Grinding device

Abstract

To provide a grinding device that is able to surely prevent adhesion of grinding chips to a contact shaft while saving water.SOLUTION: A linear gauge 31 provided in a grinding device 1 includes: a contact shaft 38; an air bearing 37 supporting the contact shaft 38 in a vertically liftable manner; a detection unit 40 that detects a height position of the contact shaft 38 lowered by its own weight; a lifting mechanism 39 that lifts the contact shaft 38; a water film formation nozzle 431 that forms a water film on a side surface of the contact shaft 38 protruding from a case 36; and a throttle valve (water amount adjustment unit) 47 that adjusts an amount of water to be supplied to the water film formation nozzle 431. The control unit 90 sets the amount of water to supplied to the water film formation nozzle 431 to a small first flow rate until a wafer W is ground to a preset finish thickness. When the wafer W is ground to the finish thickness, the control unit increases the amount of water to be supplied to the water film formation nozzle 431 to a second flow rate higher than the first flow rate.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a grinding apparatus for grinding a wafer held on a chuck table with a grinding wheel.

Background Art

[0002] In a grinding apparatus for grinding a wafer held on a chuck table with a grinding wheel, the thickness of the wafer during grinding is measured by a thickness measuring device. Some thickness measuring devices measure the upper surface height of the wafer and the upper surface height of the chuck table respectively, and obtain the thickness of the wafer from the difference between the two. Then, the wafer is ground until the thickness of the wafer measured by such a thickness measuring device reaches a predetermined thickness.

[0003] By the way, a linear gauge for detecting the height of the upper surface of the chuck table or the upper surface of the wafer held on the chuck table may be used for the thickness measuring device (see, for example, Patent Documents 1 and 2). This linear gauge includes a contact shaft whose tip is positioned in contact with the measurement surface or at a predetermined distance above the measurement surface, an air bearing that supports the contact shaft so as to be vertically movable, a detection unit that detects the height position of the contact shaft that has descended by its own weight, a raising mechanism that raises the contact shaft, a case that houses the air bearing, the detection unit, and the raising mechanism, and a water film forming nozzle that forms a water film on the side surface of a protruding portion protruding from the case of the contact shaft.

[0004] In the above linear gauge, by forming a water film on the side surface of the protruding portion protruding from the case of the contact shaft, adhesion of abrasive debris contained in the grinding water scattered around by the rotation of the grinding wheel to the contact shaft is prevented. Therefore, during grinding, water is continuously sprayed from the water film forming nozzle toward the protruding portion from the case of the contact shaft.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-118503 [Patent Document 2] Japanese Patent Publication No. 2022-067788 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In linear gauges, as mentioned above, continuously spraying water from a water film forming nozzle towards the protrusion from the case of the contact axis during wafer grinding results in the problem of consuming a large amount of water.

[0007] The present invention has been made in view of the above problems, and its purpose is to provide a grinding device that can reliably prevent grinding debris from adhering to the contact shaft while conserving water. [Means for solving the problem]

[0008] To achieve the above objective, the present invention provides a grinding apparatus for grinding a wafer held on the holding surface of a chuck table with a grinding wheel, comprising: a linear gauge for measuring the height of the upper surface of the chuck table radially outside the holding surface, which serves as the measuring surface, or the height of the upper surface of the wafer held on the holding surface of the chuck table; and a control unit, wherein the linear gauge comprises: a contact shaft whose tip is in contact with the measuring surface or positioned at a predetermined distance from the measuring surface; an air bearing that supports the contact shaft so that it can move up and down vertically; a detection unit that detects the height position of the contact shaft as it has descended by its own weight; a lifting mechanism for raising the contact shaft; a case housing the air bearing, the detection unit and the lifting mechanism; an insertion hole formed in the bottom plate of the case through which the tip portion of the contact shaft is inserted; and a part formed in the bottom plate of the case through the insertion hole. The control unit comprises a water film forming nozzle that forms a water film on the side surface of the contact shaft that communicates with and protrudes from the case, and a water volume adjustment unit that adjusts the amount of water supplied to the water film forming nozzle, wherein the control unit comprises a first flow rate control unit that sets the amount of water supplied to the water film forming nozzle by the water volume adjustment unit to a small amount, a first flow rate, until the wafer is ground to a preset finish thickness, a second flow rate control unit that increases the amount of water supplied to the water film forming nozzle to a second flow rate greater than the first flow rate when the wafer is ground to a finish thickness, and a contact shaft raising control unit that, before raising the contact shaft, ejects the water increased by the second flow rate control unit from the water film forming nozzle to fill the side surface of the contact shaft between the water film forming nozzle and the air bearing with water, and then raises the contact shaft. [Effects of the Invention]

[0009] According to the present invention, the amount of water supplied to the water film forming nozzle is set to a small amount, a first flow rate, until the wafer thickness measured by the linear gauge reaches a predetermined finish thickness. Once the wafer has been ground to the predetermined finish thickness, the amount of water supplied to the water film forming nozzle is increased to a second flow rate, which is greater than the first flow rate. This ensures that the side surface of the contact shaft of the linear gauge, which rises after the wafer grinding process, is filled with water. As a result, water conservation is achieved while reliably preventing grinding debris from adhering to the contact shaft as it rises after the wafer grinding process, and the contact shaft can be raised smoothly without resistance. [Brief explanation of the drawing]

