SEMICONDUCTOR DEVICE WITH SELF-ALIGNED CONTACT TO BURIED SUBCOLLECTOR

摘要

A P- semiconductor material substrate (10) which has been ion-implanted with N-type dopants to form an N+ subcollector layer (12) is annealed in Argon to further remove implant damage and drive the dopant ions deeper into the P substrate (10). Next a lightly doped N- epitaxial layer (14) is grown on the N+ subcollector layer (12). This forms the blanket collector. A P- well region is formed by growing a pad oxide (15) of 10nm on the N- epi layer (14) and a 200nm layer of nitride (17) is then deposited on top of the layer oxide (15). A photoresist etch mask is used to pattern the P- well region. A reactive ion etch is performed through the dielectric oxide (15) and nitride layers (17), through the epitaxial layer (14) and stopping in the subcollector layer (12). By the end of a typical bipolar process, the N+ subcollector can be as wide as 1.5 microns. The depth of the P well is limited to the thickness of the N- epi (14). A layer (16, 18) 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 (14) and includes a P+ heavily doped layer (16) and a lightly P- doped surface layer (18). The P+ doped layer (16) may also include a more lightly doped layer (14) directly in contact with the epitaxial layer (14) to improve yield from defects occurring due to immediately growing a P+ epitaxial layer (16) on top of a heavily doped N+ layer (12). The heavily doped P+ layer (16) provides the low resistance contact to the collector region and the lightly doped P- layer (18) is the collector region and its thickness is determined by the diffusion of the heavily doped layer during the entire process.