Method for polishing SiC wafers

Abstract

Easily polishes the edge surfaces of SiC wafers. [Solution] The method for polishing a SiC wafer 10 involves placing the plate surface 11 of the SiC wafer 10 on a stage 20, oxidizing the end face 12 of the SiC wafer 10 to form an SiO2 layer 15 on the surface of the end face 12, arranging an abrasive material 50 opposite the end face 12 of the SiC wafer 10, and rotating the SiC wafer 10 around a central axis P1 to polish and remove the SiO2 layer 15 with the abrasive material 50.

Description

Technical Field

[0001] This technology relates to a method for polishing the end face of a SiC wafer.

Background Art

[0002] Silicon carbide (SiC), a compound semiconductor material composed of silicon (Si) and carbon (C), is expected to be utilized as a power semiconductor material that exceeds the limitations of conventional Si. When SiC is used, a power semiconductor device that is smaller, more energy-efficient, and has excellent withstand voltage characteristics and high-temperature operation characteristics compared to Si can be realized.

[0003] On the other hand, since SiC is extremely hard and brittle compared to Si, it is difficult to mechanically polish it in a short time using the same abrasive as Si when processing it as a wafer (substrate). In addition, if diamond with high hardness is used as the abrasive for polishing, the cost will be high. Therefore, methods for improving the polishing rate of SiC wafers and the smoothness of the polished surface have been proposed, and an example thereof is disclosed in Patent Documents 1 and 2.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The polishing methods of Patent Documents 1 and 2 are easy to apply when the surface to be polished is the plate surface (wafer surface) of the SiC wafer. However, in the polishing of the end face (edge portion), it is difficult to apply because the ease of polishing is different between the plate surface side of the Si face where Si atoms are exposed and the plate surface side of the C face where C atoms are exposed. In fact, Patent Documents 1 and 2 do not mention the polishing of the end face.

[0006] The technology described in this specification was developed in consideration of the above-mentioned circumstances, and aims to facilitate the polishing of the end faces of SiC wafers. [Means for solving the problem]

[0007] The method for polishing a SiC wafer related to the technology described in this specification involves placing the surface of a SiC wafer on a stage, oxidizing the end face of the SiC wafer to form an SiO2 layer on the surface of the end face, arranging an abrasive material opposite the end face of the SiC wafer, and rotating the SiC wafer around its central axis to polish and remove the SiO2 layer with the abrasive material.

[0008] Furthermore, the stage is conductive, the SiC wafer is electrically connected to the stage, and the process of forming the SiO2 layer includes an anodizing process, in which an electrode member is placed at a position facing the end face of the SiC wafer, an electrolytic solution containing an electrolyte is filled between the electrode member and the end face of the SiC wafer facing it, the stage is used as the anode and the electrode member as the cathode, and the end face of the SiC wafer exposed to the electrolytic solution is anodized to form the SiO2 layer on the surface of the end face.

[0009] Furthermore, the plate surface of the SiC wafer may be placed on the stage so as to be aligned with the vertical direction, the electrode member that will serve as the cathode may be placed in a tank for storing the electrolytic solution below the SiC wafer, and the end face of the SiC wafer may be immersed in the electrolytic solution in the tank.

[0010] Furthermore, the step of forming the SiO2 layer may include an irradiation step, in which at least one of a laser, UV, or plasma is irradiated onto the end face of the SiC wafer to form the SiO2 layer on the surface of the end face.

[0011] Furthermore, the thickness of the SiO2 layer formed in the process of forming the SiO2 layer and the thickness of the SiO2 layer polished by the abrasive material may be substantially the same. [Effects of the Invention]

[0012] This technology allows for easy polishing of the edges of SiC wafers. [Brief explanation of the drawing]

[0013] [Figure 1] Schematic diagram showing the anodic oxidation process according to Embodiment 1 [Figure 2] Magnified partial perspective view of a wafer after the anodizing process. [Figure 3] Schematic diagram showing the polishing process [Figure 4] Magnified partial perspective view of a wafer after the polishing process. [Figure 5] Schematic diagram showing the anodic oxidation process according to Embodiment 2 [Figure 6] Figure 5, section II [Figure 7] Schematic diagram showing the laser irradiation process according to Embodiment 3 [Modes for carrying out the invention]

[0014] <Embodiment 1> A method for polishing a SiC wafer 10 according to Embodiment 1 will be described with reference to Figures 1 to 4. This polishing method is for polishing the end face 12 (edge ​​portion) of the SiC wafer 10. The method for polishing a SiC wafer 10 according to this embodiment includes an anodic oxidation step S10 in which an SiO2 layer 15 is formed on the surface of the end face 12 of the SiC wafer 10, and a polishing step S20 in which the formed SiO2 layer 15 is polished and removed.

