Development of polycrystalline diffused piezoresistors using e-beam evaporation method for MEMS applications

This paper describes an alternate experimental technique to deposit the polycrystalline silicon (Poly-Si) thin film for the fabrication of diffused piezoresistors. In this process the deposition of poly-Si film (2000 ) was carried out using e-Beam evaporation metho high vacuum with controlled deposition rate on the bed of oxidized p-type Si <100> wafers. The grain size of Poly-Si was analyzed using Scanning Electron Microscopy (SEM), which is found to be around 45 to 50 nm. The thermal doping of boron was performed at different temperature for fixed time in a horizontal quartz furnace. The sheet resistance of all samples was measured using four probe techniques. The sheet resistance of deposited film decreases continuously with doping temperature, which itself describes like the conventional polysilicon nature. The diffused piezoresistors were fabricated and their measured values are analyzed and reported in this paper. The developed experimental process provides a sufficient yield, low cost and highly repeatability in the realization of polysilicon film while developed technology for diffused resistors is useful in the fabrication of electronic sensor, gate metal in CMOS process and so on.