Patent ID: 8098927

Claim:
A method for predicting fluctuation in imaging characteristics of a projection optical system in an exposure apparatus which projects a pattern formed on a reticle onto a wafer through the projection optical system, the method comprising: a measurement step of irradiating the projection optical system with exposure light under a first exposure condition to measure first imaging characteristics fluctuation of the projection optical system and, before an imaging characteristics value is restored to an initial value at the start of irradiation after irradiation is stopped, irradiating the projection optical system with the exposure light under a second exposure condition to measure second imaging characteristics fluctuation of the projection optical system; and a calculation step, performed by a calculation unit, of calculating approximate expressions of the first and second imaging characteristics fluctuations measured in the measurement step based on an imaging characteristics model, wherein the imaging characteristics model includes an exposure model indicating imaging characteristics fluctuation during irradiation of the projection optical system with the exposure light, and a non-exposure model indicating imaging characteristics fluctuation in a state in which irradiation is stopped, and said calculation step, performed by the calculation unit, comprises the steps of: calculating the approximate expression of the first imaging characteristics fluctuation based on the exposure model, applying, to the non-exposure model, a final imaging characteristics value obtained by the approximate expression of the first imaging characteristics fluctuation, and a time that elapses from irradiation of the projection optical system with the exposure light under the first exposure condition is stopped until irradiation of the projection optical system with the exposure light under the second exposure condition is started, thus calculating an initial value of the second imaging characteristics fluctuation, and calculating the approximate expression of the second imaging characteristics fluctuation measured in said measurement step based on the exposure model to which the initial value of the second imaging characteristics fluctuation is applied.