CASSEGRAINIAN INVERSE CASSEGRAINIAN 4-ASPHERICAL MIRROR SYSTEM (MAGNIFICATION=-ORDER ABERRATIONS AND SUITABLE FOR DEEP-ULTRAVIOLET OPTICAL LITHOGRAPHY(1) DERIVED FROM THE SOLUTION OF ALL ZERO 3RD)
Ym. Cho et al., CASSEGRAINIAN INVERSE CASSEGRAINIAN 4-ASPHERICAL MIRROR SYSTEM (MAGNIFICATION=-ORDER ABERRATIONS AND SUITABLE FOR DEEP-ULTRAVIOLET OPTICAL LITHOGRAPHY(1) DERIVED FROM THE SOLUTION OF ALL ZERO 3RD), Optical engineering, 33(7), 1994, pp. 2480-2486
A four-aspherical mirror system with unit magnification is investigate
d for use in deep ultraviolet (DUV) optical lithography. It is derived
from the solution of all zero third-order aberrations for the four-sp
herical mirror system with unit magnification. We have first examined
the holosymmetric four-spherical mirror system in which all third-orde
r aberrations are zero and all orders of coma and distortion are also
zero. However, the system does not have any optical design freedom lef
t for the correction of higher order aberrations, so a new solution of
nonholosymmetric system is derived. In this system aspherizations on
the spherical surfaces are carried out to reduce the residual aberrati
ons. The aspherization is optimized to give near diffraction-limited p
erformance for DUV wavelengths of 0.193 mum (ArF excimer laser line).
The final system we have obtained consists of all aspherized mirrors w
ith a numerical aperture of 0.35. This reflective system is compact in
size and expected to be useful in optical lithographic applications.