Mechanism of reducing line edge roughness in ArF photoresist by using CF_3I plasma

摘要

The roughening mechanism of ArF photoresist during etching was investigated to find out why CF_3I gas reduces the line edge roughness (LER) in the photoresist pattern better than CF_4 gas. Since the plasma of reactive ion etching (RIE) consists of ultraviolet (UV) photons, radicals, and ions, the authors used a UV lamp and a neutral beam source for evaluating the effect of different plasma compositions on the photoresist roughness. The roughness was found not to increase only by UV photons or F radicals, but increase under the CF_4 RIE plasma which has both UV photons and F radicals. A C-F modified layer was generated on the resist surface because the UV damaged C=O bonds reacted with F radicals and the resist surface became softer and shrank. Since CF_3I plasma has a lower UV intensity and fewer F radicals compared with CF_4 plasma, the shrinkage on the sidewall of the photoresist was suppressed and resulted in a smaller LER when this plasma was used.