JP6317935B2 - Holding table - Google Patents

Description

The present invention relates to a holding table for use in the processing how the wafer to remove the ring-like reinforcing portion formed around the device area from the wafer.

  A wafer on which a plurality of devices such as IC and LSI are formed on the surface side is divided into individual devices using a dicing apparatus or the like, and is widely used by being incorporated into various electronic devices. In order to reduce the size and weight of electronic equipment, the thickness of the wafer is reduced to, for example, 50 μm to 100 μm. Such a wafer is not only rigid but also warped, making it difficult to handle and possibly damaging it during transportation. Therefore, by grinding only the back surface corresponding to the device region where the device of the wafer is formed, a ring-shaped reinforcing portion is formed on the back surface corresponding to the outer peripheral surplus region surrounding the device region, thereby increasing the rigidity of the wafer. Has been proposed (see, for example, Patent Document 1).

  There has been proposed a method of removing a ring-shaped reinforcing portion from a wafer before dividing the wafer on which the ring-shaped reinforcing portion is formed along the planned dividing line (see, for example, Patent Document 2). In the method described in Patent Document 2, the boundary portion between the device region and the ring-shaped reinforcing portion (peripheral surplus region) is cut by a cutting blade, and the ring-shaped reinforcing portion is separated from the wafer. Then, after the ring-shaped reinforcing portion is removed, the wafer in which the device region is left is cut with a cutting blade along the planned dividing line from the surface side, so that the wafer is divided into individual devices.

JP 2007-19461 A JP 2012-23175 A

  However, in the method described in Patent Document 2, the step between the thinned portion and the ring-shaped reinforcing portion increases as the thickness of the wafer in the device region is reduced. Along with this, in order to avoid contact between the blade hub and the ring-shaped reinforcing portion, it is necessary to make the cutting edge amount of the cutting blade larger than usual by the level difference. If the cutting blade is machined with a large amount of leading edge, an excessive load is applied to the cutting blade, which may cause the cutting blade to meander or break. Although it is conceivable to increase the blade width to prevent meandering and breakage, there is a problem that the groove width at the time of cutting is increased by the amount of the cutting blade and the device area is reduced.

  In particular, in recent years, in order to increase the chip size and improve the productivity, the wafer diameter has been increased. Since a large-diameter wafer has a large thickness as well as an outer diameter, it is assumed that the step of the ring-shaped reinforcing portion is increased by reducing the thickness of the wafer in the device region. Therefore, the amount of leading edge of the cutting blade is further increased, and it is difficult to appropriately remove the ring-shaped reinforcing portion from the wafer.

The present invention has been made in view of these points, and in a wafer in which a ring-shaped reinforcing portion is formed around the device region, the ring-shaped reinforcing portion can be stably removed without narrowing the device region. and to provide a holding table for use in the processing how such wafers.

The holding table of the present invention includes a wafer in which a device region in which a plurality of devices are formed and an outer peripheral surplus region surrounding the device region are formed on the surface, and a ring-shaped reinforcing portion is formed on the back surface corresponding to the outer peripheral surplus region. An annular relief groove for releasing a laser beam is formed on the upper surface of the holding table at a position corresponding to a boundary portion between the ring-shaped reinforcing portion and the device region. The bottom is formed with fine irregularities that are tapered so as to be deeper toward the center of the holding table and in which the laser beam is scattered.

According to this configuration, the device region of the wafer and the ring-shaped reinforcing portion are separated by irradiating the wafer with a laser beam along the boundary between the device region and the ring-shaped reinforcing portion (peripheral surplus region). At this time, since the fine groove is formed on the tapered groove bottom of the relief groove, the reflected light of the laser beam reflected at the groove bottom is separated from the laser light source and the intensity of the reflected light is weakened, and the laser by the reflected light is reduced. Damage to the light source is suppressed. Since the device region and the ring-shaped reinforcing portion can be separated without using a cutting blade, it is not necessary to consider the cutting edge amount and thickness of the cutting blade as in the case of separating with a cutting blade. Further, since the wafer is processed by laser beam irradiation, the processing area is minimized and the device area is not narrowed. Further, even when the thickness is increased as the wafer diameter is increased, the ring-shaped reinforcing portion can be stably removed.

