JP7703064B2 - processing equipment - Google Patents

Description

The present invention relates to a processing device for processing non-circular workpieces.

In the field of semiconductor manufacturing, back grinding is performed to grind the back side of a workpiece, such as a silicon wafer or other semiconductor wafer (hereafter referred to as the "workpiece"), to form a thin film.

As shown in Patent Document 1, a processing device for grinding the back surface of a workpiece is known 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 frictional 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.

In this type of grinding machine, 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.

Patent No. 6030265

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).

When infeed grinding such a workpiece W, that is, as shown in FIG. 9, when the grinding wheel 100 is pressed against the workpiece W while rotating the grinding wheel 100 and the workpiece W held by the chuck 101, the grinding wheel 100 cuts into the surface of the workpiece W from all angles. Therefore, the grinding resistance when the grinding wheel 100 smoothly cuts into the step 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 into the step of the workpiece so as to get caught on it (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 variation in the processed workpiece.

As a result, a technical problem arises that must be solved in order to process the workpiece to the desired thickness, and the present invention aims to solve this problem.

In order to achieve the above-mentioned object, the processing apparatus of the present invention is a processing apparatus for flattening a workpiece, and comprises a chuck that can rotate while adsorbing and holding the workpiece, and a grinding wheel attached to a grinding wheel spindle having a rotation axis parallel to the rotation axis of the chuck, the grinding wheel being pressed against the workpiece while rotating in conjunction with the rotation of the grinding wheel spindle so that the grinding wheel passes through the rotation center of the chuck, thereby flattening the workpiece, and the workpiece is adsorbed and held by the chuck in an eccentric state upstream of the offset direction of the workpiece from the rotation center of the chuck.

With this configuration, the workpiece is ground while being eccentric from the center of rotation of the chuck to the upstream side in the offset direction, and the downstream side of the workpiece in the offset direction is ground with a larger amount of grinding compared to the upstream side due to fluctuations in the contact area between the grinding wheel and the workpiece. 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 reduces the variation in thickness of the workpiece after machining.

The present invention offsets the variation in the amount of grinding that tends to cause the downstream side of the workpiece in the offset direction to be thicker than the upstream side, thereby reducing variation in the thickness of the workpiece after machining.

1 is a perspective view showing a grinding device according to an embodiment of the present invention; FIG. 2 is a plan view of the main unit shown in FIG. 1 . FIG. 2 is a side view of the main unit shown in FIG. 1 . FIG. Schematic diagram showing the direction in which the grinding wheel cuts into the workpiece surface. 1 is a plan view comparing the contact areas between the workpiece and the grinding wheel at two points in the workpiece. FIG. FIG. 4 is a diagram showing how a workpiece is ground. FIG. 1 is a schematic diagram showing the crystal structure of a workpiece surface. FIG. 11 is a plan view showing a workpiece after being ground by a conventional grinding device.

The embodiment of the present invention will be described with reference to the drawings. Note that in the following, when referring to the number, numerical value, amount, range, etc. of components, unless otherwise specified or when it is clearly limited to a specific number in principle, it is not limited to that specific number, and it may be more or less than the specific number.

In addition, when referring to the shape or positional relationship of components, etc., this includes things that are substantially similar or similar to that shape, etc., unless otherwise specified or considered in principle to be clearly different.

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

The grinding device 1 grinds the workpiece W to form a thin film. The workpiece W to be ground using the grinding device 1 is preferably a silicon wafer or the like, but is not limited to this.

The grinding device 1 includes a main unit 2 equipped with a grinding wheel 21 and a conveying unit 3 arranged below the main unit 2.

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.

The grindstone spindle 23 is housed in a groove 22b recessed in the vertical direction V on the front surface 22a of the column 22. The grindstone spindle 23 includes a saddle 23a to which the grindstone 21 is attached at its lower end, and a motor (not shown) that is provided in the saddle 23a and rotates the grindstone 21.

The linear guide 24 is a guide rail for the saddle 23a that rises and falls along the vertical direction V, and is composed of two front linear guides 24a and one rear linear guide 24b.

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

The rear linear guides 24b are arranged parallel to each other along the vertical direction V at the bottom of the groove 22b. In addition, the saddle 23a is attached to the rear linear guides 24b via a nut 25a, which will be described later.

As shown in FIG. 3, the front linear guide 24a and the rear linear guide 24b are spaced apart 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 in a plan view.

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 raises and lowers the nut 25a, and a motor 25c that rotates the ball screw 25b.

When the motor 25c is driven to rotate the ball screw 25b, the nut 25a slides in the feed direction D1 of the ball screw 25b, which is parallel to the vertical direction V, causing the saddle 23a to descend.

