The kinetics of etching of hydrogenated amorphous material by a H plasma were studied by means of in situ spectroscopic ellipsometry measurements. The formation of a H-rich sub-layer was emphasized. Its thickness increased from 7 to 27nm when the temperature during H-plasma treatment was increased from 100 to 250C. This effect was interpreted by solving the differential equation for trap-limited H diffusion through a mobile surface. By attributing the thickness of this sub-layer to the mean diffusion distance of H, values were deduced - for the effective H diffusion coefficient - that were higher than 10-14cm2/s; with an activation energy of 0.22eV. The density of H traps was found to decrease from 7.3 x 1018 to 4.5 x 1017/cm3 as the temperature of the H treatment was increased from 100 to 250C; with an activation energy of 0.43eV. This effect was interpreted in terms of a thermal equilibrium that involved H transitions between shallow states and H-trapping sites.

Hydrogen-Plasma Etching of Hydrogenated Amorphous Silicon - a Study by a Combination of Spectroscopic Ellipsometry and Trap-Limited Diffusion Model. F.Kaïl, A.Fontcuberta i Morral, A.Hadjadj, P.Roca i Cabarrocas, A.Beorchia: Philosophical Magazine, 2004, 84[6], 595- 609