[0015] The SiC wafer 10 to be polished is a disc-shaped wafer made of a hard and brittle compound semiconductor material, SiC. The type of SiC as a semiconductor material is not limited, and it may be either n-type or p-type. The electrical resistance of SiC is preferably within a range that allows easy conduction when performing the anodic oxidation process described later.

[0016] One of the plate surfaces 11 of the SiC wafer 10, the plate surface 11a, is a Si surface where Si atoms are exposed on the surface, and the other plate surface 11b is a C surface where C atoms are exposed. The end face 12 is connected to the plate surface 11a which is a Si surface and the plate surface 11b which is a C surface, respectively.

[0017] As shown in FIG. 1, the SiC wafer 10 is stably held by the stage 20 when its plate surface 11 is placed on the stage 20. The stage 20 is made of a conductive material and becomes an anode by applying a voltage described later. The SiC wafer 10 is to be placed on the stage 20 so that it becomes conductive with the stage 20 and becomes an anode when a voltage is applied to the stage 20. The shape of the stage 20, the method of installing the SiC wafer 10, and the method of conduction between the SiC wafer 10 and the stage 20 are not particularly limited.

[0018] In the anodic oxidation process S10, the electrode member 30 is disposed so as to face at least a part of the end face 12 of the SiC wafer 10. The electrode member 30 is made of a conductive material that is difficult to be oxidized by the electrolytic solution 40 described later. Also, the electrode member 30 is disposed to face a part of the end face 12 of the SiC wafer 10 with a predetermined gap G1. The planar shape of the electrode member 30 conforms to the shape of the end face 12 and, in this embodiment, is, for example, an arc shape.

[0019] The gap G1 between the electrode member 30 and the end face 12 of the SiC wafer 10 is filled with an electrolytic solution 40 containing an electrolyte (e.g., NaCl) that allows current conduction. The type of the electrolytic solution 40 is not limited, and known ones can be appropriately selected and used. The filling method of the electrolytic solution 40 is not limited, but it may be filled, for example, by flowing down from the supply source 41 of the electrolytic solution 40 as shown in FIG. 1.

[0020] In the anodic oxidation process S10, the stage 20 arranged as described above is used as the anode, and a voltage is applied with the electrode member 30 as the cathode. The applied voltage is, for example, about 20 V to 40 V. Since the SiC wafer 10 is electrically connected to the stage 20, when the electrolytic solution 40 is electrolyzed by the application of voltage, the end face 12 of the SiC wafer 10 exposed to the electrolytic solution 40 is anodically oxidized. By anodic oxidation, as shown in FIG. 2, a SiO2 layer 15 is formed on the surface of the end face 12. Let the thickness of the SiO2 layer 15 formed on the end face 12 (the thickness along the radial direction (plate surface direction) of the SiC wafer 10) be L1.

[0021] Further, the SiC wafer 10 is rotated around the central axis P1 (an axis passing through the center of the plate surface 11 and along the direction intersecting the plate surface 11), and anodic oxidation is performed on the entire region of the end face 12 of the SiC wafer 10. The rotation speed is set to a rotation speed at which the entire region of the end face 12 is sufficiently anodically oxidized. The rotation of the SiC wafer 10 is performed, for example, by rotating the stage 20, but is not limited thereto. For example, instead of the SiC wafer 10, the supply source 41 of the electrolytic solution 40 may be moved around the central axis P1.

[0022] The conditions such as the electrode member 30, the electrolytic solution 40, and the applied voltage are preferably optimized in order to improve the formation efficiency (oxidation amount) of the SiO2 layer 15. The dropping amount of the electrolytic solution 40 is preferably a sufficient dropping amount to achieve an optimal oxidation amount. The shape and distance of the gap G1 between the electrode member 30 and the end face 12 of the SiC wafer 10 are optimized by adjusting the shape of the electrode member 30 and the rotation speed of the SiC wafer 10 so that the electrolytic solution 40 can flow and fill the gap G1 stably and the end face 12 can be anodically oxidized. The electrolytic solution 40 is preferably dropped from an optimal position in an optimal direction according to its dropping amount, the shape of the electrode member 30, and the rotation speed of the SiC wafer 10.

[0023] Furthermore, the actual amount of oxidation during anodizing differs between the Si surface (plate surface 11a) and the C surface (plate surface 11b), with the C surface being more easily anodized than the Si surface. For this reason, the thickness L1 of the SiO2 layer 15 formed on the end face 12 tends to be greater in the portion closer to plate surface 11b (C surface side) than in the portion closer to plate surface 11a (Si surface side).

