Grinding device

Abstract

To provide a grinding device capable of efficiently performing grinding and measuring a wafer shape with a simple structure having fewer parts.SOLUTION: A grinding device 1 includes: a fixed-type thickness gauge 8 that performs fixed-point measurement of the thickness of a wafer W; a movable-type thickness gauge 7 that measures the thickness of the wafer W with a measurement position P1 varied in the radial direction R of the wafer W; and a controller 9 that computes the shape of the wafer W by subtracting, from a thickness variation of a measurement value T2 of the movable-type thickness gauge 7, a decrease amount of a measurement value T1 of the fixed-type thickness gauge 8 corresponding to the grinding margin of the wafer W.SELECTED DRAWING: Figure 8

Description

[Technical Field]

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

[0002] In the field of semiconductor manufacturing, grinding devices are known that grind the top surface of semiconductor wafers (hereinafter referred to as "wafers") such as silicon wafers to process the wafers into a desired shape. In recent years, wafers have become thinner and through electrodes that penetrate the front and back of wafers have been formed, increasing the need to process wafers into a substantially uniform thickness.

[0003] Furthermore, when grinding a thin wafer, a support substrate may be attached to the non-grinding side of the wafer via an adhesive resin. However, since variations in the thickness of the support substrate and the adhesive resin are transferred to the wafer shape after grinding, it is necessary to correct the wafer thickness uniformity while taking into account the unevenness of the thickness of the support substrate and the adhesive resin.

[0004] It is necessary to check the wafer thickness while performing the grinding process, but because the wafer thickness is constantly decreasing during processing, if the thickness measurement position on the wafer is changed, it is not possible to distinguish whether the change in measurement value is due to the grinding allowance or to thickness variations within the wafer.

[0005] In the grinding device described in Patent Document 1, the lowering is interrupted after grinding is completed partway, the shape of the wafer is measured, and grinding is resumed so as to correct the measured shape to a desired shape.

[0006] In addition, in the surface grinding device described in Patent Document 2, three non-contact sensors arranged at a predetermined interval in the semi-radial direction of the wafer measure the shape of the wafer by measuring the thickness of the wafer at fixed points during the grinding process. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-264913 [Patent Document 2] Japanese Patent Application Publication No. 9-85619 Summary of the Invention [Problem to be solved by the invention]

[0008] However, with the device described in Patent Document 1, when measuring the thickness of the wafer, it is necessary to move the grinding wheel away from the wafer, which increases the processing time and causes problems such as the inability to maintain continuity of the processing position before and after interrupting processing.

[0009] Furthermore, the device described in Patent Document 2 requires the provision of three non-contact sensors for fixed-point measurement, which poses a problem of complicated device configuration.

[0010] Therefore, a technical problem arises that must be solved in order to measure the wafer shape with a simple configuration that allows for efficient grinding and has a small number of parts, and the present invention aims to solve this problem. [Means for solving the problem]

[0011] In order to achieve the above object, the grinding apparatus of the present invention is a grinding apparatus that grinds the top surface of a wafer with a grinding wheel, and is equipped with a fixed-point measuring means that measures the thickness of the wafer at a fixed point during the grinding process of the wafer, a mobile measuring means that measures the thickness of the wafer by changing the measurement position in the radial direction of the wafer during the grinding process of the wafer, and a control device that calculates the shape of the wafer from the change in thickness measured by the mobile measuring means, minus the decrease in the measurement value of the fixed-point measuring means that corresponds to the grinding allowance of the wafer.

