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KR-20260065509-A - LINE-BASED END POINT DETECTION

KR20260065509AKR 20260065509 AKR20260065509 AKR 20260065509AKR-20260065509-A

Abstract

A method for preparing a sample for analysis by a charged particle microscope (e.g., by providing lamellae) comprises removing material from the surface of the sample 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, and material is removed multiple times from a working surface of the sample that is different from the newly exposed surface. The working surface is imaged multiple times to capture at least a plurality of lines, and an endpoint is determined based on the relative spatial characteristics between two or more of the plurality of lines.

Inventors

  • 프랜티스 데이빗
  • 첸 제이슨

Assignees

  • 에프이아이 컴파니

Dates

Publication Date
20260508
Application Date
20251001
Priority Date
20241101

Claims (20)

  1. As a method for preparing a sample for analysis with a charged particle microscope, the method is: (i) remove material from the surface of the sample to provide a newly exposed surface; (ii) determine the 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) remove material from the working surface of the sample, which is different from the newly exposed surface, in a plurality of steps; (v) by capturing the working surface of the sample multiple times, at least the plurality of lines are captured; and (vi) A method characterized by determining an endpoint based on the relative spatial characteristics between two or more of the plurality of lines.
  2. In paragraph 1, removing material from the upper surface of the sample is: A method characterized by including removing material parallel to the upper surface or at an angle to the upper surface.
  3. A method according to claim 1, characterized in that determining the region of interest includes applying a map to the newly exposed surface (i.e., a CAD map).
  4. In claim 1, determining the end point based on the relative spatial characteristics between two or more of the plurality of lines is: A method comprising determining the case where two adjacent lines among a plurality of lines have the same depth on the newly exposed surface of the sample, wherein the depth of the lines is the relative spatial characteristic.
  5. In claim 1, determining the end point based on the relative spatial characteristics between two or more of the plurality of lines is: A method comprising determining a case where the 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 characteristic.
  6. A method according to claim 5, wherein the predetermined distance is based on the edge position of the region of interest (ROI), and wherein at least two of the plurality of lines are formed on the newly exposed surface such that they are separated by the predetermined distance at the edge position of the ROI.
  7. In claim 1, determining the end point based on the relative spatial characteristics between two or more of the plurality of lines is: A method characterized by including determining the distance ratio between at least two of the plurality of lines.
  8. In claim 1, determining an endpoint based on relative spatial characteristics between two or more of the plurality of lines is: A method characterized by including determining the endpoint based on the relative spatial characteristics by interpreting the acquired image using a machine learning algorithm.
  9. In claim 1, forming the plurality of lines on the newly exposed surface of the sample is: A method comprising forming a series of lines arranged in parallel and offset laterally, wherein at least one end of each line of the series of lines overlaps with at least one line offset laterally from the series of lines, and wherein the depth of each line overlapping is the same.
  10. A method according to claim 9, wherein forming the series of lines comprises forming each line of the series of lines using the same ion beam parameter.
  11. In claim 1, forming the plurality of lines on the newly exposed surface of the sample is: A method comprising forming a plurality of lines arranged at angles to each other, wherein the distance between at least two sets of lines is known at least at one location along the range of the lines.
  12. In claim 1, the material is removed from the working surface of the sample multiple times, wherein the working surface of the sample is different from the newly exposed surface: A method characterized by including milling a material with a focused ion beam.
  13. In claim 1, capturing the sample multiple times to at least capture the profiles of the plurality of lines is: A method characterized by including obtaining an electron beam image of the above-mentioned work surface.
  14. A method according to claim 1, characterized in that capturing the sample multiple times to at least capture the profiles of the plurality of lines includes capturing the sample while removing the material or capturing the sample between removing the material.
  15. A method according to 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 characteristics match the edge of the region of interest determined in (ii).
  16. In paragraph 15, forming the plurality of lines on the newly exposed surface of the sample such that the edge of the region of interest determined in (ii) matches the relative spatial characteristics is: A method characterized by including forming at least two of the plurality of lines on the newly exposed surface such that the edge of the region of interest determined in (ii) and the adjacent overlapping region match.
  17. In paragraph 15, forming a plurality of lines on the newly exposed surface of the sample such that the spatial characteristics relative to the edge of the region of interest determined in (ii) match: A method characterized by comprising forming at least two of the plurality of lines on the newly exposed surface at different angles with respect to the third line; and determining the distance between the at least two lines from the edge of the region of interest determined in (ii).
  18. A method according to claim 1, characterized by repeating at least one of processes (i) to (vi) at least once.
  19. The device: An ion beam column coupled to provide an ion beam; Electron beam columns combined to provide an electron beam; Samples arranged to receive the above ion beam and electron beam; and The device comprises a controller coupled to control the ion beam and electron beam, wherein the controller comprises a non-transient computer-readable medium that stores a controller-executable command when executed by the controller, or is coupled thereto, so that the device: Remove material from the newly exposed surface of the sample using an ion beam; Determine the ROI on the newly exposed surface of the above sample; Using the above ion beam, a plurality of lines are formed on the newly exposed surface of the sample; Using the above ion beam, material is removed from the working surface of the sample multiple times, wherein the working surface is different from the newly exposed surface; By using the electron beam to image the sample multiple times, at least the plurality of lines are captured; and A device characterized by determining an end point based on the relative spatial characteristics between two or more of the aforementioned multiple lines.
  20. In paragraph 19, the controller-executable command executed to determine an endpoint based on relative spatial characteristics between two or more of the plurality of lines includes the controller-executable command, and when executed, the device: An apparatus characterized by determining the case where two adjacent lines among a plurality of lines on the newly exposed surface of the sample have the same depth, wherein the depth of the lines is the relative spatial characteristic.

