Study on Differential Astigmatism Detection Technology
|School||Harbin Institute of Technology|
|Course||Instrument Science and Technology|
|Keywords||Defocus detection Differential astigmatic IIR filter Mechanical Design|
Laser direct writing machine is to produce diffractive optics key equipment, the system's basic structure is dominated by H e-Cd laser, acousto-optic modulator, servo control systems, projection lithography lens, CCD camera defocus detection systems, control computer and other units. Defocus detection system is one of the core unit, in real time servo control system for the defocus amount the surface through the adjustment of the servo control system of the writing beam direct writing machine to precisely focus on the resist surface, so as to ensure etching quality. Defocus detection system installed in the laser writing head, followed by the servo mechanism drive write heads move together servo mechanism in order to avoid an excessive load inertia effects arising from the dynamic operating characteristics, requiring defocus detection system in size and weight both as small as possible. Project \This paper analyzes the advantages and disadvantages of existing defocus detection method based on the context of practical application to determine the differential astigmatic detection program, starting from the overall design of the system to determine the key aspects - optical parameters, mechanical structure, optical conversion, digital processing, testing, system software platform design; established under the laser beam optical differential astigmatic optical system mathematical model, using ZEMAX and MATLAB simulation analysis, by comparing the cylindrical lens focal length lens and the cylinder The distance between the mirrors of different optical path parameters on the focus error signal (FES) effects, set the parameters of the optical system; respective optical components according to size and simulation results to design a compact, high-precision mechanical structure, the use of bonding technology to achieve high-precision mechanical components mounted positioning. The system hardware and software components respectively optimized for fast, high-precision signal processing. Hardware part is mainly in the realization of photovoltaic conversion, signal conditioning, and analog filtering, AD converter, CPLD assist DSP control and other functions. Software part includes data acquisition, data processing and data communications of three parts, and use the IIR digital filter and median filtering reduces noise interference, which also includes software features optimization and performance optimization. In the above study, based on the experimental platform built optics and experimental testing, focusing on verification TMS320F2812DSP data processing chip detection accuracy of the system and the use of data on the effect of interpolation methods in the expansion of the effect on the range, the experimental results show that the measuring Sensitivity 80nm, range 60μm, laser direct writing machine to meet the performance requirements.