Method for detecting an object structure and apparatus for carrying out the method

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.

A method for detecting an object structure, the method comprising:

• illuminating at least one portion of an object with illumination light of an at least partly coherent light source from at least one preferred illumination direction;
• recording 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 a detection plane;
• and
• reconstructing at least one portion of the object structure 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 object structure is calculated and the latter is compared to the recorded diffraction image in each iteration step;
• wherein the iteration start value is obtained with aid of a start measurement of a raw object structure of the object structure to be detected, in which the start measurement is independent of the remaining detection method, and a measurement result of the start measurement is processed to match imaging parameters of the start measurement to imaging parameters of the diffractive imaging recording;
• wherein the start measurement is performed without recording a diffraction image;
• and
• wherein the start measurement is generated with at least one of (i) an optical method that is independent of the remaining detection method, (ii) aid of electron microscopy, or (iii) aid of atomic force microscopy.