[0010] [Figure 1] This is a perspective view showing a part of the grinding apparatus according to the present invention, broken off. [Figure 2] This is an enlarged detail view of section A in Figure 1. [Figure 3] This is a partial side cross-sectional view showing the configuration of the linear gauge of the grinding apparatus according to the present invention. [Figure 4] Figure 3 is a magnified detailed view of the main part, where (a) shows the state of the wafer before it is ground to the finishing thickness, and (b) shows the state of the wafer after it has been ground to the finishing thickness. [Figure 5] This figure shows the change in height of the grinding surface of the grinding wheel in the grinding apparatus according to the present invention over time. [Figure 6] This is a flowchart showing the wafer grinding procedure in the grinding apparatus according to the present invention. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below with reference to the accompanying drawings.

[0012] First, the configuration of the grinding apparatus according to the present invention will be described below with reference to Figure 1. In the following description, the arrow directions shown in Figure 1 will be the X-axis direction (left and right direction), the Y-axis direction (front and back direction), and the Z-axis direction (up and down direction), respectively.

[0013] [Configuration of the grinding machine] The grinding apparatus 1 shown in Figure 1 grinds a disc-shaped wafer W, which is a workpiece, and comprises the following components. Specifically, the grinding apparatus 1 comprises a chuck table 10 that holds the wafer W and rotates around its axis, a grinding unit 20 that grinds the wafer W held by the chuck table 10, a thickness measuring instrument 30 that measures the thickness of the wafer W during grinding, a grinding feed means 70 that moves the grinding unit 20 up and down in a vertical direction (Z-axis direction) relative to the holding surface 11a of the chuck table 10, a horizontal movement mechanism 80 that moves the chuck table 10 in a horizontal direction (Y-axis direction) relative to the holding surface 11a, and a control unit 90 (see Figure 3) as its main components.

[0014] Here, the wafer W is made of a single-crystal silicon matrix, and in the state shown in Figure 1, multiple devices (not shown) are formed on the downward-facing surface, and these devices are protected by protective tape T attached to the surface of the wafer W. The wafer W is then held by suction on its surface (bottom surface in Figure 1) to the holding surface 11a of the chuck table 10 via the protective tape T, and its back surface (top surface in Figure 1) is ground by the grinding unit 20.

[0015] Next, the configurations of the main components of the grinding apparatus 1, namely the chuck table 10, grinding unit 20, thickness measuring instrument 30, grinding feed means 70, horizontal movement mechanism 80, and control unit 90, will be explained.

[0016] (Chuck table) The chuck table 10 is a disc-shaped member, consisting of a disc-shaped frame 10A and a porous member 11 incorporated in the center of the frame 10A. Here, the porous member 11 is made of porous ceramic or the like, and its upper surface constitutes a holding surface 11a that sucks and holds the disc-shaped wafer W.

[0017] The chuck table 10 is rotationally driven at a predetermined speed about its axis by a rotational drive mechanism (not shown). That is, the chuck table 10 includes a rotating shaft 12 that extends vertically and integrally downward from its center, and this rotating shaft 12 is rotationally driven at a predetermined speed by a rotational drive mechanism (not shown). Although not shown, the porous member 11 of the chuck table 10 is selectively connected to a suction source (not shown) such as a vacuum pump.

[0018] Further, the grinding apparatus 1 according to the present embodiment includes a rectangular box-shaped base 2 that is long in the Y-axis direction (front-rear direction). The chuck table 10 faces a rectangular opening 3 that is long in the Y-axis direction and opens in the base 2. The periphery of the chuck table 10 in the opening 3 is covered by a rectangular plate-shaped cover 4. The front and rear (-Y direction and +Y direction) portions of the cover 4 in the opening 3 are respectively covered by bellows-shaped expandable and contractible covers 5 and 6 that move and expand and contract together with the cover 4. Therefore, regardless of the position of the chuck table 10 on the Y-axis, the opening 3 is always closed by the cover 4 and the expandable and contractible covers 5 and 6, preventing foreign matter from entering the base 2 from the opening 3.

[0019] (Grinding unit) The grinding unit 20 includes a spindle housing 22 fixed to a holder 21, a spindle motor 23 housed in the spindle housing 22, a vertical spindle 24 rotationally driven by the spindle motor 23, a disc-shaped mount 25 attached to the lower end of the spindle 24, and a grinding wheel 26 detachably mounted on the lower surface of the mount 25. Here, the grinding wheel 26 is composed of a disc-shaped base 26a and a plurality of annular grinding wheels 26b that are cutting tools annularly attached to the lower surface of the base 26a. The annular grinding wheel 26b is a rectangular block-shaped cutting tool for grinding the wafer W, and its lower surface constitutes a grinding surface that contacts the upper surface (grinding surface) of the wafer W.

[0020] Furthermore, a nozzle 27, which is bent in an inverted L-shape, is positioned near the chuck table 10. From this nozzle 27, grinding water such as pure water is supplied to the grinding area, which is the contact area between the grinding wheel 26b and the wafer W during grinding.

