JP5700988B2 - Wafer grinding method - Google Patents

Description

  The present invention relates to a wafer grinding method for forming a circular concave portion by grinding a back surface of a wafer and forming an annular convex portion surrounding the circular concave portion.

  In a semiconductor device manufacturing process, a plurality of regions are partitioned by dividing lines called streets arranged in a lattice pattern on the surface of a wafer, and circuit elements such as ICs and LSIs are formed in the partitioned regions. And each semiconductor device is manufactured by cutting a wafer with a cutting device along a street.

  Before the wafer is cut along the street, the back surface is ground and thinned to a predetermined thickness. In recent years, in order to achieve a reduction in weight and size of electrical equipment, it has been required to reduce the thickness of the wafer, for example, to about 50 μm.

  Such thinly ground wafers are difficult to handle and may be damaged during transportation. Accordingly, there is disclosed a grinding method in which only a back surface corresponding to a device region of a wafer is ground with a grinding wheel to form a circular concave portion on the back surface of the wafer, and an annular convex portion surrounding the circular concave portion is left as a reinforcing portion. -19461.

  On the other hand, when a workpiece is ground with a grinding wheel, a minute grinding distortion or the like occurs in the workpiece. In order not to leave such processing damage as grinding distortion, the back surface corresponding to the device region of the wafer is ground with the first grinding wheel to form a circular recess, and then abrasive grains finer than the first grinding wheel are formed. Japanese Laid-Open Patent Publication Nos. 2007-173487 and 2009-176896 propose a method in which a bottom surface of a circular recess is ground with a second grinding wheel having the grinding grind to remove grinding distortion.

JP 2007-19461 A JP 2007-173487 A JP 2009-176896 A

  In this way, when the back surface of the wafer is ground with the first grinding wheel to form the circular recess, and then the bottom surface of the circular recess is ground with the second grinding wheel, the second grinding wheel has the circular recess. It is necessary to perform grinding by positioning the second grinding wheel on the inner side of the inner peripheral wall surface of the annular convex portion so as not to contact the inner peripheral wall surface of the surrounding annular convex portion.

  That is, the bottom surface of the circular recess formed by the first grinding wheel remains in an annular shape on the outer periphery of the circular recess formed by the second grinding wheel, and the vertical cross section of the ground wafer is the outer peripheral side of the circular recess. In step form.

  However, since the portion of the circular recess formed by grinding with the first grinding wheel partially remains in an annular shape, it is not ground with the second grinding wheel, so that grinding distortion due to grinding of the first grinding wheel remains. doing.

  Therefore, starting from this grinding distortion, the wafer may be damaged during handling, and the amount of grinding with the first grinding wheel is suppressed, and more grinding is performed with the second grinding wheel. It is necessary to grind the back surface of the corresponding wafer to a predetermined thickness.

  However, the second grinding wheel having finer abrasive grains has a problem that it is difficult to increase the processing feed rate, and it takes a very long time to grind the wafer to a predetermined thickness.

  The present invention has been made in view of these points, and an object of the present invention is to provide a method for grinding a wafer that shortens the processing time and reduces the risk of the wafer being damaged during handling. .

According to the present invention, there is provided a method for grinding a wafer by grinding a back surface of a wafer to form a circular concave portion and forming an annular convex portion surrounding the circular concave portion. A first grinding grindstone containing a number of abrasive grains or less is used to grind the back surface of the wafer to form a first circular concave portion having a thickness of 150 to 200 μm , and a first circular convex portion surrounding the first circular concave portion remains. After performing the grinding step and the first grinding step, the second grinding wheel containing abrasive grains of # 1000 or more and # 2000 or less as defined by JIS standard is positioned inside the outer peripheral wall of the first circular recess. Then, after performing the second grinding step to form the second circular recess by grinding the bottom surface of the first circular recess, and abrasive grains # 3000 or more prescribed by JIS standard Including A third grinding step of positioning a third grinding wheel inside the outer peripheral wall of the second circular recess and grinding a bottom surface of the second circular recess to form a third circular recess. A method for grinding a wafer is provided.

  According to the grinding method of the present invention, after forming the first circular recess by grinding the back surface of the wafer with the first grinding wheel having relatively coarse abrasive grains, the second grinding wheel having medium roughness abrasive grains. The bottom surface of the first circular recess is ground to form a second circular recess, and then the bottom surface of the second circular recess is ground with a third grinding wheel having fine abrasive grains, thereby shortening the processing time. This can reduce the risk of wafer breakage during handling.

