JP2017094418A - Grinding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize thickness of a wafer when forming a circular recessed part at a center of the wafer.SOLUTION: A grinding device comprises: a holding table (22); a table rotating shaft (35); a grinding wheel (49) which has a diameter smaller than a radius of a wafer (W) and in which grinding stones (48) are annularly arranged; grinding means (46) comprising a grinding wheel rotating shaft (45); inclination adjustment means (31) that adjusts inclinations of the table rotating shaft and the grinding wheel rotating shaft relatively; a thickness measuring instrument (71) that measures wafer thickness of the circular recessed part (15) to be formed in the wafer; and scanning means (73) that makes the thickness measuring instrument perform scanning. In the grinding device, an inclination of the table rotating shaft is calculated from at least three thickness values at three positions of a thickness value at the center of the wafer, the maximum value of the thickness values measured by scanning by the thickness measuring instrument and a thickness value at an outer periphery of the circular recessed part, and then the inclination adjustment means is made to adjust the inclination so that a difference among the thickness values at the three positions becomes minimum.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a grinding apparatus for grinding a wafer held on a holding table with a grinding wheel.

  In the grinding apparatus, the chuck table rotates, and the wafer is ground by contacting the wafer held by the chuck table while the grinding wheel rotates. Conventionally, as this kind of grinding apparatus, one that temporarily stops the grinding of the wafer before reaching the finished thickness, confirms the thickness of the wafer in the radial direction, and corrects the inclination of the chuck table and the grinding wheel is known. (For example, refer to Patent Documents 1 and 2). In this grinding apparatus, the wafer thickness is measured in a spot manner by rotating the chuck table at three locations of the wafer center, outer periphery, and radius ½, and the wafer thickness is uneven at the three locations. In some cases, the wafer is ground to the finished thickness by correcting the tilt of the chuck table and grinding wheel.

JP 2007-54922 A JP 2013-119123 A

  By the way, as a method for grinding a wafer, there has been proposed a grinding method called TAIKO grinding in which the edge portion of the outermost periphery of the wafer is left and only the inner periphery thereof is ground and thinned. In TAIKO grinding, a circular recess is formed in the center of a wafer using a grinding wheel having a diameter smaller than the radius of the wafer. However, the tilt correction described in Patent Documents 1 and 2 is to thin the entire wafer uniformly and cannot be applied to TAIKO grinding. That is, it has been difficult to adjust the thickness of the circular concave portion of the wafer by bringing the grinding wheel for TAIKO grinding into contact with the wafer in a semicircular shape.

  This invention is made | formed in view of this point, and when forming a circular recessed part in the center of a wafer, it aims at providing the grinding apparatus which can make the thickness of the wafer in a circular recessed part uniform.

  The grinding device of the present invention is a grinding device that grinds the center of a wafer with a grindstone, forms a circular concave portion at the center and an annular convex portion on the outer peripheral portion, and grinds the thickness of the circular concave portion to a preset finish thickness. A holding table for holding the wafer, a table rotating shaft for rotating the holding table, a grinding wheel having a grinding wheel having a diameter smaller than the radius of the wafer, and a grinding wheel rotating shaft for attaching and rotating the grinding wheel. A grinding means, a grinding feed means for moving the holding table and the grinding means in a relatively approaching and separating direction, an inclination adjusting means for adjusting the inclination of the table rotating shaft and the grinding wheel rotating shaft, and holding Thickness measuring device that measures the thickness of the circular recess formed by grinding the wafer held on the table, and the thickness measuring device Scanning means for scanning, a storage unit for storing thickness values of at least three circular recesses measured by a scanning unit with a thickness measuring device and measuring the thickness of the wafer, and rotation of the grinding wheel from the thickness values stored in the storage unit A measuring section for calculating the inclination of the table rotation axis with respect to the axis, and the measuring operation for measuring the thickness value of at least three places temporarily stops the grinding feed before the thickness of the circular recess reaches the preset finish thickness. The thickness values of at least three locations are the thickness value at the center of the wafer, the maximum value of the thickness value measured by scanning the thickness measuring instrument from the center of the wafer toward the outer periphery with the scanning means, and the outer peripheral portion of the circular recess. The calculation unit calculates the inclination of the table rotation axis with respect to the grinding wheel rotation axis when the difference between the thickness values of at least three locations is the smallest. After the the table rotation axis adjustment means inclination to the inclination and the grinding wheel rotation axis relative to the tilt adjusting, ground to a thickness of finishing the thickness of the circular recess.

