Comparison of PMMA Shrinkage in Ion Beam Lithography: PMMA on Glass Substrate Vs Free-Standing PMMA Film

The present work focuses on the shrinkage of PMMA films under irradiation and its application to the creation of optical devices. We prepared the free-standing PMMA films in four different thicknesses (13, 21, 32, and 43 & mu;m), and PMMA films of the same thickness, but deposited on a glass substrate. A diffraction grating was chosen as the optical device to show the applicability of the method. The study revealed that at a film thickness of 13-32 & mu;m, the shrinkage of the free-standing film increases proportionally to its thickness, while the film on the substrate does not have a pronounced dependence. Films with the thickness of 43 & mu;m do not follow this trend. It was found that under the same irradiation conditions, the film on the substrate shrinks more compared to the free-standing film. Interference patterns from the created diffraction gratings were shown to present spurious illumination areas.