This article demonstrates and evaluates the feasibility of photo/e-beam grayscale complementary lithography processes for the fabrication of large area, high topography grayscale structure. The combination of these two techniques capitalizes on the capability of photolithography to generate large three-dimensional structures and the ability of e-beam lithography to add fine structure while maintaining high vertical resolution. The litho-etching-litho-etching process reduces the challenges associated with the etching process when transferring fine features simultaneously with deep substrate etching. As a result, this approach enables the fabrication of large-scale high topography features with fine detail. In the first lithography step, a large staircase is fabricated by direct write photolithography. After the photolithography pattern has been transferred into the substrate, e-beam resist is deposited on the patterned substrate using spray coating to obtain conformal coverage on the deep stepped structure. In the second exposure step, an e-beam system further patterns the steps with finer features. Only a small number of grayscale levels are exposed which simplifies the required proximity correction in the design. A vertical resolution of 25 ± 5 nm in a 600 nm horizontal dimension and 45 ± 6 nm in a 300 nm horizontal feature are achieved over a 2 μm to 30 μm vertical depth range. The alignment strategy of complementary lithography, overlay error, and process optimization of integrating high topography and grayscale structure are discussed.
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Liya Yu ; Richard J. Kasica ; Robert N. Newby ; Lei Chen and Vincent K. Luciani
The evaluation of photo/e-beam complementary grayscale lithography for high topography 3D structure
", Proc. SPIE 8682, Advances in Resist Materials and Processing Technology XXX, 868212 (March 29, 2013); doi:10.1117/12.2011681; http://dx.doi.org/10.1117/12.2011681