Patent Application
20240399529
The present invention relates to a polishing apparatus and a polishing method for polishing a workpiece that is, for example, a wafer made of silicon carbide (SiC) or the like.
For polishing of a surface of a wafer made of a high hardness material such as silicon carbide (SiC) (hereinafter, may be simply referred to as “workpiece”), there has been known a method of providing a polishing composition on the surface. In PTL 1 (WO2019/138846), a polishing composition is used that includes water, abrasive grain, an oxidant, and a polishing accelerator (polishing accelerator including at least one type of metal salt selected from the group consisting of alkaline metal salts and alkaline earth metal salts). The oxidant modifies the surface of the workpiece, and the modified layer is removed through friction with the abrasive grain and a polishing pad and the like. The metal salt exhibits catalytic effect of promoting the modification and the removal. With these features, a polishing rate is improved for the polishing of the surface of the workpiece made of the high hardness material.
The surface of the workpiece has a form with recess and protrusion shapes randomly distributed. Thus, with the polishing method in which the polishing composition is uniformly provided on the surface of the workpiece as described in PTL 1, the surface of the workpiece cannot be polished in consideration of the distribution of the recesses and the protrusions. More specifically, there has been a problem in that the polishing cannot be performed with short-time processability improved locally (spot by spot) for only a predetermined portion of the surface of the workpiece (the protrusions on the workpiece surface, for example).
In view of this, the present invention has been made to solve the problem described above, and an object of the present invention is to provide a polishing apparatus and a polishing method with which polishing can be performed with processability improved locally (spot by spot) for only a predetermined portion of a surface of a workpiece.
A polishing apparatus according to the present invention is a polishing apparatus that polishes a workpiece under the following requirements: the polishing apparatus including a cavitation generating emission device, the cavitation generating emission device having an inner tube in which a first liquid flow flows, the inner tube including a cavitation generating unit, the cavitation generating emission device being configured to generate cavitation in the first liquid flow and make the first liquid flow collide with the workpiece.
A polishing method according to the present invention is a polishing method for polishing a workpiece under the following requirements: the polishing method including a cavitation generating emission step of generating cavitation in a first liquid flow and causing the first liquid flow to collide with the workpiece, and a polishing step of then polishing the workpiece.
According to the present invention, the surface modification (oxidation) can be implemented on the surface of the workpiece by making the first liquid flow including the cavitation collide with the surface of the workpiece, so that the hardness can be reduced. Thus, the polishing can be performed with the short-time processability improved locally (spot by spot) only for a predetermined portion of the surface of the workpiece.
Embodiments of the present invention will be described below in detail with reference to the drawings.
First of all, the polishing apparatus 10 according to the present embodiment includes four polishing heads 12, three surface plates 14, and one cavitation generating emission device 50 as illustrated in
Meanwhile, the workpiece W, which is the processing target, is a substrate (a disk-shaped wafer for example) formed using what can be referred to as a material difficult to process such as silicon carbide (SiC) for example, and its outer diameter and thickness are not particularly limited (for example, the outer diameter is about several centimeters to several tens of centimeters, and the thickness is about several micrometers to several millimeters). More specifically, the workpiece W is a material oxidized due to the collision of the first liquid flow A including the cavitation. In the present embodiment, a case is described where the workpiece W is made of silicon carbide (SiC).
Each of the polishing heads 12 according to the present embodiment includes a head main body 20, a holding plate 22, a driving device 26, and a pressure adjustment mechanism 28. As illustrated in
The holding plate 22 is formed with two (upper and lower) plates 22a and 22b fixed, and an air chamber 22d is formed between the two (upper and lower) plates 22a and 22b. Multiple through holes 22c communicating with the air chamber 22d are formed in the lower plate 22b. Furthermore, a backing material (not illustrated) made of a porous elastic material is attached to the lower surface side of the lower plate 22b. The air in the air chamber 22d is sucked by an air suction device (not illustrated) to achieve vacuum (negative pressure) in the air chamber, resulting in suction effect on the backing material lower surface side through the through holes 22c. Thus, the workpiece W can be sucked and held on the lower surface side of the holding plate 22.
