New oxide nanoparticle extreme-UV photoresists achieve high sensitivity

There remains strong debate regarding which patterning technology will be used in next-generation electronics. The International Technology Roadmap for Semiconductors (ITRS) predicts that feature dimensions of less than 20nm will be required for semiconductor processing within the next two years. Three possible approaches are featured in the ITRS report: nanoimprint patterning, in which a resist film is molded on top of a substrate using micromachined masters; directed self-assembly, which exploits the self-assembly properties intrinsic to block copolymers; and extreme-UV (EUV) patterning—the most traditional strategy of the three methods under development— which depends on short-wavelength radiation (13nm) to create a solubility change in exposed areas. EUV patterning enables the formation of small-scale patterns with the arbitrary shapes enabled by light-based lithography. Recent improvements to light sources (in terms of both reliability and power) as well as new photoresists, such as those based on chemically amplified materials and nanoparticles, are driving significant interest in this technology. At present, the challenge lies in creating a photoresist that works well under EUV radiation, is highly sensitive, and improves on the line-edge roughness and line-width roughness (LER/LWR) performance of most EUV resists. Because of the way that materials interact with short-wavelength EUV radiation, it is believed that the incorporation of higher mass elements would be beneficial to EUV photoresists. These elements provide improvements to optical properties and increase the energy harvesting abilities of the photoresists, enabling more of the applied energy to photochemically induce solubility changes and thereby increase sensitivity. Figure 1. Schematic of the extreme-UV (EUV) nanoparticle photoresist with its core metal oxide and the organic ligand surrounding the core. ZrO2: Zirconium dioxide. HfO2: Hafnium oxide.