It is a surface side perspective view of a semiconductor wafer. It is a back surface side perspective view of a semiconductor wafer in the state where a protective tape was stuck on the surface. It is a perspective view of a grinding device suitable for carrying out the grinding method of the present invention. It is a perspective view which shows the 1st grinding step of this invention. It is explanatory drawing of a 1st grinding step. It is explanatory drawing of a 2nd grinding step. It is explanatory drawing of a 3rd grinding step. 8A is a side view of the wafer, FIG. 8B is a longitudinal sectional view of the wafer after the first grinding step, and FIG. 8C is a longitudinal sectional view of the wafer after the second grinding step. FIG. 8D is a longitudinal sectional view of the wafer after the third grinding step is performed.

  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 11 before being processed to a predetermined thickness. The semiconductor wafer 11 shown in FIG. 1 is made of, for example, a silicon wafer having a thickness of 700 μm. A plurality of streets (division lines) 13 are formed in a lattice shape on the surface 11a. A device 15 such as an IC or LSI is formed in each partitioned area.

  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.

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

  Hereinafter, the grinding method of the present invention for grinding the back surface 11b of the semiconductor wafer 11 thus configured will be described in detail. Referring to FIG. 3, a perspective view of a grinding apparatus 2 suitable for carrying out the grinding method of the present invention is shown. Reference numeral 4 denotes a base of the grinding apparatus 2, and a column 6 is erected vertically behind the base 4.

  The column 6 has two inclined surfaces 6a and 6b inclined at about 45 degrees. A block 8 is mounted on the inclined surface 6 a of the column 6 so as to be movable in the direction of arrow A. The block 8 is moved in the direction of arrow A along a guide rail (not shown) fixed to the inclined surface 6 a of the column 6 by a moving mechanism including a ball screw and a pulse motor (not shown).

  A pair of guide rails 10 are fixed to the front surface of the block 8, and a rough grinding unit (first grinding unit) 12 is mounted on the block 8 so as to be movable in the vertical direction along the guide rails 10. The rough grinding unit 12 is attached to the moving base 14 whose mounting cover 28 moves in the vertical direction along the pair of guide rails 10.

  The rough grinding unit 12 includes a rough grinding unit feeding mechanism 20 including a ball screw 16 and a pulse motor 18 that move the rough grinding unit 12 in the vertical direction along the pair of guide rails 10. When the pulse motor 18 is pulse-driven, the ball screw 16 rotates and the moving base 14 is moved in the vertical direction.

  The rough grinding unit 12 includes a housing 22, a spindle 24 (see FIG. 4) rotatably accommodated in the housing 22, a motor 26 that rotationally drives the spindle 24, and a wheel mount 30 that is fixed to the tip of the spindle 24. And a rough grinding wheel (first grinding wheel) 32 having a plurality of rough grinding grinding wheels (first grinding wheels) 33 fixed in an annular shape at the lower end thereof detachably attached to the wheel mount 30. . The grinding wheel 33 for rough grinding includes abrasive grains of # 320 or more and # 400 or less defined by JIS standard “R6001: Grain size of abrasive for grinding wheel”.

  A block 34 is mounted on the inclined surface 6b of the column 6 so as to be movable in the arrow B direction. The block 34 is moved in the direction of arrow B along a guide rail fixed to the inclined surface 6b of the column 6 by a moving mechanism including a ball screw and a pulse motor (not shown).

  A pair of guide rails 36 extending in the vertical direction are fixed to the front surface of the block 34. An intermediate grinding unit (second grinding unit) 38 is mounted along the pair of guide rails 36 so as to be movable in the vertical direction. The intermediate grinding unit 38 is attached to a moving base 40 whose attachment cover 52 moves in the vertical direction along the pair of guide rails 36.

  The intermediate grinding unit 38 includes an intermediate grinding unit feed mechanism 46 including a ball screw 42 and a pulse motor 44 that move the intermediate grinding unit 38 in the vertical direction along the pair of guide rails 36. When the pulse motor 44 is pulse-driven, the ball screw 42 rotates and the moving base 40 is moved in the vertical direction.

  The intermediate grinding unit 38 includes a housing 48, a spindle (not shown) rotatably accommodated in the housing 48, a motor 50 that rotationally drives the spindle, a wheel mount 54 fixed to the tip of the spindle, and a wheel mount 54. And a grinding wheel 56 (second grinding wheel) for intermediate grinding, which is detachably mounted.

