Grinding apparatus

Abstract

To perform TAIKO grinding of a wafer without requiring replacement of a grinding wheel due to a difference in the type of a mark indicating crystal orientation.SOLUTION: In the grinding device provided with a chuck table for holding a wafer having a mark indicating a crystal orientation formed on an outer peripheral edge, a grinding mechanism for rotating a plurality of grinding wheels 25a arranged annularly to form a circular recessed part and an annular projecting part on one surface of a wafer, a horizontal moving mechanism for moving the grinding mechanism in the horizontal direction, a vertical moving mechanism for vertically moving the grinding mechanism, and a control part, the grinding wheel has a plurality of grinding wheels 25a arranged in the radial direction at different positions in the radial direction of a circle whose center is the rotation center, and the control part has a radius setting part for setting the radius of the circular recessed part to be formed and a horizontal moving control part for moving the grinding mechanism by the horizontal moving mechanism so that a circumscribed circle Co of the plurality of grinding wheels 25a passes through the inner peripheral surface of the circular recessed part to be formed.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a grinding apparatus for grinding the central portion of one surface of a wafer to form a circular recess and an annular protrusion surrounding the circular recess. [Background technology]

[0002] In the manufacturing process of semiconductor devices such as ICs and LSIs used in electronic devices, the backside of a wafer is ground to thin the wafer to a predetermined thickness in order to reduce the size and weight of the semiconductor device. In particular, in recent years, there has been a demand for thinner semiconductor devices to meet the demand for thinner and more compact electronic devices. However, when a wafer is ground to a thickness of, for example, 50 μm or less, the flexural strength of the wafer decreases, making it more susceptible to breakage and making subsequent handling difficult.

[0003] Therefore, for example, Patent Document 1 proposes a grinding method in which only the backside of the wafer in the area where the device is formed is ground to form a circular recess in the center, and an annular protrusion of the same thickness as before grinding is left on the outer periphery of this circular recess as a reinforcing part, thereby increasing the rigidity of the wafer after grinding. Hereinafter, this type of grinding will be referred to as "TAIKO grinding." "TAIKO" is a registered trademark.

[0004] In TAIKO grinding, the wafer and grinding wheels are positioned so that the center of the cutting thickness of the multiple grinding wheels passes through the center of the wafer, and then the wafer and grinding wheels are rotated.The grinding wheels are brought into contact with one side of the wafer to grind the central part of that side, thereby forming a circular recess in the central part of one side of the wafer and forming an annular protrusion around this circular recess.

[0005] Incidentally, marks indicating the crystal orientation of the wafer are formed on a part of the outer periphery of the wafer. This mark includes a notch M1 cut in a V shape shown in Fig. 11(a) and an orientation flat M2 cut in a linear shape shown in Fig. 11(b). Here, in the notch M1 and the orientation flat M2, the amount of cut into the outer periphery of the wafer W is different, and the cut amount h2 (for example, 4.2 mm) of the orientation flat M2 is larger than the cut amount h1 (for example, 1.0 mm) of the notch M1 (h2 > h1).

[0006] In the TAIKO grinding of the wafer, the circular recess is formed so that the area of the circular recess is maximized, leaving the cut portion of the notch or the orientation flat to have the maximum diameter. Here, a circular recess W1 with a radius r1 is formed in the wafer W with the notch M1 shown in Fig. 11(a), and a circular recess W1 with a radius r2 is formed in the wafer W with the orientation flat M2 shown in Fig. 11(b). However, since the cut amount h1 of the notch M1 is smaller than the cut amount h2 of the orientation flat M2 (h1 < h2), a grinding wheel 25A with a large diameter D1 is used for the TAIKO grinding of the wafer W shown in Fig. 11(a) where the notch M1 is formed, and a grinding wheel 25B with a small diameter D2 is used for the TAIKO grinding of the wafer W shown in Fig. 12(b) where the orientation flat M2 is formed (D < D1).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, as described above, depending on whether the mark indicating the crystal orientation formed on the outer periphery of the wafer W is a notch M1 shown in Figure 11(a) or an orientation flat M2 shown in Figure 11(b), it is necessary to change to a grinding wheel 25A or 25B with a different diameter each time, and this change requires time and effort, resulting in poor productivity.

[0009] The present invention has been made in consideration of the above problems, and its purpose is to provide a highly productive grinding device that can TAIKO grind wafers without the need to change grinding wheels depending on the type of mark indicating the crystal orientation. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides a grinding device comprising: a chuck table that holds, by a holding surface, a wafer having a mark indicating crystal orientation formed on its outer periphery; a grinding mechanism that rotates a grinding wheel having a plurality of grinding stones arranged in a circle to form a circular recess in the center of one side of the wafer and an annular protrusion radially outward from the circular recess; a horizontal movement mechanism that moves the grinding mechanism and the chuck table in a horizontal direction relative to each other; an elevation mechanism that raises and lowers the grinding mechanism; and a control unit, wherein the grinding wheel has a plurality of grinding stones arranged in a circumferential direction of a circle centered on the center of rotation. the grinding wheels are arranged at different positions in the radial direction, and the control unit comprises: a radius setting unit that sets the radius of the circular recess to be formed; a horizontal movement control unit that causes the horizontal movement mechanism to horizontally move the grinding mechanism so that at least one of the plurality of grinding wheels of the rotating grinding wheel passes over the rotation axis of the chuck table and the outer circumferential circle of at least one of the grinding wheels arranged on the rotating grinding wheel passes over the inner circumferential surface of the circular recess to be formed; and a lifting control unit that raises and lowers the grinding mechanism to grind the wafer. [Effects of the Invention]

[0011] According to the present invention, in the grinding wheel, multiple grinding stones are arranged in radially staggered positions around a circle centered on the center of rotation, thereby making it possible to increase the grinding width of the grinding stones.

