Theory of Photodecomposable Base in Chemically Amplified Resist

Abstract

Photo-decomposable bases (PDBs) are basic materials that turn into neutral ones photochemically. TWE calculate the slope of the latent acid gradient after base neutralization and before diffusion and show that this gradient is generally larger when PDB is used instead of traditional non-photosensitive quencher. The gradient generally improves as more PDB is added. Two different limiting cases are calculated; one where the PDB and PAG do not compete for photons or secondary electrons but instead photolyze independently and one where the do compete. The first case may be encountered in chemically amplified resists where the overall optical absorbance is low and photons react directly with the PAG and PDB. The second case is likely to encountered in EUV lithography where replacing conventional base with PDB does not change the EUV absorbance of the resist. The calculations show that the PDB will probably give a large improvement in latent acid gradient in the second case.