JP5087375B2 - Method for manufacturing silicon carbide semiconductor device - Google Patents

Description

  The present invention relates to a method for holding a silicon carbide wafer and a wafer holder suitable for use in this holding method.

  Silicon carbide single crystals have excellent characteristics when applied to next-generation semiconductor devices. In addition, they are used in various devices such as optical devices, power devices, high-frequency devices, and heat-resistant in-vehicle devices. In order to manufacture these various semiconductor devices, a silicon carbide single crystal wafer prepared in advance is subjected to various processes such as heat treatment, film formation, and etching in a processing chamber of a semiconductor manufacturing apparatus.

  The wafer holder for holding the silicon carbide single crystal wafer in the processing chamber has a planar wafer holding surface in contact with the back surface of the silicon carbide single crystal wafer, and the silicon carbide single crystal wafer is mounted on the wafer holding surface. In such a state, the heat treatment or the like as described above is performed.

  Here, when the said process was high temperature, the surface roughness of the back surface of the silicon carbide single crystal wafer after a process might deteriorate. Since the back surface of the silicon carbide single crystal wafer is the surface opposite to the surface on which the semiconductor device is formed, even if the surface roughness of the back surface of the silicon carbide single crystal wafer deteriorates during the semiconductor device manufacturing process, the semiconductor Does not affect device quality. However, the product aesthetics as a silicon carbide single crystal wafer from which a semiconductor device is manufactured are impaired.

  Therefore, when the surface roughness of the back surface of the silicon carbide single crystal wafer after the high-temperature treatment is rough, the back surface is polished according to the degree. However, this polishing operation increases the manufacturing time of the semiconductor device and increases the manufacturing cost. Therefore, there is a demand for a method or means that can suppress an increase in surface roughness.

  Some wafer holders for holding a semiconductor wafer or a glass substrate have a large number of small protrusions on the wafer holding surface and support the wafer on the upper surface of the protrusions (Patent Document 1).

However, when a silicon carbide single crystal wafer is processed at a high temperature using a wafer holder having a large number of small protrusions on the wafer holding surface as described in Patent Document 1 or the like, the surface roughness of the back surface of the silicon carbide single crystal wafer is increased. The deterioration could not be resolved.
JP-A-6-132387

  As described above, the surface roughness of the back surface of the silicon carbide single crystal wafer after processing at a high temperature becomes a problem in the manufacturing process of a semiconductor device using the silicon carbide single crystal wafer. Therefore, the present invention advantageously solves this problem, and a silicon carbide single crystal after processing at a high temperature is obtained by a novel holding method when a silicon carbide single crystal wafer is processed at a high temperature using a wafer holder. It is an object of the present invention to provide a silicon carbide wafer holding method and a wafer holder used in this holding method, which can effectively suppress the deterioration of the surface roughness of the back surface of the wafer.

  The method for holding a silicon carbide wafer according to the present invention uses a means for preventing formation of a gap between the wafer holding surface of the wafer holder and the back surface of the silicon carbide wafer when the silicon carbide wafer is held and heated by the wafer holder. It is characterized by.

  The means for preventing the gap formation may form a protective film on the back surface of the silicon carbide wafer before heating the silicon carbide wafer, and the wafer having a wafer suction hole on the wafer holding surface. It is also possible to use a holding tool.

  The wafer holder of the present invention comprises a wafer holding surface for holding a silicon carbide wafer and a suction hole formed in the wafer holding surface, and the suction hole is connected to an exhaust means. To do.

  According to the method for holding a silicon carbide wafer of the present invention, even after the silicon carbide wafer held by the wafer holder is heated at a high temperature, deterioration of the surface roughness of the wafer back surface can be suppressed, and the appearance is good. A silicon carbide semiconductor device can be manufactured without increasing the manufacturing cost.

  According to the wafer holder of the present invention, deterioration of the surface roughness of the back surface of the silicon carbide wafer can be effectively suppressed.

  The inventors investigated to elucidate the cause of the deterioration of the surface roughness of the back surface of the silicon carbide single crystal wafer. As a result, it has been found that the deterioration of the surface roughness of the wafer back surface is caused by a gap formed between the planar holding surface of the wafer holder and the wafer back surface.

  When the silicon carbide single crystal wafer is held on the wafer holder, the back surface of the silicon carbide single crystal wafer is usually in close contact with the planar holding surface of the wafer holder. However, when the silicon carbide single crystal wafer held by the wafer holder is warped for some reason, a gap is formed between the back surface of the silicon carbide single crystal wafer and the holding surface of the wafer holder. End up. When the silicon carbide single crystal wafer is heated to a high temperature under reduced pressure in the processing chamber of the semiconductor manufacturing apparatus in a state where this gap is formed, silicon atoms and carbon are introduced from the back surface of the silicon carbide single crystal wafer where the gap is generated. It is the same as when atoms are removed, that is, thermal etching is performed. This is considered to deteriorate the surface roughness of the back surface of the wafer.

