JP2010021330A - Method of processing wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for processing a wafer without causing chipping on the back surface of a device.
SOLUTION: A plurality of division lines are formed in a lattice shape on the surface, and a device area in which a device is formed in each of a plurality of areas partitioned by the plurality of division lines, and the device area are surrounded. A wafer processing method that divides a wafer having an outer peripheral surplus area into individual devices, wherein the back surface of the wafer is ground so that slight microcracks remain on the back surface of the wafer, and is attached to an annular frame. The back surface of the wafer is attached to the top, and the wafer mounted on the annular frame is held on the chuck table of the cutting apparatus with the adhesive tape side down so that the cutting blade of the cutting blade cuts the adhesive tape. The cutting blade is positioned on the division line of the wafer to completely cut the division line. It is a sign.
[Selection] Figure 4

Description

  The present invention relates to a wafer processing method in which a back surface of a wafer such as a semiconductor wafer is ground to a predetermined thickness and then the wafer is divided into individual devices with a cutting device.

  A semiconductor wafer in which a number of devices such as IC and LSI are formed on the surface, and each device is partitioned by a line to be divided (street), the back surface is ground by a grinding machine and processed to a predetermined thickness. A dividing line is cut by a cutting device (dicing device) to be divided into individual devices, and the divided devices are used for electric devices such as mobile phones and personal computers.

  The wafer is formed to have a predetermined thickness by grinding the back surface prior to cutting by the cutting apparatus, but microcracks having a depth of about 2 to 3 μm remain on the back surface of the wafer, reducing the bending strength of the device. There is a problem.

Therefore, the present applicant has developed a grinding wheel in which abrasive grains are mixed in felt, and found that when the back surface of the wafer is polished with this grindstone, the grinding strain is removed and the bending strength is improved (Japanese Patent Laid-Open No. 2005-230867). 2000-343440 gazette).
JP 2000-343440 A

  However, if the cutting edge of the cutting blade is positioned on the wafer splitting line and the wafer is completely cut at a cutting depth that reaches the dicing tape, a relatively large chipping (chip) occurs along the cutting groove that appears on the back side of the wafer. A new problem has occurred that reduces device quality.

  In addition, if the back surface of the wafer after grinding is polished to be free of microcracks, the bending strength will increase, but if an impact exceeding the bending strength is applied to the wafer, it will explode like tempered glass. A phenomenon occurs in which the wafer is shattered.

  The present invention has been made in view of these points, and an object of the present invention is to provide a wafer processing method in which chipping does not occur on the back surface of a device after wafer cutting.

  According to the present invention, a plurality of division lines are formed in a lattice shape on the surface, and a device area in which a device is formed in each of a plurality of areas partitioned by the plurality of division lines and surrounding the device area A wafer processing method that divides a wafer having a peripheral outer peripheral region into individual devices, wherein the back surface of the wafer is ground so that slight microcracks remain on the back surface of the wafer, and is attached to an annular frame. The back surface of the wafer is stuck on the tape, the wafer mounted on the annular frame is held on the chuck table of the cutting apparatus with the adhesive tape side down, and the cutting blade of the cutting blade cuts the adhesive tape. In addition, each process was provided to completely cut the planned dividing line by positioning the cutting blade on the planned dividing line of the wafer. The wafer processing method according to claim is provided.

  Preferably, in the grinding step, diamond abrasive grains of 0.1 μm or less are bonded by vitrified bonds, and the back surface of the wafer is ground with a sintered grinding wheel. Preferably, the slight microcracks remaining on the back surface of the wafer are constituted by microcracks having a depth of 0.05 μm to 0.5 μm.

  According to the wafer processing method of the present invention, the back surface of the wafer is ground so that few microcracks remain when grinding the back surface of the wafer, or appropriate microcracks remain. The impact force is relaxed, no explosive destruction occurs due to the impact, and large chipping is prevented from occurring on both sides of the cutting groove cut by the cutting blade, so that the quality of the device can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view of a semiconductor wafer before being processed to a predetermined thickness. A semiconductor wafer 11 shown in FIG. 1 is made of, for example, a silicon wafer having a thickness of 700 μm, and a plurality of streets 13 are formed in a lattice shape on the surface 11a, and a plurality of streets partitioned by the plurality of streets 13 are formed. A device 15 such as an IC or LSI is formed in the region.

