Fabrication of silicon nitride ion sensitive field-effect transistor (ISFET)

In this work, the fabrication of silicon nitride ion sensitive field-effect transistor is presented. The ISFET structure is similar to metal oxide semiconductor field-effect transistor (MOSFET) but the gate metal electrode is replaced by a layer of ion sensitive material, also known as the sensing membrane. The fabrication process utilized four masks which consist of the source and drain, gate, contacts and metal mask. The buffered oxide etch was used for etching the silicon oxide and silicon nitride as it is easily available in the cleanroom. In this work, the self-aligned method was used to fabricate the ISFET and this method has shortened the fabrication step as compared to conventional fabrication method. The sample was inspected using high powered microscope after each step of the fabrication and has shown convincing results. The result of this work is an ISFET with silicon nitride as the gate material.