Sub-nanometer overlay, critical dimension, and lithography tool projection optic metrology systems based on measurement of exposure induced changes in photoresist on wafers
A method of processing a substrate on which a layer of photoresist has been applied, the method involving: exposing the layer of photoresist to radiation that carries spatial information to generate exposure-induced changes in the layer of photoresist that form a pattern having one or more features; and before developing the exposed photoresist, interferometrically obtaining measurements of the pattern in the exposed layer of photoresist for determining at least one of (1) locations of the one or more features of the pattern and (2) magnitudes of the exposure-induced changes.
1. A method of processing a substrate on which a layer of photoresist has been applied, said method comprising:
exposing the layer of photoresist to radiation that carries spatial information to generate exposure-induced changes in the layer of photoresist that form a pattern having one or more features;
before developing the exposed photoresist, interferometrically obtaining measurements of the pattern in the exposed layer of photoresist; and
using the interferometrically obtained measurements to determine at least one of (1) locations of the one or more features of the pattern and (2) magnitudes of the exposure-induced changes.
2. The method of claim 1 , wherein interferometrically obtaining measurements involves:
for each spot of an array of spots on the layer of photoresist,
directing a measurement beam at that spot to produce a return measurement beam;
interfering the return measurement beam with a reference beam to generate an interference beam; and
detecting the interference beam to generate an electrical interference signal value.
3. The method of claim 1 , wherein the pattern is produced by exposure-induced changes in a reflectivity of the photoresist.
4. The method of claim 1 , wherein the pattern is produced by exposure-induced changes in an index of refraction of the photoresist.
5. The method of claim 1 , wherein the pattern is produced by exposure-induced changes in a thickness of the photoresist.
6. The method of claim 1 , wherein the pattern is produced by exposure-induced changes in a density of the photoresist.
7. The method of claim 1 , wherein interferometrically obtaining measurements of the pattern in the layer of photoresist is performed concurrently with exposing the layer of photoresist to patterned radiation.
8. The method of claim 1 , further comprising interferometrically obtaining other measurements of the pattern in the layer of photoresist for identifying defects on or in the layer of photoresist.
9. The method of claim 8 , wherein using the interferometrically obtained measurements comprises using both the first-mentioned measurements and said other measurements to determine locations of the one or more features of the pattern.
10. The method of claim 9 , wherein interferometrically obtaining the second said other measurements involves using a differential interferometric microscopy system.
11. The method of claim 10 , wherein interferometrically obtaining the first-mentioned measurements involves using a linear displacement interferometric metrology system.
12. The method of claim 1 , wherein using the interferometrically obtained measurements involves determining locations of the one or more features of the pattern relative to corresponding features of a second pattern in a layer under the layer of photoresist.
13. The method of claim 1 , further comprising treating the layer of exposed photoresist prior to interferometrically obtaining measurements.
14. The method of claim 13 , wherein treating involves a post exposure bake.
15. The method of claim 13 , wherein treating involves silylating.
16. The method of claim 1 , wherein interferometrically obtaining measurements of the pattern in the exposed layer of photoresist is done in situ with exposing.
17. The method of claim 1 , wherein interferometrically obtaining measurements of the pattern involves interferometrically measuring properties of conjugated quadratures of optical fields generated by reflection/scattering or transmission/scattering of measurement beams by the pattern in exposed layer of photoresist.
18. The method of claim 17 , wherein using the interferometrically obtained measurements involves analyzing relative phases of the measured conjugated quadratures to obtain relative locations of the one or more features.
19. The method of claim 17 , wherein the properties of the conjugated quadratures of optical fields are far-field properties of those optical fields.
20. The method of claim 17 , wherein the properties of the conjugated quadratures of optical fields are near-field properties of those optical fields.
21. The method of claim 17 , wherein the properties of the conjugated quadratures of optical fields are evanescent-field properties of those optical fields.
22. The method of claim 1 , wherein interferometrically measuring properties of conjugated quadratures of optical fields involves interferometrically measuring properties of amplitudes or phases of the conjugated quadratures of the optical fields.
23. The method of claim 1 , wherein interferometrically obtaining measurements of the pattern in the exposed layer of photoresist for determining locations of the one or more features of the pattern involves using an interferometric confocal microscopy system.
24. The method of claim 1 , wherein interferometrically obtaining measurements of the pattern in the exposed layer of photoresist for determining locations of the one or more features of the pattern involves using an interferometric non-confocal imaging system.
25. The method of claim 1 , wherein interferometrically obtaining measurements of the pattern in the exposed layer of photoresist for determining locations of the one or more features of the pattern involves scanning with an interferometric metrology system.
26. The method of claim 1 , wherein the interferometric metrology system is a displacement interferometric metrology system.
27. The method of claim 1 , wherein interferometrically obtaining measurements of the pattern involves interferometrically measuring properties of conjugated quadratures of optical fields generated by backscattering of measurement beams by the pattern in exposed layer of photoresist.
28. The method of claim 1 , wherein the locations are two-dimensional locations.
29. The method of claim 1 , wherein the locations are three-dimensional locations.
30. The method of claim 1 , wherein the spatial information is a projected two-dimensional patterned mask.
31. The method of claim 8 , wherein interferometrically obtaining other measurements of the pattern in the layer of photoresist for identifying defects on or in the layer of photoresist is performed prior to interferometrically obtaining the first-mentioned measurements.
32. The method of claim 1 , wherein using the interferometrically obtained measurements involves determining locations of the one or more features of the pattern relative to corresponding features of a second pattern formed in the layer of photoresist.
33. A method of processing a substrate on which a layer of photoresist has been applied, said method comprising:
exposing the layer of photoresist to patterned radiation to generate exposure-induced changes in the layer of photoresist which form patterns having one or more features;
before developing the exposed photoresist, interferometrically obtaining measurements of the pattern in the exposed layer of photoresist; and
using the interferometrically obtained measurements to determine locations of the one or more features of the pattern.