[0024] Therefore, in order to make the thickness L1 of the SiO2 layer 15 uniform across the entire end face 12, the arrangement, shape, and material of the electrode member 30 may be changed, or the inclination of the SiC wafer 10 may be changed, in order to increase the amount of oxidation on the Si side. Specifically, the electrode member 30 and the SiC wafer 10 may be arranged at an inclination such that the gap G1 between the end face 12 on the C side is larger than the gap G1 between the end face 12 on the Si side. In addition, at least one of the shape, material, or circumferential length of the electrode member 30 may differ between the Si side and the C side. Furthermore, the electrode member 30 may be made into a structure in which two electrodes are bonded together, and the oxidation conditions may be changed, such as by applying different voltages to the Si side and the C side.

[0025] Furthermore, the adjustment of the oxidation amount (amount of SiO2 layer 15 formed) on the Si side and C side of the end face 12 described above may be performed not only to make the thickness L1 of the SiO2 layer 15 uniform, but also for other purposes. For example, it may be done to make the end face 12 into a desired edge shape and to trim the edge.

[0026] After the anodizing process S10, a polishing process S20 is performed. In the polishing process S20, as shown in Figure 3, the polishing material 50 is placed at a position facing the end face 12 of the SiC wafer 10. The type of polishing material 50 is not limited, and known materials such as tape, wheel, or grinding wheel can be appropriately selected and used. In Figure 3, a polishing tape is shown as an example of the polishing material 50. The polishing tape is pressed against the end face 12 by, for example, a pressing tool 52.

[0027] In the polishing process S20, the SiC wafer 10 is rotated around the central axis P1, and the SiO2 layer 15 formed in the anodizing process S10 is mechanically polished and removed with the polishing material 50. The SiO2 layer 15 can be easily polished with the polishing material 50 that is used in the processing of conventional Si wafers, and if high-hardness diamond or the like is used as the abrasive grain of the polishing material 50, the amount of polishing material consumed can be reduced.

[0028] Through polishing, as shown in Figure 4, the SiO2 layer 15 is removed, exposing SiC on the edge face 12 of the SiC wafer 10. Let L2 be the thickness of the SiO2 layer 15 polished by the polishing material 50. After the polishing process S20, the radius of the SiC wafer 10 will be smaller by this thickness L2.

[0029] It is preferable that the thickness L2 of the SiO2 layer 15 polished in polishing step S20 is substantially the same as the thickness L1 of the SiO2 layer 15 formed in anodizing step S10. It is preferable to adjust the amount of oxidation in anodizing step S10 and the amount of polishing in polishing step S20 so that these thicknesses L1 and L2 become substantially the same. In addition, polishing conditions such as the polishing speed and polishing time on the Si side and C side of the end face 12 of the SiC wafer 10, and the pressing force of the polishing material 50 by the pressing tool 52 may be changed.

[0030] In the SiC wafer polishing method described above, first, the end face 12 of the SiC wafer 10 is oxidized in an anodizing step S10 to form an SiO2 layer 15 on the surface of the end face 12. Then, in the next polishing step S20, the formed SiO2 layer 15 is polished. Since the SiO2 layer 15 has a sufficiently low hardness compared to SiC, it can be mechanically polished in a short time using the polishing material 50. Furthermore, there is no need to use high-cost materials such as diamond for the polishing material 50, and more common polishing materials can be used. As a result, the end face 12 of the high-hardness SiC wafer 10 can be easily polished.

[0031] If the edge face 12 of the SiC wafer 10 is polished by mechanical polishing alone without oxidation, it would be necessary to use high-hardness diamond or similar materials, resulting in high costs. Furthermore, the polishing time is long, and if coarse and fine abrasive materials are used, replacement time for these materials is also incurred. In addition, due to the long polishing time, a large amount of liquid is used for cooling frictional heat, dressing the abrasive material, and preventing the scattering of polishing debris, resulting in a large environmental burden due to wastewater, etc. Moreover, the amount of abrasive material worn (used) is large, resulting in the generation of a large amount of polishing debris and a short lifespan for the abrasive material. According to this embodiment, the edge face 12 of the SiC wafer 10 can be easily polished while suppressing these problems.

[0032] <Embodiment 2> The method for polishing the SiC wafer 10 according to Embodiment 2 will be described with reference to Figures 5 and 6. In Embodiment 2, the anodic oxidation process S110 differs from that of Embodiment 1. In Embodiment 2, redundant explanations of the same configuration and effects as in Embodiment 1 will be omitted.

[0033] In the anodic oxidation process S110 according to this embodiment, as shown in Figure 5, the SiC wafer 10 is placed on the stage 120 with its surface 11 aligned vertically. In other words, the stage 120 is configured to hold the SiC wafer 10 in a vertical position.

[0034] As shown in Figure 6, the cathode electrode member 130 is placed below the SiC wafer 10 in a tank 45 that stores the electrolytic solution 40.

