Content-addressable memory for VLSI pattern inspection

In the template-set approach to VLSI pattern inspection, all patterns in a local window (i.e. a 5*5 array of pixels) that are allowed by the design rules are collected as a template set, and an image in the window centered at each pixel position is compared to the templates to determine whether the pattern is defective. To make this method practical, the number of acceptable templates must be reasonably small and template matching must be fast. By introducing don´t-care conditions into the templates, the number of required templates was reduced. A maskable content-addressable memory was used to implement templates with don´t-care conditions and to permit parallel comparison of an incoming pattern with all templates in the set. A custom VLSI chip was designed with a 2- mu m double-metal CMOS technology, which can perform parallel template matching at the rate of 1.6*10/sup 7/ local images per second.<>