Structural studies on Si:H network before and after solid phase crystallization using spectroscopic ellipsometry: Correlation with Raman spectroscopy and transmission electron microscopy

The structure of hydrogenated silicon films (Si:H) before and after solid phase crystallization (SPC) has been investigated by detailed study of spectroscopic ellipsometry (SE). The Si:H films have been deposited by radio frequency plasma enhanced chemical vapor deposition (RF PECVD) system varying deposition power density from 0.03 W/cm2 to 0.46 W/cm2, just below the onset of amorphous to nano-crystalline transition region. Solid phase crystallization of the Si:H network has been done by thermal annealing of the films in a vacuum furnace. Different bulk compositions of the as deposited Si:H network and annealed (polycrystalline) films have been calculated from the fitted parameters obtained from the simulation of the ellipsometry data by Bruggeman effective medium approximation (BEMA) method. More compact and void free structure in the bulk layer of the as deposited films has been observed at low power deposition region. Whereas void fraction in the bulk and surface roughness layer has increased with increase of deposition power density. For the annealed films higher crystallinity at the bulk layer with fewer voids has been observed at the low power region but in the surface roughness layer void fraction dominates in all the low and high power deposited films. The results obtained from the spectroscopic ellipsometry study have been correlated with Raman spectroscopy and transmission electron microscopy for both the as deposited and annealed films.