Nanopatterning of PMMA on insulating surfaces with various anticharging schemes using 30 keV electron beam lithography

摘要

As a low cost and high throughput method for nanoscale pattern replication, step and flash imprint lithography (SFIL) with UV transparent masters is gaining prominence for its potential in photonics and integrated-circuit fabrication. However, dielectric materials appropriate for fabricating nanostruc-tured SFIL masters present a challenge when employing electron beam lithography (EBL) because insulator substrates covered by polymeric resists such as PMMA tend to accumulate charge during EBL exposures, thereby degrading the process. In this work we explore the performance of four different EBL anticharging schemes for nanofabrication of dense arrays of dots having diameters 16-30 nm in PMMA on UV transparent fused silica (FS) substrates. These include overlayers of aluminum or a water-soluble conducting polymer, as well as sandwiching of Al or Cr thin films between the substrate and PMMA. The quality of patterns transferred from PMMA into the underlying metallic layers was analyzed, and the grain size of the metal was found to be the limiting factor determining the edge roughness. The best resolution was attained employing the conducting polymer top-coating. This scheme also involves fewer processing steps. The authors have used this technique for lift-off of Cr and Au as well as Cr masked etch transfer of nanosized patterns into glass substrates for UV-transparent master mold fabrication.