[0012] The outer periphery of a wafer is typically marked with a notch or orientation flat to indicate the crystal orientation. When a wafer with such a notch or orientation flat is subjected to TAIKO grinding, the circular recess formed on one side of the wafer by TAIKO grinding is maximized in area, with the maximum diameter remaining, leaving the notch or orientation flat cutout. This is achieved by offsetting the center of rotation of the grinding wheel radially to make the circular recess eccentric relative to the wafer, and forming the notch or orientation flat at the widest point of the annular protrusion formed around the circular recess. The amount of offset of the grinding wheel is limited within the grinding width of the grinding wheel.

[0013] However, according to the present invention, since the grinding width of the grinding wheel can be increased as described above, for wafers on which notches and orientation flats with different cutting depths are formed, by offsetting the center of rotation of the grinding wheel within the grinding width range of the grinding wheel, the width of the annular convex portion formed by TAIKO grinding of the wafer with a grinding wheel of the same diameter can be changed, and a notch or orientation flat can be formed at the widest part of the annular convex portion. Therefore, wafers can be TAIKO ground with high productivity without having to change grinding wheels depending on the type of mark (notch or orientation flat) indicating crystal orientation. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view of a grinding device according to the present invention; [Figure 2] FIG. 2 is an exploded perspective view of a wafer and a protective sheet. [Figure 3]FIG. 2 is a bottom view showing an example of the arrangement of grinding stones in a grinding wheel. [Figure 4] FIG. 10 is a bottom view showing another example of the arrangement of grinding stones in the grinding wheel. [Figure 5] 2 is a block diagram showing the configuration of a control unit of the grinding device according to the present invention. FIG. [Figure 6] 1 is a partial side view showing TAIKO grinding of a wafer in a grinding apparatus according to the present invention. FIG. [Figure 7] FIG. 1 is a plan view of a wafer and a grinding wheel showing TAIKO grinding of a wafer having a notch formed on its outer periphery. [Figure 8] 8 is a cross-sectional view taken along line XX in FIG. 7. [Figure 9] FIG. 1 is a plan view of a wafer and a grinding wheel showing TAIKO grinding of a wafer having an orientation flat formed on its outer peripheral edge. [Figure 10] 10 is a cross-sectional view taken along line YY in FIG. 9. [Figure 11] FIG. 1(a) is a plan view showing conventional TAIKO grinding of a wafer having a notch formed on its outer periphery, and FIG. 1(b) is a plan view showing an example of conventional TAIKO grinding of a wafer having an orientation flat formed on its outer periphery. [Figure 12] FIG. 1( a ) is a plan view showing conventional TAIKO grinding of a wafer having a notch formed on its outer periphery, and FIG. 1( b ) is a plan view showing another example of conventional TAIKO grinding of a wafer having an orientation flat formed on its outer periphery. [Figure 13] FIG. 1( a ) is a plan view showing another example of conventional TAIKO grinding of a wafer having a notch formed on its outer periphery, and FIG. 1( b ) is a plan view showing another example of conventional TAIKO grinding of a wafer having an orientation flat formed on its outer periphery. [Figure 14] FIG. 1( a ) is a plan view showing another example of conventional TAIKO grinding of a wafer having a notch formed on its outer periphery, and FIG. 1( b ) is a plan view showing another example of conventional TAIKO grinding of a wafer having an orientation flat formed on its outer periphery. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0016] [Grinding equipment configuration] First, the configuration of a grinding device according to the present invention will be described with reference to Fig. 1. In the following description, the directions of the arrows shown in Fig. 1 are the X-axis (left-right direction), the Y-axis (front-rear direction), and the Z-axis (up-down direction), respectively.

[0017] The grinding apparatus 1 shown in FIG. 1 is an apparatus for TAIKO grinding a disk-shaped wafer W (see FIG. 2) such as a single crystal silicon wafer, and includes three chuck tables 10 arranged on a rotatable disk-shaped turntable 2, a first grinding mechanism 20 for TAIKO grinding the wafer W held on the holding surface of the chuck table 10, and a second grinding mechanism 30 for grinding the bottom surface of a circular recess W1 (see FIGS. 8 and 10) formed in the wafer W by the first grinding mechanism 20. The main components include a horizontal movement mechanism 3 that moves the first and second grinding mechanisms 20, 30 horizontally (in a direction parallel to the holding surface of the chuck table 10), a lifting mechanism 4 that raises and lowers the first and second grinding mechanisms 20, 30 in the vertical direction (Z-axis direction), thickness gauges 40, 41 that measure the thickness of the wafer W during grinding, a cleaning mechanism 50 that cleans the top surface (grinding surface) of the wafer W after grinding, and a control unit 60 that controls each component.

[0018] As other components, the grinding apparatus 1 includes a cassette 71 that stores a plurality of wafers W before grinding, a cassette 72 that stores the wafers W after grinding, a positioning table 73 that positions (centers) the wafers W, a carry-in / out robot 74 that takes out the wafers W before grinding from the cassette 71 and transports them to the positioning table 73, and also transports the wafers W cleaned by the cleaning mechanism 50 to the cassette 72 and stores them in the cassette 72, a first transport mechanism 75 that transports the wafers W positioned on the positioning table 73 to the chuck table 10, and a second transport mechanism 76 that transports the ground wafers W from the chuck table 10 to the cleaning mechanism 50.

