The present invention relates to a method for manufacturing silicon carbide in which a silicon carbide crystal is grown by a sublimation method.
Recently, inverter circuits have been commonly used in electric vehicles and electric air-conditioners. This creates demands for semiconductor crystal of silicon carbide (hereinafter may also be referred to as SiC) because of the properties of less power loss and higher breakdown voltage in devices than those using semiconductor Si crystal.
As a typical and practical method for growing a crystal with a high melting point or a crystal that is difficult to grow by liquid phase growth such as SiC, a sublimation method exists. In this method, a solid raw material is sublimated in a container at a high temperature around 2000° C. or higher, and a crystal is grown on a seed crystal located on the opposite side (Patent Document 1).
However, SiC crystal growth requires high temperature for the sublimation, and the growth apparatus requires temperature control at the high temperature. Moreover, to stabilize the pressure of the sublimated substance, it is necessary to steadily control the pressure inside the container. Further, SiC crystal growth depends on the sublimation rate, and the growth rate is relatively quite slow in comparison with Czochralski method for Si, LPE manufacturing method for GaAs and so forth, for example. Hence, long time is required for the growth. Fortunately, the developments of control units, computers, personal computers, and so forth nowadays enable long-term steady adjustments of pressure and temperature.
The growth container 104 is disposed in a vacuum quartz tube or a vacuum chamber, and filled with a gas with low reactivity once. The atmosphere is lower than the atmospheric pressure so as to increase the SiC sublimation rate.
Outside the growth container 104, a heat-insulating material (heat-insulating container) 105 is disposed. At least one hole (upper-portion temperature measurement hole) 106 for measuring the temperature with a pyrometer is provided to a portion of the heat-insulating material 105. Hence, some heat escapes through the hole.
The growth container 104 is mainly made of a carbon material and is air permeable, and the pressures inside and outside the container are equal. Nevertheless, when the sublimation starts, the sublimated gas leaks outside the container.
In practice, the solid silicon carbide raw material 103 is disposed at a lower portion of the growth container 104. The material 103 is solid, and sublimates at high temperature under reduced pressure. The sublimated material grows as a single crystal on the seed crystal 102 located on the opposite side. In the case of SiC, the single crystal includes cubic, hexagonal crystals, for example. Further, among hexagonal crystals, 4H, 6H, and so forth are known as typical polytypes.
In many cases, single crystal grows on the same type like 4H grows on a 4H type (Patent Document 2).
Here, a conventional method for manufacturing a silicon carbide single crystal will be described using a flowchart in
As described in
However, in the above-described conventional method for manufacturing a silicon carbide single crystal, carbon is incorporated as inclusions in a single crystal during the growth of the silicon carbide single crystal. When the carbon as a mass is exposed from the wafer surface in the wafer processing, the carbon mass is removed, so that a pit is left where a polishing agent and a cleaning agent accumulate. Substances generated therefrom cause contamination and scratch on the wafer surface, bringing about a problem. Such carbon inclusions can be observed by inspecting the wafer with a transmission microscope.
The present invention has been made in view of the above-described problems. An object of the present invention is to provide a method for manufacturing a silicon carbide single crystal with few carbon inclusions.
To achieve the object, the present invention provides a method for manufacturing a silicon carbide single crystal by sublimating a solid silicon carbide raw material in a growth container to grow a silicon carbide single crystal on a seed crystal substrate, the method comprising:
mixing a tantalum (Ta) powder with a carbon powder;
attaching the mixture to the solid silicon carbide raw material in the growth container; and
heating the resultant for sintering to form a tantalum carbide (TaC) coating film on a surface of the solid silicon carbide raw material, wherein
a silicon carbide single crystal is grown after or while the coating film is formed.
In this way, a silicon carbide single crystal is grown after or while a tantalum carbide (TaC) coating film is formed on the surface of the solid silicon carbide raw material. This makes it possible to prevent carbon mass from floating from the solid raw material, thereby manufacturing a silicon carbide single crystal with few carbon inclusions.
