Grinding device

Abstract

To provide a grinding device which prevents adhesion of swarf to a grinding wheel to prevent a problem of damage of a wafer caused by swarf.SOLUTION: A grinding device 1 includes: a chuck table 10; a grinding mechanism 20 which rotates a grinding wheel 25 to grind a wafer with grinding stones 25B; and a grinding water supply unit 50 which supplies grinding water to a contact part between the wafer W and the grinding stones 25B. The grinding device 1 includes a bias application unit 60 comprising a first electrode 61 disposed in the grinding wheel 25, a second electrode 62 disposed close to the chuck table 10 without making contact with the chuck table 10, and a power source part 63 for energizing the first electrode 61 and the second electrode 62. The first electrode 61 and the second electrode 62 of the bias application part 60 are electrically connected by grinding water supplied from the grinding water supply unit 50 to the contact part between the wafer W and the grinding stones 25B to energize the first electrode 61 and the second electrode 62.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a grinding apparatus that uses a grinding wheel to grind a wafer held on a holding surface of a chuck table. [Background technology]

[0002] In the manufacturing process of semiconductor devices such as ICs and LSIs used in various electronic devices, the backside of a wafer is ground by a grinding machine to thin the wafer to a predetermined thickness in order to reduce the size and weight of the semiconductor device. That is, in the grinding machine, a grinding wheel having grinding wheels arranged in an annular shape on a disk-shaped base is rotated, and the rotating grinding wheels are lowered at a predetermined speed to grind the wafer. Grinding water is supplied to the contact area between the grinding wheels and the wafer (grinding area), and this grinding water cools the contact area and also washes away and removes grinding debris generated during wafer grinding (see, for example, Patent Documents 1 and 2).

[0003] Therefore, in a grinding apparatus that grinds wafers while supplying grinding water, the grinding water containing grinding debris is atomized and scattered within the processing chamber by the centrifugal force generated by the rotation of the wafer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-036162 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-199146 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, when grinding water containing grinding chips turns into a spray and scatters inside the processing chamber, the grinding chips contained in the spray adhere to the grinding wheel, and the adhered grinding chips fall onto the wafer unexpectedly, which can cause problems such as the fallen grinding chips entering the contact area between the grinding wheel and the wafer and leaving deep chips on the surface of the wafer.

[0006] The present invention has been made in view of the above problems, and its object is to provide a grinding device that prevents grinding debris from adhering to the grinding wheel and thereby eliminates the problem of wafer damage caused by grinding debris. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the present invention provides a grinding device comprising a chuck table that rotates together with a wafer held by a holding surface, a grinding mechanism that rotates a grinding wheel having grinding wheels arranged in a ring on a base to grind the wafer with the grinding wheels, and a grinding water supply unit that supplies grinding water to the contact portion between the wafer and the grinding wheels, and is characterized in that it comprises a first electrode arranged on the grinding wheel, a second electrode arranged in close proximity to but not in contact with the chuck table, and a bias application unit that includes a power supply unit that applies electricity to the first electrode and the second electrode, and the first electrode and the second electrode of the bias application unit are electrically connected by the grinding water supplied from the grinding water supply unit to the contact portion between the wafer and the grinding wheel, thereby applying electricity to the first electrode and the second electrode, and causing grinding chips contained in the grinding water to adhere to the second electrode. [Effects of the Invention]

[0008] According to the present invention, in the bias application unit, the first electrode and the second electrode are electrically connected by conductive grinding water supplied from the grinding water supply unit to the contact area between the wafer and the grinding wheel. When a current is applied from the power supply unit to these first and second electrodes, a zeta potential is generated, and the action of the zeta potential prevents grinding debris generated during wafer grinding from adhering to the grinding wheel. In other words, the zeta potential separates the grinding debris from the grinding wheel, preventing it from adhering to the inner circumferential surface of the grinding wheel. This prevents grinding debris from entering the contact area (grinding area) between the lower surface of the grinding wheel and the upper surface of the wafer, preventing the upper surface of the wafer from being damaged by grinding debris, and enabling the wafer to be ground to a smooth, uniform thickness. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view of a grinding device according to the present invention; [Figure 2] 1 is a cutaway side view of a main part (a chuck table and a grinding wheel part) of a grinding device according to the present invention. [Figure 3] FIG. 3 is an enlarged detailed view of part A in FIG. 2. [Figure 4] FIG. 3 is an enlarged cross-sectional view taken along the line BB in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0011] [Grinding equipment configuration] First, the configuration of the grinding device according to the present invention will be described. In the following description, the arrow directions shown in Figure 1 are the X-axis (left-right direction), the Y-axis (front-rear direction), and the Z-axis (up-down direction), respectively.

