Processing device

Abstract

To provide a processing device for processing workpiece to a desired thickness.SOLUTION: A grinding device 1 for in-feed grinding workpiece W includes: a chuck 31 which is rotatable in a state of sucking and holding the workpiece W; and a grindstone 21 which is pressed against the workpiece W while rotating so as to pass through a center of rotation of the chuck 31, and grinds the workpiece W. When the workpiece W is in-feed ground, the workpiece W is suck and held on the chuck 31 in a state of being decentered to the upstream side in the offset direction of the workpiece W from the center of rotation of the chuck 31.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a machining apparatus for machining a non-circular workpiece. [Background technology]

[0002] 2. Description of the Related Art In the field of semiconductor manufacturing, back grinding is performed to grind the back surface of a semiconductor wafer such as a silicon wafer (hereinafter referred to as a "workpiece") to form a thin film.

[0003] As shown in Patent Document 1, a known processing device for grinding the back surface of a workpiece is one in which a spindle feed mechanism with a grinding wheel attached to its lower end is suspended from a constant pressure cylinder, and when the friction force acting on the grinding wheel cutting into the workpiece is higher than a predetermined value, the constant pressure cylinder raises the spindle and spindle feed mechanism vertically.

[0004] In such grinding machines, if the frictional force acting on the grinding wheel becomes excessive, the constant pressure cylinder temporarily raises the spindle and spindle feed mechanism, so that the workpiece is ground in a ductile mode without excessive contact between the grinding wheel and the workpiece, allowing the workpiece to be ground stably without damaging it. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6030265 Summary of the Invention [Problem to be solved by the invention]

[0006] As shown in Figure 8, in order to reduce crystal defects, an epitaxial film is formed on a workpiece W such as a silicon wafer with an off-angle of about 1 to 4 degrees, and the surface of the workpiece W is inclined by the off-angle with respect to the {0001} plane (basal plane).

[0007] When infeed grinding such a workpiece W, that is, when grinding by pressing the grinding wheel 100 against the workpiece W while rotating the grinding wheel 100 and the workpiece W held by the chuck 101 as shown in Figure 9, the grinding wheel 100 cuts into the surface of the workpiece W from all angles, and therefore the grinding resistance when the grinding wheel 100 smoothly cuts into the steps of the workpiece W (the grinding wheel cuts from the upstream side to the downstream side in the offset direction) is smaller than the grinding resistance when the grinding wheel cuts so as to catch on the steps of the workpiece (the grinding wheel cuts from the downstream side to the upstream side in the offset direction).As a result, the upstream side of the workpiece W in the offset direction tends to be thinner than the downstream side, resulting in a problem of thickness variations in the workpiece after processing.

[0008] Therefore, a technical problem arises that must be solved in order to process the workpiece to the desired thickness, and an object of the present invention is to solve this problem. [Means for solving the problem]

[0009] In order to achieve the above object, the processing device of the present invention is a processing device for flattening a workpiece, and comprises a chuck that can rotate while holding the workpiece by suction, and a grinding wheel that is pressed against the workpiece while rotating so as to pass through the center of rotation of the chuck, thereby flattening the workpiece, and the workpiece is held by the chuck by suction while being eccentric to the upstream side of the center of rotation of the chuck in the offset direction of the workpiece.

[0010] With this configuration, the workpiece is ground while eccentric to the upstream side in the offset direction from the center of rotation of the chuck, and the contact area between the grinding wheel and the workpiece varies, causing the downstream side of the workpiece in the offset direction to be ground with a larger amount of grinding than the upstream side.This offsets the variation in the amount of grinding that tends to make the downstream side of the workpiece in the offset direction thicker than the upstream side, and therefore reduces the variation in thickness of the workpiece after processing. [Effects of the Invention]

[0011] The present invention can reduce variations in thickness of the workpiece after machining by offsetting variations in the amount of grinding that tend to occur on the downstream side in the offset direction of the workpiece compared to the upstream side. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view showing a grinding device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a plan view of the main unit shown in FIG. 1. [Figure 3] FIG. 2 is a side view of the main unit shown in FIG. 1. [Figure 4] FIG. [Figure 5] Schematic diagram showing the direction in which the grinding wheel cuts into the workpiece surface. [Figure 6] A plan view comparing the contact areas between the workpiece and the grinding wheel at two locations within the workpiece. [Figure 7] FIG. 2 is a diagram showing how a workpiece is ground. [Figure 8] Schematic diagram showing the crystal structure of the workpiece surface. [Figure 9] FIG. 10 is a plan view showing a workpiece after being ground by a conventional grinding device. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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.

