked wafer unit 37 is returned to the cutting device 2. As shown in Figure 6(A), the cutting device 2 has a second cutting unit 34 above the chuck table, which is different from the first cutting unit 4.
[0081] The structure of the second cutting unit 34 is substantially the same as that of the first cutting unit 4. The second cutting unit 34 is also configured to be movable along the Y-axis and Z-axis using ball screw type Y-axis movement mechanisms and Z-axis movement mechanisms (neither of which are shown).
[0082] A second cutting blade 36 having an annular cutting edge is mounted at the tip of the spindle of the second cutting unit 34. The cutting edge of the second cutting blade 36 has, for example, a blade thickness of 40 μm. This cutting edge has diamond abrasive grains (grit size: #1200) and a metal bond that fixes the abrasive grains.
[0083] The second cutting unit 34 also has a blade cover 38 fixed to the tip of the spindle housing, and a pair of cooler nozzles 40 are arranged on the blade cover 38 so as to sandwich the second cutting blade 36 in the Y-axis direction. In Figure 6(A), one of the pair of cooler nozzles 40 is shown.
[0084] A nozzle block (not shown) is provided on the side of the blade cover 38 located on the tip side of the pair of cooler nozzles 40 in the X-axis direction. The nozzle block has a spray nozzle (not shown) located at approximately the same height as the pair of cooler nozzles 40.
[0085] The nozzle block further includes a shower nozzle (not shown) located slightly above the spray nozzle. The spray nozzle and shower nozzle supply cutting fluid, such as pure water, to the outer circumference of the cutting edge of the second cutting blade 36.
[0086] A second microscope camera unit (not shown) for imaging subjects with infrared light is provided near the spindle housing. The second microscope camera unit includes a focusing lens, an image sensor for infrared light, a light-emitting element for emitting infrared light, and the like.
[0087] Figure 6(A) is a perspective view of the blade splitting process S40, and Figure 6(B) is a cross-sectional view of the stacked wafer 11 in the blade splitting process S40. In the blade splitting process S40, first, the inverted stacked wafer unit 37 is held in place by suction using a chuck table.
[0088] In other words, the stacked wafer 11 is held in place by suction at the holding surface via the second dicing tape 63, and the annular frame 15 is fixed with each clamp unit. At this time, the second wafer 41 is placed on top of the first wafer 21, so the second wafer 41 is exposed.
[0089] Next, alignment is performed using the second microscope camera unit, and the orientation of the chuck table is adjusted so that the planned division line 23, which is aligned in one direction, is approximately parallel to the X-axis direction. Then, the second cutting blade 36 is rotated at high speed and positioned on the extension of the planned division line 23.
[0090] Subsequently, the lower end position 36a of the second cutting blade 36 is positioned to reach the divided groove 53, and while supplying cutting fluid such as pure water to the second cutting blade 36, the chuck table is machined along the X-axis at a predetermined machining feed rate.
[0091] This allows the second wafer 41 to be cut along one planned division line 23 using the second cutting blade 36. After the second cutting blade 36 has cut a linear region 41d of the second wafer 41 corresponding to each planned division line 23 along one direction in the thickness direction A2 of the stacked wafer 11, the chuck table is rotated 90 degrees.
[0092] Then, the linear regions 41d of the second wafer 41 corresponding to each planned division line 23 along the other directions are similarly cut with the second cutting blade 36. The cutting conditions are, for example, as follows:
[0093] Spindle rotation speed: 30,000 rpm Machining feed speed: 3mm / s Cutting fluid from a pair of cooler nozzles: 1.5 L / min Cutting fluid from spray nozzle: 1.0 L / min Cutting water flow from shower nozzle: 1.0 L / min
[0094] By cutting the linear region 41d of the second wafer 41 corresponding to each planned division line 23 in the thickness direction A2 of the stacked wafer 11 with the second cutting blade 36, the stacked wafer 11 is divided into individual device chips 19a (see Figure 6(B)).
[0095] In the blade splitting process S40, the second wafer 41 is cut by the second cutting blade 36 (so-called full cut), but at this time, since the first wafer 21 has already been cut, virtually no cracks are formed in the first wafer 21.
