Ion-surface interactions on c-Si(001) at the radiofrequency-powered electrode in low-pressure plasmas: Ex situ spectroscopic ellipsometry and Monte Carlo simulation study
- Regroupement quebecois sur les materiaux de pointe (RQMP) and Department of Engineering Physics, Ecole Polytechnique de Montreal, P.O. Box 6079, Station Centre-Ville, Montreal, Quebec H3C 3A7 (Canada)
We use variable-angle spectroscopic ellipsometry (VASE) to investigate oxide and interface formation during plasma-oxidation of monocrystalline Si(001) at the radiofrequency (rf) powered electrode of a plasma-enhanced chemical vapor deposition reactor. HF-etched c-Si(001) wafers were exposed to an oxygen plasma under conditions similar to those used in optical coatings deposition in order to ascertain the effects of plasma-bulk interactions, and to gauge to what depth O{sub 2}{sup +} and O{sup +} ions interact with and alter the structure and composition of the target in the presence of negative self-bias, V{sub B}. From VASE analyses, modifications are best described using a two-layer model: A top layer consisting of SiO{sub 2} and a defective interfacial layer (DL) composed of a mixture of c-Si, a-Si, and SiO{sub 2}. The saturation value of the modification depth (oxide and DL thickness) increases from 3.4{+-}0.4 to 9.6{+-}0.4 nm, for V{sub B} ranging from -60 to -600 V, respectively, and scales with E{sub max}{sup 1/2}, where E{sub max} is the maximum energy of ions from an rf discharge. These results are in agreement with nuclear ion-bulk interactions leading to atomic displacements and defect accumulation. The interfacial layer broadens with increasing verttical bar V{sub B} vertical bar while the fraction of a-Si detected increases from {approx}1% up to {approx}55% over the investigated V{sub B} range, indicative of ballistic and thus depth-dependent oxygen transport to the SiO{sub 2}-Si interface. Monte Carlo simulations in the binary collision approximation predict significant surface recession due to sputtering, therefore resulting in an apparent self-limiting oxidation mechanism. The surface layers reach their steady-state thicknesses within the first 2 min of plasma exposure and subsequently move into the bulk of the c-Si substrate as a result of oxide sputtering and oxygen transport.
- OSTI ID:
- 20776949
- Journal Information:
- Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films, Vol. 24, Issue 1; Other Information: DOI: 10.1116/1.2134709; (c) 2006 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1553-1813
- Country of Publication:
- United States
- Language:
- English
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