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

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, for example, 0.09 μm for silicon wafers and 0.15 μm for silicon carbide wafers. 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 and lowered.

The air cylinder 26 suspends the grinding wheel spindle 23 and the spindle feed mechanism 25 within 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.

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

The chuck 31 has an adsorbent 33 made of a porous material such as alumina on its upper surface, and a dense rotating table 34 in which the adsorbent 33 is embedded approximately in the center. The chuck 31 has a pipeline (not shown) that runs through the inside and reaches the surface. The pipeline 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.

The slider 32 can slide on the rail 35 by a slider drive mechanism (not shown), so that the chuck 31 and the slider 32 slide together in the transport direction D2.

The suction body 33 is formed into a shape corresponding to the workpiece W when viewed from above. The rotating table 34 is formed into a substantially circular shape when viewed from above, but the shape of the rotating table 34 is not limited to this. 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).

As shown in FIG. 4, the adsorbent 33 is eccentric from the rotation center O1 of the turntable 34; that is, when viewed from above, the center O2 of the adsorbent 33 is offset a predetermined distance from the rotation center O1 of the turntable 34. Note that the offset between the rotation center O1 of the turntable 34 and the center O2 of the adsorbent 33 can be changed as desired.

The direction in which the suction body 33 is offset from the rotation center O1 of the rotating table 34 is the upstream side of the offset direction D3 of the workpiece W. Note that, as shown in FIG. 5, "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, as shown in FIG. 5. Also, "upstream side of offset direction D3" refers to the side to which the tip of the normal vector p of the {0001} plane of the workpiece W projects onto a plane points. Also, hereinafter, "downstream side of offset direction D3" refers to the side opposite to the direction to which the tip of the normal vector p of the {0001} plane of the workpiece W projects onto a plane points.

The center O2 of the adsorption body 33 is offset from the center of rotation O1 of the rotary table 34, so that the amount of grinding in the workpiece W increases or decreases locally. For example, as shown in FIG. 6, when comparing an area S1 where the machining surface of the grindstone 21 contacts the workpiece W over a relatively wide area with an area S2 where the machining surface of the grindstone 21 contacts the workpiece W over a relatively small area, area S1 is larger than area S2.

When the grinding wheel 21 is brought into uniform contact with the workpiece W over its entire surface, 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 Figure 6, region S1 of the workpiece W after grinding is thicker than region S2.

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.

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.

The operation of the grinding device 1 is controlled by the control device 5. The control device 5 controls each of the components that make up the grinding device 1. The control device 5 is composed of, for example, a CPU, a memory, etc. The functions of the control device 5 may be realized by controlling it using software, or may be realized by operating it using hardware.

Next, the procedure for grinding the workpiece W using the grinding device 1 will be described.

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

Next, the workpiece W is attracted and held by the chuck 31 in an eccentric state in the offset direction D3 upstream from the rotation center O1 of the rotating table 34. The ball screw 25b is rotated forward, and the nut 25a and saddle 23a are slid in the feed direction D1 to lower the grinding wheel 21 to the vicinity of the workpiece W.

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

The spindle feed mechanism 25 brings 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.

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.

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 inside 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.

However, 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 upstream side of the workpiece W in the offset direction D3 tends to be thinner than the downstream side due to the crystal structure of the workpiece W, which can result in thickness variations in the workpiece W after machining.

However, when the workpiece W rotates around the rotation center O1 of the rotating table 34 while being eccentric to the upstream side of the offset direction D3 relative to the rotation center O1 of the rotating 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 above-mentioned variation in thickness of the workpiece W.

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

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 the amount of workpiece W ground is greatest. In other words, the area in which the amount of workpiece W ground increases locally 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).

In this way, the amount of grinding is increased or decreased 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 amount of grinding caused by the crystal structure of the workpiece W, thereby reducing the variation in the thickness of the workpiece W.

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 saddle 23a, thereby separating the grindstone 21 from the workpiece W and completing the grinding process.

The present invention can be modified in various ways without departing from the spirit of the invention, and it goes without saying that the present invention also covers such modifications.

1: Grinding device 2: Main unit 21: Grinding wheel 22: Column 22a: Front surface 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: Chuck 32: Slider 33: Adsorption body 34: Rotary table 35: Rail 4: In-process gauge 5: Control device W: Workpiece

Claims (1)

A processing device for flattening a workpiece,
a chuck that can rotate while suction-holding the workpiece;
a grindstone attached to a grindstone spindle having a rotation axis parallel to the rotation axis of the chuck, the grindstone being pressed against the workpiece while rotating with the rotation of the grindstone spindle so that the grindstone passes through the rotation center of the chuck, thereby machining the workpiece into a flat surface;
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 an offset direction of the workpiece.