The holding table of the present invention is used when the back side of the device region on the back side of the wafer is ground to remove the ring-shaped reinforcing portion formed on the back side of the outer peripheral surplus region by laser beam irradiation.

  According to the present invention, in a wafer in which a ring-shaped reinforcing portion is formed around the device region, a laser beam is irradiated along a boundary portion between the device region and the ring-shaped reinforcing portion without narrowing the device region. The ring-shaped reinforcing portion can be stably separated from the wafer.

It is a perspective view of the laser processing apparatus which concerns on this Embodiment. It is explanatory drawing of the holding table which concerns on this Embodiment. It is a figure which shows an example of the wafer sticking process which concerns on this Embodiment. It is a figure which shows an example of the alignment process which concerns on this Embodiment. It is a figure which shows an example of the ring-shaped reinforcement part isolation | separation process which concerns on this Embodiment. It is a figure which shows an example of the ring-shaped reinforcement part removal process which concerns on this Embodiment. It is a figure which shows an example of the device area | region support process which concerns on this Embodiment. It is a figure which shows an example of the division | segmentation process which concerns on this Embodiment. It is a schematic diagram explaining the escape groove | channel of the holding table which concerns on this Embodiment.

  Hereinafter, a wafer processing method according to the present embodiment will be described with reference to the accompanying drawings. The wafer processing method according to the present embodiment is performed on a so-called TAIKO wafer formed by grinding only the inner peripheral portion of the back surface of the wafer, and removing the outer peripheral portion of the TAIKO wafer. Is the method. FIG. 1 is a perspective view of a laser processing apparatus used in the wafer processing method according to the present embodiment. The laser processing apparatus is not limited to the configuration shown in FIG. 1 as long as it can be used in the wafer processing method according to the present embodiment.

  As shown in FIG. 1, the laser processing apparatus 1 is configured to process the wafer W by relatively moving a laser beam irradiation means 2 that irradiates a laser beam and a holding table 5 that holds the wafer W. The wafer W is formed in a substantially disc shape, and is divided into a plurality of regions by lattice-shaped division scheduled lines 82 arranged on the surface 80 (see FIG. 8). In the center of the wafer W, devices are formed in the respective areas partitioned by the planned dividing line 82. A surface 80 (see FIG. 2A) of the wafer W is divided into a device region 83 in which a plurality of devices are formed and an outer peripheral surplus region 84 surrounding the device region 83.

  On the back surface 81 of the wafer W, only a central portion corresponding to the device region 83 is ground into a concave shape, and a convex ring-shaped reinforcing portion 85 is formed in a portion corresponding to the outer peripheral surplus region 84. As a result, only the central portion of the wafer W is thinned, and the rigidity of the wafer W is enhanced by the ring-shaped reinforcing portion 85. Therefore, the device region 83 of the wafer W is thinned, and the warp of the wafer W is suppressed by the ring-shaped reinforcing portion 85, so that breakage or the like during transportation is prevented. The wafer W may be a semiconductor wafer such as silicon or gallium arsenide, or a ceramic, glass, or sapphire optical device wafer.

  A holding tape T1 is attached to the surface 80 of the wafer W, and the wafer W is transported to the laser processing apparatus 1 with an annular frame F1 having an opening attached to the outer periphery of the holding tape T1. On the wafer W, a step is formed by a ring-shaped reinforcing portion 85 at a boundary portion 86 (see FIG. 2B) between the device region 83 and the outer peripheral surplus region 84. In mechanical dicing using a cutting blade, since the blade hub interferes with the ring-shaped reinforcing portion 85 and appropriate processing is difficult, in this embodiment, the ring-shaped reinforcing portion 85 is separated from the wafer W by ablation processing. ing.

