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As gate dimensions continue to shrink, improving CD control is a major challenge for sub-0.25 micron DUV (248 nm) lithography. One concern is line edge roughness (LER) which takes the form of both high and low frequency effects. In this paper, high frequency line edge roughness (HFLER) refers to high frequency small amplitude CD variations (sidewall roughness) noted along the edge of a wet developed resist feature. Low frequency line edge roughness (LFLER) refers to the higher amplitude waviness (line width fluctuations) observed along the edge of developed features. Both these roughness parameters (LFLER in particular) could lead to significant variations in device characteristics. Several factors such as the resist formulation, quality of the aerial image and process conditions have in the past been attributed as possible sources of roughness. In this study, a quantitative characterization of wet developed feature roughness was conducted and attempts were made to determine the sources of its origin, along with the impact of plasma etch. High and low frequency LER was characterized using a Dektak SXM atomic force microscope (AFM) and a Hitachi 7800 scanning electron microscope (SEM).Nominal 0.20, 0.18 and 0. 16 tm isolated lines were studied following photolithography and the gate etch. Additional variables in this study included substrate type (organic and inorganic BARC), resist composition, develop time, focus and the impact of aerial image (attenuated phase shift mask in conjunction with quadropole illumination).Keywords: High frequency line edge roughness (HFLER), low frequency line edge roughness (LFLER), atomic force microscope (AFM), photolithography, critical dimension (CD) metrology.

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This paper deSCribeS the use of statistical design experimentation to improve the photoresist performance properties of Dynachem's Nova 2070. A full factorial design was employed to investigate the effects of changes in the weight percent of both the minor resin and sensitizer in the total solids and of changes in the major resin's molecular weight on the after-hardbake wall profiles. The effect of the formulation changes on lithographic properties such as process latitude and resolution has also been measured.Scanning electron micrographs (SEMs) were generated to measure wall profile, thermal, and lithographic properties. A SEM measurement technique was then developed to quantify resist thermal stability. From these measurements models were generated to show the effects of the various formulation changes and to make predictions with respect to optimum formulations. Graphs of profile tendencies as a function of formulation changes and hardbake temperature and response surfaces generated from the various models will be presented to help illustrate the optimization trends.With respect to lithographic performance, the experimental and model data indicate that the optimum resist formulation within the tested experimental matrix has the following make-up: high major resin molecular weight, low minor resin content, and high sensitizer content. With respect to thermal stability, the data suggests that the optimum resist formulation is the following: high major resin molecular weight, high minor resin content, and low to medium sensitizer content.The lithographic property optimum formula was re-tested to optimize it's performance as a function ofprocess changes according to a quadratic statistical design. Comparative process latitude graphs contrasting the optimum formula to alternative formulas under their respective optimized process conditions will also be presented.These studies are collectively analyzed to indicate the direction that future resist formulation changes could be made to further optimize resist performance.