JP2018088438A - Wafer processing method - Google Patents

Abstract

A wafer processing method combining a laser processing method and a grinding method divides the wafer so as not to cause chipping at the chip corner during grinding. A device is formed in an area partitioned by a first street S1 extending in a first direction and a second street S2 extending in a second direction orthogonal to the first direction, and a first street S1 between the first streets is formed. A method for processing a wafer W in which the second distance between the second streets is shorter than the distance, wherein the wafer W is irradiated with a laser beam along the first street S1 to form a first modified layer inside. a step of irradiating the wafer W with a laser beam along the second street S2 to form a second modified layer inside; dividing W into individual chips, wherein the modified layer forming step forms first modified layers of adjacent chips offset from each other in a second direction. [Selection drawing] Fig. 5

Description

  The present invention relates to a method for processing a wafer on which a device is formed.

  A workpiece such as a semiconductor wafer formed on a surface by dividing a plurality of devices by dividing lines called streets is divided into individual device chips along the streets and used for various electronic devices and the like.

  As a method of dividing a wafer into individual device chips, for example, so-called SDBG (Steal Dicing Before Grinding) is performed using a laser processing apparatus capable of irradiating a laser beam on the wafer and a grinding apparatus capable of grinding the wafer with a grinding wheel. There is a processing method called (see, for example, Patent Document 1). This processing method is a technique that combines laser processing and grinding. First, a laser beam having a wavelength that is transmissive to the wafer is irradiated along the street to be modified to a position at a predetermined depth inside the wafer. Form a quality layer. After that, the wafer's back surface is ground to thin the wafer to the finished thickness, and the modified layer is used as a starting point for splitting, and the wafer is split into individual device chips by extending cracks on the front side of the wafer by grinding pressure. be able to.

International Publication No. 03/077295

  However, in the processing method described in Patent Document 1, a plurality of chips formed by division are close to each other, and there is no space between corners (corners) of adjacent chips in the diagonal direction of each chip. Therefore, there is a problem that the formed chips come into contact with each other during grinding, and in particular, the corners of the chips rub against each other and the corners are easily chipped. When the chip corner is chipped, there is a problem that a crack generated from the chip extends to the device surface and the device is damaged.

  Therefore, in a wafer processing method combining laser processing and grinding, there is a problem that the wafer is divided so as not to cause chipping in the corners of individual chips during grinding.

  The present invention for solving the above-described problems has a plurality of first streets extending in a first direction and a plurality of second streets extending in a second direction orthogonal to the first direction. A device is formed in each area partitioned by the second street and the second distance between the adjacent second streets is shorter than the first distance between the adjacent first streets. A method of irradiating a laser beam having a wavelength that is transmissive to the wafer along the first street to form a first modified layer inside the wafer and to the wafer along the second street A modified layer forming step for forming a second modified layer inside the wafer by irradiating the laser beam, and after performing the modified layer forming step, the back surface of the wafer is ground to obtain a predetermined thickness. And a grinding step for dividing the wafer into individual chips starting from the first modified layer and the second modified layer, and in the modified layer forming step, In this method, the first modified layers are formed to be shifted from each other in the second direction.

  In the wafer processing method according to the present invention, when the first modified layer is formed in the modified layer forming step, the discontinuous first modified layer is formed by shifting in the second direction for each adjacent chip. Therefore, it is possible to form a gap between the corners of each chip adjacent in the diagonal direction, and to prevent the corners of each chip from rubbing in the grinding step, so that the chip corners are not chipped. It becomes possible.

  Further, in the wafer processing method according to the present invention, a continuous second modified layer is formed on the second street having a narrow street interval and a large number, and is not formed on the first street having a wider street interval and a small number. A continuous first modified layer is formed. For this reason, the process for forming the discontinuous first modified layer, which is more complicated in laser processing control and takes time for processing, is performed along the first street where the number of streets is smaller than the second street. The wafer can be processed more efficiently than in the case where a discontinuous modified layer is formed along the street.

