Sensitivity enhancement of poly(methyl methacrylate) by radiation-induced modification and degradation of PMMA by deep UV, x-ray,e-beam and proton beam irradiations

Exposure of poly(methyl methacrylate) (PMMA) film to ultraviolet, x-ray, electron, and proton radiations creates free radicals which combine with acrylic acid in a chain reaction to form copolymers with solubilities different from unexposed film. The incorporation of acrylic acid in the irradiated PMMA film was associated with growth of film thickness and weight gain. The in-situ modification of PMMA film depends on the modification conditions, such as incident dose, reaction time, temperature, and storage of preirradiated film. The residual solvents, benzene, toluene and chlorobenzene, enhance the amount of modification in UV exposures at an appropriate concentration. The impurities, naphthalene, phenanthrene, pyrene, benzophenone, and benzoin methyl ether, showed photochemical quenching effects.; Enhanced dry etch resistance can be conferred on the acrylic acid-modified PMMA by permitting it to imbibe calcium ion. An image is developed by exposure to an oxygen plasma which consumes unmodified PMMA and generates calcium oxide in the modified regions. The calcinated images are resistant to a fluorine plasma which etches exposed silicon dioxide transferring the modified image into the oxide layer.; The chemical changes in PMMA film caused by irradiation with deep UV, x-ray, electron, and proton beams were studied by gel permeation chromatography, FT-IR, UV, and NMR spectroscopy. The quantitative analysis of spectroscopic changes by Beer's law demonstrated a 1:1 correspondence between the disappearance of ester groups and the generation of double bonds in the polymer chain by all types of radiation. The ratio of main chain scission to changes in the number of ester groups and the generation of double bonds for deep UV data was very close to the quantum yielded of main chain scission of PMMA as reported in the literature. High energy radiation was about ten-times more efficient than deep UV in causing main chain scission with removal of fewer ester groups.; Four different types of unsaturated bonds generated by radiation were determined in NMR spectra of degraded PMMA films. In addition, conjugated unsaturated bonds were observed in UV-irradiated film at a high dose.; The formation of micropores in the irradiated PMMA film was determined by the sorption of naphthalene and by photoisomerization of imbibed azobenzene. The amount of trans {dollar}to{dollar} cis photoisomerization of azobenzene in the irradiated film was about two-times larger than in the unirradiated samples.