Wafer grinding method

Abstract

To reduce grinding time.SOLUTION: In a wafer grinding method, when grinding a wafer 5, only an outside area 602 of the wafer 5 is ground in an outside grinding step, and then a center area 601 is ground until the center area is made flush with the outside area 602 in a center area grinding step in a center grinding step. In other words, an upper surface 6 of the wafer 5 is divided into the center area 601 and the outside area 602, and grinding is executed for each of the areas. Therefore, contact area between the wafer 5 and a lower surface of a grinding stone 77 becomes smaller, which can reduce grinding loads acting on the wafer 5. This can increase a grinding speed, and thus can reduce total grinding time.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for grinding a wafer. [Background technology]

[0002] As disclosed in Patent Document 1, in a grinding device that uses a grinding wheel to grind a wafer held on a chuck table, the annular grinding wheel is positioned so that it passes through the center of rotation of the chuck table, and the chuck table and the grinding wheel are rotated, so that the underside of the grinding wheel comes into contact with the radius of the wafer to grind it. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-119123 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-162665 Summary of the Invention [Problem to be solved by the invention]

[0004] In the grinding apparatus described above, the tilt of the chuck table changes depending on the grinding load applied to the radius portion of the wafer, which can cause the thickness of the ground wafer to be non-uniform.

[0005] Furthermore, as disclosed in Patent Document 2, when grinding a large-diameter wafer with a grinding wheel, the contact area of ​​the grinding wheel increases, which increases the load on the grinding wheel and causes a large change in the tilt of the chuck table, making it necessary to slow down the grinding feed rate and lengthening the grinding time.

[0006] Therefore, an object of the present invention is to shorten the grinding time and to grind the wafer to a uniform thickness by reducing the grinding load. [Means for solving the problem]

[0007] Grinding method of the present invention (Grinding method) is the holding surface In this method, a chuck table that holds a wafer is rotated by rotating an annular grinding wheel attached to a spindle, and the grinding wheel is positioned above the center of the wafer held on the holding surface, and the tilt angle of the chuck table is adjusted so that the portion of the holding surface that is located below the grinding wheel is not parallel to the lower surface of the grinding wheel, thereby bringing the grinding wheel into contact with only the outer area that is the portion between the center and the outer periphery of the radius of the wafer held on the holding surface and up to the outer periphery, and grinding water is sprayed from a grinding water nozzle toward the portion of the outer area that the grinding wheel comes into contact with. an outer grinding step in which a circular central area that is not ground is formed in the center of the wafer by supplying a grinding stone thereto, and an annular outer area of ​​the wafer outside the central area is ground; an inclination changing step in which, after the outer grinding step, the inclination angle of the chuck table is adjusted so that a portion of the holding surface located below the grinding stone is parallel to the lower surface of the grinding stone; and a central grinding step in which, after the inclination changing step, the grinding stone is brought into contact with the central area of ​​the wafer, and grinding water is supplied from the grinding water nozzle toward the portion of the central area that is in contact with the grinding stone, thereby grinding the central area to make it flush with the outer area. In this grinding method, the area of ​​the lower surface of the grinding wheel that contacts the outer area of ​​the wafer in the outer grinding step and the area of ​​the lower surface of the grinding wheel that contacts the central area of ​​the wafer in the central grinding step may be equal to each other. In this grinding method, a rotation load measuring unit that measures the load current value of the motor that rotates the spindle may be used to make the load current value when grinding the outer area of ​​the wafer in the outer grinding process equal to the load current value when grinding the central area of ​​the wafer in the central grinding process. In this grinding method, a load measuring device that measures the load applied to the wafer held by the holding surface may be used to make the load value when grinding the outer area of ​​the wafer in the outer grinding step equal to the load value when grinding the central area of ​​the wafer in the central grinding step. The grinding method may include a thickness setting step for setting a finishing thickness and a surface matching thickness that is thicker than the finishing thickness, and in the outer grinding step, the outer area of ​​the wafer may be ground to the surface matching thickness, and in the center grinding step, after the central area of ​​the wafer is made flush with the outer area, the central area and the outer area may be ground to the finishing thickness. [Effects of the Invention]

[0008] In this grinding method, after grinding only the outer area of ​​the wafer in the outer grinding process, the center area is ground until it is flush with the outer area in the center grinding process. In other words, in this grinding method, the wafer is divided into the center area and the outer area, and grinding is performed for each area.

[0009] Therefore, the contact area between the wafer and the underside of the grinding wheel is reduced, which reduces the grinding load on the wafer. This allows the grinding speed to be increased in the outer grinding step and the central grinding step. Therefore, this grinding method makes it possible to shorten the total grinding time in the outer grinding step and the central grinding step.

[0010] Furthermore, since the grinding load applied to the wafer can be reduced, tilting of the chuck table during grinding can be suppressed, making it possible to grind the wafer to a uniform thickness. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a perspective view showing the configuration of a grinding device. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] 10 is a graph showing the change in height of the grinding wheel over time. [Figure 5] FIG. [Figure 6]FIG. [Figure 7] FIG. 10 is an explanatory diagram showing another outer grinding process. [Figure 8] FIG. 10 is an explanatory diagram showing another outer grinding process. DETAILED DESCRIPTION OF THE INVENTION

[0012] As shown in FIG. 1, the grinding apparatus 1 according to this embodiment is an apparatus for grinding a wafer 5, and includes a rectangular parallelepiped base 10, an upwardly extending column 11, and a control unit 3 that controls each component of the grinding apparatus 1.

