SOFT-SUBSTRATE-RIGID-FEATURE (SSRF) NANOIMPRINT LITHOGRAPHY

Two existing approaches of Nano Imprint Lithography (NIL) are defined by the mold material. In hard NIL, molds are made of rigid materials, such as Silicon or Quartz. These molds offer nanometer resolution and superior pattern fidelity, .however, they are extremely sensitive to surface contamination and defects. Alternatively, soft molds are made of cast elastomers (Poly(Dimethylsiloxane) - PDMS). They offer highly conformal contact and low contaminant sensitivity, and can imprint curved surfaces, however, their compressibility makes the pattern features deform, buckle, or collapse, resulting in pattern distortion and limited resolution

Here, we introduce a novel hybrid Soft-Substrate-Rigid-Feature (SSRF) nanoimprint mold based on soft substrate with rigid relief features. It combines the advantages of each of the traditional molding approaches, and at the same time overcomes their drawbacks: (i) High pattern fidelity and small feature size as offered by hard molds; and (ii) low sensitivity to defectsand patterning curved substrates as offered by soft molds.

We produced SSRF molds by electron-beam lithography (EBL) of Hydrogen Silsesquioxane (HSQ) on a sacrificial substrate, and transferred the obtained HSQ features to PDMS substrates. Anti-adhesive coating usually used for hard Si molds was successfully applied on SSRF mold, and found to be essential for the mold durability. The molds were used for nano imprint of UV-curable resists. Using ultra-high resolution EBL we produced SSRF mold with sub-20 nm pattern. In summary, we have demonstrated an innovative concept of robust, high-quality, and cost-effective nanoimprint, which will open a pathway to numerous applications impossible up today.