[0012] 1 grinds a disk-shaped wafer W (see FIG. 2) that is a workpiece, and includes the following components: a chuck table 10 that holds the wafer W and rotates around its axis, a grinding mechanism 20 that grinds the wafer W held by suction on the chuck table 10, a thickness gauge 30 that measures the thickness of the wafer W during grinding, an elevation mechanism 40 that raises and lowers the grinding mechanism 20 in the direction perpendicular to the holding surface of the chuck table 10 (the Z-axis direction), a grinding water supply unit 50 that supplies grinding water to the contact area (grinding area) between the wafer W and the grinding wheel 25B, and a bias application unit 60 that generates a zeta potential.

[0013] Here, the wafer W is made of a single-crystal silicon base material, and a plurality of devices (not shown) are formed on the surface facing downward in the state shown in FIG. 2 , and these devices are protected by a protective tape T attached to the surface of the wafer W. The front surface (the bottom surface in FIG. 2) of the wafer W is held by suction on the holding surface of the chuck table 10 via the protective tape T, and the back surface (the top surface in FIG. 1) is ground by the grinding mechanism 20. Note that if no devices are formed on the front surface of the wafer W, the front surface of the wafer W may be brought into contact with the holding surface of the chuck table 10 without the protective tape T attached to the front surface of the wafer W, and the holding surface may hold the wafer W by suction, and the wafer W may be ground by the grinding mechanism 20.

[0014] Next, the configurations of the chuck table 10, grinding mechanism 20, thickness measuring device 30, lifting mechanism 40, grinding water supply unit 50, and bias application unit 60, which are the main components of the grinding device 1, will be described.

[0015] (Chuck table) 2, a disk-shaped porous member 10A is incorporated into the upper center of a disk-shaped frame 11. Here, the porous member 10A is made of porous ceramic or the like, and its upper surface forms a holding surface that suction-holds the disk-shaped wafer W. The porous member 10A of the chuck table 10 is selectively connected to a suction source (not shown), such as a vacuum pump.

[0016] The chuck table 10 is rotated around an axial center CL1 at a predetermined speed in the direction of the arrow by a rotation mechanism 12 shown in Fig. 2. The upper surface of the chuck table 10 forms a conical holding surface with its apex at the center. Note that the conical shape of the holding surface of the chuck table 10 is exaggerated in Fig. 2, but in reality, the inclination of the cone of the holding surface is so slight that it cannot be seen with the naked eye.

[0017] Here, as shown in Figure 2, a protective tape T is attached to the surface of the wafer W (the lower surface in Figure 2), and the wafer W is suction-held on the holding surface of the chuck table 10 with the protective tape T facing downward.

[0018] 1, the grinding device 1 according to the present invention has a rectangular box-shaped base 2 that is long in the Y-axis direction (front-rear direction), and a chuck table 10 faces a rectangular opening 2a that is long in the Y-axis direction and opens into this base 2. The periphery of chuck table 10 at opening 2a is covered with a rectangular plate-shaped cover 3, and the front and rear parts (-Y-axis direction and +Y-axis direction) of cover 3 at opening 2a are covered by bellows-shaped expandable covers 4 and 5 that move and expand together with cover 3.

[0019] The tilt of the chuck table 10 can be adjusted by a tilt adjustment mechanism (not shown). Specifically, the axis center CL1 of the chuck table 10 is tilted by an angle α shown in the figure with respect to the perpendicular line N so that the conical holding surface of the chuck table 10 is parallel to the grinding surface (lower surface) of a grinding wheel 25B (described later).

[0020] Furthermore, the chuck table 10 can be moved back and forth in the Y-axis direction by a Y-axis movement mechanism 13 (see FIG. 2) housed in the base 2. Note that the Y-axis movement mechanism 13 is configured by a known ball screw mechanism or the like, and therefore illustration and description of its specific configuration will be omitted.

