High resolution patterning on nonplanar substrates with large height variation using electron beamlithography 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 beamlithography 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.
The authors would like to thank Dr. Pilar Herrera-Fierro for the fabrication of Si wafers with etched trenches, Mr. David Yates for designing and machining the fixtures to hold the nonplanar substrates, and Mr. Kevin Owen for his expertise in dry etching techniques. This work was carried out at the Lurie Nanofabrication Facility at the University of Michigan. It was partially supported by the National Science Foundation under NSF grant number ECCS-0922972.
II. DESCRIPTION OF METHODS
A. External height mapping of nonplanar substrate and integration with electron-beam lithography tool
B. Electron beam resist and exposure conditions
III. RESULTS AND DISCUSSION
A. High resolution gratingpatterns on 3 in. inclined Si wafer with 7.08 mm height variation
B. Field stitching accuracy on 3 in. inclined Si wafer with 5.24 mm height variation
C. Field placement accuracy on 3 in. inclined Si wafer with 5.24 mm height variation
D. Patterning on a 1 in. diameter planoconvex lens with R = 30.9 mm
E. Patterning on top and bottom of Si etched trenches
- Electron beams
- Diffraction gratings
- Surface patterning
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