NEW TECHNOLOGY FOR EASY AND FULLY IC-COMPATIBLE FABRICATION OF BACKSIDE-CONTACTED ISFETS

A simple and fully IC-compatible microelectronic technology has been developed for the fabrication of backside-contacted (BSC) ISFETs based on commercially available bond and etch-back silicon on insulator (BESOI) wafers. Problems related to photolithographic steps on the microstructured wafer surfaces have been avoided and only standard processes have been used. Wet anisotropic etching in tetramethyl ammonium hydroxide (TMAH) or deep dry etching of silicon have been alternatively used to define the thin silicon membrane where the ISFET gate is defined. The buried SiO2 layer has been used as the etch-stop barrier in both cases. The BSC-ISFET electrical characteristics are comparable to those obtained with standard ISFET devices. The chemical sensitivity is 56 mV pH(-1), as is usual in LPCVD Si3N4-gate ISFETs.