[0013] The wafer 5 is, for example, a circular semiconductor wafer. An upper surface 6 of the wafer 5 is a surface to be processed, which is subjected to grinding.

[0014] An opening 13 is provided on the upper surface side of the base 10. A wafer holding mechanism 30 is disposed within the opening 13. The wafer holding mechanism 30 includes a chuck table 20 having a holding surface 22 that holds the wafer 5, and a table rotation mechanism 28 that supports and rotates the chuck table 20.

[0015] The chuck table 20 includes a porous member 21 and a frame 23 that houses the porous member 21 so that the upper surface of the porous member 21 is exposed. The upper surface of the porous member 21 is a holding surface 22 that holds the wafer 5 by suction. The holding surface 22 is formed as a conical surface with an apex at the center (see FIG. 3). The holding surface 22 is connected to a suction source (not shown) to hold the wafer 5 by suction. That is, the chuck table 20 holds the wafer 5 by means of the holding surface 22. Furthermore, as shown in FIG. 1, a frame surface 24, which is the upper surface of the frame 23, is formed to be flush with the holding surface 22.

[0016] The table rotation mechanism 28 supports the chuck table 20 from below. The table rotation mechanism 28 is configured to rotate the chuck table 20 around the center of the holding surface 22 as an axis. Furthermore, the wafer holding mechanism 30 has a load measuring device 29, for example, inside the table rotation mechanism 28 below the chuck table 20. The load measuring device 29 measures the load applied to the wafer 5 held by the holding surface 22 of the chuck table 20.

[0017] A cover plate 39 that moves along the Y-axis direction together with the chuck table 20 is provided around the periphery of the chuck table 20. A bellows cover 12 that expands and contracts in the Y-axis direction is connected to the cover plate 39. A Y-axis direction moving mechanism 90 is disposed below the wafer holding mechanism 30.

[0018] The Y-axis direction moving mechanism 90 moves the chuck table 20 and the grinding mechanism 70 relatively in the Y-axis direction parallel to the holding surface 22. In this embodiment, the Y-axis direction moving mechanism 90 is configured to move the chuck table 20 in the Y-axis direction relative to the grinding mechanism 70.

[0019] The Y-axis direction movement mechanism 90 includes a pair of Y-axis guide rails 92 parallel to the Y-axis direction, a Y-axis movement table 95 that slides on these Y-axis guide rails 92, a Y-axis ball screw 93 parallel to the Y-axis guide rails 92, a Y-axis motor 94 connected to the Y-axis ball screw 93, a Y-axis encoder 96 for detecting the rotation angle of the Y-axis ball screw 93, and a holding base 91 that holds these.

[0020] The Y-axis moving table 95 is slidably installed on the Y-axis guide rail 92. A nut portion (not shown) is fixed to the Y-axis moving table 95. A Y-axis ball screw 93 is threadedly engaged with this nut portion. The Y-axis motor 94 is connected to one end of the Y-axis ball screw 93, as shown in FIG. 1.

[0021] In the Y-axis direction moving mechanism 90, a Y-axis motor 94 rotates a Y-axis ball screw 93, thereby moving a Y-axis moving table 95 in the Y-axis direction along a Y-axis guide rail 92. The table rotation mechanism 28 of the wafer holding mechanism 30 is placed on the Y-axis moving table 95. Therefore, as the Y-axis moving table 95 moves in the Y-axis direction, the wafer holding mechanism 30, including the table rotation mechanism 28 and the chuck table 20, moves in the Y-axis direction.

[0022] In this embodiment, the wafer holding mechanism 30 is moved along the Y-axis direction by the Y-axis direction moving mechanism 90 between a workpiece placement position on the -Y direction side for holding the wafer 5 on the holding surface 22 and a grinding position on the +Y direction side where the wafer 5 is ground.

[0023] The Y-axis encoder 96 is rotated by the Y-axis motor 94 rotating the Y-axis ball screw 93, and can recognize the rotation angle of the Y-axis ball screw 93. Based on the recognition result, the Y-axis encoder 96 can detect the position in the Y-axis direction of the chuck table 20 of the wafer holding mechanism 30, which is moved in the Y-axis direction.

[0024] 1, a column 11 is erected on the rear (+Y direction side) of the base 10. A grinding mechanism 70 for grinding the wafer 5 and a grinding feed mechanism 60 are provided in front of the column 11.

[0025] The grinding feed mechanism 60 moves the chuck table 20 and the grinding wheel 77 of the grinding mechanism 70 relatively in the Z-axis direction (grinding feed direction) perpendicular to the holding surface 22. In this embodiment, the grinding feed mechanism 60 is configured to move the grinding wheel 77 in the Z-axis direction relative to the chuck table 20.

[0026] The grinding feed mechanism 60 includes a pair of Z-axis guide rails 61 parallel to the Z-axis direction, a Z-axis moving table 63 that slides on the Z-axis guide rails 61, a Z-axis ball screw 62 parallel to the Z-axis guide rails 61, a Z-axis motor 64, a Z-axis encoder 65 for detecting the rotation angle of the Z-axis ball screw 62, and a holder 66 attached to the Z-axis moving table 63. The holder 66 supports the grinding mechanism 70.

