High resolution patterning on nonplanar substrates with large height variation using electron beam lithography

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High resolution patterning on nonplanar substrates with large height variation using electron beam lithography is reported. Using an automatic, high precision, noncontact laser probe microscope, a three-dimensional map of the nonplanar substrate to be patterned is obtained first. This data are converted to a format for the electron beam lithography system, which performs the write by adjusting the plane of electron beam focus based on the mapping data. As a proof of concept of this patterning scheme, three different kinds of nonplanar substrates were used including a tilted Si wafer for a uniform and unidirectional tilt, a planoconvex lens for a multidirectional tilt, and deep Si trenches with a step height variation. The patterning scheme was tested for resolution, field stitching accuracy, and field placement accuracy. The results of these tests are in very close agreement with typical results that are obtained for flat substrates with similar patterning conditions. For wafers with 10 mm tilt, 50 nm gratings show a line width variation of 18%, average field stitching error of 1.06 nm with a 3σ of 24.62 nm, and field placement error of 20.53 nm with a 3σ variation of 31.92 nm. The simplicity of this method and the fact that it can be applied for various nonplanar substrates with nanometer scale precision and over large areas open up a new avenue for the fabrication of devices based on nonplanar substrates.