Micro/nanotribological studies of polysilicon and SiC films for MEMS applications

Microelectromechanical (MEMS) devices are currently made from single-crystal silicon, various polysilicon films and other ceramic materials. Silicon carbide (SiC) film has recently been pursued as a material for use in MEMS devices owing to its excellent mechanical properties and high-temperature capabilities. Since surface properties, friction and wear are important issues in such small-scale devices, it is essential that the materials used in MEMS have good micro/nanotribological properties. Using atomic force/friction force microscopy (AFM/FFM), surface roughness, microscale friction and microscale scratch/wear resistance of 3C-SiC (cubic SiC) Alms, as well as undoped single-crystal Si(100) and doped and undoped polysilicon films for comparison were measured. Nanohardness and modulus of elasticity were measured using a Nanoindenter. Surface roughness values showed that the as-deposited films of SiC and undoped polysilicon were rougher than the doped polysilicon film and Sit 100). Polishing of the as-deposited samples resulted in comparable values of roughness between SiC and undoped and doped polysilicon films, while Si(100) still remained the smoothest and the doped polysilicon him, the roughest. It was found that the polished SiC and doped polysilicon films showed the lowest friction followed by undoped polysilicon film, while Si(100) showed high friction. Microscale scratch/wear studies clearly showed that SiC film was much more scratch/wear resistant than the other materials, which showed comparable resistance levels. SiC also showed higher hardness and modulus of elasticity compared to the other materials. These results show that 3C-SiC film possesses desirable micro/nanotribological characteristics that make it an ideal material for use in MEMS devices. (C) 1998 Elsevier Science S.A.,All rights reserved.