[0027] The Z-axis moving table 63 is slidably installed on the Z-axis guide rail 61. A nut portion (not shown) is fixed to the Z-axis moving table 63. A Z-axis ball screw 62 is threadedly engaged with this nut portion. A Z-axis motor 64 is connected to one end of the Z-axis ball screw 62.

[0028] In the grinding feed mechanism 60, the Z-axis motor 64 rotates the Z-axis ball screw 62, causing the Z-axis moving table 63 to move in the Z-axis direction along the Z-axis guide rail 61. As a result, the holder 66 attached to the Z-axis moving table 63 and the grinding mechanism 70 supported by the holder 66 also move in the Z-axis direction together with the Z-axis moving table 63.

[0029] Z-axis encoder 65 is rotated by Z-axis motor 64 rotating Z-axis ball screw 62, and can recognize the rotation angle of Z-axis ball screw 62. Based on the recognition result, Z-axis encoder 65 can detect the height position of grinding wheel 77 of grinding mechanism 70, which is moved in the Z-axis direction.

[0030] The grinding mechanism 70 includes a spindle housing 71 fixed to the holder 66, a spindle 72 rotatably held in the spindle housing 71, a spindle motor 73 that drives the spindle 72 to rotate, a wheel mount 74 attached to the lower end of the spindle 72, and a grinding wheel 75 supported by the wheel mount 74.

[0031] The spindle housing 71 is held by the holder 66 so as to extend in the Z-axis direction. The spindle 72 extends in the Z-axis direction so as to be perpendicular to the holding surface 22 of the chuck table 20, and is rotatably supported by the spindle housing 71.

[0032] The spindle motor 73 is connected to the upper end side of the spindle 72. The spindle motor 73 rotates the spindle 72 about a rotation axis extending in the Z-axis direction.

[0033] The wheel mount 74 is formed in a disk shape and is fixed to the lower end (tip) of the spindle 72. The wheel mount 74 supports the grinding wheel 75.

[0034] The grinding wheel 75 is formed so that its outer diameter is approximately the same as the outer diameter of the wheel mount 74. The grinding wheel 75 includes an annular wheel base 76 made of a metal material. A plurality of grinding stones 77 are fixed to the underside of the wheel base 76, arranged in an annular shape, around the entire circumference. The grinding stones 77 are rotated around their center by the spindle motor 73 together with the spindle 72, and grind the upper surface 6 of the wafer 5 held on the chuck table 20.

[0035] In addition, a first grinding water source 69 is connected to the top of the grinding mechanism 70, and grinding water from the first grinding water source 69 is supplied to the grinding wheel 77 and the upper surface 6 of the wafer 5 through a grinding water passage (not shown) inside the spindle 72.

[0036] Furthermore, a grinding water nozzle mechanism 33 is attached to the end portions on the +X side and +Y side of the Y-axis moving table 95 of the Y-axis moving mechanism 90.

[0037] The grinding water nozzle mechanism 33 has a grinding water nozzle 34 and a turning motor 35 that turns the grinding water nozzle 34, and is connected to a second grinding water source 38. During grinding, the grinding water nozzle 34 supplies grinding water from the second grinding water source 38 from the outer periphery of the chuck table 20 to the upper surface 6 of the wafer 5 held on the holding surface 22. It should be noted that this grinding water nozzle mechanism 33 may not be provided, for example, when the grinding water from the first grinding water source 69 is sufficiently supplied to the grinding wheel 77 and the upper surface 6 of the wafer 5.

[0038] Further, a thickness measuring device 56 for measuring the thickness of the wafer 5 held on the holding surface 22 is disposed on the side of the opening 13 in the base 10 .

[0039] The thickness measuring device 56 has a wafer height measuring section 57 and a holding surface height measuring section 58, which are contact or non-contact height gauges. The wafer height measuring unit 57 measures the height of the wafer 5 held on the holding surface 22. The holding surface height measuring unit 58 measures the height of the frame surface 24 of the frame 23, which is flush with the holding surface 22. Then, the thickness measuring device 56 calculates the thickness of the wafer 5 based on the difference between the measured height of the wafer 5 and the height of the holding surface 22.

[0040] For example, the holding surface height measuring unit 58 irradiates a laser beam onto the frame surface 24 of the frame 23 of the chuck table 20, and measures the height of the upper surface of the frame 23 (i.e., the height of the holding surface 22) based on the reflected light. On the other hand, the wafer height measuring unit 57 irradiates a laser beam onto the upper surface 6 of the wafer 5, and measures the height of the upper surface of the wafer 5 based on the reflected light.

[0041] In addition, the holding surface height measuring unit 58 and the wafer height measuring unit 57 may be configured to measure the height of the holding surface 22 and the height of the upper surface of the wafer 5 by irradiating sound waves onto the frame 23 and the upper surface of the wafer 5.

