METHOD AND APPARATUS FOR MAINTAINING FOCUS AND MAGNIFICATION OF A PROJECTED IMAGE

摘要

A method for operating an optical projection system including projection optics is disclosed. The projection optics project an image of the object on the substrate at an image distance from the projection optics. The image has a size dependent on the size of the object and the ratio of the image distance to the optical distance of the object from the projection optics. The image distance can change with changes in the condition of the projection optics such as changes in the temperature of elements of the projection optics. The image distance is monitored. If the image distance changes, the substrate is moved to the new image distance and the optical distance of the object is correspondingly changed such that the ratio of the image distance to the object distance stays the same.