Process for fabricating a pedestal transistor

Claim 1

A method for fabricating a monolithic integrated circuit including at least one pedestal transistor device using a single epitaxial layer process comprising the steps of: a. providing a substrate of a first conductivity type, b. forming a raised pedestal region on said substrate by forming an oxide layer and an overlying masking layer on said substrate in an area substantially conforming to said pedestal region, the masking layer being selected to limit thermal growth thereunder, and then converting selected non-pedestal regions of the original substrate to an oxide and then removing the oxide and masking layer, c. diffusing an impurity of a second conductivity type into a limited surface area larger than and encompassing said pedestal region, said second conductivity type being opposite to said first conductivity type, so as to convert a second region of the substrate to a second conductivity type, said second region constituting a pedestal subcollector region, d. growing and forming a substantially flat epitaxial layer over said pedestal region by removing a reproduced pedestal region formed on the upper surface of the epitaxial layer, removing said reproduced pedestal region formed on the upper surface of the epitaxial layer by converting said reproduced pedestal region to an oxide, and etching away said converted oxide, e. forming said substantially flat epitaxial layer of a material having a higher resistivity than said pedestal subcollector region, f. diffusing a base region into said epitaxial collector layer over said subcollector pedestal region, and g. diffusing an emitter region into said base region so as to define a base-emitter junction located substantially coextensive with the pedestal subcollector region.

Claim 2

A method for fabricating a monolithic integrated circuit including at least one pedestal transistor device using a single epitaxial layer process comprising the steps of: a. providing a substrate of a first conductivity type, b. forming a raised pedestal region on said substrate by forming an oxide layer and an overlying masking layer on said substrate in an area substantially conforming to said pedestal region, the masking layer being selected to limit thermal growth thereunder, and then converting selected non-pedestal regions of the original substrate to an oxide and then removing the oxide and masking layer, c. diffusing an impurity of a second conductivity type into a limited surface area larger than and encompassing said pedestal region, said second conductivity type being opposite to said first conductivity type, so as to convert a second region of the substrate to a second conductivity type, said second region constituting a pedestal subcollector region, d. growing and forming a substantially flat epitaxial layer over said pedestal region by removing a reproduced pedestal region formed on the upper surface of the epitaxial layer, removing said reproduced pedestal region formed on the upper surface of the epitaxial layer by converting said reproduced pedestal region to an oxide, and etching away said converted oxide, e. forming said substantially flat epitaxial layer of a material having a higher resistivity than said pedestal subcollector region, f. diffusing a base region into said epitaxial collector layer over said subcollector pedestal region, and g. diffusing an emitter region into said base region so as to define a base-emitter junction located substantially coextensive with the pedestal subcollector region.