Effect of trace oxygen on the selective silicon deposition in a single-wafer RTP CVD reactor

The effect of trace oxygen on the selectivity as well as on the properties of selectively deposited silicon has been investigated. Silicon films were deposited with controlled added oxygen at low ppm levels in the growth ambient in a rapid thermal chemical vapor deposition (RTP CVD) system with SiCl2H2 (DCS) as the silicon source gas. It has been found that oxygen has no observable influence on the selectivity as well as on the growth rate in the temperature range of 800-900 degrees C. With increasing oxygen concentration, the deposited silicon exhibits a surface morphology typical of poly-Si. Silicon grown at higher temperatures can tolerate a higher oxygen concentration before turning polycrystalline. The effect of introducing oxygen at different stages in the deposition process as well as the effect of growth rate have also been examined for microstructure control. A novel technique to achieve selective poly-Si deposition has also been demonstrated. Trace oxygen is introduced during the growth cycle to destroy the Si lattice network. It is shown that poly-Si can be obtained with an oxygen concentration in the film below that typically observed in Czochralski (Cz) substrates. The results demonstrate a potential for facet-free selective silicon deposition (SSD) for the fabrication of elevated source/drain (E S/D) MOSFET devices.