Self-aligned bipolar transistor using double thermal oxidation

A novel process is proposed to self-align the emitter and extrinsic base in a bipolar transistor. The process involves the use of double thermal oxidation and RIE to create a steep oxide emitter sidewall. The method avoids the potential problems of LPCVD oxide and can remove the residual poly on the extrinsic base, both of which lead to base-emitter shorts. It also eliminates the need for growth of adhesion oxide and annealing of LPCVD oxide. The devices thus fabricated exhibit a high current gain of 130 and high punch-through voltage of 20 V