[0042] Furthermore, thickness measuring device 56 may include a single non-contact thickness measuring unit, such as a laser-type thickness measuring unit, instead of wafer height measuring unit 57 and holding surface height measuring unit 58. This thickness measuring unit, for example, irradiates wafer 5 with a laser beam having a wavelength that transmits through wafer 5, receives light reflected from the lower surface 6 of wafer 5 and light reflected from the upper surface 6 of wafer 5, and measures the thickness of wafer 5 based on the optical path difference between the reflected light. Note that one non-contact thickness measuring unit may be a spectroscopic interference wafer thickness meter that measures the thickness of wafer 5 by analyzing the interference light between light reflected from the lower surface 6 of wafer 5 and light reflected from the upper surface 6 of wafer 5. Note that this thickness measuring unit may include an SLD (Super Luminescent Diode) as a light source that emits measurement light.

[0043] The control unit 3 of the grinding apparatus 1 includes a CPU that performs arithmetic processing according to a control program, and a storage medium such as a memory. The control unit 3 controls the above-mentioned components of the grinding apparatus 1 to perform grinding on the wafer 5. The control unit 3 also controls the current supplied to the spindle motor 73 that rotates the spindle 72 in the grinding mechanism 70 so that the rotation speed of the spindle motor 73 is set to a preset rotation speed. The control unit 3 is also configured to function as a rotation load measuring unit that measures the load current value of the current supplied to the spindle motor 73 to maintain the preset rotation speed when a load that slows the rotation speed is applied due to the grinding wheel 77 coming into contact with the wafer 5.

[0044] The following describes a method for grinding the wafer 5 in the grinding device 1, which is controlled by the control unit 3. This grinding method involves rotating the chuck table 20, which holds the wafer 5 by the holding surface 22, and rotating the annular grinding wheel 77 attached to the spindle 72, thereby grinding the wafer 5.

[0045] [1. Thickness setting process] In this embodiment, first, an operator sets a finishing thickness and a surface matching thickness that is thicker than the finishing thickness in the grinding device 1 as the thickness of the wafer 5 to be ground, using an input device not shown.

[0046] [2. Holding process] Next, the operator holds the wafer 5 on the holding surface 22 of the chuck table 20 shown in FIG. 1 so that the upper surface 6 faces upward.

[0047] [3. External grinding process] In this process, the control unit 3 brings the grinding wheel 77 close to the area between the center and the outer periphery of the radius of the wafer 5 held by the holding surface 22, up to the outer periphery, thereby forming a circular central area in the center of the wafer 5 that is not ground, and grinding an annular outer area outside the central area on the wafer 5.

[0048] Specifically, the control unit 3 adjusts the position of the chuck table 20 in the Y-axis direction using the Y-axis direction movement mechanism 90, thereby positioning the grinding wheel 77 above the area between the center and the outer periphery of the radius portion of the wafer 5 held by the holding surface 22 of the chuck table 20, as shown in Fig. 2. The grit size of the grinding wheel 77 is, for example, 8000 grit.

[0049] Next, the control unit 3 controls the spindle motor 73 of the grinding mechanism 70 shown in FIG. 1 to rotate the grinding wheel 77 together with the spindle 72 (see arrow 301 in FIG. 2). The rotation speed of the spindle 72 and the grinding wheel 77 is, for example, 3000 rpm. Furthermore, the control unit 3 controls the table rotation mechanism 28 shown in FIG. 1 to rotate the chuck table 20 that holds the wafer 5 by the holding surface 22 (see arrow 302 in FIG. 2). The rotation speed of the chuck table 20 is, for example, 300 rpm.

[0050] 3, the chuck table 20 is rotated as indicated by arrow 302 with the inclination angle θ of the chuck table 20 adjusted so that the portion of the conical holding surface 22 located below the grinding wheel 77 is parallel to the lower surface of the grinding wheel 77. In this embodiment, the inclination angle θ of the chuck table 20 is the angle between the rotation axis 221 of the chuck table 20 and the Z-axis direction, as shown in FIG.

[0051] Next, the control unit 3 uses the grinding feed mechanism 60 to lower the grinding mechanism 70, which is at the origin height position, and bring the grinding wheel 77 closer to the holding surface 22 in a direction perpendicular to the holding surface 22, thereby bringing the rotating grinding wheel 77 into contact with the upper surface 6 of the rotating wafer 5 and grinding the upper surface 6.

[0052] Fig. 4 shows the change over time in the height (grinding wheel height) of the lower surface of the grinding wheel 77. In Fig. 4, the change over time in the height of the grinding wheel 77 in the grinding method according to this embodiment is shown by a solid line, while the change over time in the height of the grinding wheel in the conventional grinding method is shown by a dashed line.

[0053] As shown in FIG. 4, in this embodiment, the control unit 3 first lowers the grinding mechanism 70 at a relatively high initial speed V1 so as to approach the chuck table 20 until the height of the grinding wheel 77 reaches a predetermined air cut start height h1 from the origin height h0 (time range T1).

[0054] After the lower surface of the grinding wheel 77 reaches a predetermined air-cutting start height h1, the control unit 3 sets the lowering speed of the grinding mechanism 70 to an air-cutting speed V2 that is slower than the initial speed V1, using the grinding feed mechanism 60. Then, the control unit 3 causes the grinding mechanism 70 to approach the chuck table 20 at the air-cutting speed V2 by the grinding feed mechanism 60 (time range T2).