[0012] With this configuration, the mobile measuring means and the fixed-point measuring means measure the wafer thickness during grinding, and the wafer shape can be calculated without interrupting processing based on the measurements from the mobile measuring means and the fixed-point measuring means. In addition, because the wafer shape is calculated using the mobile measuring means and the fixed-point measuring means, the device can be constructed with a small number of parts. [Effects of the Invention]

[0013] In the present invention, the mobile measuring means and the fixed-point measuring means measure the thickness of the wafer during the grinding process, and the shape of the wafer can be calculated without interrupting the process based on the measurements from the mobile measuring means and the fixed-point measuring means. Furthermore, since the shape of the wafer is calculated using the mobile measuring means and the fixed-point measuring means, the device can be constructed with a small number of parts. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view showing a grinding device according to an embodiment of the present invention; [Figure 2] FIG. [Figure 3] FIG. 2 is a partially cutaway side view showing the internal structure of the tip portion of the mobile thickness measuring device. [Figure 4] FIG. 2 is a schematic diagram showing the swing range of a mobile thickness measuring device. [Figure 5] FIG. 1 is a schematic diagram showing the structure of a fixed-point thickness measuring device. [Figure 6] FIG. 2 is a side view showing the position where the mobile thickness measuring device measures the wafer thickness. [Figure 7] FIG. 10 is a diagram showing the measurement results of wafer thickness. [Figure 8] 10A to 10C are diagrams for explaining a process of deriving a wafer shape from the measurement results of a wafer thickness. [Figure 9] FIG. 8 is a diagram showing a wafer shape based on the measurement results of FIG. 7. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described below with reference to the drawings. When referring to the number, numerical value, amount, range, etc. of components, unless otherwise specified or when the number is clearly limited to a specific number in principle, the number is not limited to the specific number, and may be greater than or less than the specific number.

[0016] Furthermore, when referring to the shape or positional relationship of components, etc., it includes things that are substantially similar or approximate to those shapes, etc., unless otherwise specified or when it is clearly considered otherwise in principle.

[0017] In addition, the drawings may exaggerate characteristic parts to make the features easier to understand, and the dimensional proportions of the components may not be the same as in reality. In addition, in cross-sectional views, hatching of some components may be omitted to make the cross-sectional structure of the components easier to understand.

[0018] Fig. 1 is a perspective view showing a grinding apparatus 1 according to one embodiment of the present invention. Fig. 2 is a plan view showing the polishing apparatus. The grinding apparatus 1 grinds the top surface of a wafer W held by suction on a wafer chuck 2, thereby forming the wafer W into a desired shape.

[0019] The grinding device 1 includes a wafer chuck 2 and a grinding means 3 .

[0020] The wafer chuck 2 is provided so as to be rotatable in a rotation direction C1 around a rotation axis a1 that passes through the center of the wafer chuck 2. Note that the grinding apparatus 1 is equipped with a plurality of wafer chucks 2 in order to continuously grind a plurality of wafers W. The plurality of wafer chucks 2 are arranged on the index table 4 at predetermined intervals on a circle centered on the rotation axis of the index table 4. Note that the reference numeral 10 in FIG. 2 denotes a casing that houses the grinding apparatus 1.

[0021] An adsorbent 21 made of a porous material such as alumina is embedded on the upper surface of the wafer chuck 2. The wafer chuck 2 is provided with a conduit (not shown) that passes through the interior and extends to the surface of the adsorbent 21. The conduit is connected to a vacuum source, a compressed air source, or a water supply source via a rotary joint (not shown). When the vacuum source is activated, the wafer W placed on the wafer chuck 2 is adsorbed and held by the wafer chuck 2. When the compressed air source or the water supply source is activated, the adsorption between the wafer W and the wafer chuck 2 is released.

[0022] The wafer W is mounted on a support substrate such as a backgrind tape, a glass substrate, or a silicon substrate and is held by suction on the wafer chuck 2. In particular, as the wafer W becomes thinner and larger in diameter, a support substrate is often used.

[0023] The grinding means 3 includes a grinding wheel 31 and a spindle 32 to which the grinding wheel 31 is attached.

[0024] The grinding wheel 31 is attached horizontally to the tip of the spindle 32. The grinding wheel 31 is pressed against the wafer W, thereby grinding the wafer W.

[0025] The spindle 32 rotates the grinding wheel 31 in a rotation direction C2 around a rotation axis a2 by a motor (not shown). The spindle 32 is cantilevered by a spindle feed mechanism (not shown) and can be raised and lowered in the vertical direction by the spindle feed mechanism.

