Preparation of hydrogen passivated silicon for UHV-CVD low temperature epitaxy

Abstract

A critical step for successful growth of ultra-high vacuum chemical vapor deposition (UHV-CVD) epitaxial silicon films at low temperatures is the preparation and maintenance of a hydrogen passivated surface. A final 10:1 HF dip has been shown to provide a robust and extremely clean substrate for this purpose; interfacial oxygen and carbon levels of less than 1×1013 atoms/cm2 and low levels of structural defects are routinely observed after epitaxial growth. In this work, our understanding of the Si(100) hydrogen passivated surface is reviewed with emphasis on its stability to air and moisture exposure. Additionally, in an effort to reduce interfacial contamination levels even further and explore clusterable processes, other precleaning chemistries such as high pH NH4F and vapor HF have also been evaluated. While surface analysis measurements suggest that the NH4F preparation should be as good or better than the HF dip, the epitaxial film defect density is higher by several orders of magnitude than for the dilute HF preparation. The vapor HF process, while potentially clusterable and therefore desirable, has generally not provided hydrogen passivated surfaces that are clean enough for this application.