Fundamentals of the Reaction-Diffusion Process in Model EUV Photoresists § Kristopher A. Lavery* a , Kwang-Woo Choi* b , Bryan D. Vogt a , Vivek M. Prabhu* a , Eric K. Lin a , Wen-li Wu a , Sushil K. Satija c , Michael J. Leeson d , Heidi B. Cao d , George Thompson b , Hai Deng b , David S. Fryer d a Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD b Intel Corporation, Santa Clara, CA c Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD d Intel Corporation, Hillsboro, OR ABSTRACT More demanding requirements are being made of photoresist materials for fabrication of nanostructures as the feature critical dimensions (CD) decrease. For extreme ultraviolet (EUV) resists, control of line width roughness (LWR) and high resist sensitivity are key requirements for their success. The observed LWR and CD values result from many factors in interdependent processing steps. One of these factors is the deprotection interface formed during the post- exposure bake (PEB) step. We use model EUV photoresist polymers to systematically address the influence of exposure-dose on the spatial evolution of the deprotection reaction at a model line edge for fixed PEB time using neutron reflectivity. The bilayer consists of an acid feeder layer containing photoacid generator (PAG) and a model photoresist polymer, poly(hydroxystyrene-co-tert-butylacrylate) with perdeuterated t-butyl protecting group. The deuterium labeling allows the protection profile to be measured with nanometer resolution. The evolution of two length scales that contribute to the compositional profile is discussed. Keywords: Photolithography, chemically amplified photoresists, diffusion INTRODUCTION Next-generation advances in semiconductor technologies rely on the continued development of lithographic processes towards the target of sub-50 nm structure fabrication. The chemical amplification process remains the predominant platform for photolithography 1 , however, reaction-diffusion processes occurring within the resist during the post- exposure bake (PEB) step 2-4 contribute to image blurring and line-width roughness (LWR) 5 . The desire to control LWR to levels below 2 nm (3σ) necessitates an understanding of the reaction front propagation at the exposure line edge 6,7 . Material factors 8,9 related to the coupled acid diffusion and deprotection reaction chemistry 10 must be thoroughly understood to deconvolute the origins of LWR. As critical dimensions are driven below 45 nm, extreme ultra-violet (EUV) lithography is a candidate for achieving this goal. Exposures at 13.4 nm, however, carry their own sets of challenges. For example, source limitations will tend to keep exposure doses low; likely below 10 mJ/cm 2 . In order to compensate for these low doses, large PAG loadings are expected 11 , pushing loading levels as high as 40 % by mass. Thinner photoresist films are anticipated 12 to accommodate transparency and etch resistance, as well as feature aspect ratio criteria. Much work on reaction-diffusion front fundamental analyses 13-17 has been performed on homopolymer-based resist systems. However, high sensitivity, copolymeric resists will certainly need to be utilized in EUV applications. In addition, additives, such as base § Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States * klavery@nist.gov, kwang-woo.choi@intel.com, vprabhu@nist.gov Advances in Resist Technology and Processing XXIII, edited by Qinghuang Lin Proc. of SPIE Vol. 6153, 615313, (2006) · 0277-786X/06/$15 · doi: 10.1117/12.656831 Proc. of SPIE Vol. 6153 615313-1