TECHNICAL FIELD

The present invention relates to a semiconductor device that has a structure in which a SiO2layer is formed on a SiC semiconductor layer, and relates to a method for manufacturing the semiconductor device.

BACKGROUND ART

It has been known that a structure in which a SiO2layer is formed on a SiC semiconductor layer has the problem of an increase in interface state density in an interfacial region contiguous to the SiO2layer in the SiC semiconductor layer. Although the interface state density is increased by various causes, interfacial defects in an interfacial region between the SiC semiconductor layer and the SiO2layer can be mentioned as its one main cause. Such interfacial defects can be produced by carbon atoms existing in the interfacial region.

The interface state density has a correlation with channel mobility (which is also called “carrier mobility”). More specifically, an increase in interface state density causes a decrease in channel mobility. An example of a method for improving the interface state density is disclosed by Patent Literature 1 and Patent Literature 2.

Patent Literature 1 discloses a semiconductor device manufacturing method that includes a step of forming a SiO2layer on a SiC semiconductor substrate and a step of applying heat treatment onto the SiO2layer in an inert gas atmosphere including Ar (argon).

Patent Literature 2 discloses a semiconductor device manufacturing method that includes a step of forming a SiO2layer on a SiC semiconductor substrate and a step of applying heat treatment onto the SiO2layer and adding phosphorus to the SiO2layer in an atmosphere including POCl3(phosphoryl chloride).

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent Application Publication No. 2001-345320

Patent Literature 2: International Publication No. WO 2011/074237 A1

SUMMARY OF INVENTION

Technical Problem

According to the manufacturing method of Patent Literature 1, it is possible to detach carbon atoms from an interfacial region contiguous to the SiO2layer in the SiC semiconductor layer. This makes it possible to reduce interfacial defects. However, in this case, carbon atoms remain in the SiO2layer, and therefore it is impossible to obtain satisfactory insulating properties.

According to the manufacturing method of Patent Literature 2, it is possible to allow the carbon atoms in the SiO2layer and the oxygen atoms in the atmosphere to react together. This makes it possible to remove the carbon atoms in the SiO2layer, hence making it possible to reduce interfacial defects. However, in this case, P (phosphorus) added to the SiO2layer functions as a charge trap, and therefore there is a fear that time-dependent deterioration of the SiO2layer will be caused.

A preferred embodiment of the present invention provides a semiconductor device that is capable of reducing interfacial defects between a SiC semiconductor layer and a SiO2layer and that has a good-quality SiO2layer, and provides a method for manufacturing the semiconductor device.

Solution to Problem

A preferred embodiment of the present invention provides a semiconductor device that includes a SiC semiconductor layer that has a carbon density of 1.0×1022cm−3or more, a SiO2layer that is formed on the SiC semiconductor layer and that has a connection surface contiguous to the SiC semiconductor layer and a non-connection surface positioned on a side opposite to the connection surface, a carbon-density-decreasing region that is formed at a surface layer portion of the connection surface of the SiO2layer and in which a carbon density gradually decreases toward the non-connection surface of the SiO2layer, and a low carbon density region that is formed at a surface layer portion of the non-connection surface of the SiO2layer and that has a carbon density of 1.0×1019cm−3or less.

A preferred embodiment of the present invention provides a semiconductor device manufacturing method that includes a step of preparing a SiC semiconductor layer, a step of forming a SiO2layer on the SiC semiconductor layer, and an oxygen atom introducing step of introducing oxygen atoms into the SiO2layer by applying annealing treatment in a low-oxygen partial pressure atmosphere.

The aforementioned or yet other objects, features, and effects of the present invention will be clarified by the following description of preferred embodiments given below with reference to the accompanying drawings.

