Hydrogen-induced breakdown of low-temperature molecular-beam epitaxy of Si

Low-temperature molecular-beam epitaxy of Si is characterized by the existence of an epitaxial thickness ${\mathit{h}}_{\mathrm{epi}}$, below which the film is epitaxial and above which the film turns amorphous. Epitaxial films with a thickness beyond ${\mathit{h}}_{\mathrm{epi}}$ can be grown, provided a rapid-thermal-anneal (RTA) step to a sufficient temperature, ${\mathit{T}}_{\mathrm{RTA}}$, is executed before reaching ${\mathit{h}}_{\mathrm{epi}}$. Positron-annihilation spectroscopy shows that ${\mathit{T}}_{\mathrm{RTA}}$=450 °C is not sufficient but 500 °C is. We explain this cutoff in RTA temperature using a model based on Si-H bond breaking. Nuclear reactions analysis support this model and show a high concentration of hydrogen in films grown with RTA below 450 °C. According to the proposed model, a reduction of the hydrogen content in the growth ambient should lead to larger ${\mathit{h}}_{\mathrm{epi}}$.