[0019] Here, as shown in FIG. 2, the wafer W, which is the workpiece to be ground, is a thin, disc-shaped member made of, for example, single-crystal silicon (Si). The surface of the wafer W (the top surface in FIG. 2) is partitioned into multiple rectangular regions by mutually orthogonal dividing lines L1 and L2 arranged in a grid pattern, and each rectangular region has a device DV, such as an IC or LSI, formed therein. Therefore, the surface of the wafer W includes a circular device region S1 in which the device DV is formed, and a ring-shaped peripheral excess region S2 formed around the device region S1. A thin, circular protective sheet T is attached to the surface of the wafer W to protect the device DV. A mark (a notch in the illustrated example) M indicating the crystal orientation of the wafer is formed on the outer periphery of the wafer. The wafer W may be made of a material other than silicon (Si), such as silicon carbide (SiC), glass, ceramics, or sapphire, which has high hardness.

[0020] Next, the configurations of the main components of the grinding device 1, namely the chuck table 10, the first and second grinding mechanisms 20, 30, the horizontal movement mechanism 3, the lifting mechanism 4, the thickness measuring devices 40, 41, the cleaning mechanism 50 and the control unit 60, will be described.

[0021] (Chuck table) The three chuck tables 10 are disk-shaped members arranged at equal angular pitches (120° pitches) in the circumferential direction on a turntable 2 that rotates intermittently about a vertical central axis. These chuck tables 10 revolve at 120° intervals around an axis perpendicular to the Z-axis direction of the turntable 2 as the turntable 2 intermittently rotates, and move sequentially between a wafer loading / unloading region R1, a recess formation region R2, and a bottom grinding region R3, while also rotating about their axes at a predetermined speed by a rotation mechanism (not shown).

[0022] 6, each chuck table 10 rotates (spins) about the vertical axis at a predetermined speed in the direction of the arrow in the figure by rotating a rotation shaft 12 extending vertically downward from the center of the chuck table 10 by being rotationally driven by a rotation mechanism (not shown). A disk-shaped porous member 11 made of porous ceramic or the like is incorporated into a circular recess 10a formed in the upper part of a disk-shaped frame 10A of each chuck table 10, and the upper surface of each porous member 11 forms a holding surface that suction-holds a wafer W. In each chuck table 10, the porous member 11 is selectively connected to a suction source 15, such as a vacuum pump or an ejector, via a communication passage 13 formed in the center of each of the frame 10A and the rotation shaft 12 and a pipe 14 connected to the communication passage 13.

[0023] (First and second grinding mechanisms) The first and second grinding mechanisms 20, 30 are arranged vertically along the X-axis direction (left-right direction) at the +Y-axis direction end (rear end) of a rectangular box-shaped base 100 that is long in the Y-axis direction (front-back direction). Here, the first grinding mechanism 20 is a mechanism that performs TAIKO grinding on the wafer W held on the holding surface of the chuck table 10 located in the recess formation region R2, and the second grinding mechanism 30 is a mechanism that grinds the bottom surface of a circular recess W1 (see FIGS. 9 and 11) formed in the center of the wafer W by TAIKO grinding using the first grinding mechanism 20, and both have the same basic configuration.

[0024] That is, the first grinding mechanism 20 includes a spindle motor 22 fixed to a holder 21, a vertical spindle 23 that is rotationally driven by the spindle motor 22, a mount 24 attached to the lower end of the spindle 23, and a grinding wheel 25 that is detachably attached to the mount 24. A plurality of grinding stones 25a in the shape of rectangular blocks are attached to the grinding wheel 25 and are arranged in an annular shape. The spindle motor 22 is electrically connected to a control unit 60, and its operation is controlled by the control unit 60.

[0025] Here, the multiple grinding wheels 25a are arranged at different positions in the radial direction of a circle centered on the rotation center O1, at equal angular pitches in the circumferential direction of the circle, and in staggered positions in the radial direction. For example, in the example shown in FIG. 3, a total of 24 grinding wheels 25a are arranged, four along each side of a regular hexagon. In addition, in the example shown in FIG. 4, multiple grinding wheels 25a are arranged at equal angular pitches on the circumference of three circles of different diameters. In other words, a total of eight sets of three grinding wheels 25a (24 grinding wheels in total), each set consisting of three grinding wheels 25a, are arranged at equal angular pitches in the circumferential direction and in staggered positions in the radial direction. Note that the multiple grinding wheels 25a may be arranged at equal angular pitches in the circumferential direction and in staggered positions in the radial direction, and the number and arrangement of the grinding wheels 25a are not limited to those shown in FIGS. 3 and 4 and can be set arbitrarily.

[0026] As shown in FIGS. 3 and 4, the circumscribing circle C of the plurality of grinding wheels 25a arranged at equal angular pitches in the circumferential direction and at different levels in the radial direction is o The diameter of D o , inscribed circle C i The diameter of D i Then, the grinding width B of these grinding wheels 25a can be calculated by the following formula. B=(D o -D i ) / twenty one) In contrast, the grinding width of multiple grinding wheels 25a arranged on the same circumference is equal to the width b of each grinding wheel 25a, so the grinding width B calculated by equation (1) for multiple grinding wheels 25a arranged as shown in Figures 3 and 4 is greater than the width b of each grinding wheel 25a (B>b).

[0027] The grinding wheels 25a do not have to be arranged at equal angular pitches in the circumferential direction. o is the outer circumferential circle of the rotation locus of the grinding wheel 25a when the spindle 23 to which the grinding wheel 25a is attached is rotated.

[0028] Similarly to the first grinding mechanism 20, the second grinding mechanism 30 also includes a spindle motor 32 fixed to a holder 31, a vertical spindle (not shown) that is rotationally driven by the spindle motor 32, a mount (not shown) attached to the lower end of the spindle, and a grinding wheel 35 that is detachably attached to the mount, and the grinding wheel 35 has a plurality of grinding stones 35a in the shape of rectangular blocks arranged in an annular shape attached thereto. The spindle motor 32 is electrically connected to a control unit 60, and its operation is controlled by the control unit 60. In the second grinding mechanism 30, the plurality of grinding stones 35a of the grinding wheel 35 are also arranged as shown in FIG. 3 or 4, and therefore illustration and description thereof will be omitted.