  The semiconductor wafer 11 configured as described above includes a device region 17 in which the device 15 is formed, and an outer peripheral surplus region 19 that surrounds the device region 17. A notch 21 is formed on the outer periphery of the semiconductor wafer 11 as a mark indicating the crystal orientation of the silicon wafer.

  A protective tape 23 is attached to the surface 11a of the semiconductor wafer 11 by a protective tape attaching process. Therefore, the front surface 11a of the semiconductor wafer 11 is protected by the protective tape 23, and the back surface 11b is exposed as shown in FIG.

  Referring to FIG. 3, there is shown a perspective view of a grinding apparatus 2 suitable for carrying out the wafer processing method of the present invention. Reference numeral 4 denotes a housing of the grinding device 2, and two columns 6 a and 6 b are erected vertically on the rear side of the housing 4. A pair of guide rails (only one is shown) 8 extending in the vertical direction is fixed to the column 6a.

  A rough grinding unit 10 is mounted along the pair of guide rails 8 so as to be movable in the vertical direction. The rough grinding unit 10 is attached to a moving base 12 whose housing 20 moves up and down along a pair of guide rails 8.

  The rough grinding unit 10 includes a housing 20, a spindle (not shown) rotatably accommodated in the housing 20, a servo motor 22 that rotationally drives the spindle, and a plurality of rough grinding grinding wheels fixed to the tip of the spindle. A grinding wheel 24 having 26 is included.

  As shown in FIG. 4A, the rough grinding unit 10 has a spindle 25 accommodated in a housing 20, and a mounter 27 is fixed to the tip of the spindle 25. A grinding wheel 24 having a grinding wheel 26 for rough grinding is screwed to the mounter 27.

  The rough grinding unit 10 includes a rough grinding unit moving mechanism 18 including a ball screw 14 and a pulse motor 16 that move the rough grinding unit 10 up and down along a pair of guide rails 8. When the pulse motor 16 is pulse-driven, the ball screw 14 rotates and the moving base 12 is moved in the vertical direction.

  A pair of guide rails 19 (only one is shown) 19 extending in the vertical direction are also fixed to the other column 6b. A finish grinding unit 28 is mounted along the pair of guide rails 19 so as to be movable in the vertical direction.

  The finish grinding unit 28 is attached to a moving base (not shown) in which the housing 36 moves in the vertical direction along the pair of guide rails 19. The finish grinding unit 28 includes a housing 36, a spindle (not shown) rotatably accommodated in the housing 36, a servo motor 38 that rotationally drives the spindle, and a grinding wheel 42 for finish grinding fixed to the tip of the spindle. A grinding wheel 40 is included.

  As shown in FIG. 4B, the finish grinding unit 28 has a spindle 37 accommodated in a housing 36, and a mounter 39 is fixed to the tip of the spindle 37. A grinding wheel 40 having a grinding wheel 42 for finish grinding is screwed to the mounter 39.

  The rough grinding wheel 26 is formed by bonding diamond abrasive grains having a particle size of 20 μm to 30 μm with a relatively large particle size with a metal bond and sintering. On the other hand, the finish grinding wheel 42 is formed by bonding diamond abrasive grains of 0.1 μm or less with vitrified bonds and sintering.

  The finish grinding unit 28 includes a finish grinding unit moving mechanism 34 including a ball screw 30 and a pulse motor 32 that move the finish grinding unit 28 in the vertical direction along the pair of guide rails 19. When the pulse motor 32 is driven, the ball screw 30 rotates and the finish grinding unit 28 is moved in the vertical direction.

  The grinding device 2 includes a turntable 44 disposed so as to be substantially flush with the upper surface of the housing 4 on the front side of the columns 6a and 6b. The turntable 44 is formed in a relatively large-diameter disk shape, and is rotated in a direction indicated by an arrow 45 by a rotation drive mechanism (not shown).

  On the turntable 44, three chuck tables 46 are arranged so as to be rotatable in a horizontal plane, spaced from each other by 120 ° in the circumferential direction. The chuck table 46 has a suction chuck formed in a disk shape by a porous ceramic material, and sucks and holds the wafer placed on the holding surface of the suction chuck by operating a vacuum suction means.

