No abstract

In this paper, we report the design, analysis, and simulation of a novel quadrupleband metamaterial absorber at microwave frequencies. The absorber is composed of delicate periodic patterned structures and a metallic background plane, which are separated by a dielectric substrate. By manipulating the periodic patterned structures, nearly perfect absorption can be obtained at four specific resonance frequencies. Moreover, the significantly high absorptions of quadruple peaks are insensitive to polarization independence, and the influence of the incident angle on the absorption for both TE and TM modes was also analyzed. To explain the absorption mechanism of the suggested structures, the electric and magnetic field distributions and the resistance matching principle were given. Importantly, the design idea has the ability to be extended to other frequencies, such as terahertz, infrared, and optical frequencies.

The alignment method based on moiré imaging has been wildly used for its high accuracy of physical measurement, which utilized the phase of moiré fringe to measure the relative linear displacement between the mask and the wafer. However, this method is only theoretically accurate due to the affection of certain parameters, such as the optical beam collimation. In this paper, the influence of collimation on the alignment accuracy is thoroughly analyzed. The theoretical analyses and simulation results indicate that the alignment accuracy, which was observed just behind the test grating, is sensitive to the divergence or convergence angle of incident light. On this basis, the method for the error correction is proposed and confirmed.

Focusing of wafer plane is an essential factor to determine the ultimate feature size of the stepper such as projection lithographic system. Based on Michelson interferometeric system, this paper demonstrates an interferometric focusing scheme for projection lithography to coaxially locate the ideal focal plane of the projective objective. The collimated incident laser beam is divided into the reference arm and object arm. The latter propagates through the objective lens and then interferes with the slightly deflected reference beam that reflected back by a fixed mirror, giving rise to an interferential pattern on the CCD. Any amounts of defocusing can be directly indicated from the demodulated phase of the interferential pattern. In this manner, the focusing sensitivity at nanometer scale is experimentally attainable, which shows great superiority over traditional methods, particularly the limited focal length of current projective objective lens.

Focusing and leveling are two imperative processes to adjust the wafer onto the ideal focal plane of projection lithography tools. Based on moiré fringes formed by particularly designed dual-grating marks, the four-channel focusing and leveling scheme is proposed and demonstrated. These relationships between the tilted amount of wafer, the vertical defocusing amount, and the phase distributions of moiré fringes are deduced. A single-channel experimental setup is constructed to verify the performances of proposed method. Results indicate that the tilted amount and the vertical defocusing amount can be precisely detected with accuracy at 10 À4 rad and several nanometers level, respectively, and therefore meet the demand of the high-demanding focusing and leveling processes.