JP6232230B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a wafer processing method for forming a modified layer inside a wafer by laser beam irradiation.

  As a method of dividing a wafer, which is a workpiece, into individual devices, a laser beam is irradiated inside the wafer along the street to form a modified layer that serves as the starting point of the division. There is a processing method in which after cracks are generated toward the front surface side in the vertical direction, the back surface of the wafer is ground and divided into individual devices (for example, see Patent Document 1 below).

Japanese Patent No. 3762409

  When a wafer is laser processed using the above processing method, if there is a region where cracks reaching the surface of the wafer are not formed over a long distance, a region where the wafer is not divided even if the back surface of the wafer is ground. May occur.

  However, the wafer processing method as described above forms a modified layer on the front surface side of the wafer, but the wafer is formed with a narrow street width in order to increase the number of devices. A laser beam is irradiated from the back side of the wafer while the front side is held.

  Therefore, it cannot be recognized during processing whether or not a crack reaching the surface of the wafer is formed, and an area that is not divided is detected only by grinding the back surface of the wafer. Thus, if the wafer is not divided into individual devices, there is a problem that the wafer itself becomes defective and the productivity is very poor, and improvement of the wafer processing method is eagerly desired.

  The present invention has been made in view of the above circumstances, and there is a problem to be solved by the present invention in order to reduce the possibility that the wafer itself becomes defective.

The present invention is a method for processing a wafer in which a plurality of intersecting division lines are set,
A holding step for holding the front surface side of the wafer by a holding means including a holding surface for holding the wafer and having a holding portion made of a transparent material to expose the back side of the wafer, and after performing the holding step, In the state where the condensing point of the laser beam having a wavelength having transparency is positioned inside the wafer, the laser beam is irradiated from the back surface side of the wafer along the planned division line to form a modified layer, and A laser beam irradiation step for generating a crack from the modified layer to the surface of the wafer, a crack detection step for imaging the surface side of the wafer through the holding unit, and detecting the presence or absence of the crack reaching the surface of the wafer, After performing the laser beam irradiation step and the crack detection step, the rear surface side of the wafer is ground to remove the modified layer and the crack. And a grinding step of dividing along the dividing lines of the wafer by.

The present invention includes an additional processing step of irradiating a laser beam again from the back side of the wafer to a region where the crack detected in the crack detection step is not continuously formed until reaching the front surface of the wafer.

In the wafer processing method according to the present invention, after the holding step of holding the front surface side of the wafer by the holding means is performed, a modified layer is formed inside the wafer by irradiating a laser beam from the back side of the wafer. The laser beam irradiation step for generating cracks from the wafer surface to the wafer surface is performed, and the crack detection step for detecting the presence or absence of cracks by imaging from the wafer surface side is performed. It is possible to detect whether or not a crack reaching the surface of the wafer is formed by imaging the surface side of the wafer. Therefore, an area where the wafer is not divided can be detected in advance.
In addition, in the wafer processing method, since an additional machining step is performed after the crack detection step, a modified layer is formed by irradiating a laser beam again to a region where a fixed-length crack is not formed on the wafer. Therefore, cracks reaching the surface of the wafer can be reliably generated. Therefore, the possibility that the wafer itself becomes defective can be further reduced, and the productivity of the product can be improved.

It is a perspective view which shows the structure of a laser processing apparatus. It is a perspective view which shows the structure inside the housing | casing with which a laser processing apparatus is equipped. It is a perspective view which shows the state which sticks a surface protection tape on the surface of a wafer. It is sectional drawing which shows a holding | maintenance step. It is sectional drawing which shows a laser beam irradiation step and a crack detection step. It is sectional drawing which shows an additional process step. It is sectional drawing which shows a grinding step.

  A laser processing apparatus 10 shown in FIG. 1 has an apparatus base 100. On the upper surface of the apparatus base 100, a holding means 11 for holding the wafer, a first X-axis direction feeding means 13 for processing and feeding the holding means 11 in the X-axis direction, and a processing means for feeding the holding means 11 in the Y-axis direction. First Y-axis direction feeding means 18 is disposed. The holding unit 11 includes a holding surface 12 that holds a wafer and includes a holding unit 110 made of a transparent material, and is configured to be rotatable.