  The three chuck tables 46 arranged on the turntable 44 are rotated in accordance with the turntable 44, so that the wafer loading / unloading area A, rough grinding area B, finish grinding area C, and wafer loading / unloading are performed. The region A is sequentially moved.

  The front portion of the housing 4 includes a first wafer cassette 50, a second wafer cassette 52, a wafer transfer robot 54, a positioning table 56 having a plurality of positioning pins 58, and a wafer carry-in mechanism (loading arm) 60. A wafer unloading mechanism (unloading arm) 62 and a spinner unit 63 are disposed.

  The grinding operation of the grinding device 2 configured as described above will be described below. The semiconductor wafer accommodated in the first wafer cassette 50 is transported by the vertical motion and the forward / backward motion of the wafer transport robot 54 and is placed on the wafer positioning table 56.

  The wafer placed on the wafer positioning table 56 is centered by a plurality of positioning pins 58 and then moved to the chuck table 46 positioned in the wafer loading / unloading area A by the turning operation of the loading arm 60. It is placed and sucked and held by the chuck table 46.

  Next, the turntable 44 is rotated 120 °, and the chuck table 46 holding the wafer is positioned in the rough grinding region B. While rotating the chuck table 46 with respect to the wafer positioned in this manner at, for example, 300 rpm, the grinding wheel 24 is rotated in the same direction as the chuck table 46 at, for example, 6000 rpm, and the rough grinding unit moving mechanism 18 is operated to perform roughing. A grinding wheel 26 for grinding is brought into contact with the back surface of the wafer.

  Then, the grinding wheel 24 is ground and fed downward by a predetermined amount at a predetermined grinding feed speed (for example, 3 to 5 μm / second), and rough grinding of the wafer is performed. The wafer is finished to a desired thickness while measuring the thickness of the wafer with a contact-type thickness measurement gauge (not shown).

  The chuck table 46 holding the wafer after the rough grinding is positioned in the finish grinding region C by rotating the turntable 44 by 120 °, and finish grinding by the finish grinding unit 28 having the grinding wheel 42 for finish grinding. Is implemented.

  As shown in FIG. 4B, the finish grinding process by the finish grinding unit 28 is performed by rotating the chuck table 46 in the same direction as the chuck table 46 while rotating the chuck table 46 at, for example, 300 rpm as shown by an arrow A. While rotating in the direction of arrow B at, for example, 6000 rpm, the finish grinding unit moving mechanism 34 is operated to bring the grinding wheel 42 for finish grinding into contact with the back surface of the wafer.

  Then, the grinding wheel 40 is ground and fed downward by a predetermined amount at a predetermined grinding feed rate (for example, 0.2 to 0.5 μm / second), and finish grinding of the wafer is performed. In this finish grinding, finish grinding is performed so that the microcracks remaining on the back surface of the wafer have a depth of 0.05 μm to 0.5 μm, preferably 0.1 to 0.2 μm. Therefore, few microcracks or moderate microcracks remain on the back surface of the wafer after finish grinding.

  As shown in FIG. 4A, when rough grinding is performed, grinding striations 47 having a pattern in which a large number of arcs are radially drawn remain on the surface of the wafer 11 to be ground. The grinding streak 47 is a microcrack formed by the grinding wheel 26.

  The grinding striation 47 formed by the rough grinding process is removed by the finish grinding process. However, as shown in FIG. 4B, a new grinding striation 49 is formed when the finish grinding process is performed. The grinding streaks 49 are also microcracks formed by the grinding wheel 42, and the depth thereof is in the range of 0.05 μm to 0.5 μm, preferably in the range of 0.1 μm to 0.2 μm.

  The chuck table 46 holding the wafer after finish grinding is positioned in the wafer loading / unloading area A by rotating the turntable 46 by 120 °.

  After the suction and holding of the wafer held on the chuck table 46 is released, the wafer is adsorbed by the transfer pad 62b of the wafer unloading mechanism (unloading arm) 62, and the arm 62a rotates to transfer it to the spinner unit 63. Is done.

  The wafer conveyed to the spinner unit 63 by the unloading arm 62 is cleaned and spin-dried here. Next, the wafer is stored in a predetermined position of the second wafer cassette 52 by the wafer transfer robot 54.

