1. Field of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning devices, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist).
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
It has been found that the position of the stage or substrate holder (i.e., substrate holder) with respect to the projection beam is disturbed under many circumstances. This disturbance was thought largely due to mechanical influences, because moving parts, such as a moving measuring stage in a two stage apparatus, would exert forces on, for example, the substrate holder through the medium of the mounts, the suspension, and in general through the (mechanical) rest of the apparatus. In fact, suspension and mechanical decoupling techniques were much improved, but still a residual disturbance remained. This residual disturbance may limit the minimum feature size and the minimum overlay error during projection.