Patent ID: 11927500
Assignee: CARL ZEISS SMT GMBH
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 17:
18. A method for characterizing a surface shape of an optical element, the method comprising:
a) carrying out a first interferogram measurement, said first interferogram measurement being carried out on the optical element in an interferometric test arrangement by superposing a first reference wave, which has not been reflected at the optical element, on a first test wave, which has been generated by diffraction of electromagnetic radiation at a diffractive element and reflected at the optical element;
b) carrying out at least one second interferogram measurement, said second interferogram measurement being carried out on the optical element by superposing a second reference wave, which has not been reflected at the optical element, on a second test wave, which has been generated by diffraction of electromagnetic radiation at the diffractive element and reflected at the optical element, wherein the first and the second interferogram measurements differ from one another in polarization state of the electromagnetic radiation; and
c) determining parameters characterizing a three-dimensional structure of the diffractive element based on subtracting interferogram phases obtained respectively during the first interferogram measurement and the second interferogram measurement, wherein the parameters comprise at least one of etching depth, slope angle, edge rounding and duty cycle.