Abstract: The invention comprises an improved integrated circuit structure wherein an active device is formed in a silicon substrate for forming an intrinsic base region over a buried collector and an emitter is formed on the intrinsic base region to comprise three electrodes of the active device and at least one extrinsic base segment is formed in the substrate adjacent to the intrinsic base region to provide a contact for the intrinsic base; the improvement which comprises: separating the extrinsic base segment from the emitter formed on the intrinsic base to prevent the formation of a parasitic P-N junction between the extrinsic base and the emitter.

Abstract: The invention comprises an improved isolation slot in an integrated circuit structure which minimizes damage to the silicon substrate. The improved isolation slot is formed by etching a slot in the substrate of an integrated circuit structure; depositing a buffer layer in the slot adjacent the walls of the slot; and forming an isolation oxide layer in the slot over the buffer layer; whereby the presence of the buffer layer between the substrate and the isolation oxide minimizes damage to the substrate by the oxide. In a preferred embodiment, the buffer layer comprises polysilicon which is partially oxidized to form the isolation oxide layer. A barrier layer is formed between the slot walls and the polysilicon buffer layer to electrically insulate the polysilicon from the adjoining integrated circuit structure.