[0096] In the first embodiment, the amount of cracks formed when the first cutting groove 27 is formed in the first wafer 21 can be reduced, and the second wafer 41 can be cut with the second cutting blade 36 without the blade thickness of the second cutting blade 36 being limited by the width of the laser processing grooves 29 and 33.
[0097] By the way, in the alignment process S40, instead of using infrared light, the second wafer 41 of the inverted stacked wafer unit 37 may be cut with the second cutting blade 36 using a chuck table that is partially transparent in the thickness direction and a visible light microscope camera unit located below the chuck table.
[0098] (Second Embodiment) Next, a second embodiment will be described with reference to Figures 7 to 9. Figure 7 is a flowchart of the method for splitting the stacked wafer 11 according to the second embodiment. In the second embodiment as well, the stacked wafer 11 is processed, but the second wafer 41 in the second embodiment has the same single-crystal substrate as the first wafer 21, instead of a glass substrate.
[0099] The surface 41a of the second wafer 41 is located on the side of the adhesive layer 31. The second wafer 41 is fixed to the back surface 21b of the first wafer 21 via the adhesive layer 31. Devices 25, wiring layers, etc. may or may not be formed on the surface 41a of the second wafer 41.
[0100] In the method for splitting the stacked wafer 11 according to the second embodiment, after the first cutting groove formation step S10, the process proceeds to the inversion step S30 without going through the split groove formation step S20. Then, in the second cutting groove formation step S32, a second cutting groove 43 (see Figure 8(B)) is formed on the second wafer 41.
[0101] Subsequently, in the laser splitting process S42, the remaining areas of the first wafer 21 and the second wafer 41, corresponding to the planned splitting lines 23 in the thickness direction A2 of the stacked wafer 11, and the adhesive layer 31 are removed by ablation (see Figure 9(B)).
[0102] Since this differs from the first embodiment, the description will mainly focus on the content from the second cutting groove formation process S32 onward. Note that the same reference numerals are used for parts, structures, processes, etc., as in the first embodiment, and their descriptions may be omitted.
[0103] Figure 8(A) is a perspective view of the second cutting groove formation process S32, and Figure 8(B) is a cross-sectional view of the stacked wafer 11 during the second cutting groove formation process S32. In the second cutting groove formation process S32, the second wafer 41 transports the inverted stacked wafer unit 37, which is placed on top of the first wafer 21, to the cutting apparatus 2.
[0104] Then, the stacked wafer 11 is held in place by suction at the holding surface via the second dicing tape 63, and the annular frame 15 is fixed with each clamp unit. Next, alignment is performed using the second microscope camera unit, and the orientation of the chuck table is adjusted so that the planned division line 23 along one direction is approximately parallel to the X-axis direction.
[0105] With the second cutting blade 36 rotating at high speed, it is positioned on the extension of the planned division line 23. Then, the lower end position 36a of the second cutting blade 36 is positioned between the front surface 41a and the back surface 41b of the second wafer 41. While supplying cutting fluid such as pure water to the second cutting blade 36, the chuck table is fed along the X-axis at a predetermined machining feed rate.
[0106] As a result, the second cutting blade 36 cuts the linear region 41d of the second wafer 41 corresponding to each planned division line 23 along one direction in the thickness direction A2 of the stacked wafer 11, forming a second cutting groove 43 with a predetermined depth 43b that does not reach the surface 41a.
[0107] In particular, the lower end position 36a of the second cutting blade 36 is positioned at a predetermined depth 43b that does not reach the surface 41a and reduces the amount of cracks formed at the bottom 43a of the second cutting groove 43.
[0108] In the second embodiment, the predetermined depth 43b is 85% to 90% of the thickness 21c of the second wafer 41, from the back surface 41b. For example, if the thickness 21c is 300 μm, the predetermined depth 43b is 255 μm to 270 μm.
[0109] In other words, the second cutting groove 43 is not a so-called full-cut groove that cuts the second wafer 41, but rather a so-called half-cut groove that leaves a region uncut without cutting the second wafer 41.