[0021] (Thickness measuring instrument) The thickness measuring device 30 measures the thickness of a wafer W being ground while it is held in the chuck table 10. It includes a linear gauge 31 that contacts the upper surface of the wafer W being ground to measure the height of the upper surface, and a linear gauge 32 that contacts the upper surface of the frame 10A of the chuck table 10 to measure the height of the upper surface. The thickness of the wafer W being ground is determined by subtracting the height of the upper surface of the frame 10A measured by the other linear gauge 32 from the height of the upper surface of the wafer W measured by the other linear gauge 31.

[0022] As shown in Figures 1 and 2, a cylindrical support column 33 is erected near the chuck table 10 on the base 2, and linear gauges 31 and 32 are attached to the ends of a pair of arms 34 and 35 that extend horizontally from this support column 33 upwards toward the chuck table 10. Further details of the configuration of this thickness measuring instrument 30 will be described later.

[0023] (Grinding feed mechanism) The grinding feed mechanism 70 raises and lowers the grinding unit 20 in a direction perpendicular to the holding surface 11a of the chuck table 10 (Z-axis direction), and is positioned on the -Y-axis end face (front face) of a rectangular box-shaped column 71 that is erected vertically on the +Y-axis end (rear end) of the upper surface of the base 2. This grinding feed mechanism 70 raises and lowers a rectangular plate-shaped lifting plate 72 attached to the back of the holder 21 in the Z-axis direction along a pair of left and right guide rails 73, together with the holder 21 and the spindle 24 and grinding wheel 26 held in the holder 21. Here, the pair of left and right guide rails 73 are arranged perpendicularly and parallel to each other on the front face of the column 71.

[0024] Furthermore, a rotatable ball screw 74 is erected vertically along the Z-axis direction (up and down direction) between a pair of left and right guide rails 73, and the upper end of the ball screw 74 is connected to a pulse motor 75 that is capable of forward and reverse rotation and is the drive source. Here, the pulse motor 75 is mounted vertically on the column 71 via a rectangular plate-shaped bracket 76 attached to the upper surface of the column 71. The lower end of the ball screw 74 is rotatably supported by the column 71, and a nut member (not shown) that protrudes horizontally toward the rear (+Y-axis direction) from the back of the lifting plate 72 is screwed onto this ball screw 74.

[0025] Therefore, by starting the pulse motor 75 and rotating the ball screw 74 in the forward and reverse directions, the lifting plate 72, to which a nut member (not shown) that screws onto the ball screw 74 is attached, moves up and down along a pair of guide rails 73 together with the grinding unit 20, causing the grinding unit 20 to move up and down and setting the amount of grinding (grinding allowance) of the grinding wheel 26b relative to the wafer W.

[0026] (Horizontal movement mechanism) The horizontal movement mechanism 80 is a mechanism for moving the chuck table 10 horizontally (in the Y-axis direction) relative to the holding surface 11a, and as shown in Figure 1, it is disposed on a rectangular block-shaped internal base 81 housed inside the base 2. This horizontal movement mechanism 80 is equipped with a block-shaped slider 82, which is slidable in the Y-axis direction along a pair of left and right guide rails 83 that are arranged parallel to each other along the Y-axis direction (front-rear direction). Therefore, the chuck table 10 and a rotational drive mechanism (not shown), supported by the slider 82, are slidable along the Y-axis direction together with the slider 82.

[0027] A rotatable ball screw 84 extending in the Y-axis direction (front-to-back direction) is positioned between a pair of left and right guide rails 83 on the internal base 81. One end of the ball screw 84 in the Y-axis direction (left end in Figure 1) is connected to a pulse motor 85 that is a drive source and can rotate in both forward and reverse directions. The other end of the ball screw 84 in the Y-axis direction (right end in Figure 1) is rotatably supported on the internal base 81 by a bearing 86 erected on the internal base 81. A nut member (not shown) protruding downward from the slider 82 is screwed onto the ball screw 84.

[0028] Therefore, when the pulse motor 85 is activated to rotate the ball screw 84 in forward and reverse directions, a nut member (not shown) that screws onto the ball screw 84 slides along the ball screw 84 in the Y-axis direction (forward and backward direction) together with the slider 82. As a result, the chuck table 10 also moves integrally along the Y-axis direction along with the slider 82. Consequently, the wafer W held by suction on the holding surface 11a of the chuck table 10 also moves along the Y-axis direction.

[0029] (Control Unit) The control unit 90 includes a CPU (Central Processing Unit) that performs calculations according to a control program, and memory units such as ROM (Read Only Memory) and RAM (Random Access Memory). This control unit 90 controls the chuck table 10, grinding unit 20, thickness measuring instrument 30, grinding feed means 70, and horizontal movement mechanism 80, respectively. It includes a first flow rate control unit 91 that sets the amount of water supplied to the supply ports 433 and 65 (see Figure 2), which are provided on the linear gauges 31 and 32 of the thickness measuring instrument 30, to a first flow rate; a second flow rate control unit 92 that increases the amount of water supplied to the supply ports 433 and 65 to a second flow rate greater than the first flow rate; and a contact shaft raising control unit 93 that raises the contact shafts 38 (see Figure 3), which are provided on each linear gauge 31 and 32, as described below (see Figure 3). The details of the operation of these first flow rate control unit 91, second flow rate control unit 92, and contact shaft raising control unit 93 will be described later.

[0030] Herein, the details of the configuration of the thickness measuring instrument 30, which constitutes the main part of the present invention, will be described below with reference to Figures 2 and 3.