  Therefore, in the method for holding a silicon carbide wafer according to the present invention, means for preventing formation of a gap between the wafer holding surface of the wafer holder and the back surface of the silicon carbide wafer is used. By preventing the formation of gaps, it is possible to suppress the removal of silicon atoms and carbon atoms from the back surface of the silicon carbide single crystal wafer where the gaps are generated, and thus the deterioration of the surface roughness of the back surface of the silicon carbide wafer. Can be suppressed.

  In a specific embodiment of the means for preventing the gap formation, a protective film may be formed on the back surface of the silicon carbide wafer before the silicon carbide wafer is heated. FIG. 1 is a schematic cross-sectional view illustrating this embodiment. The silicon carbide wafer 11 is held by the wafer holder 21 in the processing chamber of the semiconductor manufacturing apparatus. FIG. 1A shows an example in which the wafer holder 21 is a susceptor. The wafer holder 21 has a concave portion large enough to hold the silicon carbide wafer 11, and the bottom surface of the concave portion is a planar wafer holding surface 21a. The material of the wafer holder 21 is, for example, silicon carbide.

  A protective film 12 is formed on the back surface of the silicon carbide wafer 11. This protective film is made of a material that does not volatilize at a high temperature when the silicon carbide wafer 11 is heated. For example, a thermosetting resin such as a phenol resin can be used. The thickness of the protective film 12 can be greater than or equal to a thickness that can prevent the silicon carbide wafer 11 from being thermally etched when the silicon carbide wafer 11 is heated. The protective film 12 can be formed by coating the above material.

  FIG. 1B shows that the silicon carbide wafer 11 on which the protective film 12 is formed is placed and held on the wafer holding surface 21 a of the wafer holder 21. Since the protective film 12 is formed on the back surface of the silicon carbide wafer 11, even if the silicon carbide wafer 11 on the wafer holding surface 21 a of the wafer holder 21 is warped, the back surface of the silicon carbide wafer 11 is left in the gap. There is no exposure, thus preventing gap formation. For this reason, it is suppressed that a silicon atom and a carbon atom remove | deviate from a back surface of the silicon carbide wafer 11 by high temperature, Therefore, the deterioration of the surface roughness of the silicon carbide wafer 11 back surface is suppressed.

  Another specific embodiment of the means for preventing gap formation may use a wafer holder having a wafer suction hole on the wafer holding surface. FIG. 2 is an explanatory view of an embodiment using the wafer holder 22 having such a configuration. FIG. 2A is a schematic sectional view of the wafer holder 22, and FIG. 2B is a wafer holder. 3 is a plan view of a main part of the tool 22. FIG. In the gap formation preventing means of this embodiment, as shown in FIG. 2A, the wafer holder 22 has a plurality of suction holes 22b penetrating in the thickness direction and exposed to the wafer holding surface 22a. . These suction holes 22 b are connected to the suction device 30 through a conduit 31. When the silicon carbide wafer 11 is placed on the wafer holding surface 22a of the wafer holder 22 having the suction holes 22b and the suction device 30 is operated, the silicon carbide wafer 11 is moved to the wafer holding surface 22a of the wafer holder 22 by the suction force. Close contact with. Therefore, a gap is prevented from being formed between the wafer holding surface 22a and the back surface of the silicon carbide wafer 11. Even if the silicon carbide wafer 11 is warped on the wafer holding surface 22a, the formation of a gap can be prevented by adjusting the suction force by the suction device 30 so as to eliminate the warp.

  In this embodiment, the suction holes 22b are arranged in a concentric shape and a plurality of diametrical line segments as shown in FIG. 2B. In the holder, the arrangement of the suction holes is not limited to the illustrated example. Corresponding to the many variations in the in-plane distribution of warpage of the silicon carbide wafer, the suction holes are arranged so that the silicon carbide wafer can be brought into close contact with the holding surface.

  FIG. 3 is a schematic sectional view of a wafer holder 23 having a wafer suction hole according to another embodiment. In the wafer holder 23 of this embodiment shown in FIG. 3, the portion including the wafer holding surface 23 a that holds the silicon carbide wafer 11 is made of a porous material 23 b, and the porous material 23 b is sucked through a conduit 31. 30. The holes of the porous material 23b function as suction holes. As the porous material 23b, silicon carbide or other ceramic materials that are not decomposed by a high temperature during heating can be used.

