Patterning nanoscale crossed grating with high uniformity by using two-axis Lloyd's mirrors based interference lithography.

A two-axis Lloyd's mirrors interferometer based optical fabrication system was theoretically investigated and constructed for patterning high-uniformity nanoscale crossed grating structures over a large area with a high throughput. The current interferometer was configured with two reflected mirrors and a grating holder, which are placed edge by edge and orthogonal with each other. In such a manner, the two beams reflected from the two mirrors interfere with the incident beam, respectively, forming a crossed grating patterns with only one exposure. Differing from the conventional solution for elimination of unexpected interference between the two reflected beams, a systematical analysis, that is based on the proposed index indicating the non-orthogonality between the two beams at different incident angles, was conducted by using a spatial full polarization tracing method. Without polarization modulation to eliminate the additional interference, an optimal exposure condition with small non-orthogonality between reflected beams was found at a certain incident angle range, while the two required interferences to construct cross grating still remain high. A pattern period of ∼1 µm-level crossed grating structure could be obtained through balancing the structure area and the non-orthogonality. Finally, the exposure setup with orthogonal two-axis Lloyd's mirrors interferometer is established, and the crossed grating structure with the periods of 1076 nm along X-direction and 1091 nm along Y-direction was successfully fabricated on a silicon substrate via microfabrication technology over a large area of 400 mm. The uniformity of crossed grating array over the whole area was evaluated by an atomic force microscope, and the standard deviations of structure periods along X- and Y-directions smaller than 0.3% are achieved. It is demonstrated that the orthogonal two-axis Lloyd's mirrors interferometer based on single-beam single-exposure scheme with non-orthogonality systematic analysis is an effective approach to fabricate crossed grating patterns of 1 µm-level period with high uniformity over a large area.