METHODS OF CONTROLLING EUV EXPOSURE DOSE, EUV LITHOGRAPHIC METHODS AND APPARATUS USING SUCH METHODS

摘要

PROBLEM TO BE SOLVED: To provide new dose control methods in order to optimize the number of dies that can be exposed per unit of time.SOLUTION: The EUV exposure dose in a lithographic apparatus is controlled pulse by pulse by varying the conversion efficiency with which a pulse of EUV radiation is generated from excitation of a fuel material by a corresponding pulse of excitation laser radiation. The conversion efficiency can be varied in several different ways, by varying the proportion of a fuel material that interacts with a laser beam, and/or by varying quality of the interaction. Mechanisms of varying the conversion efficiency can be based on variation of laser pulse timing, variation of pre-pulse energy, and/or variable displacement of a main laser beam in one or more directions. Steps of maintaining symmetry of the generated EUV radiation can be included.