| 摘要 |
A process for forming a semiconductive device in which after a base region has been formed, a layer of polysilicon is deposited over the region. A protective covering, such as silicon nitride, is formed over areas of the polysilicon which overlay selected emitter sites and base contact sites. The protective covering prevents the replacing of the unprotected polysilicon with a dielectric such as silicon dioxide. The step of replacing the unprotected polysilicon is performed in one embodiment by a series of steps such as etching to remove the unprotected polysilicon and depositing silicon dioxide where the polysilicon was removed. In another embodiment, the unprotected polysilicon is first subjected to an electrolytic hydrofluoric solution, and then oxidized directly into silicon dioxide. If the polysilicon originally deposited was not doped with a conductivity-determining impurity, such an impurity may be ion-implanted into the remaining polysilicon. The polysilicon overlaying the base contact sites is removed to expose a portion of the base diffusion region. The conductivity-determining impurity is then diffused into the emitter site to form an emitter suitably protected by the overlaying polysilicon and electrically separated from a base contact site by silicon dioxide. |
