Method for grinding stacked wafers

Abstract

To more securely remove an annular region of a peripheral part of a first wafer in a laminated wafer.SOLUTION: There is provided a laminated wafer grinding method including: a modified layer forming step of applying a laser beam having such a wavelength as to be transmitted through a first wafer to the first wafer along a first annular line to be processed set on an inner side of a peripheral edge of the first wafer to form a first annular modified layer and applying the laser beam to the first wafer along one or more second lines to be processed set in an annular region from the first line to be processed to the peripheral edge of the first wafer to form a second modified layer that partitions the annular region into two or more parts; a trimming step of causing a cutting blade to cut into the annular region to a predetermined depth of the first wafer in a depth direction to cut the annular region; and a grinding step of grinding a second surface side of the first wafer to thin the first wafer to a finished thickness and removing the annular region.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a method for grinding a laminated wafer in which a first wafer and a second wafer, both of which have chamfered outer peripheries on both sides, are laminated, and which involves grinding and thinning the first wafer. [Background technology]

[0002] When the back side of a semiconductor wafer (hereinafter simply referred to as wafer) having chamfered portions formed on the outer periphery of each of the front and back sides is ground to thin the wafer to, for example, half or less of its original thickness, a so-called knife edge (also called a sharp edge) is formed on the outer periphery of the wafer after thinning.

[0003] When a knife edge is formed, the wafer is likely to crack from the knife edge during grinding or transportation of the wafer. To prevent this, a processing method has been proposed in which a cutting blade is inserted into the outer periphery of the wafer from the front surface to a specified depth corresponding to the finishing thickness, the chamfer on the front surface is removed by cutting (i.e., edge trimming is performed), and then the back surface of the wafer is ground.

[0004] Also, a method has been proposed in which, instead of using a cutting blade, a laser beam having a wavelength that passes through the wafer or a laser beam having a wavelength that is absorbed by the wafer is used to remove the outer periphery of a wafer having a chamfer formed on the outer periphery (see, for example, Patent Document 1).

[0005] Incidentally, in a laminated wafer in which two wafers (first and second wafers) each having a chamfered portion formed on the outer periphery of the front and back sides and a device such as an IC (Integrated Circuit) formed on the front side are fixed together with an adhesive, there are cases in which only the first wafer is thinned.

[0006] In this case, the back side of the second wafer is held by suction on a chuck table so that the back side of the first wafer is exposed upward, and a cutting blade is inserted into the outer periphery of the back side of the first wafer to remove the chamfered portions on the front and back sides of the first wafer.

[0007] However, in order to remove the chamfered portion on the front side as well as the chamfered portion on the back side, it is necessary to precisely position the bottom end of the cutting blade at the boundary between the front side of the first wafer and the front side of the second wafer during cutting. If the cutting blade cuts in even slightly deeper than the boundary, the front side of the second wafer will be cut.

[0008] For example, if a wiring layer made of copper is provided in the peripheral excess region on the front surface side of the second wafer, there is a problem that burrs containing copper will be generated when a cutting blade cuts into the peripheral excess region on the front surface side of the second wafer.

[0009] To solve this problem, for example, a laser beam having a wavelength that passes through the wafer may be used to form a modified layer on the outer periphery of the first wafer, and then the back side of the first wafer may be ground to apply an external force to the first wafer, thereby removing the outer periphery of the first wafer.

[0010] Specifically, first, a laser beam is focused at a predetermined depth position in the thickness direction of the first wafer, and then the laser beam is irradiated along a circular first processing line located a predetermined distance inside the outer periphery of the wafer, thereby forming a ring-shaped first modified layer.

[0011] Next, with the laser beam focused at the same depth position, the laser beam is irradiated along each of a plurality of second processing lines that are set radially in the annular region between the first processing line and the outer peripheral edge of the wafer, thereby forming a plurality of second modified layers that are each linear.

[0012] Then, an external force is applied to the first wafer by grinding the back side of the first wafer. If this external force can sufficiently extend cracks starting from the first and second modified layers, it seems possible to remove the outer periphery of the first wafer from the boundary between the first and second modified layers.