  According to this configuration, the thickness measurement unit is scanned by the scanning unit, so that the thickness value at the center of the wafer, the thickness value at the position where the thickness value measured from the center of the wafer toward the outer periphery is maximized, and the circular shape At least three thickness values are measured together with the thickness value of the outer peripheral portion of the recess. The inclination of the table rotating shaft and the grinding wheel rotating shaft is relatively adjusted by the inclination adjusting means so that the difference between the thickness values is minimized. Therefore, even when the in-plane thickness variation occurs in the circular concave portion of the wafer, the in-plane thickness variation can be corrected to make the wafer thickness uniform in the circular concave portion.

  According to the present invention, when the circular recess is formed in the center of the wafer, the thickness of the wafer in the circular recess can be made uniform.

It is a perspective view of the grinding means of the grinding device concerning this embodiment. It is a perspective view which shows the inclination adjustment means which concerns on this Embodiment. It is a figure for demonstrating the measurement location of the wafer in TAIKO grinding. It is explanatory drawing of inclination adjustment of the holding table which concerns on this Embodiment. It is a figure which shows an example of the inclination adjustment which concerns on this Embodiment. It is a transition diagram of the grinding operation of the wafer concerning this embodiment.

  Hereinafter, the grinding apparatus according to the present embodiment will be described with reference to the accompanying drawings. The grinding of the wafer according to the present embodiment leaves only the outer peripheral portion of the back surface of the wafer. FIG. 1 is a perspective view of the grinding means of the grinding apparatus according to the present embodiment.

  In the grinding apparatus 1, the front side of the wafer W is held on the holding table 22 via the grinding tape 18 with the back surface 12 of the wafer W facing upward. The surface of the wafer W is divided into a device region in which a plurality of devices are formed and an outer peripheral surplus region surrounding the device region. The wafer W is brought close to the holding table 22 while the grinding wheel 49 of the grinding apparatus 1 rotates around the Z axis, and the grinding wheel 49 and the back surface 12 of the wafer W are brought into rotational contact so that the back surface side of the device region is ground. . Thereby, on the back surface 12 of the wafer W, the circular concave portion 15 is formed in the region corresponding to the device region, and the annular convex portion 16 is formed in the region corresponding to the outer peripheral surplus region.

  The wafer W is thinned only at the central portion where the circular concave portion 15 is formed, and the rigidity is enhanced by the annular convex portion 16 surrounding the circular concave portion 15. Therefore, the device area of the wafer W is thinned, and the warpage of the wafer W is suppressed by the annular convex portion 16, thereby preventing breakage during transportation. The wafer W may be a semiconductor wafer such as silicon or gallium arsenide, or a ceramic, glass, or sapphire optical device wafer.

  A column 41 is erected in the vicinity of the holding table 22. The column 41 is provided with a grinding feed means 61 for moving the grinding means 46 up and down. The grinding feed means 61 has a pair of guide rails 62 arranged in front of the column 41 and parallel to the Z-axis direction, and a motor-driven Z-axis table 63 slidably installed on the pair of guide rails 62. ing.

  A grinding means 46 is supported on the front surface of the Z-axis table 63 via a housing 64. A ball screw 65 is screwed to the back side of the Z-axis table 63, and a drive motor 66 is connected to one end of the ball screw 65. The ball screw 65 is rotationally driven by the drive motor 66 and the grinding means 46 is moved along the guide rail 62 in the Z-axis direction.

  The grinding means 46 is configured by providing a mount 47 at the lower end of a cylindrical grinding wheel rotating shaft 45. In the grinding means 46, a grinding wheel 49 in which a plurality of grinding wheels 48 are annularly arranged is rotatably attached to the lower surface of the mount 47 of the grinding means 46. The diameter of the grinding wheel 49 is smaller than the radius of the wafer W. The grinding wheel 48 is composed of, for example, a diamond wheel in which diamond abrasive grains are hardened with a binder such as resin bond or vitrified bond. In the grinding process, the thickness of the circular recess 15 of the wafer W is ground and thinned by the grinding wheel 48 to a preset finish thickness.