The workpiece W may be held by the holding plate 22 by means of surface tension of a liquid (water for example).
The top plate 20a according to the present embodiment is provided with a hollow head shaft 18. A configuration is employed in which when the head shaft 18 is rotated by a rotation driving device (not illustrated), the polishing head 12 rotates about the rotation axis of the head shaft 18.
A space surrounded by the top plate 20a, the side wall 20b, and the holding plate 22 (22a) is divided by a partitioning plate 25 into an atmospheric chamber 24a on the upper side and a pressurized chamber 24b on the lower side.
The polishing head 12 is coupled to the vertical movement driving device (not illustrated). Thus, a configuration is achieved in which the holding plate 22 (that is, the workpiece W) is moved toward or away from the polishing pad 16.
Reference numeral 26 denotes an air cylinder that is an example of a driving device. The air cylinder 26 has a cylinder main body fixed on the partitioning plate 25 in the atmospheric chamber 24a, and has a rod extending through the through hole of the partitioning plate 25 and in the pressurized chamber 24b. A configuration is employed in which the cylinder of the air cylinder 26 comes into contact with the upper surface of the upper plate 22a with a pressing pad (not illustrated) provided in between. The air cylinder 26 can locally press multiple portions at least in a circumference direction on the upper surface of the upper plate 22a. For example, the air cylinders 26 are formed as one air cylinder 26 that presses the center portion of the upper plate 22a, and four air cylinders 26 each provided at a 90° phase in plan view to be in contact with the outer circumference portion of the upper plate 22a. Each of the air cylinders 26 is coupled to a first control unit 32. The number and the arrangement of the air cylinders 26 are not limited to these. With the air cylinders 26 provided, the distribution of the pressure of the workpiece W against the polishing pad 16 can be adjusted.
As illustrated in
The surface plate 14 according to the present embodiment is placed on a table 34 as illustrated in
Each table 34 is rotatably supported by a rotation driving device 38, using a bearing 36. A configuration is employed in which a shaft portion 34a of the table 34 is coupled to the rotation driving device 38, and is rotated by the rotation driving device 38 to make the surface plate 14 and the polishing pad 16 rotate within a horizontal plane. At the same time, the polishing head 12 is rotated, so that the lower surface of the workpiece W can be polished.
The polishing apparatus 10 according to the present embodiment has a configuration including a slurry supply unit not illustrated. The slurry supply unit provides slurry onto each of the polishing pads 16. As described below, the polishing apparatus 10 according to the present embodiment includes, for example, the surface plates 14 for respectively performing rough polishing, intermediate polishing, and finish polishing in this order. Thus, slurry corresponding to each of the polishing processes is provided to each of the surface plates 14. With the slurry supply unit provided, the polishing rate of the workpiece W can be improved.
Next, the arrangement of the polishing heads 12, the surface plates 14, and the cavitation generating emission device 50 will be described. While the arrangement of the polishing heads 12 and the surface plates 14 is not limited at all, and the numbers of the polishing heads 12 and the surface plates 14 are not limited, these members may be arranged as follows for example.
The temporary stand 70 is provided with the cavitation generating emission device 50. The cavitation generating emission device 50 is coupled with an orthogonal driving device 60 with a forward end portion 54g, described below, pointing the upper surface (that is, toward the lower surface of the workpiece W held by the polishing heads 12). The orthogonal driving device 60 is configured to be capable of moving the cavitation generating emission device 50 in an X-axis direction, a Y-axis direction, and a Z-axis direction for example. With this configuration, the liquid flow (a mixed flow of a first liquid flow A and a second liquid flow B) including cavitation can collide with a predetermined portion of the surface of the workpiece W. The cavitation generating emission device 50 will be described in detail in (Cavitation generating emission device).