[0013] However, experiments conducted by the applicant revealed that simply applying an external force by grinding the back side may not be enough to extend the cracks sufficiently, and the annular region on the outer periphery may not be completely removed. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] JP 2006-108532 A Summary of the Invention [Problem to be solved by the invention]

[0015] The present invention has been made in consideration of these problems, and has an object to more reliably remove an annular region on the outer periphery of a first wafer in a laminated wafer in which first and second wafers are stacked. [Means for solving the problem]

[0016] According to one aspect of the present invention, there is provided a method for grinding laminated wafers, in which a first surface of a first wafer having a first surface and a second surface located opposite to the first surface, with outer peripheries on the first surface side and the second surface side respectively chamfered, and a third surface of a second wafer having a third surface and a fourth surface located opposite to the third surface, with outer peripheries on the third surface side and the fourth surface side respectively chamfered, are bonded together in a facing state, and a laser beam having a wavelength that transmits the first wafer is irradiated onto the first wafer along a first annular line to be processed that is set inside an outer periphery of the first wafer, to form a first annular modified layer inside the first wafer, and a laser beam having a wavelength that transmits the first wafer is irradiated ... The present invention provides a method for grinding laminated wafers, comprising: a modified layer forming step of irradiating a first wafer with a laser beam along one or more second processing lines set in an annular region up to the outer periphery of the first wafer, to form a second modified layer that divides the annular region into two or more regions when the first surface is viewed in a plane; a trimming step of cutting the annular region from the second surface to a predetermined depth in the thickness direction of the first wafer with a cutting blade and cutting the annular region by moving the laminated wafers and the cutting blade relatively along the outer periphery after the trimming step; and a grinding step of grinding the second surface side of the first wafer to thin it to a finishing thickness and removing the annular region after the trimming step.

[0017] Preferably, in the trimming step, the annular region is cut with a predetermined depth into which the cutting blade is cut positioned below the first modified layer and the second modified layer.

[0018] According to another aspect of the present invention, there is provided a method for grinding laminated wafers, in which a first surface of a first wafer having a first surface and a second surface located opposite to the first surface, with outer peripheries on the first surface side and the second surface side respectively chamfered, and a third surface of a second wafer having a third surface and a fourth surface located opposite to the third surface, with outer peripheries on the third surface side and the fourth surface side respectively chamfered, are bonded together in a facing state, and a laser beam having a wavelength that is absorbed by the first wafer is irradiated from above the laminated wafers onto the second surface of the first wafer along a first annular line to be processed that is set inside an outer periphery of the first wafer, to form a first annular laser-processed groove that penetrates the first wafer in a thickness direction of the first wafer, and to draw a first laser-processed groove through the first wafer from the first annular line to be processed. a laser processed groove forming step of irradiating a laser beam from above the second surface of the stacked wafers along one or more third planned processing lines set in an annular region to the outer periphery of the stacked wafer, dividing the annular region into two or more when the first surface is viewed in a plane, and forming one or more second laser processed grooves penetrating the first wafer in the thickness direction of the first wafer; a trimming step of cutting the annular region by cutting a cutting blade from the second surface to a predetermined depth in the thickness direction of the first wafer and moving the stacked wafers and the cutting blade relatively along the outer periphery after the trimming step; and a grinding step of grinding the second surface side of the first wafer to thin it to a finishing thickness and removing the annular region after the trimming step. Effect of the Invention

[0019] In one embodiment of the wafer grinding method of the present invention, a first modified layer is formed along a circular first processing line set inside the outer peripheral edge of a first wafer, and a second modified layer is formed along one or more second processing lines set in an annular region from the first processing line to the outer peripheral edge of the first wafer, dividing the annular region into two or more regions (modified layer formation process).

[0020] After the modified layer forming step, a cutting blade is inserted into the annular region to a predetermined depth in the thickness direction of the first wafer to cut the annular region (trimming step). Furthermore, after the trimming step, the second surface side of the first wafer is ground to thin the first wafer to a finishing thickness and remove the annular region (grinding step).

[0021] When a modified layer is formed in the annular region, if a load is applied directly to the annular region with a cutting blade in the trimming process, cracks will extend to the surface and the bonding strength between the annular region of the first wafer and the second wafer will decrease. Therefore, the annular region can be removed more reliably in the grinding process than if the trimming process was not performed.

[0022] In addition, in a wafer grinding method according to another aspect of the present invention, a first laser processed groove is formed that penetrates the first wafer in the thickness direction of the first wafer along an annular first planned processing line, and a second laser processed groove is formed that penetrates the first wafer in the thickness direction of the first wafer by dividing the annular region into two or more along one or more third planned processing lines set in the annular region from the first planned processing line to the outer peripheral edge of the first wafer (processing groove forming process).

