Polycrystalline Silicon Layers for Shallow Junction Formation: Phosphorus Diffusion from In Situ Spike-Doped Chemical Vapor Deposited Amorphous Silicon

Shallow and lateral homogeneous delineated n+p-junctions were formed utilizing solid source diffusion from a deposited amorphous silicon layer with an in situ imbedded ultrathin phosphorus-rich zone. SIMS, AES, and TEM investigations were carried out to analyze the dopant behavior in correlation to morphological and structural changes during subsequent heat treatments. After heat treatments up to 950°C the layer remained flat, surface roughness was found to be less than 3 nm. Dopant pile up at the Si-layer/Si-substrate interface was observed and interpreted on the basis of segregation phenomena. From the time dependence the P segregation-pile-up was found to be diffusion limited except for a small starting period. The dopant concentration in the Si-substrate drops down over more than 2 orders of magnitude in a thickness range less than 20 nm.