CN-121994844-A - Line-based endpoint detection

Abstract

Methods of preparing a sample for charged particle microscopy analysis, such as by providing a sheet, include removing material from the sample surface to provide a newly exposed surface and determining a region of interest (ROI) on the newly exposed surface. A plurality of lines are formed on the newly exposed surface of the sample and material is removed multiple times from the processed surface of the sample (different from the newly exposed surface). The processing surface is imaged a plurality of times to capture at least a plurality of lines and an endpoint is determined based on relative spatial features between two or more lines of the plurality of lines.

Inventors

• D. Prentice
• CHEN HONGSHENG

Assignees

• FEI公司

Dates

Publication Date

20260508

Application Date

20251013

Priority Date

20241101

Claims (20)

1. 1. A method of preparing a sample for charged particle microscopy analysis, comprising: (i) Removing material from the surface of the sample to provide a newly exposed surface; (ii) Determining a region of interest (ROI) on the newly exposed surface of the sample; (iii) Forming a plurality of lines on the newly exposed surface of the sample; (iv) Removing material from a processing surface of the sample a plurality of times, wherein the processing surface of the sample is different from the newly exposed surface; (v) Imaging the sample multiple times to capture at least multiple lines, and (Vi) An endpoint is determined based on the relative spatial characteristics between two or more lines of the plurality of lines.
2. 2. The method of claim 1, wherein removing material from the top surface of the sample comprises removing material parallel to the top surface or at an angle relative to the top surface.
3. 3. The method of claim 1, wherein determining the region of interest comprises applying a map to the newly exposed surface (i.e., CAD map).
4. 4. The method of claim 1, wherein determining the endpoint based on the relative spatial features between two or more lines of the plurality of lines comprises determining when two adjacent lines of the plurality of lines have the same depth in a newly exposed surface of the sample, wherein the depth of the lines is the relative spatial feature.
5. 5. The method of claim 1, wherein determining the endpoint based on the relative spatial characteristics between two or more of the plurality of lines comprises determining when a distance between two of the plurality of lines is equal to a predetermined distance, wherein the distance between the two lines is the relative spatial characteristics.
6. 6. The method of claim 5, wherein the predetermined distance is based on an edge position of a region of interest (ROI), and wherein at least two lines of the plurality of lines are formed on the newly exposed surface to be separated by the predetermined distance at the edge position of the ROI.
7. 7. The method of claim 1, wherein determining the endpoint based on the relative spatial characteristics between two or more of the plurality of lines comprises determining a ratio of distances between at least two of the plurality of lines.
8. 8. The method of claim 1 wherein determining an endpoint based on the relative spatial features between two or more lines of the plurality of lines comprises analyzing the acquired image using a machine learning algorithm that determines an endpoint based on the relative spatial features.
9. 9. The method of claim 1, wherein forming a plurality of lines on the newly exposed surface of the sample comprises forming a series of lines arranged in parallel and laterally offset, wherein at least one end of each line in the series of lines overlaps at least one laterally offset line in the series of lines, and wherein the depth of each line of line overlap is the same.
10. 10. The method of claim 9, wherein forming a series of lines comprises forming each line in the series of lines using the same ion beam parameters.
11. 11. The method of claim 1, wherein forming a plurality of lines on the newly exposed surface of the sample comprises forming a plurality of lines disposed at an angle to each other, wherein a distance between at least two sets of lines is known at least at one location along its extent.
12. 12. The method of claim 1, wherein removing material from the processing surface of the sample a plurality of times, wherein the processing surface of the sample is different from the newly exposed surface, comprises milling the material with a focused ion beam.
13. 13. The method of claim 1, wherein imaging the sample a plurality of times to capture at least the contours of the plurality of lines comprises acquiring an electron beam image of the processing surface.
14. 14. The method of claim 1, wherein imaging the sample multiple times to capture at least contours of multiple lines comprises imaging the sample while removing material or imaging the sample between removing material.
15. 15. The method of claim 1, wherein forming a plurality of lines on the newly exposed surface of the sample comprises forming a plurality of lines on the newly exposed surface of the sample such that the relative spatial features are aligned with edges of the region of interest determined in (ii).
16. 16. The method of claim 15, wherein forming the plurality of lines on the newly exposed surface of the sample such that the relative spatial feature is aligned with the edge of the region of interest determined in (ii) comprises forming at least two lines of the plurality of lines on the newly exposed surface such that adjacent overlapping regions are aligned with the edge of the region of interest determined in (ii).
17. 17. The method of claim 15, wherein forming a plurality of lines on the newly exposed surface of the sample such that the relative spatial feature is aligned with the edge of the region of interest determined in (ii) comprises forming at least two lines of the plurality of lines at different respective angles with respect to a third line on the newly exposed surface and determining a distance between the at least two lines at the edge of the region of interest determined in (ii).
18. 18. The method of claim 1, wherein at least one of steps (i) through (vi) is repeated one or more times.
19. 19. An apparatus, comprising: an ion beam column coupled to provide an ion beam; an electron beam column coupled to provide an electron beam; A sample arranged to receive the ion beam and the electron beam, and A controller coupled to control the ion beam and the electron beam, wherein the controller comprises or is coupled to a non-transitory computer readable medium storing instructions that, when executed by the controller, cause the apparatus to: removing material from the newly exposed surface of the sample with an ion beam; determining an ROI on the newly exposed surface of the sample; Forming a plurality of lines on the newly exposed surface of the sample with an ion beam; removing material from a processing surface of the sample a plurality of times with an ion beam, wherein the processing surface is different from the newly exposed surface; Imaging the sample multiple times with an electron beam to capture at least a plurality of lines, and An endpoint is determined based on the relative spatial characteristics between two or more lines of the plurality of lines.
20. 20. The device of claim 19, wherein controller-executable instructions that are executed to determine an endpoint based on relative spatial features between two or more lines of a plurality of lines comprise controller-executable instructions that, when executed, cause a device to determine when two adjacent lines of a plurality of lines have the same depth in a newly exposed surface of a sample, wherein depth of a line is a relative spatial feature.