  In the present embodiment, in the vicinity of the grinding position, the first gauge 91 for measuring the height of the upper surface (holding surface) of the holding table 22 and the height of the surface to be ground of the wafer W held by the holding table 22 are measured. A second gauge 92 is provided. The 1st gauge 91 and the 2nd gauge 92 are comprised with a contact-type gauge. The first gauge 91 is brought into contact with the holding surface 22a, the second gauge 92 is brought into contact with the bottom surface of the circular recess 15 of the wafer W, and the wafer is determined from the difference between the height of the holding surface 22a and the bottom surface of the circular recess 15. The thickness of the W circular recess 15 is measured.

  Further, in the vicinity of the first gauge 91 and the second gauge 92, a non-contact type thickness measuring device 71 that measures the wafer thickness of the circular recess 15 formed by grinding the wafer W held on the holding table 22. Is provided. The scanning unit 73 includes a rotatable stand 74 and an arm 75 extending from the stand 74. A thickness measuring device 71 is fixed to the tip of the arm 75 of the scanning means 73, and the thickness measuring device 71 is scanned in the radial direction of the wafer W by the rotation of the stand 74. That is, the radial direction of the wafer W is a concept including not only a linear direction from the center of the wafer W toward the outer periphery but also a turning direction in which the wafer W is turned between the center and the outer periphery. The thickness measuring device 71 is, for example, a reflection type optical displacement sensor, which irradiates the measurement light toward the wafer W and receives the reflected light reflected from the upper surface of the wafer W and the reflected light reflected from the lower surface of the wafer W. Then, the thickness of the wafer W is measured by the optical path difference between the reflected light reflected from the upper surface and the reflected light reflected from the lower surface. The thickness value (measured value) of the wafer W is output to the control unit 85.

  The control unit 85 is provided with a storage unit 86 and a calculation unit 87. The storage unit 86 stores the thickness value of the circular recess 15 measured by the thickness measuring device 71. The calculation unit 87 calculates the inclination of the table rotation shaft 35 (see FIG. 2) with respect to the grinding wheel rotation shaft 45 from the thickness value stored in the storage unit 86. The control unit 85 includes a processor that executes various processes, a memory, and the like. The memory is composed of one or a plurality of storage media such as a ROM (Read Only Memory) and a RAM (Random Access Memory) depending on the application. The control unit 85 controls the inclination of the table rotation shaft 35 according to the output result from the calculation unit 87. A method for controlling the table rotation shaft 35 will be described later. The calculating unit 87 can calculate the tilt angle (tilt amount) and tilt direction of the table rotation shaft 35.

  FIG. 2 is a perspective view showing the tilt adjusting means according to the present embodiment. The inclination adjusting means 31 includes a flange portion 32 connected to the holding table 22, a pair of movable shafts 33 a and 33 b (see FIG. 4 for the movable shaft 33 b) and a fixed shaft 34 provided in the circumferential direction of the flange portion 32. It is composed of The inclination adjusting means 31 adjusts the inclination of the table rotation shaft 35 by moving the movable shafts 33a and 33b and inclining the flange portion 32 with the fixed shaft 34 as a fulcrum.

  Each of the movable shafts 33 a and 33 b is attached to the turntable 42 via a cylindrical portion 36, and is configured by screwing a male screw shaft 37 into a female screw inside the cylindrical portion 36. The tip of the male screw shaft 37 is connected to the flange portion 32, and the motor 38 is connected to the lower end of the male screw shaft 37. When the male screw shaft 37 is rotationally driven by the motor 38, the flange portion 32 is moved in the vertical direction. A belt 39 a is wound around the table rotation shaft 35 and the table rotation means 39. As the table rotating means 39 rotates, the rotational force is transmitted to the table rotating shaft 35 via the belt 39a. The holding table 22 is configured to rotate as the table rotation shaft 35 rotates.