It is a perspective view which shows the state which affixes a protective tape on the surface of the wafer in which the 2nd distance between the adjacent 2nd streets was set narrower than the 1st distance between the adjacent 1st streets. It is sectional drawing which shows the state which irradiates a laser beam with respect to a wafer along a 2nd street using a laser processing apparatus, and forms the 2nd modified layer in the inside of a wafer. It is explanatory drawing at the time of seeing the state in which the 2nd modified layer extended continuously linearly along a 2nd street is formed in the inside of a wafer from the upper direction of a wafer. It is explanatory drawing at the time of seeing the state in which the 1st modified layer extended discontinuously along the 1st street is formed in the inside of a wafer from the upper part of a wafer. The state in which the first modified layer formed in a discontinuous manner along the first street and shifted in the second direction with respect to the previously formed first modified layer is viewed from above the wafer. It is explanatory drawing. It is sectional drawing which shows the state which grind | polishes the back surface of a wafer and thins a wafer to predetermined thickness, and divides | segments a wafer into each chip | tip from the 1st modified layer and the 2nd modified layer.

  A wafer W shown in FIG. 1 is, for example, a semiconductor wafer having a disk-like outer shape, and a plurality of first wafers extending in a first direction (X-axis direction in FIG. 1) on the surface Wa of the wafer W. Streets S1 and a plurality of second streets S2 extending in a second direction (Y-axis direction in FIG. 1) orthogonal to the first direction in the horizontal plane are arranged. The distance between one first street S1 and another adjacent first street S1 (the distance between the center lines of the first streets S1) is equal to the first distance L1. Also, the distance between one second street S2 and another second street S2 located next to it (the distance between the center lines of each second street S2) is also The second distance L2 is equally spaced. The second distance L2 between the adjacent second streets S2 is set narrower than the first distance L1 between the adjacent first streets S1, and the first street S1 and the second street S2 A device D such as an IC is formed in each of the partitioned rectangular regions. For example, the device D is formed in a rectangular shape corresponding to the shape of each region.

  When the wafer W is divided into chips each including the device D along the first street S1 and the second street S2, for example, a modified layer serving as a division starting point is formed by the laser processing apparatus 1 illustrated in FIG. Formed inside. Therefore, the protective tape T shown in FIG. 1 is stuck on the surface Wa.

  The protective tape T is, for example, a disk-shaped film having an outer diameter that is approximately the same as the outer diameter of the wafer W, and includes an adhesive surface Ta having adhesive strength. For example, the adhesive surface Ta is made of UV curable paste made of an acrylic base resin or the like that cures and decreases its adhesive strength when irradiated with ultraviolet rays. The surface Wa of the wafer W is protected by the protective tape T by attaching the adhesive surface Ta of the protective tape T to the surface Wa of the wafer W.

  Hereinafter, each step in the case where the wafer processing method according to the present invention is performed to divide the wafer W into individual device chips will be described.

(1) Modified Layer Formation Step A laser processing apparatus 1 shown in FIG. 2 includes, for example, a chuck table 10 that sucks and holds a wafer W, and a laser beam that irradiates a laser beam onto the wafer W held on the chuck table 10. And at least irradiation means 11. The chuck table 10 has, for example, a circular outer shape, and sucks and holds the wafer W on a holding surface 10a made of a porous member or the like. The chuck table 10 can be rotated around the axis in the vertical direction (Z-axis direction) and can be reciprocated in the X-axis direction by the processing feed means 12.

  The laser beam irradiation means 11 includes, for example, a laser beam oscillator 110 (for example, a YAG laser or a YVO4 laser) that can oscillate a laser beam having a predetermined wavelength that is transmissive to the wafer W. In addition, it is connected to the condenser 111 via a transmission optical system such as an optical fiber. Then, the laser beam irradiation means 11 focuses the laser beam inside the wafer W by causing the laser beam oscillated from the laser beam oscillator 110 to enter the condensing lens 111 a inside the condenser 111. Can do. The laser processing apparatus 1 includes ON / OFF switching means 119 for switching ON / OFF of laser beam irradiation by the laser beam oscillator 110.

  In the vicinity of the laser beam irradiation means 11, an alignment means 14 for detecting the first street S1 and the second street S2 of the wafer W shown in FIG. The alignment unit 14 includes an infrared irradiation unit (not shown) that irradiates infrared rays, and an infrared camera 140 that includes an optical system that captures infrared rays and an image sensor (infrared CCD) that outputs electrical signals corresponding to the infrared rays. Based on the image acquired by the infrared camera 140, the first street S1 and the second street S2 on the surface Wa of the wafer W can be detected by image processing such as pattern matching. The laser beam irradiation means 11 is integrated with the alignment means 14, and both move in the Y-axis direction and the Z-axis direction in conjunction with each other. The chuck table 10, the laser beam irradiation means 11, the processing feed means 12, and the alignment means 14 are composed of a CPU and a storage element such as a memory, and are connected to a control means (not shown) that controls the entire laser processing apparatus 1. The control means controls the operation of each component described above based on the machining conditions and the like input by the operator to the control means.

