Electron beam lithography process using radiation sensitive carboxylate metalorganic precursors

Abstract

A bilayer process has been developed for electron beam lithography using radiation sensitive metalorganic precursors as imaging layers in conjunction with organic planarizing layers. Upon electron beam irradiation, the precursor is converted to a metal oxide which serves as an etch mask for subsequent pattern transfer through the planarizing layer. In this article, a titanium(n-butoxide)₂(2-ethylhexanoate)₂ precursor was investigated that exhibits sensitivity and contrast of 495 μC/cm² and 2.75, respectively, 10 keV accelerating potential. The sensitivity was further enhanced to 72 μC/cm² using a pre-exposure thermal bake to partially convert the precursor to metal oxide prior to electron beam imaging. Additionally, it was found that combining the titanium(n-butoxide)₂(2-ethylhexanoate)₂ precursor with a similar precursor containing a higher atomic number metal center, barium(2-ethylhexanoate)₂ in this work, also enhanced the sensitivity to 157 μC/cm² for a 1:1 molar mixture of the precursors. After imaging and development, the patterns were completely converted to metal oxide by thermal baking to improve the etch resistance of the hard mask. This postdevelopment thermal conversion step was found to result in vertical shrinkage of the features and minimal lateral shrinkage. For bilayer processing, the titanium precursor was imaged on top of hard baked novolac and the pattern was transferred through the novolac using an O₂ reactive ion etch. Sub-100 nm patterning is demonstrated using both single layer and bilayer processes with these materials, with aspect ratios greater than five achieved with the bilayer process.