Sub-50nm half-pitch imaging with a low activation energy chemically amplified photoresist

Abstract

Critical lithographic dimensions are rapidly approaching the sub-50nm regime where there is a concern that image blur due to acid diffusion will impose a practical limit to the resolution of chemically amplified (CA) resists. Although recent EUV and 193- and 157nm immersion interferometric experiments have reportedly resolved line-space arrays with individual dimensions on the order of ∼40nm, smaller nested features are likely to prove problematic. Numerous reports suggest that conventional photoresist performance degrades rapidly at half-pitch dimensions in this range. New approaches to processing and materials development of photoresists will likely be required if the concept of chemical amplification is to be extended to the 32nm node and beyond. In this article we show that through materials choice and proper processing, image blur can be controlled to an extent where dense features below 40nm can routinely be resolved in CA resists. We describe our studies on high-sensitivity resists of differing activation energies and demonstrate the effect of postexposure bake conditions on the ultimate resolution. Most notably, electron-beam exposure of a CA resist that requires no postexpose bake has demonstrated half-pitch resolution down to 30nm with reasonable process latitude. Acid diffusion measurements performed on the same systems using a 193nm top surface-imaging-technique correlate with the observed resolution of the different resists and processing conditions. Additionally, this system has been probed to explore the effect of humidity on the rate of the resist deprotection reactions in order to determine the impact this might have on resolution.