| 摘要 |
<p>An optical focusing system is provided for accurately focusing a wafer surface, thereby enabling the production of sharp microcircuit images. Accurate focusing is achieved despite non-parallel and non-flat wafer surfaces, despite differences in reflectivity of different portions of the wafer surface, and despite changes in environmental conditions such as temperature during system operation. The system comprises a full aperture focus detection apparatus, a kinematic lens positioning apparatus, and a kinematic wafer chuck differential leveling or positioning apparatus. The full aperture focus detection apparatus detects the extent to which a wafer surface is out of focus with respect to the image plane of a projection lens, and produces an amplified differential signal having magnitude and polarity indicative of the extent and direction, relative to the image plane, that the wafer surface is out of focus. When the center of the wafer surface is to be focused and is positioned along the optical axis of the system, the amplified differential signal causes the kinematic lens positioning apparatus to focus the center of the wafer surface by moving the projection lens a distance and direction corresponding to the magnitude and polarity of the amplified differential signal. The kinematic wafer chuck differential leveling or positioning apparatus provides for differentially leveling the chuck at three selected off-center locations. When a point on the wafer surface corresponding to one of these three locations is to be focused and is positioned along the optical axis of the system, the amplified differential signal causes the kinematic wafer chuck differential leveling or positioning apparatus to focus that point by raising or lowering the chuck at exactly that point.</p> |
