Focusing method and apparatus for high-resolution projection patterning

A novel focusing method and apparatus for determining the position of the i mage plane of a coherently illuminated object is presented. The principle o f this method is based on the light distribution in the defocused image pla ne of a luminous knife-edge object. The radiation energy extending beyond t he geometrical image is a function of the relative position of the projecti on objective and its minimum indicates the best location of the image plane . The photodetected energy can be used as a feedback signal to focus variou s optical systems in applications such as high-resolution laser patterning. Preliminary results obtained by means of a 193 nm excimer laser radiation and a reflecting objective are also reported. (C) 2001 American Institute o f Physics.