Metrology method and associated metrology device

Disclosed is a method of determining at least one parameter of interest relating to a structure formed in at least one respective layer on a substrate, the method comprising: obtaining a measured metrology data relating to a measurement of the structure; obtaining a model, the model describing the structure in terms of a plurality of model parameters, the model parameters comprising estimated values; and performing in sequence a plurality of optimization steps, based on the measured metrology data, to determine the plurality of model parameters, each of the plurality of optimization steps determining a subset of the plurality of model parameters.