Abstract
Low stress silicon carbide films with good uniformity in thickness and composition were deposited by varying the deposition parameters in a PECVD unit. The effects of deposition parameters on structure, chemical state and stress distribution of these films in as-deposited state were investigated. The as-deposited films were amorphous and under compressive stress typically. A low compressive film with a stress level of –160 MPa was obtained at low substrate temperature (250℃) under a appropriate deposition pressure of 1100 mtorr. The chemical state and stress distribution were studied as a function of the annealing temperatures in the range from 400℃ to 650℃. The hydrogenated bonds decreased with the increase in annealing temperatures around 500℃ ~ 600℃, causing the out-diffusion of hydrogen. Owing to breaking of hydrogenated bonds, the recombination of unsatisfied bonds on silicon and carbon atoms was promoted, enhancing the bond density of Si-C stretching mode. Meanwhile, the stress could be further reduced to achieve the stress-free film (0.7 MPa) by a post-deposition annealing and transited from the compressive region to the tensile region. The stress relaxation was ascribed to the dissociation of hydrogenated bonds and incorporation of hydrogen. As a result, the Si-C bonds were created, leading to the formation of tensile stress. Residual stress in films is normally created in the process and brings about the unwanted deformation or fail of structures, particularly the free-standing structures without constraint in the substrates. Low stress silicon carbide films are deposited by adjustment of deposition parameters and controlled by an effective method through rapid thermal annealing. The final stress could be controlled effectively and precisely by a discrete annealing method, approaching a steady state after several minutes. In addition, self-deformed micromachined cantilevers are fabricated to exhibit the gradient stress from the curvature of beams. The gradient stress is negative in the as-deposited state and then recently. The etching rate are less than 10A/hr in both 33 wt.% transforms to positive after annealing. Furthermore, PECVD silicon carbide is a potential material used as etching mask (85℃) KOH and 49 wt.% (R.T.) HF etchants after immersion for 4.5 and 5 hours, respectively