Selective etching of silicon nitride over silicon oxide using ClF/H remote plasma.

Precise and selective removal of silicon nitride (SiN) over silicon oxide (SiO) in a oxide/nitride stack is crucial for a current three dimensional NOT-AND type flash memory fabrication process. In this study, fast and selective isotropic etching of SiN over SiO has been investigated using a ClF/H remote plasma in an inductively coupled plasma system. The SiN etch rate over 80 nm/min with the etch selectivity (SiN over SiO) of ~ 130 was observed under a ClF remote plasma at a room temperature. Furthermore, the addition of H to the ClF resulted in an increase of etching selectivity over 200 while lowering the etch rate of both oxide and nitride due to the reduction of F radicals in the plasma. The time dependent-etch characteristics of ClF, ClF & H remote plasma showed little loading effect during the etching of silicon nitride on oxide/nitride stack wafer with similar etch rate with that of blank nitride wafer.