Method of making an article comprising nanoscale patterns with reduced edge roughness
View Patent ↗In accordance with the invention, an article comprising a nanoscale surface pattern, such as a grating, is provided with a nanoscale patterns of reduced edge and/or sidewall roughness. Smooth featured articles, can be fabricated by nanoimprint lithography using a mold having sloped profile molding features. Another approach uses a mold especially fabricated to provide smooth sidewalls of reduced roughness, and a third approach adds a post-imprint smoothing step. These approaches can be utilized individually or in various combinations to make the novel articles.
1. A method of making an article comprising a nanoscale surface pattern having reduced edge and/or sidewall roughness comprising the steps of:
providing a mold with a molding surface having one or more nanoscale protruding regions tapering toward the end distal the surface, the protruding regions arranged complementary to the pattern, at least one of the protruding features having a minimum lateral dimension less than 200 nanometers and smooth edges and sidewalls having a minimum surface roughness of less than 5 nanometers;
providing a workpiece comprising a substrate and a moldable surface layer;
pressing together the molding surface and the moldable surface to reduce the thickness of the moldable surface layer under the protruding features; and
separating the mold from the moldable surface;
wherein providing the mold comprises
providing a mold substrate having a nanoscale pattern of etch resistant masking material;
anisotropically etching portions of the masked mold substrate to etch recessed regions with converging walls, thereby leaving tapered protruding regions under the masking material;
removing the masking material;
depositing a second etch resistant material on portions of the tapered protruding regions by to form masked protruding regions; and
etching the masked protruding regions to produce substantially vertical sidewalls on the unmasked portions of the protruding regions.
2. The method of claim 1 wherein the article is a grating and protruding regions comprise an array of parallel lines.
3. The method of claim 1 wherein the pattern comprises a linear array of parallel protruding lines and the angle of the oblique coating is adjusted to control the spacing between successive lines.
4. The method of claim 1 wherein the mold substrate comprises crystalline material and the surface is parallel to one of the (100) crystalline planes.
5. The method of claim 4 wherein the crystalline material is silicon and the silicon is etched with an anisotropic wet etchant having an etching rate normal to the (100) plane that is higher than the rate normal to the (111) plane.