Disorder in silicon films grown epitaxially at low temperature

Homoepitaxial Si films were prepared by electron cyclotron resonance plasma enhanced chemical vapor deposition on $\mathrm{Si}\text{(100)}$ substrates at temperatures of 325–500 °C using ${\mathrm{H}}_2,$ Ar, and ${\mathrm{SiH}}_4$ as process gases. The gas composition, substrate temperature, and substrate bias voltage were systematically varied to study the breakdown of epitaxial growth. Information from ion beam techniques, like Rutherford backscattering and heavy-ion elastic recoil detection analysis, was combined with transmission and scanning electron micrographs to examine the transition from ordered to amorphous growth. The results suggest that the breakdown proceeds in two stages: (i) highly defective but still ordered growth with a defect density increasing with increasing film thickness and (ii) formation of conically shaped amorphous precipitates. The hydrogen content is found to be directly related to the degree of disorder which acts as sink for excessive hydrogen. Only in almost perfect epitaxially grown films is the hydrogen level low, and an exponential tail of the H concentration into the crystalline substrate is observed as a result of the diffusive transport of hydrogen.