Abstract
The concept of system invariance is the principle of scaling law in optical lithography. Both the conservation of the intensity threshold of the aerial image and the invariant pupil filling of the diffracted light with the normalized numerical aperture (NA) have to be satisfactory in order to ensure the invariance for a system in a variety of optical settings. Two well-known scaling equations with k 1 and k 2 factors characterize the capability of the manufacturing process in microlithography. In theory, the validity of these two equations has to be based on the principle of invariance. Therefore, any optical parameters in exposure tool could be scaling validly and properly, once they obey the principle of invariance.