Correction of imaging errors in alignment system with several measurement planes located in succession in the beam path
A method for correction of the measured values of optical alignment systems with at least two measurement planes which are located in succession in the beam path. From each measurement plane, the beam path to the light source is transformed back in order to compute new incidence points using a beam which has been corrected by taking into consideration imaging errors.
1. Method for the alignment of objects with respect to each other, comprising the steps of:
directing a light beam of low divergence from a light source arranged on a first object, through an optical system of an alignment device with at least two detectors which are arranged on a second object, the detectors being located in succession in the beam path for determining the incidence points of the light beam on measurement planes of the detectors,
mathematically transforming the point of incidence of the beam on each measurement plane according to optical rules backwards through the optical system to the light source,
with the transformation, determining a measurement beam with corrected incidence points on the individual measurement planes, and
using the corrected incident points for determination of the existence of any misalignment of the objects with respect to each other; and
correcting the alignment of the objects based on any misalignment of the objects determined to exist.
2. Method in accordance with claim 1 , further comprising, in the case of unequal optical conditions, computing a common light beam which reaches the incidence points based on imaging errors from the incidence points which result from a first light beam and at least one other light beam.
3. Method in accordance with claim 1 , wherein at least one systematic imaging error backwards through the optical system to the light source is used in said mathematical transforming step.
4. Method in accordance with claim 3 , wherein the systematic imaging error is aperture aberration.
5. Method in accordance with claim 3 , wherein the systematic imaging error is spherical aberration.
6. Method in accordance with claim 3 , wherein the systematic imaging error is coma.
7. Method in accordance with claim 3 , wherein the systematic imaging error is astigmatism.
8. Method in accordance with claim 1 , wherein linearization of the detectors which form the measurement planes is performed based on at least one systematic imaging error.
9. Method in accordance with claim 1 , wherein linearization of the detectors which form the measurement planes is carried out using beams near the center of the detectors.