A Hydrogen Plasma Treatment for Soft and Selective Silicon Nitride Etching

In this paper, the development of a soft and selective method to increase the etching rate and control accurately the etched thickness of Si3N4 material is reported. This technique combines the low damage characteristics of wet etching with the anisotropy of plasma etching which is compatible with the requirements of many surface sensitive electronic devices such as MOS transistors. This consists on a local modification of the Si3N4 layer using hydrogen-based plasma followed by wet chemical etching in buffered oxide etch solution. The plasma conditions are optimized and a relatively high etch rate is demonstrated. FTIR analyses show clear evidence that the formation of N-H and Si-H species in the hydrogenated Si3N4 layer contributes effectively to the increase of the etching rate. Finally, a chemical etching model is proposed to explain the higher etch rate of hydrogenated Si3N4.