  In the present embodiment, for example, first, a laser beam is irradiated along the second street S2 using the laser processing apparatus 1 shown in FIG. 2 to form a second modified layer inside the wafer W, and then Then, a first modified layer is formed by irradiating a laser beam along the first street S1. The second modified layer is continuously and linearly formed in the center of the second street S2, but the first modified layer is alternately and discontinuously formed at positions shifted from the center of the first street S1 to both sides. To do. In order to perform such processing, processing conditions are set for a control unit (not shown) included in the laser processing apparatus 1 before the formation of the second modified layer and the first modified layer. The processing conditions set in advance include the processing feed speed of the wafer W, the processing start positions of the first street S1 and the second street S2, the values of the first distance L1 and the second distance L2, and the like. The processing feed speed of the wafer W is input by an operator from an input means (not shown) provided in the laser processing apparatus 1. The processing start positions of the first street S1 and the second street S2 are detected by the alignment means 14. Since the values of the first distance L1 and the second distance L2 are known, the values are input by an operator from input means (not shown) provided in the laser processing apparatus 1. Moreover, in order to make the 1st modified layer formed in 1st street S1 discontinuous, ON time and OFF time switched by the ON / OFF switching means 119 are determined, and it sets to a control means. Such ON time and OFF time are calculated by performing a calculation process by a control means (not shown) based on the value of the second distance L2, the value of the processing feed speed of the wafer W, and the like. The ON time and the OFF time are equal, and each time is a time required for the chuck table 10 to move in the X-axis direction by the second distance L2, and is set to repeat ON and OFF alternately. .

  First, alignment is performed so that the holding surface 10a of the chuck table 10 of the laser processing apparatus 1 shown in FIG. 2 and the front surface Wa side protected by the protective tape T of the wafer W face each other, and the wafer W is placed on the rear surface Wb side. Is placed on the chuck table 10 with the side facing up. A suction source (not shown) connected to the chuck table 10 operates to suck and hold the wafer W on the chuck table 10.

  Next, the chuck table 10 that holds the wafer W is rotated around the axis in the Z-axis direction so that the first street S1 of the wafer W is parallel to the X-axis direction, and the direction thereof is adjusted. Then, the wafer W held on the chuck table 10 is sent in the −X direction (forward direction) by the processing feeding means 12, and the first street S <b> 1 is detected by the alignment means 14. Here, the front surface Wa of the wafer W on which the first street S1 is formed is located on the lower side and does not directly face the alignment means 14, but is transmitted from the rear surface Wb side of the wafer W by the infrared camera 140. The first street S1 can be imaged. With the image of the first street S1 captured by the infrared camera 140, the alignment unit 14 performs image processing such as pattern matching, and the position of the first street S1 to be irradiated with the laser beam first, for example, the most − in FIG. The first street S1 on the Y side is detected. Then, the detected Y coordinate value of the first street S1 is stored in the control means.

  Next, the chuck table 10 that holds the wafer W rotates around the axis in the Z-axis direction so that the second street S2 of the wafer W is parallel to the X-axis direction. Then, the second street S2 is detected by the alignment means 14. For example, the second street S2 on the most −X side in FIG. 1 is detected.

  As the second street S2 is detected, the laser beam irradiation means 11 is driven in the Y-axis direction, and the second street S2 that irradiates the laser beam and the condenser 111 are aligned in the Y-axis direction. The This alignment is performed, for example, so that the center line of the second street S <b> 2 is located immediately below the condenser lens 111 a included in the condenser 111.

