Diffusion and adsorption mechanism of metallic impurities from chemically amplified photoresist onto silicon-based substrates

The radioactive tracer technique was applied to investigate the diffusion and adsorption behaviors of metallic impurities (i.e., Ba, Cs, Zn and Mn) from chemically amplified photoresist onto silicon-based underlying substrates. Two important process parameters, i.e., baking temperatures and substrate types (e.g., bare silicon, polysilicon, silicon dioxide, and silicon nitride) were evaluated. Our results indicated that the transition metals (Zn and Mn) could have lower diffusion ratios than alkali metal (Cs) and alkaline earth metal (Ba), irrespective of the substrate types and baking temperatures. It was found that the transition metals would form stable complex with the coexisting solvents and/or hydrolysis species in the photoresist layer. The size of metal complex, the drag force of solvent evaporation, and the baking process were found to have significant effects on impurity migration. In addition, a new diffusion-adsorption model was proposed to explain the effect of substrate types. Our model successfully explained the substrate effect for bare silicon with lower diffusion ratios as compared with silicon nitride. The coverage of substrate surface with silanol group could be attributed to the formation of native oxide. The effects, including the concentration of surface adsorption metal, the equilibrium constant, the surface concentration of silanol group, the concentration of metallic impurity and the pH value, played very important role on the diffusion ratios for Ba, Cs, Zn and Mn.