Patent ID: 11892769
Assignee: CARL ZEISS SMT GMBH
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 13:
14. An apparatus configured to detect a structure of a lithography mask, the apparatus comprising:
an at least partly coherent light source for providing illumination light, a spatially resolving detector, arranged in a detection plane, for detecting a diffraction intensity when recording a diffraction image, and
a mask holder which is displaceable for changing between portions to be illuminated of a lithography mask;
wherein the apparatus is configured to:
illuminate at least one portion of the lithography mask with the illumination light from at least one preferred illumination direction;
record at least one diffraction image of the illuminated portion by spatially resolved detection of the diffraction intensity of the illumination light, diffracted by the illuminated portion, in the detection plane; and
reconstruct at least one portion of the lithography mask from the at least one recorded diffraction image by way of an iterative method in which, starting from an iteration start value, an iteration diffraction image of a raw structure of the lithography mask is calculated and the calculated diffraction image of the raw structure of the lithography mask is compared to the recorded diffraction image of the at least one portion of the lithography mask in each iteration step;
wherein the iteration start value is taken by starting from a raw structure of the lithography mask to be detected, which is obtained by an iteration start value ascertainment method that is independent of the remaining steps of reconstructing the at least one portion of the lithography mask;
wherein the iteration start value is obtained by a simulation of the object; and
wherein the iteration start value is selected to accelerate a convergence of the iterative reconstruction.