Micromechanical and tribological characterization of doped single-crystal silicon and polysilicon films for microelectromechanical systems devices

Microelectromechanical systems (MEMS) devices are made of doped single-crystal silicon, LPCVD polysilicon films, and other ceramic films. Very little is understood about tribology and mechanical characterization of these materials on micro- to nanoscales. Micromechanical and tribological characterization of p-type (lightly boron-doped) single-crystal silicon (referred to as “undoped”), p⁺-type (boron doped) single-crystal silicon, polysilicon bulk, and n⁺-type (phosphorous doped) LPCVD polysilicon films have been carried out. Hardness, elastic modulus, and scratch resistance of these materials were measured by nanoindentation and microscratching using a nanoindenter. Friction and wear properties were measured using an accelerated ball-on-flat tribometer. It is found that the undoped silicon and polysilicon bulk as well as n⁺-type polysilicon film exhibit higher hardness and elastic modulus than the p⁺-type silicon. The polysilicon bulk and n⁺-type polysilicon film exhibit the lowest friction and highest resistance to scratch and wear followed by the undoped silicon and with the poorest behavior of the p⁺-type silicon. During scratching, the p⁺-type silicon deforms like a ductile metal.