  FIG. 3 is a diagram for explaining the measurement points of the wafer in TAIKO grinding. As shown in FIG. 3A, in general grinding of a wafer W, a grinding wheel 50 having a diameter substantially the same as the diameter of the wafer W is used to form an arc-shaped grinding region (for example, approximately 1/3 of a half circumference of the grinding wheel 50). Is applied to the wafer W for grinding. At this time, the grinding wheel 50 easily hits either the center O side or the outer periphery C1 side of the wafer W. In the case of FIG. 3B, since the grinding wheel 50 hits the center O side of the wafer W strongly and the grinding wheel 50 hits the outer periphery C1 side of the wafer W weakly, the thickness of the wafer W increases from the center O toward the radially outer side. . For this reason, the thickness of the wafer W is spot-measured at three locations: the center O of the wafer W, the outer periphery C1, and the location C2 having a radius ½, and the table rotation shaft 35 is adjusted in inclination. Thereby, the thickness of the wafer W is ground uniformly.

  As shown in FIG. 3C, in the TAIKO grinding of the wafer W according to the present embodiment, a semicircular grinding region is applied to the wafer W with a grinding wheel 49 having a diameter smaller than the radius of the wafer W, and a circle is formed in the center of the wafer W. A recess 15 is formed. The bottom surface of the circular concave portion 15 is curved in a concave shape between the center O of the wafer W and the outer peripheral portion C. In TAIKO grinding, it is necessary to grind the holding surface 22a of the holding table 22 in advance so as to be parallel to the concave curved surface of the wafer W in order to make the thickness of the circular recess 15 uniform. Since the diameter of the holding surface 22a is larger than that of the wafer W, if a grinding wheel 49 having the same diameter is used for the wafer W and the holding surface 22a, a portion that cannot be ground is formed on the outer peripheral portion of the holding surface 22a. An outer peripheral part will float from the holding surface 22a. For this reason, the wafer W and the holding surface 22a are ground by the grinding wheels 49 having different diameters. However, since the curvature of the bottom surface of the circular recess 15 and the curvature of the holding surface 22a are different, the in-plane thickness difference is made zero. I can't.

  In the case of FIG. 3C, since the grinding wheel 49 is strongly applied at the position P0 slightly inward of the radius W of the wafer W, the thickness of the wafer W decreases from the center O toward the position P0, and the circular recess from the position P0. 15 increases toward the outer peripheral portion C. That is, when the wafer W is ground by the grinding wheel 49, the portion where the difference is the maximum with respect to the thickness value of the center O of the wafer W is not necessarily the portion having the radius 1/2 of the wafer W. Therefore, the in-plane thickness variation cannot be accurately measured only by spot-measuring the same three points as the entire surface grinding. In addition, since the grinding area of the grinding wheel 49 is also semicircular, the tilt of the table rotation shaft 35 cannot be adjusted with high accuracy by an adjustment method similar to that for full-surface grinding.

  Therefore, in the present embodiment, the thickness measuring device 71 is scanned in the radial direction to measure the thickness of the wafer W, and the thickness value at the center O of the wafer W and the thickness value at the position where the thickness value of the wafer W is maximized. And the thickness value of the outer peripheral portion C of the circular recess 15 is acquired. The thickness of the wafer W is made uniform by grinding the wafer W by adjusting the tilt by the table rotating shaft 35 by the tilt adjusting means 31 so that the difference between these thickness values is minimized.

  FIG. 4 is an explanatory diagram of tilt adjustment of the holding table according to the present embodiment. As the tilt adjusting means 31 of the holding table 22, two movable shafts 33 a and 33 b and one fixed shaft 34 are provided at 120 ° intervals in the circumferential direction of the flange portion 32 (see FIG. 2). In the case of the entire surface grinding of the wafer, the grinding area of the grinding wheel 50 is arcuate, and the strength with which the grinding wheel 50 strikes the wafer W can be adjusted by moving only one side of the pair of movable shafts 33a and 33b up and down. For example, the degree of contact of the grinding wheel 50 on the center O side or the outer periphery C1 side with the grinding wheel 50 can be adjusted by moving the movable shaft 33b substantially in the extending direction of the grinding region. By moving up and down the movable shaft 33a in the direction orthogonal to the grinding region, the contact condition can be adjusted to the location C2 of the radius W of the wafer W by the grinding wheel 50.

