CRITICAL ION ENERGY AND ION FLUX IN THE GROWTH OF FILMS BY PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION

Dual-mode microwave/radio frequency plasma-enhanced chemical-vapor dep osition allows one to decouple ion bombardment effects from processes in the discharge volume. This approach has been used to deposit three types of hydrogenated amorphous films at low substrate temperature and high deposition rate (approximately 10-20 angstrom/s): SiN(x), SiO2, and a-C:H. For each of these materials, we have determined critical va lues of the negative bias potential, V(B,C), of the average ion energy , E(i,c)BAR, and of the ion/condensing-atom flux ratio (phi(i)/phi(n)c , which characterize the transition from a porous to a densely packed microstructure. The evaluations are based on measurements of the films ' resistivity, dielectric loss tangent, microhardness, density, and st ress. The E(i,c)BAR, (phi(i)/phi(n))c values found are: 170 eV, 0.60 f or SiN(x); 70 eV; 0.26 for SiO2; and 80 eV, 0.28 for a-C:H. Ion bombar dment at energies above E(i,c)BAR has been found to account for a larg e portion of hydrogen in the films which is not chemically bonded. The results are interpreted in terms of a growth process involving surfac e diffusion of precursor species, and subplantation in hydrogen-rich s urfaces.