SiGeHBT Device inMixedDryWetEtching

IInthispaper,a self-aligned SiGe/Si HBT was fabricated basedon dry/wet etching, inwhichSiandSiGe materials wereetched byKOH (potassium hydroxide) solution andSF6(sulfur hexafluoride). InthetermsofmesaSiGeHBT production, itisakeytechnology tocontrol theetchofultra-thin SiandSiGefllm. WhenN+/Nsilicon inemitter region isetched, thelength ofetchtimeiscritical. Ifetchtimeistoolong, SiGe layer isapttobeetched, sothatnoHBT isavailable; ifetchtime istooshort, N+/NSiremains onbasecontact, sothatemitter and baseareshorted. Despite asmall lateral etch, dryetching doesn't benefit therealization ofself-alignment process, norbenefit improvement ofyield andfmax.Inthispaper,basedonthe chemical properties ofsilicon andgermanium, dryandwetetches wereproperly combined toetchsilicon andsilicon germanium. First, N+/NSioutside emitter wasetched withintentional lateral etchusing KOH solution. Then,SiGewasetched bySF6.Asa result, SiGeHBT withself-alignment ofemitter tobasehasbeen developed. The measuredresults are:cutofffrequency fT=103.3GHz, maximumoscillation frequency fmax=124.2GHz.