[0029] (Horizontal movement mechanism) The horizontal movement mechanism 3 is a mechanism for moving the first and second grinding mechanisms 20, 30 horizontally, and is disposed between a movable column 101 that supports the first and second grinding mechanisms 20, 30 so that they can be raised and lowered, and a fixed column 102 fixed on the base 100.

[0030] Each movable column 101 supporting the first and second grinding mechanisms 20 and 30 has an inclined surface 101a inclined at an angle of 45° in a plan view, and the fixed column 102 has inclined surfaces 102a inclined at an angle of 45° in a plan view on both the left and right sides (both sides in the X-axis direction) of the fixed column 102 facing the inclined surfaces 101a of the movable columns 101. Each horizontal movement mechanism 3 is disposed between the inclined surface 102a of the fixed column 102 and the inclined surface 101a of the movable column 101. Each horizontal movement mechanism 3 is configured using a known ball screw mechanism, and therefore illustrations and descriptions thereof are omitted. However, each horizontal movement mechanism 3 can horizontally move the movable column 101 and the first and second grinding mechanisms 20 and 30 supported thereon in a direction of an angle of 45° in a plan view. Each horizontal movement mechanism 3 is electrically connected to the control unit 60, and its operation is controlled by the control unit 60.

[0031] (Lifting mechanism) The pair of lifting mechanisms 4 are mechanisms that raise and lower the first grinding mechanism 20 and the second grinding mechanism 30 in the Z-axis direction, respectively. Since both lifting mechanisms 4 have the same configuration, corresponding components will be described below with the same symbols.

[0032] Each lifting mechanism 4 includes a rectangular plate-shaped lifting plate 5 and a pair of left and right guide rails 6 for guiding the lifting and lowering movement of the lifting plate 5. A first grinding mechanism 20 and a second grinding mechanism 30 are attached to each lifting plate 5. The pair of left and right guide rails 6 are disposed perpendicular to the front surface of the movable column 101 and parallel to each other.

[0033] A rotatable ball screw 7 is installed vertically along the Z-axis direction (up and down direction) between the pair of left and right guide rails 6, and the upper end of the ball screw 7 is connected to a servo motor 8 that can rotate forward and backward and serves as a drive source. The lower end of the ball screw 7 is rotatably supported by a movable column 101 via a bearing (not shown), and a nut member (not shown) that protrudes horizontally backward (in the +Y-axis direction) from the back surface of the lifting plate 5 is screwed onto the ball screw 7. The servo motor 8 is electrically connected to a control unit 60, and its operation is controlled by the control unit 60.

[0034] Therefore, when the servo motors 8 of each lifting mechanism 4 configured as described above are started to rotate each ball screw 7 forward and backward, each lifting plate 5, on which a nut member (not shown) that screws onto each ball screw 7 protrudes, moves up and down along a pair of left and right guide rails 6, and the first grinding mechanism 20 and second grinding mechanism 30 attached to each lifting plate 5 also move up and down independently of each other along the Z-axis direction (up and down direction).

[0035] (Thickness measuring instrument) A pair of thickness gauges 40, 41 provided in the center of the turntable 2 measure the thickness of the wafer W being ground by the first grinding mechanism 20 and the wafer W being ground by the second grinding mechanism 30, respectively, and each includes a first probe 40a, 41a that contacts the top surface of the wafer W held on the chuck table 10 and a second probe 40b, 41b that contacts the top surface of the chuck table 10. Therefore, each thickness gauge 40, 41 can measure the thickness of the wafer W by subtracting the height of the top surface of the chuck table 10 detected by the second probe 40b, 41b from the height of the top surface of the wafer W detected by the first probe 40a, 41a. Note that the thickness gauges 40, 41 may be non-contact thickness gauges.

[0036] (cleaning mechanism) The cleaning mechanism 50 cleans the wafer W ground by the second grinding mechanism 30 to remove grinding debris and the like adhering to the ground surface (upper surface), and includes a spinner table 51 that holds the ground wafer W and rotates at high speed, and a cleaning water nozzle 52 that sprays cleaning water toward the center of the ground surface of the wafer W. Note that pure water is preferably used as the cleaning water.

[0037] (Control unit) The control unit 60 includes a CPU (Central Processing Unit) that performs arithmetic processing according to a control program, and storage units such as a ROM (Read Only Memory) and a RAM (Random Access Memory). In particular, in this embodiment, as shown in Fig. 5, the control unit 60 includes a radius setting unit 61 that sets the radius r of a circular recess W1 (see Figs. 9 and 11) that is formed in the center of the back surface of the wafer W by TAIKO grinding using the first grinding mechanism 20 (described later), and a radius setting unit 62 that sets the radius r of a circumscribing circle C of the plurality of grinding wheels 25a shown in Figs. 3 and 4. oThe grinding machine includes a horizontal movement control unit 62 that horizontally moves the first and second grinding mechanisms 20, 30 using the horizontal movement mechanisms 3 so that the first and second grinding mechanisms 20, 30 pass through the inner peripheral surface of the circular recess W1 to be formed, and a lifting control unit 63 that raises and lowers the first and second grinding mechanisms 20, 30 using the lifting mechanism 4 to grind the wafer W.

[0038] The control unit 60 also includes a table rotation speed setting unit 64 that sets the rotation speed of the chuck table 10, a table rotation control unit 65 that rotates the chuck table 10 at the rotation speed set by the table rotation speed setting unit 64, a grinding wheel rotation speed setting unit 66 that sets the rotation speeds of the grinding wheels 25, 35 of the first and second grinding mechanisms 20, 30, and a grinding wheel rotation control unit 67 that rotates the grinding wheels 25, 35 at the rotation speeds set by the grinding wheel rotation speed setting unit 66. The control unit 60 also includes a rotation speed changing unit 68 that changes the rotation speed of the chuck table 10 or the rotation speed of the grinding wheels 25, 35 so that the ratio between the rotation speed of the chuck table 10 set by the table rotation speed setting unit 64 and the rotation speed of the grinding wheels 25, 35 set by the grinding wheel rotation speed setting unit 66 does not become an integer.

