Semiconductor substrate and process for preparing the same

Claim 2

A process for preparing a semiconductor substrate which comprises bringing a first substrate and a second substrate each provided with at least one of boron and phosphorus on the surface of an insulating layer on the surface of the substrate in so contact with each other that the insulating layers are in contact with each other, and integrating both of the substrates by a heat treatment.

Claim 3

A process according to Claim 1 or 2, wherein the boron and the phosphorus are provided on the surface of the insulating layer as accelerated, charged particles.

Claim 4

A process according to Claim 1 or 2, wherein the boron and phosphorus are provided on the surface of the insulating layer as adsorbable particles from a gas phase.

Claim 5

A process according to any one of claims 1 to 4, wherein the first substrate and the second substrates are a single element semiconductor, a compound semiconductor or glass.

Claim 6

A process for preparing a semiconductor substrate which comprises a step of making an entire silicon monocrystalline substrate as a first substrate porous by anodization, a step of making a silicon monocrystalline thin film to epitaxially grow on one of the porous surfaces, a step of oxidizing the surface of the silicon monocrystalline thin film, a step of forming an insulating layer capable of producing a softening phenomenon by heat treatment on the oxidized surface, a step of making the insulating layer of the first substrate to tightly adhere to a second substrate, and a step of heat treating the first substrate and the second substrate tightly adhered to each other, and a step of selectively etching the porous region.

Claim 7

A process for preparing a semiconductor substrate which comprises a step of making the surface layer on one side of a silicon monocrystalline substrate as a first substrate porous, a step of making a silicon monocrystalline thin film to epitaxially grow on the porous surface, a step of oxidizing the surface of the silicon monocrystalline thin film, a step of forming an insulating layer capable of producing a softening phenomenon by heat treatment on the oxidized surface, a step of making the insulating layer of the first substrate to tightly adhere to a second substrate, and a step of heat treating the first substrate and the second substrate tightly adhered to each other, a step of removing the non-porous monocrystalline substrate region of the first substrate, and a step of selectively etching the porous silicon region.

Claim 8

A process according to Claim 6 or 7, wherein before making the first substrate to tightly adhere to the second substrate, the first substrate is heat treated, thereby softening the insulating layer formed on the surface of the first substrate once to improve the surface flatness.

Claim 9

A process according to any one of Claims 6 to 8, wherein the insulating layer capable of producing a softening phenomenon by the heat treatment of the first substrate is composed of SiO₂ containing an impurity at a high concentration or a two-layer structure of SiO₂ containing an impurity at a high concentration and Si x N y wherein x and y ≠ 0.

Claim 10

A process according to Claim 9, wherein the impurity is boron or phosphorus.

Claim 11

A process according to any one of Claims 6 to 10, wherein the selective etching of the porous silicon is carried out in a mixed etching solution containing hydrofluoric acid and hydrogen peroxide or further containing an alcohol.

Claim 12

A semiconductor substrate prepared according to a process according to any one of Claims 1 to 11.