[0023] Furthermore, after the groove forming step, a trimming step and a grinding step are performed in sequence. When a laser groove is formed in the annular region, if a load is applied directly to the annular region by a cutting blade in the trimming step, the bonding force between the annular region of the first wafer and the second wafer is reduced. Therefore, the annular region can be removed more reliably in the grinding step than when the trimming step is not performed. [Brief description of the drawings]

[0024] [Figure 1] FIG. 2 is a cross-sectional view of a laminated wafer. [Diagram 2] FIG. 2 is a flow diagram of a method for grinding laminated wafers according to the first embodiment. [Diagram 3] FIG. 2 is a plan view of a laminated wafer showing first and second processing lines. [Figure 4] FIG. 4 is a diagram showing a state in which a first modified layer is formed. [Diagram 5] FIG. 4 is a diagram showing a state in which a second modified layer is formed. [Figure 6] FIG. [Figure 7] FIG. [Figure 8] FIG. 11 is a flow diagram of a grinding method for laminated wafers according to a second embodiment. [Figure 9] FIG. 2 is a plan view of a laminated wafer showing first and third processing lines. [Figure 10] 10 is a cross-sectional view taken along line CC in FIG. 9 after a laser groove forming step. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] An embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. First, a laminated wafer 11 to be processed, such as ground, in each embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view of the laminated wafer 11.

[0026] The laminated wafer 11 is mainly made of silicon (Si) and has a first wafer 13 and a second wafer 15 each having approximately the same diameter. A chamfered portion 13a1 is formed on the outer periphery of the front surface (first surface) 13a side of the first wafer 13, and a chamfered portion 13b1 is also formed on the outer periphery of the back surface (second surface) 13b side located opposite the front surface 13a.

[0027] Similarly, a chamfered portion 15a1 is formed on the outer periphery of the front surface (third surface) 15a of the second wafer 15, and a chamfered portion 15b1 is also formed on the outer periphery of the back surface (fourth surface) 15b, which is located opposite the front surface 15a.

[0028] The first wafer 13 and the second wafer 15 are bonded together with a resin adhesive with the surfaces 13a and 15a facing each other so that the center of the surface 13a and the center of the surface 15a are substantially aligned. Therefore, the outer periphery 13c of the first wafer 13 and the outer periphery 15c of the second wafer 15 are substantially aligned in the thickness direction of the laminated wafers 11.

[0029] A plurality of planned division lines (streets) are set in a lattice pattern on the front surface 13a of the first wafer 13. Devices (not shown), such as ICs and LSIs (Large Scale Integration), are formed in each rectangular area surrounded by the plurality of streets.

[0030] The circular region including the multiple devices is referred to as device region 13d1 (see FIGS. 1 and 3). Around device region 13d1, there exists an annular peripheral excess region (annular region) 13d2 (see FIGS. 1 and 3) in which no devices are formed.

[0031] Similarly, a plurality of streets are set in a lattice pattern on the surface 15a of the second wafer 15, and devices (not shown) are formed in each rectangular region surrounded by the plurality of streets. In the second wafer 15, a circular device region 15d1 in which a plurality of devices are formed is surrounded by an annular peripheral excess region 15d2 in which no devices are formed.

[0032] Next, a description will be given of a method for grinding the laminated wafers 11 by grinding the back surface 13b side of the first wafer 13 to thin it. Fig. 2 is a flow diagram of the grinding method for the laminated wafers 11 according to the first embodiment.

[0033] In the first embodiment, first, a laser processing device 2 is used to form a plurality of modified layers in the peripheral excess region 13d2 of the first wafer 13 (modified layer forming step S10). Here, the configuration of the laser processing device 2 will be described with reference to FIG.

[0034] 4 is, for example, a vertical direction, and the X-axis and Y-axis directions are substantially parallel to the horizontal direction. The laser processing device 2 has a disk-shaped chuck table 4. The chuck table 4 has a disk-shaped frame body made of metal.

[0035] A disk-shaped recess (not shown) is formed in the center of the frame, and a disk-shaped porous plate is fixed in this recess. The upper surface of the frame and the upper surface of the porous plate are substantially flush with each other, forming a substantially flat holding surface 4a.

