Silicon nitride gate ISFET fabrication based on four mask layers using standard MOSFET technology

In this work, we present a simple fabrication method of Ion Sensitive Field Effect Transistor (ISFET) using cost effective equipments in a cleanroom laboratory environment. The ISFET has a structure similar to that of a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) except without the metal layer on top of the gate oxide and uses silicon nitride insulating layer as the ion sensing material. A conventional metal gate MOSFET technology is used to fabricate the ISFET where no extra mask or post processing step is required. This process only requires four mask layers and uses buffered hydrofluoric acid (BHF) for the etching of silicon nitride and silicon dioxide to form contact holes before metallization process. The result of this work is a simple ISFET structure with silicon nitride and silicon dioxide as the gate material.