Direct reticle to wafer alignment using fluorescence for integrated

Abstract

A mask alignment system for integrated circuit lithography achieves reticle to wafer referencing. A detection system located below the main projection lens detects the image of reticle alignment marks while also detecting wafer alignment marks. The reticle marks are imaged in light at the exposure wavelength. A first detection method images the fluorescence produced in the photoresist by the reticle mark images. A microscope located below the main projection lens produces the image and also images the wafer marks with broadband non-actinic illumination. The second method images the reticle marks in exposure light using a microscope which images and detects the exposure wavelength while maintaining the illumination and detection of the wafer marks. The third method collects directly both the exposure light and fluorescent light that is scattered and reflected from the wafer surface; the presence of wafer alignment marks changes this light collection. Scanning the wafer relative to the reticle produces a signal indicating the relative position of reticle and wafer alignment marks. All three methods provide information for complete field-by-field alignment including offsets, reticle-to-wafer magnification, rotation, and skew for both step-and-repeat and scanning exposure systems.