Grinding device

Abstract

This invention provides a grinding apparatus that can efficiently perform grinding and measure wafer shape with a simple configuration that has few parts. [Solution] The grinding apparatus 1 includes a fixed thickness measuring instrument 8 that measures the thickness of the wafer W at a fixed point, a mobile thickness measuring instrument 7 that measures the thickness of the wafer W at multiple measurement positions P1 in the radial direction R of the wafer W, and a control device 9 that calculates the shape of the wafer W by subtracting the measured value T1 of the fixed thickness measuring instrument 8 from the measured value T2 of the mobile thickness measuring instrument 7.

Description

[Technical Field]

[0001] The present invention relates to a grinding apparatus for grinding wafers. [Background Art]

[0002] In the field of semiconductor manufacturing, grinding apparatuses that grind the top surface of a semiconductor wafer such as a silicon wafer (hereinafter referred to as a "wafer") to process the wafer into a desired shape are known. In recent years, with the progress of wafer thinning and the formation of through electrodes penetrating the front and back sides of wafers, there has been an increasing demand for processing wafers to a substantially uniform thickness.

[0003] In addition, when grinding a thin wafer, grinding is sometimes performed with a support substrate attached to the non-grinding surface side of the wafer via an adhesive resin. However, since variations in the thickness of the support substrate and uneven thickness of the adhesive resin are transferred to the wafer shape after grinding, it is necessary to perform sheet-to-sheet correction of the wafer thickness after taking into account the thickness non-uniformity of the support substrate and the adhesive resin.

[0004] It is necessary to perform grinding while checking the wafer thickness, but since the thickness of the wafer continues to decrease constantly during processing, if the thickness measurement position on the wafer is changed, it cannot be distinguished whether the change in the measured value is caused by the grinding allowance or by the thickness variation within the wafer.

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

[0006] Further, in the surface grinding apparatus described in Patent Document 2, three non-contact sensors arranged at predetermined intervals in the semi-radial direction of the wafer measure the thickness of the wafer being ground at fixed points, thereby measuring the shape of the wafer. [Prior Art Documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2008-264913 [Patent Document 2] Japanese Patent Application Publication No. 9-85619 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, the apparatus described in Patent Document 1 requires the grinding wheel to be moved away from the wafer when measuring the wafer thickness, which results in longer processing times and the inability to maintain continuity of the processing position before and after the processing interruption.

[0009] Furthermore, the device described in Patent Document 2 required three non-contact sensors for fixed-point measurement, which resulted in a complex device configuration.

[0010] Therefore, a technical challenge arises in order to efficiently perform grinding and measure the wafer shape with a simple configuration that has few parts. The present invention aims to solve this problem. [Means for solving the problem]

[0011] To achieve the above objective, the grinding apparatus according to the present invention is a grinding apparatus for grinding the upper surface of a wafer with a grinding wheel, comprising: a fixed measuring means for measuring the thickness of the wafer at a fixed point during the grinding process of the wafer; a plurality of radial position measuring means for measuring the thickness of the wafer at a plurality of measuring positions in the radial direction of the wafer during the grinding process of the wafer; and a control device for calculating the shape of the wafer by subtracting the measurement value of the fixed measuring means from the measurement value of the plurality of radial position measuring means.

[0012] With this configuration, multiple radial position measuring means and a fixed measuring means measure the thickness of the wafer during grinding, and the wafer shape can be calculated based on the measurements from the multiple radial position measuring means and the fixed measuring means without interrupting the process. Furthermore, because the wafer shape is calculated using multiple radial position measuring means and a fixed measuring means, the device can be constructed with a small number of parts. [Effects of the Invention]

[0013] This invention allows for the measurement of wafer thickness during grinding using multiple radial position measuring means and a fixed measuring means, and enables the calculation of wafer shape without interrupting processing based on the measurements from the multiple radial position measuring means and the fixed measuring means. Furthermore, because the wafer shape is calculated using multiple radial position measuring means and a fixed measuring means, the apparatus can be constructed with a small number of parts. [Brief explanation of the drawing]

[0014] [Figure 1] A perspective view showing a grinding device according to one embodiment of the present invention. [Figure 2] A plan view showing the grinding device. [Figure 3] A partially cutaway side view showing the internal structure of the tip of a mobile thickness measuring instrument. [Figure 4] A schematic diagram showing the oscillation range of a mobile thickness measuring instrument. [Figure 5] A schematic diagram showing the structure of a fixed-point thickness measuring instrument. [Figure 6] A side view showing the position where the mobile thickness measuring device measures wafer thickness. [Figure 7] A diagram showing the measurement results of wafer thickness. [Figure 8] A diagram illustrating the process of deriving the wafer shape from the wafer thickness measurement results. [Figure 9] Figure 7 shows the wafer shape based on the measurement results. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described with reference to the drawings. In the following, when reference is made to the number, numerical values, amounts, ranges, etc. of constituent elements, unless explicitly specified otherwise or clearly limited to a specific number in principle, the present invention is not limited to the specific number, and may be more than or less than the specific number.

