Method of fabricating n-type silicon regions and associated contacts

Abstract

Disclosed are improved bipolar and field effect transistors having n-type silicon regions and associated electrical contacts comprising monocrystalline silicon doped with arsenic and phosphorus. The transistors are fabricated by depositing on a silicon substrate a coating of amorphous silicon comprising a first layer heavily doped with phosphorus and a second layer below the first doped with arsenic. Energy is selectively applied to melt the coating. As the coating resolidifies and cools, arsenic diffuses into the substrate to form shallow n-type regions which are annealed by heat from the coating. Heavily phosphorus-doped, conductive monocrystalline silicon forms above the n-type regions on the substrate, whereas polycrystalline silicon forms above dielectric or other materials. Selective removal of the polysilicon yields shallow, annealed n-type regions integral with self-registered contacts. The resulting transistors have low RC time constants and low contact resistance.