精密光学系统的热像差

为了精确控制与补偿物镜的热像差,设计了一套三镜实验光学系统,基于该系统验证了热像差计算方法的准确性。介绍了热像差分析方法及验证实验方案。开展不同热载工况下热像差测试实验,并与仿真结果进行了对比。最后,综合实验与仿真结果,分析了特定热载条件下系统热像差中非轴对称像差成分以及系统最佳焦面的变化趋势,获得了热像差的瞬态特性。实验结果显示:在输入热载大小之比为1∶4∶9的情况下,实验和仿真获得的热像差均方根(RMS)值之比分别为1∶3.75∶9和1∶4.01∶9.01,光学系统所加热载和热像差之间呈线性关系;在实验热载荷作用下,系统最佳焦面的稳态时间小于450min,而热像差中一阶像散(标准Zernike Z4)的稳态时间小于48min,一阶四叶(标准Zernike Z11)的稳态时间小于9min,最佳焦面稳态时间远大于非轴对称成分的稳态时间。基于该三镜实验光学系统所获得的热像差特性能够为投影光刻物镜或其它精密光学系统的热像差控制与补偿提供有力支撑。

Thermal aberration in precision optical system

To control and compensate the thermal aberration of objective lens accurately, a special three lens integrated experiment optical system was designed, and the calculation method for the thermal aberration was verified based on the designed system. Firstly, thermal aberration simulation method and corresponding verified experiment were introduced. Then, a series of experiments were carried out in different thermal load conditions and comparison of experimental and simulated results were also presented. Finally, combining experimental and simulated results, asymmetric aberrations and focus drift trends of the optical system under a certain thermal load were analyzed, and transient properties of thermal aberration were obtained. The results show that the ratios of RMS(Root Mean Square) values of thermal aberration from the experiments and simulations are 1:3.75:9.00 and 1:4.01:9.01 when the thermal load ratio of the optical system is 1:4:9. The data suggests that the thermal aberration is proportional to a heat load it suffers. For transient thermal aberration, simulation results show that stable time of the best focus position is less than 450 min whereas the stable time of Z₄ and Z₁₁ are 48 min and 9 min respectively. The stable time of best focus is much longer than that of asymmetrical aberration. Thermal aberration properties obtained through the three lens integrated optical system provide references for thermal aberration reduction and calibration strategies both for lithography objective lenses and other similar optical systems.