[0039] [Function of grinding equipment] Next, the operation of the grinding device 1 configured as above will be described.

[0040] When grinding a wafer W, a single unprocessed wafer W stored in a cassette 71 shown in Fig. 1 is taken out by a carry-in / out robot 74 and transported to a positioning table 73. Then, on the positioning table 73, the wafer W is positioned (centered), and the positioned wafer W is transported by a first transport mechanism 75 to a chuck table 10 located in a wafer carry-in / out area R1, and placed on the holding surface of the chuck table 10 with the protective sheet T facing down (see Fig. 6).

[0041] As shown in Figure 6, when a wafer W is transported to a chuck table 10 located in the wafer loading / unloading area R1 and placed on the holding surface of the chuck table 10, the porous member 11 of the chuck table 10 is connected to a suction source 15, and a negative pressure is generated in the porous member 11, and the wafer W is attracted by this negative pressure and held on the holding surface of the chuck table 10.

[0042] Then, the turntable 2 is rotated by an angle of 120° in the direction of the arrow in FIG. 1 by a rotation mechanism (not shown), the chuck table 10 holding the wafer W is moved from the wafer loading / unloading area R1 to the recess formation area R2, and the wafer W is TAIKO ground by the first grinding mechanism 20 to form a circular recess W1 in the center (the portion corresponding to the device area S1 on the front surface) of the back surface (the surface on which the device DV shown in FIG. 2 is not formed) of the wafer W. Then, an annular convex portion W2 is formed around the circular recess W1 on the back surface of the wafer W (the portion corresponding to the peripheral excess area S2 on the front surface) (see FIGS. 8 and 10 ). That is, when the circular recess W1 is formed in the center of the back surface of the wafer W by TAIKO grinding using the first grinding mechanism 20, the wafer W is positioned below the grinding wheel 25 of the first grinding mechanism 20.

[0043] Incidentally, on the outer peripheral edge of the wafer W, as a mark indicating the crystal orientation of the wafer W, a notch M1 cut in a V shape shown in FIGS. 7 and 8, or an orientation flat M2 cut linearly shown in FIGS. 9 and 10 is formed. As will be described later, when a circular concave portion W1 is formed in the central portion of the back surface of the wafer W and an annular convex portion W2 is formed around the circular concave portion W1 as shown in FIGS. 7 to 10 by TAIKO grinding by the first grinding mechanism 20, the cut amount h2 of the orientation flat M2 is larger than the cut amount h1 of the notch M1 (h2>h1). For this reason, the maximum width H2 of the portion where the orientation flat M2 of the annular convex portion W2 formed on the wafer W shown in FIGS. 9 and 10 having the orientation flat M2 formed on the outer peripheral edge is formed is set larger than the maximum width H1 of the portion where the notch M1 of the annular convex portion W2 formed on the wafer W shown in FIGS. 7 and 8 having the notch M1 formed on the outer peripheral edge is formed (H2>H1). In other words, by TAIKO grinding by the first grinding mechanism 20, the minimum widths (H1-h1, H2-h2) of the annular convex portion W2 of the wafer W are set to the same value so that the diameter of the circular concave portion W1 formed in the central portion of the wafer W becomes the maximum.

[0044] Conventionally, TAIKO grinding of the wafer W having the notch M1 with the cut amount h1 shown in FIG. 11(a) formed on the outer peripheral edge is performed using a grinding wheel 25A with a diameter D1 and a constant blade width (for example, 2.0 mm) to form an annular convex portion W2 with a constant width H1 on the outer peripheral portion of the wafer W, and TAIKO grinding of the wafer W having the orientation flat M2 with a cut amount h2 larger than the cut amount h1 of the notch M1 (>h1) formed on the outer peripheral edge is performed using a grinding wheel 25B with a diameter D2 (<D1) smaller than the diameter D1 to form an annular convex portion W2 with a constant width H2 larger than the width H1 on the outer peripheral portion of the wafer W.

[0045] Further, as shown in Fig. 12(a), in the TAIKO grinding of the wafer W with the notch M1 formed on the outer peripheral edge, the grinding wheel 25C with a constant blade width was offset by ε1 at a diameter D3 to perform the grinding so that the annular projection W2 would have a minimum width (H1 - h1). In this case, the circular recess W1 draws an eccentric circle with a radius r3 that is offset by ε1 with respect to the true circular wafer W. On the other hand, as shown in Fig. 12(b), in the TAIKO grinding of the wafer W with the orientation flat M2, the grinding wheel 25D with a constant blade width was offset by ε2 at a diameter D4 to perform the grinding so that the annular projection W2 would have a minimum width (H2 - h2). In this case, the circular recess W1 draws an eccentric circle with a radius r4 that is offset by ε2 with respect to the true circular wafer W.

[0046] Therefore, as described above, the conventional method shown in Figs. 11 and 12 has a problem that it is necessary to exchange between the grinding wheels 25A, 25B, 25C, and 25D with different diameters.

[0047] Thus, in the present embodiment, as shown in Figs. 7 to 10, the grinding wheel 25a with the same diameter is used, and the center O1 of this grinding wheel 25a is offset by ε1 and ε2 radially outward from the center O' (hereinafter, the conventional center O') of the circular recess W1 whose center coincides with the center O of the wafer W as shown in Fig. 11, and the TAIKO grinding is performed. By doing so, a circular recess W1 with a necessary and sufficient area is ensured while securing the minimum widths (H1 - h1, H2 - h2) of the annular projection W2 on the wafer W. Here, the offset amount of the grinding wheel 25a is limited within the grinding width B of the grinding wheel 25a in order not to generate ungrinded portions at the center of the wafer W.

