12.5 The Mechanism of Deposition of Silicon Dioxide from TEOS

The pyrolytic decomposition of TEOS (tetraethoxysilane, $\mathrm{Si(OC_2H_5)_4}$) resulting in the deposition of SiO$_2$ films on silicon wafers is a popular LPCVD (low pressure chemical vapor deposition) process. Process temperatures are usually in the range of $650\,\text{\textcelsius}$ to $750\,\text{\textcelsius}$ and thus not high enough to cause the diffusion of dopants in silicon. Other advantages are that high quality films can be deposited, that TEOS is relatively low cost, easy to handle, and not as dangerous as other chemicals used in CVD processes.

Three models for the TEOS deposition reaction have been proposed: a heterogeneous deposition model, a homogeneous intermediate-mediated deposition model and a heterogeneous deposition with byproduct inhibition model. These are discussed, e.g., in [100] and summarized in the following. Raupp et al. conclude that ``TEOS pyrolysis likely occurs through the heterogeneous deposition mechanism in which TEOS decomposition products readsorb on the growing film and inhibit deposition'' [100].