On stress reduction of tetrahedral amorphous carbon films for moving mechanical assemblies

Abstract

The as deposited amorphous carbon (a-C) films, prepared at −80 V by filtered cathodic vacuum arc system, exhibit high intrinsic compressive stress and which limits the thickness of the film to 150–180 nm. The quest to overcome the above limitation results in several stress reduction techniques. Annealing, metal, silicon or boron incorporation, preparation of films in conjunction with substrate pulse biasing, and ion irradiation are major techniques that are being studied for stress reduction. Rapid thermal annealing of the a-C films (∼100 nm) prepared at −80 V reveals that, stress reduction of approximately 80% can be easily achieved by annealing the film at 200 °C for 2 min. Incorporation of approximately 1.7 at.% Al in the film combined with annealing (600 °C, for 2 min) can reduce the stress to a value as low as 200 MPa. However, the effort (repetitive steps of deposition and annealing) required in growing a micron or thicker film can be extensive. Stress reduction by depositing the film in conjunction with high substrate pulse biasing is found to be very effective. Stress reduction of approximately 90–95% can be easily achieved by varying the pulse parameters. However, this results in a relatively softer film with slightly higher surface roughness. Finally, a two-step approach has been attempted to acquire superior quality low stress thick a-C films. Thick multi-layered (layers of soft and hard) a-C films with superior quality were deposited in the first step, followed by rapid thermal annealing of the film. The annealing of the thick multi-layered a-C film at 200 °C for 2 min results in a stress reduction of approximately 35–40%, and that at 600 °C results in a stress reduction of approximately 55% retaining stress values of approximately 2.8 and 1.89 GPa, respectively. The studies suggest that preparation of films in conjunction with substrate pulse biasing by varying the pulse parameters is the best way to prepare low stress films for moving mechanical assemblies.