New self-aligned complementary bipolar transistors using selective-oxidation mask

This paper describes a new self-aligned complementary transistor structure which makes a high-speed and high-accuracy analog bipolar LSI possible. This device structure consists of a 2 µm epitaxial layer, a non-LOCOS trench isolation burried with polycrystalline silicon, and complementary (NPN and vertical PNP) transistors which have self-aligned active base and emitter. The principal feature of the fabrication process is forming an active base and an emitter by ion implantations through the silicon nitride film using an oxidation film as a mask which lies upon an inactive base region. Because residual defects induced by the ion implantations are confined into the emitter region, the leakage current at the base-emitter junction is minimized. Current gains of the both transistors (NPN and PNP) are constant down to low current region IC=10^-9A. The distribution of base-emitter offsets (ΔVBE) of transistor pairs is O.2mV as the standard deviation; 3σ. Maximum values of fTof NPN and PNP transistors are 6 GHz and 1.5 GHz, respectively.