Polarization-independent high diffraction efficiency two-dimensional grating based on frustum array

In the displacement measurement of the wafer stage in lithography machines, signal quality is affected by the relative angular position between the encoder head and the grating. When the measurement orientation is tangential to the center of the chuck, the influence of the homogeneous expansion of the chuck on the measurement can be reduced. In this research, we propose a reflective two-dimensional metal dielectric grating based on frustum array. With an incident azimuth angle of 45 degrees, the (-1, -1) order diffraction efficiencies of transverse electric polarization (TE) and transverse magnetic polarization (TM) are 81.4% and 84.8% at 1550 nm incident wavelength under Littrow mounting, respectively. the diffraction efficiency balance is 95.99%. The high efficiency of TE and TM polarization makes them have great application potential in grating displacement measurement. Furthermore, the structure based on the frustum of a cone performs well in manufacturing tolerance, which provides possibility for practical applications.