[0055] When the lower surface of the grinding wheel 77 reaches a height h2 at which it contacts the upper surface 6 of the wafer 5, the control unit 3 grinds the upper surface 6 of the wafer 5 with the grinding wheel 77 at a first grinding speed V3 (time range T3). The first grinding speed V3 is slower than the initial speed V1 and is, for example, the same speed as the air-cut speed V2, e.g., 0.9 μm / sec. The control unit 3 also supplies grinding water from the grinding water nozzle 34 to the upper surface 6 of the wafer 5 using the grinding water nozzle mechanism 33 (see arrow 303 in FIG. 2). The control unit 3 also adjusts the direction (landing point) of the grinding water supplied from the grinding water nozzle 34 using the swing motor 35 (see arrow 304 in FIG. 2).

[0056] At this time, as described above, the grinding wheel 77 is positioned above the area between the center and the outer periphery of the radius portion of the wafer 5 held by the holding surface 22. Therefore, the grinding wheel 77 approaches the area between the center and the outer periphery of the radius portion of the wafer 5 and grinds this area. As a result, as shown in Figures 2 and 3, the central area 601 on the top surface 6 of the wafer 5 is not ground, and an annular outer area 602 outside the central area 601 is ground. That is, in the outer grinding process, an unground circular central area 601 is formed in the center of the wafer 5, and the annular outer area 602 outside the central area 601 of the wafer 5 is ground. 2 shows a first contact portion 771 of the grinding wheel 77 that comes into contact with the outer area 602 of the upper surface 6 of the wafer 5. As shown in FIG.

[0057] In this outer grinding step, the control unit 3 grinds the outer area 602 to the surface-matching thickness set in the thickness setting step. That is, the control unit 3 appropriately uses the thickness gauge 56 to measure the thickness of the outer area 602 of the wafer 5 being ground. Then, when the height of the lower surface of the grinding wheel 77 reaches height h3 (see FIG. 4) and the thickness of the outer area 602 reaches the surface-matching thickness, the control unit 3 uses the grinding feed mechanism 60 to retract the grinding wheel 77 to the air-cut start height h1 at a relatively high retraction speed V4 (time range T4). This causes the lower surface of the grinding wheel 77 to separate from the upper surface 6 of the wafer 5.

[0058] [4. Central grinding process] [4-1. Central area grinding process] Next, the control unit 3 adjusts the position of the chuck table 20 using the Y-axis movement mechanism 90, thereby positioning the grinding wheel 77 above the center of the holding surface 22 of the chuck table 20 that holds the wafer 5, as shown in Figure 5.

[0059] Next, the control unit 3 uses the grinding feed mechanism 60 to lower the grinding mechanism 70 and bring the grinding wheel 77 closer to the holding surface 22 in a direction perpendicular to the holding surface 22, thereby grinding the central area 601 of the upper surface 6 of the wafer 5 and making the central area 601 and the outer area 602 flush with each other.

[0060] Specifically, the control unit 3 uses the grinding feed mechanism 60 to move the grinding mechanism 70 toward the chuck table 20 at an air cutting speed V5 (time range T5), as shown in Fig. 4. This air cutting speed V5 is, for example, the same speed as the air cutting speed V2 described above. When the lower surface of the grinding wheel 77 reaches a height h2 at which it comes into contact with the upper surface 6 of the wafer 5, the control unit 3 grinds the upper surface 6 of the wafer 5 with the grinding wheel 77 at a second grinding speed V6 (time range T6). The second grinding speed V6 is, for example, the same speed as the air cut speed V2 and the first grinding speed V3, and is, for example, 0.9 μm / sec. The control unit 3 also supplies grinding water to the upper surface 6 of the wafer 5 using the grinding water nozzle mechanism 33 (see arrow 303 in FIG. 5).

[0061] At this time, as described above, the grinding wheel 77 is positioned above the center of the holding surface 22 that holds the wafer 5. Therefore, as shown in Fig. 5, the central area 601 of the upper surface 6 of the wafer 5 that was not ground in the outer grinding step is ground. 5 shows a second contact portion 772 of the grinding wheel 77 that contacts the central area 601 of the upper surface 6 of the wafer 5. As shown in FIG.

[0062] The control unit 3 appropriately uses the thickness measuring device 56 to measure the thickness of the central area 601 of the wafer 5 being ground. Then, the control unit 3 continues grinding the central area 601 at the second grinding speed V6 until the height of the lower surface of the grinding wheel 77 reaches height h3 (see FIG. 4), the thickness of the central area 601 reaches the surface alignment thickness, which is the thickness of the outer area 602, and the central area 601 and the outer area 602 become flush with each other.

[0063] [4-2. Full surface grinding process] Furthermore, after the central area 601 and the outer area 602 become flush with each other, the control unit 3 grinds the central area 601 and the outer area 602 until they reach the finishing thickness. Specifically, the control unit 3 continues the grinding process (time range T7; finish grinding) by using the grinding feed mechanism 60 to slow the lowering speed of the grinding mechanism 70 from the second grinding speed V6 to a third grinding speed V7, as shown in Fig. 4. In this grinding process, the entire upper surface 6 of the wafer 5, including the central area 601 and the outer area 602, is ground, as shown in Fig. 6. The third grinding speed V7 is, for example, 0.3 µm / sec.

