| Development and relaxation in spin cast poly (methyl methacrylate) (PMMA) thin films on silicon substrates were studied as a function of spin speed, initial PMMA concentration, molecular weight (MW) and final film thickness. Stress in the film was determined from the curvature of the substrate. Measurements were conducted on a coherent gradient sensing system (CGS), a multiple beam optical sensing system and a scanning beam radius of curvature system. Fits to a diffusion model of stress development allowed determination of the final film stress sigmaf and the diffusivity of the anisole solvent Da in the film. For films thicker than ∼350 nm, sigmaf is independent of MW, initial PMMA concentration, spin speed and final film thickness. For films thinner than ∼350 nm, sigmaf decreased with decreasing film thickness; the initial polymer concentration and spin speed affected sigmaf only through their effects on thickness. Da decreased with decreasing film thickness. Da for 495K MW films at room temperature varied with film thickness from 0.05 * 10-12 to 1.5 * 10-12 cm 2/s. These values are consistent with those of both the 950K films and the 270.1K film.; Isothermal stress relaxation was studied between 50°C and 88°C. Results were analyzed by fitting to the Kohlrausch Williams-Watts function, which yielded the characteristic relaxation time (tau) and the exponent (beta), and by fitting to viscosity that increases linearly in time, which yielded the rate of the viscosity increase ( h&d2; ) and the initial viscosity ( h0 ). None of the four parameters depend on film thickness. Both beta and tau showed a slight dependence on molecular weight, while h&d2; and h0 did not. The activation enthalpy for h&d2; was Q&parl0;h&d2;&parr0; = 0.436 +/- 0.072 eV. The activation enthalpy for isoconfigurational flow was determined from h&d2; (T) and h before and after a temperature step, Qiso = (1.18 +/- 0.62) eV. The glass transition temperature of the films was determined from stress measurements during slow cooling. |
