Impact of Transmitted Reflected Light Inspection on Mask Inspectability, Defect Sensitivity, and Mask Design Rule Restrictions

摘要

The application of aggressive optical proximity correction (OPC) has permitted the extension of advanced lithographic technologies. OPC is also the source of challenges for the mask-maker. Sub-resolution features, small shapes between features and highly-fragmented edges in the design data are difficult to reproduce on masks and even more difficult to inspect. Since the inspection step examines every image on the mask, it is required to guarantee the total plate quality. The patterns themselves must be differentiated from defects, and the ability to recognize small deviations must be maintained. In other words, high inspectability at high defect sensitivities must be achieved simultaneously. This must be done without restricting necessary OPC designs features. Historically, transmitted light has been deployed for mask pattern inspection. Recently, the inspection challenge has been both enhanced and complicated by the introduction of reflected light pattern inspection. Reflected light reverses the image contrast of features, creating a new set of design limits. This paper introduces these new reflected inspection limits. Multiple platform capabilities will be incorporated into the study of reflected and transmitted inspection capability. The benefits and challenges of integrating a combination of transmitted and reflected light pattern inspection into manufacturing will be explored. Aerial Image Measurement System (AIMS) analysis will be used to help understand how to leverage the enhanced inspection capability while avoiding unnecessary restrictions on OPC.