Metrology methods, metrology apparatus and device manufacturing method

A method comprising:

• irradiating a structure with radiation including radiation in a first waveband and radiation in a second waveband;
• directing at least a portion of the radiation after interaction with the structure to a first spectroscopic grating;
• detecting a spectrum in a first waveband using one or more higher orders of radiation diffracted by the first spectroscopic grating;
• directing at least a portion of zero order radiation after interaction with the structure to a second spectroscopic grating;
• and
• detecting a spectrum in the second waveband using one or more higher orders of radiation diffracted by the second spectroscopic grating.

A device manufacturing method comprising:

• transferring a pattern from a patterning device onto a substrate using a lithographic process, the pattern defining at least one structure;
• measuring one or more properties of the structure to determine a value for one or more parameters of the lithographic process;
• and
• applying a correction in subsequent operations of the lithographic process in accordance with the measured property,
• wherein the measuring comprises measuring a property using the method comprising:
• irradiating a structure with radiation including radiation in a first waveband and radiation in a second waveband;
• directing at least a portion of the radiation after interaction with the structure to a first spectroscopic grating;
• detecting a spectrum in a first waveband using one or more higher orders of radiation diffracted by the first spectroscopic grating;
• and
• directing at least a portion of zero order radiation after interaction with the structure to a second spectroscopic grating;
• and
• detecting a spectrum in the second waveband using one or more higher orders of radiation diffracted by the second spectroscopic grating.