Scranton Gregg, Bhargava Samarth, Ganapati Vidya, Yablonovitch Eli
Opt Express. 2014 Oct 20;22(21):25027-42. doi: 10.1364/OE.22.025027.
Traditionally, aberration correction in extreme ultraviolet (EUV) projection optics requires the use of multiple lossy mirrors, which results in prohibitively high source power requirements. We analyze a single spherical mirror projection optical system where aberration correction is built into the mask itself, through Inverse Lithography Technology (ILT). By having fewer mirrors, this would reduce the power requirements for EUV lithography. We model a single spherical mirror system with orders of magnitude more spherical aberration than would ever be tolerated in a traditional multiple mirror system. By using ILT, (implemented by an adjoint-based gradient descent optimization algorithm), we design photomasks that successfully print test patterns, in spite of these enormous aberrations. This mathematical method was tested with a 6 plane wave illumination source. Nonetheless, it would have poor power throughput from a totally incoherent source.
传统上，极紫外（EUV）投影光学中的像差校正需要使用多个有损反射镜，这导致对光源功率的要求高得令人望而却步。我们分析了一种单球面镜投影光学系统，其中通过逆光刻技术（ILT）将像差校正内置到掩模本身中。由于反射镜数量较少，这将降低EUV光刻的功率要求。我们对一个单球面镜系统进行建模，其球差比传统多镜系统所能容忍的球差大几个数量级。通过使用ILT（由基于伴随的梯度下降优化算法实现），尽管存在这些巨大的像差，我们仍设计出了能够成功打印测试图案的光掩模。该数学方法在6平面波照明源下进行了测试。然而，对于完全非相干光源，它的功率通量会很差。