[0021] (Grinding mechanism) The grinding mechanism 20 includes a spindle motor 22 housed in a holder 21, a vertical spindle 23 that is driven to rotate about a vertical axis CL2 by the spindle motor 22, a disk-shaped mount 24 attached to the lower end of the spindle 23, and a grinding wheel 25 that is detachably attached to the underside of the mount 24. Here, the grinding wheel 25 is composed of a disk-shaped base 25A and a plurality of grinding stones 25B that are processing tools attached to the underside of the base 25A in an annular arrangement. The grinding stone 25B is a rectangular block-shaped processing tool for grinding the wafer W, and its underside forms a grinding surface that comes into contact with the upper surface (surface to be ground) of the wafer W.

[0022] (Thickness measuring instrument) The thickness measuring device 30 is a height gauge that measures the thickness of the wafer W held on the chuck table 10 during grinding, and includes a first probe 31 that contacts the top surface of the wafer W and a second probe 32 that contacts the top surface of the frame 11 of the chuck table 10. In the thickness measuring device 30, the first probe 31 measures the height of the top surface of the wafer W during grinding, and the thickness of the wafer W is determined from the difference between the height of the top surface of the wafer W measured by the first probe 31 and the height of the top surface of the frame 11 of the chuck table 10 measured by the second probe 32. The thickness measuring device 30 may also be configured to oscillate ultrasonic vibrations toward the wafer W and receive the ultrasonic vibrations reflected by the top and bottom surfaces of the wafer W to measure the thickness of the wafer W.

[0023] (Lifting mechanism) 1, the lifting mechanism 40 is disposed on the −Y axis direction end face (front face) of a rectangular box-shaped column 6 that is erected vertically on the +Y axis direction end face (rear end face) of the upper surface of the base 2. The lifting mechanism 40 has the function of lifting and lowering a rectangular plate-shaped lifting plate 41 attached to the back face of the holder 21 of the grinding mechanism 20, together with the holder 21 and the spindle 23 and grinding wheel 25 held by the holder 21, in the Z axis direction along a pair of left and right guide rails 42. The pair of left and right guide rails 42 are disposed perpendicular to the front face of the column 6 and parallel to each other.

[0024] A rotatable ball screw 43 is provided vertically along the Z-axis direction (up-down direction) between the pair of left and right guide rails 42, and the upper end of the ball screw 43 is connected to a servo motor 44, which serves as a drive source and can rotate forward and backward. The servo motor 44 is attached in a vertical position to the column 6 via a rectangular plate-shaped bracket 45 attached to the upper surface of the column 6. The lower end of the ball screw 43 is rotatably supported by the column 6, and a nut member (not shown) that protrudes horizontally from the back surface of the lifting plate 41 toward the rear (+Y-axis direction) is screwed onto the ball screw 43.

[0025] Therefore, when the servo motor 44 is started to rotate the ball screw 43 forward and backward, the lifting plate 41, to which a nut member (not shown) that screws onto the ball screw 43 is attached, moves up and down in the Z-axis direction together with the grinding mechanism 20 along a pair of guide rails 42, so that the grinding mechanism 20 moves up and down and the grinding amount (grinding allowance) of the grinding wheel 25B on the wafer W is set.

[0026] (Grinding water supply unit) The grinding water supply unit 50 supplies grinding water such as pure water toward the contact portion (grinding portion) between the grinding wheel 25B and the wafer W during grinding, and sprays the grinding water from inside the rotating annular grinding wheel 25B during grinding. More specifically, as shown in Fig. 1, the grinding water supply unit 50 includes a grinding water supply source 51 such as a water pump, and a pipe 52 extending from the grinding water supply source 51 is connected to a supply path (not shown) formed perpendicular to the axis of the spindle motor 22. The supply path (not shown) formed in the spindle motor 22 is connected to a supply path 23a formed perpendicular to the axis of the spindle 23 shown in Fig. 2, and the supply path 23a is connected to a plurality of (eight in the illustrated example) supply paths 24a extending radially outward from the center of the mount 24, as shown in Fig. 4. Furthermore, a base 25A of the grinding wheel 25 is formed with a plurality of nozzles 25a extending vertically downward from each supply passage 24a formed in the mount 24.