[0026] A tilt mechanism 5 that tilts the rotation axis a1 is provided on the wafer chuck 2. The tilt mechanism 5 includes a tilt table 51, a fixed support part 52, and two movable support parts 53 and .

[0027] The tilt table 51 is formed in a substantially triangular shape in a plan view. The tilt table 51 has a fixed support portion 52 and movable support portions 53 and 54 arranged at equal intervals on a concentric circle centered on a rotation axis a1.

[0028] The fixed support portion 52 is a bolt that fastens the tilt table 51 to the index table 4.

[0029] The movable support parts 53 and 54 are slide mechanisms using ball screws interposed between the index table 4 and the tilt table 51. The movable support parts 53 and 54 move the tilt table 51 toward or away from the index table 4 in accordance with the rotation of the ball screws, thereby tilting the rotation axis a1. The movable support part 53 is disposed upstream of the fixed support part 52 in the rotation direction C1 of the wafer chuck 2. The movable support part 54 is disposed downstream of the fixed support part 52 in the rotation direction C1 of the wafer chuck 2.

[0030] The grinding apparatus 1 includes a coolant supply mechanism 6. The coolant supply mechanism 6 supplies coolant from the tip of a nozzle 61 toward the upper surface of the wafer W. The nozzle 61 is disposed upstream of the grinding wheel 31 in the rotation direction C1 of the wafer chuck 2.

[0031] The grinding device 1 is equipped with a mobile thickness measuring device 7 and a fixed thickness measuring device 8 as a fixed point measuring means.

[0032] The mobile thickness measuring device 7 measures the wafer thickness while moving in the radial direction on the wafer W. The mobile thickness measuring device 7 includes a sensor 71 and an arm 72 having the sensor 71 attached to the tip thereof.

[0033] The sensor 71 is a film thickness sensor that measures the thickness of the wafer W in a non-contact manner during grinding. The sensor 71 is preferably, for example, a spectral interference film thickness sensor. A spectral interference film thickness sensor is resistant to external disturbances such as vibrations and can measure the thickness of the wafer W with high accuracy. The following description will be given taking as an example a case where a spectral interference film thickness sensor is used as the sensor 71.

[0034] A sensor head (not shown) of the sensor 71 irradiates light from the sensor head toward the wafer W and receives reflected light resulting from interference between the light reflected on the upper and lower surfaces of the wafer W. The reflected light is separated by a spectroscope, and a control device 9 (described later) calculates the thickness of the wafer W based on the optical path difference between the light reflected on the upper surface of the wafer W and the light reflected on the lower surface of the wafer W.

[0035] 3, a resin light-transmitting window 73 is provided on the optical path of the sensor 71. This prevents the coolant supplied to the upper surface of the wafer W from entering the inside of the sensor 71.

[0036] The sensor 71 is also provided with an air supply port 74 connected to an external compressed air source. Compressed air supplied from the air supply port 74 is sprayed onto the upper surface of the wafer W via the air discharge port 75. This allows the coolant present in the measurement range of the sensor 71 to be removed by the air blow, thereby suppressing light scattering due to the coolant and enabling the thickness of the wafer W to be measured with high accuracy.

[0037] The arm 72 can swing around the drive shaft 76 in the radial direction of the wafer W. Specifically, as shown in FIG. 4, the arm 72 can swing so that the sensor 71 can scan from the outer periphery of the wafer W to a position where it does not interfere with the grinding wheel 31.

[0038] The fixed thickness gauge 8 measures the wafer thickness at a fixed point at a predetermined radial position on the wafer W. The fixed thickness gauge 8 is equipped with a pair of sensor heads 81 and 82. As shown in FIG. 5, the sensor head 81 is disposed so as to be able to contact the upper surface of the wafer W, and measures the height of the lower end of the sensor head 81. The sensor head 82 is disposed outside the sensor head 81, and is disposed so as to be able to contact the upper surface of the wafer chuck 2, and measures the height of the lower end of the sensor head 82. The difference between the measured values of the sensor heads 81 and 82 is the thickness of the wafer W.

