This article demonstrates and evaluates 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 process, alignment strategy, overlay error, and process optimization of integrating high topography and grayscale structure are discussed.
February 25-March 28, 2013
San Jose, CA
SPIE Advanced Lithography
3D structure, grayscale, complementary lithography, mix and match, e-beam, direct write, spray coating, high topography