Effect of Fluoride‐based Plasma Treatment on the Performance of AlGaN/GaN MISHFET

This paper demonstrates the effect of fluoride‐based plasma treatment on the performance of Al₂O₃/AlGaN/GaN metal‐insulator‐semiconductor heterostructure field effect transistors (MISHFETs) with a T‐shaped gate length of 0.20 μm. For the fabrication of the MISHFET, an Al₂O₃ layer as a gate dielectric was deposited using atomic layer deposition, which greatly decreases the gate leakage current, followed by the deposition of the silicon nitride layer. The silicon nitride layer on the gate foot region was then selectively removed through a reactive ion etching technique using CF₄ plasma. The etching process was continued for a longer period of time even after the complete removal of the silicon nitride layer to expose the Al₂O₃ gate dielectric layer to the plasma environment. The thickness of the Al₂O₃ gate dielectric layer was slowly reduced during the plasma exposure. Through this plasma treatment, the device exhibited a threshold voltage shift of 3.1 V in the positive direction, an increase of 50 mS/mm in trans conductance, a degraded off‐state performance and a larger gate leakage current compared with that of the reference device without a plasma treatment.