  As shown in FIG. 5, the wafer 11 that has been ground is pasted on a dicing tape (adhesive tape) 43 having an outer peripheral edge stuck to the annular frame 41, and the protective tape 23 is attached to the surface of the wafer 11. Is peeled off.

  Thus, the wafer 11 supported by the annular frame 41 and the dicing tape 43 is cut by a cutting device (dicing device) 64 as shown in FIG. 6, and the wafer 11 is divided into individual devices 15. . Hereinafter, cutting of the wafer 11 by the cutting device 64 will be described.

  On the front side of the cutting device 64, operating means 66 is provided for an operator to input instructions to the device such as machining conditions. In the upper part of the apparatus, there is provided a display means 68 such as a CRT on which a guide screen for an operator and an image taken by an imaging means described later are displayed.

  As shown in FIG. 5, a plurality of (for example, 25) wafers 11 supported by the annular frame 41 via the dicing tape 43 are accommodated in the wafer cassette 70 shown in FIG. The wafer cassette 70 is placed on a cassette elevator 71 that can move up and down.

  Behind the wafer cassette 70, a loading / unloading means 72 is provided for unloading the wafer 11 from the wafer cassette 70 and loading the wafer after cutting into the wafer cassette 70.

  Between the wafer cassette 70 and the carry-in / out means 72, a temporary placement area 74, which is an area on which a wafer to be carried in / out, is temporarily placed is provided. In the temporary placement area 74, the wafer 11 is placed. Positioning means 76 for positioning at a fixed position is provided.

  In the vicinity of the temporary placement region 74, a transport means 78 having a turning arm that sucks and transports the frame 41 integrated with the wafer 11 is disposed. The wafer 11 that has been transported to the temporary placement region 74 is It is attracted by the conveying means 78 and conveyed onto the chuck table 80 and is sucked by the chuck table 80, and is held on the chuck table 80 by fixing the frame 41 by a plurality of fixing means 81.

  The chuck table 80 is configured to be rotatable and capable of reciprocating in the X-axis direction. Above the movement path of the chuck table 80 in the X-axis direction, an alignment unit 82 that detects a street to be cut of the wafer 11 is provided. It is arranged.

  The alignment unit 82 includes an imaging unit 84 that images the surface of the wafer 11, and can detect a street to be cut by image processing such as pattern matching based on an image acquired by imaging. The image acquired by the imaging unit 84 is displayed on the display unit 68.

  On the left side of the alignment means 82, a cutting means 86 for cutting the wafer 11 held on the chuck table 80 is disposed. The cutting means 86 is configured integrally with the alignment means 82, and both move in conjunction with each other in the Y-axis direction and the Z-axis direction.

  The cutting means 86 is configured by mounting a cutting blade 90 on the tip of a rotatable spindle 88 and is movable in the Y-axis direction and the Z-axis direction. The cutting edge of the cutting blade 90 is located on the extended line of the image pickup means 84 in the X-axis direction.

  In the cutting device 64 configured as described above, the wafer 11 accommodated in the wafer cassette 70 is sandwiched by the frame 41 by the loading / unloading means 72, and the loading / unloading means 72 moves rearward (Y-axis direction) to temporarily When the nipping is released in the placement area 74, it is placed in the temporary placement area 74. Then, the wafer 11 is positioned at a certain position by the positioning means 76 moving in a direction approaching each other.

  Next, the frame 41 is adsorbed by the conveyance unit 78, and the wafer 11 integrated with the frame 41 is conveyed to the chuck table 80 and held by the chuck table 80 by the rotation of the conveyance unit 78. Then, the chuck table 80 moves in the X-axis direction, and the wafer 11 is positioned directly below the alignment means 82.

  The image used for pattern matching at the time of alignment in which the alignment means 82 detects the street to be cut needs to be acquired in advance before cutting. Therefore, when the wafer 11 is positioned directly below the alignment unit 82, the imaging unit 84 captures the surface of the wafer 11 and causes the display unit 68 to display the captured image.

  The operator of the cutting device 64 operates the operation unit 66 to move the image pickup unit 84 slowly and also move the chuck table 80 as necessary to search for a key pattern that is a pattern matching target.

