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Hydrogen-plasma etching of hydrogenated amorphous silicon: a study by a combination of spectroscopic ellipsometry and trap-limited diffusion model |
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| Authors: | F Kaïl A Fontcuberta I Morral A Hadjadj P Roca I Cabarrocas A Beorchia |
| Institution: | 1. Dynamique des Transferts aux Interfaces (Unité Mixte de Recherche associée au CNRS 6107) , Faculté des Sciences , Moulin de la Housse BP 1039, 51687 Reims Cedex 2, France;2. Laboratoire de Physique des Interfaces et des Couches Minces (Unité Mixte de Recherche associée au CNRS 7647) , Ecole Polytechnique , 91128 Palaiseau Cedex, France;3. Laboratoire de Physique des Interfaces et des Couches Minces (Unité Mixte de Recherche associée au CNRS 7647) , Ecole Polytechnique , 91128 Palaiseau Cedex, France;4. Dynamique des Transferts aux Interfaces (Unité Mixte de Recherche associée au CNRS 6107) , Faculté des Sciences , Moulin de la Housse BP 1039, 51687 Reims Cedex 2, France |
| Abstract: | The kinetics of etching hydrogenated amorphous silicon by a hydrogen plasma has been studied by in-situ spectroscopic ellipsometry measurements. The formation of a hydrogen-rich sublayer is clearly emphasized. Its thickness increases from 7 to 27?nm when the temperature during the hydrogen-plasma treatment is raised from 100 to 250°C. This effect is interpreted by solving the differential equation for trap-limited hydrogen diffusion through a mobile surface. By assigning the thickness of this sublayer to the mean diffusion distance of hydrogen we determined values of the effective diffusion coefficient of hydrogen higher than 10?14?cm2s?1 with an activation energy of 0.22?eV. The density of hydrogen traps is found to decrease from 7.3 × 1018 to 4.5 × 1017?cm?3 as the temperature of the hydrogen treatment increases from 100 to 250°C with an activation energy of 0.43?eV. This effect is interpreted by a thermal equilibrium involving hydrogen transitions between shallow states and hydrogen-trapping sites. |
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