[0110] After forming a second cutting groove 43 in the linear region 41d corresponding to each planned division line 23 along one direction, a second cutting groove 43 is similarly formed in the linear region 41d corresponding to each planned division line 23 along the other direction. The cutting conditions may be the same as those for the first cutting groove formation step S10. The cutting conditions for the second cutting groove formation step S32 are, for example, as follows.
[0111] Spindle rotation speed: 30,000 rpm Machining feed rate: 20 mm / s Cutting fluid from a pair of cooler nozzles: 1.5 L / min Cutting fluid from spray nozzle: 1.0 L / min Cutting water flow from shower nozzle: 1.0 L / min
[0112] In the second embodiment, the second cutting blade 36 has approximately the same blade thickness as the first cutting blade 6 and approximately the same grain size as the abrasive grains of the first cutting blade 6. The second cutting blade 36 has, for example, a blade thickness of 60 μm, and diamond abrasive grains are fixed with an electroformed bond.
[0113] In the first cutting groove formation step S10 of the second embodiment, by leaving 10% to 15% of the thickness 21c of the first wafer 21, the effect of the cushioning action of the adhesive layer 31 can be almost eliminated, thereby reducing the amount of cracks extending from the bottom 27a of the first cutting groove 27 to the adhesive layer 31. At the same time, the amount of cracks extending from the adhesive layer 31 to the second wafer 41 can also be reduced.
[0114] Furthermore, in the second cutting groove formation step S32, by leaving 10% to 15% of the thickness 41c of the second wafer 41, the cushioning effect of the adhesive layer 31 can be almost eliminated, thereby reducing the amount of cracks extending from the bottom 43a of the second cutting groove 43 to the adhesive layer 31. At the same time, the amount of cracks extending from the adhesive layer 31 to the first wafer 21 can also be reduced.
[0115] After the second cutting groove formation step S32, as shown in Figures 9(A) and 9(B), a water-soluble resin film 51 is formed on the back surface 41b side of the second wafer 41 in the inverted stacked wafer unit 37, and then the laser splitting step S42 is performed with the laser processing apparatus 12.
[0116] Figure 9(A) is a perspective view of the laser splitting process S42, and Figure 9(B) is a cross-sectional view of the stacked wafer 11 during the laser splitting process S42. In the laser splitting process S42, a laser beam L is irradiated along each second cutting groove 43 to ablate the second wafer 41, the adhesive layer 31, and the first wafer 21.
[0117] This cuts the remaining portion of the second wafer 41, the adhesive layer 31, and the remaining portion of the first wafer 21 along each planned division line 23, dividing the stacked wafer 11 into multiple device chips 19b (see Figure 9(B)) (laser division process S42).
[0118] The laser processing conditions are, for example, the same as those used in the division groove formation process S20 described above. After division, the debris (not shown) generated by the laser processing is removed together with the water-soluble resin film 51 using a spinner coating and cleaning device, and the back surface 41b is cleaned.
[0119] In the second embodiment, the amount of cracks formed when the first cutting groove 27 and the second cutting groove 43 are formed can be reduced, and the second wafer 41 can be cut with the second cutting blade 36 without the cutting edge thickness of the second cutting blade 36 being limited by the width of the laser-processed grooves 29 and 33.
