SOI device and a fabrication process thereof

Claim 1

A method for fabricating a semiconductor device, comprising the steps of: forming a depression on an upper major surface of a substrate, said depression having a bottom surface and side walls and extending from said upper major surface toward a lower, opposing major surface of the substrate; bonding a plate of a single crystal semiconductor material having upper and lower major surfaces and characterized by a first thickness, on the upper major surface of the substrate to establish a contact thereto such that a closed space is formed in the substrate in correspondence to said depression; reducing the thickness of said plate from the first thickness to a second, smaller thickness; forming a penetrating opening through said plate in communication to said space to form a bridging part in said plate in correspondence to a part that is located on said space as a region left from the formation of the penetrating opening, such that the bridging part is defined by upper and lower major surfaces and a side wall; after said step of reducing the thickness of the plate being achieved and after said step of providing the penetrating opening through said plate being achieved, forming an insulation film of an insulating material to cover at least said lower major surface and both side walls of said bridging part; filling said space by depositing polysilicon through the penetrating opening; doping said polysilicon filling said space to a desired conductivity, removing the polysilicon that has been deposited on the upper major surface of the bridging part to expose a crystal surface of the semiconductor material forming said plate at the upper major surface of the bridging part; and forming an active device on said bridging part.

Claim 2

A method for fabricating a semiconductor device, comprising the steps of: forming a depression on an upper major surface of a substrate, said depression having a bottom surface and side walls and extending from said upper major surface toward a lower, opposing major surface of the substrate; bonding a plate of a single crystal semiconductor material having upper and lower major surfaces and characterized by a first thickness, on the upper major surface of the substrate to establish a contact thereto such that a closed space is formed in the substrate in correspondence to said depression; reducing the thickness of said plate from the first thickness to a second, smaller thickness; forming a penetrating opening through said plate in communication to said space to form a bridging part in said plate in correspondence to a part that is located on said space as a region left from the formation of the penetrating opening, such that the bridging part is defined by upper and lower major surfaces and a side wall; after said step of reducing the thickness of the plate being achieved and after said step of providing the penetrating opening through said plate being achieved, forming an insulation film of an insulating material to cover at least said lower major surface and both side walls of said bridging part; filling said space by depositing polysilicon through the penetrating opening; doping said polysilicon filling said space to a desired conductivity, removing the polysilicon that has been deposited on the upper major surface of the bridging part to expose a crystal surface of the semiconductor material forming said plate at the upper major surface of the bridging part; and forming an active device on said bridging part.