[0036] A flow path is formed in the frame, and one end of the flow path is connected to the porous plate. The other end of the flow path is connected to a suction source (not shown) such as an ejector. When negative pressure from the suction source is transmitted to the holding surface 4a, the laminated wafers 11 placed on the holding surface 4a are sucked and held by the holding surface 4a.

[0037] A rotation drive source (not shown) such as a motor is disposed below the chuck table 4. A rotation shaft 6 of the rotation drive source is connected to the lower part of the chuck table 4, so that when the rotation drive source is operated, the chuck table 4 rotates around the rotation shaft 6. The rotation drive source is supported by an X-axis moving plate (not shown).

[0038] The X-axis moving plate is slidably supported by a pair of guide rails (not shown) that are substantially parallel to the X-axis direction. A nut portion (not shown) is provided on the lower surface side of the X-axis moving plate, and a ball screw (not shown) that is disposed substantially parallel to the X-axis direction is rotatably connected to the nut portion.

[0039] A drive source (not shown) such as a pulse motor is connected to one end of the ball screw, and when the drive source is operated, the X-axis moving plate moves along the X-axis direction together with the chuck table 4 (see FIG. 5). The X-axis moving plate, guide rail, ball screw, etc. constitute an X-axis direction moving unit.

[0040] A laser beam irradiation unit 8 is disposed above the holding surface 4a. The laser beam irradiation unit 8 has a laser oscillator (not shown) and a condenser 10 including a condenser lens (not shown) that condenses the laser beam L.

[0041] A pulsed laser beam L having a wavelength (e.g., 1064 nm) that is transmitted through the first wafer 13 is emitted from the collector 10 onto the back surface 13b of the stacked wafers 11 from above. The laser beam L is collected at a predetermined depth position of the first wafer 13.

[0042] In the modified layer formation process S10, a laser beam L is irradiated along a ring-shaped first processing line 17 (see Figure 3) located a predetermined distance inward from the outer peripheral edge 13c in the radial direction of the first wafer 13 and set at the boundary between the device region 13d1 and the outer peripheral excess region 13d2.

[0043] In the modified layer formation process S10, further, in the outer circumferential excess region 13d2 from the first to-be-processed line 17 to the outer circumferential edge 13c, a laser beam L is irradiated along one or more (18 in this example) second to-be-processed lines 19 (see Figure 3) set radially at approximately equal intervals along the outer circumferential edge 13c.

[0044] 3 is a plan view of the laminated wafers 11, showing a first processing line 17 and a second processing line 19 to be irradiated with a laser beam L in the modified layer forming step S10. In the modified layer forming step S10, first, the back surface 15b side of the second wafer 15 is suction-held by the holding surface 4a.

[0045] Next, the condenser 10 is placed directly above the first line to be processed 17, and the focal point of the laser beam L is positioned at a predetermined depth corresponding to the distance B1 from the surface 13a (see FIG. 4). In this state, the chuck table 4 is rotated.

[0046] The processing conditions are set, for example, as follows: Wavelength: 1064nm Average power output: 1W Repetition frequency: 100kHz Rotation speed: 180° / s

[0047] Since multiphoton absorption occurs at the focal point and its vicinity inside the first wafer 13, a ring-shaped first modified layer 13e1 is formed along the first planned processing line 17. Fig. 4 is a cross-sectional view taken along line AA in Fig. 3, and shows how the first modified layer 13e1 is formed.

[0048] In Fig. 4, the first modified layer 13e1 is shown as a circle for convenience. When the first modified layer 13e1 is formed, cracks 13f are formed that extend from the first modified layer 13e1 to the front surface 13a and the back surface 13b. However, at the time of the modified layer forming step S10, the cracks 13f do not necessarily reach the front surface 13a and the back surface 13b.

[0049] The distance B1 is greater than the distance B2 and the finishing thickness B3 described later. For example, the distance B1 is equal to or greater than half the thickness of the first wafer 13 (i.e., the distance between the front surface 13a and the back surface 13b), and when the thickness of the first wafer 13 is 775 μm, the distance B1 is 700 μm.

[0050] In this embodiment, one annular first modified layer 13e1 is formed, but two or more annular first modified layers 13e1 may be formed by rotating the chuck table 4 while positioning the focal point at a depth different from the distance B1.

[0051] After the first modified layer 13e1 is formed, the rotation of the chuck table 4 is stopped, and with the focusing point positioned at a distance B1 from the surface 13a, the chuck table 4 is moved in the X-axis direction by the X-axis moving unit to form a second modified layer 13e2 along one second planned processing line 19.