[0031] [Details of the thickness measuring instrument configuration] Since the basic configuration of the pair of linear gauges 31 and 32 that make up the thickness measuring instrument 30 is the same, the configuration of one of the linear gauges 31 will be mainly described below. Note that in Figure 3, the arms 34 and 35 shown in Figure 2 are omitted for simplification.

[0032] As shown in Figure 3, the linear gauge 31 comprises a rectangular box-shaped case 36. Inside this case 36 are a contact shaft 38 supported by an air bearing 37 to move vertically (in the Z-axis direction) without contact, a lifting mechanism 39 for raising the contact shaft 38, and a detection unit 40 for detecting the height position of the contact shaft 38 at which its tip contacts the upper surface of the wafer W due to its own weight. The detection unit 40 includes a vertically positioned scale 401 and a sensor 402 for optically reading the markings on the scale 401. The upper end of the scale 401 and the upper end of the contact shaft 38 are connected by a horizontally positioned connecting plate 41. Therefore, the scale 401 and the contact shaft 38 move up and down together with the connecting plate 41. The sensor 402 is fixed to the inner wall of the case 36 at a location opposite the scale 401.

[0033] The housing 371 of the air bearing 37 has a plurality of air passages 372 formed therein, and these air passages 372 open toward the outer circumferential surface of the contact shaft 38. An air supply source 42, such as an air compressor, is connected to the air passages 372 by air piping 68. The tip (lower end) of the contact shaft 38 protrudes downward from the case 36 through an insertion hole 36a formed in the bottom plate 36A of the case 36, and a water film forming means 43 attached to the bottom plate 36A of the case 36 is provided around the protruding portion 38A of the contact shaft 38. A small-diameter probe 38a extends integrally downward from the lower end of the protruding portion 38A of the contact shaft 38, and the tip of this probe 38a is in contact with the upper surface of the wafer W held on the holding surface 11a of the chuck table 10. In this embodiment, the tip of the probe 38a of the contact shaft 38 is in contact with the wafer W, but the contact shaft 38 may be positioned such that the tip of the probe 38a is located at a predetermined distance from the upper surface of the wafer W.

[0034] The water film forming means 43 includes a water film forming nozzle 431 through which a protruding portion 38A, which protrudes downward from the case 36 of the contact shaft 38, passes through the center. Multiple water channels 432 are formed within this water film forming nozzle 431. One end of each water channel 432 opens toward the outer circumferential surface of the protruding portion 38A of the contact shaft 38, and the other end of each water channel 432 is connected to a supply port 433 attached to the water film forming nozzle 431. The supply port 433 is connected to a water source 45 such as a water pump via a water pipe (second supply channel) 44, and an electromagnetic on-off valve (second valve) 46 and a flow rate adjustment valve (flow rate adjustment valve) 47 are connected to the water pipe 44. The electromagnetic on-off valve 46 and the flow rate adjustment valve 47 are electrically connected to a control unit 90, and their opening and closing operations are controlled by the control unit 90.

[0035] Furthermore, the lifting mechanism 39 housed within the case 36 comprises a cylinder 391, a piston 392 fitted within the cylinder 391 so as to be vertically slidable, and a piston rod 393 extending integrally upward from the piston 392. Here, the piston rod 393 passes through the cylinder 391 and protrudes upward, with its upper end selectively contacting the lower surface of the connecting plate 41.

[0036] Incidentally, the inside of the cylinder 391 is divided into an upper chamber S1 and a lower chamber S2 by a piston 392, and air is selectively supplied to these upper chamber S1 and lower chamber S2 from an air supply source 42. That is, an electromagnetic switching valve 49 is provided in the air pipe 48 extending from the air supply source 42, and two air pipes 50 and 51 extending from this electromagnetic switching valve 49 are connected to the upper chamber S1 and lower chamber S2 inside the cylinder 391 of the lifting mechanism 39, respectively. The electromagnetic switching valve 49 is electrically connected to the control unit 90, and its switching operation is controlled by the control unit 90.

[0037] The above-mentioned contact shaft 38, an air bearing 37 that supports the contact shaft 38 so that it can move up and down without contact, a lifting mechanism 39 that raises the contact shaft 38, and a detection unit 40 that detects the height position of the contact shaft 38 are housed in a case 36. An exhaust port 36b is opened at the top of the side plate 36B of the case 36, and the inside of the case 36 is selectively opened to the atmosphere by an exhaust pipe 52 connected to the exhaust port 36b and an exhaust valve 53 provided in the exhaust pipe 52. The exhaust valve 53 is electrically connected to a control unit 90, and its opening and closing operation is controlled by the control unit 90. Alternatively, the orifice diameter is adjusted by the control unit 90. The exhaust valve 53 is configured to adjust the orifice diameter so that the inside of the case 36 is at a constant pressure using a regulator with a spring inside, and does not necessarily have to be electrically connected.

