Some Effects At Ion-Beam Modification Of Poly(Methyl Methacrylate

Measurements of the sensitivity of polymethyl methacrylate to ion irradiation are presented. The results of these studies show for ion energies (40 keV—1.8 MeV) and for the heavier ions (He + , Ar + ) a higher sensitivity of the resist than in H + , electron or X-ray exposures. The measured sensitivity shows a dependence on electronic stopping power. In order to understand this relation an electron excitation spike mechanism is suggested. This mechanism is in accordance with investigations of sputtering rate of PMMA during ion bombardment. The effects of low energy ion induced nuclear reactions in the polymer layer and in masks and wafer are also discussed.