Process for forming semiconductor devices with polycrystalline diffusion pathways and devices formed thereby

Abstract

Abstract A process wherein epitaxial silicon is grown on a substrate of single-crystal silicon with islands of silicon dioxide thereon, whereby single crystal epitaxial material is grown over the single-crystal substrate areas, but polycrystalline silicon is grown over the silicon dioxide islands. Since impurity diffusion occurs more rapidly through polycrystalline material than through single-crystalline material diffusion schemes can be obtained using the rapid diffusion pathway provided by the polycrystalline material to provide subsurface configurations which are completely enclosed by single-crystal material, for instance, a buried subcollector can be formed by growing polycrystalline silicon material horizontally, extending a narrow polycrystalline channel upward to the device surface, and subsequently diffusing impurities down through the narrow vertical polycrystalline channel into the lateral polycrystalline subcollector. Further, an electrical underpass can be formed which has a very low resistance by again using the rapid diffusion characteristics of polycrystalline silicon to grow polycrystalline silicon of the desired shape which can be rapidly diffused to provide, in comparison to background, a high conductivity path. By control of the substrate crystalline orientation, polycrystalline material can be grown which terminates because of sidewall convergence. This is desirable where it is required to terminate polycrystalline growth and begin single-crystal growth without any alteration in process conditions. The devices described are also claimed.

Inventors

• 👤 Joseph J Chang
• 👤 Madhukar B Vora

Bibliographic Details