PHOTOVOLATILIZATION OF THIN POLYSILANE FILMS DETECTED BY SURFACE-PLASMON SPECTROSCOPY

Surface-plasmon optical techniques (attenuated total internal reflection and surface plasmon microscopy, in particular) are employed to characterize the optical and structural properties of thin films of poly (methyl-phenyl-silane) in the thickness range d0 = 40-400 nm. Irradiation with deep UV light (90% at lambda = 253.7 nm) is shown to cause photovolatilization which results in a self-development of illuminated areas. The time dependence of this etching process is investigated, and substantial differences between irradiation in air or in an Ar atmosphere of 10(-3) MPa partial pressure are found: For 40-nm-thick films in the presence of oxygen an ablation rate of 1.3 nm/min is derived for the first 5-10 min which drops rather abruptly to zero (irradiation power density approximately 0.4 mW/cm2). In Ar atmosphere the etching rate is approximately 0.1 nm/min but constant for more than 1 h. UV-absorption spectra and gel permeation chromatography are performed to gain some insight into the molecular mechanisms of these photochemical and photophysical differences which are of great importance for the photolithographic application of these materials.