193-nm single-layer positive resists: building etch resistance into a high-resolution imaging system

Abstract

Our approach to the design of positive, single layer resists for 193 nm lithography is discussed. Phenolic resins, the archetype in positive photoresist materials, cannot be used at this wavelength due to optical opacity. Methacrylate polymers combine the required optical transparency at 193 nm with easily tailored properties, however. The methacrylate polymer materials used in our 193 nm resists are completely different from phenolics used in traditional (248 nm) chemically amplified resists but the imaging chemistry is very similar. With a design based on methacrylate terpolymers, we have recently developed a high resolution positive resist for 193 nm lithography with excellent imaging at both 193 and 248 nm. Our recent work has centered on gaining further insight into methacrylate polymer structure/property relationships, improving the imaging performance and finally increasing the etch resistance. Towards that end, we have developed a class of dissolution inhibitors for 193 nm resists that are combined with methacrylate polymers to provide 3-component resists. A family of B-steroid dissolution inhibitors that also increase etch resistance is described. Imaging and etch performance of four versions of our resist are disclosed. These methacrylate resists show resolution capability below 0.25 micron, etch rates 20% higher than novolak resins, good environmental stability in contrast to traditional DUV resists and dual wavelength (193/248) imaging.