US 12,333,748 B2
Industrial metrology of workpiece surface based on depth map
Tomas Aidukas, Brugg (CH); Sören Schmidt, Jena (DE); and Daniel Plohmann, Lauingen (DE)
Assigned to Carl Zeiss Industrielle Messtechnik GmbH, Oberkochen (DE); and Carl Zeiss Microscopy GmbH, Jena (DE)
Filed by Carl Zeiss Industrielle Messtechnik GmbH, Oberkochen (DE); and Carl Zeiss Microscopy GmbH, Jena (DE)
Filed on Mar. 30, 2022, as Appl. No. 17/709,323.
Claims priority of application No. 10 2021 108 238.2 (DE), filed on Mar. 31, 2021.
Prior Publication US 2022/0319027 A1, Oct. 6, 2022
Int. Cl. G06T 7/55 (2017.01)
CPC G06T 7/55 (2017.01) [G06T 2207/10028 (2013.01)] 26 Claims
OG exemplary drawing
 
1. A computer-implemented method for generating a depth map of a region of a surface of a workpiece, the computer-implemented method comprising:
receiving a focal image stack, wherein:
the focal image stack includes a plurality of images of the workpiece,
the images image the region of the surface of the workpiece with defined focal plane positions that are different in a depth direction,
a focal plane position is assigned to each of the images, and
image points of the images are respectively assigned to a corresponding object point on the surface of the workpiece;
determining a focus value of each image point of each image of the focal image stack;
fitting a function along the depth direction to the focus values of those image points of the images that are assigned to the same object point;
determining a depth value of each object point on the surface of the workpiece in the depth direction based on an extremum of the fitted function;
generating the depth map of the region of the surface of the workpiece based on the determined depth values;
for each point of the depth map, determining third and fourth correction values; and
generating a depth map of a calibration object before measuring the workpiece,
wherein the respective correction value is determined based on a deviation of the depth map of the calibration object with respect to a known surface profile of the calibration object,
wherein the calibration object is a point grid, and
wherein determining the third and fourth correction values includes:
determining a respective third correction value and a respective fourth correction value for each point of the point grid based on a cost function between an astigmatism model and the depth values of the respective point, and
interpolating the third and fourth correction values based on the respective third and fourth correction values of each point of the point grid.