Patent ID: 7852459

Claim:
An inspection apparatus configured to determine a value related to a parameter of a target pattern printed on a substrate by a lithographic process used to manufacture a device layer on a substrate, the apparatus comprising: a radiation source configured to produce a first and a second beam, further arranged to selectively emit the first beam of radiation having a first wavelength in a first wavelength range or the second beam of radiation having a second wavelength in a second wavelength range, the second wavelength range being distinct from the first wavelength range, wherein the radiation source comprises a first radiation sub-source configured to generate radiation of the first wavelength and a second radiation sub-source configured to generate radiation of the second wavelength; an optical system arranged to direct the selected one of the first or second beams of radiation on to the target pattern and a first adjustable optical element arranged to selectively project radiation redirected by the target pattern onto a detector in synchronism with the selected wavelength of the first or second beam of radiation to obtain a scatterometric spectra; and a second adjustable optical element arranged to selectively effect a chromatic correction of the optical system in synchronism with when the selected wavelength of the first or second beam of radiation is emitted by the radiation source.