1. A method of determining the profile of a single feature formed on a wafer, the method comprising: focusing a beam of light onto the single feature; detecting beams of light diffracted from the single feature; obtaining an optical signature from the diffracted beams of light; and selecting a simulated optical signature based on a comparison of the obtained optical signature to a set of simulated optical signatures, wherein each simulated optical signature corresponds to a hypothetical profile of the single feature, and wherein each simulated optical signature is modeled based on the hypothetical profile.