Self-Aligned SiGe HBT Based on Combined Dry and Wet Etching

Abstract

In this paper, a self-aligned SiGe/Si HBT has been fabricated based on dry/wet etching, where Si and SiGe materials were etched by KOH (potassium hydroxide) solution and SF6(sulfur hexafluoride). It is a key technology to control the etch of ultra-thin Si and SiGe film. When N+/N silicon in emitter region is etched, the length of etch time is critical. Despite a small lateral etch, dry etching doesn't benefit the realization of self-alignment process, nor benefit improvement of yield and fmax. In this paper, based on the chemical properties of silicon and germanium, dry and wet etches were properly combined to etch silicon and silicon germanium. First, N+/N Si outside emitter was etched with intentional lateral etch using KOH solution. Then, SiGe was etched by SF6. Finally, SiGe HBT with self-alignment of emitter to base has been developed. The measured results are: cutoff frequency fT=103GHz, maximum oscillation frequency fmax=124GHz.