[0064] Then, when the height of the lower surface of the grinding wheel 77 reaches height h4 (see FIG. 4) and the thickness of the wafer 5 measured by the thickness gauge 56 reaches the finish thickness set in the thickness setting step, the control unit 3 stops the lowering of the grinding mechanism 70 by the grinding feed mechanism 60 and performs so-called spark-out processing (time range T8). This spark-out processing removes grinding spots on the upper surface 6 of the wafer 5.

[0065] After the spark-out process is completed, the control unit 3 performs the escape cut process (time range T9). At this time, the control unit 3 uses the grinding feed mechanism 60 to slowly raise the grinding mechanism 70 at a preset escape cut process speed V9, thereby performing the escape cut process on the wafer 5 with the grinding wheel 77.

[0066] The escape cut processing is performed, for example, until the lower surface of the grinding wheel 77 separates from the upper surface 6 of the wafer 5. After the escape cut processing is completed, the control unit 3 uses the grinding feed mechanism 60 to retract the grinding mechanism 70 to the origin height position at a relatively high retraction speed V10 (time range T10). This retraction speed V10 is, for example, the same speed as the retraction speed V4 described above.

[0067] As described above, in this embodiment, after only the outer area 602 of the wafer 5 is ground in the outer grinding step, the central area grinding step of the center grinding step grinds the central area 601 until it is flush with the outer area 602. That is, in this embodiment, when adjusting the thickness of the wafer 5 to the surface matching thickness, the upper surface 6 of the wafer 5 is divided into the central area 601 and the outer area 602, and grinding is performed for each area.

[0068] Therefore, the contact area between the wafer 5 and the underside of the grinding wheel 77, i.e., the area of ​​the first contact portion 771 (see FIG. 2) and the second contact portion 772 (see FIG. 5), is reduced, thereby reducing the grinding load (vertical load) applied to the wafer 5. This allows the first grinding speed V3, which is the grinding speed in the outer grinding step, and the second grinding speed V6, which is the grinding speed in the central area grinding step, to be increased. For example, the first grinding speed V3 and the second grinding speed V6 can be set equal to each other, and this speed can be set to three times (0.9 μm / sec) the third grinding speed V7 (0.3 μm / sec) used when finish-grinding the entire upper surface 6. Therefore, in this embodiment, the total grinding time in the outer grinding step and the central grinding step can be shortened compared to the grinding time in the conventional method in which the entire upper surface 6 is ground at once from the beginning.

[0069] For example, as shown by the dashed line in Fig. 4, in the conventional grinding method, after the lower surface of the grinding wheel 77 reaches a predetermined air-cut start height h1, the entire upper surface 6 of the wafer 5 is ground at a fourth grinding speed V12 slower than the first grinding speed V3, and then finish-ground at an even slower fourth grinding speed V13. Therefore, as shown in Fig. 4, the time t1 taken from the start to the end of grinding is longer than the time t0 taken from the start to the end of grinding in this embodiment.

[0070] In this embodiment, after the outer grinding process (after the time range T3), the grinding wheel 77 is retracted to the air cut start height h1 without performing the spark-out process or the escape cut process, and then the center grinding process is performed. Therefore, the grinding time can be further reduced.

[0071] Furthermore, in this embodiment, the grinding load applied to the wafer 5 in the outer grinding step and the central area grinding step can be reduced, which can prevent the chuck table 20 from tilting during grinding. Therefore, it is possible to grind the wafer 5 to have a uniform thickness.

[0072] In this embodiment, the control unit 3 may make the area of ​​the first contact portion 771 (see Figure 2), which is the area of ​​the underside of the grinding wheel 77 that contacts the outer area 602 of the wafer 5 in the outer grinding process, equal to the area of ​​the second contact portion 772 (see Figure 5), which is the area of ​​the underside of the grinding wheel 77 that contacts the central area 601 of the wafer 5 in the central area grinding process of the central grinding process.

[0073] This makes it possible to equalize the grinding loads applied to the wafer 5 and the loads applied to the grinding wheel 77 in the outer grinding step and the central area grinding step. In this case, in the outer grinding step, the control unit 3 controls the Y-axis direction moving mechanism 90 based on, for example, the outer diameter of the grinding wheel 77 and the outer diameter of the wafer 5, to set the position of the chuck table 20 in the Y-axis direction relative to the grinding wheel 77 so that the area of ​​the first contact portion 771 and the area of ​​the second contact portion 772 are equal to each other. The area of ​​the first contact portion 771 and the area of ​​the second contact portion 772 are calculated in advance from the position of the chuck table 20 in the Y-axis direction relative to the grinding wheel 77 and the width of the grinding wheel 77 in the radial direction.

[0074] Furthermore, the control unit 3 may control grinding using the load current value of the spindle motor 73 that rotates the spindle 72 in the grinding mechanism 70. For example, the control unit 3 may measure the load current value of the spindle motor 73 when grinding the outer area 602 in the outer grinding step and the load current value of the spindle motor 73 when grinding the central area 601 in the central area grinding step of the central grinding step, and make these values ​​equal to each other.