  A holding table moving mechanism 4 that moves the holding table 5 in the X-axis direction and the Y-axis direction is provided on the upper surface of the base 11 of the laser processing apparatus 1. The holding table moving mechanism 4 includes a pair of guide rails 41 arranged on the base 11 and parallel to the X-axis direction, and a motor-driven X-axis table 42 slidably installed on the pair of guide rails 41. doing. The holding table moving mechanism 4 includes a pair of guide rails 43 arranged on the upper surface of the X-axis table 42 and parallel to the Y-axis direction, and a motor-driven Y-axis table 44 slidably installed on the pair of guide rails 43. And have.

  Further, nut portions (not shown) are formed on the back sides of the X-axis table 42 and the Y-axis table 44, and ball screws 45 and 46 are screwed to these nut portions. Then, when the drive motors 47 and 48 connected to one end portions of the ball screws 45 and 46 are rotationally driven, the holding table 5 is moved along the guide rails 41 and 43 in the X-axis direction and the Y-axis direction. A θ table 49 is provided above the Y-axis table 44, and a holding table 5 that holds the wafer W is provided above the θ table 49.

  The holding table 5 is formed in a disk shape from a metal material such as stainless steel, and has a holding surface 51 for holding the wafer W on the upper surface. A plurality of suction grooves 57 and 58 (see FIG. 2A) are formed on the holding surface 51, and the wafer W is sucked and held by the negative pressure generated in the suction grooves 57 and 58. Further, around the holding table 5, four air-driven clamp portions 60 are provided, and the frame F 1 around the wafer W is sandwiched and fixed by each clamp portion 60. A standing wall portion 12 is erected on the rear side of the holding table 5. An arm portion 13 protrudes from the standing wall portion 12, and the laser beam irradiation means 2 is provided on the arm portion 13 so as to face the holding table 5.

  The laser beam application means 2 has a processing head 21 provided at the tip of the arm portion 13. In the arm portion 13 and the processing head 21, optical system components of the laser beam irradiation means 2 are provided. The processing head 21 collects a laser beam oscillated from an oscillator (not shown) by a condenser lens and irradiates the wafer W held on the holding table 5. In this case, the laser beam has a wavelength having an absorptivity with respect to the wafer W, and is adjusted so as to be condensed inside the holding tape T1 at the back of the wafer W by an optical system component. The wafer W is ablated by this laser beam irradiation.

  Ablation means that when the irradiation intensity of a laser beam exceeds a predetermined processing threshold, it is converted into electronic, thermal, photochemical and mechanical energy on the solid surface, resulting in neutral atoms, molecules, positive and negative A phenomenon in which ions, radicals, clusters, electrons, and light are explosively emitted and the solid surface is etched.

  Further, an image pickup means 3 for picking up an image of the outer peripheral edge 90 (see FIG. 2B) of the wafer W is provided on the side of the laser beam irradiation means 2. The imaging means 3 irradiates the outer peripheral edge 90 of the wafer W with imaging light, captures the reflected light, and images the outer peripheral edge 90 of the wafer W. The image pickup means 3 picks up any three locations on the outer peripheral edge 90 of the wafer W, and performs image processing on each captured image to detect the coordinates of the three points on the outer peripheral edge 90. Based on the coordinates of the outer peripheral edge 90, the center of the wafer W is calculated, and alignment is performed based on the calculated center of the wafer W.

  In the laser processing apparatus 1 configured as described above, after the alignment is performed, the processing head 21 is positioned at the boundary 86 between the device region 83 and the ring-shaped reinforcing portion 85 (the outer peripheral surplus region 84) (see FIG. 5A). ). Then, the holding table 5 is rotated in a state where the laser beam is irradiated from the processing head 21 toward the wafer W, whereby the wafer W is cut together with the holding tape T1. Thereby, the frame F <b> 1 is separated from the wafer W together with the ring-shaped reinforcing portion 85. Thereafter, the ring-shaped reinforcing portion 85 supported by the frame F1 via the holding tape T1 is detached from the holding table 5 together with the frame F1, and the ring-shaped reinforcing portion 85 is removed from the wafer W (see FIG. 6).

