A STUDY OF THE OXIDATION SLOW-DOWN MECHANISM INDUCED BY CARBON CONTAMINATION ON SILICON SURFACE

Carbon incorporation on the silicon surface by reactive ion etching sl ows down subsequent rapid thermal oxidation of the surface. Carbon eff ects on O-2 partial pressure dependency and activation energy of the o xidation rate were measured. Both the carbon-containing sample and the monitor sample shared the square-root dependency on O-2 pressure and activation energy of about 1.44 eV. The results strongly suggest invol vement of oxygen dissociation in the oxidation reaction. The dissociat ion moderates substantial depletion of [O-2](i) (concentration of mole cular oxygen at the silicon/oxide interface) into mild reduction of [O ](i) (concentration of atomic oxygen at the interface) which is actual ly proportional to the oxidation rate. Hence, the slowdown must be att ained by severely depleting [O-2](i) at the interface without any furt her impacts on the basic mechanism of the oxidation. The depletion was brought about by forming an anomalous layer at the silicon/oxide inte rface during the oxidation. The layer disfavors the presence of oxygen by increasing its free energy, rather than strongly obstructing its t ransport by heightening the energy barrier against it. The formation o f the layer seems to be triggered by carbon incorporation from the sub strate into the layer and integration into the oxide network with C-O bonding.