Amine photobase generators (PBGs) are uncommon yet useful compounds. Rarer still are examples of PBGs that are active at visible wavelengths. We report the synthesis and characterization of new photolabile amine protecting groups that are active under visible light. The new chromophore, benzothiophene imino-phenylacetonitrile (BTIPA), was synthesized in four steps without use of chromatography and found to release any one of several amines upon exposure to 405 nm light. The chromophore was also demonstrated to be useful as a Merrifield synthesis protecting group. Experimental evidence suggests a sequential, two stage photolysis mechanism which leads to a nonlinear response to dose.
The authors have studied the influence of Si–O bonding in the polymer structure of Si-containing resists on O2 plasma etch behavior. Three polymers were synthesized with the same Si wt % (12.1%) and varying number of Si–O bonds (0, 1, or 2). The etch resistance during the plasma process was measured by monitoring the film thickness removed using real-time in situ ellipsometry. After plasma exposure, surface chemical changes and roughness were characterized by x-ray photoelectron spectroscopy and atomic force microscopy, respectively. For O2 plasma exposure without substrate bias, all polymers showed the formation of a ∼1 nm SiO2 layer at the surface that acted as a barrier to further oxygen etching. Adding Si–O bonds to the polymer structure at constant wt % Si greatly reduced the etch rate and Si loss during oxygen plasma etching relative to the case of no such bonds. Polymers with one Si–O bond in the polymer structure showed identical etch behavior to polymers with the same wt % Si and two Si–O bonds. However, increasing the number of Si–O bonds in the structure decreased the glass transition temperature of the polymer, leading to the formation of micron-sized wrinkles after plasma exposure. When a substrate bias was applied, the etch rate and the rate of Si loss increased due to sputtering of the SiO2 layer by energetic ions. For 90% N2/O2 discharges with substrate bias, a typical oxygen-based pattern transfer plasma condition, the etch rates of the polymers with the Si–O bond were lower and the SiO2 layer thickness formed was larger than that formed in pure O2 discharges with substrate bias. For all gas discharge conditions, polymers with pre-existing Si–O bonds showed less Si loss.
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