[0038] Here, the other linear gauge 32, which detects the height of the upper surface of the frame 10A of the chuck table 10, is configured in the same way as the first linear gauge 31 described above. However, in order to prevent thermal deformation of these linear gauges 31 and 32 and to detect the thickness of the wafer W with high precision, as shown in Figure 2, each linear gauge 31 and 32 and the arms 34 and 35 that support them are cooled by cooling water supplied from cooling nozzles 54 and 55. That is, as shown in Figure 2, two nipples 56 and 57 attached to the upper surface of the support column 33 are connected to water pipes (first supply lines) 58 and 59 extending from a water source 45, respectively, and each water pipe 58 and 59 is provided with electromagnetic on / off valves (first valves) 60 and 61 and flow rate adjustment valves (flow rate adjustment valves) 62 and 63, respectively. Each nipple 56, 57 is connected to a water supply passage 54A, 55A formed inside the support column 33 and in each cooling nozzle 54, 55, respectively. Multiple branch passages 54a, 55a branch downward from these water supply passages 54A, 55A at appropriate intervals along the longitudinal direction of each cooling nozzle 54, 55. These branch passages 54a, 55a open toward each arm 34, 35 and the linear gauges 31, 32 attached to the ends of each arm 34, 35, respectively. The electromagnetic valves 60, 61 and throttle valves 62, 63 are electrically connected to the control unit 90, respectively, and their opening and closing operations are controlled by the control unit 90.

[0039] Furthermore, as shown in Figure 2, the water pipe 64 branching off from the water pipe 59 is connected to a supply port 65 provided on the other linear gauge 32. The water pipe 64 is equipped with an electromagnetic on-off valve (second valve) 66 and a throttle valve (flow rate adjustment valve) 67. These electromagnetic on-off valves 66 and throttle valves 67 are electrically connected to the control unit 90, and their opening and closing operations are controlled by the control unit 90.

[0040] [Operation of grinding equipment] Next, the operation of the grinding apparatus 1 configured as described above will be explained below with reference to Figures 4 to 6.

[0041] When grinding a wafer W using the grinding apparatus 1, first, the wafer W to be ground is held on the holding surface 11a of the chuck table 10. That is, when the wafer W is placed on the holding surface 11a of the chuck table 10 with the protective tape T (see Figure 1) facing downwards, the porous member 11 of the chuck table 10 is connected to a suction source (not shown), such as a vacuum pump, and the porous member 11 is evacuated. This generates negative pressure in the porous member 11, and the wafer W is attracted and held on the holding surface 11a of the chuck table 10 by this negative pressure.

[0042] Next, the horizontal movement mechanism 80 shown in Figure 1 is driven to move the chuck table 10 in the +Y axis direction (rearward), positioning the wafer W, which is held by suction on the chuck table 10, below the grinding wheel 26 of the grinding unit 20. That is, when the pulse motor 85 is activated and the ball screw 84 rotates, a slider 82, to which a nut member (not shown) that screws onto the ball screw 84 is attached, slides along a pair of left and right guide rails 83 in the +Y axis direction together with the chuck table 10, etc., so that the wafer W held on the holding surface 11a of the chuck table 10 is positioned below the grinding wheel 26 of the grinding unit 20. At this time, the horizontal positional relationship between the two is adjusted so that the lower surface (grinding surface) of the grinding wheel 26b passes through the center of the wafer W.

[0043] Subsequently, the grinding feed means 70 is driven to lower the grinding unit 20, and grinding of the wafer W is started by the grinding wheel 26b attached to the grinding 26 of the grinding unit 20 (step S1 in Figure 6). At the same time, the first flow rate control unit 91 of the control unit 90 supplies water at a first flow rate from the water source 45 to the supply ports 433 and 65 (see Figure 2) provided in the linear gauges 31 and 32 of the thickness measuring instrument 30, respectively (step S2 in Figure 6).

[0044] In the grinding of the wafer W, the grinding wheel 26b of the grinding wheel 26 descends for a time T1 while idling from the origin height h0 shown in FIG. 5 to the height h1 at which the air cut starts at a speed V1 on its grinding surface (lower surface). Then, when the grinding surface of the grinding wheel 26b descends at time t1 until the height of the grinding surface of the grinding wheel 26b reaches h1, the air cut is performed at a speed V2 (<V1) slower than the speed V1 for a time T2 until the height of the grinding surface of the grinding wheel 26b becomes h2 shown in FIG. 5.

[0045] When the above air cut is performed and the grinding wheel 26b is processed until the height of its grinding surface becomes h2 shown in FIG. 5 (time t2), the grinding surface of the grinding wheel 26b contacts the upper surface (grinding surface) of the wafer W. When the grinding surface of the grinding wheel 26b contacts the upper surface of the wafer W in this way, the grinding wheel 26b descends at the first feed speed V3, and the upper surface of the wafer W is ground until time t3. The grinding of this wafer W is performed only for a time T3 when the height of the grinding surface of the grinding wheel 26b becomes h3 shown in FIG. 5. The grinding cost of the wafer W in this grinding is (h2 - h3). Note that the first feed speed V3 is set to be approximately the same as the descending speed V2 of the grinding wheel 26b during air cutting (V3 ≒ V2).

[0046] Then, when the grinding wheel 26b descends to h3 shown in FIG. 5 at time t3 and the wafer W is ground by the grinding wheel 26b for a time T3 (= t3 - t2), the grinding wheel 26b descends at a speed V4 (<V3) slower than the first speed V3 for a time T4 (= t4 - t3) until the height of its grinding surface becomes h4 shown in FIG. 5 to further grind the wafer W. The grinding cost of the wafer W at this time is (h4 - h3). Eventually, by two-stage grinding, the wafer W is ground to a predetermined finish thickness by the amount of grinding cost of (h2 - h4).