  The holding table according to the present embodiment will be described in detail with reference to FIG. FIG. 2 is an explanatory diagram of the holding table according to the present embodiment. 2A shows a perspective view of the holding table according to the present embodiment, and FIG. 2B shows a cross-sectional view of the holding table according to the present embodiment. In FIG. 2B, the wafer held on the holding table is indicated by a two-dot chain line.

  As shown in FIGS. 2A and 2B, an annular relief groove 53 is formed on the upper surface of the holding table 5 to allow the laser beam to escape during ablation processing. The escape groove 53 corresponds to a boundary portion 86 between the device region 83 of the wafer W and the ring-shaped reinforcing portion 85 (outer peripheral surplus region 84), and is formed along the outer periphery of the holding table 5. A radially inner side of the escape groove 53 on the upper surface of the holding table 5 is a holding surface 51 that holds the wafer W, and corresponds to the device region 83 of the wafer W. The holding surface 51 is formed with a cross-shaped suction groove 57 orthogonal to the center of the holding table 5 and a concentric ring-shaped suction groove 58 centering on the intersection of the cross-shaped suction grooves 57.

  The cross-shaped suction groove 57 and the ring-shaped suction groove 58 are formed in series, and are connected to a suction source (not shown) via a suction path 59 in the holding table 5. Due to the negative pressure generated in the suction grooves 57 and 58, the wafer W is sucked and held on the holding surface 51 via the holding tape T1. Further, the outer peripheral edge 52 on the outer surface in the radial direction of the escape groove 53 on the upper surface of the holding table 5 is formed at the same height as the holding surface 51, and supports the holding tape T <b> 1 outside the wafer W. Accordingly, the holding tape T1 is maintained in a horizontal state between the holding surface 51 and the outer peripheral edge portion 52, and the ring-shaped reinforcing portion 85 is not bent toward the inside of the escape groove 53 (downward). Misalignment of the irradiation position is prevented.

  The groove bottom 54 of the escape groove 53 is inclined so as to become deeper toward the center of the holding table 5. On the tapered surface of the groove bottom 54, fine irregularities for scattering the laser beam are formed by sandblasting or the like. The reflected light of the laser beam reflected by the groove bottom 54 is removed from the laser light source and the intensity of the reflected light is weakened, so that the laser light source is prevented from being damaged by the reflected light. Although details will be described later, at the time of alignment, the reflected light of the imaging light reflected by the groove bottom 54 is detached from the imaging means 3 (see FIG. 4) and the intensity of the reflected light is weakened. The contrast of light and dark is shown.

  In the wafer processing method according to the present embodiment, after the ring-shaped reinforcing portion is removed from the wafer by the laser processing apparatus described above, the device region of the wafer is divided into individual chips. The wafer processing method according to the present embodiment will be described below with reference to FIGS. 3 is a wafer sticking process, FIG. 4 is an alignment process, FIG. 5 is a ring-shaped reinforcing part separating process, FIG. 6 is a ring-shaped reinforcing part removing process, FIG. 7 is a device region supporting process, and FIG. FIG. FIG. 5A is a side view of the ring-shaped reinforcing portion separating step, FIG. 5B is a partially enlarged view of FIG. 5A, and FIG. 5C is a view of the ring-shaped reinforcing portion separating step viewed from above.

  As shown in FIG. 3, a wafer sticking process is first performed. In the wafer attaching process, the wafer W is accommodated in the opening of the frame F1, and the holding tape T1 is attached to the surface 80 of the wafer W and the frame F1. Thus, the wafer W is supported by the frame F1 via the holding tape T1 with the ring-shaped reinforcing portion 85 facing upward. The wafer W is carried into the above-described laser processing apparatus 1 (see FIG. 1) while being supported inside the frame F1 via the holding tape T1. The wafer sticking step may be performed manually by an operator or may be performed by a tape mounter (not shown).

