Fracture behavior of single-crystal silicon microstructure coated with stepwise bias-graded a-C:H film

Abstract

Fracture behavior in the tensile testing of a single-crystal silicon (SCS) microstructure with a stepwise bias-graded hydrogenated amorphous carbon (a-C:H) coating was investigated to explore the fracture mechanism of the coating−substrate system. All sides of the SCS microstructure (120 × 4 × 5 μm3) were coated uniformly with a 300-nm-thick a-C:H film deposited by plasma enhanced chemical vapor deposition (PECVD). In this research, four different bias conditions with stepwise changes were applied during deposition to make the hard−compliant or compliant−hard gradient in the coating film. The microstructure, chemical composition, and mechanical properties were evaluated by scanning electron microscopy, Raman spectroscopy, nanoindentation, and surface profilometry. A tensile test showed a significant increase in tensile strength for samples with a multilayer gradient coating, which was 6.3–56.6% higher than that of the SCS sample, and a similar increase was observed for fracture toughness. The fracture mechanisms were elaborated by analyzing the chemical composition and stress intensity factor. The results indicate that the tensile behavior was strongly affected by the surface energy and stress state of the a-C:H coating.