New shallow trench isolation scheme with α-Si absorption layer for sub-0.18 μm technology

α-Si Absorption Layer (AL) was used in the sub 0.18 μm 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 α-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 (3σ) without AL to 14 nm (3σ) with α-Si. This α-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 α-Si AL is 10~15 nm for the sub-0.18 μm STI process