Apparatus and method for focusing light beam and exposure apparatus

摘要

Focusing method and exposure apparatus for focusing both a parallel light beam (16) and a non-parallel light beam (16) through a movable objective lens (3) onto an object (4). A negative feedback loop is provided which has a detector (6) for receiving a reflection light beam (5) of the non-parallel light beam (2) passed through the movable objective lens (3), reflected at the object (4) and passed through the movable objective lens (3), for generating a detection signal (6a, 6b) corresponding to a focus deviation of the non-parallel light beam (2), and a driver (9) for receiving the detection signal to control a position of the movable objective lens (3) in accordance with the detection signal (8), so that the detection signal is decreased. The negative feedback loop further includes a correction signal generator (13) for generating a correction signal (14) and supplying it to the negative feedback loop as a disturbance of the loop so that the parallel light beam is focused onto the object.