  As shown in FIG. 4, an alignment process is implemented after a wafer sticking process. In the alignment step, the wafer W supported by the frame F1 is held on the holding surface 51 of the holding table 5, and the frame F1 is clamped and fixed by the clamp unit 60. Then, the imaging unit 3 is positioned above the ring-shaped reinforcing portion 85 of the wafer W, and the outer peripheral edge 90 of the wafer W is imaged by the imaging unit 3. At this time, imaging light is irradiated from the imaging unit 3 around the outer peripheral edge 90 of the wafer W, and reflected light around the outer peripheral edge 90 is captured to generate a captured image.

  A horizontal upper surface 87 of the ring-shaped reinforcing portion 85 exists inside the outer peripheral edge 90, and incident light (imaging light) from the imaging means 3 is reflected (halated) by the upper surface 87 of the ring-shaped reinforcing portion 85. Are taken into the imaging means 3. On the other hand, the escape groove 53 exists outside the outer peripheral edge 90, and the incident light from the imaging means 3 passes through the holding tape T <b> 1 and is reflected by the tapered groove bottom 54 of the escape groove 53. As a result, the light reflected by the groove bottom 54 moves toward the center of the wafer W and is scattered by fine irregularities on the groove bottom 54. Therefore, the reflected light reflected outside the outer peripheral edge 90 is difficult to be taken into the imaging means 3.

  In the captured image around the peripheral edge 90, the inside of the peripheral edge 90 where the reflected light is captured by the imaging unit 3 is displayed brightly, while the outside of the peripheral edge 90 where the reflected light is difficult to be captured by the imaging unit 3 is displayed darkly. . Therefore, the contrast of light and dark at the outer peripheral edge 90 of the wafer W becomes clear, and the outer peripheral edge 90 is accurately recognized. Similarly, the outer peripheral edge 90 is imaged at a plurality of locations on the wafer W, and various image processing is performed based on the plurality of captured images to detect the coordinates of the outer peripheral edge 90. The center of the wafer W is calculated based on the position coordinates of the plurality of outer peripheral edges 90, and alignment is performed.

  As shown in FIGS. 5A to 5C, after the alignment step, a ring-shaped reinforcing portion separating step is performed. In the ring-shaped reinforcing portion separation step, a first processing step is performed in which a laser processing groove 92 is formed in the boundary portion 86 between the device region 83 and the ring-shaped reinforcing portion 85 (the outer peripheral surplus region 84). In the first processing step, the boundary portion 86 between the device region 83 and the ring-shaped reinforcing portion 85 is positioned directly below the processing head 21. After the condensing point position of the laser beam and the spot diameter 91 are adjusted, the laser beam indicated by the broken line has a predetermined spot diameter 91 toward the boundary 86 between the device region 83 and the ring-shaped reinforcing portion 85 of the wafer W. Irradiated.

  Then, by rotating the holding table 5 in the state of being irradiated with the laser beam, the boundary portion 86 between the device region 83 and the ring-shaped reinforcing portion 85 is removed with a laser beam spot diameter 91 (see FIG. 5C) indicated by a broken line. The At this time, the laser beam passes through the wafer W and the holding tape T <b> 1 and is reflected toward the center of the holding table 5 at the groove bottom 54 of the escape groove 53. Further, since the groove bottom 54 is provided with fine irregularities, the laser beam is scattered and the intensity is weakened. For this reason, it becomes difficult for the laser beam reflected by the groove bottom 54 to return directly to the processing head 21, and even if the reflected laser beam returns into the processing head 21, the intensity is reduced and the laser light source is damaged. There is no.

  In this way, in the first processing step, the boundary portion 86 between the device region 83 and the ring-shaped reinforcing portion 85 is cut together with the holding tape T1, and the laser processing groove 92 is formed. However, the laser processing groove 92 has a narrow groove width and may be filled with debris generated by ablation processing. Therefore, after the first processing step, a second processing step of expanding the laser processing groove 92 so that the ring-shaped reinforcing portion 85 and the device region 83 are separated is performed. As shown in FIGS. 5B and 5C, in the second processing step, the processing head 21 (only a distance smaller than a predetermined spot diameter 91 of the laser beam from the portion irradiated with the laser beam indicated by the broken line in the first processing step). The laser beam irradiation means 2) is moved in the radial direction of the wafer.

