Manufacturing method for semiconductor device

A manufacturing method for a semiconductor device includes introducing an impurity into a SiC substrate, forming a mixed material layer, which is made from a resin and a fibrous carbon material, on a surface of the SiC material into which the impurity is introduced, performing heat treatment of the SiC substrate in which the mixed material layer is formed on the surface of the SiC substrate, and removing the mixed material layer after the heat treatment.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2013-003361 filed on Jan. 11, 2013 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a manufacturing method for a semiconductor device.

2. Description of Related Art

In a manufacturing method for a semiconductor device using a SiC substrate, heat treatment is carried out in order to, for example, activate an impurity introduced into the SiC substrate. During the heat treatment, sublimation of Si (silicon) on a surface of the SiC substrate happens, which can cause deterioration of flatness of the surface of the SiC substrate. In a manufacturing method for a semiconductor device described in Japanese Patent Application Publication No. 2001-068428 (JP 2001-068428 A), a photoresist layer is formed on a surface of a SiC substrate before carrying out heat treatment of the SiC substrate. Once the SiC substrate is heat-treated, the photoresist layer is carbonized, and a graphite layer is formed. The graphite layer works as a protective coat during heat treatment. Therefore, sublimation of Si on the surface of the SiC substrate is restrained.

However, the photoresist layer contains components other than carbon, such as oxygen and sulfur. While oxygen, sulfur and so on are lost from the photoresist layer, carbon remains, thereby forming the graphite layer. Thus, density of carbon present inside the graphite layer is relatively low. As a result, heat resistance of the graphite layer may not be sufficient.

SUMMARY OF THE INVENTION

The present invention provides a manufacturing method for a semiconductor device, by which heat resistance of a protective coat during heat treatment of a SiC substrate is improved.

A first aspect of the present invention relates to a manufacturing method for a semiconductor device. The manufacturing method for the semiconductor device includes introducing an impurity into a SiC substrate. The manufacturing method includes forming a mixed material layer, which is made of a resin and a fibrous carbon material, on a surface of the SiC substrate into which the impurity is introduced. The manufacturing method includes performing heat treatment of the SiC substrate in which the mixed material layer is formed on the surface of the SiC substrate. The manufacturing method includes removing the mixed material layer after the heat treatment.

In the first aspect of the present invention, the fibrous carbon material protects the surface of the SiC substrate during the heat treatment of the SiC substrate. Therefore, it is possible to improve heat resistance of a protective coat.

DETAILED DESCRIPTION OF EMBODIMENTS

Some elements of the examples described in this specification will be stated below. Each of the items stated below has separate technical utility.

In a manufacturing method for a semiconductor device described in this specification, forming a mixed material layer may include forming a resin layer on a surface of a SiC substrate. Forming the mixed material layer may include introduction of a fibrous carbon material into the formed resin layer.

In the above-mentioned manufacturing method of the semiconductor device, the resin layer is formed on the surface of the SiC substrate, and thereafter, the mixed material layer is formed by introducing the fibrous carbon material into the resin layer. Thus, it is possible to form the mixed material layer, which is made from a resin and the fibrous carbon material, on the surface of the SiC substrate.

In a manufacturing method for a semiconductor device described in this specification, the mixed material layer may be formed by applying a mixed material, which is made by mixing the resin and the fibrous carbon material, onto the surface of the SiC substrate.

In the above-mentioned manufacturing method for the semiconductor device, the mixed material layer is formed on the surface of the SiC substrate by the mixed material that is made by mixing the resin and the fibrous carbon material. Thus, it is also possible to form the mixed material layer, which is made from the resin and the fibrous carbon material, on the surface of the SiC substrate.

First Example

A manufacturing method according to this example is a manufacturing method for a semiconductor device such as MOSFET. However, the semiconductor device may be IGBT, a diode, and so on. In the manufacturing method according to this example, impurity regions6aare formed in a surface of a SiC substrate2in order to form an element structure of MOSFET and the like in the SiC substrate (FIG. 3). A publicly known structure is used for the structure of the semiconductor device such as MOSFET, and explanation of the structure is thus omitted.

