Patent ID: 6449031
Filing Date: 2002-09-10
Classification: G03F

Abstract:
A method for monitoring performance of an exposure tool comprising the acts of:providing an image forming layer overlying a substrate in an image plane of said exposure tool, said image forming layer having an image forming empirical constant determined for said image forming layer and for image processing thereof; blanking a portion of an exposure field of said exposure tool while exposing, at a nominal exposure energy, a remaining portion of said image forming layer in said exposure field through a reticle positioned in an object plane of said exposure tool; performing a first exposure of a first feature, at a first exposure energy, within said previously blanked portion, said first feature having a critical dimension and a first orientation, wherein said first exposure energy is less than said nominal exposure energy; performing a second exposure of a second feature, at a second exposure energy, within said previously blanked portion, said second feature having a second critical dimension, approximately equal to said first critical dimension, and a second orientation, wherein said second orientation overlaps a portion of said first orientation and is rotated with respect to said first orientation by a predetermined angle, and wherein said second exposure energy is less than said nominal exposure energy and wherein a sum of said first and second exposure energies is approximately equal to said nominal exposure energy, thereby forming a critical dimension test structure in said overlap portion; measuring a dimension of said critical dimension test structure; and determining a critical dimension from said measured dimension.