Coherence management in lithography printing systems

In proximity lithography, interference and diffraction effects arise when printing small features because of the proximity gap. Different techniques are used in order to control and take advantage of theses effects. In this paper, the focus is set on the MO Exposure Optics developed to shape the angular spectrum of the exposure light. The MO Exposure Optics contains several elements including microlens arrays that have certain symmetry and sampling. The MO Exposure Optics allows to set the angle of illumination and can be used to define spatial coherence. We study here in detail the influence of different illumination settings on optical proximity correction (OPC) structures. We apply this concept for the first time to a LED illumination. The propagation of light after an optical proximity correction structure is measured by recording aerial images over a distance of up to 60 pm behind the mask with a high resolution microscope setup.(1) As an example structure, we investigate here an optical proximity correction structure that is intended to make the edge of a line sharper. Using illumination filter plates that limit the angle of illumination and increase the coherence lead to pronounced interference effects in aerial images as expected. But special settings of the illumination allow to achieve comparable results with much larger illumination angles and higher throughput. We will show examples and analyze the results.