US 12,283,457 B2
Multiple particle beam microscope and associated method with an improved focus setting taking into account an image plane tilt
Nicole Rauwolf, Birkhausen (DE); Nico Kaemmer, Koenigsbronn (DE); Michael Behnke, Eislingen (DE); Ingo Mueller, Aalen (DE); Dirk Zeidler, Oberkochen (DE); Arne Thoma, Heidenheim (DE); Christof Riedesel, Aalen (DE); and Gunther Scheunert, Muenster (DE)
Assigned to Carl Zeiss MultiSEM GmbH, Oberkochen (DE)
Filed by Carl Zeiss MultiSEM GmbH, Oberkochen (DE)
Filed on Jan. 24, 2022, as Appl. No. 17/582,504.
Claims priority of application No. 102021200799.6 (DE), filed on Jan. 29, 2021.
Prior Publication US 2022/0246388 A1, Aug. 4, 2022
Int. Cl. H01J 37/21 (2006.01); G01N 21/95 (2006.01); H01J 37/26 (2006.01)
CPC H01J 37/21 (2013.01) [G01N 21/9501 (2013.01); H01J 37/26 (2013.01)] 16 Claims
OG exemplary drawing
 
1. A method of operating a multi-beam particle microscope comprising a multi-beam device configured to generate primary beams, comprising:
A) positioning a surface of an object in a first setting plane with a first z-position z1;
B) determining parameters for a focusing series with z-positions zi with i=1 to P;
C) generating J primary beams with the multi-beam generation device of the multi-beam particle microscope, projecting the J primary beams onto a specimen, detecting the secondary electrons emitted by the specimen to form an image, selecting L primary beams, selecting a contrast measure, extracting the sections of the image resulting from the L primary beams, and calculating contrast measures K1(i) to KL(i) for the L selected primary beams, L being less than or equal to J;
D) displacing the first setting plane into a second or further setting plane at a second or further z-position z2 to zP;
E) repeating C) and D) until contrast measures K1(i) to KL(i) with i=1 to P are measured for each of the z-positions z1 to zP;
F) determining a focal position for each of the L selected primary beams by finding the z-position at which the contrast measure K1(i) is maximized; and
G) determining a curved image surface and an image plane tilt from the L focal positions; and
H) determining an actuation signal for a compensator for an image plane tilt, and providing the actuation signal to the compensator for the image plane tilt,
wherein C) comprises measuring L contrast measures K1(i) to KL(i) for the L selected primary beams comprises a method selected from the group consisting of:
i) using a one-dimensional Fourier transform perpendicular to an edge of an image field;
ii) using a normalized maximum of ratios of two pixels spaced from each other in an image section;
iii) using a histogram from a grayscale value distribution of selected image sections;
iv) comparing differences of each pair of pixel values in an image section to a threshold;
v) using a normalized sum of all scalar gradients which are based on differences of adjacent pixels in an image section;
vi) using a normalized maximum value of local gradients which are based on differences of adjacent pixels in an image section; and
vii) selecting a first derivative of digital image data from an image section, convolving the digital image data with a point spread function, calculating a second derivative of the convolved digital image data, and determining a ration of the first and second derivatives.