  On the other hand, in the case of TAIKO grinding as in the present embodiment, since the grinding area of the grinding wheel 49 is semicircular, the wafer can be moved even if only one of the pair of movable shafts 33a and 33b is moved up and down. The strength with which the grinding wheel 49 hits W cannot be adjusted. In order to adjust the strength with which the grinding wheel 49 hits the wafer W, it is necessary to adjust the pair of movable shafts 33a and 33b in combination. For example, when the movable shaft 33a is raised and the movable shaft 33b is lowered, the intermediate position P3 of the semicircular grinding region of the grinding wheel 49 strongly hits the center O of the wafer W. When the movable shaft 33a is lowered and the movable shaft 33b is raised, the one end P1 and the other end P2 of the semicircular grinding region of the grinding wheel 49 strongly contact the center O of the wafer W and the outer peripheral portion C of the circular recess 15. When both the movable shaft 33a and the movable shaft 33b are raised, one end P1 of the semicircular grinding region of the grinding wheel 49 strongly hits the center O of the wafer W. When both the movable shaft 33a and the movable shaft 33b are lowered, the other end P2 of the semicircular grinding region of the grinding wheel 49 strongly hits the outer peripheral portion C of the circular recess 15 of the wafer W.

  Next, an example of tilt adjustment of the holding table according to the present embodiment will be described. FIG. 5 is a diagram illustrating an example of tilt adjustment according to the present embodiment. In FIG. 5, the left side of the drawing shows the thickness of the wafer when measured while being paused, and the right side of the drawing shows the state of tilt adjustment. In FIG. 5, for convenience of explanation, the grinding wheel is illustrated as being inclined, but the holding table is actually inclined.

  As shown in FIG. 5, in the TAIKO grinding, when the wafer W is ground by the grinding wheel 49 to form the circular recess 15, the thickness value measured from the center O of the wafer W toward the outer periphery is maximized in the circular recess 15. A local maximum is generated. FIG. 5E shows a state in which the wafer W is ground and the circular recess 15 is well formed. A maximum value exists near the center of the wafer W, and the thickness value of the outer peripheral portion C of the circular recess 15 and the thickness value of the center O of the wafer W are substantially equal. The wafer W in FIG. 5E is used as a reference.

  FIG. 5A shows a state where the thickness of the intermediate position between the center O of the wafer W and the outer peripheral portion C of the circular recess 15 is larger than the thickness of the center O and the outer peripheral portion C, that is, between the center O and the outer peripheral portion C. A state in which a maximum value exists at the position is shown. In the wafer W in FIG. 5A, the thickness value of the outer peripheral portion C of the circular recess 15 is slightly smaller, the maximum value is larger, and the thickness value of the center O of the wafer W is slightly smaller than the reference wafer W in FIG. 5E. Becomes smaller. In this case, the movable shaft 33a (see FIG. 4) is raised by one step (1 μm), and the movable shaft 33b is lowered by two steps (2 μm). Thereby, the intermediate position P3 (see FIG. 4) of the semicircular grinding region of the grinding wheel 49 strongly hits the intermediate position between the outer peripheral portion C of the circular recess 15 of the wafer W, and the intermediate position is ground. The thickness of the wafer W can be made uniform.

  FIG. 5B shows a state where the thickness of the intermediate position between the center O of the wafer W and the outer peripheral portion C of the circular recess 15 is reduced. In the wafer W in FIG. 5B, the thickness value of the outer peripheral portion C of the circular recess 15 is slightly larger than the reference wafer W in FIG. 5E, and the maximum value near the center of the wafer W is smaller. The thickness value of the center O is slightly increased. In this case, the movable shaft 33a is lowered by one step (1 μm), and the movable shaft 33b is raised by two steps (2 μm). As a result, one end P1 and the other end P2 (see FIG. 4) of the semicircular grinding region of the grinding wheel 49 strike the center O of the wafer W and the outer peripheral portion C of the circular recess 15 so that the center O and the outer peripheral portion C Can be ground to make the thickness of the wafer W uniform.

  FIG. 5C shows a state where the thickness of the center O of the wafer W is increased. In the wafer W in FIG. 5C, the thickness value of the outer peripheral portion C of the circular recess 15 is smaller, the maximum value near the center of the wafer W is larger, and the center O of the wafer W is larger than the reference wafer W in FIG. The thickness value of increases. In this case, each of the movable shaft 33a and the movable shaft 33b is raised by one step (1 μm). Thereby, one end P1 of the semicircular grinding region of the grinding wheel 49 hits the center O of the wafer W, and the center O is ground to make the thickness of the wafer W uniform.

