Reducing roughness in extreme ultraviolet lithography

Pattern roughness is a major problem in advanced lithography for semiconductor manufacturing, especially for the insertion of extreme ultraviolet (EUV) lithography as proposed in the coming years. Current approaches to roughness reduction have not yielded the desired results. Here, a global optimization approach is proposed, taking advantage of the different strengths and weaknesses of lithography and etch. Lithography should focus on low-frequency roughness by minimizing both the low-frequency power spectral density (PSD) and the correlation length. Etch should focus on high frequency roughness by growing the correlation length. By making unbiased measurements of the roughness, including the PSD, the parameters needed to guide these optimization efforts become available. The old approach, of individually seeking to reduce the 3σ roughness of pre- and postetch features, is unlikely to lead to the required progress in overall roughness reduction for EUV.