[0039] The mobile thickness gauge 7 and the fixed thickness gauge 8 are disposed downstream of the grinding wheel 31 in the rotation direction C1 of the wafer chuck 2. As a result, the coolant containing sludge that passes through the grinding wheel 31 is scattered to the outside of the wafer W by the centrifugal force that accompanies the rotation of the wafer W, so that the mobile thickness gauge 7 and the fixed thickness gauge 8 can perform thickness measurements without being hindered by the sludge and coolant.

[0040] The operation of the grinding apparatus 1 is controlled by a control device 9. The control device 9 controls each of the components that make up the grinding apparatus 1. The control device 9 is configured with, for example, a CPU, a memory, etc. The functions of the control device 9 may be realized by control using software, or may be realized by operation using hardware.

[0041] Next, the operation of the grinding apparatus 1 will be described using a wafer with a diameter of 300 mm as an example.

[0042] [Processing preparation] First, the wafer W is held by suction on the wafer chuck 2, and the grinding wheel 31 is lowered to the vicinity of the wafer W. Next, the grinding wheel 31 and the wafer chuck 2 are rotated. In addition, a coolant is supplied to the upper surface of the wafer W.

[0043] The tip of sensor head 81 is placed on the wafer W, and the tip of sensor head 82 is placed on the wafer chuck 2. Sensor head 81 is placed at a position R=145 mm in a radius (R) direction coordinate system with the center of rotation of the wafer W as its origin. The control device 9 stores the difference between the sensor heads 81 and 82 before the start of grinding, i.e., the initial thickness of the wafer W (e.g., 224 μm).

[0044] The arm 72 is swung to move the sensor 71 to a position of R=145 mm (measurement position P1). Also, the supply of compressed air is started, and air blowing from the air outlet 75 toward the top surface of the wafer W is started.

[0045] [Grinding] The spindle 32 is further lowered from the state where it is in contact with the wafer W, and the grinding wheel 31 is pressed against the wafer W, thereby grinding the wafer W. The fixed thickness measuring device 8 continues to measure the thickness of the wafer W throughout the processing.

[0046] When the measurement value of the fixed thickness measuring device 8 reaches the target thickness after grinding (e.g., 206 μm), the control device 9 stops the grinding wheel 31 and the wafer chuck 2 and moves the grinding wheel 31 upward, thereby completing the grinding process.

[0047] [Shape calculation] The procedure for calculating the shape of the wafer W during grinding will be described. When the difference between the sensor heads 81 and 82 decreases by approximately 5 μm from the initial thickness, the sensor 71 measures the thickness of the wafer W at the measurement position P1 until the wafer W rotates one full revolution. The start and end of measurement by the sensor 71 are controlled in synchronization with the rotation angle θ of the motor that rotates the wafer chuck 2.

[0048] When the thickness measurement for one revolution of the wafer W at the measurement position P1 is completed, the control device 9 swings the arm 72 to move the sensor 71 to a position R=140 mm (measurement position P2), and measures the thickness of the wafer W until the wafer W rotates one revolution, similar to the measurement at the measurement position P1.

[0049] Similarly, thickness measurements of the wafer W are performed at the following positions: R = 120 mm (measurement position P3), R = 110 mm (measurement position P4), R = 80 mm (measurement position P5), R = 60 mm (measurement position P6), R = 40 mm (measurement position P7), and R = 20 mm (measurement position P8). The positional relationship of the above-mentioned measurement positions P1 to P8 is shown in FIG. 6. Note that the radial coordinates and number of measurement positions of the sensor 71 are not limited to the above-mentioned combinations, and other combinations may be used.

[0050] 7 is a graph in which the horizontal axis represents the elapsed time t (ms) with the origin being the time when measurement by mobile thickness gauge 7 was started, the left vertical axis represents the measurement values T (μm) from mobile thickness gauge 7 and fixed thickness gauge 8, and the right vertical axis represents the difference ΔT (μm) between the measurement values from mobile thickness gauge 7 and fixed thickness gauge 8. The continuous line in FIG. 7 (measurement value T1) is the measurement value from fixed thickness gauge 8, and the discontinuous line above measurement value T1 (measurement value T2) along the measurement value T1 is the measurement value from mobile thickness gauge 7. The measurement values from mobile thickness gauge 7 correspond to P1 to P8 from the left in FIG. 7.

