Novel ARC optimization methodology for KrF excimer laser lithography at low K1 factor

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Abstract
This paper describes a new anti-reflective coating (ARC) optimization methodology, and reports a practical new ARC material and its actual performance for KrF excimer laser lithography as an application of this methodology. First, the optimal optical conditions, refractive index and thickness, for ARC are defined as those values that cause the minimal energy absorption fluctuation for various in a photoresist thicknesses. To find optimal optical conditions, we calculated the energy absorbed in a photoresist for continuously different ARC optical conditions using a multi thin-film interference simulator based on the matrix method for various photoresist thicknesses. As an application results of this method, we show optimal ARC optical conditions, i.e. refractive indices for various thicknesses, for a tungsten silicide (W-Si) substrate, which is highly reflective and the critical layer for KrF excimer laser lithography. Next, we searched for a practical material to be used as an ARC whose refractive indices were closest to the optimal conditions. From these results, we found a novel and practical material for optical lithography. Silicon carbide (SiC) films satisfied optimal optical conditions as an ARC for W-Si substrates. For the swing ratio, a photoresist absorption variation of ±21% without SiC was reduced to less than ±1% with SiC. Finally, in order to achieve an ARC performance on actual structures, we optimized the SiC refractive index as an ARC for W-Si substrates using various ECR Plasma CVD conditions. As a result, we obtained a high performance ARC for W-Si substrates. A critical dimension variation of 0.12pm without SiC was reduced to less than 0.02pm with SiC for 0.35pm L/S.

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