  The first X-axis direction feeding means 13 extends along the X-axis direction ball screw 14, a motor 15 connected to one end of the ball screw 14, a pair of guide rails 16 extending in parallel to the ball screw 14, and the guide rails 16. And a moving base 17 guided in the X-axis direction. The movable base 17 has a nut provided therein screwed into the ball screw 14 and a lower portion in sliding contact with the guide rail 16. The first X-axis direction feeding means 13 can move the moving base 17 in the X-axis direction along the pair of guide rails 16 by driving the motor 15 and rotating the ball screw 14.

  The first Y-axis direction feeding means 18 includes a ball screw 19 extending in the Y-axis direction, a motor 20 connected to one end of the ball screw 19, a pair of guide rails 21 extending in parallel with the ball screw 19, and the guide rails 21. The housing 22 is guided in the Y-axis direction. The housing 22 has a ball screw 19 screwed into a nut provided therein, and a lower portion in sliding contact with the pair of guide rails 21. The first Y-axis direction feeding means 13 can move the housing 22 in the Y-axis direction along the pair of guide rails 21 by driving the motor 20 and rotating the ball screw 19.

  The laser processing apparatus 10 includes a scale 25 that is disposed along one guide rail 16 of the first X-axis direction feeding means 13 and detects the machining feed amount in the X-axis direction of the holding means 11, and a first Y-axis. A scale 26 is provided along one guide rail 21 of the direction feed means 18 and detects the machining feed amount of the holding means 11 in the Y-axis direction.

  A column 101 extending in the Z-axis direction is erected on the upper surface of the apparatus base 100, and a casing 102 extending in the Y-axis direction is connected to a side portion of the column 101. The tip of the casing 102 has a laser irradiation head 31 for irradiating a laser beam downward, a laser beam irradiation means 30 for irradiating the inside of the wafer with a laser beam to form a modified layer, and a laser beam for the wafer. Imaging means 32 for detecting a position to be irradiated.

  The laser processing apparatus 10 includes a control unit 40 that controls at least the operations of the first X-axis direction feeding unit 13, the first Y-axis direction feeding unit 18, the laser beam irradiation unit 30, and the imaging unit 32. The control unit 40 includes a CPU 41 that performs arithmetic processing according to a control program, a ROM 42 that is accessible from the CPU 41 and stores data, a RAM 43 that can read and write calculation results by the CPU 41, a counter 44 connected to the CPU 41, and a scale 25. Control signals are output to the input interface 45 to which detection signals from the scale 26 and the alignment unit 32 are input, the first X-axis direction feeding unit 13, the first Y-axis direction feeding unit 18, and the laser beam irradiation unit 30. And at least an output interface 46.

  As shown in FIG. 1, the housing 22 of the first Y-axis direction feeding means 18 supports the holding means 11 from below. In addition, an imaging unit 50 having a camera unit 51 shown in FIG. 2 for imaging the wafer held by the holding unit 11 from below is provided inside the housing 22. As shown in FIG. 2, a circular opening 23 is formed at the top of the housing 22, and a second X for processing and feeding the imaging means 50 in the X-axis direction at the bottom 24 of the housing 22. An axial direction feeding means 60 and a second Y axis direction feeding means 65 for processing and feeding the imaging means 50 in the Y axis direction are disposed.

The second X-axis direction feeding means 60 is provided along a ball screw 61 extending in the X-axis direction, a motor 62 connected to one end of the ball screw 61, a pair of guide rails 63 extending parallel to the ball screw 61, and the guide rails 63. And a moving base 64 guided in the X-axis direction.
The moving base 64 has a nut provided therein screwed into the ball screw 61 and a lower portion in sliding contact with the pair of guide rails 63. When the motor 62 is driven and the ball screw 61 rotates, the moving base 64 can be moved in the X-axis direction.

  The second Y-axis direction feed means 65 extends along the ball screw 66 extending in the Y-axis direction, a motor 67 connected to one end of the ball screw 66, a pair of guide rails 68 extending parallel to the ball screw 66, and the guide rails 68. And a moving base 69 guided in the Y-axis direction. An imaging means 50 is disposed on one surface of the movable base 69, and a nut provided at the center of the other surface is screwed into the ball screw 66, and the lower portion is in sliding contact with the pair of guide rails 68. Yes. When the motor 67 is driven and the ball screw 66 rotates, the moving base 69 can be moved in the Y-axis direction.

  A column 70 is erected on the moving base 69, and lifting means 71 for lifting the camera unit 51 is disposed in front of the column 70. The elevating means 71 includes a ball screw 72 extending in the Z-axis direction, a motor 73 connected to the upper end of the ball screw 72, and a pair of guide rails 74 extending in parallel with the ball screw 72. A nut provided in the camera unit 51 is screwed into the ball screw 72 and the side portion is in sliding contact with the pair of guide rails 74. When the motor 73 is driven and the ball screw 72 is rotated, the camera unit 51 can be moved up and down in the Z-axis direction.

