9 June 1995 Process optimization of a positive-tone chemically amplified resist for 0.25-um lithography using a vector scan e-beam tool
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Electron-beam (e-beam) lithography is one technique that offers subquarter micron resolution. Advancements in tool design and resist materials make it possible to print nanometer structures. In this paper, we focus on the process optimization of an e-beam positive tone chemically amplified resist. The resist system is based on protected polyhydroxystyrene and an acid generator. The exposures were performed on an e-beam system equipped with a variable- shape spot operating at 50 keV. The process was examined with a statistical experimental design. The process parameters considered in this evaluation are softbake time, softbake temperature, developer concentration, and developer time. The lithographic responses studied are: linewidth variation with dose, contrast (gamma), unexposed film loss, profile angle, bulk sensitivity, and writing bias. A central composite design with 4 independent variables and 25 experimental runs was employed. Statistical analysis of data yielded a significance level of the different process parameters and their interactions. Also, regression analysis fit each response in terms of the process parameters. These relationships were used to define process parameters, yielding the desired responses. The optimized process yielded subquarter micron images in 0.8 micrometers resist film with nearly vertical profiles. The resist exhibited a high contrast (> 50) and a large develop latitude. The resist resolution and linearity extended to below 250 nm for the nested features. In addition, the resist exhibits excellent environmental stability, withstanding long delays (> 24 hr) between different process steps. A detailed discussion of the resist performance and process latitude is presented. This material performed well in this application with 0.25 micrometers design rules and has the potential of performing well at smaller linewidths.
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Ahmad D. Katnani, Ahmad D. Katnani, Dominic Schepis, Dominic Schepis, Ranee W. Kwong, Ranee W. Kwong, Wu-Song Huang, Wu-Song Huang, Zoilo C. H. Tan, Zoilo C. H. Tan, Charles A. Sauer, Charles A. Sauer, } "Process optimization of a positive-tone chemically amplified resist for 0.25-um lithography using a vector scan e-beam tool", Proc. SPIE 2438, Advances in Resist Technology and Processing XII, (9 June 1995); doi: 10.1117/12.210374; https://doi.org/10.1117/12.210374

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