Illuminator for dark field inspection

Abstract

Light from a single source is divided among several illumination arms, each of which directs light via a multimode fiber bundle from the source to the wafer location. The arms are arranged circumferentially around a common illumination region, so that the region is illuminated from several directions. For each arm, light exiting the fiber bundle enters a turning prism, reflects off the hypotenuse of the prism, and is diverged in one dimension by a negative cylindrical surface on the exiting face of the prism. The beam then reflects off an anamorphic mirror and propagates to the illumination region on the wafer. The beam has an asymmetric footprint, so that it illuminates a nearly circular region of the wafer when viewed at normal incidence. The fiber bundle is at the front focal plane in the meridional dimension. The illumination region is at the rear focal plane in both dimensions.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Patent Application No. 60 / 587,206, filed Jul. 12, 2004, which is hereby incorporated by reference in its entirety.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to inspection of materials, and more particular to illuminators for dark-field inspection of material, inspection systems for dark-field inspection of material, and methods for illuminating a target for dark-field inspection. [0004] 2. Description of the Related Art [0005] As more manufacturing processes use wafer-based technology, and utilize increasingly smaller features on these wafers, it becomes increasingly important to inspect the wafers for defects at various stages throughout the manufacturing process. Wafer inspection systems have evolved to keep pace with these demanding requirements. [0006] In a typical wafer inspection system, a wafer is attached to a movable s...

AI Technical Summary

Benefits of technology

[0009] Advantageously, the present invention provides for a dark-field illumination system that is compact, or illuminates a large illumination region on the target, or provides uniform illumination and a uniform angular spectrum across an illumination region on the target, or has a low range of incident angles and a broad circumferential azimuth for an illumination region on the target, or is bright throughout an illumination region on the target. The various embodiments of the invention respectively achieve one or more of these advantages.

Problems solved by technology

The illumination for a dark-field system greatly affects the overall performance of the inspection system.

For instance, a “ring-lamp” device, similar to those used to illuminate dark-field microscopes, does not work very well for the dark-field wafer inspection systems.

As a result, the sensitivity of the inspection system can vary over the field of view, which is highly undesirable.

This variation in sensitivity can require additional processing time for each image, thereby slowing down the system and reducing efficiency.

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