  Next, a method for performing laser processing on a wafer using the laser processing apparatus 10 will be described. A circular wafer 1 shown in FIG. 3 is an example of a workpiece, and a device 5 is formed in each region partitioned by a plurality of division lines 4 that intersect vertically and horizontally. In the wafer 1, the surface on which the device 5 is formed is the front surface 2, and the surface opposite to the front surface 2 is the back surface 3 held by the holding means 11 shown in FIG. 1. At the time of laser processing, as shown in FIG. 3, a surface protection tape 6 having the same diameter as that of the wafer 1 is attached to the surface 2 of the wafer 1.

(1) Holding Step As shown in FIG. 4, the wafer 1 with the surface protection tape 6 attached to the surface 2 is turned over and the surface protection tape 6 side is placed on the holding surface 12 of the holding means 11. The back surface 3 is exposed upward. Next, a suction source (not shown) is activated to suck and hold the surface 2 of the wafer 1 by the holding means 11.

(2) Laser beam irradiation step After performing the holding step, as shown in FIG. 5, a laser beam 7 having transparency to the wafer 1 is used to form a modified layer inside the wafer 1. Perform laser processing. As the laser processing conditions, for example, the following processing conditions are set in the laser beam irradiation means 30.

[Processing conditions]
Light source: YAG pulse laser / YVO 4 pulse laser Wavelength: 1064 nm
Output: 1.5W

  First, the planned dividing line 4 is detected by the imaging means 32 shown in FIG. Then, while moving the holding unit 11 in the X-axis direction by the X-axis direction feeding unit 13, the laser beam irradiation unit 30 sets the condensing point of the laser beam 7 inside the wafer 1 on the surface based on the processing conditions. The laser beam 7 is irradiated toward the back surface 3 side of the wafer 1 from the laser irradiation head 31 shown in FIG. 5 along the division line 4 shown in FIG.

  As described above, the modified layer 8 is formed inside the wafer 1 by irradiating the inside of the wafer 1 with the laser beam 7 as shown in the partially enlarged view of FIG. When the modified layer 8 is formed, a crack 9 is generated from the position where the modified layer 8 is formed to the surface 2. The modified layer is a region melted and re-cured by laser beam irradiation. When the modified layer 8 and the crack 9 are formed by irradiating the laser beam 7 along all the planned dividing lines 4 that are vertically and horizontally shown in FIG. 3, the laser beam irradiation step is finished. The modified layer 8 is formed at a height position that is ground and removed in a subsequent grinding step.

(3) Crack detection step When the laser beam irradiation step is performed, the surface 2 side of the wafer 1 held by the holding unit 11 by the camera unit 51 shown in FIG. An image is taken to detect whether or not a crack 9 is formed on the surface 2 side. In the crack detection step, for example, the image pickup means 32 shown in FIG. 1 picks up the divisional line 4 in advance and stores its position information in the RAM 43, whereby the second X-axis direction feed shown in FIG. The means 60 and the second Y-axis direction feed means 65 position the camera unit 51 below the division line 4 to be irradiated with the laser. And the crack 9 is detected by imaging from the downward direction along the division | segmentation scheduled line 4 in which the modified layer 8 was formed. Since the holding unit 110 constituting the holding unit 11 is made of a transparent material, the camera unit 51 can image the surface 2 via the holding unit 110. When there is a portion where the crack 9 is not continuously formed by such imaging, the position information is stored in the RAM 43 as the non-cracking position information.

  The crack detection step may be performed in parallel with the laser beam irradiation step, or may be performed after the modified layer 8 is formed on one line or a plurality of scheduled division lines 4. For example, the crack detection step can also be performed after laser processing of the 5 or 10 scheduled division lines 4. Since the case 22 provided with the camera unit 51 supports the holding unit 11 from below, when the crack detection step is performed in parallel with the laser beam irradiation step, the case 22 is adjusted in accordance with the movement of the holding unit 11 in the X-axis direction. Thus, the camera unit 51 can also be moved in the X-axis direction.

