Vapour development of PMMA resists under x‐ray exposure

Abstract

AbstractPoly (methyl methacrylate) PMMA films of approximately 3 μm thickness have been irradiated with Al x‐rays. The amount of vapour development is shown to increase as the initial molecular weight decreases and the rate of vapour development is shown to decrease with increasing dose. A model to describe this behaviour is presented. This model indicates that unlike the vapour development of poly (olefin sulphones), the vapour development characteristics of PMMA are not consistent with an unzipping mechanism as in the depolymerization process. Despite this there is shown to be connections between depolymerization and vapour development. Poly (methyl acrylate) PMA which has a higher depolymerization temperature is shown to vapour develop less than PMMA. Consistent with the view that irradiating reduces the depolymerization temperature, irradiated PMMA is shown to vapour develop further if it is heated after the irradiation. If the irradiation dose is high enough however (12–16 μA min cm−2), this enhanced vapour development is found to decrease. This decrease is in a dose region in which the radiation damaging process is believed to be dominated by cross‐linking. XPS analysis of the irradiated PMMA shows that, with irradiation, the oxygen content of the PMMA initially increases and then decreases. The oxygen increase is consistent with the formation of hydroxyl groups at the surface and the decrease in the oxygen content is shown to occur preferentially from the COCH3 sites of PMMA.