Verification metrology targets and their design
Metrology target design methods and verification targets are provided. Methods comprise using OCD data related to designed metrology target(s) as an estimation of a discrepancy between a target model and a corresponding actual target on a wafer, and adjusting a metrology target design model to compensate for the estimated discrepancy. The dedicated verification targets may comprise overlay target features and be size optimized to be measureable by an OCD sensor, to enable compensation for inaccuracies resulting from production process variation. Methods also comprise modifications to workflows between manufacturers and metrology vendors which provide enable higher fidelity metrology target design models and ultimately higher accuracy of metrology measurements.
1. A metrology target design method comprising:
using optical critical dimension data related to at least one designed overlay metrology target as an estimation of a discrepancy between a target model and a corresponding actual target on a wafer, wherein the optical critical dimension data is at least partially derived from a measurement, with a critical dimension metrology sensor, of at least one verification target comprising one or more overlay target features, wherein the one or more overlay target features of the at least one verification target comprise at least one of: a pitch, a segmentation and a topography which is identical to a corresponding feature of at least one overlay metrology target as the at least one designed overlay metrology target; and
adjusting a metrology target design model to compensate for the discrepancy, wherein the adjusting is carried out with respect to at least one of a critical dimension, an optical material characteristic, a film thickness, topography or presence of process variation, wherein the process variation relates to at least one of an induced topography, a deposited topography, an etched topography, or chemical mechanical planarization dishing.
2. A verification metrology target comprising:
a single cell with at least one layer having overlay target features, wherein the single cell has a cell side dimension of at least 10 μm, wherein optical critical dimension data is derivable from a measurement, with a critical dimension metrology sensor, of the overlay target features of the single cell, wherein one or more overlay target features comprise at least one of: a pitch, a segmentation and a topography which is identical to a corresponding feature of at least one overlay metrology target as the at least one designed overlay metrology target.
3. The verification metrology target of claim 2 , wherein the single cell comprises:
a single periodic structure that is identical in a pitch and a CD to a previous layer periodic structure of a corresponding metrology target.
4. The verification metrology target of claim 2 , wherein the single cell comprises:
at least two periodic structures that are identical in a pitch and a CD to periodic structures in one of the cells of a corresponding metrology target.
5. The verification metrology target of claim 2 , wherein the verification metrology target is designed and produced next to the corresponding metrology target.
6. A metrology target design method comprising:
using film data related to at least one designed overlay metrology target as an estimation of a discrepancy between a target model and a corresponding actual target on a wafer, wherein the film data is at least partially derived from a measurement, with a critical dimension metrology sensor, of at least one verification target comprising a film stack which is identical to a corresponding feature of the target model; and
adjusting a metrology target design model to compensate for the discrepancy.
7. The method of claim 6 , wherein the adjusting is carried out with respect to at least one of: a critical dimension, an optical material characteristic, a film thickness, a topography, or a presence of process variation.
8. The method of claim 7 , wherein the process variation relates to at least one of: an induced topography, a deposited topography, an etched topography, or chemical mechanical planarization dishing.
9. The method of claim 8 , wherein the process variation comprises symmetric and/or asymmetric process variation.
10. The method of claim 6 , wherein the film data relates to a previous layer of the at least one designed overlay metrology target.
11. The method of claim 6 , wherein the film data comprises at least one of workbook data or simulation results.
12. The method of claim 6 , wherein the at least one verification target comprises overlay target features, wherein the method further comprises: measuring the at least one verification target with an OCD sensor to derive the film data.
13. The method of claim 12 , further comprising:
optimizing at least one of: a location, a size or a proximity to surrounding structures of the at least one verification target.
14. The method of claim 13 , wherein the measuring is carried out by optical or SEM CD metrology.
15. The method of claim 13 , wherein the overlay target features of the at least one verification target comprise at least one of: a pitch, a segmentation and a topography which is identical to a corresponding feature of at least one overlay metrology target as the at least one designed overlay metrology target.
16. The method of claim 6 , further comprising:
improving a match between measurement and simulation of the at least one overlay target by using a measurement of the at least one verification target.
17. The method of claim 16 , further comprising:
improving a design of subsequently printed metrology targets using the match.
18. The method of claim 6 , further comprising:
optimizing a metrology recipe setup of overlay measurements of the at least one overlay metrology target, by using a measurement of the at least one verification target.
19. The method of claim 18 , wherein the optimization is carried out with respect to at least one of: a metrology accuracy, a metrology precision, a metrology robustness, or a combination thereof.