Polymethylmethacrylate (PMMA) materials have been utilized for electron beam lithography for many years, offering high resolution capability and wide process latitude. Their poor sensitivity has, however, limited them until recently to R&D applications. MOSFET 0.25 im T-gate fabrication utilizing PMMA in a multi-layer system has caused an increase in the volume of resist used in commercial applications, prompting a need to evaluate formulations for optimum process performance. Results are presented from a study undertaken to evaluate resist casting solvent composition and molecular weight variation in PMMA for electron beam exposure. PMMA cast in several solvent systems have been evaluated for lithographic performance. Additionally, formulations in chlorobenzene with minor variations in molecular weight have beenevaluated for batch-to-batch uniformity. A 10 KeV MEBES electron beam system has been used to study resist sensitivity, contrast, and process latitude. Using a two-factor, three level factorial designed experiment, prebake and development time have been varied as controlled process factors. Samples with varying molecular weights were shown to have wide process latitude. These samples gave comparable performance while their molecular weights varied from 539K to 614K, and polydispersity varied from 3.3 to 6.1. Resist samples with chlorobenzene, PGMEA (propylene glycol monomethyl ether acetate) and anisole as the casting solvent resulted in equivalent performance.
Date of creation, presentation, or exhibit
Department, Program, or Center
Microelectronic Engineering (KGCOE)
Bruce W. Smith, Todd D. Eakin, Donald W. Johnson, "Characterization of safe solvent PMMA resist variables for electron-beam application", Proc. SPIE 2194, Electron-Beam, X-Ray, and Ion-Beam Submicrometer Lithographies for Manufacturing IV, (13 May 1994); doi: 10.1117/12.175825; https://doi.org/10.1117/12.175825
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