A lilhographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of intcgrated circuits (ICs). Driven by the growing demand of manufacturing modern integrated circuits with ever shrinking sizes, lithographic technologies that can offer higher resolution and belter reliability are under a fasl-paced and extensive development. One of such advancing lithographic technologies is the extreme ultra-violet lithography (also known as EUV or EUVL). which allows for sub-10 nanometre (nm) scale resolution. In lilhographic processes, it is desirable frequently to make measurements of the structures created, e.g.. for process control and verification. Driven by such a demand, various inspection and metrology tools have been made available, including scanning electron microscopes (SEMs). which are often used to measure critical dimension (CD), and specialized optical metrology tools, such as various forms of scatleromelers. to measure overlay, a measure of ihc accuracy of alignment of two layers in a device. The basic principle of scanning electron microscopy is the scanning of an electron beam (e-beam) over a sample to build up an image. In order to boost the inspection speed and thus the Ihroughput. multiple beam c-hcam inspection (MBI) tools have been developed and are now commercially available.
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