Differential interferometer system and lithographic step-and-scan apparatus equipped with this system

摘要

Differential interferometer system for measuring the mutual position and moving a second object and (WH) the object (57) [Abstract] The first and the (MH) is described. The system includes a second interferometer (5, 6, 7, 8) having a first interferometer unit having (RW) first measurement second measurement reflector and reflector (1, 2, 3, 4) and (RM) I comprises a. (Bm) passes through both the second interferometer unit and the first measuring beam is reflected by both the second measurement reflector and the first reference beam and the measurement beam (br) is the interferometer unit of at least two further Because through the same path in between, it is possible to make accurate measurements very fast. The interferometer system, very effective when used in a step-and-scan lithographic projection apparatus.