Atomic force microscope studies of nanolithographic exposure and development of polymethylmethacrylate

Atomic force microscopy was employed to study e-beam exposure and pattern development of polymethylmethacrylate (PMMA) in molecular weights (MWs) of 950 and 50 K. The work focuses on the development of dense high resolution patterns. PMMA was found to have a nodular morphology with an average particle diameter of similar to 53 nm. Submersion of unexposed PMMA in both water and mixtures of isopropanol (IPA) and 0-33% methylisobutylketone (MIBK) did not change the surface morphology. IPA mixtures with greater than or equal to 50% MIBK roughened the surface. Latent images of exposed resist were consistent with Monte Carlo simulations. The particle size limited the ability to resolve a 40 nm grating. A pillar type morphology was observed between the lines in the 40 nm period grating in 950 K MW PMMA developed in 25% and 50% MIBK. The particle size was not reduced in 50 K MW PMMA. In fact, the ability to define a 40 nm grating in 50 K molecular weight PMMA was worse. Patterns of large pads and 100 nm grating's did not exhibit the pillar morphology nor a difference in morphology between the two molecular weight resists.