Measuring microscope for measuring masks for lithographic methods and measuring method and calibration method therefor

A method for measuring structured elements for lithographic methods, said method utilizing a measuring microscope by use of which images of the structured elements can be created, wherein the structured elements to be measured are arranged in an object plane of the measuring microscope,

• wherein one or more coordinates of the structured elements to be measured are captured in the direction of an optical axis of the measuring microscope, wherein an interferometric measurement is carried out for the purpose of capturing the coordinates in the direction of the optical axis by an interferometer having a z mirror being perpendicular to the optical axis,
• wherein the captured coordinates in the direction of the optical axis serve as a reference value and coordinates ascertained after the reference value in time and in the direction of the optical axis of the elements to be measured are corrected by use of a change in a refractive index influencing the imaging of the measuring microscope, said change having taken place during the corresponding time interval,
• wherein the method for measuring structured elements is utilized in a self-calibration algorithm in which a calibration mask is imaged and measured in various positions in the measuring microscope, wherein the surface profile of the calibration mask measured in a measuring appliance which differs from the measuring microscope is ascertained and taken into account during the calibration, and/or
• wherein use is made of an error correction ascertained in a method for calibrating the measuring microscope in which a calibration mask is utilized in a self-calibration algorithm in order to ascertain the error correction data of the measuring microscope, wherein, in the self-calibration algorithm, the calibration mask is imaged and measured in various positions in the measuring microscope, wherein the surface profile of the calibration mask measured in a measuring appliance which differs from the measuring microscope is ascertained and taken into account during the calibration.