[0048] Moreover, in the present embodiment, in the grinding wheel 25 of the first grinding mechanism 20, as shown in Fig. 3 or Fig. 4, since a plurality of grinding wheels 25a are arranged at equal angular pitches in the circumferential direction and in a stepped manner in the radial direction, the grinding width B of the grinding wheel 25a obtained by the above formula (1) is larger than the width b of each grinding wheel 25a as described above (B > b). Therefore, the offset amount of the center O1 of the grinding wheel 25a can be expanded within the range of the grinding width B.

[0049] 9 and 10, which is a mark indicating the crystal orientation, is larger than the cutting depth h1 of the notch M1 shown in FIGS. 7 and 8 (h2>h1). Therefore, the maximum width required for the annular protrusion W2 formed on the outer periphery of the wafer W by TAIKO grinding is larger for the wafer W shown in FIGS. 9 and 10 than for the wafer W shown in FIGS. 7 and 8. As a result, the offset amount ε1 of the center O1 of the grinding wheel 25a in TAIKO grinding of the wafer W shown in FIGS. 7 and 8, which has the notch M1 formed on its outer periphery, can be relatively small, and the offset amount ε2 of the center O1 of the grinding wheel 25a in TAIKO grinding of the wafer W shown in FIGS. 9 and 10 is larger than ε1 (ε2>ε1). O

[0050] As shown in Figures 11(a) and 13(a), when the wafer W is ground with a grinding wheel 25a so that the center O of the outer circumferential circle of the wafer W having a notch M1 on its outer edge coincides with the center of the circular recess W1 and the distance between the outer circumferential circle of the wafer W and the outer periphery of the circular recess W1 is a predetermined distance (2.0 mm), the circular recess W1 has the maximum diameter.

[0051] In the above embodiment, the circumscribing circle C of the grinding wheel 25a o In the TAIKO grinding, the outer surface of the grinding wheel 25a is also worn. Even when the outer surface of the grinding wheel 25a is worn, in order to prevent the occurrence of grinding residue at the center of the circular recess W1 of the wafer W, as shown in FIG. 14(a), the circumscribing circle C of the grinding wheel 25a is o In other words, the outermost rotational path of the grinding wheel 25a overlaps the center O of the circular recess W1 of the wafer W by δ1 during grinding.

[0052] 13(b), when the center O of the outer circumferential circle of the wafer W having an orientation flat M2 on its outer periphery coincides with the center of the circular recess W1 and the wafer W is ground with the grinding wheel 25a so that the distance between the orientation flat M2 and the outer periphery of the circular recess W1 is a predetermined distance (2.0 mm), the circular recess W1 has a minimum diameter. In this case, the grinding wheel 25a overlaps the center of the circular recess W1 by δ, preventing any residual grinding from occurring at the center of the circular recess W1.

[0053] FIG. 14(b) is a diagram showing the case where a circular recess W1 with the minimum diameter is formed by the grinding wheel 25a, and the inscribed circle C of the grinding wheel 25a i In other words, the outermost rotational path of the grinding wheel 25a overlaps the center O of the circular recess W1 of the wafer W during grinding.

[0054] Thus, TAIKO grinding of a wafer having a diameter D by the first grinding mechanism 20 is performed as follows: First, the radius r of the circular recess W1 to be formed in the wafer W is set by the radius setting unit 61 of the control unit 60 shown in FIG. 5. For the wafer W shown in FIGS. 7 and 8, which has a notch M1 formed on its outer periphery, the horizontal movement mechanism 3 (see FIG. 1) controlled by the horizontal movement control unit 62 (see FIG. 5) of the control unit 60 moves the first grinding mechanism 20 horizontally so that the center O1 of the grinding wheel 25a is radially offset by ε1 from the conventional center O'. For the wafer W shown in FIGS. 9 and 10, which has an orientation flat M2 formed on its outer periphery, the horizontal movement mechanism 3 (see FIG. 1) controls the first grinding mechanism 20 so that the center O1 of the grinding wheel 25a is radially offset by ε2 from the conventional center O'.

[0055] Next, the chuck table 10 and the wafer W held at a position offset by ε1 and ε2 from the rotation center O of the chuck table 10 are rotated at a predetermined speed in the direction of the arrow in FIG. 6 . At the same time, the spindle motor 22 (see FIG. 1 ) of the first grinding mechanism 20 is started to rotate the grinding wheel 25a at a predetermined speed in the direction of the arrow in FIG. 6 . The elevation control unit 63 (see FIG. 5 ) of the control unit 60 controls the elevation mechanism 4 shown in FIG. 1 to lower the grinding wheel 25a at a predetermined speed. The grinding wheel 25a then contacts the back surface of the wafer W (the upper surface in FIG. 6 ), and the back surface of the wafer W is ground by TAIKO. As shown in FIGS. 7 to 10 , a circular recess W1 is formed in the center of the back surface of the wafer W, and an annular protrusion W2 is formed around the circular recess W1. Here, as shown in FIGS. 7 to 10 , the circular recess W1 formed in the center of the back surface of the wafer W is located within the circumscribed circle C of the grinding wheel 25a. o Specifically, the circle is radially eccentric by ε1 and ε2 with respect to the circular wafer W of diameter D.

