The use of surfactant in the rinse to improve collapse behavior of chemically amplified photoresists

摘要

In this study we investigated a production relevant process to reduce pattern collapse by adding a low concentration of surfactant to the final rinse liquid in the resist development process. X-ray lithography was used to print test structures with critical dimensions as small as 70 nm in an experimental EUV photoresist, XP-1449-L-400, generously supplied by Shipley. By controlling the dimensions of the test structures, the in-plane capillary forces that act to deform the resist structures during drying were well-defined and easily varied. Commercially available fluorosurfactants (Zonyl~(~R) FSK and FSO) from DuPont Chemicals were used at concentrations of 0.1% and 0.01% in water. Using surfactants, the capillary forces that act on the structures were reduced and the critical aspect ratio of collapse (CARC) of the structures was increased by an average of 20 to 30%, from 2.5 to 3.2, allowing industry to meet the SIA roadmap requirements. The use of surfactants in the rinse in conjunction with the test structures provided insight into the fundamental chemical physics of pattern collapse. Using independently measured receding contact angles (θ) of the rinse liquid on the resist and the surface tensions (γ) of the rinsing solutions, the collapse data could be generalized in terms of the magnitude of the capillary forces that were estimated using classical thermodynamics. The principle conclusion of this study is that the criteria for choosing the optimum rinse liquid to reduce resist collapse is to minimize the magnitude of 2γcosθ.