Thus, the back surface of the workpiece W sucked and held by the polishing head 12 (corresponding to the polishing head 12 in a lower portion in
Next, the cavitation generating emission device 50 according to the present embodiment includes an inner tube 54 having a small diameter and a first outer tube 52 having a larger diameter than the inner tube 54 as illustrated in
The inner tube 54 includes a cavitation generating unit 54a and a first flow path 54b. The first flow path 54b communicates with a first pipe 80. The first liquid flow A from a liquid source (which is not illustrated and is a water source for example) of a liquid supply unit 84 is adjusted by a second control unit 86 to be in a predetermined amount, at a predetermined speed and at a predetermined pressure, and flows into the first pipe 80. Next, the first liquid flow A flows into the first flow path 54b from the first pipe 80. Next, the first liquid flow A passes through the cavitation generating unit 54a. The cavitation generating unit 54a includes a third tapered pipe portion 54c having a diameter decreasing toward the forward end portion 54g, a first tapered pipe portion 54d having a diameter decreasing toward the forward end portion 54g to be even smaller than that of the third tapered pipe portion 54c, a parallel portion 54e having the same diameter as the small diameter portion of the first tapered pipe portion 54d, and a second tapered pipe portion 54f having a diameter increasing toward the forward end portion 54g. A configuration is employed in which the first liquid flow A is squeezed in the third tapered pipe portion 54c and the first tapered pipe portion 54d to have a higher flow rate (that is, pressure decreased), passes through the parallel portion 54e, and in the second tapered pipe portion 54f, has the flow rate lowered (that is, pressure increased) and, at the same time, has the cavitation produced therein. Then, the first liquid flow A with the cavitation produced therein is discharged from the forward end portion 54g. The shape of the inner tube 54 is preferably changed based on the condition for producing the cavitation. For example, a configuration may be employed in which the cavitation generating unit 54a does not include one (or both) of the third tapered pipe portion 54c and the parallel portion 54e, and includes at least the first tapered pipe portion 54d and the second tapered pipe portion 54f.
The first outer tube 52 includes the second flow path 52a through which the second liquid flow B flows. The second flow path 52a includes a fourth tapered tube 52b and a communication portion 52c. A gap 52d surrounded by the fourth tapered tube 52b and the forward end portion 54g also has a squeezed shape, meaning that the second liquid flow B has a higher flow rate (that is, pressure decreased) in the gap 52d.
The cavitation generating emission device 50 according to the present embodiment includes a second outer tube 56. The second outer tube 56 has a communication portion 56a fit in the communication portion 52c. The second outer tube 56 communicates with a second pipe 82. The second liquid flow B from the liquid source (which is not illustrated and is a water source for example) of the liquid supply unit 84 is adjusted by the second control unit 86 to be in a predetermined amount, at a predetermined speed and at a predetermined supply pressure, and flows into the second pipe 82. Next, the second liquid flow B flows into the second outer tube 56 from the second pipe 82. Then, the second liquid flow B flows into the gap 52d through the inner diameter of the second outer tube 56.
The liquid supply unit 84 is configured to include a valve, a pump, a pressure adjustment mechanism, and the like (none of which is illustrated) as appropriate.
With the configuration described above, the cavitation generating emission device 50 discharges the first liquid flow A covered by the second liquid flow B. Thus, the cavitation is confined in the first liquid flow and the cavitation can be prevented from collapsing, so that the cavitation can reliably collide with a predetermined portion of the surface of the workpiece W.