  Next, the laser beam oscillator 110 from the laser beam oscillator 110 in a state where the condensing point of the laser beam having transparency to the wafer W is positioned at a predetermined height position inside the wafer W corresponding to the second street S2 by the condenser 111. While irradiating the laser beam oscillated and condensed by the condenser lens 111a along the second street S2, the wafer W is processed and fed in the -X direction at a predetermined processing feed rate, and as shown in FIG. The second modified layer M2 is formed inside. The formation position of the second modified layer M2 in the thickness direction (Z-axis direction) of the wafer W is, for example, a position higher than the position above the surface Wa of the wafer W by the finished thickness of the device chip. The second modified layer M2 is formed so as to overlap with the center line of the second street S2 extending in the second direction of the wafer W (Y-axis direction in FIG. 1).

  A second modified layer M2 is continuously formed inside the wafer W along the center line of the second street S2, and, for example, a predetermined X-axis direction finishes irradiating a single second street S2 with a laser beam. When the wafer W advances to the position in the −X direction, as shown by a broken line in FIG. 3, the first streets S <b> 1 are formed along the second street S <b> 2 from one end to the other end of the second street S <b> 2. A second modified layer M2 is formed that extends continuously in a straight line so as to cross.

  Next, the irradiation of the laser beam is stopped, the processing feed of the wafer W in the −X direction (forward direction) is once stopped, the laser beam irradiation means 11 is moved in the + Y direction, and the second irradiated with the laser beam. The second street S2 located next to the street S2 and not yet irradiated with the laser beam is aligned with the condenser 111 in the Y-axis direction. Next, the processing feed unit 12 processes and feeds the wafer W in the + X direction (return direction), and the second street S2 is irradiated with the laser beam in the same manner as the laser beam irradiation in the forward direction. By sequentially irradiating the same laser beam, the laser beam is irradiated from the back surface Wb side of the wafer W along all the second streets S2 extending in the X-axis direction, and the second modification that becomes the division starting point inside the wafer W is performed. The quality layer M2 is formed.

  Next, a first modified layer extending in the first direction is formed inside the wafer W by irradiating a laser beam having a wavelength that is transmissive to the wafer W along the first street S1.

  First, the chuck table 10 holding the wafer W rotates around the axis in the Z-axis direction so that the first street S1 of the wafer W shown in FIG. 2 is parallel to the X-axis direction. Then, the wafer W held on the chuck table 10 is sent in the −X direction (forward direction) by the processing feeding means 12.

  Next, the position of the light collector 111 in the Y-axis direction is set to the first street S11 shown in FIG. 4 to be irradiated with the laser beam first. This alignment is performed, for example, so that the position immediately below the condenser lens 111a included in the condenser 111 is shifted in the −Y direction by a predetermined distance from the center line of the first street S11.

  Next, in a state where the condensing point of the laser beam having transparency with respect to the wafer W is positioned at a predetermined height position inside the wafer W corresponding to the first street S11 by the concentrator 111, the laser beam oscillator 110 is placed. The wafer W is processed and fed in the −X direction at a predetermined processing feed speed while irradiating the laser beam oscillated from the laser beam and collected by the condenser lens 111a along the first street S11. The first modified layer M11 indicated by the alternate long and short dash line is formed. For example, in the thickness direction (Z-axis direction) of the wafer W, the first modified layer M11 is formed at a position higher than the position above the surface Wa of the wafer W by the finished thickness of the device chip, In the second direction of the wafer W, the wafer W is shifted to the −Y direction side by a predetermined distance from the center line of the first street S11.

  For example, the wafer W is processed and fed by the second distance L2, and the ON time of the laser beam oscillator 110 determined by the control means has elapsed, and the second distance L2 in the first direction from the second modified layer M21 shown in FIG. If the first modified layer M11 is formed so as to extend linearly to the second modified layer M22 that is formed only by being spaced apart, the ON time of the laser beam oscillator 110 determined by the control means has passed. / OFF switching means 119 switches the laser beam irradiation to OFF. Then, the state in which the wafer W is processed and fed in the −X direction at a predetermined processing feed rate is maintained, but the irradiation of the laser beam is stopped, so the second modified layer M22 from the second modified layer M22 in the first street S11 is stopped. Until the modified layer M23, the inside of the wafer W is not irradiated with the laser beam and the first modified layer is not formed.

  When a predetermined OFF time elapses when the wafer W is further processed and fed by the second distance L2 at a predetermined processing feed rate in the −X direction, the ON / OFF switching unit 119 switches the laser beam irradiation to ON. Therefore, the wafer W is processed and fed in the −X direction at a predetermined processing feed rate, so that the laser beam is irradiated inside the wafer W and is separated from the second modified layer M23 by the second distance L2 in the first direction. The first modified layer M11 indicated by the alternate long and short dash line is formed inside the wafer W along the first street S11 up to the second modified layer M24 shown in FIG.