Description

Line-based endpoint detection Technical Field The present invention relates generally to endpoint detection. And more particularly to a new application of endpoint detection on back-end-of-line (BEOL) semiconductor chips/test strips. Background Sample preparation using a charged particle microscope (e.g., a dual beam microscope comprising both an ion column and an electron column) typically produces nanoflakes that can be imaged, for example, in a transmission electron microscope. This manufacturing process is elaborate, especially for sheets having a thickness of the order of 10 nm a after formation. Such flakes are formed by milling away material from both sides of the sample using an ion beam to obtain flakes. However, knowing or determining when to stop milling is a critical aspect and difficult to process electron-based images. Line Indicated Termination (LIT) is an automated process for sheet thinning in AutoTEM, as described in US11355313B 2. The LIT marks (alpha marks, lambda marks, etc.) are milled or deposited (i.e., "placed") on the chip surface prior to thinning. These markers are used in AutoTEM to automatically determine the sample endpoint (using a neural network or other process) during the thinning process. However, LIT is generally suitable for end-of-line (FEOL) thinning, in which case the structure is more uniform, more accessible and more imageable, and thus easier to apply the necessary lines. The methods and apparatus described herein enable LIT for back-end-of-line (BEOL) endpoint determination/thinning. This is surprising and unexpected because BEOL structures are high and non-uniform and the region of interest (ROI) is obscured by surrounding material. In general, for BEOL devices, the LIT marks placed on the surface (BEOL layer/large linewidth metal layer/upper metal layer/lower metal layer) may be several to tens of microns vertically from the FEOL ROI. This results in a substantial decrease in the utility of the LIT line to precisely and automatically determine the endpoint. The inverted take-off orientation places the LIT wire at the bottom of the sheet, subject to the curtain effect, both the inverted take-off orientation and the top-down take-off orientation may amplify the accidentally applied minute take-off tilt to an excessive offset at the ROI that affects accuracy. The methods described herein allow for precise localization of the ROI and reduce the curtain effect on the sheet surface caused by surrounding materials. Disclosure of Invention The present application seeks to address at least some of the above mentioned problems by providing a method and a use as defined in the present application. Accordingly, the present application provides a method for preparing a sample (e.g. by providing a sheet) for charged particle microscopy analysis, the method comprising: -removing material from the surface of the sample to provide a newly exposed surface; -determining a region of interest (ROI) on the newly exposed surface of the sample; -forming a plurality of lines on the newly exposed surface of the sample; -removing material from the working surface of the sample a plurality of times, wherein the working surface of the sample is different from the newly exposed surface; imaging a working surface of the sample (i.e. a surface that has been newly exposed by removing material from the working surface) a plurality of times to capture at least a plurality of lines, and -Determining an endpoint based on the relative spatial features between two or more lines of the plurality of lines. The application also provides a device comprising at least an ion beam column coupled to provide an ion beam, an electron beam column coupled to provide an electron beam, a sample arranged to receive the ion beam and the electron beam, and a controller coupled to control the ion beam and the electron beam. The controller includes or is coupled to a non-transitory computer readable medium storing instructions that, when executed by the controller, cause the apparatus to: -removing the surface of the sample with an ion beam to provide a newly exposed surface; -determining a region of interest on the newly exposed surface; -forming a plurality of lines on the newly exposed surface of the sample with an ion beam; -removing material from a processing surface of the sample a plurality of times with an ion beam, the processing surface being different from the top surface; imaging the sample with the electron beam a plurality of times to capture at least a plurality of lines, each of the plurality of occurrences occurring between at least one removal step, and -Determining an endpoint based on the relative spatial features between two or more lines of the plurality of lines. The foregoing and other features and advantages of the disclosed methods will become more apparent from the following detailed description of the invention, which is described in connection with the accompanying drawings. Brief Descript