Importance

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Abstract

The present invention provides a method and system for controlling the refractive index of gaseous mixture of the projection optics of a lithographic tool. In one embodiment, the present invention corrects projection optic aberrations due to altitude specific barometric pressure variations. Furthermore, the present invention provides control over the aberrations of an optical system, the ability to compensate for altitude changes, the ability to compensate for pressure changes, and the ability to purge gases from the optical system. In an embodiment, the system of the present invention includes at least one gas supply to provide a gas for a mixture, at least one mass flow controller associated with each gas supply, where the mass flow controller measures and controls the quantity of a respective gas for the mixture, and at least one flow gauge to substantially maintain laminar flow within the lithography apparatus. According to another embodiment of the present invention, the system further includes at least one filter to purify each gas for each gas supply, and at least one temperature control unit to maintain the temperature of the mixture at predetermined thermal specifications.

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First Claim