[0035] The lower part of the edge face 12 of the SiC wafer 10 is immersed in the electrolytic solution 40 in the tank 45. In this way, the edge face 12 of the SiC wafer 10 is reliably exposed to the electrolytic solution 40, and the edge face 12 can be anodized to stably form the SiO2 layer 15.

[0036] <Embodiment 3> A method for polishing a SiC wafer 10 according to Embodiment 3 will be described with reference to Figure 7. Embodiment 3 differs from Embodiments 1 and 2 in that an SiO2 layer 15 is formed on the edge face 12 of the SiC wafer 10 by irradiation with a laser, UV (ultraviolet light), or plasma. In Embodiment 3, redundant explanations of the same configuration and effects as in Embodiments 1 and 2 will be omitted.

[0037] The polishing method for the SiC wafer 10 according to this embodiment includes a laser irradiation step S30 in which laser light 60 is irradiated from a laser supply source 61 onto the end face 12 of the SiC wafer 10 to form an SiO2 layer 15 on the surface of the end face 12, as shown in Figure 7. After the laser irradiation step S30, the polishing step S20 described in Embodiment 1 is performed. Although Figure 7 shows an example of laser irradiation, UV irradiation or plasma irradiation may also be used as long as the SiO2 layer 15 can be formed.

[0038] The irradiation conditions (specifically, irradiation energy, irradiation time, wavelength, pulse width, pulse frequency, depth of focus, spot diameter, spot overlap ratio, irradiation angle, scanning speed, number of scans, scanning range, etc.) are preferably optimized to improve the formation efficiency (amount of oxidation) of the SiO2 layer 15. In addition, the irradiation conditions for the Si side and the C side of the end face 12 of the SiC wafer 10 may be changed.

[0039] <Other Embodiments> This technology is not limited to the embodiments described above and in the drawings, and the following embodiments, for example, are also included in the technical scope of this technology.

[0040] (1) The planar shape of the SiC wafer is not limited to circular; it may be a square or other shape. By adjusting the shape of the electrode members 30 and 130 and the irradiation by the laser light 60 to match the planar shape of the SiC wafer, the edge face 12 of the SiC wafer 10 can be oxidized in the same way even if it is not circular.

[0041] (2) The anodizing steps S10 and S110 according to Embodiments 1 and 2 and the laser irradiation step S30 according to Embodiment 3 may be used in combination. For example, the laser irradiation step S30 may be performed immediately after the anodizing steps S10 and S110, and the polishing step S20 may be performed after these steps.

[0042] (3) This technology is applicable not only to SiC wafers but also to other hard and brittle compound semiconductor materials (e.g., GaN). [Explanation of Symbols]

[0043] 10: SiC wafer, 11: Plate surface, 12: Edge, 20, 120: Stage, 30, 130: Electrode material, 40: Electrolytic solution, 50: Polishing material, P1: Central axis, S10, S110: Anodizing process, S30: Laser irradiation process

Claims

1. The surface of the SiC wafer is placed on the stage, The end face of the SiC wafer is oxidized, and SiO is formed on the surface of the end face. ２ Forming layers, The abrasive material is placed at a position facing the end face of the SiC wafer, The SiC wafer is rotated around its central axis, and the SiO ２ A method for polishing a SiC wafer, comprising polishing and removing a layer with the aforementioned polishing material.

2. The aforementioned stage is conductive, The SiC wafer is electrically connected to the stage. The SiO ２ The process of forming the layer includes an anodizing process. In the aforementioned anodic oxidation process, The electrode member is positioned opposite the end face of the SiC wafer, An electrolytic solution containing an electrolyte is filled between the electrode member and the end face of the SiC wafer facing it. The stage is used as the anode and the electrode member as the cathode, and the end face of the SiC wafer exposed to the electrolytic solution is anodized, so that the surface of the end face is SiO ２ A method for polishing a SiC wafer according to claim 1, wherein a layer is formed.

3. The surface of the SiC wafer is placed on the stage so as to be aligned with the vertical direction. The electrode member that serves as the cathode is installed below the SiC wafer in a tank that stores the electrolytic solution. The method for polishing a SiC wafer according to claim 2, wherein the end face of the SiC wafer is immersed in the electrolytic solution in the tank.

4. The SiO ２ The process of forming the layer includes an irradiation process. In the irradiation step, at least one of a laser, UV, or plasma is irradiated onto the end face of the SiC wafer so that the SiO on the surface of the end face is ２ A method for polishing a SiC wafer according to any one of claims 1 to 3, wherein a layer is formed.

5. The SiO ２ layer formed in the step of forming the SiO ２ layer thickness, and the SiO ２ layer thickness polished by the abrasive are substantially the same. The method for polishing a SiC wafer according to any one of claims 1 to 3.

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