[0051] According to the measured value T1, it can be seen that the thickness of the wafer W gradually decreases as the grinding process progresses. Furthermore, the measured value T2 indicates the thickness of one circumference of the wafer W at the measurement positions P1 to P8. Then, the shape of the wafer W can be obtained by subtracting the measured value T1 from the measured value T2.

[0052] To explain this in more detail using measurement position P1 as an example, as shown in Figure 8, at measurement position P1, the measurement point moves while the wafer W makes one revolution at the position R = 145 mm, so it is not possible to determine whether the change in measurement value T2 is due to the grinding allowance or the thickness variation within the wafer W.

[0053] On the other hand, since the fixed thickness measuring device 8 measures the thickness of the wafer W at a fixed point, the measured value T1 corresponds to the thickness decrease from the time when measurement by the mobile thickness measuring device 7 began, which corresponds to the amount of cutting allowance in the grinding process.

[0054] Therefore, by subtracting measurement value T1 from measurement value T2, the effect of the grinding allowance can be eliminated from the change in measurement value T2. The discontinuous line (T3) on the lower side in Figure 7 is measurement value T2 minus measurement value T1, and corresponds to P1 to P8 from the left in Figure 7.

[0055] Then, the control device 9 calculates the shape of the wafer W based on the measurement value T3 at the coordinates (R, θ) of the measurement point where the thickness was measured by the mobile thickness measuring device 7. Fig. 9 shows a contour diagram illustrating the shape of the wafer W calculated based on the measurement value T3 in Fig. 8. Note that, since scanning is not performed by the mobile thickness measuring device 7 between the measurement positions P1 to P8 and in the region where R<20 mm, the shape of the wafer W is predicted by referring to, for example, the shape of another wafer that has been acquired in advance.

[0056] As a result, in the grinding apparatus 1 according to this embodiment, the mobile thickness gauge 7 and the fixed thickness gauge 8 measure the thickness of the wafer W during the grinding process, and by subtracting the measurement value T1 of the fixed thickness gauge 8 from the measurement value T2 of the mobile thickness gauge 7, changes in thickness resulting from the grinding allowance are removed from the change in thickness measured by the mobile thickness gauge 7, and the shape of the wafer W can be calculated without interrupting processing. Furthermore, because the shape of the wafer W is calculated using the mobile thickness gauge 7 and the fixed thickness gauge 8, the apparatus can be constructed with a small number of parts.

[0057] Furthermore, the present invention can be modified in various ways other than those described above without departing from the spirit of the present invention, and it goes without saying that the present invention also covers such modifications. [Explanation of symbols]

[0058] 1. Grinding device 2. Wafer chuck 21 Adsorbent 3. Grinding means 31 Grinding wheel 32 Spindle 4 Index Table 5 Tilt mechanism 51 Tilt table 52...Fixed support part 53, 54...Movable support part 6 Coolant supply mechanism 61 Nozzle 7. Mobile thickness measuring instrument 71 Sensor 72 Arm 73 Translucent window 74 Air supply port 75...Air outlet 76 Drive shaft 8. Fixed thickness gauge 81, 82: Sensor head 9. Control device C1: Rotation direction (of wafer chuck) C2: Direction of rotation (of the grinding wheel) W: Wafer a1: Rotation axis (of wafer chuck) a2: Rotation axis (of the grinding wheel)

Claims

[Claim 1] A grinding apparatus for grinding an upper surface of a wafer with a grindstone, a fixed-point measuring means for measuring the thickness of the wafer at a fixed point during the wafer grinding process; a movable measuring means for measuring the thickness of the wafer by changing a measuring position in a radial direction of the wafer during the grinding process of the wafer; a control device that calculates the shape of the wafer by subtracting a decrease in the measurement value of the fixed point measuring means corresponding to the wafer removal amount from the thickness change measured by the mobile measuring means; A grinding device comprising:

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