Background:

Laser interference lithography has been widely used as an effective and inexpensive technique for the fabrication of uniform nanopatterns and photonic materials on substrates. There are various geometrical configurations of interference lithography (IL) systems, the two major system configurations being the Lloyd's mirror interferometer and the conventional two-beam interferometer, such as a Mach-Zehnder interferometer. A Lloyd's mirror interferometer includes a mirror oriented perpendicular to a substrate stage, where a simple angular rotation of the entire device results in a nanoscale patterning (also referred to as “nanopatterning”) with controlled pattern periodicity. However, the effective pattern coverage area is dependent on the mirror size and the optical coherence length in such a way that the coverage area is usually much less than the size of either. In contrast, a conventional two-beam interference lithography system provides two separate beams which are individually expanded and then recombined directly over the substrate to form interference patterns. Such a system may provide a greater pattern coverage area with less dependency on the optical coherence length. However, the fixed optical path of the conventional two-beam IL system makes it difficult to tune the pattern periodicity, in that it requires the laborious realignment of the entire optical path to vary the pattern period. Additionally, it is necessary to provide a large optical table and a costly high-power laser to provide enough exposure power over the long distance travelled by the expanded beams.

Summary:

In an embodiment of the present invention, a two-beam interference lithography system offers large-area nanopatterning with tunability of pattern periodicities. The tunable feature is achieved by placing two rotatable mirrors in the two expanded beam paths which can conveniently be regulated for the designed pattern periodicities. While the effective interference pattern coverage is mainly determined by the optical coherence length and mirror size, the minimum pattern coverage area of the invention is as large as the effective coherence length of the laser and the selected mirror size over a wide range of periodicities. Only three components must be adjusted to select the periodicity of the pattern and the area covered by the pattern: the rotatable mirrors must be set to the desired angles and the substrate support must be translated along a line to the desired distance from the rotatable mirrors.

Benefits:

- System offers large area nanopatterning with tunability of pattern periodicities

Applications:

- New fabrication methods of nanopatterning that involve large areas

Full Patent: Tunable Two-Mirror Interference Lithography System

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