AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP21
The AFM Study of the Growth Process of a-Si:H Films Deposited by Low Frequency PECVD

Wednesday, October 4, 2000, 11:00 am, Room Exhibit Hall C & D

Session: Poster Session
Presenter: M.N. Meytin, Moscow Institute of Electronic Technology, Russia
Authors: B.G. Budaguan, Moscow Institute of Electronic Technology, Russia
M.N. Meytin, Moscow Institute of Electronic Technology, Russia
A.A. Aivazov, UniSil Corp.
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In this work the growth process and surface morphology of a-Si:H films fabricated by the low frequency (55 kHz) PECVD at substrate temperatures from 40°C to 325°C was investigated.The results of the mass-spectra measurements of LF plasma have shown the presence of SiH3 and Si2Hx radicals.We detected large powder particles in plasma by laser beam scattering.The intensity of Si2Hx mass spectra peaks as well as the intensity of laser beam scattering decrease with the Ts increase, indicating on the decreasing of the probability of polymerization processes. The AFM analysis of a-Si:H surface reveals the island type morphology. The average diameter of islands increases with Ts, while the concentration of islands decreases. The dependence of the RMS roughness,w, on the thickness of the films,d, is w~d^b,where b~6. The high value of b (b>0.5 for a conventional 13.56MHz PECVD) and the dependence of islands diameter on Ts are proposed to be due to the participation of powder particles in the film growth. In that case the formation of a-Si:H surface morphology is controlled by two types of precursors-SiH3 radicals and powder particles. We performed computer modeling of the growth process. The initial diameter of islands formed from the powder particles and the rate of islands formation,Ci, were determined by the fitting of simulated RMS and islands diameter distribution to the experimental data. It was found that Ci decreases with increase of Ts,which correlates with the experimental data. The dependence of the island diameter on Ts is explained by the participation of SiH3 radicals in the growth process. The sticking of the SiH3 radicals to the film surface leads to the growth of island diameter, which is restricted by the boundaries of the neighbor islands. So,the higher the number of islands the lower their diameters and vice verse. This mechanism of island growth allows to explain the increase of the island diameter with the substrate temperature.