大口径石英基底衍射透镜的高精度制备方法

针对传统接触式曝光过程中掩模版因自身重力产生形变从而引入不可忽视的线宽误差和位置误差的问题,提出了一种大口径石英基底衍射透镜的高精度制备方法.采用背面具有真空道的高平面度、高强度金属校正工装吸附在掩模版上,利用掩模版上下表面的压强差使其与工装高度贴合,确保掩模版的高平面度.待石英基底所有区域均与掩模版结构面紧密贴合后取下工装.完成接触式曝光和显影后,采用反应离子刻蚀技术对大口径石英基底进行刻蚀,最终得到高精度微纳米结构.经有限元分析,使用该校正工装后,掩模版的形变量由28.85μm减小为0.88μm.实验结果表明,采用该方法制备的口径430mm两台阶石英基底菲涅尔衍射透镜波像差优于1/25λ,平均衍射效率为38.24%,达到理论值的94.35%,具有良好的聚焦和光学成像效果.

High Precision Fabrication Method of Diffractive Lens on Large Aperture Quartz Substrate

Aiming at the problem that the mask deformation due to its own gravity during the traditional contact exposure process,which can introduce nonnegligible linewidth errors and position errors,a set of high-precision fabrication methods for large-diameter quartz substrate diffractive lenses was proposed.A high-flatness and high-strength metal calibration fixture with vacuum channel on the back is adopted to attract the mask,and the pressure difference between the upper and lower surface of the mask is used to make it highly fit with the fixture to ensure the high flatness of the mask.Then the fixture is removed after all areas of the quartz substrate are in close contact with the structure surface of the mask.After the contact exposure and development are completed,the large-diameter quartz substrate is etched by reactive ion etching technology,and finally a high-precision micro-nano structure is obtained.The results of finite element analysis show that the deformation of the mask was reduced from 28.85μm to 0.88μm after using the calibration fixture.The experimental results show that the wave-front error of the 430 mm two-step quartz substrate Fresnel diffraction lens prepared by this method is better than 1/25λ,the average diffraction efficiency is 38.24%,reaching 94.35% of the theoretical value,and it has well focusing and optical imaging effect.