Diaphragm formation and pressure sensitivity in batch-fabricated silicon pressure sensors

The formation of thin silicon diaphragms for batch-fabricated pressure sensors is examined. Several anisotropic silicon etchants are compared with respect to their etch rates and the surface finishes produced. Concentrated potassium hydroxide and ethylene diamine-pyrocatechol are found to be most compatible with sensor requirements. Both V-groove and boron etch-stop techniques are capable of controlling diaphragm thickness to within one micron or better, the latter removing wafer taper as a major source of variability. The effects of several process-induced diaphragm irregularities on the pressure sensitivities of piezoresistive and capacitive structures are examined using a finite-difference computer program. Diaphragm thickness is the most important parameter influencing pressure sensitivity in these structures, with resistor-diaphragm alignment and plate separation important secondary parameters in piezoresistive and capacitive devices, respectively.