[0047] During the grinding process of the wafer W, the thickness of the wafer W is measured by the thickness measuring instrument 30 (step S3 in Figure 6). The thickness of the wafer W is measured by the thickness measuring instrument 30 and calculated by subtracting the height of the top surface of the frame 10A of the chuck table 10, measured by the other linear gauge 32, from the height of the top surface of the wafer W, measured by the other linear gauge 31. The measurement of the height of the top surface of the wafer W using the one linear gauge 31 will be described below.

[0048] When measuring the top surface height of the wafer W using the linear gauge 31, the electromagnetic switching valve 49 shown in Figure 3 is switched as shown, and air from the air supply source 42 is supplied from the air pipe 50 to the upper chamber S1 in the cylinder 391 of the lifting mechanism 39, while the air in the lower chamber S2 in the cylinder 391 is discharged into the atmosphere from the air pipe 51 through the electromagnetic switching valve 49. As a result, the piston 392 and piston rod 393 descend due to the pressure in the upper chamber S1, and the piston rod 393 is separated from the connecting plate 41 and positioned below the connecting plate 41.

[0049] At the same time, air is supplied from the air supply source 42 through the air piping 68 to the air passages 372 formed in the housing 371 of the air bearing 37. The air supplied to these air passages 372 is blown from the opening end of each air passage 372 toward the outer surface of the contact shaft 38. As a result, the contact shaft 38 is supported by the air bearing 37 so that it can slide up and down without contact. Consequently, the tip of the probe 38a of the contact shaft 38 contacts the upper surface of the wafer W due to its own weight, and moves up and down in response to changes in the height of the upper surface of the wafer W. As a result, the connecting plate 41 connected to the contact shaft 38 and the scale 401 of the detection unit 40 attached to the connecting plate 41 move up and down together with the contact shaft 38, and the scale of the scale 401 is optically read by the sensor 402, thereby measuring the height of the upper surface of the wafer W with high precision. Similarly, the other linear gauge 32 also accurately measures the upper surface height of the frame 10A of the chuck table 10. Therefore, the thickness of the wafer W during grinding can be determined by subtracting the upper surface height of the frame 10A of the chuck table 10 measured by the other linear gauge 32 from the upper surface height of the wafer W measured by the one linear gauge 31 (step S3 in Figure 6).

[0050] As mentioned above, some of the air supplied from the air supply source 42 through the air piping 68 to the air passage 372 formed in the housing 371 of the air bearing 37 leaks out of the housing 371 and accumulates inside the case 36. However, this air is discharged into the atmosphere through the exhaust port 36b formed in the side plate 36B of the case 36, thus preventing a pressure increase in the case 36.

[0051] While the thickness of the wafer W is being measured by the thickness measuring instrument 30, cooling water is supplied from the water source 45 shown in Figure 2 to the cooling nozzles 54 and 55 via water pipes 58 and 59. The cooling water supplied to the cooling nozzles 54 and 55 flows from the water supply passages 54A and 55A to the branch passages 54a and 55a, and is ejected from the branch passages 54a and 55a towards the arms 34 and 35 and the linear gauges 31 and 32. As a result, the arms 34 and 35 and the linear gauges 31 and 32 are cooled by the cooling water, preventing thermal deformation of these arms 34 and 35 and the linear gauges 31 and 32. Consequently, the thickness of the wafer W during grinding can be measured with high precision by the linear gauges 31 and 32.

[0052] Furthermore, during the grinding process of the wafer W, for example, for one of the linear gauges 31, water is supplied from the water source 45 shown in Figure 3 through the water pipe 44 to the supply port 433 of the water film forming means 43, and the water supplied to the supply port 433 is sprayed from the water channel 432 formed in the water film forming nozzle 431 toward the outer circumferential surface of the protruding portion 38A that protrudes downward from the case 36 of the contact shaft 38. In this case, the amount of water injected is a small amount, as described above, the first flow rate (0.25 liters / min in this embodiment), and the water pressure is also relatively low (7 kPa in this embodiment). As shown in Figure 4(a), the water injected from the supply port 433 through the water channel 432 toward the contact shaft 38 forms a relatively thin water film f1 on the outer surface of the protrusion 38A of the contact shaft 38 and the probe 38a at its tip. This water film f1 prevents grinding water and grinding debris contained in the grinding water from adhering to the outer surface of the protrusion 38A of the contact shaft 38 and the probe 38a. In addition, the air used in the air bearing 37 is exhausted outside the thin water film f1.

[0053] As described above, when the water film forming means 43 sprays water toward the protrusion 38A of the contact shaft 38 to form a water film f1 on the protrusion 38A and the outer circumferential surface of the probe 38a, and the thickness of the wafer W being ground is measured by the thickness measuring instrument 30 (step S3 in Figure 6), the control unit 90 determines whether the measured thickness of the wafer W has reached a predetermined finish thickness (step S4 in Figure 6). When the thickness of the wafer W measured by the thickness measuring instrument 30 reaches a predetermined finish thickness at time t4 shown in Figure 5 (the time when the height of the grinding surface of the grinding wheel 26b reaches h4) (Step S4: Yes), for example, in one linear gauge 31, the second flow rate control unit 92 of the control unit 90 closes the electromagnetic valve 60 to block the flow of cooling water toward the cooling nozzle 54, opens the electromagnetic valve 46, and increases the orifice diameter (opening) of the throttle valve 47 to increase the amount of water supplied to the water film forming nozzle 431 to a second flow rate greater than the first flow rate (Step S5 in Figure 6). Similarly, in the other linear gauge 32, the amount of water supplied to the supply port 65 (see Figure 2) is also increased to the second flow rate.

