| 摘要 |
PROBLEM TO BE SOLVED: To correct the nonlinear defocus (image plane warpage) of a projection optical system which is deteriorated by the change of environmental conditions such as the atmospheric pressure around the projection optical system, the absorption of an exposure lighting light or the bent of a reticle, etc. SOLUTION: Among lens elements 25-38A of which a projection optical system is composed, the lens elements 36A and 37A only are made of fluorite and the other lens elements are made of quarts. Gas whose temperature is controlled is supplied to a gas chamber surrounded by the lens elements 36A and 37A and a lens frame G2 from a temperature controller 13a and the gas which is made to flow through the gas chamber is returned to the temperature controller 13a. A field curvature which is produced by the lens elements made of quartz is eliminated by the temperature control of the lens elements 36A and 37A and, further, the residual linear magnification error is eliminated by the pressure control of gas in a gas chamber between the lens elements 33 and 34. |
