Kenji Yoshimoto

Local dynamic mechanical properties in model free-standing polymer thin films.

High-frequency sinusoidal oscillations of a coarse-grained polymer model are used to calculate the local dynamic mechanical properties (DMPs) of free-standing polymer thin films. The storage modulus G() and loss modulus G() are examined as a function of position normal to the free surfaces. It is found that mechanically soft layers arise near the free surfaces of glassy thin films, and that their thickness becomes comparable to the entire film thickness as the temperature approaches the glass transition T(g). As a result, the overall stiffness of glassy thin films decreases with film thickness. It is also shown that two regions coexist in thin films just at the bulk T(g); a melt-like region (G()G()) in the middle of the film. Our findings on the existence of a heterogeneous distribution of DMPs in free-standing polymer thin films provide insights into recent experimental measurements of the mechanical properties of glassy polymer thin films.

A two-dimensional model of the deformation of photoresist structures using elastoplastic polymer properties

A model was developed for predicting the collapse behavior of photoresist structures due to the drying of rinse liquids during wet chemical processing. The magnitude of the capillary forces was estimated using the classical thermodynamics of surface tension, and the deformation of the structure was modeled using beam bending mechanics that accounts for both elastic and plastic modes of deformation. The two-dimensional model can predict the critical beam height of collapse as a function of the wetting behavior of the rinse liquid on the beam, the elastic and plastic mechanical properties of the polymeric photoresist, and the beam dimensions. Collapse behavior was predicted for polymer nanostructures with elastoplastic mechanical properties similar to those of bulk poly(methyl methacrylate). We have compared the collapse predictions from our model with the results of models that account only for elastic or plastic deformation behavior. Regimes in the elastic-plastic mechanical property space for which it is...

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

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 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.