[0052] The processing conditions are set, for example, as follows: Wavelength: 1064nm Average power output: 1W Repetition frequency: 100kHz Machining feed speed: 800mm / s

[0053] As a result, a first modified layer 13e1 and a second modified layer 13e2 are formed at a depth position of the distance B1 from the surface 13a. Fig. 5 is a diagram showing the formation of the second modified layer 13e2. In Fig. 5, one second modified layer 13e2 formed at the distance B1 from the surface 13a along one second line to be processed 19 is shown by multiple circles for convenience.

[0054] When the front surface 13a is viewed in a plan view, the one second modified layer 13e2 divides the first wafer 13 into two in the circumferential direction. In this embodiment, the outer circumferential surplus region 13d2 is divided into 18 regions by 18 second processing lines 19, as shown in FIG.

[0055] When the second modified layer 13e2 is formed, cracks 13f are also formed, which extend from the second modified layer 13e2 to the front surface 13a and the back surface 13b. In Fig. 5, the cracks 13f are shown by dashed lines, but at the time of the modified layer forming step S10, the cracks 13f do not necessarily reach the front surface 13a and the back surface 13b.

[0056] After the modified layer forming process S10, the back surface 13b side of the outer peripheral excess region 13d2 is cut using a cutting device 12 (trimming process S20). The cutting device 12 has a disk-shaped chuck table 14. The configuration of the chuck table 14 is substantially the same as that of the above-mentioned chuck table 4, but the frame of the chuck table 14 is formed of resin instead of metal.

[0057] A rotating shaft 16 of a rotary drive source (not shown) such as a motor is connected to the lower part of the chuck table 14. A cutting unit is provided above the chuck table 14. The cutting unit has a cylindrical spindle (not shown).

[0058] The height direction of the spindle is disposed approximately parallel to the horizontal direction. A rotary drive source such as a motor is provided at one end of the spindle, and a cutting blade 18 is attached to the other end of the spindle. The cutting blade 18 has a relatively large blade thickness 18a.

[0059] The blade thickness 18a is greater than the distance from the first line to be processed 17 to the outer peripheral edge 13c (i.e., the width of the outer peripheral surplus region 13d2). In this embodiment, the blade thickness 18a is 3 mm, and the width of the outer peripheral surplus region 13d2 is 2 mm.

[0060] In the trimming step S20, first, the back surface 15b side of the second wafer 15 is suction-held by the holding surface 14a. At this time, the back surface 13b of the first wafer 13 is exposed upward. Next, the spindle is rotated at high speed (e.g., 20,000 rpm) and the cutting blade 18 is caused to cut into the outer peripheral excess region 13d2.

[0061] Specifically, the cutting blade 18 is caused to cut into the outer peripheral excess region 13d2 so that the lower end 18b of the cutting blade 18 is at a predetermined depth corresponding to the distance B2 from the front surface 13a in the thickness direction of the first wafer 13.

[0062] The distance B2 (also referred to as the thickness of the remaining portion after cutting in this specification) is smaller than the above-mentioned distance B1. That is, in the trimming step S20, the lower end 18b of the cutting blade 18 is positioned below the first modified layer 13e1 and the second modified layer 13e2.

[0063] With the lower end 18b cut to a predetermined depth, the chuck table 14 is rotated at a predetermined rotation speed, whereby the first wafer 13 is moved relatively to the cutting blade 18 along the outer circumferential edge 13c.

[0064] In this embodiment, the chuck table 14 is rotated at 2° / s (that is, 120° / min) to rotate once over three minutes, thereby removing the outer peripheral excess region 13d2 on the back surface 13b side.

[0065] In the trimming step S20, a load can be applied directly to the outer circumferential excess region 13d2. Therefore, the cracks 13f originating from the first modified layer 13e1 and the second modified layer 13e2 can be reliably extended to reach the front surface 13a.

[0066] In addition, the second modified layer 13e2 is removed by the trimming step S20, which makes it possible to increase the flexural strength of device chips manufactured from the laminated wafers 11, compared to a case in which the second modified layer 13e2 remains.

[0067] After the trimming step S20, the back surface 13b side of the first wafer 13 is ground using a grinding device 22 (grinding step S30). As shown in Fig. 7, the grinding device 22 has a disk-shaped chuck table 24. The chuck table 24 has a disk-shaped frame body made of non-porous ceramics.

