| 摘要 |
An autofocus unit is provided to an immersion lithography apparatus for having a fluid over a target surface of a workpiece and an image pattern projected on this target surface through the fluid. The autofocus unit has an optical element such as a projection lens disposed opposite and above the target surface. An autofocus light source is arranged to project a light beam obliquely at a specified angle such that this light beam passes through the fluid and is reflected by the target surface of the workpiece at a specified reflection position which is below the optical element. A receiver receives and analyzes the reflected light. Correction lenses may be disposed on the optical path of the light beam for correcting propagation of the light beam. |
