Effects of molecular properties on nanolithography in polymethyl methacrylate

High-resolution lithographic performance of polymethyl methacrylate (PMMA) of molecular weights (MWs) of 50, 100, 496, and 950 K is compared. A chain scission model is used to analyze the behavior of the four molecular weight resists. The chain scission model is combined with an empirical dissolution model to successfully describe the edge profile of a bar pattern. Isolated linewidth data for the 100 and 496 K resists both fit a Monte Carlo code generated linespread function that was convolved with a Gaussian of standard deviation 9 nm. The width was comparable to that in the 950 K resist, but a factor of 3 narrower than that found for the 50 K resist. The higher molecular weight, 496 and 950 K resists showed more developer induced swelling than the lower molecular weight resists. In fact, the developer induced swelling limited the ability to develop 40 nm gratings in the 496 and 950 K resists. Reduction in developer strength produced some improvement. Etching of the supporting resist structure in the gratings was also observed, particularly in the 50 and 100 K resists. The 50 K MW resist exhibited the worst grating contrast upon development. Grating enhanced etching relative to 10 mu m bar areas exposed with comparable area dose was observed. A 40 nm period grating was defined in the 100 K resist.