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Chemical and Structural Investigation of High-Resolution Patterning with HafSOx Richard P. Oleksak,† Rose E. Ruther,†,‡ Feixiang Luo,§ Kurtis C. Fairley,∥ Shawn R. Decker,‡ William F. Stickle,⊥ Darren W. Johnson,∥ Eric L. Garfunkel,§ Gregory S. Herman,*,† and Douglas A. Keszler*,‡ †
School of Chemical, Biological, and Environmental Engineering, Oregon State University, Corvallis, Oregon 97331-2072, United States ‡ Department of Chemistry, Oregon State University, 153 Gilbert Hall, Corvallis, Oregon 97331-4003, United States § Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901-8554, United States ∥ Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403-1253, United States ⊥ Hewlett Packard Company, 1000 Northeast Circle Boulevard, Corvallis, Oregon 97330-4239, United States ABSTRACT: High-resolution transmission electron microscopy (TEM) imaging and energy-dispersive X-ray spectroscopy (EDS) chemical mapping have been used to examine key processing steps that enable sub-20-nm lithographic patterning of the material Hf(OH)4−2x−2y(O2)x(SO4)y·qH2O (HafSOx). Results reveal that blanket films are smooth and chemically homogeneous. Upon exposure with an electron beam, the films become insoluble in aqueous tetramethylammonium hydroxide [TMAH(aq)]. The mobility of sulfate in the exposed films, however, remains high, because it is readily exchanged with hydroxide from the TMAH(aq) solution. Annealing the films after soaking in TMAH(aq) results in the formation of a dense hafnium hydroxide oxide material that can be converted to crystalline HfO2 with a high electronbeam dose. A series of 9 nm lines is written with variable spacing to investigate the cross-sectional shape of the patterned lines and the residual material found between them. KEYWORDS: inorganic resist, electron beam lithography, solution film deposition, hafnium oxide, thin film, cross-sectional TEM
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INTRODUCTION In this contribution, we describe results from high-resolution imaging and chemical analysis of thin films and patterned structures of Hf(OH)4−2x−2y(O2)x(SO4)y·qH2O, commonly known as HafSOx.1 HafSOx is representative of a new approach involving the chemistry of nanosized inorganic clusters for addressing the resolution, line-width roughness (LWR), and sensitivity (RLS) trade-offs that limit lithographic performance of conventional organic materials at resolutions
