MeV ion exposure behaviour of PMMA resist polymer studied by synchrotron light spectroscopies

The behaviour of poly-(methyl methacrylate) (PMMA) resist exposed with 2 MeV 1H+ and 6 MeV 12C3+ ions has been investigated by using the photo-electron spectroscopy (PES) and X-ray absorption spectroscopy (XAS) techniques. Preliminary PES results were difficult to analyse without special precautions to counteract surface charging. XAS was on the other hand almost insensitive to the effects of surface charging. XAS investigations of the bonding in the near surface and deeper in PMMA revealed significant changes of the bonding of carbon atoms at fluences correspond to clearing (positive resist mode) and cross-linking (negative resist mode). In the clearing fluence regime the CC bonds increase in the surface and at greater depths which is consistent with our earlier work with Raman spectroscopy. In the high fluence regime where cross-linking takes place, a reduction of C-O and CO bonding is seen which might be indicative that the cross linking is associated with side-chain scission.