A process for the fabrication of large areas of high resolution, high aspect ratio silicon structures using a negative tone Novolak based e-beam resist

The non-chemically amplified negative resist ARN 7520 produced by ALLRESIST GmbH shows excellent suitability for fabricating stamps for nanoimprinting with a pitch resolution as high as 70 nm and dense periodical structures using e-beam lithography and dry etching. Due to its chemical formulation, the resist does not swell in the developer, has good sensitivity and contrast. The adhesion of such class of resists is provided by silane containing promoters used before the spin-coating. However, for the lower exposure doses, the bonding of the nanostructures to the surface is still insufficient. Instead of the promoter, we evaporate 3–5 nm Ti layer before the resist spin-coating. This strongly improves the resist adhesion in a wide range of exposure doses, suppresses the influence of the substrate conductivity on the electron beam lithography parameters and also improves the structure profile during dry etching. Reducing ion voltage from 400 to 200 V midway through dry etching also helps to keep the structure walls more vertical. Silicon stamps with lines and spacings of 70–100 nm periods and an area of 3 × 3 mm2 have been successfully fabricated.