Study and Application of In-Situ Phosphorus Doped Thick Polysilicon Films at Low Temperature for Post CMOS-MEMS Integration

This paper reports the film property and application of in-situ doped evaporated silicon films at ultra-high vacuum for temperatures ranging from 200-625°C at various doping concentrations and deposition rates. Micromachining process for the studied polysilicon film has been developed and accelerometer and comb-drives of 22μm thick have been fabricated at low temperature for the first time. Detailed studies of the film crystallinity using Raman Spectroscopy and X-TEM have been conducted. The average and gradient stresses of the films have been measured along with Young's Modulus. The result shows, for the first time, the formation of thick fully crystallized electrically active silicon films with low average stress and stress gradient by optimizing the phosphorous doping and deposition rate at temperature less than 500°C. Moreover, we have successfully fabricated an inertial sensor and comb-drive actuator using the film. The inertial sensor shows linear sensitivity of 195mV/g with a readout circuit consisting of amplifier and demodulator. The actuator moves 240nm at driving voltage of 15VDC and measures a resonance frequency of 2.1 KHz.