Depth Profile and Line-Edge Roughness of Low-Molecular-Weight Amorphous Electron Beam Resists

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Abstract
We have investigated the possibility of using amorphous low-molecular-weight polyphenols as chemically amplified positive-tone electron-beam (EB) resists. Low-molecular-weight polyphenol, 4,4'-methylenebis[2-[di(2-methyl-4-hydroxy-5-cyclohexylphenyl)]methyl] phenol (3M6C-MBSA) as a base matrix, was protected by 1-ethoxyethyl (EE) groups to control the dissolution rate in aqueous 0.26 N tetramethylammonium hydroxide developer. The film distribution in the depth direction for resist components determined with time-of-flight secondary ion mass spectometry (TOF-SIMS) and the Fourier amplitude spectra of line-edge roughness (LER) have been investigated to understand the relationship between them for the resists formulated with 3M6C-MBSA and two photo-acid generators (PAG), triphenylsulfonium perfluoro-1-butanesulfonate (TPS-PFBS) and triphenylsulfonium n-octanesulfonate (TPS-nOS). From these results, it was found that the resist film consisting of TPS-nOS showed more homogeneity in the depth direction of the film than did TPS-PFBS, which showed low surface energy and diffused easily to the resist surface through the matrix during a coating and post-applied bake step. The resist with TPS-nOS indicated a lower LER value of 5.1 nm in the wide frequency range, especially in the lower frequency region below 10 µm-1. Therefore, the homogeneity of the film is one of important factors for LER control.