1. Field of the Invention
The present invention relates to a silicon carbide (SiC) structure, a method of forming the SiC structure, in particular, the invention relates to a single crystal SiC structure, a method of the single crystal SiC structure, and an electronic device having the single crystal SiC structure.
2. Background Arts
An electronic device implementing an SiC substrate has been drawn attention because of not only excellent breakdown voltage but also higher operable frequencies thereof. For instance, an electronic device operable at higher temperatures, having excellent breakdown voltages and losses in higher frequencies is realizable by using a channel made of silicon carbide (SiC) like an SiC-MOSFET (SiC metal-oxide-semiconductor filed effect transistor). Also, an electronic device with a graphene layer on the SiC substrate may be operable at higher frequencies.
A Japanese Patent Application laid open No. of JP-2004-022878A has disclosed an SiC-MOSFET having (000-1) crystal plane as a primary surface thereof in order to enhance carrier mobility in a channel. An international Patent Applications laid open No. WO2009/063844 has disclosed an SiC substrate with an non-polar surface macroscopically but with a composite surface having a non-polar surface and a polar surface in which one of Si-polar surface and C-polar surface dominate. Another international patent application laid open No. WO2011/074237 has disclosed a technique to reduce defects formed at an interface between an SiC substrate and an insulating film by adding phosphorous (P) in the insulating film. Still another international patent application laid open No. WO2013/145023 has disclosed a technique to suppress variation in a threshold voltage of an FET by providing a laminated insulating film having a charge capturing function as the gate insulating film.
A Japanese Patent Application laid open No. JP-2004-152813A has disclosed a device, which has a layer made of an SiC film of 3C-SiC type on an SiC substrate having a 6H-SiC type, which is operable in a high frequency by localizing electrons within the layer of 3C-SiC type. A Japanese Patent Application laid open No. JP-2013-197167A has disclosed a technique of forming a gate insulating film made of 3C-SiC type on an SiC substrate of 4H-SiC type. A conference report of Solid State Devices and Materials, Tokyo (1987) has disclosed a technique often called as the step controlling epitaxy where a lateral growth on a surface of an SiC substrate offset from a closest packed surface is carried out.
A document of Nature Materials volume 8, pages 171 and 172 (2009) has disclosed a technique for growing a graphene layer on an SiC substrate by raising a temperature of the SiC substrate higher than 1100° C. by reducing the SiC substrate. An international patent application laid open No. WO2010/023934 has disclosed another technique for forming a graphene layer on an SiC substrate by exposing Si surface of the SiC substrate by removing a native oxide layer of the SiC substrate, oxidizing Si surface to form SiO2 layer, and heating the SiC substrate within a vacuum. A Japanese patent application laid open No. JP-2015-110485A and an international patent application laid open No. WO2013/125669 each have disclosed a technique to form a graphene layer by heating an SiC substrate within an inactive atmosphere to vaporize Si atoms. A Japanese patent application laid open No. JP-2013-510071A has disclosed a technique of hydrogenating a graphene layer.
A Japanese patent application laid open No. JP-2014-162683A has disclosed a technique of removing hydrocarbons in a graphene layer by forming a carbon buffer layer on an SiC substrate by heating the SiC substrate, decomposing bonds between Si atoms in the SiC substrate and the carbon buffer by exposing the carbon buffer in hydrogen (H2) atmosphere, terminating Si bonds in the SiC substrate by hydrogen (H2), and heating the SiC substrate in a vacuum. A Japanese patent application laid open No. JP-2014-152051A has disclosed a technique of forming a graphene layer by removing native oxide on the surface of an SiC substrate to expose the C-polar surface of the SiC substrate, forming an SiC layer on the C-polar surface of the substrate, and heating the SiC substrate in argon (Ar) atmosphere. A Japanese patent application laid open No. JP-2013-180930A has disclosed a technique of forming a graphene layer by segregating carbon (C) atoms between an SiC substrate and an SiO2 film covering the SiC substrate to form a state where excess carbons are on the SiC substrate, and heating the SiC substrate at a temperature so as not to sublimate Si atoms. A Japanese patent application laid open No. JP-2014-240173A has disclosed a technique of forming a graphene layer by forming an SiC layer on a Si substrate, and heat-treating a surface of the SiC layer by using hydrogen (H2).
Thus, various trials and experiments have been carried out for enhancing the carrier mobility and reducing defects in an SiC-MOSFET. Also, various techniques have been proposed for forming a graphene layer having less defects and superior quality on an SiC substrate. However, no reports have seemed to be proposed how the SiC substrate has a preferable surface structure when a single crystal SiC substrate forms a film thereon.