Patterning of Non-Planar Diamond Anvils for High Pressure Materials Characterization via Electron Beam Lithography
Increasingly nanotechnology and MEMS applications require high resolution patterning of irregularly shaped non-planar substrates. Electron beam lithography (EBL) of planar substrates requires precise measurement of the sample to final lens distance and the in-situ laser height readings typically used are not compatible with non-planar samples. This work uses an advanced external height mapping system integrated into the external alignment microscope of the Raith EBPG5200 e-beam writer to efficiently pattern over a 10mm height range. This capability enables complex patterning for applications such as patterning electrodes on diamond anvil cells (DAC), which are used for electrical and optical characterization of materials at pressures >100GPa. The diamond anvils have a flat culet surface of 200µm to 1mm dia., electrical leads need to be patterned down the angled diamond face. Traditionally these leads are pre-patterned, and samples simply are placed on the leads making poor contact. While adequate for resistance measurements, materials such as layered transition metal dichalcogenides (TMDs) require high quality evaporated contacts and ideally need to be electrostatically gated. The ability to deterministically transfer these materials with submicron precision coupled with non-planar electron beam lithography (EBL) allows high quality devices with submicron features to be fabricated on these diamond anvils.
We present a non-planar EBL process to pattern diamond anvils and fabricate TMD devices with high quality evaporated contacts. First, the anvil is sputtered with a conformal Mo film and placed on a carrier wafer patterned with alignment markers. A height map is produced using the external height mapping system of the Raith EBPG5200 e-beam writer. Z-lift positions at every position during patterning can be obtained or inferred from this height map data. The pattern data is divided into zones of 20μm height change. This allows for improved write time, improved focus over the field and improved field stitching errors. The resist is then exposed, developed and the electrodes etched.