Semiconductor device with self-aligned contact to buried subcollector

Abstract

A P- semiconductor material substrate which has been ion-implanted with N-type dopants to form an N+ subcollector layer is annealed in Argon to further remove implant damage and drive the dopant ions deeper into the P substrate. Next a lightly doped N- epitaxial layer is grown on the N+ subcollector layer. This forms the blanket collector. A P- well region is formed by growing a pad oxide of 10 nm on the N-epi layer and a 200 nm layer of nitride is then deposited on top of the layer oxide. A photoresist etch mask is used to pattern the P- well region. A reactive ion etch is performed through the dielectric oxide and nitride layers, through the epitaxial layer and stopping in the subcollector layer. A layer of low temperature expitaxial material is grown over the structure using ultra-high vacuum/chemical vapor depositions such that the epitaxial layer extends above the surface of the epitaxial layer and includes a P+ heavily doped layer and a lightly P-doped surface layer. The heavily doped P+ layer provides the low resistance contact to the collector region and the lightly doped P-layer is the collector region and its thickness is determined by the diffusion of the heavily doped layer during the entire process.