[0075] In this case as well, it is possible to equalize the grinding load applied to the wafer 5 and the load applied to the grinding wheel 77 in the outer grinding process and the central area grinding process. In this case, the control unit 3 adjusts, for example, the areas of the first contact portion 771 and the second contact portion 772 so that the load current values ​​of the spindle motor 73 in the outer grinding process and the central area grinding process are equal to each other. That is, the control unit 3 measures the load current value (outer load current value) of the spindle motor 73 when grinding the outer area 602 in the outer grinding step. Furthermore, the control unit 3 measures the load current value (center load current value) of the spindle motor 73 when grinding the center area 601 in the center area grinding step in the center grinding step. Then, the control unit 3 adjusts, for example, the areas of the first contact portion 771 and the second contact portion 772 so that the outer load current value and the center load current value are equal to each other.

[0076] Furthermore, instead of or in addition to adjusting the areas of the first contact portion 771 and the second contact portion 772, the control unit 3 may be configured to control the table rotation mechanism 28 shown in FIG. 1 to adjust the rotation speed of the chuck table 20 holding the wafer 5, thereby making the load current values ​​of the spindle motor 73 equal in the outer grinding process and the central area grinding process. Furthermore, instead of or in addition to adjusting the rotational speed of the chuck table 20, the control unit 3 may be configured to adjust the rotational speed of the spindle motor 73 to equalize the load current value of the spindle motor 73 in the outer grinding process and the central area grinding process.

[0077] In addition, the control unit 3 may use the load measuring device 29 provided in the wafer holding mechanism 30 to make the load value when grinding the outer area 602 of the upper surface 6 of the wafer 5 in the outer grinding process equal to the load value when grinding the central area 601 of the upper surface 6 of the wafer 5 in the central grinding process.

[0078] That is, the control unit 3 uses the load measuring device 29 to measure the load (outer grinding load) applied to the wafer 5 when grinding the outer area 602 in the outer grinding step. Furthermore, the control unit 3 uses the load measuring device 29 to measure the load (center grinding load) applied to the wafer 5 when grinding the center area 601 in the center area grinding step in the center grinding step. Then, the control unit 3 adjusts the areas of the first contact portion 771 and the second contact portion 772 and / or controls the table rotation mechanism 28 to adjust the rotation speed of the chuck table 20 holding the wafer 5 so that the outer grinding load and the center grinding load are equal to each other. This makes it possible to equalize the grinding loads applied to the wafer 5 and the loads applied to the grinding wheels 77 in the outer grinding step and the center area grinding step.

[0079] In the central area grinding process, the control unit 3 detects that the central area 601 and the outer area 602 have become flush with each other using the thickness measuring device 56. In this regard, the control unit 3 may detect that the central area 601 and the outer area 602 have become flush with each other using the load current value of the spindle motor 73. That is, when the central area 601 and the outer area 602 become flush with each other, the lower surface of the grinding wheel 77 comes into contact with the entire upper surface 6 of the wafer 5, increasing the frictional resistance between the lower surface of the grinding wheel 77 and the upper surface 6 of the wafer 5, and increasing the load current value of the spindle motor 73. The control unit 3 may detect that the central area 601 and the outer area 602 have become flush with each other based on this change in the load current value.

[0080] Alternatively, the control unit 3 may detect that the central area 601 and the outer area 602 have become flush with each other based on the measurement value of the load measuring device 29 provided in the wafer holding mechanism 30. That is, when the central area 601 and the outer area 602 become flush with each other, the lower surface of the grinding wheel 77 comes into contact with the entire upper surface 6 of the wafer 5, and the grinding load value that the wafer 5 receives from the grinding wheel 77 increases. The control unit 3 may detect that the central area 601 and the outer area 602 have become flush with each other by detecting this change in the grinding load value using the load measuring device 29.

[0081] In addition, in this embodiment, in the outer grinding process, in order to grind the outer area 602 by bringing the grinding wheel 77 close to the area between the center and outer periphery of the radius part of the wafer 5 up to the outer periphery, the grinding wheel 77 is positioned above the area between the center and outer periphery of the radius part of the wafer 5 by adjusting the position in the Y axis direction on the chuck table 20 using the Y axis direction moving mechanism 90. In this regard, instead of adjusting the relative positional relationship between the chuck table 20 and the grinding wheel 77 in the Y-axis direction, the outer area 602 may be ground by the grinding wheel 77 by changing the inclination angle of the chuck table 20.

[0082] In this case, as shown in FIG. 7, the control unit 3 positions the grinding wheel 77 above the center of the holding surface 22 of the chuck table 20 that holds the wafer 5 in the outer grinding step. 8, the control unit 3 adjusts the tilt angle θ of the chuck table 20 so that the lower surface of the grinding wheel 77 contacts only the portion between the center and the outer periphery of the radius portion of the wafer 5 and the outer periphery, i.e., the outer area 602 of the wafer 5. In this case, the tilt angle θ of the chuck table 20 is larger than the tilt angle θ shown in FIGS.

[0083] Next, the control unit 3 uses the grinding feed mechanism 60 to lower the grinding mechanism 70, which is at the origin height position, and bring the grinding wheel 77 closer to the holding surface 22 in a direction perpendicular to the holding surface 22, thereby forming a circular central area 601 on the wafer 5 that is not ground, and grinding an annular outer area 602 on the wafer 5 outside the central area 601. 7 shows a first contact portion 771 of the grinding wheel 77 that comes into contact with the outer area 602 of the upper surface 6 of the wafer 5. As shown in FIG.