Moreover, when the growth container is made of carbon, a mixture of a tantalum (Ta) powder and a carbon powder is preferably further attached to an inner wall of the growth container.
Such
When the growth container is made of carbon, attaching a mixture of a tantalum (Ta) powder with a carbon powder also to the inner wall of the growth container as described above makes it possible to prevent reaction between the raw-material gas and the carbon of the growth container, and consequently inclusion of the carbon into the single crystal during the growth.
As described above, the inventive method for manufacturing a silicon carbide single crystal makes it possible to prevent carbon mass from floating from the solid raw material. This enables production of a silicon carbide single crystal with few carbon inclusions.
Hereinafter, the present invention will be described in detail with reference to the drawings as an example of embodiments. However, the present invention is not limited thereto.
Herein below, a method for manufacturing a silicon carbide single crystal according to a first embodiment of the present invention will be described with reference to
As shown in
In the method for manufacturing a silicon carbide single crystal according to the first embodiment of the present invention, first, as described in
Note that the solid silicon carbide raw material 3 is obtained by melting a SiC powder and cooling it into a block form.
Next, as described in
Next, as described in
Next, as described in
Next, as described in
Finally, as described in
According to the manufacturing method as described above, a silicon carbide single crystal is grown while the tantalum carbide (TaC) coating film 10 is being formed on the surface of the solid silicon carbide raw material 3. This makes it possible to prevent a carbon mass from floating from the solid raw material, thus reducing carbon inclusion in the grown silicon carbide crystal.
Next, a method for manufacturing a silicon carbide single crystal according to a second embodiment of the present invention will be described with reference to
In the method for manufacturing a silicon carbide single crystal according to the second embodiment of the present invention, first, as described in
Next, as described in
Next, as described in
Next, as described in
Next, as described in
Next, as described in
Next, as described in
Finally, as described in
According to the manufacturing method as described above, a silicon carbide single crystal is grown after the tantalum carbide (TaC) coating film is formed on the surface of the solid silicon carbide raw material and on the inner wall of the growth container. This makes it possible to prevent a carbon mass from floating from the solid raw material, and to prevent a reaction between the raw-material gas and the carbon of the growth container and consequently incorporation of the carbon as inclusion in the growing single crystal. Thus, more effective reduction of carbon inclusion is achieved in the grown silicon carbide crystal.
Note that, in this second embodiment, the TaC coating film is formed on the inner wall of the growth container, too. Nevertheless, as long as the TaC coating film is formed on the surface of the solid silicon carbide raw material, it is not always necessary to form the coating film on the surface of the formation container. It should be noted however that carbon inclusion can be further suppressed by growing on the inner wall of the growth container.
Hereinafter, the present invention will be more specifically described by showing Examples and Comparative Example. However, the present invention is not limited thereto.
Under the following growth conditions, a SiC single crystal with a diameter of 4 inches (100 mm) was grown.
The SiC single crystal was prepared according to the procedure as described in
The prepared single crystal was sliced. The distribution and average number (density) of carbon inclusions in the wafer plane were examined with a microscope.
Under the following growth conditions, a SiC single crystal with a diameter of 4 inches (100 mm) was grown.
The SiC single crystal was prepared according to the procedure as described in
The prepared single crystal was sliced. The distribution and average number (density) of carbon inclusions in the wafer plane were examined with a microscope.
Under the following growth conditions, a SiC single crystal with a diameter of 4 inches (100 mm) was grown.
The SiC single crystal was prepared according to the procedure as described in
The prepared single crystal was sliced. The distribution and average number (density) of carbon inclusions in the wafer plane were examined with a microscope.
It should be noted that the present invention is not limited to the above-described embodiments. The embodiments are just examples, and any examples that have substantially the same feature and demonstrate the same functions and effects as those in the technical concept disclosed in claims of the present invention are included in the technical scope of the present invention.
Number | Date | Country | Kind |
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2018-042289 | Mar 2018 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2019/005388 | 2/14/2019 | WO | 00 |