Transistors with boron bases predeposited by ion implantation and annealed in various oxygen ambients

When implanted boron is used as a replacement for a chemically predeposited base on silicon and driven-in in an oxidizing ambient, the gain (hFE) of the transistor is lower for a given base charge, Qb, and the emitter-base junction is leaky. A simple process which results in excellent junctions and transistor gain has been developed, featuring implantation into bare Si and a one-step anneal-diffusion drive-in in a % O2ambient. A comparative study of transistor properties was made for different processing: implanting into bare silicon and through oxides, and doing drive-in diffusions in various ambients from "no oxygen" (N2) to 100% O2. The reduced gain for the high percentage O2ambient is interpreted in terms of enhanced recombination near stacking fault-like defects in the emitter-base space charge region. For the low-percentage O2ambient the median standard deviation of the base sheet resistance improved from 7% (diffused) to 2% (implanted) and the median standard deviation of the hFEimproved from 19% to 15%.