[0014] 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.

[0015] In addition, the drawings may exaggerate characteristic parts to make the features easier to understand, and the dimensional ratios of the components may not be the same as in reality.

[0016] The grinding apparatus 1 grinds a workpiece W to form a thin film. The workpiece W to be ground using the grinding apparatus 1 is preferably a silicon wafer or the like, but is not limited thereto.

[0017] The grinding device 1 includes a main unit 2 having a grinding wheel 21 and a transport unit 3 disposed below the main unit 2.

[0018] The main unit 2 includes an arch-shaped column 22, a grinding wheel spindle 23 to which a grinding wheel 21 is attached, three linear guides 24 that support the grinding wheel spindle 23 so that it can slide in the vertical direction V, and a spindle feed mechanism 25 that raises and lowers the grinding wheel spindle 23 in the vertical direction V.

[0019] The grinding wheel spindle 23 is housed in a groove 22b recessed in the vertical direction V in the front surface 22a of the column 22. The grinding wheel spindle 23 includes a saddle 23a having the grinding wheel 21 attached to its lower end, and a motor (not shown) that is provided in the saddle 23a and rotates the grinding wheel 21.

[0020] The linear guide 24 is a guide rail for the saddle 23a that moves up and down along the vertical direction V, and is composed of two front linear guides 24a and one rear linear guide 24b.

[0021] The front linear guides 24a are disposed on the edge of the groove 22b in front of the column 22, and are provided parallel to each other along the vertical direction V. In addition, the saddle 23a is directly attached to the front linear guides 24a.

[0022] The rear linear guides 24b are provided in parallel to each other at the bottom of the groove 22b along the vertical direction V. A saddle 23a is attached to the rear linear guide 24b via a nut 25a, which will be described later.

[0023] As shown in Figure 3, the front linear guide 24a and the rear linear guide 24b are arranged at a distance from each other so that the center of gravity G of the grinding wheel spindle 23 is located within the triangle T formed by the front linear guide 24a and the rear linear guide 24b when viewed in a plane.

[0024] The spindle feed mechanism 25 includes a nut 25a that connects the saddle 23a and the rear linear guide 24b, a ball screw 25b that moves the nut 25a up and down, and a motor 25c that rotates the ball screw 25b.

[0025] When the motor 25c is driven to rotate the ball screw 25b, the nut 25a slides in a feed direction D1 of the ball screw 25b parallel to the vertical direction V, and the saddle 23a moves down.

[0026] The main unit 2 is provided with air cylinders 26. The air cylinders 26 are provided on both sides of the spindle feed mechanism 25 in the horizontal direction H. The air cylinders 26 are of a known configuration including a cylinder, a piston, a piston rod, a compressor, etc., which are not shown.

[0027] The driving pressure of the air cylinder 26 is set to a value equal to or less than the value corresponding to the frictional force acting on the grinding wheel 21 when the grinding wheel 21 cuts into the workpiece W by the critical cutting depth (Dc value). The Dc value differs depending on the material of the workpiece W, and is 0.09 μm for a silicon wafer and 0.15 μm for a silicon carbide wafer, for example. Furthermore, by adjusting the pressure (air pressure) of the compressed air supplied to the air cylinder 26, the pressure with which the air cylinder 26 presses the grinding wheel 21 against the workpiece W via the spindle feed mechanism 25 can be adjusted, and the position (height position) of the grinding wheel 21 in the vertical direction V can be raised or lowered.

[0028] The air cylinder 26 suspends the grinding wheel spindle 23 and the spindle feed mechanism 25 in the groove 22b, and the piston rod of the air cylinder 26 is connected to the motor 25c. By providing the air cylinders 26 on both sides of the spindle feed mechanism 25 in the horizontal direction H, the spindle feed mechanism 25 is prevented from tilting in the horizontal direction H when it moves up and down.

[0029] The transport unit 3 includes a chuck 31 capable of suction-holding the workpiece W, and a slider 32 on which the chuck 31 is placed.