  As described above, the first modified layer M11 is discontinuously formed in the wafer W along the first street S11 so as to be spaced apart in the first direction by a predetermined interval. The wafer W advances in the -X direction to a predetermined position in the X-axis direction where the laser beam is completely irradiated. Next, the irradiation of the laser beam is stopped and the processing feed of the wafer W in the −X direction (forward direction) is once stopped, and the laser beam irradiation means 11 shown in FIG. 2 is moved in the + Y direction so that the laser beam is irradiated. The first street S12 shown in FIG. 4 that is positioned next to the first street S11 that has not yet been irradiated with the laser beam and the condenser 111 shown in FIG. 4 are aligned in the Y-axis direction. Next, the processing feeding means 12 processes and feeds the wafer W in the + X direction (return direction), and the first street S12 is irradiated with the laser beam in the same manner as the laser beam irradiation in the forward direction. By sequentially irradiating the same laser beam, the laser beam is irradiated from the back surface Wb side of the wafer W along all the first streets S1 extending in the X-axis direction, and the first modification that becomes the division starting point inside the wafer W is performed. The quality layer M11 is formed discontinuously along each first street S1.

  Next, the first modified layer M11 and the first modified layer that is shifted in the second direction and extends in the first direction are irradiated with a laser beam having a wavelength that is transmissive to the wafer W along the first street S1. Then, it is formed inside the wafer W. First, the wafer W held on the chuck table 10 is sent in the −X direction (forward direction) by the processing feeding means 12 shown in FIG.

  Then, the first street S11 that irradiates the laser beam and the condenser 111 are aligned in the Y-axis direction. This alignment is performed, for example, such that the position immediately below the condensing lens 111a included in the concentrator 111 is shifted in the + Y direction by a predetermined distance from the center line of the first street S11. Next, a condensing point of a laser beam having a predetermined wavelength is positioned at a predetermined height position inside the wafer W corresponding to the first street S11 by the condenser 111. Further, the wafer W is processed and fed in the −X direction at a predetermined processing feed speed.

  For example, when the ON / OFF switching unit 119 turns off the irradiation of the laser beam, even if the wafer W is processed and fed in the -X direction at a predetermined processing feed rate, the first street S11 shown in FIG. Between the second modified layer M21 and the second modified layer M22, the inside of the wafer W is not irradiated with the laser beam, and the first modified layer M11 and the first modified layer M11 are shifted in the second direction and extend in the first direction. The modified layer is not formed.

  When a predetermined OFF time elapses when the wafer W is further processed and fed by the second distance L2 at a predetermined processing feed rate in the −X direction, the ON / OFF switching unit 119 switches the laser beam irradiation to ON. Therefore, the wafer W is further processed and fed at a predetermined processing feed rate in the −X direction, so that the laser beam is irradiated inside the wafer W, and the second modified layer M22 shown in FIG. A first modified layer M12 indicated by a two-dot chain line is formed inside the wafer W along the first street S11 up to the layer M23. The formation position of the first modified layer M12 is, for example, a position above the position above the surface Wa of the wafer W by the finished thickness of the device chip in the thickness direction (Z-axis direction) of the wafer W, In the second direction of the wafer W, the wafer W is shifted to the + Y direction side by a predetermined distance from the center line of the first street S11. Therefore, the first modified layer M12 is formed so as to be shifted in the second direction with respect to the first modified layer M11.

  For example, when the wafer W is processed and fed by the second distance L2, and the first modified layer M12 is formed to extend linearly from the second modified layer M22 to the second modified layer M23 shown in FIG. The ON / OFF switching means 119 switches the laser beam irradiation to OFF. The state in which the wafer W is processed and fed in the −X direction at a predetermined processing feed rate is maintained, but a laser beam is placed inside the wafer W between the second modified layer M23 and the second modified layer M24. Is not irradiated and the first modified layer M11 is not formed with the first modified layer that is shifted in the second direction and extends in the first direction.