  Then, when the holding table 5 is rotated in a state where the laser beam indicated by the alternate long and short dash line is irradiated, the boundary portion 86 between the device region 83 and the ring-shaped reinforcing portion 85 is removed with the spot diameter 91 of the laser beam. The spot diameter 91 of the laser beam at this time partially overlaps the laser processing groove 92 formed in the first processing step. For this reason, the groove width of the laser processing groove 92 is slightly expanded while the debris remaining in the laser processing groove 92 is removed. If the ring-shaped reinforcing portion 85 and the device region 83 are not separated by the two laser processings, the second processing step is performed again.

  The second processing step is repeated until the laser processing groove 92 is sufficiently enlarged and the wafer W and the holding tape T1 are completely separated. As described above, in the ring-shaped reinforcement portion separation step, the ring-shaped reinforcement is performed from the wafer W by repeating the second processing step even if the ring-shaped reinforcement portion 85 is not separated from the wafer W in the first processing step. Part 85 is cut off. In the first and second processing steps of the present embodiment, for example, the laser beam spot diameter is set to 90 μm, the laser processing line interval (index) is set to 0.015 μm, and 2 reciprocations (4 passes) per line. Laser processing is performed.

  As shown in FIG. 6, after the ring-shaped reinforcing portion separating step, a ring-shaped reinforcing portion removing step is performed. In the ring-shaped reinforcing portion removing step, the clamping and fixing of the frame F1 by the clamp portion 60 is released, and the conveying means 71 is positioned above the holding table 5. Then, the frame F1 is held by the suction pad 72 of the transport means 71, and the ring-shaped reinforcing portion 85 supported by the frame F1 via the holding tape T1 is detached from the holding table 5 together with the frame F1. As a result, the ring-shaped reinforcing portion 85 is removed from the wafer W on the holding table 5, and only the device region 83 of the wafer W is left. The wafer W from which the ring-shaped reinforcing portion 85 has been removed is unloaded from the laser processing apparatus 1 (see FIG. 1).

  As shown in FIG. 7, a device region support step is performed after the ring-shaped reinforcing portion removing step. In the device region supporting step, the wafer W from which the ring-shaped reinforcing portion 85 (see FIG. 6) has been removed is accommodated in the opening of another frame F2, and a holding tape T2 is newly attached to the back surface 81 and the frame F2 of the wafer W. Worn. Thus, the wafer W is supported by the frame F2 via the holding tape T2 with the front surface 80 side of the wafer W facing upward. Further, the holding tape T1 left on the surface 80 of the wafer W is peeled off from the wafer W. The wafer W is carried into the cutting device 73 (see FIG. 8) while being supported inside the frame F2 via the holding tape T2. The device region support step may be performed manually by an operator or may be performed by a tape mounter (not shown).

  As shown in FIG. 8, after the device region supporting step, a dividing step is performed. In the dividing step, the wafer 80 is held on the holding table 74 of the cutting device 73 with the surface 80 facing upward. The cutting blade 75 is aligned with the division line 82 outside the wafer W in the radial direction, and is lowered to a height at which the cutting tape 75 can be cut halfway through the holding tape T2. Then, the wafer W on the holding table 74 is cut and fed to the cutting blade 75 that rotates at a high speed, whereby the wafer W is cut along the scheduled division line 82. By repeating the cutting operation along all the planned dividing lines 82, the wafer W is divided into individual devices.

