THE MECHANISM OF POLY-SI ETCHING DURING POLY/W GATE CLEANING BY FLUORINE BASED CLEANING SOLUTION

摘要

When W/WN/poly gate stack was etched, an oxide-like polymer was formed on the sidewall and the bottom. To remove the polymer, fluoride based chemicals had been used because it had oxide etch ability. These were excellent to clean the polymer, however, these solutions also etched poly silicon resulting in the undercut of gate poly-Si. It had been believed that poly-Si showed very low etch rate in fluoride based chemicals but there was a considerable change of etch characteristic according to the crystallographic change by heat treatment. The more interesting result is that the etch rate of poly-Si highly depend on the types and the concentration of dopant. From these results, we could explain the severe gate poly-Si undercut was due to the increased etch rate of gate poly-Si, which was implanted by phosphorous, by heat treatment effect during mask SiN deposition process.