[0030] The chuck 31 has an adsorbent 33 made of a porous material such as alumina on its upper surface, and a dense rotary table 34 with the adsorbent 33 embedded in the approximate center. The chuck 31 has a conduit (not shown) that runs through the interior and extends to the surface. 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 workpiece W placed on the adsorbent 33 is adsorbed and held by the adsorbent 33. When the compressed air source or water supply source is activated, the adsorption between the workpiece W and the adsorbent 33 is released.

[0031] The slider 32 is slidable on the rail 35 by a slider drive mechanism (not shown), whereby the chuck 31 and the slider 32 slide together in the conveying direction D2.

[0032] The attraction body 33 is formed in a shape corresponding to the workpiece W when viewed from above. Furthermore, the rotary table 34 is formed in a substantially circular shape when viewed from above, but the shape of the rotary table 34 is not limited to this. Furthermore, the chuck 31 can be rotated around a vertical axis passing through the rotation center O1 of the chuck 31 by a servo motor (not shown).

[0033] 4, the adsorber 33 is eccentric from the rotation center O1 of the turntable 34. In other words, when viewed from above, the center O2 of the adsorber 33 is offset a predetermined distance from the rotation center O1 of the turntable 34. The offset amount between the rotation center O1 of the turntable 34 and the center O2 of the adsorber 33 can be changed as desired.

[0034] The direction in which the attraction body 33 is offset from the rotation center O1 of the turntable 34 is the upstream side of the offset direction D3 of the workpiece W. As shown in FIG. 5, the "offset direction D3" refers to the direction from the tip to the base end of the vector obtained by projecting the normal vector p of the {0001} plane of the workpiece W onto a plane. The "upstream side of the offset direction D3" refers to the side toward which the tip of the normal vector p of the {0001} plane of the workpiece W onto a plane faces. Hereinafter, the "downstream side of the offset direction D3" refers to the side opposite to the direction toward which the tip of the normal vector p of the {0001} plane of the workpiece W onto a plane faces.

[0035] The center O2 of the adsorption body 33 is disposed offset from the rotation center O1 of the rotary table 34, thereby locally increasing or decreasing the amount of grinding within the workpiece W. For example, as shown in Fig. 6, when comparing an area S1 where the processing surface of the grinding wheel 21 contacts the workpiece W over a relatively wide area with an area S2 where the processing surface of the grinding wheel 21 contacts the workpiece W over a relatively small area, the area S1 is larger than the area S2.

[0036] When the grinding wheel 21 is brought into uniform contact with the entire surface of the workpiece W, as the contact area between the workpiece W and the grinding wheel 21 increases, the amount of workpiece W ground decreases, and the workpiece W becomes thicker after grinding. Therefore, when comparing the thicknesses in regions S1 and S2 shown in Fig. 6, in the workpiece W after grinding, region S1 is thicker than region S2.

[0037] In this way, the workpiece W vacuum-adsorbed onto the chuck 31 is transported by the slider 32 to below the grinding wheel 21 before grinding, and is transported from below the grinding wheel 21 to the rear of the main unit 2 after grinding.

[0038] The grinding device 1 is provided with an in-process gauge 4 that measures the thickness of the workpiece W. The in-process gauge 4 measures the thickness of the workpiece W during processing.

[0039] The operation of the grinding apparatus 1 is controlled by a control device 5. The control device 5 controls each of the components that make up the grinding apparatus 1. The control device 5 is configured with, for example, a CPU, a memory, etc. The functions of the control device 5 may be realized by control using software, or may be realized by operation using hardware.

[0040] Next, a procedure for grinding the workpiece W using the grinding device 1 will be described.

[0041] First, the offset direction D3 of the workpiece W is measured using a known X-ray diffraction device.

[0042] Next, the workpiece W is attracted and held by the chuck 31 in a state where it is eccentric to the upstream side in the offset direction D3 with respect to the rotation center O1 of the rotary table 34. In addition, the ball screw 25b is rotated forward, and the nut 25a and the saddle 23a are slid in the feed direction D1, so that the grinding wheel 21 is lowered to the vicinity of the workpiece W.

[0043] Next, the grindstone 21 and the chuck 31 are rotated. For example, the rotation speed of the grindstone spindle 23 is set to 2000 rpm, and the rotation speed of the chuck 31 is set to 300 rpm. The grit size of the grindstone 21 is, for example, #8000.