[0120] Furthermore, the structures, methods, etc., according to the above embodiments can be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of symbols]
[0121] 2: Cutting device, 4: First cutting unit, 6: First cutting blade, 6a: Lower end position 8: Blade cover, 10: Cooler nozzle 11: Multilayer wafer, 13: First dicing tape 12: Laser processing device, 14: Laser irradiation unit, 16: Focuser 15: Annular frame, 15a: One side, 15b: Opening, 15c: Other side 17: Stacked wafer unit, 19a, 19b: Device chip 21: First wafer, 21a: Front surface, 21b: Back surface, 21c: Thickness 23: Planned splitting line, 25: Device 27: First cutting groove, 27a: Bottom, 27b: Determined depth 29,33: Laser-cut grooves 31: Adhesive layer, 31c: Thickness 34: Second cutting unit, 36: Second cutting blade, 36a: Lower end position 37: Inverted stacked wafer unit 38: Blade cover, 40: Cooler nozzle 41: Second wafer 41a: Front surface (one side), 41b: Back surface (other side), 41c: Thickness, 41d: Linear region 43: Second cutting groove, 43a: Bottom, 43b: Determined depth 51: Water-soluble resin film 53: Dividing groove 63: Second dicing tape A1, A2: Thickness direction, L: Laser beam S10: First cutting groove formation process, S20: Division groove formation process S30: Inversion process, S32: Second cutting groove formation process S40: Blade splitting process, S42: Laser splitting process
Claims
1. A method for dividing a laminated wafer into individual device chips, wherein a second wafer is attached to the back surface of a first wafer via an adhesive layer, and each region of the first wafer has a device in it, defined by a plurality of intersecting division lines set on the surface of the first wafer, the second wafer having a device in each region, the second wafer having a device in each region, the second wafer having a device in each region, the second wafer having a device on the back surface of the first wafer With the first wafer placed on the second wafer, the lower end of the first cutting blade is positioned between the front and back surfaces of the first wafer, and the first wafer is cut with the first cutting blade along each planned division line to form a first cutting groove of a predetermined depth that does not reach the back surface and reduces the amount of cracks formed at the bottom; A division groove formation step is performed after the first cutting groove formation step, in which a pulsed laser beam having a wavelength absorbed by the first wafer is irradiated along the first cutting groove to ablate the first wafer and the adhesive layer, thereby cutting the first wafer and the adhesive layer along each planned division line and forming division grooves leading to the second wafer. After the division groove formation step, with the second wafer placed on the first wafer, the lower end of the second cutting blade is positioned to reach the division groove, and the linear region of the second wafer corresponding to each planned division line in the thickness direction of the stacked wafer is cut with the second cutting blade to divide the stacked wafer in a blade division step. A method for dividing a stacked wafer, characterized by comprising the following:
2. The method for splitting a stacked wafer according to claim 1, characterized in that the first wafer has a silicon substrate formed of single-crystal silicon, and the second wafer has a glass substrate formed of glass material.
3. The method for dividing a laminated wafer according to claim 1 or 2, characterized in that the predetermined depth is a thickness of 85% or more and 90% or less of the thickness of the first wafer from the surface.
4. A method for dividing a laminated wafer into individual device chips, wherein a second wafer is attached to the back surface of a first wafer via an adhesive layer, and each region of the first wafer has a device in it, defined by a plurality of intersecting division lines set on the surface of the first wafer, the second wafer having a device in each region, the second wafer having a device in each region, the second wafer having a device in each region, the second wafer having a device on the back surface of the first wafer With the first wafer placed on the second wafer, the lower end of the first cutting blade is positioned between the front and back surfaces of the first wafer, and the first wafer is cut with the first cutting blade along each planned division line to form a first cutting groove of a predetermined depth that does not reach the back surface and reduces the amount of cracks formed at the bottom; A second cutting groove formation step is performed after the first cutting groove formation step, with the second wafer placed on the first wafer, the lower end of the second cutting blade is positioned between one surface of the second wafer located on the adhesive layer side and another surface located on the opposite side in the thickness direction of the second wafer, and the second cutting blade is used to cut a linear region of the second wafer corresponding to each planned division line in the thickness direction of the stacked wafer, thereby forming a second cutting groove of a predetermined depth that does not reach the surface and reduces the amount of cracks formed at the bottom. After the second cutting groove formation step, with the second wafer placed on the first wafer, a pulsed laser beam having a wavelength absorbed by the first wafer and the second wafer is irradiated along the second cutting groove to ablate the second wafer, the adhesive layer and the first wafer, thereby cutting the second wafer, the adhesive layer and the first wafer along each planned division line and dividing the stacked wafer in a laser division step. A method for dividing a stacked wafer, characterized by comprising the following:
5. The predetermined depth of the first cutting groove is 85% to 90% of the thickness of the first wafer from the surface. The method for dividing a laminated wafer according to claim 4, characterized in that the predetermined depth of the second cutting groove is 85% or more and 90% or less of the thickness of the second wafer from the other surface.