Koji Kaise

Optical displacement metrology using alternating direction Moire

Abstract. We develop a new double exposure Moire method for an optical registration metrology system in photolithography. Our method enables us to achieve at least a factor of 10 improvements in precise displacement metrology using a conventional optical sensor. We utilize a new registration mark printed to the photoresist on a bare silicon wafer using a double exposure of the gratings. The mark consists of two types of Moire with opposite phases. The two types of Moire are oriented in alternate directions. Displacement is measured from the distance between the positions of the two types of Moire in analogy with the conventional registration method. This concept is called alternating direction Moire. Performance is experimentally confirmed using an i-line wafer exposure apparatus. Precision is improved by up to 32 times as compared with the conventional method and can be applied to other Moire metrologies.