ABSTRACT
This chapter discusses the ultrahigh vacuum chemical vapor deposition (UHV/CVD) is compared to other silicon and silicon–germanium epitaxial deposition methods with emphasis on the ultralow temperature regime below 700°C and on 200 to 300 mm substrate size. It explores the UHV low-temperature reaction-limited silane deposition characteristics. The adsorption coefficients of silane, disilane, and trisilane molecules under UHV conditions were found to be dissimilar but only weakly temperature-dependent. Contamination originating from the reactor’s inner periphery is minimized by evacuating the chamber to UHV pressures. Epitaxial UHV/CVD of silicon–germanium is typically achieved by adding diluted germane or digermane to the precursor gas flow. The use of low temperatures during growth, as enabled by UHV/CVD, is expected to result in better alloy metastability because relaxation exhibits stronger thermally activated behavior as compared to growth. The concept of nucleation delay was extended to UHV/CVD in order to further reduce deposition temperatures.
