"Etude du mécanisme de croissance des couches a-Si :H élaborées par pulvérisation cathodique"

Abstract

"The present work deals with the study of interaction plasma-substrate effect on sputtered a-Si :H films growth mechanism. The experimental part was carried by varying two parameters : the RF power of electric discharge and substrate nature. The caracterization by scanning electronic microscopy of samples prepared on glass substrate at substrate temperature of 200°C, revealed a change of the surface morpholy with the variation of RF power. Indeed, a polycristallization was detected on sample surface deposited with higher power 400W. This result was confirmed by transmission electronic microscopy. The infrared spectroscopy (FTIR) showed a decrease of hydrogen content with increasing RF power. Besides this, an increase of material densification was detected by UV visible spectroscopy. On the other hand, the caractrization by SEM of the deposited films on various substrates with RF power fixed at 400W and substrate temperature at 200°C, showed a light surface roughness of the film prepared on single-crystalline silicon sustrate. However, the surface of film deposited on aluminum subtrate remains amorphous. In order to explain these results, we proceeded to the study of the plasma by three approaches : i) by calculating the strength generated by the impact of the plasma particules on the growing film according to pressure and to RF power, ii) by developping a physical model which allows to calculate the energy distribution of argon ions reaching the substrate, iii) we have also proposed a numerical model which allows temperature calculation of growing film with the deposition time. This study showed that the temperature of growing film is the most controlling parameter of a-Si :H films growth mechanism."