4 May 2005 Characterization of property variation in ultra-thin polymer films from molecular simulation
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Abstract
Molecular simulations of atactic poly(propylene) films were carried out to characterize the general behavior of ultra-thin supported polymer films. Insight into the origin of property changes as a function of film thickness was obtained from these simulations. These property changes are of critical importance in light of the ever decreasing dimensions of polymer constructs in photolithography. These simulations were focused on the seemingly contradictory results obtained from experimental measurements. Specifically, the observed decrease in the glass transition temperature (Tg) seems to be explained by increased mobility at the free surface of simulated films, but this explanation contradicts the observed decrease in diffusivity with decreasing film thickness. The simulations, like previous simulations, indicate that increased mobility at the free film surface occurs on a length scale commensurate with the decrease in Tg. However, a redistribution of the fractional free volume (FFV) also occurred in the simulated films as a function of film thickness. These results suggest that the FFV distribution becomes more homogeneous as films become thinner. This reduces the amount of FFV accessible to various diffusing molecules and may explain the observed decrease in diffusivity that occurs as film thickness decreases. Both the simulated redistribution of FFV and the observed decrease in diffusivity occur on a larger length scale than simulated mobility changes and the associated decrease in Tg. The theory that a redistribution of FFV is the origin of the observed behavior of diffusivity as a function film thickness is a new one that ultimately requires further validation from Positron Annihilation Lifetime Spectroscopy experiments and more extensive film simulations.
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Lovejeet Singh, Lovejeet Singh, Clifford L. Henderson, Clifford L. Henderson, Peter J. Ludovice, Peter J. Ludovice, } "Characterization of property variation in ultra-thin polymer films from molecular simulation", Proc. SPIE 5753, Advances in Resist Technology and Processing XXII, (4 May 2005); doi: 10.1117/12.607435; https://doi.org/10.1117/12.607435
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