Description

Line-Based End Point Detection The present invention generally relates to endpoint detection. More specifically, it relates to a new application of endpoint detection in back-end of line (BEOL) semiconductor chips/coupons. The preparation of a sample using a charged particle microscope, such as a dual-beam microscope equipped with both an ion column and an electron column, typically results in thin lamellae with a thickness of nanometers that can be imaged, for example, by a transmission electron microscope. This type of fabrication is particularly delicate for lamellae with a thickness of about 10 nm after formation. Such lamellae are formed using an ion beam to obtain thin lamellae by milling the material from both sides of the sample. However, recognizing or determining the timing to stop milling is a critical factor, and this is difficult in electron beam imaging. As described in US11355313B2, LIT (Line Indicated Termination) is an automated process in AutoTEM for thinning lamellae. LIT marks (alpha marks, lambda marks, etc.) are milled and deposited (i.e., "placed") on the chip surface before thinning. Marks are used to perform automatic endpointing of samples (using processing such as neural networks) with AutoTEM during thinning processing. However, typically, LIT is applied to the end point/thinning of the FEOL (front end of line), which is a more uniform, accessible, and image-capable structure, making it easy to apply to the required line. The method and device described herein can be used for LIT to BEOL (back end of line) endpointing/thinning. This is surprising and unexpected because the BEOL structure is high, non-uniform, and the region of interest (ROI) is obscured by surrounding material. Generally, in a BEOL device, a LIT mark placed on the surface (BEOL layer/large area metal layer/upper metal layer/backer metal layer) may be located at a vertical distance of several to tens of microns from the FEOL ROI. As a result, the usefulness of the LIT line's fine automatic endpoint is significantly reduced. Inverted lift-out orientations place the LIT line at the bottom of the lamella and expose the LIT line by cutting, and both inverted and top-to-bottom lift-out orientations propagate a small lift-out slope applied by chance with a sufficiently large offset in the ROI, which can impair accuracy. The method of the present invention described herein enables precise positioning of the ROI and enables a reduction in cutting on the surface of the lamellar by surrounding material. FIG. 1 is a diagram showing the structure of a sample that can be used in the method of the present invention. FIG. 2a is a diagram of an exemplary orientation of an ion gun used in the method of the present invention, in which the side of the sample (often referred to as the “side”) (i.e., the side of the sample perpendicular to the upper surface of the sample) is perpendicular to a focused ion beam (FIB). FIG. 2b is a drawing of an exemplary orientation of an ion gun used in the method of the present invention, in which the upper surface or lower surface (i.e., the silicon substrate layer) is perpendicular to the FIB. FIG. 3 is a drawing of a charged particle microscope that can be used in the method of the present invention. FIG. 4 is a diagram showing how a reference and a LIT mark are applied to a device/sample/chunk in the method of the present invention. FIGS. 5A and 5B are drawings regarding the use of relative spatial characteristics of lines to determine endpoints, such as the edges of an ROI. FIGS. 6a and FIGS. 6b are drawings of a line configuration that can be used by the disclosed method. The detailed description of the present invention is exemplary for explaining, without limitation, the principles of the invention, particularly in the context of a dual-beam charged particle microscope implementing line-based endpoint detection technology. This technique includes the formation of a line on the surface of a sample, i.e., endpoint detection, which is used to determine the timing for stopping the removal of material from the sample. Such lines may have relative spatial characteristics that are monitored and measured to determine processing endpoints, such as the depth of the groove forming the line, or the distance between multiple sets of lines satisfying the conditions. These technologies are explained in more detail below. The method of the present invention as defined herein comprises a process of removing material from the surface of a sample to provide a newly exposed surface. In the method of the present invention, the sample may be an unprocessed sample, i.e., a microchip that has not been milled in advance, or a segment of a microchip extracted from a microchip that has been milled in advance. In addition, when a sample is extracted by pre-milling from a large sample, such as a microchip, the sample is sometimes referred to as a chunk. Samples such as chunks of microchips may be of any stage, from parti