The first liquid flow A flowing through the inner tube 54 (first flow path 54b) preferably has a higher flow rate than the second liquid flow B flowing through the first outer tube 52 (second flow path 52a). Thus, the cavitation can be more effectively prevented from collapsing, so that the cavitation can reliably collide with a predetermined portion of the surface of the workpiece W. The supply pressure for supplying the first liquid flow A from the liquid supply unit 84 is preferably set to be higher than the supply pressure for supplying the second liquid flow B from the liquid supply unit 84. Thus, the first liquid flow A flowing through the first pipe 80 preferably has a higher flow rate than the second liquid flow B flowing through the second pipe 82. The supply pressure is a pressure for supplying the liquid flows A and B respectively into the pipes 80 and 82 using a pump (not illustrated) or the like of the liquid supply unit 84, meaning that it is different from the pressure of the liquid flows A and B.
The configuration of the polishing apparatus 10 according to the present embodiment is described above. The polishing apparatus 10 can also be used to perform a polishing method according to the present embodiment. Specifically, the orthogonal driving device 60 is operated to dispose the cavitation generating emission device 50 immediately below a predetermined portion of the workpiece W (for example, a protrusion on the surface of the workpiece W). Then, the liquid flows A and B respectively flow in the inner tube 54 and the second outer tube 56. Thus, the first liquid flow A flows in the inner tube 54 (first flow path 54b), and the second liquid flow B flows in the first outer tube 52 (second flow path 52a). Next, a cavitation generating emission step is performed in the cavitation generating unit 54a, in which the cavitation is generated in the first liquid flow A, and the first liquid flow A collides with the predetermined portion of the workpiece W. In this process, the first liquid flow A is discharged while being covered by the second liquid flow B. The first liquid flow A preferably flows in the inner tube 54 (first flow path 54b) at a higher flow rate than the second liquid flow B flowing in the first outer tube 52 (second flow path 52a). Thus, the supply pressure for the first liquid flow A may be set to be a value higher than the supply pressure for the second liquid flow B as appropriate, in accordance with the cavitation generation condition. Thus, the first liquid flow A preferably flows in the first pipe 80 at a higher flow rate than the second liquid flow B flowing in the second pipe 82. Then, the vertical movement driving device (not illustrated) makes the polishing pad 16, attached to the surface plate 14, press the surface modified workpiece W sucked and held by the polishing head 12. Then, the polishing head 12 and the polishing pad 16 are rotated in directions opposite to each other, to move (slide) relative to each other (polishing step). Thus, the surface of the workpiece W can be polished in consideration of the distribution of the recesses and the protrusions on the workpiece W and with the short-time processability improved. Preferably, the cavitation generating emission step includes a step of oxidizing the surface of the workpiece W by making the first liquid flow A collide with the predetermined portion of the workpiece W. More preferably, the cavitation generating emission step includes a step of making the second liquid flow B flow and discharging the first liquid flow A including the cavitation while being covered by the second liquid flow B. More preferably, the first liquid flow A is at lower pressure than the second liquid flow B.
As an example, the surface of the workpiece W made of silicon carbide (SiC) was polished after the surface modification (oxidation) performed by the cavitation generating emission device 50 of the polishing apparatus 10 according to the present embodiment.
First of all, qualitative analysis was performed, using X-ray photoelectron spectroscopy (XPS), on the predetermined portion of the workpiece W before being irradiated with the cavitation (that is, the mixed flow of the first liquid flow A and the second liquid flow B), and on the predetermined portion of the workpiece W after being irradiated with the cavitation. ESCALAB250 manufactured by VG Scientific was used as the device used.
The results are illustrated in
Next,
Next, the state of the surface before and after the polishing was evaluated for three predetermined portions of the workpiece W oxidized, using a surface roughness meter.
As described above, according to the present invention, a predetermined portion of the workpiece W is polished after local (spot-by-spot) surface modification (oxidation), whereby the distribution of recesses and protrusions on the workpiece W can be taken into consideration, and the short-time processability can be improved.
Note that the present invention is not limited to the embodiment described above, and can be modified in various ways without departing from the scope of the present invention. For example, the polishing apparatus 10 may be a double-sided polishing apparatus.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-086390 | May 2022 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2023/013752 | 4/3/2023 | WO |
