I n s i t u spectroellipsometric study of the nucleation and growth of amorphous silicon

Abstract

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 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.

Surface roughening during plasma-enhanced chemical-vapor deposition of hydrogenated amorphous silicon on crystal silicon substrates

“…Drévillon and co-workers 34,35 and Collins and co-workers 5,[34][35][36][37][38] have examined a-Si:H grown on a variety of substrates. 5,[36][37][38][39][40] We compare our results with those for the silicon substrates with the native oxide, which should most closely resemble our surface.…”

In situ single wavelength ellipsometry studies of high rate hydrogenated amorphous silicon growth using a remote expanding thermal plasma

“…In the literature it has frequently been shown, that by including extra overlayers in the optical growth model the ellipsometric fit of a-Si:H growth improves. 1,3,13,[22][23][24] This top layer can be regarded as the surface roughness and has a smaller refractive index than the bulk. The roughness is modeled by a top layer consisting of a certain volume fraction of voids.…”

Spectroscopic ellipsometry of germanium growth on hydrogen-terminated silicon (111)

“…The deposition process is monitored in situ by RTSE to obtain the evolution of the optical functions and to get information about the microstructure and nucleation process. 3 The depositions were carried out in a turbo-pumped UHV chamber with a base pressure below 10 Ϫ8 mbar. The Ge 2 H 6 and He, used to flush the laser entry windows, were fed into the system via mass flow controllers to ensure defined partial pressures.…”