An Orthogonal Type Two-Axis Lloyd’s Mirror for Holographic Fabrication of Two-Dimensional Planar Scale Gratings with Large Area

Abstract

In this paper, an orthogonal type two-axis Lloyd’s mirror interference lithography technique was employed to fabricate two-dimensional planar scale gratings for surface encoder application. The two-axis Lloyd’s mirror interferometer is composed of a substrate and two reflective mirrors (X- and Y-mirrors), which are placed edge by edge perpendicularly. An expanded and collimated beam was divided into three beams by this interferometer, a direct beam and two reflected beams, projected onto the substrate, X- and Y-mirrors, respectively. The unexpected beam sections having twice reflected off the mirrors were blocked by a filter. The remaining two reflected beams interfered with the direct beam on the substrate, generating perpendicularly cross patterns thus forming two-dimensional scale gratings. However, the two reflected beams undesirably interfere with each other and generate a grating pattern along 45-degree direction against the two orthogonal direction, which influence the pattern uniformity. Though an undesired grating pattern can be eliminated by polarization modulation with introduction of waveplates, spatial configuration of waveplates inevitably downsized the eventual grating, which is a key parameter for grating interferometry application. For solving this problem, theoretical and experimental study was carefully carried out to evaluate the fabrication quality with and without polarization modulation. Two-dimensional scale gratings with a 1 μm period in X- and Y-directions were achieved by using the constructed experiment system with a 442 nm He-Cd laser source. Atomic force microscopy (AFM) images and the result of diffraction performances demonstrated that the orthogonal type two-axis Lloyd’s mirror interferometer can stand a small order undesired interference, that is, a degree of orthogonality between two reflected beams, denoted by γ, no larger than a nominal value of 0.1.

Special Issue on Precision Dimensional Measurements

“…In the area of grating diffraction-based interferometer, a double diffraction heterodyne interferometer was developed by Chang [26]. Li et al of Tsinghua University designed two innovate key components for planar grating interferometers, namely the Lloy's mirror [27] and the prism module [28].…”

Modeling and test of an absolute four-degree-of-freedom (DOF) grating encoder

“…The grating interferometer can measure the distance mainly based on the grating pitch (physical structure) and the light path is also shorter than the laser interferometer [14][15][16][17], which means it is more stable [15,18]. The grating manufacturing [19][20][21][22] of the current grating encoder has also made considerable progress, which enables the grating encoder to measure with a smaller and more accurate measurement benchmark, and the accuracy can reach sub nanometer [23,24]. At the same time, the grating encoder has also been applied to the lithography machine [25,26].…”

A four-step laser interference lithography for patterning pixelated micro-polarizer array

“…The laser interference lithography technology is very suitable for the fabrication of periodic micro-nano structures similar to gratings. It has the advantages of high efficiency and low cost, and can achieve large-scale and rapid manufacturing [39][40][41][42][43].…”