Fabrication and characterization of amorphous Si films by PECVD for MEMS

Thick and smooth amorphous Si film of 2 mum without hillocks has been obtained at low temperature of 300 degreesC by plasma-enhanced chemical vapor deposition (PECVD) technology. In comparison with conventional sputtering deposition, PECVD-deposited thick amorphous Si film has better adhesion to Si or oxide substrate without cracking or peeling. The film quality depends on the following process parameters: RF power, frequency mode and gas flow ratio as well as substrate material. The deposition rate increases with the RF power for both RF modes of 380 kHz and 13.56 MHz, and higher deposition rate together with lower compressive stress occurs at high frequencies of 13.56 MHz. Amorphous Si film without hillocks is formed on the 100 nm oxide/Si(100) substrate while some hillocks appear on the top of the amorphous Si film deposited on the crystalline Si(100) substrate. Good quality of amorphous Si at low temperature is very important for the fabrication of MEMS devices. Fabrication of suspended MEMS microstructure and sensor array has been demonstrated using the smooth amorphous Si films as sacrificial layer in surface micromachining.