DIFFUSION BARRIER MECHANISM OF EXTREMELY THIN TUNGSTEN SILICON-NITRIDE FILM FORMED BY ECR PLASMA NITRIDATION

The diffusion barrier mechanism of tungsten silicon nitride (WSIN) fil m formed by ECR plasma nitridation is investigated. For this purpose, we examined film thickness, nitrogen content, surface composition, and local atomic ordering of this WSiN and correlated these characteristi cs with its barrier capability. It is revealed that WSIN shows good ba rrier capability when RF bias is applied to the substrate during nitri dation even though it is less than 6-nm thick. Applying RF bias increa ses the nitrogen content in WSiN. Moreover, Si atoms are preferentiall y sputtered and the local atomic ordering in WSiN is lowered because t he effect of ion bombardment is remarkably pronounced. It is supposed that these film characteristics contribute to the suppression of phosp horus diffusion through interstitial sites. As a result, WSiN function s as an excellent barrier layer even though it is extremely thin.