Study on cone-defects during the pattern fabrication process with silicon nitride

Abstract

When resist patterns are formed directly on silicon nitride (SiN), it is common for cone defects to arise after the SiN dry-etching process. When subsequent layers are deposited, the layers pile up around a cone defect like a side wall, causing it to expand. These expanded cone defects can cause short circuits in the pattern. To improve yields, therefore, it is vital to understand the factors that lead to the occurrence of cone defects and those which suppress their generation. As a result of our investigations, we were able to determine that these cone defects are caused by metal impurities (especially, iron atoms) in the developer. These become trapped in the resist residue. The complex that is formed by the polymer in the resist residue and the metal then acts as an etching mask. We also determined that trap sites, where the metal can settle, exist on the SiN surface and the metal atoms that thus accumulate on the SiN surface act as an etching mask. Given these results, the number of cone defects can be reduced by suppressing this resist residue generation through the use of high-contrast resists and reducing the metallic impurities in both the developer and chemicals discharged onto SiN.