Estudo do processo de deposição e das propriedades estruturais e opticas de filmes polimericos preparados em plasmas de C2 H2, C2 H2-SF6 e hexametildisiloxano

AUTOR(ES)
DATA DE PUBLICAÇÃO

1992

RESUMO

Plasma polimerization amorphous thin films were deposited in glow discharge plasmas of C2H2, C2H2 - SF6, C2H2 - Ar, and hexamethyldisiloxane ( HMDS ). Both the discharges and films were studied. Two vaccum systems have been used for the depositions. In one of the systems, d.c. discharge was sustained between two circular parallel plate electrodes, inside a stainless stell vaccum chamber. ln the other, the discharge was excited by r.f. fields ( 120 MHz ) in a Pyrex barrel reactor. Plasma diagnosis were performed in the r .f. system by actinometric optical emission spectroscopy ( AOES ) using He, N2 and Ar as actinometers. An intense molecular fragmentation was detected in the r.f. plasmas and AOES allowed relative measurements of the density of reactive species as a function of the discharge parameters ( gas composition and pressure and applied r.f. power ). The reactive species measured were: CH for C2H2; H,F, CH, CF and CF2 from C2H2 - SF6; and SiH, CO, H and C H from HMDS. The molecular structure of the films wa.s studied by infrared transmission spectroscopy. Upon integration of the infrared bands, relative bond densities could be determined. For some of the films, the relative densities of the C - H and C - F bonds were taken as the relative densities of H and F, respectively. Several interesting correlations were found to exist between the composition and structure of the films and the plasma parameters. As examples: ( 1 ) the F density of samples prepared in C2H2 - SF6 discharges increases with increasing plasma concentration of CF and CF2 species; ( 2 ) in the C2H2 - Ar d.c. discharges, a polymeric highly hydrogenated film structure gradually turns to a graphytic structure as the voltage between the electrodes in the chamber is raised. Also, the plasma parameters correlate well with the rate of film deposition and the data indicate that. both the concentratin or reactive species in the plasma and the bombardment of the film surface by charged particles from the discharge contribute to film growth. From uv-visible transmission spectra of both d.c. and r.f. films, the indcx or refraction, n, the absorption coefficient, a, and the optical gap E04, could be determined. The dependence of n and a on the photon energy, discharge composition, applied voltage of r.f. power, was examined. For the films prepared in C2H2 and C2H2 - Ar plasmas, E04 is found to incrcase strongly with increasing C - H bond density, nH. The dependence of E04 on the C - H bond density is similar to the observed in the other amorphous materials like hydrogenated amorphous silicon: E04 increases strongly with increasing nH

ASSUNTO(S)

fisico-quimica polimero e polimerização fisica

ACESSO AO ARTIGO

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