  The grinding wheel 56 has a plurality of intermediate grinding grinding wheels (second grinding wheels) 57 (see FIG. 6) fixed to the lower end in an annular shape. The grinding wheel 57 for intermediate grinding includes abrasive grains of # 1000 or more and # 2000 or less defined by JIS standard “R6001: Grain size of abrasive for grinding wheel”.

  A column 58 is vertically provided on one side surface of the base 4. A pair of guide rails 60 extending in the horizontal direction are fixed to the side surfaces of the column 58. A moving member 62 is mounted on the column 58 along the guide rail 60 so as to be moved in the direction of arrow C by a moving mechanism 66 composed of a pulse motor 64 and a ball screw (not shown).

  A pair of guide rails 68 extending in the vertical direction are fixed to the moving member 62. A finish grinding unit (third grinding unit) 70 is mounted along the pair of guide rails 68 so as to be movable in the vertical direction. The finish grinding unit 70 is attached to a moving base 72 whose mounting cover 84 moves in the vertical direction along a pair of guide rails 68.

  The finish grinding unit 70 includes a finish grinding unit feed mechanism 78 including a ball screw 74 and a pulse motor 76 that move the finish grinding unit 70 in the vertical direction along a pair of guide rails 68. When the pulse motor 76 is pulse-driven, the ball screw 74 is rotated and the moving base 72 is moved in the vertical direction.

  The finish grinding unit 70 includes a housing 80, a spindle (not shown) rotatably accommodated in the housing 80, a motor 82 for rotationally driving the spindle, a wheel mount 86 fixed to the tip of the spindle, and a wheel mount 86. And a finish grinding wheel (second grinding wheel) 88 that is detachably mounted.

  The finish grinding wheel 88 has a plurality of grinding wheels for finishing grinding (third grinding wheel) 89 (see FIG. 7) fixed in an annular shape at the lower end thereof. The grinding wheel 89 for finish grinding includes # 3000 or more abrasive grains defined by JIS standard “R6001: Grain size of abrasive for grinding wheel”.

  The grinding apparatus 2 includes a turntable 90 disposed on the front side of the column 6 so as to be substantially flush with the upper surface of the base 4. The turntable 90 is formed in a relatively large-diameter disk shape, and is rotated in a direction indicated by an arrow D by a rotation driving mechanism (not shown).

  On the turntable 90, four chuck tables 92 are arranged so as to be rotatable in a horizontal plane, spaced apart from each other by 90 degrees in the circumferential direction. The chuck table 92 has a suction holding portion formed in a disk shape by a porous ceramic material, and sucks and holds the wafer 11 placed on the holding surface of the suction holding portion by operating a vacuum suction means. To do.

  The four chuck tables 92 arranged on the turntable 90 rotate the turntable 90 as appropriate so that a wafer loading / unloading area A, a rough grinding area B, an intermediate grinding area C, and a finish grinding area D are obtained. And the wafer carry-in / carry-out area A sequentially.

  The front portion of the base 4 is configured to be higher than that of the base 4, and cassette mounting tables 94 and 96 are fixed to the front end of the base 4. A cassette 98 containing the wafer 11 before grinding is placed on the cassette placing table 94, and the cassette 100 is placed on the cassette placing table 96 and the wafer 11 that has undergone grinding processing is housed in the cassette 100.

  A recess 101 is formed in the base 4 adjacent to the cassette mounting tables 94 and 96, and a wafer transfer robot 102 is accommodated in the recess 101. The front side portion of the base 4 further includes a positioning table 104 having a plurality of positioning pins 106, a wafer carry-in mechanism (loading arm) 108, a wafer carry-out mechanism (unloading arm) 110, and a ground wafer. A spinner cleaning device 112 for drying is provided.

  Hereinafter, the grinding method of the present invention for grinding the back surface 11b of the wafer 11 using the grinding device 2 configured as described above will be described in detail. The semiconductor wafer 11 accommodated in the cassette 98 is transported by the wafer transport robot 102 in the up / down motion and the forward / backward motion, and is placed on the wafer positioning table 104.

  After the wafer 11 placed on the wafer positioning table 104 is centered by a plurality of positioning pins 106, the wafer 11 is placed on the chuck table 92 positioned in the wafer loading / unloading area A by the turning operation of the loading arm 108. It is placed and sucked and held by the chuck table 92.

