<title>Optimization of dissolution-rate characteristics of chemically amplified positive resist</title>

Abstract

The dissolution kinetics of a 3-component chemically amplified DUV positive resist (base resin; t-BOC protected polyhydroxystyrene, PAG; benzenesulfonic acid derivative, dissolution inhibitor; t-BOC protected bisphenol A;) was investigated under various conditions. Particularly, the effects of the dissolution inhibitor on the dissolution rate characteristics together with the effect of the t-BOC protection ratio of the base resin were studied. Moreover, in order to obtain ideal dissolution characteristics, a resist profile simulation analysis was carried out. The dissolution rate contrast as well as the slope N of log(dissolution rate)-log(exposure dose) plots increased with increasing inhibitor concentrations. However, a very high inhibitor concentration induced a severe standing wave effect and T-topping profile, resulting in the deterioration of resist performance. Therefore, it was discovered that inhibitor concentration has an optimum value in this resist system. These results are similar to those of t-BOC protection ratio in base resin. According to resist simulation, the slope N was closely related to resist performance, but the dissolution rate contrast was not. A slope value of more than 15 was necessary for 0.25 micrometers patterning (focus margin > 1.3 micrometers ). In addition, the acid diffusion length was one of the key factors: suitable diffusion length was essential for achieving a good resist profile; short diffusion length induces a severe standing wave profile and a long diffusion length deteriorates resolution capability. Based on the analysis of the dissolution characteristics and resist profile simulation, it was concluded that the optimization of the base resin structure and inhibitor concentration is effective for modifying the dissolution parameter. Moreover, it was also found that a steep slope (> 15), moderate dissolution contrast (approximately 10,000) and adequate acid diffusion length (approximately 35) can bring about ideal dissolution characteristics leading to 0.25 micrometers pattern formation.