The manufacturing method according to this example will be explained below usingFIG. 1toFIG. 7. First of all, in step S2, an impurity (impurity ion)6is introduced into the SiC substrate2(FIG. 4). It is possible to introduce the impurity into the SiC substrate2by ion implantation. Since it is possible to carry out the impurity introduction step in S2similarly to a publicly known method, detailed explanation of S2is omitted.

Step S4is a step for forming a mixed material layer18on the surface of the SiC substrate2. As shown inFIG. 2, step S4in this example includes step S402and step S404.

Step S402is a step for applying a liquid resin10on the surface of the SiC substrate2(FIG. 5). For the resin10, a phenolic resin, for example, may be used. A resin used as a resist mask may also be used as the resin10. A spin coat method, for example, may be used as a method for applying the resin10. A temperature for applying the resin10may be, for example, an ambient temperature.

Step S404is a step for introducing carbon nanotubes16inside the resin10. Specifically, the carbon nanotubes16are sprinkled into the liquid-state resin10(FIG. 6).

Therefore, the carbon nanotubes16are mixed into the resin10. As the carbon nanotubes16are mixed into the resin10, a mixed material layer18is formed. In the following explanation, the mixed material layer18will be sometimes referred to as a protective coat18.

Next, in step S6, heat treatment of the SiC substrate2is carried out. First of all, a temperature of the SiC substrate2is increased to, for example, 100° C. Thus, a volume of the resin10that forms the protective coat18is decreased (FIG. 7). As a result, the carbon nanotubes16are closely packed inside the protective coat18. Thus, a carbon layer14is formed inside the protective coat18. The carbon layer14is formed at a position that is in contact with the surface of the SiC substrate2

Next, the temperature of the SiC substrate2is increased to, for example, 1800° C. As a result, the carbon nanotubes16that form the carbon layer14are bonded to each other by intermolecular force. As the temperature of the SiC substrate2is increased, the impurity introduced into the SiC substrate2is activated. Further, the impurity introduced is diffused within the SiC substrate2. Thus, the impurity regions6aare formed in the SiC substrate2. The surface of the SiC substrate2is covered by the protective coat18. Therefore, sublimation of Si (silicon) on the surface of the SiC substrate2is restrained.

Step S8is a step for removing the protective coat18. For example, oxygen plasma ashing is used for removal of the protective coat18. By removing the protective coat18, the above-mentioned state shown inFIG. 3is achieved.

In the technology described in JP 2001-068428 A, a graphite layer is formed by carbonizing a photoresist layer formed on a surface of a SiC substrate. However, the photoresist contains components other than carbon, such as oxygen and sulfur. While oxygen, sulfur and so on are lost from the photoresist layer, carbon remains, thereby forming the graphite layer. Thus, density of carbon present inside the graphite layer is relatively low. As a result, the graphite layer may not have sufficient heat resistance. In the manufacturing method according to this example, the protective coat18made from the resin10and the carbon nanotubes16is formed on the surface of the SiC substrate2. The carbon nanotubes16are formed of carbon. The carbon nanotubes16are bonded to each other, and form the carbon layer14. As a result, it is possible to improve heat resistance of the protective coat18during the heat treatment of the SiC substrate2.

JP 2001-068428 A describes a method in which DLC (diamond-like carbon) is used as a protective coat during heat treatment of a SiC substrate. However, an ECR-CVD system is required for forming DLC. Therefore, manufacturing cost for a semiconductor device is increased. In the manufacturing method according to this example, an ECR-CVD system is not required for forming the protective coat18. Therefore, in the manufacturing method according to this example, an increase in manufacturing cost of the semiconductor device is restrained.