  As described above, the first modified layer M12 is discontinuously formed in the wafer W along the first street S11 so as to be spaced apart in the first direction by a predetermined interval. The wafer W advances in the -X direction to a predetermined position in the X-axis direction where the laser beam is completely irradiated. Next, the irradiation of the laser beam is stopped and the processing feed of the wafer W in the −X direction (forward direction) is once stopped. The laser beam irradiation unit 11 moves in the + Y direction, and the first irradiated with the laser beam. The first street S12 located next to the street S11 and not yet irradiated with the laser beam is aligned with the condenser 111 in the Y-axis direction. Next, the processing feeding means 12 processes and feeds the wafer W in the + X direction (return direction), and the first street S12 is irradiated with the laser beam in the same manner as the laser beam irradiation in the forward direction. By sequentially irradiating the same laser beam, the laser beam is irradiated from the back surface Wb side of the wafer W along all the first streets S1 extending in the X-axis direction, and the first modified layer M11 and the second direction mutually. The first modified layer M12 extending in the first direction is discontinuously formed inside the wafer W along each first street S1. The first modified layer M12 is formed at the X coordinate position where the laser is turned off when the first modified layer M11 is formed. Therefore, the first modified layers M11 and the second modified layers M12 are alternately formed in the first direction on the first streets S11, S12,. The layer M11 and the second modified layer M12 are formed so as to be shifted from each other in the second direction.

(2) Grinding step After the modified layer forming step is completed, the back surface Wb of the wafer W is ground to thin the wafer W to a predetermined thickness, and the first modified layer M11 and the first modified layer shown in FIG. Starting from M12 and the second modified layer M2, a grinding step for dividing the wafer W into individual chips C shown in FIG. 5 is performed.

  The grinding apparatus 2 shown in FIG. 6 includes, for example, at least a holding table 20 that sucks and holds the wafer W and a grinding unit 21 that grinds the wafer W held on the holding table 20. The holding table 20 has, for example, a circular outer shape, and sucks and holds the wafer W on a holding surface 20a made of a porous member or the like. The holding table 20 can rotate around the vertical axis, and can be reciprocated in the Y-axis direction by the Y-axis direction feeding means 23.

  The grinding means 21 can be moved up and down by a grinding feed means 22 for grinding and feeding the grinding means 21 in the Z-axis direction that is separated from or approaches the holding table 20. The grinding feed means 22 is, for example, a ball screw mechanism that is operated by a motor or the like. The grinding means 21 includes a rotating shaft 210 whose axial direction is the vertical direction (Z-axis direction), a motor 212 that rotationally drives the rotating shaft 210, an annular mount 213 connected to the lower end of the rotating shaft 210, and a mount And a grinding wheel 214 detachably connected to the lower surface of 213.

  The grinding wheel 214 includes a wheel base 214a and a plurality of substantially rectangular parallelepiped grinding wheels 214b disposed in an annular shape on the bottom surface of the wheel base 214a. The grinding wheel 214b is formed by, for example, fixing diamond abrasive grains or the like with a resin bond or a metal bond. In addition, the shape of the grinding wheel 214b may be formed integrally in an annular shape.

  For example, a flow path (not shown) that communicates with a grinding water supply source and serves as a path for grinding water is formed inside the rotating shaft 210 so as to penetrate in the axial direction (Z-axis direction) of the rotating shaft 210. The path passes through the mount 213 and is open at the bottom surface of the wheel base 214a so that grinding water can be ejected toward the grinding wheel 214b.

  In the grinding step, first, the wafer W is placed on the holding surface 20a with the back surface Wb facing upward so that the center of the holding table 20 and the center of the wafer W are substantially matched. Then, the suction force generated by a suction source (not shown) is transmitted to the holding surface 20a, so that the holding table 20 sucks and holds the wafer W.

  Next, the holding table 20 holding the wafer W moves in the + Y direction to below the grinding unit 21, and the grinding wheel 214 provided in the grinding unit 21 and the wafer W are aligned. For example, as shown in FIG. 6, the rotation center of the grinding wheel 214 is shifted in the + Y direction by a predetermined distance with respect to the rotation center of the holding table 20, and the rotation trajectory of the grinding wheel 214 b rotates the holding table 20. It is done through the center.