[0027] Therefore, the grinding water supplied from the grinding water supply source 51 to the spindle motor 22 via the piping 52 passes through the supply path 23a formed in the spindle 23 shown in Figure 2 and the multiple supply paths 24a formed in the mount 24, and is sprayed toward the top surface of the wafer W from the multiple nozzles 25a formed in the base 25A of the grinding wheel 25.

[0028] (Bias application section) As shown in Figure 2, the bias application unit 60 is composed of a first electrode 61 arranged on the grinding wheel 25, a second electrode 62 arranged in close proximity to the chuck table 10 but without contact, and a power supply unit 63 that applies electricity to these first electrode 61 and second electrode 62.

[0029] Here, a fixed terminal 64 formed in a ring shape from a conductive material is embedded in the inner periphery of housing 22A of spindle motor 22, and a ring-shaped movable terminal 65 is embedded in the outer periphery of spindle 23, facing spindle 23 and motor housing 22A across a minute cylindrical gap δ1. Like fixed terminal 64, movable terminal 65 is also made of a conductive material, and electrical continuity is established between fixed terminal 64 and movable terminal 65 by a plurality of brushes 66 that extend from the inner periphery of fixed terminal 64 toward movable terminal 65 and come into contact with movable terminal 65.

[0030] As shown in FIG. 1, the second electrode 62 is a circular member that follows the outer periphery of the chuck table 10, and this second electrode 62 is positioned close to the chuck table 10 with a predetermined gap δ2 between it and the outer periphery of the chuck table 10.

[0031] The power supply unit 63 is a DC power supply such as a battery. The positive terminal of the power supply unit 63 is electrically connected to the second electrode 62 via a lead wire 67, and the negative terminal of the power supply unit 63 is electrically connected to a fixed terminal 64 provided on the motor housing 22A via a lead wire 68. A movable terminal 65 provided on the spindle 23 and the first electrode 61 are electrically connected to each other via a lead wire 69. Note that the polarities of the first electrode 61 and the second electrode 62 may be reversed depending on the material of the wafer W. For example, when the material of the wafer W set in the material setting unit 70 shown in FIG. 2 is silicon, current is applied with the above polarity. On the other hand, when the material of the wafer W is sapphire, the polarity is reversed by the electrode switching unit 80 shown in FIG. 2.

[0032] [Function of grinding equipment] Next, the operation of the grinding apparatus 1 configured as above, that is, the method for grinding the wafer W, will be described.

[0033] 2, when grinding the wafer W, the wafer W is placed on the holding surface of the chuck table 10 with the protective tape T facing down. Then, a suction source (not shown) connected to the porous member 10A of the chuck table 10 is driven to evacuate the porous member 10A. This generates a negative pressure in the porous member 10A, and the wafer W placed on the holding surface of the porous member 10A via the protective tape T is suction-held onto the holding surface by the negative pressure.

[0034] 2 is driven to move the chuck table 10 in the +Y-axis direction (rearward), and the wafer W held by suction on the chuck table 10 is positioned below the grinding wheel 25 of the grinding mechanism 20. At this time, the horizontal positional relationship between the two is adjusted so that the lower surface (machined surface) of the grinding stone 25B of the grinding wheel 25 passes through the center of the wafer W.

[0035] 2 is driven to rotate the chuck table 10, and the chuck table 10 and the wafer W held thereon are rotated at a predetermined rotational speed in the direction of the arrow in the drawing, and the spindle motor 22 of the grinding mechanism 20 shown in FIG. 1 is started to rotate the grinding wheel 25 at a predetermined rotational speed in the direction of the arrow in FIG. 2.

[0036] As described above, when the lifting mechanism 40 is driven to lower the grinding wheel 25 in the −Z-axis direction while the wafer W and the grinding wheel 25 are rotating, the grinding stone 25B of the grinding wheel 25 comes into contact with the upper surface of the wafer W, and when the grinding stone 25B is further lowered from that state, the upper surface of the wafer W is ground and flattened by a predetermined amount by the grinding stone 25B. During the grinding process of the wafer W with the grinding stone 25B, the grinding water supplied from the grinding water supply source 51 of the grinding water supply unit 50 through the piping 52 to the grinding mechanism 20 flows from a supply path (not shown) formed at the axial center of the spindle motor 22 to a supply path 23a formed at the axial center of the spindle 23 shown in FIG. 2.

