New shallow trench isolation scheme with /spl alpha/-Si absorption layer for sub-0.18 /spl mu/m technology

/spl alpha/-Si Absorption Layer (AL) was used in the sub 0.18 /spl mu/m Shallow Trench Isolation (STI) patterning to improve the pattern uniformity without additional removal step. It was confirmed by the results of reflectivity simulation at 248 nm that the thickness of /spl alpha/-Si for AL on the pad nitride was at least 10 nm to obtain uniform reflection to Photo Resist (PR). The pattern uniformity within 8" wafer was improved by a factor of 3 from 39 nm (3/spl sigma/) without AL to 14 nm (3/spl sigma/) with /spl alpha/-Si. This /spl alpha/-Si up to 15 nm was fully converted to the oxide after thermal oxidation steps to recover the damaged trench surface. Our results corroborate that the optimum thickness of CVD /spl alpha/-Si AL is 10/spl sim/15 nm for the sub-0.18 /spl mu/m STI process.