Fabrication of Low-Stress Plasma Enhanced Chemical Vapor Deposition Silicon Carbide Films

Abstract

Low stress silicon carbide films with good uniformity in thickness and composition were deposited by varying the deposition parameters in a plasma enhanced chemical vapor deposition (PECVD) unit. The effects of deposition parameters on structure, chemical state and stress distribution of these films in the as-deposited state were investigated. The as-deposited films were typically amorphous and under compressive stress. A low compressive film with a stress level of -160 MPa was obtained at low substrate temperature (250°C) under an appropriate deposition pressure of 1100 mTorr. The chemical state and stress distribution were studied as a function of annealing temperatures in the range from 400°C to 650°C. The hydrogenated bonds decreased with the increase in annealing temperatures around 500–600°C, causing the outdiffusion of hydrogen. Owing to the breakage of the hydrogenated bonds, the recombination of unsaturated bonds on silicon and carbon atoms was promoted, enhancing the bond density of the Si–C stretching mode. Meanwhile, the stress could be further reduced to achieve a stress-free film (0.7 MPa) by post deposition annealing and shifting from the compressive region to the tensile region. The stress relaxation was ascribed to the dissociation of the hydrogenated bonds and the incorporation of hydrogen. As a result, Si–C bonds were created, leading to the formation of tensile stress.