Encoder head designs
Encoder systems provide measurement and reference optical paths based on propagation in a common set of optical elements along paths that are displaced angularly or spatially. Associated measurement and reference beams are reflected by corner cubes to as to define first paths and second paths. The measurement and reference beams are combined to determine a work piece displacement in a manufacturing process.
1. An encoder apparatus, which measures a relative movement with respect to a grating, the apparatus comprising:
a light source situated to emit a measurement beam and first and second reference beams;
an optical system including a beam splitter situated to reflect or transmit the measurement beam from the light source and situated to transmit or reflect the first and second reference beams, to direct the measurement beam from the beam splitter to a diffraction grating, to direct first and second diffracted beams which are caused by diffraction of the measurement beam irradiated on the diffraction grating, received from the diffraction grating, from first and second positions on the beam splitter and along first and second propagation directions respectively, and to direct the first reference beam from the first position along the first propagation direction and the second reference beam from the second position along the second propagation direction; and
a detector situated to detect an interference of the first diffracted beam and the first reference beam, and an interference of the second diffracted beam and the second reference beam.
2. The encoder apparatus of claim 1 , wherein the optical system further comprises a retro-reflector situated to direct the first and second reference beams from the beam splitter to the beam splitter.
3. The encoder apparatus of claim 1 , wherein the optical system is situated to direct the first diffracted beam to the diffraction grating so as to diffract and to be received at the first position, and to direct the second diffracted beam to the diffraction grating so as to diffract and to be received at the second position.
4. The encoder apparatus of claim 1 , further comprising a beam divider situated to divide a beam from the light source so as to generate the measurement beam and the first and second reference beams based on the divided beam.
5. The encoder apparatus of claim 1 , wherein the measurement beam and the first and second reference beams propagating from the light source to the optical system are displaced from each other.
6. The encoder apparatus of claim 5 , wherein the measurement beam and the first and second reference beams propagating from light source to the optical system are displaced by at least 0.5, 1.0, 1.5, or 2.0 times a beam diameter.
7. The encoder apparatus of claim 1 , wherein the measurement beam and the first and second reference beams propagating from light source to the optical system are non-parallel to each other.
8. The encoder apparatus of claim 7 , wherein the measurement beam and the first and second reference beams propagating from light source to the optical system are displaced by at least 0.2, 0.4, 0.6, 0.8, or 1.0 degrees.
9. An exposure apparatus which expose a pattern on a workpiece, comprising:
a frame;
a stage which holds the workpiece and which is movable along at least a first direction with respect to the frame; and
the encoder apparatus of claim 1 situated to measure a relative movement of the frame and the stage along at least the first direction.
10. A device manufacturing method including a lithographic process, comprising exposing a workpiece by using the exposure apparatus of claim 9 in the lithographic process.
11. The encoder apparatus of claim 1 , wherein the light source is situated to emit the first reference beam to propagate along a first axis and the second reference to propagate along a second axis different from the first axis.