Journal of The Electrochemical Society, 147 (10) 3833-3839 (2000) 3833 S0013-4651(99)09-090-4 CCC: $7.00 © The Electrochemical Society, Inc. Chemically amplified resist based on acid catalysis for deep UV lithography is a promising technology for patterns of 0.18 m or less. To improve the process stability and resist performance, exten- sive efforts have been made to understand how each component in resist formation influences lithographic performance. 1-13 Previously, the main problems for deep ultraviolet (DUV) resists were airborne contamination and linewidth change with different delay times. For the positive DUV resist, the generation of “T-top” at the resist-air interface is attributed to neutralization of the photogenerated acid by airborne organic bases, such as ammonia, during postexposure delay (PED). Employing a carbon filtration system, overcoat films and pre- treating the substrate, can minimize the effects of contamination. 1-5 Linewidth variation is mainly induced by the effect of acid diffusion during exposure and baking. Therefore, the diffusion behavior of photogenerated acid has been widely investigated for both high and low activation energy (Ea) resist systems. 7-20 Adding base additives has been reported to reduce linewidth slimming of low Ea system such as acetal-based resists owing to reducing acid diffusion. 7,21 To stabilize the latent acid image of high Ea resist systems such as tert- butoxycarbonyl (t-BOC) containing resins, an additional base com- ponent was added not only to quench photogenerated acid, but also to suppress the acid diffusion reaction within the resist film. 8 Theo- retical studies have also indicated that limited diffusion is essential for achieving high resolution chemically amplified DUV resists. 26,27 While inherent resist characteristics such as acid diffusion behav- ior, the effect of base components, and phenomenon of linewidth variation have been widely studied, presently no relationship has been established for these three components. This work evaluated the influence of organic base additive on acid concentration and lith- ographic performance in t-BOC-protected type chemically amplified positive DUV resist. A resist system comprising of a chemically am- plified positive resist and an organic base, such as N-methyl pyrroli- done (NMP), not only prevents a T-top formation, but also suppress- es acid diffusion reaction within resist film. 1 Based on the mecha- nism of neutralization of organic base and photogenerated acid, a model is established herein to describe the behavior of linewidth variation. Furthermore, a very useful equation has also been derived based on the diminution of photogenerated acid in resist film. This equation can accurately predict linewidth variation based on the delay time for various pattern sizes. The concentration of photogenerated acid is defined by the aeri- al image of the resist by a power equal to the reaction order of the acid. Therefore, the effect of exposure energy was investigated to clarify the behavior of linewidth variation during postexposure de- lay. The simulation result, calculated from the lithographic modeling tool PROLITH/2, has been used to evaluate exposure energy depen- dence on linewidth variation. The clear relationship between line- width broadening and additional organic base was obtained based on theoretical derivation and experimental analysis. This investigation assessed how postexposure delay (PED) affects exposure latitude (EL) and depth of focus (DOF). Utilizing the characteristic of postexposure delay can extend the EL and DOF for both 0.18 and 0.22 m line-and-space patterns. Experimental Materials and processing.—The influence of an additional base component, N-methyl pyrrolidone (NMP), was investigated in t- BOC-protected type chemically amplified positive DUV resist. The Postexposure Delay Effect on Linewidth Variation in Base Added Chemically Amplified Resist Chin-Yu Ku, a Jia-Min Shieh, b Tsann-Bim Chiou, b Hwang-Kuen Lin, c and Tan Fu Lei a,z a Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, Hsinchu 300,Taiwan b National Nano Device Laboratories, Hsinchu 300, Taiwan c Vanguard International Semiconductor Corporation, Hsinchu 300, Taiwan To elucidate the linewidth variation caused by postexposure delay (PED) in resist films, the distribution of photogenerated acid, the role of additional base component, and the effect of exposure energy were investigated in tert-butoxycarbonyl protected-type chemically amplified positive deep ultraviolet resist. The resist system included an N-methyl pyrrolidone organic base which was evaluated via KrF excimer laser lithography. Using various line-and-space patterns formed with a KrF scanner, this work also inves- tigated the change of linewidth caused by the delay time between exposure and postexposure bake. Experimental results indicate that the linewidth broadened immediately following exposure and became a constant value rather than continuously expanding for various pattern sizes. Based on the mechanism of neutralizing organic base and photogenerated acid, a model was established to describe the linewidth according to PED time. Moreover, the effect of exposure energy on linewidth variation was investigated to not only assess the influence of exposure energy but also clarify the relationship between linewidth broadening and delay time. Experimental analysis demonstrates that the exposure latitude and depth of focus can be improved by employing PED. © 2000 The Electrochemical Society. S0013-4651(99)09-090-4. All rights reserved. Manuscript submitted September 23, 1999; revised manuscript recieved March 8, 2000. z E-mail: tflei@cc.nctu.edu.tw Figure 1. Schematic view of the photoly- sis of onium salt. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 140.113.38.11 Downloaded on 2014-04-28 to IP