  FIG. 5D shows a state where the thickness of the outer peripheral portion C of the circular concave portion 15 of the wafer W is increased. In the wafer W in FIG. 5D, the thickness value of the outer peripheral portion C of the circular recess 15 is larger, the local maximum value near the center of the wafer W is smaller than the reference wafer W in FIG. The thickness value of becomes smaller. In this case, each of the movable shaft 33a and the movable shaft 33b is lowered by one step (1 μm). Accordingly, the other end P2 of the semicircular grinding region of the grinding wheel 49 strongly hits the outer peripheral portion C of the circular concave portion 15 of the wafer W, and the outer peripheral portion C is ground to make the thickness of the wafer W uniform. it can.

  Next, the grinding operation of the wafer W according to the present embodiment will be described. FIG. 6 is a transition diagram of the grinding operation of the wafer according to the present embodiment.

  As shown in FIG. 6A, during grinding of the center of the wafer W on the holding table 22 with the grinding wheel 49, the grinding feed is temporarily stopped before the thickness of the circular recess 15 reaches the preset finish thickness. The At this time, rotation of the holding table 22 and the grinding wheel 49 is maintained, and the grinding wheel 49 is lifted from the wafer W. Further, the thickness measuring device 71 is located immediately above the outer periphery of the wafer W.

  As shown in FIG. 6B, when the grinding wheel 49 rises from the wafer W, the scanning unit 73 scans the thickness measuring device 71 in the radial direction of the wafer W and measures the thickness of the wafer W. At this time, the thickness value at the center of the wafer W is compared with the thickness value measured by scanning the thickness measuring device 71 with the scanning means 73 and the thickness value at the center of the wafer W, and the circular concave portion. The thickness values of at least three of the 15 outer peripheral thickness values are selectively stored in the storage unit 86 (see FIG. 1). In addition, the inclination of the grinding wheel rotation shaft 45 with respect to the table rotation shaft 35 is calculated by the calculation unit 87 so that the difference between the thickness values of the wafer W in the storage unit 86 is reduced.

  As shown in FIG. 6C, when the inclination of the grinding wheel rotation shaft 45 with respect to the table rotation shaft 35 is calculated by the calculation unit 87 (see FIG. 1), the thickness measuring instrument 71 is moved again to the outside of the wafer. At this time, the inclination of the table rotating shaft 35 is adjusted by the inclination adjusting means 31 based on the inclination of the table rotating shaft 35 and the grinding wheel rotating shaft 45 calculated by the calculating unit 87. When the inclination of the table rotation shaft 35 is adjusted, the grinding wheel 49 descends and contacts the wafer W, and the grinding of the wafer W is started again. The wafer W is ground until the thickness of the circular recess 15 of the wafer W reaches a predetermined thickness.

  As described above, in the grinding apparatus 1 according to the present embodiment, the thickness measuring unit 71 is scanned by the scanning unit 73, so that the thickness value of the center O of the wafer W and the center O of the wafer W toward the outer periphery. The thickness value at the position where the measured thickness value is maximum and the thickness value of the outer peripheral portion C of the circular recess 15 are measured at least at three locations. The tilt adjusting means 31 relatively adjusts the tilt of the table rotating shaft 35 and the grinding wheel rotating shaft 45 so that the difference between these three thickness values is minimized. Therefore, even when the in-plane thickness variation occurs in the circular recess 15 of the wafer W, the in-plane thickness variation can be corrected to make the thickness of the wafer W in the circular recess 15 uniform.

  In addition, this invention is not limited to the said embodiment, It can change and implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  For example, in the above-described embodiment, a configuration in which a grinding wheel having a diameter different from that of the grinding wheel 49 used for grinding the circular recess 15 of the wafer W is used to shape the holding surface 22a of the holding table 22 before grinding. Although described, it is not limited to this configuration. For shaping the holding surface 22a of the holding table 22 before grinding, a grinding wheel having the same diameter as the grinding wheel 49 used for grinding the circular recess 15 of the wafer W can be used. In this case, the holding surface 22a is ground deeply so as to be a concave curved surface with a grinding wheel, and then the outer peripheral portion is ground flat (see, for example, JP-A-2015-072971). By using a grinding wheel of the same diameter, it is theoretically possible to make the in-plane thickness difference zero, but even in such a case, when in-plane thickness variation occurs, The adjustment method of the holding table 22 according to the present embodiment can be used. In addition, as thickness values, in-plane thickness variation can be obtained by measuring three locations of the center O of the circular concave portion 15 of the wafer W, the outer peripheral portion C of the circular concave portion 15, and the radius ½ of the circular concave portion 15. .