[0068] A disk-shaped recess (not shown) is formed in the center of the frame, and a disk-shaped porous plate is fixed in this recess. The upper surface of the frame and the upper surface of the porous plate are substantially flush with each other to form a holding surface 24a, but the holding surface 24a has a conical shape with the center protruding slightly compared to the outer periphery.

[0069] A flow path is formed in the frame, one end of which is connected to the porous plate, and the other end of which is connected to a suction source (not shown) such as an ejector, and negative pressure from the suction source is transmitted to the holding surface 24a.

[0070] A rotating shaft 26 of a rotation drive source (not shown) such as a motor is connected to the lower part of the chuck table 24. The rotating shaft 26 is tilted by an inclination adjustment mechanism (not shown) so that a part of the conical holding surface 24a is approximately parallel to the horizontal plane.

[0071] A grinding unit 28 is disposed above the holding surface 24a. The grinding unit 28 has a cylindrical spindle 30 disposed approximately parallel to the Z-axis direction. A motor is provided at the upper end of the spindle 30, and a disk-shaped mount 32 is fixed to the lower end of the spindle 30.

[0072] An annular grinding wheel 34 is attached to the underside of the mount 32. The grinding wheel 34 has an annular wheel base 34a made of metal. A plurality of block-shaped grinding stones 34b are arranged on the underside of the wheel base 34a at predetermined intervals along the circumferential direction of the wheel base 34a.

[0073] 7 is a diagram showing the grinding step S30. In the grinding step S30, first, the back surface 15b side of the second wafer 15 is suction-held by the holding surface 24a. At this time, the back surface 13b of the first wafer 13 is exposed upward.

[0074] Next, the chuck table 24 and the grinding wheel 34 are rotated, and the grinding wheel 34 is lowered at a predetermined grinding feed rate. The grinding surface defined by the lower surfaces of the multiple grinding wheels 34b comes into contact with the back surface 13b, whereby the back surface 13b side of the first wafer 13 is ground, and the first wafer 13 is thinned to the finishing thickness B3.

[0075] At this time, the first modified layer 13e1 is removed from the first wafer 13. Note that the distance between the front surface 13a and the back surface 13b after the grinding step S30, which corresponds to the finishing thickness B3, is smaller than both the distance B1 where the first modified layer 13e1 etc. are formed and the distance B2 corresponding to the thickness remaining after cutting.

[0076] In the outer circumferential surplus region 13d2, the cracks 13f have reached the front surface 13a through the trimming step S20, and therefore the bonding force between the outer circumferential surplus region 13d2 on the front surface 13a side of the first wafer 13 and the outer circumferential surplus region 15d2 on the front surface 15a side of the second wafer 15 is reduced. Therefore, in the grinding step S30, the outer circumferential surplus region 13d2 is divided and removed from the laminated wafers 11 by external forces such as centrifugal force and vibration.

[0077] In this manner, in the present embodiment, the first modified layer 13e1 and the second modified layer 13e2 are formed in the peripheral surplus region 13d2, so that when a load is applied directly to the peripheral surplus region 13d2 in the trimming process S20, the crack 13f extends and reliably reaches the surface 13a.

[0078] This reduces the bonding force between the outer circumferential surplus region 13d2 of the first wafer 13 and the second wafer 15. Therefore, the outer circumferential surplus region 13d2 can be removed more reliably in the grinding step S30 than in the case where the trimming step S20 is not performed.

[0079] Next, a second embodiment will be described. Fig. 8 is a flow diagram of a method for grinding a laminated wafer 11 according to a second embodiment. In the second embodiment, a laser processed groove forming step S12 is performed instead of the modified layer forming step S10.

[0080] In the second embodiment, the same annular first processing line 17 as in the first embodiment is set, but multiple third processing lines 21 different from those in the first embodiment are set in a grid pattern in the outer circumferential surplus area 13d2 (see Figure 9).

[0081] Fig. 9 is a plan view of the laminated wafer 11, showing the first line to be processed 17 and the third line to be processed 21. Fig. 10 is a cross-sectional view taken along CC in Fig. 9 after the laser processing groove forming step S12.

[0082] In the laser processing groove forming process S12, the first wafer 13 is processed using a laser processing device 36 (see FIG. 10), which is substantially similar to the laser processing device 2 shown in FIG. 4, but which irradiates a pulsed laser beam having a wavelength (e.g., 355 nm) that is absorbed by the first wafer 13.

