Improved NPN Process and Structure
Original Publication Date: 1981-Feb-01
Included in the Prior Art Database: 2005-Feb-10
A self-aligned NPN transistor with an oxide insulator bounding the extrinsic base layer is shown in Fig 1. The key steps (not shown) in forming the SiO(2) layer between the P/+/ polysilicon and the underlying subcollector (N/+/) involve etching the epi layer down to the subcollector prior to forming the base and emitter regions, and oxidizing thermally at low temperature. This produces a much thicker SiO(2) film on the N/+/ subcollector as compared to the N /-/epi exposed on the sidewall of the etched depression. A dip etch can then be used to completely remove the oxide on the N/-/ sidewall while leaving an SiO(2) film over the subcollector region. Subsequent polysilicon deposition to fill the depression, etc., results finally in the structure of Fig. 1.