A two-axis Lloyd's mirror interferometer with elastically bent mirrors for fabrication of variable-line-spacing scale gratings

A cost-effective and flexible laser interference lithography system with an exposure area of approximately 100 mm × 100 mm for fabrication of two-axis variable-line-spacing (VLS) scale gratings is newly proposed and developed. Two elastically bent mirror (EBM) modules, each of which is composed of an elastically bent mirror and a loading mechanism, are integrated into a non-orthogonal two-axis Lloyd's mirror interferometer. The deflections of the X- and Y-EBMs can generate nonlinear components in the wavefronts of the X- and Y-beams, resulting in a stationary interference fringe field with variable pitches along the X- and Y-directions, respectively. The pitch specifications (the center pitch and the pitch variation range) of the grating can be adjusted by changing the corresponding module parameters (the tilt angle and the applied load). Theoretical calculations and experimental results indicate that for EMBs with a dimension of 450 mm (length) × 250 (width) × 2 mm (thickness), the center pitch can be linearly adjusted within the range of 680 nm–1290 nm with respect to a tilt angle range of 10°, while the pitch variation range is independently adjustable from 60 nm to 130 nm with respect to an applied load range of 8 N. Two-axis VLS grating structures with a center pitch of 1000 nm and a pitch variation of ±45 nm are successfully fabricated over a fabrication area of 100 mm × 100 mm, which demonstrates the feasibility of the developed system.