SiGe HBT Device in Mixed Dry Wet Etching

I In this paper, a self-aligned SiGe/Si HBT was fabricated based on dry/wet etching, in which Si and SiGe materials were etched by KOH (potassium hydroxide) solution and SF6 (sulfur hexafluoride). In the terms of mesa SiGe HBT production, it is a key technology to control the etch of ultra-thin Si and SiGe fllm. When N+/N silicon in emitter region is etched, the length of etch time is critical. If etch time is too long, SiGe layer is apt to be etched, so that no HBT is available; if etch time is too short, N+/N Si remains on base contact, so that emitter and base are shorted. 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. As a result, SiGe HBT with self-alignment of emitter to base has been developed. The measured results are: cutoff frequency fT=103.3GHz, maximum oscillation frequency fmax=124.2GHz.