[0083] The laser processing device 36 has a Y-axis moving plate (not shown) that is provided on the X-axis moving plate and supports the rotary drive source, in addition to the chuck table 4, the rotary drive source, and the X-axis moving unit. The Y-axis moving plate is slidably attached on a pair of guide rails (not shown) that are arranged substantially parallel to the Y-axis direction and fixed on the X-axis moving plate.

[0084] A nut portion (not shown) is provided on the lower surface side of the Y-axis moving plate, and a ball screw (not shown) arranged approximately parallel to the Y-axis direction is rotatably connected to the nut portion. A drive source (not shown) such as a pulse motor is connected to one end of the ball screw.

[0085] When the drive source is operated, the Y-axis moving plate moves along the Y-axis direction together with the chuck table 4. The Y-axis moving plate, guide rail, ball screw, etc. configure a Y-axis direction moving unit. Note that the laser beam irradiation unit 8 is omitted in Fig. 10.

[0086] Specifically, in the laser groove forming step S12, first, a laser beam is irradiated from above the laminated wafers 11 to the back surface 13b along the first processing line 17, while the chuck table 4 is rotated.

[0087] The processing conditions are set, for example, as follows: As a result, a ring-shaped first laser processed groove 13g1 penetrating the first wafer 13 in the thickness direction of the first wafer 13 is formed (see FIG. 10).

[0088] Wavelength: 355nm Average power output: 1W Repetition frequency: 100kHz Rotation speed: 180° / s

[0089] Next, the chuck table 4 is rotated to adjust the orientation of the laminated wafers 11 so that the third processing line 21a parallel to the first direction among the multiple third processing lines 21 becomes approximately parallel to the X-axis direction. Then, the X-axis direction moving unit irradiates a laser beam along one of the third processing lines 21a to form a second laser processing groove 13g2.

[0090] The processing conditions are set, for example, as follows: Wavelength: 355nm Average power output: 1W Repetition frequency: 100kHz Machining feed speed: 800mm / s

[0091] After forming a second laser processing groove 13g2 along one of the third processing lines 21a, the Y-axis direction moving unit changes the irradiation position of the laser beam, and the laser beam is irradiated along another third processing line 21a adjacent to the one of the third processing lines 21a.

[0092] The timing of application of the laser beam is appropriately adjusted so that the second laser processed grooves 13g2 are formed only in the peripheral excess region 13d2 and the second laser processed grooves 13g2 are not formed in the device region 13d1.

[0093] After forming the second laser processing grooves 13g2 along all of the third processing lines 21a parallel to the first direction, the Y-axis direction moving unit is used to similarly form the second laser processing grooves 13g2 along all of the third processing lines 21b parallel to the second direction perpendicular to the first direction.

[0094] In this embodiment, the second laser processing grooves 13g2 are formed along 13 x 13 third processing lines 21a that are perpendicular to each other, but the number of third processing lines 21 is not limited to this example.

[0095] The third processing lines 21a may be 10 lines x 10 lines that cross each other at right angles, or may be 20 lines x 20 lines that cross each other at right angles. In this embodiment, the third processing lines 21 that coincide with each other when extended beyond the device region 13d1 are counted as one line.

[0096] When the front surface 13a is viewed in plan, it is sufficient that the outer circumferential surplus region 13d2 can be divided into two or more by one or more third processing lines 21. However, it is preferable to divide the outer circumferential surplus region 13d2 into a larger number of regions, since this tends to reduce the bonding strength between the outer circumferential surplus region 13d2 of the first wafer 13 and the second wafer 15.

[0097] In the second embodiment, too, when a load is applied directly to the peripheral surplus region 13d2 by the cutting blade 18 in the trimming process S20 after the laser groove forming process S12, the bonding force between the peripheral surplus region 13d2 of the first wafer 13 and the second wafer 15 is reduced.

[0098] Therefore, the annular region can be removed more reliably in the grinding step S30 than in the case where the trimming step S20 is not performed. In addition, the structures, methods, etc. according to the above-described embodiments can be appropriately modified and implemented without departing from the scope of the present invention.

[0099] In the first embodiment, a plurality of second planned processing lines 19 are set radially, but as in the second embodiment, one or more second planned processing lines 19 may be set in a lattice pattern. Also, in the second embodiment, one or more third planned processing lines 21 may be set radially, as in the first embodiment.