[0084] For example, the control unit 3 grinds the outer area 602 until a portion of the outer area 602 (the outer periphery of the wafer 5) reaches the surface-matching thickness, and then causes the grinding mechanism 70 to raise using the grinding feed mechanism 60 to move the lower surface of the grinding wheel 77 away from the upper surface 6 of the wafer 5. Alternatively, the control unit 3 temporarily stops the grinding mechanism 70, and then adjusts (decreases) the inclination angle θ of the chuck table 20 so that the portion of the conical holding surface 22 located below the grinding wheel 77 becomes parallel to the lower surface of the grinding wheel 77, as shown in FIG. 6 . Then, the control unit 3 performs the above-mentioned center grinding process, grinding the central area 601 to the surface-matching thickness in the center area grinding process, and grinding the central area 601 and the outer areas 602 to the finishing thickness in the full surface grinding process.

[0085] This method also reduces the contact area between the wafer 5 and the underside of the grinding wheel 77 in the outer grinding step and the central area grinding step, thereby reducing the grinding load on the wafer 5 and increasing the grinding speed. Therefore, it is possible to shorten the total grinding time in the outer grinding step and the central grinding step. Furthermore, with this method, when shifting from the outer grinding process to the central grinding process, there is no need to change the position of the chuck table 20 in the Y-axis direction relative to the grinding mechanism 70 using the Y-axis direction moving mechanism 90. Therefore, the grinding time can be further shortened. [Explanation of symbols]

[0086] 1: Grinding device, 3: Control unit, 5: Wafer, 6: Upper surface, 10: Base, 11: column, 12: bellows cover, 13: opening, 20: chuck table, 21: porous member, 22: holding surface, 23: frame, 24: frame surface, 28: table rotation mechanism, 29: load measuring device, 30: wafer holding mechanism, 33: grinding water nozzle mechanism, 34: grinding water nozzle, 35: turning motor, 38: Second grinding water source, 39: Cover plate, 56: Thickness measuring device, 57: Wafer height measuring unit, 58: Holding surface height measuring unit, 60: Grinding feed mechanism, 61: Z-axis guide rail, 62: Z-axis ball screw, 63: Z-axis moving table, 64: Z-axis motor, 65: Z-axis encoder, 66: Holder, 69: First grinding water source, 70: grinding mechanism, 71: spindle housing, 72: spindle, 73: spindle motor, 74: wheel mount, 75: grinding wheel, 76: Wheel base, 77: Grinding wheel, 90: Y-axis direction movement mechanism, 91: support base, 92: Y-axis guide rail, 93: Y-axis ball screw, 94: Y-axis motor, 95: Y-axis moving table, 96: Y-axis encoder, 601: central area, 602: outer area, 771: 1st contact part, 772: 2nd contact part

Claims

1. A wafer grinding method for grinding a wafer by rotating a chuck table that holds a wafer by a holding surface and rotating an annular grinding wheel attached to a spindle, comprising: an outer grinding step in which the grinding wheel is positioned above the center of the wafer held on the holding surface, and the tilt angle of the chuck table is adjusted so that the portion of the holding surface located below the grinding wheel is non-parallel to the lower surface of the grinding wheel, thereby bringing the grinding wheel into contact with only an outer area that is a portion between the center and the outer periphery of the radius of the wafer held on the holding surface and up to the outer periphery, and grinding water is supplied from a grinding water nozzle toward the portion of the outer area that is in contact with the grinding wheel, thereby forming a circular central area in the center of the wafer that is not ground, and grinding the annular outer area of ​​the wafer outside the central area; an inclination changing step of adjusting the inclination angle of the chuck table after the outer grinding step so that a portion of the holding surface located below the grinding wheel is parallel to a lower surface of the grinding wheel; a center grinding step of bringing the grinding wheel into contact with the central area of ​​the wafer after the tilt changing step and supplying grinding water from the grinding water nozzle toward the portion of the central area that is in contact with the grinding wheel, thereby grinding the central area to make it flush with the outer area. Wafer grinding method.

2. an area of ​​the lower surface of the grinding wheel that contacts the outer area of ​​the wafer in the outer grinding step and an area of ​​the lower surface of the grinding wheel that contacts the central area of ​​the wafer in the central grinding step are made equal to each other; 2. The method for grinding wafers according to claim 1.

3. a rotation load measuring unit for measuring a load current value of a motor that rotates the spindle, and making the load current value when grinding the outer area of ​​the wafer in the outer grinding step equal to the load current value when grinding the central area of ​​the wafer in the central grinding step; 2. The method for grinding wafers according to claim 1.

4. a load measuring device for measuring the load applied to the wafer held by the holding surface is used to equalize the load value when grinding the outer area of ​​the wafer in the outer grinding step and the load value when grinding the central area of ​​the wafer in the central grinding step.

2. The method for grinding wafers according to claim 1.

5. a thickness setting step for setting a finishing thickness and a surface matching thickness that is thicker than the finishing thickness; In the outer grinding step, the outer area of ​​the wafer is ground to the surface alignment thickness; In the center grinding step, after the center area of ​​the wafer is made flush with the outer area, the center area and the outer area are ground to the finishing thickness.

2. The method for grinding wafers according to claim 1.

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