Building high-performance chemically amplified resists with polymer blends

The greatly compressed resist development cycle and the explosion of the number of resists at a specific lithographic wavelength have necessitated a hastened pace in developing high-performance resists. Traditionally, high- performance chemically amplified resists have been developed by copolymerization of monomers with various functionalities to achieve the desired properties. This approach, while immensely successful, however suffers from long lead times to deliver successful products to the markplace. In this paper, we report a more rapid approach to developing high- performance chemically amplified resists by blending different polymers with complementary properties. As a model system, a 248nm negative-tone bilayer resist has been demonstrated based on acid catalyzed cross-linking of blends of silicon-containing polymers with a non-silicon-containing polymer. The silicon-containing polymers and the non- silicon-containing polymer used were poly(p- hydroxybenzylsilesquioxane-co-p-methoxybenzylsilsesquioxane) (PHBS/MBS), poly(p-hydroxyphenylethylsilesquioxane-co-t- butylsilsesquioxane)(PHPES/BS) and poly(p- hydroxystyrene)(PHS), respectively. The resist based on this simple polymer blend approach has achieved lithographic performance comparable to that based on more elaborate copolymers that require time-consuming synthetic optimization. Differential scanning calorimetry (DSC), quartz crystal microbalance (QCM), and atomic force microscopy (AFM) were employed to probe the properties of the polymer blends and the resist. DSC results suggested that PHBS/MSB and PHS are miscible throughout the entire composition range. Addition of the phenolic polymer into the silicon-containing polymer dramatically improves the lithographic performance of the bilayer resist. This improvement in lithographic performance is attributed to the enhancement of thermal properties (i.e. glass transition temperature), the modulation of dissolution properties, and more cross-linkable sites for the acid catalyzed cross-linking. O2 RIE etch selectivity of the blends vs. and organic underlayer increases with increasing concentration of the silicon-containing polymer in the blends. The present approach could also be applied to developing other high-performance resists more swiftly at other lithographic wavelengths.