In this paper, a grating defect detection system based on the principle of darkfield imaging is proposed for the surface defect detection of existing large-size gratings, and the corresponding mechanical device is built. The device mainly includes two categories: hardware system and software system, of which the hardware system has lighting module, image acquisition and displacement module, and the software system has target edge reconstruction module and target edge detection module. Through the device, the surface defects of two-dimensional diffraction gratings of different sizes and different process conditions (substrate, mask grating, etching grating and coating grating) are automatically detected, and the statistical data of different types of defects are given. Through the analysis and study of the cause, transmittance and how to avoid different kinds of grating defects, whether it will affect the optical performance of grating use.The experimental results show that the proposed system meets the needs of large-size grating surface defect detection and evaluation in terms of accuracy and accuracy of defect detection, and the mechanical structure of the device is simple and compact, which has the potential of industrial large-scale detection. The device is of great significance for evaluating large-size high-precision grating manufacturing technology.
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°, 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.
This paper introduces a new device for one-dimensional grating period measurement with high accuracy. The scheme includes two subsystems: a grating interferometer and a laser interferometer. As the grating moves, the grating interferometer obtains periodic signal related to the grating period, while the laser interferometer measures the displacement simultaneously. The grating period is then obtained through data processing and least-square-fitting. Most of the grating period measurement devices have scattered structures, poor stability, which could be affected by the environment easily. In order to overcome this shortcoming, we adopt the structure of glued prisms, which is compact, and will significantly improve the stability of the system. Thus, the scheme has advantages in measurement accuracy as well as resolution. The system benefits from simple structure and cheap components, which can be widely used in grating period measurement technology.
A single-groove grating for four-port TE-polarization beam splitting under normal incidence at the wavelength of 632.8nm is presented. The total efficiency of the beam splitter is over 77% with beam split uniformity better than 5%. Rigorous coupled-wave analysis (RCWA) and the simulated annealing (SA) algorithm are employed to design this beam splitter grating. The tolerance of fabrication errors of the grating is analyzed.
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