Sidewall epitaxial piezoresistor process and characterisation for in-plane force sensing applications

A selective epitaxial fabrication method to form piezoresistors on the sidewalls of microfabricated cantilevers for in-plane force sensing applications and their preliminary characterisation results is reported. The piezoresistors were made of a doped silicon epitaxial layer using a selective deposition technique by tailoring the process conditions. Silicon oxide was used as a mask, dichlorosilane (DCS) was used as a source gas in a reduced pressure environment and HCl was used to improve selectivity. The authors found that the deposition rates were dependent on the trench widths. The authors further characterised the current–voltage behaviour, noise and sensitivity of these epitaxial sidewall piezoresistors. A typical cantilever had resistance of 0.6 kV, 1/f coefficient, a 1⁄4 8, sensitivity of 1100 V/N (880 V/m) and resolution of 9.5 nN integrated over the band 10 Hz–10 kHz. Its sensitivity and resolution are comparable to single-crystal ion implanted piezoresistors and better than most polysilicon or diffused piezoresistors.