[0016] In addition, when reference is made to the shapes and positional relationships of constituent elements, etc., unless explicitly specified otherwise or it is considered otherwise apparent in principle, the expression includes those substantially approximate or similar to the shapes, etc.

[0017] In addition, in the drawings, characteristic portions may be enlarged or exaggerated for facilitating understanding of features, and dimensional ratios of constituent elements are not necessarily the same as those in reality. Further, in cross-sectional views, hatching for some constituent elements may be omitted to facilitate understanding of the cross-sectional structure of the constituent elements.

[0018] Fig. 1 is a perspective view showing a grinding apparatus 1 according to an embodiment of the present invention. Fig. 2 is a plan view showing the grinding apparatus. The grinding apparatus 1 grinds the top surface of a wafer W suction-held by a wafer chuck 2 to form the wafer W into a desired shape.

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

[0020] The wafer chuck 2 is provided rotatably along a rotation direction C1 around a rotation axis a1 passing through the center of the wafer chuck 2. In order to continuously grind a plurality of wafers W, the grinding apparatus 1 includes a plurality of wafer chucks 2. The plurality of wafer chucks 2 are arranged on an index table 4 at predetermined intervals along a circumference centered on the rotation axis of the index table 4. In Fig. 2, reference numeral 10 denotes a casing that houses the grinding apparatus 1.

[0021] The wafer chuck 2 has an adsorbent body 21 made of a porous material such as alumina embedded in its upper surface. The wafer chuck 2 is equipped with a conduit (not shown) that runs through its interior and extends to the surface of the adsorbent body 21. The conduit is connected to a vacuum source, a compressed air source, or a water 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 water source is activated, the adsorption between the wafer W and the wafer chuck 2 is released.

[0022] The wafer W is held by the wafer chuck 2 by suction while mounted on a support substrate such as a bag grind tape, glass substrate, or silicon substrate. Support substrates are often used, especially as the wafer W becomes thinner and larger in diameter.

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

[0024] The grinding wheel 31 is mounted horizontally at the tip of the spindle 32. The wafer W is ground when the grinding wheel 31 is pressed against it.

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

[0026] The wafer chuck 2 is provided with a tilt mechanism 5 that tilts the rotation axis a1. The tilt mechanism 5 comprises a tilt table 51, a fixed support part 52, and two movable support parts 53 and 54.

[0027] The tilt table 51 is formed in a roughly triangular shape when viewed from above. The tilt table 51 has fixed support parts 52 and movable support parts 53 and 54 arranged concentrically around the rotation axis a1 at equal intervals.

[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 sliding 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, respectively, in accordance with the rotation of the ball screws, causing the rotation axis a1 to tilt. The movable support part 53 is positioned upstream of the fixed support part 52 in the rotation direction C1 of the wafer chuck 2. The movable support part 54 is positioned downstream of the fixed support part 52 in the rotation direction C1 of the wafer chuck 2.

[0030] The grinding apparatus 1 is equipped with 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 positioned upstream of the grinding wheel 31 in the rotation direction C1 of the wafer chuck 2.

[0031] The grinding device 1 includes a mobile thickness measuring instrument 7 and a fixed thickness measuring instrument 8 as a fixed-point measurement means.

[0032] The mobile thickness measuring device 7 measures the wafer thickness while moving radially on the wafer W. The mobile thickness measuring device 7 comprises a sensor 71 and an arm 72 with the sensor 71 at its tip.

[0033] Sensor 71 is a film thickness sensor that measures the thickness of the wafer W in a non-contact manner during grinding. For example, a spectral interference type film thickness sensor is preferred for sensor 71. Spectroscopic interference type film thickness sensors are resistant to disturbances such as vibration and can measure the thickness of the wafer W with high accuracy. The following explanation will use a spectral interference type film thickness sensor as an example.

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

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

[0036] Furthermore, the sensor 71 is provided with an air supply port 74 connected to an external compressed air source. The compressed air supplied from the air supply port 74 is sprayed onto the upper surface of the wafer W via an air outlet 75. As a result, any coolant present in the measurement range of the sensor 71 is removed by the air blow, suppressing light scattering caused by the coolant and enabling accurate measurement of the wafer W thickness.

[0037] The arm 72 is oscillating radially around the wafer W with the drive shaft 76 as the pivot point. Specifically, as shown in Figure 4, the arm 72 is oscillating so that the sensor 71 can scan from the outer edge of the wafer W to a position where it does not interfere with the grinding wheel 31.

[0038] The fixed thickness measuring device 8 measures the wafer thickness at a predetermined radial position on the wafer W. The fixed thickness measuring device 8 is equipped with a pair of sensor heads 81 and 82. As shown in Figure 5, sensor head 81 is positioned to be in contact with the upper surface of the wafer W and measures the height of its lower end. Sensor head 82 is positioned outside sensor head 81 and is provided to be in contact with the upper surface of the wafer chuck 2 and measures the height of its lower end. The difference between the measurements of sensor heads 81 and 82 is the thickness of the wafer W.