[0054] For example, in one linear gauge 31, if the amount of water supplied to the water film forming nozzle 431 is increased from a first flow rate to a second flow rate (2.0 liters / min in this embodiment), the water pressure in the water channel 432 also increases accordingly (100 kPa in this embodiment). As shown in Figure 4(b), the water sprayed from the supply port 433 through the water channel 432 toward the contact shaft 38 forms a relatively thick water film f2 on the outer circumferential surface of the protrusion 38A of the contact shaft 38 and the probe 38a at its tip. This thick water film f2 effectively prevents the adhesion of grinding water and grinding debris contained in the grinding water to the outer circumferential surface of the protrusion 38A of the contact shaft 38 and the probe 38a. In other words, the water film f2 fills the space between the protrusion 38A of the contact shaft 38 and the probe 38a, and the water pressure of the water film f2 removes the grinding debris contained in the grinding water, preventing the adhesion of grinding debris. Furthermore, when increasing the amount of water supplied to the water film-forming nozzle 431 from the first flow rate to the second flow rate, instead of increasing the orifice diameter (opening) of the throttle valve 47, the water that was flowing through the water piping (first supply passage) 58 may be diverted to the water piping (second supply passage) 44. For this purpose, a connecting pipe 99 and valves 95 and 97 are provided, and the control unit closes valve 95 and opens valve 97. Here, 96 and 98 shown in Figure 3 are valves provided on the other side of the linear gauge 32.

[0055] Furthermore, the outer surface of the contact shaft 38 is coated with a water-repellent and water-sliding coating as disclosed in Japanese Patent Publication No. 2018-070832. When the amount of water supplied to the water film forming nozzle 431 is increased to the second flow rate, the water pressure of the water film f2 makes it easy to remove the grinding water and the grinding debris contained in the grinding water.

[0056] As described above, when the wafer W is ground to a predetermined finish thickness at time t4 shown in Figure 5 (Step S4: Yes), the amount of water supplied to the water film forming nozzle 431 is increased from the first flow rate to the second flow rate (Step S5), and while the height of the grinding surface of the grinding wheel 26b is maintained at h4 shown in Figure 5 (i.e., the depth of cut of the grinding wheel 26b is kept at 0), spark-out grinding is performed in which the surface of the wafer W to be ground is ground by the rotating grinding wheel 26b for a predetermined time T5 until time t5. Therefore, the downward speed V5 of the grinding wheel 26b in this spark-out grinding is 0 (V5=0).

[0057] Once the spark-out grinding described above is complete, the grinding wheel 26b is slowly raised at a speed V6 from time t5 as shown in Figure 5, and escape cuts are made on the wafer W by the grinding wheel 26b until time t6 (time T6) when the grinding wheel 26b leaves the surface of the wafer W. Then, once this escape cut is complete, the grinding wheel 26b is retracted to the origin height position h0 at a relatively high retraction speed V7 from time t6 to time t7 (time range T7) as shown in Figure 5.

[0058] Incidentally, as mentioned above, when the wafer W is ground to a predetermined finish thickness at time t4 shown in Figure 5 (Step S4: Yes), the amount of water supplied to the water film forming nozzle 431 is increased from the first flow rate to the second flow rate (Step S5), and the lifting mechanism 39 is driven by the contact shaft lifting control unit 93 of the control unit 90, causing the contact shaft 38 to rise (Step S6 in Figure 6). That is, when the electromagnetic switching valve 49 shown in Figure 3 is switched, and air from the air supply source 42 flows from the air pipe 48 through the electromagnetic switching valve 49 to the air pipe 51, air is supplied from this air pipe 51 to the lower chamber S2 in the cylinder 391 of the lifting mechanism 39, and the piston 392 receives air pressure on its lower surface and rises inside the cylinder 391, so that the piston rod 393 rises together with the piston 392 and pushes up the connecting plate 41. As a result, the contact shaft 38 attached to the connecting plate 41 rises together with the connecting plate 41, and the probe 38a at its tip moves away from the surface of the wafer W (the surface to be ground). At this time, a relatively thick water film f2 (see Figure 4(b)) is formed on the outer surface of the protruding portion 38A of the rising contact shaft 38 and the probe 38a by the increased amount of water. Therefore, grinding water and grinding debris contained in the grinding water do not adhere to the outer surface of the protruding portion 38A of the contact shaft 38 and the probe 38a, and the rising of the contact shaft 38 is smooth.

[0059] Subsequently, the spark-out grinding and escape cut are performed, completing the series of grinding processes on the wafer W (step S7 in Figure 6).

[0060] As described above, in the grinding apparatus 1 according to this embodiment, the amount of water supplied to the supply ports 433 and 65 is set to a small amount, a first flow rate, until the thickness of the wafer W measured by the linear gauges 31 and 32 of the thickness measuring instrument 30 reaches a predetermined finish thickness. When the wafer W is ground to the predetermined finish thickness, the amount of water supplied to the supply ports 433 and 65 is increased to a second flow rate, which is greater than the first flow rate, so that the sides of the contact shafts 38 of the linear gauges 31 and 32 that rise after the wafer W is ground are filled with water. This makes it possible to conserve water while reliably preventing grinding debris from adhering to the contact shafts 38 that rise after the wafer W is ground, and provides the effect of allowing the contact shafts 38 to rise smoothly without resistance.

