Imaging properties of a patterned rough surface: Effects of roughness correlation and partial coherence

An investigation of partially coherent speckle is performed, including the effects of a pattern structure in the object plane of an imaging system. It is demonstrated that, when forming an image of a patterned rough surface into a binary photoresist, the width variations produced in the resultant pattern (also called line edge roughness) can increase as the imaging system becomes more incoherent. This unusual behavior occurs because of an interaction between the speckle produced by a rough surface and the partially coherent imaging properties of the pattern structure. It is shown that the increase in line edge roughness for a more incoherent system requires that the surface roughness of the object structure have a correlation length that is substantially smaller than the resolution of the imaging system.