Japanese Patent Application Publication No. 2011-233780 (JP 2011-233780 A) describes a method for forming a graphene layer by carbonizing a surface of a SiC substrate. The graphene layer serves as a protective coat during heat treatment of the SiC substrate. In this method, a distance between carbon molecules arranged in a crystal lattice of the graphene layer formed by carbonization of the SiC substrate coincides with a distance between carbon molecules in a crystal lattice of the SiC substrate that is located in a layer directly beneath the graphene layer. Therefore, the graphene layer and the SiC substrate are bonded to each other relatively tightly. As a result, when general ashing is performed as cleaning of the SiC substrate, the protective coat18may not be fully removed.

On the contrary, in the manufacturing method according to this example, the mixed material layer18, which is made from the resin10and the carbon nanotubes16, is used as the protective coat during the heat treatment. When the SiC substrate2is heat-treated, the carbon layer14, in which the plurality of carbon nanotubes16are bonded to each other, is formed on the surface of the SiC substrate2. Bonding between the carbon layer14and the SiC substrate2is weaker than bonding between the graphene layer and the SiC substrate2. Therefore, in the manufacturing method according to this example, it is possible to remove the protective coat18by general ashing.

In the manufacturing method according to this example, the resin10is used for forming of the protective coat18. The resin10is easily immersed into uneven portions (for example, trenches) on the surface of the SiC substrate2. Therefore, with the manufacturing method according to this example, occurrence of voids are restrained even in a case where the uneven portions are present on the surface of the SiC substrate2.

Second Example

Next, a second manufacturing method for a semiconductor device using a SiC substrate2will be explained. First of all, similarly to the manufacturing method according to the first example, step S2is carried out. In step S2, an impurity is introduced into the SiC substrate2.

In this example, after step S2shown inFIG. 1, step S104shown inFIG. 8is carried out instead of step S4. Step S104is a step for forming a mixed material layer18. As shown inFIG. 8, the step S104includes step S412. In step S412, a mixed material (10,16) is applied on a surface of the SIC substrate2(a state that is the same asFIG. 6is achieved). The mixed material (10,16) is formed by mixing a resin10and carbon nanotubes16. Thus, the mixed material layer18(a protective coat18) is formed on the surface of the SiC substrate2. A spin coat method, for example, may be used as a method for applying the mixed material (10,16).

Next, in step S6inFIG. 1, heat treatment of the SiC substrate2is carried out similarly to the first example. Due to the heat treatment, a carbon layer14is formed on the surface of the SiC substrate2(a state that is the same asFIG. 7is achieved). Due to the heat treatment, the impurity is activated inside the SiC substrate2. Further, the impurity is diffused inside the SiC substrate2. Thus, impurity regions6aare formed in the surface of the SiC substrate2.

In the above-mentioned manufacturing method for the semiconductor device, the mixed material (10,16), in which the resin10and the carbon nanotubes16are mixed, is applied on the SiC substrate2. Thus, the protective coat18, which is made of the resin10and the carbon nanotubes16, is formed on the surface of the SiC substrate2.

In the above-mentioned manufacturing method for the semiconductor device, the carbon nanotubes16are used as a material for forming the protective coat18. However, other fibrous carbon material may be used as a material for forming the protective coat18. For example, carbon fiber and carbon nanofiber may be used as the fibrous carbon material.

However, carbon nanotubes have higher aggregating effect than that of other fibrous carbon materials. This means that carbon nanotubes easily aggregate and are adsorbed to each other when the carbon nanotubes are introduced into the resin10. Thus, when carbon nanotubes are used as a fibrous carbon material, the protective coat may be formed while reducing density of the fibrous carbon material to be introduced into the resin10.

According to the foregoing manufacturing method for the semiconductor device, the semiconductor device is manufactured using the SiC substrate2. However, the semiconductor device may be manufactured using a Si (silicon) substrate.

Although specific examples of the present invention have been explained so far in detail, the examples are illustrative only, and do not limit the scope of the claims. The techniques described in the scope of the claims include various modifications and changes of the specific examples illustrated above. In addition, each or various combinations of the technical elements explained in this specification and the drawings exert technical utility. The techniques exemplified in this specification and the drawings are able to achieve a plurality of objectives simultaneously, and have technical utility only by achieving one of the objectives.