Abstract
A design of four-mirror optical system with reduction magnification 5X for deep UV ($\lambda$=248 nm of KrF excimer laser) submicron lithography is presented. Initially by using the paraxial quantities, the domain of solution for $t=d_1+d_2+d_3$<0 (d;: distance between the mirror $c_i$ and $c_{i+1}$ is found for the system which is free from the four off-axial Seidel first order aberrations that are coma, astigmatism, field curvature, and distortion. The solution with $d_5$=2.95 (normalized with respect to $c_i$= -1) is choosen and the aspherization is carried out to the spherical mirror surfaces ($c_3$ and $c_4$ in order to reduce the axial and residual off-axial higher order aberrations. The numerical aperture of the final system is as large as 0.4, which gives Rayleigh resolution of 0.38 $\mu\textrm{m}$.
축소배율(5$\times$)을 갖고, Seidel 1차 수차중 4개의 비축수차인 코마(coma), 비점수차(astigmatism), 상면만곡(field curvature) 그리고 왜곡수차(distortion)가 제거된 마이크로 리소그라피를 위한 4-구면 반사경 광학계를 해석적으로 구하였다. 이때, $t=d_1+d_2+d_3$<0, (di는 반사거울 $c_i$와 $c_{i+1}$ 사이의 거리)이고, 축상 수차인 구면수차와 잔류고차수차는 반사거울 $c_3$와 $c_4$를 비구면화 하므로서 제거하였다. 이렇게 설계된 4-반사경 광학계의 N.A.는 0.4로서 Rayleigh분해능은 0.38 $\mu\textrm{m}$이다.