  For example, although the grinding means 46 is configured to move in the grinding feed direction (Z-axis direction) with respect to the holding table 22, it is not limited to this configuration. For example, the holding table 22 and the grinding means 46 may be moved in a direction relatively approaching and separating from the grinding feed direction (Z-axis direction). For example, the holding table 22 is moved in the grinding feed direction with respect to the grinding means 46. It may be moved.

  Further, for example, the inclination of the table rotation shaft 35 is adjusted by the inclination adjusting means 31, but the invention is not limited to this structure. The tilt adjusting means 31 may be configured to relatively adjust the tilt of the table rotating shaft 35 and the grinding wheel rotating shaft 45. For example, the tilt adjusting means 31 may be configured to adjust the tilt of the grinding wheel rotating shaft 45.

  In addition, for example, the movable shafts 33a and 33b are provided in the tilt adjusting means 31, but the present invention is not limited to this configuration. A configuration in which three or more movable shafts are provided in the tilt adjusting means 31 may be adopted.

  As described above, the present invention has the effect that the thickness of the wafer in the circular recess can be made uniform when forming the circular recess in the center of the wafer, and in particular, the wafer held on the holding table. It is useful for a grinding apparatus that grinds with a grinding wheel.

DESCRIPTION OF SYMBOLS 1 Grinding device 15 Circular recessed part 16 Annular convex part 22 Holding table 31 Inclination adjusting means 35 Table rotating shaft 45 Grinding wheel rotating shaft 46 Grinding means 48 Grinding wheel 49 Grinding wheel 61 Grinding feed means 71 Thickness measuring device 73 Scanning means 86 Storage part 87 Calculation part O Wafer center P0 Location where the difference between the thickness value measured by scanning the thickness measuring instrument and the thickness value at the center of the wafer is the largest C The outer peripheral part of the circular recess W Wafer

Claims (1)

A grinding device that grinds the center of a wafer with a grindstone, forms a circular concave portion at the center and an annular convex portion on an outer peripheral portion, and grinds the thickness of the circular concave portion to a preset finish thickness,
A holding table for holding a wafer, a table rotating shaft for rotating the holding table, a grinding wheel for arranging the grindstone in an annular shape with a diameter smaller than the radius of the wafer, and a grinding wheel rotating shaft for attaching and rotating the grinding wheel Grinding means provided, grinding feed means for moving the holding table and the grinding means in a relatively approaching and separating direction, and tilt adjustment for relatively tilting the table rotating shaft and the grinding wheel rotating shaft. Means, a thickness measuring device for measuring the wafer thickness of the circular recess formed by grinding the wafer held on the holding table, scanning means for scanning the thickness measuring device in the radial direction of the wafer, and the thickness measurement A storage unit for storing thickness values of at least three portions of the circular recesses obtained by scanning the wafer with the scanning unit and measuring the thickness of the wafer; and storing the storage unit in the storage unit And a calculation unit for calculating an inclination of the table rotating shaft with respect to the grinding wheel rotation axis from the thickness values,
The measuring operation for measuring the thickness value of at least three places is performed by temporarily stopping the grinding feed before the thickness of the circular recess reaches the preset finish thickness,
The thickness values of the at least three locations are
The thickness value at the center of the wafer,
A maximum value of the thickness value measured by scanning the thickness measuring device from the center of the wafer toward the outer periphery with the scanning means;
A thickness value of the outer periphery of the circular recess, and
Calculating the inclination of the table rotation axis with respect to the grinding wheel rotation axis when the difference between the thickness values of the at least three locations is minimized, by the calculation unit;
A grinding apparatus for performing grinding until the thickness of the circular recess becomes the finished thickness after the tilt adjusting means relatively adjusts the tilt of the table rotating shaft and the grinding wheel rotating shaft to the tilt calculated by the calculating unit. .

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