Bipolar transistor and methods of forming bipolar transistors

摘要

A bipolar transistor comprises a base region and an an extrinsic base region being located generally adjacent to the base region. The extrinsic base region has implanted therein a dopant and a dopant diffusion-retarding substance. The dopant diffusion-retarding substance serves to reduce the diffusion of the dopant into the base region. Preferably, the dopant and diffusion-retarding substances are implanted such that there is a buffer zone in the extrinsic base region immediately adjacent to the base region into which the dopant may diffuse after implantation. The dopant may for example be boron, and the dopant diffusion-retarding substance may for example be a group IV element such as carbon or germanium.