[0044] The spindle feed mechanism 25 moves the grinding wheel spindle 23 close to the workpiece W, and grinding begins when the grinding wheel 21 is seated on the workpiece W. For example, the feed speed of the spindle feed mechanism 25 is set to 0.4 μm / s.

[0045] The grinding process is performed by ductile mode grinding of the workpiece W in a so-called floating state, in which the abrasive grains of the grinding wheel 21 do not come into excessive contact with the workpiece W during the grinding process.

[0046] Specifically, the grinding wheel spindle 23 performs grinding while pressing the grinding wheel 21 against the workpiece W with its own weight (e.g., 20 kg), and when the frictional force acting on the grinding wheel 21 is transmitted to the piston rod, the piston is raised so as to push back the compressed air filled in the cylinder of the air cylinder 26. Therefore, if the grinding wheel 21 attempts to cut deeper than the desired grinding amount (e.g., Dc value) and the frictional force acting on the grinding wheel 21 becomes excessive, the grinding wheel spindle 23 and spindle feed mechanism 25 are temporarily raised. This prevents the grinding wheel 21 from cutting deeper than the Dc value.

[0047] In infeed grinding, in which the grinding wheel 21 is pressed against the workpiece W while rotating the grinding wheel 21 and the workpiece W, the workpiece W is ground. Due to the crystalline structure of the workpiece W, the upstream side in the offset direction D3 tends to be thinner than the downstream side, which can result in thickness variations in the workpiece W after processing.

[0048] However, when the workpiece W rotates around the rotation center O1 of the rotary table 34 while being eccentric to the upstream side of the offset direction D3 relative to the rotation center O1 of the rotary table 34, the contact area between the grinding wheel 21 and the workpiece W changes according to the rotation angle of the chuck 31, thereby reducing the thickness variation of the workpiece W described above.

[0049] Specifically, as shown in Figures 7(a) to (d), when the rotation angle of the chuck 31 is changed to Θ degrees, (Θ+90) degrees, (Θ+180) degrees, and (Θ+270) degrees, the contact area between the grinding wheel 21 and the workpiece W (the range indicated by the arrow in Figure 7) is compared. When the rotation angle of the chuck 31 is Θ degrees, the contact area between the grinding wheel 21 and the workpiece W is the widest, and therefore the amount of workpiece W ground is the smallest.

[0050] On the other hand, when the rotation angle of the chuck 31 is (Θ+180) degrees, the contact area between the grinding wheel 21 and the workpiece W is smallest, and therefore the amount of workpiece W ground is greatest. In other words, the range in which the amount of workpiece W ground locally increases is set downstream of the offset direction D3 of the workpiece W. Note that the arrows (a) to (d) in the figure indicate the direction in which the grinding wheel 21 cuts into the workpiece W in Figures 7(a) to (d).

[0051] In this way, the grinding amount increases or decreases according to the change in the contact area between the grinding wheel 21 and the workpiece W, so as to offset the variation in the grinding amount caused by the crystalline structure of the workpiece W, thereby reducing the variation in the thickness of the workpiece W.

[0052] Then, when the measurement value of the in-process gauge 4 reaches the finishing thickness of the workpiece W, the ball screw 25b is rotated in the reverse direction to raise the nut 25a and the saddle 23a, thereby separating the grinding wheel 21 from the workpiece W and completing the grinding process.

[0053] It should be noted that the present invention can be modified in various ways 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]

[0054] 1: Grinding equipment 2: Main unit 21: Grindstone 22: Column 22a:Front 22b: Groove 23: Grinding wheel spindle 23a: Saddle 24: Linear guide 24a: Front linear guide 24b: Rear linear guide 25: Spindle feed mechanism 25a: Nut 25b: Ball screw 25c: Motor 26: Air cylinder 3: Transport unit 31: Zipper 32: Slider 33: Adsorbent 34: Rotating table 35: Rail 4: In-process gauge 5: Control device W: Work

Claims

[Claim 1] A processing device for flattening a workpiece, a chuck that can rotate while suction-holding the workpiece; a grinding wheel that is pressed against the workpiece while rotating so as to pass through the rotation center of the chuck, and that flattens the workpiece; Equipped with The processing device is characterized in that the workpiece is attracted and held by the chuck in an eccentric state from the center of rotation of the chuck to the upstream side in the offset direction of the workpiece.

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