TaN Etch in CF4/CHF3 gas for MEMS/Sensor application

TaN was widely used as Cu diffusion barrier in CMOS Cu-BEOL technology, in which it was removed by CMP process. Some work was done on TaN etch by Br/Cl-based gas for metal gate application. But seldom work was done for TaN etch in CF-based gas. In this work TaN etching in CF4/CHF3 gas was investigated on CVD alpha-Si substrate for CMOS compatible MEMS/Sensor application. To avoid resist poisoning problem of metal nitrides, a thin layer of SiON and oxide was deposited on TaN. The patterning sequence included 248 nm lithography, etching thin SiON and oxide, followed by TaN etching. It was found serious residue problem on the unpatterned area. After EDX check, Ta was found in the residue. Assumption was made for the mechanism of residue formation. Based on this model, the process was optimized and a 4-step etching process was developed. The main feature of this process is TaN etching in CF4/CHF3 gas with low power and pressure including a post-etching de-fencing process to solve the residue problem. The optimized process can well control the TaN etching profile and Si loss during TaN over-etch, and was successfully used in the MEMS/Sensor patterning process.