  Next, the turntable 90 is rotated 90 degrees in the direction of arrow D, and the chuck table 92 holding the wafer 11 is positioned in the rough grinding region B. In the rough grinding region B, only the back surface 11b of the wafer 11 corresponding to the device region 17 of the wafer 11 is ground, and the relationship between the wafer 11 sucked and held by the chuck table 92 and the rough grinding wheel 33 is shown in FIG. It is necessary to set as follows.

  That is, the rotation center P1 of the chuck table 92 and the rotation center P2 of the rough grinding wheel 33 arranged in an annular shape are positioned so as to be eccentric, and the grinding wheel 33 passes through the rotation center P1 of the wafer 11 and is arranged in an annular shape. The outer peripheral edge of the grinding wheel 33 is set to an outer diameter corresponding to the outer periphery of the device region 17.

  In the rough grinding step (first grinding step), as shown in FIGS. 4 and 5, while rotating the chuck table 92 in the direction indicated by the arrow E at, for example, 300 rpm, the grinding wheel 33 is rotated in the direction indicated by the arrow F, for example, 6000 rpm. And the rough grinding unit feed mechanism 20 is driven to bring the grinding wheel 33 of the grinding wheel 32 into contact with the back surface 11 b of the wafer 11. Then, the grinding wheel 32 is ground and fed downward by a predetermined amount at a predetermined grinding feed speed (2.0 to 6.0 μm / s).

  While measuring the thickness of the wafer 11 with a contact-type or non-contact-type thickness measurement gauge (not shown), the wafer 11 is finished to a desired thickness, for example, 150 to 200 μm. As a result, on the back surface 11b of the wafer 11, as shown in FIG. 8B, the region corresponding to the device region 17 is ground and removed to form the first circular recess 114, and the outer peripheral surplus region 19 remains. As a result, an annular projection 116 is formed. The width of the annular protrusion 116 is preferably about 2.1 mm from the outer periphery of the wafer 11.

  The chuck table 92 holding the wafer after the rough grinding is positioned in the intermediate grinding region C by rotating the turntable 90 by 90 degrees, and an intermediate grinding unit (second grinding) having a grinding wheel 57 for intermediate grinding. An intermediate grinding step (second grinding step) by the unit 56 is performed.

  In this intermediate grinding step, as shown in FIG. 6, the second grinding wheel 57 is positioned about 0.4 mm inside the inner peripheral wall of the annular convex portion 116 (the outer peripheral wall of the first circular concave portion 114). 57, the bottom surface of the first circular recess 114 is ground to form the second circular recess 114A.

  Also in the intermediate grinding step (second grinding step), as in the rough grinding step (first grinding step), the rotation center P1 of the chuck table 92 and the rotation center P2 of the second grinding wheel 57 arranged in an annular shape are decentered. The second grinding wheel 57 passes through the rotation center P1 of the wafer 11, and the outer peripheral edge of the second grinding wheel 57 is positioned so as to pass about 0.4 mm from the inner peripheral wall of the annular convex portion 116. .

  Then, while rotating the chuck table 92 in the direction of arrow E at, for example, 300 rpm, the second grinding wheel 57 is rotated in the direction of arrow F, for example, at 6000 rpm, and the intermediate grinding unit feed mechanism 46 is driven to drive the second grinding wheel 56. The grinding wheel 57 is brought into contact with the bottom surface of the first circular recess 114 formed on the back surface of the wafer 11. Then, the grinding wheel 56 is ground and fed downward by a predetermined amount at a predetermined grinding feed speed (1.0 to 2.0 μm / s).

  While measuring the thickness of the wafer 11 with a contact-type or non-contact-type thickness gauge, the wafer 11 is ground to a desired thickness (80 to 100 μm), and as shown in FIG. Form. When the second grinding step is completed, the outermost peripheral portion 118 on the bottom surface of the first circular recess 114 formed in the first grinding step remains in an annular shape with a width of about 0.4 mm.

  Since this intermediate grinding step (second grinding step) is performed with the second grinding wheel 57 containing abrasive grains of # 1000 or more and # 2000 or less as defined in JIS standards, the wafer 11 is made to have a desired thickness relatively quickly. It can be ground (80-100 μm).

  The chuck table 92 holding the wafer 11 after the intermediate grinding is positioned in the finish grinding region D by rotating the turntable 90 by 90 degrees, and has a grinding wheel (third grinding wheel) 89 for finish grinding. Finish grinding by the finish grinding unit (third grinding unit) 70 is performed.

