Inspection method and apparatus and lithographic processing cell

Abstract

A method of calculating process corrections for a lithographic tool, and associated apparatuses. The method comprises measuring process defect data on a substrate that has been previously exposed using the lithographic tool; fitting a process signature model to the measured process defect data, so as to obtain a model of the process signature for the lithographic tool; and using the process signature model to calculate the process corrections for the lithographic tool.

The invention claimed is: 
     
       1. A method of calculating a process correction for a lithographic tool comprising:
 measuring process data on a substrate that has been previously exposed using the lithographic tool;   fitting, by a processing unit, a process signature model to the measured process data, so as to obtain a fitted process signature model for the lithographic tool; and   calculating, by the processing unit directly after the fitting, the process correction for the lithographic tool for any location on the substrate based on the fitted process signature model using all possible relevant degrees of freedom of the lithographic tool.   
     
     
       2. The method of  claim 1  wherein the process data comprises data describing a deviation from ideal of a position of a layer relative to a preceding layer. 
     
     
       3. The method of  claim 2  wherein the process signature model is a Zernike function comprising radial and tangential overlay components. 
     
     
       4. The method of  claim 1  further comprising applying the calculated process correction for each exposed field in a subsequent exposure using the lithographic tool. 
     
     
       5. The method of  claim 4 , further comprising:
 repeating the measuring, fitting, calculating, and applying prior to exposure of each substrate lot to obtain an updated process correction.   
     
     
       6. The method of  claim 1  wherein the process signature model comprises over ten parameters. 
     
     
       7. The method of  claim 1  wherein the calculating further comprises interpolating and extrapolating the fitted process signature model to determine the process correction. 
     
     
       8. The method of  claim 1  wherein the measuring comprises performing fewer than 500 measurements on the substrate. 
     
     
       9. The method of  claim 8  wherein the measuring comprises performing fewer than 200 measurements on the substrate. 
     
     
       10. An inspection apparatus comprising:
 a projection system configured to project a radiation beam onto a substrate that has been previously exposed using a lithographic tool;   a detector configured to detect scattered radiation having interacted with the substrate; and   a processor configured to:   measure process data from the detected scattered radiation;   fit a process signature model to the measured process data, so as to obtain a fitted process signature model for the lithographic tool; and   calculate, directly after fitting the process signature model, a process correction for the lithographic tool for any location on the substrate based on the fitted process signature model using all possible relevant degrees of freedom of the lithographic too.   
     
     
       11. The inspection apparatus of  claim 10  wherein the process data comprises data describing a deviation from ideal of a position of a layer relative to a preceding layer. 
     
     
       12. The inspection apparatus of  claim 11  wherein the process signature model is a Zernike function comprising radial and tangential overlay components. 
     
     
       13. The inspection apparatus of  claim 10  wherein the process signature model comprises over ten parameters. 
     
     
       14. The inspection apparatus of  claim 10  wherein the processor uses all possible relevant degrees of freedom of the inspection apparatus to calculate the process correction. 
     
     
       15. The inspection apparatus of  claim 10  wherein the processor calculates the process correction using interpolation and extrapolation of the fitted process signature model. 
     
     
       16. The inspection apparatus of  claim 10 , wherein the processor is further configured to calculate the process correction directly after obtaining the fitted process signature model. 
     
     
       17. An apparatus comprising:
 a projection system configured to project a radiation beam onto an exposed substrate;   a detector configured to detect the radiation beam after reflection from the substrate; and   a processor configured to:
 measure process data from the reflected radiation beam; 
 fit a process signature model to the measured process data to obtain a fitted process signature model for a lithographic tool used to expose the substrate; and 
 calculate, directly after fitting the process signature model, a process correction for the lithographic tool for any location on the substrate based on the fitted process signature model using all possible relevant degrees of freedom of the lithographic tool. 
   
     
     
       18. The apparatus of  claim 17 , wherein:
 the radiation beam comprises a plurality of radiation beams,   the detector is configured to detect the plurality of radiation beams after reflection from the substrate as a plurality of measurements,   the process correction comprises a plurality of process corrections per field of the substrate, and   the process signature model comprises a plurality parameters, the plurality of measurements being, less than the plurality of process corrections.   
     
     
       19. A method of calculating a process correction for a lithographic tool, the method comprising:
 receiving measured process data having a first number of measurement points from a substrate, wherein a plurality of fields on the substrate have been previously exposed using the lithographic tool;   fitting, by a processing unit, a fingerprint model including a plurality of parameters to the measured process data, so as to obtain a fitted fingerprint model;   using the fitted fingerprint model to determine the measured process data on a dense grid across the substrate, wherein the dense grid comprises a second number of measurement points being larger than the first number of measurement points; and   calculating, by the processing unit, the process correction comprising correction values for at least six degrees of freedom of the lithographic tool for each field out of the plurality of fields based on the measured process data as determined on the dense grid.   
     
     
       20. The method of claim 19, wherein the measured process data comprises overlay data describing a deviation from ideal of a position of a layer relative to a preceding layer. 
     
     
       21. The method of claim 19, further comprising applying the calculated process correction to an exposed field in a subsequent exposure. 
     
     
       22. The method of claim 21, further comprising:
 repeating the receiving, fitting, calculating, and applying prior to exposure of a substrate lot to obtain an updated process correction.   
     
     
       23. The method of claim 19, wherein the fingerprint model comprises over ten parameters. 
     
     
       24. The method of claim 19, wherein the calculating further comprises interpolating and extrapolating the fitted fingerprint model to determine the process correction. 
     
     
       25. The method of claim 19, wherein the measured process data comprises fewer than 500 measurements on the substrate. 
     
     
       26. The method of claim 25, wherein the measured process data comprises fewer than 200 measurements on the substrate. 
     
     
       27. A non-transitory computer-readable medium for calculating a process correction for a lithographic tool comprising instructions for, when executed on a computer, cause:
 receiving measured process data having a first number of measurement points from a substrate, wherein a plurality of fields on the substrate have been previously exposed using the lithographic tool;   fitting, by a processing unit, a fingerprint model including a plurality of parameters to the measured process data, so as to obtain a fitted fingerprint model;   using the fitted fingerprint model to determine the measured process data on a dense grid across the substrate, wherein the dense grid comprises a second number of measurement points being larger than the first number of measurement points; and   calculating, by the processing unit, the process correction comprising correction values for at least six degrees of freedom of the lithographic tool for each field out of the plurality of fields based on the measured process data as determined on the dense grid.