Fracture Behavior of Single- and Polycrystalline Silicon Films for MEMS Applications
Fracture behaviors of silicon films were evaluated by microtensile methods. We fabricated two types of specimens using surface micromachining, one for a test device for microtensile testing only and the other for a microtensile-compatible resonating device driven by alternating electrostatic force. The piezoelectric-driven uniaxial stress-strain measurement system was designed to evaluate the mechanical properties of thin films. We used UV adhesive to grip the device to the microtensile system, and the grip was made of UV-transparent glass in order to cure the underlying UV adhesive layer. To assess fracture toughness, we used newly proposed methods combining resonance frequency and microtensile methods. The fracture strength of single- and polycrystalline silicon showed dependence on geometry and doping condition. By varying the geometry, we analyzed the effect of the CMP side and the dry-etched side on changes in the mean fracture strength. Atomic force microscopy observation showed that the larger flaws of the dry-etched side were significant in decreasing the mean fracture strength. Fracture toughness based on fracture mechanics with a precrack was evaluated by newly proposed methods combining resonance frequency and microtensile techniques. The measured toughness was independent of specimen geometry but dependent on doping condition. The measured fracture toughness of notched specimens was 33% higher than that of pre-cracked specimens, even though the notch radius was as small as 1.4µm. The effects of notch-tip radius and doping on fracture toughness of silicon film were also analyzed.
Young-Jin Kim, Dong-Ho Bae and Yun-Jae Kim
D. I. Son et al., "Fracture Behavior of Single- and Polycrystalline Silicon Films for MEMS Applications ", Key Engineering Materials, Vols. 297-300, pp. 551-556, 2005