No abstract

An infrared near-field scanning optical microscope (NSOM) is used in a controlled environment chamber to detect water vapor uptake in thin polymer films. A chemically amplified photoresist sample composed of alternating 2 µm lines of the original 1000 nm thick poly-(tert-butylmethacrylate) (PTBMA) and the photochemically modified 500 nm thick poly(methacrylic acid) (PMAA) is studied both in low and high water vapor environments. The degree of water vapor absorption by the sample is measured using the infrared transmission of 2.85 µm light on a small spatial scale (<500 nm). The accompanying topographic swelling of the samples is measured using a shear-force feedback loop. Distortion of the topographic structure and variation in transmission contrast indicate that the PMAA zones absorb more water than the PTBMA regions in the water vapor environment. The PMAA swells 280 nm more than PTBMA when exposed to a partial pressure of water vapor of 2.1 kPa (16 Torr), whereas the infrared optical contrast is increased to a 6 ( 1% difference in the PMAA regions compared to the PTBMA.

ABSTRACT:Fourier-Transform Infrared (FTIR) absorption spectroscopy is implemented to measure the infrared spectrum of water absorbed by the Poly(t-butoxycarbonylstyrene) (tBOC) and the ketal-protected Poly(hydroxystyrene) (KRS-XE) polymer photoresists.The shape and intensity of the OH stretching band of the water spectrum is monitored in a variety of humidity conditions in order to obtain information on the hydrogen-bonding interactions between the water and the polymer chains. The band is deconvoluted into four sub-bands, which represent four types of water molecules in different environments.Because of the hydrophilicity of the polymers studied, a large portion of the sorbed water molecules is believed to be strongly bound to the polar sites of the polymer. The ratios of each type of water are found to be dependent on the humidity conditions to which the sample was exposed. At higher humidities, there is an increase in the fraction of free and weakly-bound water molecules. These findings are used to explain the humidity dependence of the deprotection reaction rates, since certain types of water may slow transport of reactive species within the polymer network.2