Method and apparatus for determining an overlay error

摘要

A method of determining an overlay error. Measuring an overlay target having process-induced asymmetry. Constructing a model of the target. Modifying the model, e.g., by moving one of the structures to compensate for the asymmetry. Calculating an asymmetry-induced overlay error using the modified model. Determining an overlay error in a production target by subtracting the asymmetry-induced overlay error from a measured overlay error. In one example, the model is modified by varying asymmetry p(n′), p(n″) and the calculating an asymmetry-induced overlay error is repeated for a plurality of scatterometer measurement recipes and the step of determining an overlay error in a production target uses the calculated asymmetry-induced overlay errors to select an optimum scatterometer measurement recipe used to measure the production target.

主权项

1. A method comprising:
measuring scattering properties of a first target comprising a first structure having an asymmetric distortion; constructing a model of the first structure using the measured scattering properties, the model being a parameterized model that reconstructs the shape of first structure and the asymmetric distortion; modifying the model based on the asymmetric distortion of the reconstructed first structure; calculating an asymmetry-induced overlay error between the reconstructed first structure and a second model structure, the reconstructed first structure and the second model structure being overlaid with respect to each other in the modified model; and determining an overlay error in a second target using the calculated asymmetry-induced overlay error.