Method and apparatus for image analysis

1. A method comprising:

obtaining a first dataset representing a reference image object, the reference image object representing a lithographic structure at a nominal condition of a parameter;

obtaining a second dataset representing a template image object, the template image object representing the lithographic structure at a non-nominal condition of the parameter; and

generating, by a hardware computer processor system, a deformation field by transforming the second dataset to project the template image object onto the reference image object.

2. The method of claim 1 , further comprising determining a measure of difference between the template image object and the reference image object based on the deformation field.

3. The method of claim 2 , wherein the measure of difference between the template image object and the reference image object comprises a determinant of a deformation matrix representing the deformation field.

4. The method of claim 3 , further comprising classifying the object obtained at the non-nominal condition as unacceptable if the measure of difference between the template image object and the reference image object is greater than a given threshold.

5. The method according to claim 1 , wherein the deformation field is representative of a difference between the first dataset and the second dataset; and

obtaining a dependence relationship between the deformation field and the parameter through variation of the parameter to obtain a plurality of deformation fields corresponding to a plurality of non-nominal conditions, wherein the dependence relationship is evaluating a change in the deformation fields to the plurality of non-nominal conditions of the parameter.

6. The method of claim 5 , further comprising determining an optimal value for the parameter based on the dependence relationship.

7. The method of claim 5 , further comprising predicting, using the dependence relationship, an effect of a variation in the parameter on a further image of the structure, to enable differentiation between a change in the further image because of a defect in the structure and a change in the further image because of variation in the parameter.

8. The method of claim 1 , wherein obtaining the deformation field comprises determining a transformation matrix describing a transformation of the second dataset into the first dataset.

9. The method of claim 1 , wherein the deformation field is quantified as a material strain of the structure.

10. The method of claim 1 , wherein the parameter comprises one or more selected from: focus, exposure dose, numerical aperture, a film stack property, lens aberration, coherence, and/or illumination intensity distribution.

11. A method of manufacturing devices wherein a device pattern is applied to a series of substrates using a lithographic process, the method including evaluating a lithographic structure imaged using the lithographic process using the method of claim 1 and controlling the lithographic process for one or more of the substrates in accordance with the result of the method.

12. The method of claim 11 , wherein the lithographic structure is imaged on at least one of the substrates and controlling the lithographic process for later substrates in accordance with the result of the method.

13. A non-transitory computer program product comprising a computer-readable medium storing machine-readable instructions configured to cause a processor to:

obtain a first dataset representing a reference image object, the reference image object representing a lithographic structure at a nominal condition of a parameter;

obtain a second dataset representing a template image object, the template image object representing the lithographic structure at a non-nominal condition of the parameter; and

generate a deformation field by transforming the second dataset to project the template image object onto the reference image object.

14. A system comprising:

a scanning electron microscope configured to provide an image of a lithographically created structure; and

an image analysis engine comprising the non-transitory computer program product of claim 13 .

15. The system of claim 14 , further comprising a lithographic apparatus comprising a support structure configured to hold a patterning device to modulate a radiation beam and a projection optical system arranged to project the modulated onto a radiation-sensitive substrate.

16. The non-transitory computer program product of claim 13 , wherein the instructions are further configured to cause determination of a measure of difference between the template image object and the reference image object based on the deformation field.

17. The method of claim 1 , wherein the first dataset and/or the second dataset is a binarized function representing the reference image object and/or the template image object respectively.

18. The method of claim 1 , further comprising determining a cost function based on a magnitude of the deformation field, wherein the cost function is representative of a degree of difference between the reference image object and the template image object.

19. The method of claim 1 , wherein the lithographic structure comprises a circuit feature of an integrated circuit.

20. The method of claim 1 , wherein the reference image and the template image are obtained with a low-dose scanning electron microscope.