  After the grinding wheel 214 provided in the grinding means 21 and the wafer W are aligned, the grinding wheel 214 rotates as the rotary shaft 210 is rotated counterclockwise as viewed from the + Z direction side. . Further, the grinding means 21 is sent in the −Z direction by the grinding feed means 22, and the grinding wheel 214 b of the rotating grinding wheel 214 is brought into contact with the back surface Wb of the wafer W to perform grinding. During grinding, as the holding table 20 rotates counterclockwise as viewed from the + Z direction side, the wafer W held on the holding surface 20a also rotates. Grind the entire surface. Further, during the grinding process, the grinding water is supplied to the contact portion between the grinding wheel 214b and the wafer W through the flow path in the rotating shaft 210, and the contact portion between the grinding wheel 214b and the back surface Wb of the wafer W is determined. Cool and wash.

  When the grinding is continued, the crack extends toward the surface Wa of the wafer W by applying the grinding pressure along the first modified layer M11, the first modified layer M12, and the second modified layer M2 shown in FIG. The wafer W is divided into rectangular individual chips C shown in FIG. Then, grinding is continued even after the division, and when the wafer W is formed to have a finished thickness, the grinding feed means 22 raises the grinding means 21 in the + Z direction and finishes the grinding.

  When the first modified layer is formed in the modified layer forming step, the wafer processing method according to the present invention is shifted in the second direction for each adjacent chip C including the device D as shown in FIG. The discontinuous first modified layer M11 and the first modified layer M12 are formed. Therefore, an interval can be formed in the corner Cd portion of each chip C adjacent in the diagonal direction, and the corner Cd of each chip C is prevented from rubbing during and after the division of the wafer W in the grinding step. It is possible to prevent the corner Cd of C from being chipped.

  In the wafer processing method according to the present invention, a continuous second modified layer M2 is formed on the second street S2 extending in the second direction where the interval between adjacent streets is short and the number of the streets is large. A discontinuous first modified layer M11 and a first modified layer M12 are formed so as to be displaced from each other on the first street S1 extending in the first direction with a long interval and a small number. For this reason, the steps for forming the discontinuous first modified layer M11 and the first modified layer M12, which require more complicated laser processing control and processing time, are performed in the first street S1 having a smaller number of streets. The wafer W can be processed more efficiently than when the discontinuous modified layer is formed on the second street S2.

  The wafer processing method according to the present invention is not limited to the above embodiment, and the configurations of the laser processing apparatus 1 and the grinding apparatus 2 shown in the attached drawings are not limited to this. These can be appropriately changed within a range where the effects of the present invention can be exhibited.

  For example, in the modified layer forming step, first, the laser beam is irradiated to the wafer W along the first street S1 to form the first modified layer M11 and the first modified layer M12 inside the wafer W. Then, the second modified layer M2 may be formed inside the wafer W by irradiating the wafer W with the laser beam along the second street S2.

W: Wafer Wa: Wafer surface Wb: Wafer back surface S1: First street S2: Second street D: Device M11, M12: First modified layer M2: Second modified layer T: Protective tape Ta: Protective tape Adhesive surface 1: Laser processing apparatus 10: Chuck table 10 a: Chuck table holding surface 11: Laser beam irradiation means 110: Laser beam oscillator 111: Light collector
111a: condenser lens 119: ON / OFF switching means 12: processing feeding means 14: alignment means 140: infrared camera 2: grinding device 20: holding table 20a: holding surface of holding table
23: Y-axis direction feeding means 21: Grinding means 210: Rotating shaft 212: Motor 213: Mount
214: Grinding wheel 214a: Wheel base 214b: Grinding wheel

Claims (1)

Each having a plurality of first streets extending in a first direction and a plurality of second streets extending in a second direction orthogonal to the first direction, each partitioned by the first street and the second street A device is formed in each region, and a wafer processing method in which a second distance between adjacent second streets is shorter than a first distance between adjacent first streets,
A laser beam having a wavelength that is transmissive to the wafer is irradiated along the first street to form a first modified layer inside the wafer, and the laser beam is applied to the wafer along the second street. A modified layer forming step of forming a second modified layer inside the wafer by irradiating
After performing the modified layer forming step, the back surface of the wafer is ground to thin the wafer to a predetermined thickness, and the wafer is made into individual chips starting from the first modified layer and the second modified layer. And a grinding step to divide, and
In the modified layer forming step, the first modified layer of adjacent chips is formed so as to be shifted from each other in the second direction.

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