[0100] Incidentally, in the modified layer forming step S10, the first modified layer 13e1 may be formed after the second modified layer 13e2 is formed. Also, in the laser processed groove forming step S12, the first laser processed groove 13g1 may be formed after the second laser processed groove 13g2 is formed. [Explanation of symbols]

[0101] 2, 36: laser processing device, 4: chuck table, 4a: holding surface 6: Rotating shaft, 8: Laser beam irradiation unit, 10: Condenser 11: Stacked wafer 12: cutting device, 14: chuck table, 14a: holding surface, 16: rotating shaft 13: first wafer, 13a: front surface (first surface), 13b: back surface (second surface) 13a1, 13b1: chamfered portion, 13c: outer periphery 13d1: device area, 13d2: peripheral surplus area (ring area) 13e1: first modified layer, 13e2: second modified layer, 13f: crack 13g1: 1st laser processed groove, 13g2: 2nd laser processed groove 15: second wafer, 15a: front surface (third surface), 15b: back surface (fourth surface) 15a1, 15b1: chamfered portion, 15c: outer periphery 15d1: Device area, 15d2: Surplus outer area 17: First processing line, 19: Second processing line 18: cutting blade, 18a: blade thickness, 18b: lower end 21, 21a, 21b: Third processing line 22: grinding device, 24: chuck table, 24a: holding surface, 26: rotating shaft 28: Grinding unit, 30: Spindle, 32: Mount 34: grinding wheel, 34a: wheel base, 34b: grinding stone B1, B2: distance, B3: finishing thickness, L: laser beam

Claims

1. A method for grinding laminated wafers, comprising the steps of: In the laminated wafer, a first wafer has a first surface and a second surface located opposite to the first surface, and outer peripheries of the first surface side and the second surface side are chamfered, and a third surface of a second wafer has a third surface and a fourth surface located opposite to the third surface, and outer peripheries of the third surface side and the fourth surface side are chamfered, the first surface being bonded together in a facing state; a modified layer forming step of irradiating the first wafer with a laser beam having a wavelength that transmits through the first wafer along a first annular processing line set inside the outer periphery of the first wafer to form a first annular modified layer inside the first wafer, and irradiating the first wafer with a laser beam along one or more second processing lines set in an annular region from the first processing line to the outer periphery of the first wafer to form a second modified layer that divides the annular region into two or more when the first surface is viewed in a plane; a trimming step of cutting the annular region by cutting a cutting blade into the annular region from the second surface to a predetermined depth in the thickness direction of the first wafer and moving the stacked wafers and the cutting blade relatively along the outer circumferential edge after the modified layer forming step; a grinding step after the trimming step of grinding the second surface side of the first wafer to a finish thickness and removing the annular region; A method for grinding laminated wafers, comprising:

2. The method for grinding laminated wafers as described in claim 1, characterized in that in the trimming process, the annular region is cut with the predetermined depth to which the cutting blade is cut positioned below the first modified layer and the second modified layer.

3. A method for grinding laminated wafers, comprising the steps of: In the laminated wafer, a first wafer has a first surface and a second surface located opposite to the first surface, and outer peripheries of the first surface side and the second surface side are chamfered, and a third surface of a second wafer has a third surface and a fourth surface located opposite to the third surface, and outer peripheries of the third surface side and the fourth surface side are chamfered, the first surface being bonded together in a facing state; a laser-machined groove forming step of irradiating a laser beam having a wavelength absorbed by the first wafer from above the stacked wafers onto the second surface of the first wafer along an annular first planned processing line set inside the outer periphery of the first wafer to form an annular first laser-machined groove penetrating the first wafer in the thickness direction of the first wafer, and irradiating a laser beam from above the stacked wafers onto the second surface along one or more third planned processing lines set in an annular region from the first planned processing line to the outer periphery of the first wafer to divide the annular region into two or more when the first surface is viewed in plan, and forming one or more second laser-machined grooves penetrating the first wafer in the thickness direction of the first wafer; a trimming step of cutting the annular region by cutting a cutting blade into the annular region from the second surface to a predetermined depth in the thickness direction of the first wafer and moving the stacked wafers and the cutting blade relatively along the outer periphery, after the laser groove forming step; a grinding step after the trimming step of grinding the second surface side of the first wafer to a finish thickness and removing the annular region; A method for grinding laminated wafers, comprising:

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