  In the dividing step, the method for dividing the wafer W is not particularly limited. For example, after the wafer W is half-cut to form a cutting groove, the wafer W may be divided by a breaking process. Further, the wafer W may be divided by fully cutting the wafer W by ablation processing, or after forming the modified layer in the wafer W by SD processing, an external force is applied to the modified layer to form the wafer W. It may be divided. The modified layer refers to a region where the density, refractive index, mechanical strength, and other physical characteristics of the wafer W are different from the surroundings due to the irradiation of the laser beam, and the strength is lower than the surroundings. . The modified layer is, for example, a melt treatment region, a crack region, a dielectric breakdown region, or a refractive index change region, and may be a region in which these are mixed.

  Subsequently, the positional relationship between the groove width of the escape groove of the holding table and the ring-shaped reinforcing portion will be described with reference to FIG. FIG. 9A is an enlarged view around the escape groove according to the present embodiment, and FIG. 9B is an enlarged view around the escape groove according to the comparative example. In the comparative example of FIG. 9B, the same names as those in the present embodiment will be described with the same reference numerals.

  As shown in FIG. 9A, the relief groove 53 according to the present embodiment is wider than the ring-shaped reinforcing portion 85 and is formed at a position corresponding to the ring-shaped reinforcing portion 85. The inner surface 55 of the escape groove 53 is located at a slight distance X1 from the inner peripheral surface 88 of the ring-shaped reinforcing portion 85 to the inside. Further, the outer side surface 56 of the escape groove 53 is positioned with a sufficient distance X2 from the outer peripheral surface 89 of the ring-shaped reinforcing portion 85 to the outside. Thus, the escape groove 53 according to the present embodiment is formed such that the inner side surface 55 is close to the ring-shaped reinforcing portion 85 and the outer side surface 56 is far from the ring-shaped reinforcing portion 85.

  Since the inner surface 55 of the escape groove 53 is brought close to the inner peripheral surface 88 of the ring-shaped reinforcing portion 85, the wafer W is held on the holding surface 51 of the holding table 5 in a wide range. Therefore, at the time of laser processing, the vicinity of the boundary portion 86 between the device region 83 and the ring-shaped reinforcing portion 85 (peripheral surplus region 84) is stably supported by the holding surface 51, and thus the laser beam irradiation position on the boundary portion 86 is displaced. It does not occur. Further, at the time of alignment, since the outer surface 56 of the escape groove 53 is sufficiently separated from the outer peripheral surface 89 of the ring-shaped reinforcing portion 85, the amount of light directed from the imaging means 3 (see FIG. 4) into the escape groove 53 increases. Therefore, the darkly displayed part in the captured image becomes clear and the outer peripheral edge 90 of the wafer W can be easily recognized.

  On the other hand, as shown in FIG. 9B, the clearance groove 53 according to the comparative example is also wider than the ring-shaped reinforcing portion 85 and is formed at a position corresponding to the ring-shaped reinforcing portion 85. However, the inner surface 55 of the escape groove 53 is located at a sufficient distance X3 (X3> X1) from the inner peripheral surface 88 of the ring-shaped reinforcing portion 85. The outer surface 56 of the escape groove 53 is located at a slight distance X4 (X4 <X2) from the outer peripheral surface 89 of the ring-shaped reinforcing portion 85. Thus, the escape groove 53 according to the comparative example is formed such that the inner side surface 55 is far from the ring-shaped reinforcing portion 85 and the outer side surface 56 is close to the ring-shaped reinforcing portion 85.

  Since the inner surface 55 of the escape groove 53 is far from the inner peripheral surface 88 of the ring-shaped reinforcing portion 85, the holding range of the wafer W on the holding surface 51 is narrower than that in FIG. 9A. Therefore, at the time of laser processing, the vicinity of the boundary portion 86 between the device region 83 and the ring-shaped reinforcing portion 85 (the outer peripheral surplus region 84) is not stably supported by the holding surface 51. Misalignment may occur. Further, at the time of alignment, since the outer surface 56 of the escape groove 53 is brought close to the outer peripheral surface 89 of the ring-shaped reinforcing portion 85, the amount of light directed from the imaging means 3 (see FIG. 4) into the escape groove 53 is reduced. Therefore, the darkly displayed part in the captured image becomes ambiguous, and the outer peripheral edge 90 of the wafer W becomes difficult to recognize.

