Large-field scanning laser ablation system

A large-field scanning imaging system has been developed to perform imaging ablation using 308-nm excimer laser light. A 1× Dyson-like lens images a portion of the mask onto a portion of the substrate to be ablated. The lens has a field of 12 mm and a numerical aperture of 0.05, providing a resolution of about 6 µm. A mirror system comprising a roof and a plane mirror, with all three surfaces mutually orthogonal, ensures that the mask and the substrate have identical orientations. A common stage is used to hold the mask and the substrate. The stage is scanned in a serpentine manner to transfer the entire image. The illuminated region is diamond-shaped, and adjacent scans overlap by half its width to ensure uniformity. Illumination uniformity is provided by a light tunnel in the illumination system. Alignment is performed by optically combining images of mask marks and substrate marks formed by a pair of microscope objectives, one viewing the mask and the other viewing the substrate. The substrate is leveled, focused, and registered relative to the image of the mask by a stage with six degrees of freedom.