Insituspectroellipsometric study of the nucleation and growth of amorphous silicon

A. Canillas, E. Bertran, J. L. Andújar, B. Drévillon
1990 Journal of Applied Physics  
A detailed in situ spectroellipsometric analysis of the nucleation and growth of hydrogenated amorphous silicon (a:Si:H) is presented. Photoe1ectronic quality a-Si:H films are deposited by plasma-enhanced chemical vapor deposition on smooth metal (NiCr alloy) and crystalline silicon (c-Si) substrates. The deposition of a-Si:H is analyzed from the first monolayer up to a final thickness of 1.2 Jim. In order to perform an improved analysis, real time ellipsometric trajectories are recorded, using
more » ... are recorded, using fixed preparation conditions, at various photon energies ranging from 2.2 to 3.6 eV. The advantage of using such a spectroscopic experimental procedure is underlined. New insights into the nucleation and growth mechanisms of a-Si:H are obtained. The nucleation mechanism on metal and c-Si substrates is very accurately described assuming a columnar microstructural development during the early stage of the growth. Then, as a consequence of the incomplete coalescence of the initial nuclei, a surface roughness at the 10-15 A scale is identified during the further growth of a-Si:H on both substrates. The bulk a-Si:H grows homogeneously beneath the surface roughness. Finally, an increase of the surface roughness is evidenced during the long term growth of a-Si:H. However, the nature of the substrate influenced the film growth. In particular, the film thickness involved in the nucleation-coalescence phase is found lower in the case of c-Si (67 ± 8 A) as compared to NiCr (118 ± 22 A). Likewise films deposited on c-Si present a smaller surface roughness even if thick samples are considered ( > 1 /-lm). More generally, the present study illustrates the capability of in situ spectroellipsometry to precisely analyze fundamental processes in thin-film growth, but also to monitor the preparation of complex structures on a few monolayers scale.
doi:10.1063/1.346452 fatcat:f5bdcqy6xvgr7onzm7sbnrfq6q