Semiconductor integrated circuit device and fabrication method thereof

Claim 1

A method of fabricating a semiconductor integrated circuit device comprising: (a) oxidizing predetermined regions of a semiconductor layer to form an oxide layer to an intermediate depth of said semiconductor layer in the direction of its thickness, thereby to divide said semiconductor layer into a first region in which a normal transistor is to be formed and a second region in which an inverse transistor is to be formed; (b) covering the first region in which a normal transistor element portion is to be formed with an oxidation-resistant mask while leaving the second region in which said inverse transistor is to be formed uncovered; and (c) further oxidizing the predetermined regions of said semiconductor layer to make said oxide layer penetrate through said semiconductor layer in the direction of its thickness, thereby isolating the first and second regions from each other, and, at the same time, oxidizing the uncovered surface of said second region to form a surface oxide film of said second region in which said inverse transistor is to be formed, said surface oxide film of said second region being thicker than a surface oxide film of said first region in which said normal transistor element portion is to be formed so that said second region is made thinner than said first region.

Claim 2

A method of fabricating a semiconductor integrated circuit device comprising: (a) oxidizing predetermined regions of a semiconductor layer to form an oxide layer to an intermediate depth of said semiconductor layer in the direction of its thickness, thereby to divide said semiconductor layer into a first region in which a normal transistor is to be formed and a second region in which an inverse transistor is to be formed; (b) covering the first region in which a normal transistor element portion is to be formed with an oxidation-resistant mask while leaving the second region in which said inverse transistor is to be formed uncovered; and (c) further oxidizing the predetermined regions of said semiconductor layer to make said oxide layer penetrate through said semiconductor layer in the direction of its thickness, thereby isolating the first and second regions from each other, and, at the same time, oxidizing the uncovered surface of said second region to form a surface oxide film of said second region in which said inverse transistor is to be formed, said surface oxide film of said second region being thicker than a surface oxide film of said first region in which said normal transistor element portion is to be formed so that said second region is made thinner than said first region.

Claim 9

A method of fabricating a semiconductor integrated circuit device comprising: (a) forming a semiconductor layer of a first conductivity type on the surface of a semiconductor substrate of a second conductivity type opposite to said first conductivity type; (b) selectively oxidizing a predetermined portion of said semiconductor layer to an intermediate depth of said semiconductor layer in the direction of its thickness, thereby to form an oxide layer having a thickness and to make first and second surface portions separated from each other by said oxide layer; (c) masking said first surface portion with an oxidation-resistant mask while leaving said second surface portion unmasked; and thereafter (d) increasing said thickness of said oxide layer by thermal oxidation growth to make an oxide isolation layer for dividing said semiconductor layer into a first region in which a normal transistor is to be formed and a second region in which an inverse transistor is to be formed and, at the same time, oxidizing said unmasked second surface portion by said thermal oxidation growth to make a surface oxide film of said second surface portion that is thicker than a surface oxide film of said first surface portion so that said second region is made thinner than said first region.

Claim 10

A method of fabricating a semiconductor integrated circuit device comprising: (a) forming a semiconductor layer of a first conductivity type on the surface of a semiconductor substrate of a second conductivity type opposite to said first conductivity type; (b) selectively oxidizing a predetermined portion of said semiconductor layer to an intermediate depth of said semiconductor layer in the direction of its thickness, thereby to form an oxide layer having a thickness and to make first and second surface portions separated from each other by said oxide layer; (c) masking said first surface portion with an oxidation-resistant mask while leaving said second surface portion unmasked; and thereafter (d) increasing said thickness of said oxide layer by thermal oxidation growth to make an oxide isolation layer for dividing said semiconductor layer into a first region in which a normal transistor is to be formed and a second region in which an inverse transistor is to be formed and, at the same time, oxidizing said unmasked second surface portion by said thermal oxidation growth to make a surface oxide film of said second surface portion that is thicker than a surface oxide film of said first surface portion so that said second region is made thinner than said first region.

Claim 13

A method of fabricating a semiconductor integrated circuit device comprising: (a) forming a semiconductor layer of a first conductivity type on the surface of a semiconductor substrate of a second conductivity type opposite to said first conductivity type; (b) forming a first oxidation-resistant masking layer on a first predetermined surface portion of said semiconductor layer and a second oxidation-resistant masking layer on a second predetermined surface portion of said semiconductor layer, said second predetermined surface portion being separated from said first predetermined surface portion; (c) selectively etching the unmasked portion of said semiconductor layer to a depth of said semiconductor layer in the direction of its thickness; (d) oxidizing the etched portion of said semiconductor layer to form an oxide layer having a thickness; (e) removing said second oxidation-resistant masking layer, while leaving said first oxidation-resistant masking layer on said first predetermined surface portion; and (f) increasing said thickness of said oxide layer by thermal oxidation growth to make an oxide isolation layer for dividing said semiconductor layer into a first region in which a normal transistor is to be formed and a second region in which an inverse transistor is to be formed and, at the same time, oxidizing said unmasked second surface portion by said thermal oxidation growth to make a surface oxide film of said second surface portion that is thicker than a surface oxide film of said first surface portion so that said second region is made thinner than said first region.

Claim 14

A method of fabricating a semiconductor integrated circuit device comprising: (a) forming a semiconductor layer of a first conductivity type on the surface of a semiconductor substrate of a second conductivity type opposite to said first conductivity type; (b) forming a first oxidation-resistant masking layer on a first predetermined surface portion of said semiconductor layer and a second oxidation-resistant masking layer on a second predetermined surface portion of said semiconductor layer, said second predetermined surface portion being separated from said first predetermined surface portion; (c) selectively etching the unmasked portion of said semiconductor layer to a depth of said semiconductor layer in the direction of its thickness; (d) oxidizing the etched portion of said semiconductor layer to form an oxide layer having a thickness; (e) removing said second oxidation-resistant masking layer, while leaving said first oxidation-resistant masking layer on said first predetermined surface portion; and (f) increasing said thickness of said oxide layer by thermal oxidation growth to make an oxide isolation layer for dividing said semiconductor layer into a first region in which a normal transistor is to be formed and a second region in which an inverse transistor is to be formed and, at the same time, oxidizing said unmasked second surface portion by said thermal oxidation growth to make a surface oxide film of said second surface portion that is thicker than a surface oxide film of said first surface portion so that said second region is made thinner than said first region.