| 摘要 |
<p>A projection system (PS) is provided which includes, in an embodiment, two frames. The optical elements of the projection system are mounted on a first frame (200). The position of the optical elements is measured relative to a second frame (300) using a first measurement system (910). A second measurement system (920) is used to measure a parameter associated with a deformation of the second frame. The measurement made by the second measurement system can be used to compensate for any errors in the position of the optical elements as measured by the first measurement system resulting from deformations of the second frame. Typically, deformations of the frames are due to resonant oscillation and thermal expansion. Having two frames enables the optical elements of the projection system to be positioned with a high degree of accuracy. Optionally, a temperature control system (780, 790) may be provided to drive the temperature of at least one of the frames back to a desired value after the lithographic apparatus has been taken off line.</p> |