[0039] The mobile thickness measuring device 7 and the fixed thickness measuring device 8 are positioned 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 accompanying the rotation of the wafer W, so that the mobile thickness measuring device 7 and the fixed thickness measuring device 8 can measure the thickness without being hindered by the sludge and coolant.

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

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

[0042] [Processing preparation] First, the wafer W is held in place by suction in 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. Coolant is also 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 positioned at R=145mm in a radial coordinate system with the rotation center of wafer W as the origin. The control device 9 stores the difference between sensor heads 81 and 82 before grinding begins, i.e., the initial thickness of wafer W (for example, 224 μm).

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

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

[0046] When the measurement value of the fixed thickness measuring instrument 8 reaches the target thickness after grinding (for example, 206 μm), the control device 9 stops the grinding wheel 31 and the wafer chuck 2, and retracts the grinding wheel 31 upward, thereby ending the grinding process.

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

[0048] Once the measurement of the wafer W's thickness over one full rotation is complete at measurement position P1, the control device 9 moves the arm 72 to move the sensor 71 to a position R=140mm (measurement position P2), and measures the wafer W's thickness until it has rotated a full rotation, similar to the measurement at measurement position P1.

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

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

[0051] The measurement value T1 shows that the thickness of the wafer W gradually decreases as the grinding process progresses. The measurement value T2 represents the thickness of one circumference of the wafer W at measurement positions P1 to P8. By subtracting the measurement value T1 from the measurement value T2, the shape of the wafer W can be obtained.

[0052] To explain this in detail using measurement position P1 as an example, as shown in Figure 8, at measurement position P1, the measurement point moves as the wafer W completes one rotation at a position R=145mm. Therefore, it is impossible to determine whether the change in the measured value T2 is due to the amount of material removed by grinding or to variations in the thickness within the wafer W.

[0053] On the other hand, the fixed thickness measuring instrument 8 measures the thickness of the wafer W at a fixed point, so the measured value T1 corresponds to the thickness reduction from the time when the measurement by the mobile thickness measuring instrument 7 was started, which corresponds to the amount of material removed during grinding.

[0054] Therefore, by subtracting the measured value T1 from the measured value T2, the effect of the material removed by grinding can be excluded from the change in the measured value T2. The discontinuous line at the bottom of Figure 7 (T3) is obtained by subtracting the measured value T1 from the measured value T2, and corresponds to P1 to P8 from left to right in Figure 7.

[0055] The control device 9 then calculates the shape of the wafer W based on the measured value T3 at the coordinates (R, θ) of the measurement point where the mobile thickness measuring instrument 7 performed the thickness measurement. Figure 9 shows a contour map illustrating the shape of the wafer W calculated based on the measured value T3 in Figure 8. Note that scanning by the mobile thickness measuring instrument 7 is not performed between measurement positions P1 to P8 and in the region where R < 20 mm, so 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 this embodiment, the grinding apparatus 1 measures the thickness of the wafer W during grinding using a mobile thickness measuring device 7 and a fixed thickness measuring device 8. By subtracting the measured value T1 of the fixed thickness measuring device 8 from the measured value T2 of the mobile thickness measuring device 7, changes due to the grinding allowance are removed from the thickness change of the measured value T2 of the mobile thickness measuring device 7, and the shape of the wafer W can be calculated without interrupting the process. Furthermore, since the shape of the wafer W is calculated using the mobile thickness measuring device 7 and the fixed thickness measuring device 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, as long as it does not deviate from the spirit of the invention, and it goes without saying that the present invention extends to such modified forms. [Explanation of Symbols]

[0058] 1. Grinding device 2 ···wafer chuck 21 ···Adsorbent 3. Grinding methods 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 Gauge 71 ···Sensor 72 ···arm 73 ···Translucent window 74 ···Air supply port 75...Air outlet 76 ···Drive shaft 8 ···Fixed thickness measuring instrument 81, 82... Sensor head 9 ···Control device C1 ···(Wafer chuck) rotation direction C2 ···(direction of rotation of the grinding wheel) W ···wafer a1 ···(Wafer chuck) rotation axis a2 ···(The rotation axis of the grinding wheel)

Claims

[Claim 1] A grinding apparatus that grinds the upper surface of a wafer with a grinding wheel, A fixed measuring means for measuring the thickness of the wafer at a fixed point during the grinding process of the wafer, A plurality of radial position measuring means for measuring the thickness of the wafer at multiple measurement positions in the radial direction of the wafer during the grinding process of the wafer, A control device that calculates the shape of the wafer by subtracting the measurement value of the fixed measuring means from the measurement value of the plurality of radius position measuring means, A grinding device characterized by having the following features.

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