[0056] As described above, the eccentricity ε1 of the circular recess W1 formed in the center of the back surface of the wafer W shown in Figures 7 and 8, which has a notch M1 formed on its outer periphery, by TAIKO grinding using the grinding wheel 25a is smaller than the eccentricity ε2 of the circular recess W1 formed in the center of the back surface of the wafer W shown in Figures 9 and 10, which has an orientation flat M2 formed on its outer periphery, by TAIKO grinding using the grinding wheel 25a (ε1 < ε2).Therefore, the maximum width of the annular protrusion W2 formed on the outer periphery of the back surface of the wafer W is smaller than the maximum width formed on the outer periphery of the back surface of the wafer W shown in Figures 9 and 10, but a notch M1 is formed at the widest part of this annular protrusion W2.

[0057] On the other hand, since the eccentricity ε2 of the circular recess W1 formed in the center of the back surface of the wafer W shown in Figures 9 and 10 is larger than the eccentricity ε1 of the circular recess W1 formed in the center of the back surface of the wafer W by TAIKO grinding with the grinding wheel 25a of the wafer W shown in Figures 7 and 8 having a notch M1 formed on its outer periphery (ε2>ε1), the maximum width of the annular protrusion W2 formed on the outer periphery of the back surface of the wafer W is larger than the maximum width of the annular protrusion B2 formed on the outer periphery of the back surface of the wafer W shown in Figures 7 and 8. Therefore, an orientation flat M2 can be formed at the widest portion of this annular protrusion W2.

[0058] While the back surface of the wafer W is being TAIKO-ground by the grinding wheel 25a, the thickness of a circular recess W1 formed in the center of the back surface of the wafer W is measured by a thickness gauge 40, and TAIKO grinding of the wafer W by the grinding wheel 25a is continued until the thickness of the circular recess W1 of the wafer W reaches a predetermined thickness. During TAIKO grinding of the wafer W by the grinding wheel 25a, grinding water is supplied from a grinding water supply source (not shown) to the contact area (grinding area) between the grinding wheel 25a and the wafer W. This grinding water cools the contact area (grinding area) between the grinding wheel 25a and the wafer W, and also washes away and removes grinding debris generated by grinding. Pure water is preferably used as the grinding water.

[0059] As described above, in this embodiment, in the grinding wheel 25, as shown in Figure 3 or Figure 4, multiple grinding stones 25a are arranged in radially staggered positions around a circle centered on the rotation center O1, so that the grinding width B of the grinding stones 25a can be increased.

[0060] Therefore, for a wafer W having a notch M1 and an orientation flat M2 formed thereon with different cutting depths, offsetting the rotation center O1 of the grinding wheel 25a within the grinding width B of the grinding wheel 25a allows the width of the annular convex portion W2 formed by TAIKO grinding of the wafer W with the grinding wheel 25a of the same diameter to be varied, and the notch M1 or the orientation flat M2 can be formed at the widest portion of the annular convex portion W2. As a result, it is not necessary to change the grinding wheel 25a depending on the type of mark indicating the crystal orientation (notch M1 or orientation flat M2), and the effect is obtained that the wafer W can be TAIKO ground with good productivity.

[0061] In this embodiment, in TAIKO grinding of the wafer W by the first grinding mechanism 20, the rotation speed of the chuck table 10 is set by the table rotation speed setting unit 64 of the control unit 60, and a rotation mechanism (not shown) is controlled by the table rotation control unit 65 (see Figure 5) so that the chuck table 10 rotates at the rotation speed set by the table rotation speed setting unit 64.

[0062] On the other hand, the rotation speed of the grinding wheel 25 is set by a grinding wheel rotation speed setting unit 66 shown in FIG. 5 of the control unit 60, and the spindle motor 22 is controlled by a grinding wheel rotation control unit 67 shown in FIG. 5 so that the grinding wheel 25 rotates at the rotation speed set by the grinding wheel rotation speed setting unit 66.

[0063] 5 changes either the rotational speed of the chuck table 10 or the rotational speed of the grinding wheel 25 so that the ratio between the rotational speed of the chuck table 10 set by the table rotational speed setting unit 64 and the rotational speed of the grinding wheel 25 set by the grinding wheel rotational speed setting unit 66 is not an integer. Changing either the rotational speed of the chuck table 10 or the rotational speed of the grinding wheel 25 by the rotational speed changing unit 68 in this manner prevents the grinding wheel 25a and the wafer W from always coming into contact at the same location, and the entire wafer W is ground uniformly by the grinding wheel 25a.

[0064] Thus, a circular recess W1 of a predetermined thickness is formed in the center of the back surface of the wafer W by TAIKO grinding of the wafer W by the first grinding mechanism 20, and a ring-shaped protrusion W2 is formed around the circular recess W1. Then, the elevating mechanism 4 shown in FIG. 1 moves the grinding wheel 25a away from the wafer W. From this state, the turntable 2 shown in FIG. 1 is rotated by an angle of 120° in the direction of the arrow by a rotation mechanism (not shown), and the chuck table 10 and the wafer W held on the holding surface of the chuck table 10 move from the recess formation region R2 to the bottom surface grinding region R3. Once the chuck table 10 and the wafer W held thereon have moved to the bottom surface grinding region R3, the circular recess W1 of the wafer W is ground by the second grinding mechanism 30.

[0065] The grinding of the bottom surface of the circular recess W1 of the wafer W by the second grinding mechanism 30 is performed in the same manner as the TAIKO grinding of the wafer W by the first grinding mechanism 20, so a detailed explanation of this will be omitted. However, by grinding the bottom surface of the circular recess W1 of the wafer W, grinding marks that were generated on the bottom surface of the circular recess W1 of the wafer W by the TAIKO grinding by the first grinding mechanism 20 in the previous process are removed, and cracks in the wafer W originating from the grinding marks are prevented.

