# US 2022/0044907 A1 · Method of automatically focusing a charged particle beam on a surface region of a sample, method of calculating a converging set of sharpness values of images of a charged particle beam device and charged particle beam device for imaging a sample > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2022/0044907 A1 - Document ID: US20220044907A1 - Status: Published application - Kind: A1 - Application number: 17/507,342 - Filed: 2021-10-21 - Published: 2022-02-10 - Earliest claimed: 2020-09-03 - Assignees: Applied Materials, Inc. - Applicants: Applied Materials, Inc. - Inventors: Robert TRAUNER; Bernhard SCHÜLER; Bernhard G. MUELLER; Nikolai KNAUB; Kulpreet Singh VIRDI - Web page: https://patentgrep.com/patent/US20220044907A1 ## CPC - H01J 37/222: {Image processing arrangements associated with the tube} - G06T 7/0004: {Industrial image inspection} - H01J 37/21: Means for adjusting the focus - H10P 72/0616: {Monitoring of warpages, curvatures, damages, defects or the like} - G06T 2207/30148: Semiconductor; IC; Wafer - G06T 2207/30168: Image quality inspection - H01J 2237/216: Automatic focusing methods - H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H) - G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL - H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10 ## Abstract A method of automatically focusing a charged particle beam on a surface region of a sample is provided. The method includes acquiring a plurality of images for a corresponding plurality of focusing strength values; calculating a plurality of sharpness values based on the plurality of images, the plurality of sharpness values are calculated with a sharpness function provided as a sum in a frequency space based on the plurality of images; and determining subsequent focusing strength values of the plurality of focusing strength values with a golden ratio search algorithm based one the calculated sharpness values. ## Claims ### Claim 1 A method of focusing a charged particle beam on a surface region of a sample, comprising: calculating a first sharpness value of a first image, wherein the first sharpness value is calculated with a sharpness function including a sum in a frequency space; determining a second focusing strength value based on the calculated first sharpness value and based on a golden ratio or Fibonacci numbers; and acquiring a second image for the second focusing strength value. ### Claim 2 (depends on 1) The method of claim 1, wherein: the first image is an image of a plurality of images and is for a first focusing strength value; the first focusing strength value and the second focusing strength value are focusing strength values of a plurality of focusing strength values; and the first sharpness value is a sharpness value of a plurality of sharpness values, and wherein a subsequent focusing strength value of the plurality of focusing strength values is based on four previous sharpness values of the plurality of sharpness values. ### Claim 3 (depends on 1) The method of claim 1, wherein the sharpness function calculates the sharpness value based on a Fourier transform of an image. ### Claim 4 (depends on 3) The method of claim 3, wherein the sharpness function calculates the sharpness value based on a discrete Fourier transform of the image. ### Claim 5 (depends on 3) The method of claim 3, wherein the Fourier transform is filtered with a filter in the frequency space. ### Claim 6 (depends on 5) The method of claim 5, wherein the filter is a bandpass filter. ### Claim 7 (depends on 3) The method of claim 3, wherein the sharpness function is based on a limited range Discrete Fourier transform. ### Claim 8 (depends on 1) The method of claim 1, wherein a number of iterations of the golden ratio or the Fibonacci numbers is predetermined by a starting range of focusing strength values and a focusing strength accuracy. ### Claim 9 (depends on 2) The method of claim 2, wherein the plurality of focusing strength values are provided by one or more parameters of a charged particle beam device. ### Claim 10 (depends on 1) The method of claim 1, further comprising: controlling a start of scan deflectors at a predetermined starting time after determining the second focusing strength value and before acquiring the second image for the second focusing strength value. ### Claim 11 (depends on 10) The method of claim 10, wherein the predetermined starting time is varied for acquiring at least a further image. ### Claim 12 A method of calculating a converging set of sharpness values of images of a charged particle beam device, comprising: providing a first focusing strength range and a focusing strength accuracy as input parameters to a convergence algorithm; calculating a first focusing strength value based on a golden ratio or Fibonacci numbers and depending on the first focusing strength range; calculating a second focusing strength value based on a golden ratio or Fibonacci numbers; imaging a sample with the first focusing strength value and the second focusing strength value to obtain images; calculating sharpness values from the images with a sharpness function, wherein the sharpness function is based on at least one of a Fourier transform of an image or a sum in a frequency space; determining a second focusing strength range narrower than the first focusing strength range based on the sharpness values; and iteratively replacing the first focusing strength range with the second focusing strength range and imaging the sample to obtain further images and calculating further sharpness values from the further images. ### Claim 13 (depends on 12) The method of claim 12, wherein: the first focusing strength range is provided by a first lower focusing strength value and a first upper focusing strength value; and wherein iteratively replacing the first focusing strength range with the second focusing strength range includes replacing one of the first lower focusing strength value or the first upper focusing strength value with a neighboring focusing strength value selected from the first focusing strength value or the second focusing strength value. ### Claim 14 (depends on 13) The method of claim 13, providing the first lower focusing strength value or the first upper focusing strength value based on the sharpness values as an output after a predetermined number of iterations. ### Claim 15 (depends on 12) The method of claim 12, wherein the second focusing strength value is calculated depending on the first focusing strength range and the first focusing strength value. ### Claim 16 A charged particle beam device for imaging a sample, comprising: a charged particle source configured to emit a charged particle beam; an objective lens configured to focus the charged particle beam propagating along an optical axis on the sample with a focusing strength value; and a controller configured to adjust the focusing strength value according to a method of focusing the charged particle beam on a surface region of the sample, comprising: calculating a first sharpness value of a first image, wherein the first sharpness value is calculated with a sharpness function including a sum in a frequency space; determining a second focusing strength value based on the calculated first sharpness value and based on a golden ratio or Fibonacci numbers; and acquiring a second image for the second focusing strength value. ### Claim 17 (depends on 16) The charged particle beam device of claim 16, wherein the sample is provided on a large area substrate. ### Claim 18 (depends on 16) The charged particle beam device of claim 16, wherein the sample is a wafer for semiconductor manufacturing. ### Claim 19 (depends on 17) The charged particle beam device of claim 17, wherein the sample is provided on the large area substrate for electron beam review of a surface portion of the sample during display manufacturing. ### Claim 20 (depends on 18) The charged particle beam device of claim 18, wherein the charged particle beam device is an EBI tool having two or more charged particle beams. ### Claim 21 (depends on 16) The charged particle beam device of claim 16, wherein the charged particle beam device is configured to cover a focal range up to a few hundred μm. ### Claim 22 A charged particle beam device for imaging a sample, comprising: a charged particle source configured to emit a charged particle beam; an objective lens configured to focus the charged particle beam propagating along an optical axis on the sample with a focusing strength value; and a controller configured to adjust the focusing strength value according to a method of calculating a converging set of sharpness values of images of a charged particle beam device, comprising: providing a first focusing strength range and a focusing strength accuracy as input parameters to a convergence algorithm; calculating a first focusing strength value based on a golden ratio or Fibonacci numbers and depending on the first focusing strength range; calculating a second focusing strength value based on a golden ratio or Fibonacci numbers; imaging a sample with the first focusing strength value and the second focusing strength value to obtain images; calculating sharpness values from the images with a sharpness function, wherein the sharpness function includes a Fourier transform of an image and/or wherein the sharpness function is provided as a sum in a frequency space; determining a second focusing strength range narrower than the first focusing strength range based on the sharpness values; and iteratively replacing the first focusing strength range with the second focusing strength range and imaging the sample to obtain further images and calculating further sharpness values from the further images.