  As described above, according to the method for processing the wafer W according to the present embodiment, the laser beam is irradiated onto the wafer W along the boundary portion 86 between the device region 83 and the ring-shaped reinforcing portion 85 (outer peripheral surplus region 84). As a result, the device region 83 of the wafer W and the ring-shaped reinforcing portion 85 are separated. Then, the ring-shaped reinforcing portion 85 is removed from the wafer W by detaching the ring-shaped reinforcing portion 85 after separation from the holding table 5. Thus, since the device region 83 and the ring-shaped reinforcing portion 85 can be separated without using a cutting blade, there is no need to consider the cutting edge amount and thickness of the cutting blade as in the case of separation with a cutting blade. Further, since the wafer W is processed by the laser beam irradiation, the processing area is minimized and the device area 83 is not narrowed. Further, even when the thickness of the wafer W increases as the diameter of the wafer W increases, the ring-shaped reinforcing portion 85 can be stably removed.

  In addition, this invention is not limited to the said embodiment, It can change and implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  For example, in the above-described embodiment, the escape groove 53 is formed on the upper surface of the holding table 5, but the present invention is not limited to this configuration. If the laser light source is not damaged by the reflection of the laser beam, the escape groove 53 may not be formed on the upper surface of the holding table 5.

  In the above-described embodiment, the groove bottom 54 of the escape groove 53 is inclined so as to become deeper toward the center of the holding table 5, but is not limited to this configuration. The groove bottom 54 of the escape groove 53 may be formed in any way as long as it can reflect the imaging light at the time of alignment and the laser beam at the time of laser processing so as not to return to the irradiation source. For example, the groove bottom 54 is formed by the holding table 5. You may incline so that it may become deep toward the outer periphery.

  In the above-described embodiment, the laser beam irradiation position is indexed and fed radially inward in the first and second processing steps of the ring-shaped reinforcing portion removing step. However, the present invention is not limited to this configuration. In the first and second processing steps, the laser beam irradiation position may be indexed and sent radially outward.

As described above, the present invention has an effect that the ring-shaped reinforcing portion can be stably removed without narrowing the device region. In particular, the ring-shaped reinforcing portion can be removed from a large-diameter wafer. This is useful for a holding table used in a method for processing a wafer to be removed from a wafer.

DESCRIPTION OF SYMBOLS 1 Laser processing apparatus 2 Laser beam irradiation means 3 Imaging means 4 Holding table moving mechanism 5 Holding table 51 Holding surface 52 Outer peripheral edge 53 Relief groove 54 Groove bottom 55 Relief groove inner surface 56 Relief groove outer surface 80 Wafer surface 81 Wafer Back surface 82 Line to be divided 83 Device region 84 Peripheral surplus region 85 Ring-shaped reinforcing portion 86 Boundary portion 87 Upper surface of ring-shaped reinforcing portion 88 Inner peripheral surface of ring-shaped reinforcing portion 89 Outer peripheral surface of ring-shaped reinforcing portion 90 Outer peripheral edge 91 Spot Diameter 92 Laser processing groove F1, F2 Frame T1, T2 Holding tape W Wafer

Claims (2)

A holding table for holding a wafer in which a device region in which a plurality of devices are formed and an outer peripheral surplus region surrounding the device region are formed on the surface, and a ring-shaped reinforcing portion is formed on the back surface corresponding to the outer peripheral surplus region. There,
On the upper surface of the holding table, an annular relief groove for escaping a laser beam is formed at a position corresponding to the boundary portion between the ring-shaped reinforcing portion and the device region, and the holding table is held at the bottom of the relief groove. A holding table, characterized in that fine irregularities on which the laser beam is scattered are formed in a tapered shape that is inclined so as to become deeper toward the center of the table.   The holding table according to claim 1, which is used when grinding the back side of the device region on the back side of the wafer and removing the ring-shaped reinforcing portion formed on the back side of the outer peripheral surplus region by laser beam irradiation.

Images