  In this finish grinding step (third grinding step), as shown in FIG. 7, the center of rotation P1 of the chuck table 92 and the center of rotation P2 of the third grinding wheel 89 are positioned so as to be decentered. The outer peripheral edge is positioned so as to pass about 0.4 mm from the outer periphery of the second circular recess 114A.

  Then, as shown in FIG. 7, while rotating the chuck table 92 in the direction of arrow E at 300 rpm, for example, the third grinding wheel 89 is rotated in the direction of arrow F at 6000 rpm, for example, and the finish grinding unit feed mechanism 78 is driven. Then, the grinding wheel 89 of the grinding wheel 88 is brought into contact with the bottom surface of the second circular recess 114A. Then, the grinding wheel 88 is ground and fed downward by a predetermined amount at a predetermined grinding feed speed (0.3 to 1.0 μm / s).

  While measuring the thickness of the wafer 11 with a contact-type or non-contact-type thickness gauge, the wafer 11 is ground to a desired thickness (for example, 50 μm), and a third circle is formed on the back surface of the wafer 11 as shown in FIG. A recess 114B is formed. When this finish grinding step (third grinding step) is completed, the outermost peripheral portion 120 on the bottom surface of the second circular recess 114A remains in an annular shape.

  The chuck table 92 holding the wafer 11 for which finish grinding has been completed is positioned in the wafer carry-in / out area A by rotating the turntable 90 by 90 degrees. If the chuck table 92 is positioned in the wafer carry-in / out area A, the suction of the chuck table 92 is released, and then the wafer 11 is adsorbed by the wafer carry-out mechanism (unloading arm) 110, and the unloading arm 110 turns. By doing so, it is conveyed to the spinner cleaning unit 112.

  The wafer 11 conveyed to the spinner cleaning unit 112 is cleaned here and spin-dried. Next, the wafer 11 is transported by the wafer transport robot 102 and stored in a predetermined position of the cassette 100.

  According to the grinding method of the embodiment described above, after the first circular recess 114 is formed by grinding the back surface of the wafer 11 corresponding to the device region 17 with the first grinding wheel 33 having relatively coarse abrasive grains, The second circular recess 114A is ground by grinding the bottom surface of the first circular recess 114 with a second grinding wheel 57 having coarse abrasive grains, and then the second circular recess with a third grinding wheel 89 having fine abrasive grains. Since the third circular recess 114B is formed by grinding the bottom surface of 114A, the grinding time can be shortened and the grinding distortion is reduced, so that the risk of damage to the wafer during handling such as conveyance is reduced. can do.

  Furthermore, the outer peripheral side of the circular concave portion has a stepped shape, so that the processing liquid such as the etching processing liquid can be easily discharged in an application example in which a rewiring layer is formed in the circular concave portion later.

2 Grinding device 11 Semiconductor wafer 12 Rough grinding unit (first grinding unit)
17 Device region 19 Peripheral surplus region 32 Coarse grinding wheel (first grinding wheel)
33 Coarse grinding wheel (1st grinding wheel)
38 Intermediate grinding unit (second grinding unit)
56 Intermediate grinding wheel (second grinding wheel)
57 Intermediate grinding wheel (second grinding wheel)
70 Finish grinding unit (3rd grinding unit)
88 Finish grinding wheel (3rd grinding wheel)
89 Finish grinding wheel (3rd grinding wheel)
90 turntable 92 chuck table 114 first circular recess 114A second circular recess 114B third circular recess 116 annular convex

Claims (1)

A method for grinding a wafer, wherein the back surface of a wafer is ground to form a circular concave portion and an annular convex portion surrounding the circular concave portion is formed,
The back surface of the wafer is ground with a first grinding wheel containing # 320 or more and # 400 or less abrasive grains defined by JIS standards to form a first circular recess having a thickness of 150 to 200 μm, and the first circular shape. A first grinding step for leaving an annular convex portion surrounding the concave portion;
After performing the first grinding step, a second grinding wheel containing abrasive grains of # 1000 or more and # 2000 or less as defined by JIS standard is positioned inside the outer peripheral wall of the first circular recess, and the first grinding step is performed. A second grinding step of grinding a bottom surface of one circular recess to form a second circular recess;
After carrying out the second grinding step, a third grinding wheel containing # 3000 or more abrasive grains defined by JIS standards is positioned inside the outer peripheral wall of the second circular recess, and the second circular recess A third grinding step of grinding the bottom surface to form a third circular recess;
A method for grinding a wafer, comprising:

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