  When the operator determines a key pattern, an image including the key pattern is stored in a memory provided in the alignment unit 82 of the cutting device 64. Further, the distance between the key pattern and the center line of the street 13 is obtained by a coordinate value or the like, and the value is also stored in the memory.

  Further, by moving the image pickup means 84, an interval between the adjacent streets (street pitch) is obtained by a coordinate value or the like, and the street pitch value is also stored in the memory of the alignment means 82.

  At the time of cutting along the street of the wafer 11, the alignment unit 82 performs pattern matching between the stored key pattern image and the image actually acquired by the imaging unit 84.

  When the patterns match, the cutting means 86 is moved in the Y-axis direction by the distance between the key pattern and the street center line, thereby aligning the street to be cut with the cutting edge of the cutting blade 90. I do.

  When the position of the street to be cut and the cutting edge of the cutting blade 90 is aligned, the chuck table 80 is moved in the X-axis direction and the cutting means 86 is lowered while the cutting blade 90 is rotated at a high speed. , The aligned street is cut.

  By performing cutting while the cutting means 86 is index-fed in the Y-axis direction for each street pitch stored in the memory, all the streets 13 in the same direction are cut. Furthermore, when the chuck table 80 is rotated by 90 ° and then the same cutting is performed, the streets 13 in the other direction are all cut and divided into individual devices 15.

  The wafer 11 that has been cut is moved in the X-axis direction by the chuck table 80, and then is held by the transfer means 92 that is movable in the Y-axis direction and transferred to the cleaning device 94. The cleaning device 94 cleans the wafer by rotating the wafer 11 at a low speed (for example, 300 rpm) while jetting water from the cleaning nozzle.

  After cleaning, the wafer 11 is dried by rotating the wafer 11 at a high speed (for example, 3000 rpm) to dry the wafer 11, and then the wafer 11 is adsorbed by the conveying means 78 and returned to the temporary storage area 74, and then the loading / unloading means. 72, the wafer 11 is returned to the original storage location of the wafer cassette 70.

  According to the wafer processing method of the embodiment of the present invention described above, the back surface of the wafer is ground so that few micro cracks or moderate micro cracks remain when the back surface of the wafer is ground. The impact force is reduced, the explosive destructive force is suppressed, the occurrence of large chipping on both sides of the cutting groove cut by the cutting blade is prevented, and the device quality can be improved.

It is a surface side perspective view of a semiconductor wafer. It is a back surface side perspective view of the semiconductor wafer where the protective tape was stuck. It is an external appearance perspective view of the grinding device suitable for implementing the processing method of this invention. FIG. 4A is an explanatory diagram of rough grinding, and FIG. 4B is an explanatory diagram of finish grinding. It is a perspective view of the wafer of the state supported by the annular frame via the dicing tape. It is an external appearance perspective view of the cutting device suitable for implementing the processing method of this invention.

Explanation of symbols

2 Grinding device 10 Coarse grinding unit 11 Semiconductor wafer 28 Finish grinding unit 44 Turntable 46 Chuck table 64 Cutting device 80 Chuck table 82 Alignment means 84 Imaging means 86 Cutting means 90 Cutting blade

Claims (3)

A device area in which a plurality of division lines are formed in a lattice pattern on the surface, and devices are formed in a plurality of areas partitioned by the plurality of division lines, and an outer peripheral surplus area surrounding the device area A wafer processing method for dividing a wafer having
Grind the backside of the wafer so that a few microcracks remain on the backside of the wafer,
Stick the back of the wafer on the adhesive tape attached to the annular frame,
Hold the wafer mounted on the annular frame on the chuck table of the cutting device with the adhesive tape side down,
The cutting blade is positioned on the planned dividing line of the wafer so that the cutting blade of the cutting blade cuts the adhesive tape, and the planned dividing line is completely cut.
A wafer processing method comprising each step.   2. The wafer processing method according to claim 1, wherein in the grinding step, diamond abrasive grains of 0.1 [mu] m or less are bonded with vitrified bonds, and the back surface of the wafer is ground with a grinding wheel formed by sintering.   3. The wafer processing method according to claim 1, wherein in the grinding step, the slight microcracks remaining on the back surface of the wafer comprise microcracks having a depth of 0.05 μm to 0.5 μm. .

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