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 k??, 1/f coefficient, ?? = 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.