  By using the wafer holder 23 of the present embodiment shown in FIG. 3, the silicon carbide wafer 11 is placed on the wafer holding surface 22a of the wafer holder 22 having the porous material 23b, and the suction device 30 is operated. Then, the silicon carbide wafer 11 comes into close contact with the wafer holding surface 22a of the wafer holder 22 by the suction force. Therefore, a gap is prevented from being formed between the wafer holding surface 22a and the back surface of the silicon carbide wafer 11. Even if the silicon carbide wafer 11 is warped on the wafer holding surface 22a, the formation of a gap can be prevented by adjusting the suction force by the suction device 30 so as to eliminate the warp.

  FIG. 4 shows a conventional wafer holder 201 for comparison. This wafer holder 201 is an example of a susceptor, and has a concave portion large enough to hold a silicon carbide wafer, and the bottom surface of this concave portion is a planar wafer holding surface 201a. FIGS. 5A to 5C show a state in which the silicon carbide wafer 101 is placed on the wafer holding surface 201a of the conventional wafer holder 201. FIG. FIG. 5A shows an example in which the wafer 101 is not warped on the wafer holding surface 201a of the wafer holder 201. In this case, the wafer holding surface 201a of the wafer holder 201 and the silicon carbide wafer 101 are shown. There is no gap between the surface of the silicon carbide wafer 101 and the surface roughness of the back surface does not deteriorate even when the silicon carbide wafer 101 is subjected to high temperature treatment.

  However, as shown in FIG. 5B, when the wafer 101 is warped on the wafer holding surface 201 a of the wafer holder 201, the wafer holding surface 201 a of the wafer holder 201 and the back surface of the wafer 101 are There is a gap between 101a. In this case, when the high-temperature treatment is performed on the silicon carbide wafer 101, as shown in FIG. 5C, the roughness 101b is generated on the back surface of the silicon carbide wafer 101.

  On the other hand, since the holding method and the holding device according to the embodiment of the present invention do not cause deterioration of the surface roughness of the back surface of the silicon carbide wafer as shown in FIGS. Has a remarkable effect.

  A first group of silicon carbide wafers having a diameter of 50.8 mm, a back surface roughness of 0.4 to 1.0 nm and a warpage of 10 to 20 μm, and a diameter of 50.8 mm and a back surface roughness of 10 to 20 μm. A plurality of second groups of silicon carbide wafers having a thickness of 30 to 100 nm and a warpage amount of 30 to 50 μm were prepared.

  When each of the first group silicon carbide wafer and the second group silicon carbide wafer is heat-treated, a protective film is formed on the back surface of the silicon carbide wafer shown in FIG. 1 as a method for holding the silicon carbide wafer. An example using the gap formation preventing means (Example 1), an example using the gap formation preventing means using the wafer holder having the suction holes shown in FIG. 2 (Example 2), and these gap formation preventing means. Any of the three types of examples (comparative example) which were not used was performed. The heating conditions were heating at 1650 ° C. for 1.5 hours in a reduced pressure atmosphere of 120 mbar.

The surface roughness of the back surface of each silicon carbide wafer was measured after heating. The results are shown in Table 1.

  As is clear from Table 1, Example 1 and Example 2 are compared with the comparative example in the case of either the first group of silicon carbide wafers or the second group of silicon carbide wafers. The deterioration of the surface roughness of the wafer back surface was effectively suppressed before and after.

  As described above, the silicon carbide wafer holding method and the wafer holder according to the present embodiment have been described with reference to the drawings. However, the silicon carbide wafer holding method and the wafer holder according to the present invention are not limited to the drawings and the embodiments. It goes without saying that various modifications are possible without departing from the spirit of the present invention.

It is typical sectional drawing which shows an example of the holding method of the silicon carbide wafer which concerns on embodiment of this invention. It is typical sectional drawing which shows an example of the holding method of the silicon carbide wafer which concerns on another embodiment of this invention. It is typical sectional drawing which shows an example of the holding method of the silicon carbide wafer which concerns on another embodiment of this invention. It is sectional drawing of the wafer holder used for the holding method of the conventional silicon carbide wafer. It is explanatory drawing of the holding method of the conventional silicon carbide wafer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Silicon carbide wafer 12 Protective film 21 Wafer holder 21a Holding surface 21b Suction hole

Claims (1)

Before heating the silicon carbide wafer, forming a protective film on the back surface of the silicon carbide wafer by coating with a phenol resin ; and
Placing the silicon carbide wafer on the holding surface of the wafer holder so that the protective film formed on the back surface of the silicon carbide wafer and the holding surface of the wafer holder are brought into close contact with each other;
Forming the semiconductor device on the surface side of the silicon carbide wafer by heating the silicon carbide wafer in a state of being placed on the wafer holder. .

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