[0037] The grinding water flowing through the supply path 23a of the spindle 23 flows through multiple supply paths 24a formed in the mount 24 toward the outer periphery of the mount 24 as shown by the arrows in Fig. 4, and is sprayed from nozzles 25a opening at the outer periphery end of each supply path 24a toward the upper surface of the wafer W on the inner periphery side of the grinding wheel 25B as shown in Fig. 2. Therefore, the grinding water is supplied to the contact area (grinding portion) between the grinding surface (lower surface) of the grinding wheel 25B and the upper surface of the wafer W, and the contact area is cooled by the grinding water, and grinding chips generated by grinding the wafer W are washed away and removed by the grinding water.

[0038] As mentioned above, the grinding debris generated by grinding the wafer W is washed away and removed by the grinding water, but as mentioned above, there is a problem in that the grinding water containing the grinding debris is atomized by the centrifugal force caused by the rotation of the wafer W and scattered within the processing chamber, and then adheres to the grinding wheel 25.

[0039] Therefore, in this embodiment, the bias application unit 60 is provided. In this bias application unit 60, the first electrode 61 and the second electrode 62 are electrically connected by conductive grinding water supplied from the grinding water supply source 51 to the contact portion (grinding portion) between the wafer W and the grinding wheel 25B. A zeta potential is generated by applying electricity from the power supply unit 63 to the first electrode 61 and the second electrode 62, and the action of the zeta potential prevents grinding chips generated by grinding the wafer W from adhering to the grinding wheel 25. In other words, the zeta potential separates the grinding chips from the grinding wheel 25B, preventing them from adhering to the inner circumferential surface of the grinding wheel 25B. This prevents grinding chips from entering the contact portion (grinding portion) between the lower surface of the grinding wheel 25B and the upper surface of the wafer W. This prevents the upper surface of the wafer W from being damaged by the grinding chips, and allows the wafer W to be ground to a flat, uniform thickness.

[0040] It should be noted that the present invention is not limited to the application of the above-described embodiments, and various modifications are possible within the scope of the claims and the technical ideas described in the specification and drawings. [Explanation of symbols]

[0041] 1: grinding device, 2: base, 2a: opening of base, 3: cover, 4, 5: telescopic cover, 6: column, 10: chuck table, 10A: porous member, 11: frame, 12: Rotation mechanism, 13: Y-axis movement mechanism, 20: Grinding mechanism, 21: Holder, 22: spindle motor, 22A: motor housing, 23: spindle, 23a: supply channel, 24: mount, 24a: supply channel, 25: grinding wheel, 25A: base, 25B: grinding wheel, 25a: nozzle, 30: thickness measuring device, 31: first probe, 32: second probe, 40: lifting mechanism, 41: lifting plate, 42: guide rail, 43: ball screw, 44: servo motor, 45: bracket, 50: grinding water supply unit, 51: grinding water supply source, 52: piping, 60: bias application unit, 61: first electrode, 62: second electrode, 63: power supply unit, 64: fixed terminal, 65: movable terminal, 66: brush, 67 to 69: Lead wire, 70: Material setting unit, 80: Electrode switching unit, CL1: axial center of chuck table, L2: axial center of spindle, N: perpendicular line, T: protective tape, W: wafer, α: tilt angle of chuck table, δ1, δ2: minute gap

Claims

1. a chuck table that rotates together with the wafer held by the holding surface; a grinding mechanism that rotates a grinding wheel having grinding stones arranged in a ring shape on a base and grinds the wafer with the grinding stones; a grinding water supply unit that supplies grinding water to a contact portion between the wafer and the grinding wheel; A grinding device comprising: a bias application unit including a first electrode disposed on the grinding wheel, a second electrode disposed close to the chuck table but not in contact with the grinding wheel, and a power supply unit that applies current to the first electrode and the second electrode; A grinding device characterized in that the first electrode and the second electrode of the bias application unit are electrically connected by the grinding water supplied from the grinding water supply unit to the contact portion between the wafer and the grinding wheel, and electricity is passed through these first electrode and second electrode, causing grinding chips contained in the grinding water to adhere to the second electrode.

2. an electrode switching unit that switches electrodes; and a material setting unit that sets the material of the wafer; 2. The grinding device according to claim 1, wherein the electrode is switched by the electrode switching unit depending on the material of the wafer.

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