[0066] Thus, once the bottom surface of the circular recess W1 of the wafer W has been ground by the second grinding mechanism 30 as described above, the grinding wheel 35a is moved away from the wafer W by the lifting mechanism 4 shown in Fig. 1. From this state, the turntable 2 shown in Fig. 1 is rotated by an angle of 120° in the direction of the arrow by a rotation mechanism (not shown), and the chuck table 10 and the wafer W held on the holding surface of the chuck table 10 are moved from the bottom surface grinding region R3 to the wafer transfer region R1. Then, the wafer W held by the chuck table 10 that has moved to the wafer transfer region R1 is transferred to the cleaning mechanism 50 by the second transfer mechanism 76.

[0067] In the cleaning mechanism 50, the wafer W is held by suction on a spinner table 51, and the spinner table 51 and the wafer W held thereon are rotated at high speed, while cleaning water (pure water) is sprayed from a cleaning water nozzle 52 toward the center of the wafer W. The cleaning water sprayed toward the center of the wafer W from the cleaning water nozzle 52 is scattered radially outward from the wafer W by centrifugal force caused by the rotation of the wafer W, and foreign matter such as grinding debris adhering to the surface of the wafer W is blown off and removed by the cleaning water, thereby cleaning the upper surface of the wafer W.

[0068] As described above, after the back surface (surface to be ground) of the wafer W is cleaned in the cleaning mechanism 50, the wafer W is transported from the spinner table 51 to the cassette 72 by the transport robot 74 shown in FIG. 1 and stored in the cassette 72, thereby completing the series of grinding processes on the wafer W.

[0069] In the above embodiment, the grinding apparatus 1 is provided with a second grinding mechanism 30 that grinds the bottom surface of the circular recess W1 of the wafer W, but this second grinding mechanism 30 may be provided as needed and is not an essential component of the grinding apparatus 1 of the present invention.

[0070] Furthermore, the present invention is not limited to the application of the above-described embodiments, and it goes without saying that various modifications are possible within the scope of the claims and the technical ideas described in the specification and drawings. [Explanation of symbols]

[0071] 1: Grinding device, 2: Turntable, 3: Horizontal movement mechanism, 4: Lifting mechanism, 5: Lifting plate, 6: Guide rail, 7: Ball screw, 8: Servo motor, 10: Chuck table, 10A: frame body, 10a: circular recess, 11: porous member, 12: rotating shaft, 13: communication passage, 14: Piping, 15: Suction source, 20: First grinding mechanism, 21: Holder, 22: spindle motor, 23: spindle, 24: mount, 25: grinding wheel, 25a: grinding wheel, 30: second grinding mechanism, 31: holder, 32: spindle motor, 33: spindle, 34: mount, 35: grinding wheel, 35a: grinding stone, 40, 41: thickness measuring device, 401, 41a: first probe, 40b, 41b: second probe, 50: cleaning mechanism, 51: spinner table, 52: cleaning water nozzle, 60: control unit, 61: radius setting unit, 62: horizontal movement control unit, 63: Elevation control unit, 64: Table rotation speed setting unit, 65: Table rotation control unit, 66: grinding wheel rotation speed setting unit, 67: grinding wheel rotation control unit, 68: rotation speed change unit, 100: base, 101: movable column, 101a: slope of movable column, 102: fixed column, 102a: slope of fixed column, B: grinding width of grinding wheel, b: width of grinding wheel, C i : Inscribed circle of grinding wheel, C o : circumscribed circle of grinding wheel, D: diameter of wafer, D i : diameter of the inscribed circle of the grinding wheel, D o : circumscribed circle diameter of grinding wheel, DV: device, H1, H2: maximum width of annular convex part of wafer, h1: Notch depth of cut, h2: Orientation flat depth of cut, L1, L2: planned division line, M1: notch (mark), M2: Orientation flat (mark), O: Center of wafer, O1: Center of grinding wheel, R1: Wafer loading / unloading area, R2: Recess formation area, R3: bottom grinding area, r: radius of circular recess, S1: device area, S2: peripheral excess area, T: protective sheet, W: wafer, W1: circular recess, W2: annular protrusion, ε1, ε2: Offset amount of grinding wheel

Claims

1. a chuck table that holds, by a holding surface, a wafer having a mark indicating a crystal orientation formed on its outer periphery; a grinding mechanism that rotates a grinding wheel having a plurality of grinding stones arranged in a circle to form a circular recess in the center of one surface of the wafer and an annular protrusion radially outward from the circular recess; a horizontal movement mechanism for moving the grinding mechanism and the chuck table relatively in a horizontal direction; a lifting mechanism for lifting and lowering the grinding mechanism; A control unit; A grinding device comprising: The grinding wheel is A plurality of the grinding wheels are arranged at different positions in the radial direction around a circle having a rotation center as its center, The control unit a radius setting unit that sets a radius of the circular recess to be formed; a horizontal movement control unit that horizontally moves the grinding mechanism by the horizontal movement mechanism so that at least one of the plurality of grinding stones of the rotating grinding wheel passes over the rotation axis of the chuck table and so that an outer circumferential circle formed by at least one of the grinding stones arranged on the rotating grinding wheel passes over an inner circumferential surface of the circular recess to be formed; a lifting control unit that lifts and lowers the grinding mechanism to grind the wafer; A grinding device comprising:

2. The control unit a table rotation speed setting unit that sets the rotation speed of the chuck table; a table rotation control unit that rotates the chuck table at the rotation speed set by the table rotation speed setting unit; a grinding wheel rotation speed setting unit that sets the rotation speed of the grinding wheel; a grinding wheel rotation control unit that rotates the grinding wheel at the rotation speed set by the grinding wheel rotation speed setting unit; a rotational speed changing unit that changes the rotational speed of the chuck table or the rotational speed of the grinding wheel so that the ratio between the rotational speed of the chuck table set by the table rotational speed setting unit and the rotational speed of the grinding wheel set by the grinding wheel rotational speed setting unit does not become an integer; 2. The grinding device according to claim 1, further comprising:

Images