[0061] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the technical idea described in the claims, specification, and drawings. [Explanation of Symbols]

[0062] 1: Grinding device, 2: Base, 3: Opening, 4: Cover, 5, 6: Expandable cover, 10: Chuck table, 10A: Frame, 11: Porous member, 11a: Holding surface, 12: Rotating shaft, 20: Grinding unit, 22: Spindle housing, 23: Spindle motor, 24: Spindle, 25: Mount, 26: Grinding wheel 26a: Base, 26b: Grinding wheel, 27: Nozzle, 30: Thickness measuring instrument, 31,32: Linear gauge, 33: Support column, 34,35: Arm, 36: Case, 36A: Case bottom plate, 36a: Through hole, 36B: Case side plate, 36b: Exhaust vent, 37: Air bearing, 371: Housing, 372: Air passage, 38: Contact shaft, 38A: Projection of contact shaft, 38a: Probe, 39: Lifting mechanism, 391: Cylinder, 392: Piston, 393: Piston rod, 40: Sensing unit, 401: Scale, 402: sensor, 41: connecting plate, 42: air supply source, 43: water film forming means, 431: Water film forming nozzle, 432: Water channel, 433: Supply port, 44: Water piping (second supply channel), 45: Water source, 46: Solenoid valve (second valve), 47: Throttle valve (flow control valve), 48: Air piping, 49: Solenoid switching valve, 50, 51: Air piping, 52: Exhaust pipe, 53: Exhaust valve, 54, 55: Cooling nozzles, 54A, 55A: Water supply channels, 54a, 55a: Branch channels, 56, 57: Nipples, 58, 59: Water piping (first supply channel), 60, 61: Solenoid valve (first valve), 62, 63: Throttle valve (flow control valve), 64: Water piping (first supply line), 65: Supply port, 66: Electromagnetic on / off valve (second valve), 67: Throttle valve (flow control valve), 68: Air piping, 70: Grinding feed mechanism, 71: Column, 72: Lifting plate, 73: Guide rail, 74: Ball screw, 75: Pulse motor, 76: Bracket, 80: Horizontal movement mechanism, 81: Internal base, 82: Slider, 83: Guide rail, 84: Ball screw, 85: Pulse motor, 86: Bearing, 90: Control unit, 91: First flow control unit, 92: Second flow control unit, 93: Contact shaft elevation control unit, 95-98: Valve, 99: Connecting tube, f1, f2: Water film, S1: Upper chamber, S2: Lower chamber, T: Protective tape, W: Wafer

Claims

1. A grinding apparatus for grinding a wafer held on the holding surface of a chuck table with a grinding wheel, A linear gauge that measures the height of the upper surface of the chuck table radially outward from the holding surface, or the height of the upper surface of the wafer held on the holding surface of the chuck table, Control unit and Equipped with, The linear gauge in question is, The device comprises: a contact shaft whose tip contacts the measuring surface or is positioned at a predetermined distance from the measuring surface; an air bearing that supports the contact shaft so that it can move up and down vertically; a detection unit that detects the height position of the contact shaft as it descends by its own weight; a lifting mechanism that raises the contact shaft; a case that houses the air bearing, the detection unit and the lifting mechanism; a through hole formed in the bottom plate of the case through which the tip portion of the contact shaft is inserted; a water film forming nozzle formed in the bottom plate of the case that communicates with the through hole and protrudes from the case to form a water film on the side surface of the contact shaft; and a water volume adjustment unit that adjusts the amount of water supplied to the water film forming nozzle. The control unit is A grinding apparatus comprising: a first flow rate control unit that sets the amount of water supplied to the water film forming nozzle to a small amount (first flow rate) by the water volume adjustment unit until the wafer is ground to a preset finish thickness; a second flow rate control unit that increases the amount of water supplied to the water film forming nozzle to a second flow rate greater than the first flow rate when the wafer is ground to a finish thickness; and a contact shaft raising control unit that, before raising the contact shaft, sprays the increased amount of water from the water film forming nozzle by the second flow rate control unit to fill the side surface of the contact shaft between the water film forming nozzle and the air bearing with water, and then raises the contact shaft.

2. The linear gauge is equipped with a cooling nozzle that supplies water to the outer surface of the case to prevent thermal deformation of the linear gauge. The system comprises a first supply passage that connects a water source to the cooling nozzle and supplies water to the cooling nozzle, a first valve that opens and closes the first supply passage, a second supply passage that connects the water source to the water film forming nozzle and supplies water to the water film forming nozzle, a second valve that opens and closes the second supply passage, and a flow rate adjustment valve that adjusts the amount of water in the second supply passage. The grinding apparatus according to claim 1, wherein the second flow control unit closes the first valve, opens the second valve, and increases the orifice diameter of the flow control valve, thereby supplying the water that was supplied to the cooling nozzle to the water film forming nozzle.

3. The grinding apparatus according to claim 1, wherein the entire surface of the side surface of the contact shaft is coated with a water-repellent and water-sliding coating.

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