Thin-base bipolar technology by low-temperature photo-epitaxy

Due to the continuous reduction of pattern size in VLSIs, there is an urgent problem in vertical scaling for MOS and bipolar devices. Especially for high speed bipolar VLSIs, a very thin base with a high carrier concentration is required because the minimum delay at high power dissipation is predominantly determined by the intrinsic base width. A base region is conventionally fabricated by boron ion implantation into a collector region. The tailing of implanted boron distribution, channeling, prevents further reduction of base thickness and increase of boron concentration¹⁾. This paper presents a new bipolar transistor for high speed VLSIs. This transistor, called epitaxially-grown base transistor (EBT), is constructed with an epitaxial base layer photochemically-grown. This photo-epitaxy enables us to fabricate a very thin, highly-doped layer with little redistribution of dopants. Therefore, a very thin base layer can be realized for shorter base transit time, still maintaining a reasonable base resistance and avoiding punchthrough.