Micro-pattern recognition using a microscope coherent optical processor (M-COP) [IC inspection]

The application of a microscope coherent optical processor to the recognition of the micro-patterns on the plane reflecting surface of a silicon wafer is examined. The system employs microscope optics to form an enlarged image of the object at the input to a conventional Vander Lugt optical correlator. High efficiency holographic matched filters are synthesised to provide the necessary sharp correlation peak. The characteristics of the system have been studied with particular emphasis on the measurement of critical dimension changes between micro-patterns. Experimental and theoretical results show that a scale change of 0.5% and a 0.4 μm absolute dimensional change can be measured