光刻物镜六自由度调节支撑中耦合像差产生与抑制机理研究

Multi-DOF adjustment of optical elements is an important measure for system image quality compensation in lithographic projection lens, but the generation mechanism of coupling aberrations is unknown. The latest study found that the RMS value and Zernike coefficients of the surface figure vary linearly with the adjusting force during axial adjusting of optical elements. Our previous studies have demonstrated that coupling aberrations can be reduced when eccentric adjusting force is restricted to transmit from mount to the optical element. Accordingly, we speculate that the rational design of mechanism stiffness can reduce lens deformation and coupling rigid motion in the six DOF adjusting mount, thereby system coupling aberrations introduced by adjusting can be decreased. Design method of six DOF adjusting mount is established based on compliance matrix method and sensitivity analysis of coupling aberrations. The root of coupling aberrations introduced by adjusting can be revealed. Coupling aberrations can be decreased using stiffness optimization in designing process. Indirect testing results of mount rigid motion by sensor are calibrated online with direct testing results of optical element rigid motion by Fizeau phase-shifting interferometer. The mapping relationship between testing results of the interferometer and the sensor is found. Ultimately, sensor measurement is applied in projection lens online and closed-loop control is utilized to reduce the coupling rigid motion of the mechanism. This project describes the relationship between multi-DOF adjustment of optical elements and the generation mechanism of coupling aberrations for the first time. A new way of image quality compensation is provided.

光刻物镜中光学元件多自由度调节是系统像质补偿的重要措施，但其引入耦合像差的机制不详。最新研究发现,光学元件轴向调节时面形RMS值和Zernike系数随调节力线性变化。我们前期研究证实，限制偏心调节力向光学元件传递，可以降低耦合像差。据此，我们推测“六自由度调节支撑中，合理设计机构的刚度，可以减小光学元件自身变形和耦合刚体位移，从而减小调节引入的系统耦合像差”。本课题提出基于柔度矩阵法和耦合像差敏感度分析的六自由度调节支撑设计方法，揭示调节引入耦合像差的根源，通过结构刚度优化从设计上减小引入的耦合像差。用Fizeau相移干涉仪直接测试的光学元件刚体位移结果在线标定机构上传感器间接测试镜框的刚体位移，建立干涉仪和传感器测试结果之间的映射关系，最终在物镜中应用传感器在线检测，并应用闭环控制减小机构耦合刚体位移。本课题首次阐述光学元件多自由度调节与耦合像差产生机制的关系，为像质补偿提供一种新思路。

投影物镜是光刻机的核心部件之一，随着节点向小于10nm方向发展，投影物镜的像差对成像质量的影响越来越突出。光学元件的支撑结构不仅需要满足固定支撑要求，还应适应外力和温度变化等对光学面形造成的不利影响。当光学元件受到外部振动干扰时，可能偏离其在光学系统中的理想位置，需要实时对其进行位置调节。系统中有一些光学元件对多个自由度公差都很敏感，这时需要对其多个自由度调节。. 本课题研究内容包括三方面：（1）建立光学元件六自由度调节机构模型，揭示多自由度调节引入耦合像差的根源；（2）优化六自由度调节机构模型，探索抑制多自由度调节产生耦合像差的机构设计方法；（3）探索光学元件多自由度调节引入的耦合刚体位移测试方法。.在本课题的资助下，分析了六自由度调节支撑中力的传递链路上刚度变化与引入的耦合像差变化的规律和特点，揭示了机构刚度对像质补偿效果的影响，理清了影响多自由度调节产生耦合刚体位移和耦合像差的因素，分析了各个因素的敏感度，揭示了耦合像差产生的根本机理。形成了一套通过优化刚度降低耦合度的多自由度调节机构设计方法。实现了六自由度调节支撑引入耦合像差抑制。最后通过实验验证了提出的假说。. 结果表明，机构的六个自由度开环分辨率为10nm × 10nm × 5nm × 100nrad × 100nrad × 200nrad，闭环调节精度为30nm × 30nm × 15nm × 150nrad × 150nrad × 300nrad，自由模态测试得到的一阶固有频率为162.061Hz。光学元件在运动学支撑结构上粘胶前的面形为1.963nm，粘胶固化后的面形为2.133nm，当其沿着X向调节±30um时，引入面形误差最大值小于0.2nm。当光学元件在在312mW热载作用下时，其面形RMS为2.297nm，表明设计的运动学支撑绝热性能良好。. 在本课题的资助下，系统研究了光刻物镜六自由度调节机构工作原理、设计方法及耦合像差产生机理。本课题的完成为多自由度调节引入耦合像差的抑制提供了一种解决思路，对促进集成电路产业发展有重要的理论意义和应用价值。