Sidewall Contact for npn/pnp Transistors by Selective Oxidation (SELOX)

The feasibility of a selfaligned sidewall base contact npn-transistor for high-speed integrated circuits using selective oxidation (Selox) for the definition of the polysilicon sidewall contact region has been shown. The selective oxidation is based on the increased low-temperature oxidation rate of n-type monosilicon for dopings above ¿ 10¹⁹cm^¿3. Besides npn transistors with reduced collector-base capacitance, lateral pnp transistors with p+ polysilicon emitters have been realized. Due to the underlying oxide, these do not exhibit the usual excessive charge storage in and below the emitter, so that fT = 130 MHz has been achieved with a basewidth of 2.5 ¿m.