(4) Additional machining step When a region where the crack 9 reaching the surface 2 of the wafer 1 is not formed is detected by performing the crack detection step, as shown in FIG. Perform additional machining according to the operation. That is, for example, the laser beam 7 having the same conditions as in the laser beam irradiation step is divided from the back surface 3 side of the region where the crack 9 is not formed (the position indicated by the crack non-formation position information stored in the RAM 43 in the crack detection step). Irradiation along the planned line 4 forms the modified layer 8. Thereby, the crack 9 from the position where the modified layer 8 is newly formed to the surface 2 is generated. In the additional processing step, the laser beam may be irradiated with an output higher than the output of the laser beam 7 irradiated in the laser beam irradiation step. In addition, after performing an additional process step, you may confirm whether the crack 9 was formed again by implementing a crack detection step. Moreover, when the area | region where the crack 9 is not formed in a crack detection step is not detected, an additional process step is not implemented.

(5) Grinding step After performing the laser beam irradiation step and the crack detection step (or after the additional machining step), the wafer 1 is transferred to the holding means 11a shown in FIG. The back surface 3 is ground. The grinding means 80 includes a spindle 81 having a vertical axis, a grinding wheel 83 attached to a lower end of the spindle 81 via a mounter 82, a grinding wheel 84 fixed in an annular shape to a lower portion of the grinding wheel 83, At least.

  The grinding means 80 descends in the vertical direction while rotating the grinding wheel 83 as the spindle 81 rotates, and grinds the wafer 1 until the modified layer 8 is removed by the rotating grinding wheel 84. As a result, the wafer 1 can be divided into the individual devices 5 shown in FIG.

As described above, in the processing step shown in the present embodiment, a crack reaching the surface 2 of the wafer 1 by the imaging means 50 during laser processing of the wafer 1 by performing the laser beam irradiation step and the crack detection step. Whether or not 9 is formed can be detected. Therefore, before the wafer 1 is ground, an undivided region of the wafer 1 can be detected in advance.
In addition, after performing the crack detection step, an additional processing step is performed, so that the modified layer 8 is formed by irradiating the laser beam 7 again to the region where the crack 9 having a certain length is not formed on the wafer 1. Therefore, the crack 9 reaching the surface 2 of the wafer 1 can be reliably generated. Therefore, the possibility that the wafer 1 itself becomes defective can be reduced, and the productivity of the product can be improved.

1: Wafer 2: Front surface 3: Back surface 4: Line to be divided 5: Device 6: Surface protective tape 7: Laser beam 8: Modified layer 9: Crack 10: Laser processing apparatus 100: Apparatus base 101: Column 102: Casing 11 : Holding means 110: Holding portion 12: Holding surface 13: First X-axis direction feeding means 14: Ball screw 15: Motor 16: Guide rail 17: Moving base 18: First Y-axis direction feeding means 19: Ball screw 20 : Motor 21: Guide rail 22: Housing 23: Opening 24: Bottom 25, 26: Scale 30: Laser beam irradiation means 31: Laser irradiation head 32: Imaging means 40: Control unit 41: CPU 42: ROM 43: RAM 44: Counter 45: Input interface 46: Output interface 50: Imaging means 51: Camera unit 0: Second X-axis direction feeding means 61: Ball screw 62: Motor 63: Guide rail 64: Moving base 65: Second Y-axis direction feeding means 66: Ball screw 67: Motor 68: Guide rail 69: Moving base 70: Column 71: Z-axis direction feeding means 72: Ball screw 73: Motor 74: Guide rail 80: Grinding means 81: Spindle 82: Mounter 83: Grinding wheel 84: Grinding wheel

Claims (2)

A wafer processing method in which a plurality of intersecting division lines are set,
A holding step of holding the front side of the wafer with a holding means including a holding surface that holds the wafer and having a holding portion made of a transparent material, and exposing the back side of the wafer;
After carrying out the holding step, the laser beam is irradiated along the planned dividing line from the back side of the wafer with the converging point of the laser beam having a wavelength transparent to the wafer positioned inside the wafer. Forming a modified layer, and a laser beam irradiation step for generating a crack from the modified layer to the surface of the wafer;
A crack detection step of imaging the surface side of the wafer through the holding unit and detecting the presence or absence of the crack reaching the surface of the wafer;
After performing the laser beam irradiation step and the crack detection step, grinding the back surface side of the wafer to remove the modified layer and dividing the wafer along the division line by the crack, A wafer processing method provided. 2. The process according to claim 1, further comprising an additional processing step of irradiating the laser beam again from the back side of the wafer to a region where the crack detected in the crack detection step is not continuously formed until reaching the surface of the wafer. Wafer processing method.

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