Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition of Epitaxial Silicon onto (100) Silicon: I . The Influence of Prebake on (Epitaxy/Substrate) Interfacial Oxygen and Carbon Levels

Abstract

This investigation is concerned with the influence of a vacuum prebake on oxygen and carbon levels at epitaxial silicon/silicon (100) interfaces. The epitaxial layers are deposited in an ultrahigh vacuum, rapid thermal reactor using chemical vapor deposition techniques. Secondary ion mass spectroscopy (SIMS) is used to evaluate carbon and oxygen levels at the epitaxy/substrate interface. We show that a vacuum prebake can be effectively used following a standardex situ clean that consists of an RCA clean, a dilute (5%) dip, and a rinse in deionized water. The results show that if epitaxial deposition is initiated by introducing the reactive gases into the chamber at the prebake temperature, oxygen and carbon levels below the sensitivity limits of secondary ion mass spectroscopy are obtained at the epitaxy/substrate interface. This result can be reproducibly achieved with a low thermal budget prebake of even after a relatively long rinse (∼300 s) in deionized water. We propose that the mechanism responsible for cleaning is thermal desorption of oxygen and hydrocarbons from the (100) surface of silicon. We show that the surface obtained with this ex situ clean is very stable and, hence, the wafer can be left in a clean ultrahigh vacuum environment for many hours without detectable changes in the oxygen and carbon levels. On the other hand, results indicate that when the prebake is terminated by cooling the wafer to the ambient temperature of the reactor, carbon is readsorbed on the silicon surface at a peak concentration of . We also show that when a small amount of hydrogen is introduced into the reactor during the prebake, a higher thermal budget is required to remove oxygen from the surface. This observation is attributed to a higher background associated with the presence of hydrogen. It is concluded that vacuum prebake is an attractive surface preparation technique which effectively reduces oxygen and carbon levels on a silicon (100) surface below the SIMS sensitivity limits.