Method for characterizing optical systems using holographic reticles
View Patent ↗Characterization of an optical system is quickly and easily obtained in a single acquisition step by obtaining image data within a volume of image space. A reticle and image plane are positioned obliquely with respect to each other such that a reticle having a plurality of feature sets thereon, including periodic patterns or gratings, is imaged in a volume of space, including the depth of focus. Metrology tools are used to analyze the detected or recorded image in the volume of space through the depth of focus in a single step or exposure to determine the imaging characteristics of an optical system. Focus, field curvature, astigmatism, spherical, coma, and/or focal plane deviations can be determined. The present invention is particularly applicable to semiconductor manufacturing and photolithographic techniques used therein, and is able to quickly characterize an optical system in a single exposure with dramatically increased data quality and continuous coverage of the full parameter space. In embodiments, the test reticle is holographically generated by interfering two or more beams of optical radiation. The resulting interference pattern is recorded on a reticle and used for testing the optical system. The geometry of the holographic interference pattern is tightly controlled by the properties of the interfering beams and is therefore more accurate than conventional reticle writing techniques.
1. A method of using a holographic reticle to characterize an optical system, the method comprising the steps of:
(1) configuring the optical system such that a first plane containing the holographic reticle is positioned obliquely to a second plane where an image is recorded;
(2) placing the holographic reticle in a path of an optical beam within the optical system; and
(3) recording the image produced by the path of the optical beam passing through the holographic reticle;
wherein the image is configured to characterize the optical system for at least one of field curvature, astigmatism, coma, distortion, telecentricity, spherical aberrations, and variation of coherence.
2. The method of claim 1 , wherein the holographic reticle has a plurality of feature sets thereon.
3. The method of claim 2 , wherein the plurality of feature sets includes at least one of a periodic pattern and a grating pattern.
4. The method of claim 1 , wherein the second plane is positioned in a volume of space that includes a depth of focus of the optical system.
5. The method of claim 1 , wherein step (3) comprises:
recording the image produced by the path of the optical beam passing through the holographic reticle in a recording medium.
6. The method of claim 1 , wherein the image includes information indicative of a feature image shift.
7. The method of claim 1 , wherein step (3) comprises:
recording the image produced by the optical beam passing through the holographic reticle in real time using a demodulating device.
8. The method of claim 1 , wherein the image includes information indicative of a Zernike aberration.
9. The method of claim 1 , wherein
the image includes information indicative of higher order aberrations in the optical system.
10. The method of claim 9 , wherein
the image includes information indicative of shift differences due to partial coherence conditions.
11. The method of claim 1 , wherein the holographic reticle includes a pattern of linewidths such that each linewidth is an integral multiple of a fundamental linewidth.
12. The method of claim 11 , wherein
the image includes information indicative of relative image shifts at a single interferometric angle.
13. The method of claim 5 , wherein the recording medium is a photo-sensitive substrate.
14. The method claim 1 , further comprising the step of:
(4) producing an interferogram having one or more tilts and one or more pistons that represent at least one optical parameter of the optical system.
15. The method of claim 14 , wherein the interferogram includes information based on the one or more pistons indicative of an image shift and information based on the one or more tilts indicative of magnification parameters.
16. The method of claim 14 , wherein the interferogram includes information based on the one or more pistons and the one or more tilts indicative of non-uniform distortion parameters.
17. The method of claim 16 , wherein the non-uniform distortion parameters are detected as a function of a variation in linewidth.
18. The method of claim 16 , wherein the non-uniform distortion parameters are detected from a non-linear phase front of a chirped grating structure.