High accuracy beam placement for local area navigation

• US 8,059,918 B2
• Filed: 10/11/2009
• Issued: 11/15/2011
• Est. Priority Date: 10/12/2008
• Status: Active Grant

• Current Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Original Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Inventors: Young, Richard J., Rue, Chad, Carleson, Peter D.
• Primary Examiner(s): LE, BRIAN Q
• Application Number:
  US12/577,200
• Publication Number:
  US 20100092070A1
• Time in Patent Office: 765 Days
• Field of Search: 382/1, 382 3- 4, 382 6- 9, 382 11- 15, 382 17- 18, 382 20- 23, 382 26- 27, 382/29, 382/31, 382/103, 382/104, 382/105, 382/106, 382/107, 382/293, 382/294, 382/295, 382141-152
• US Class Current: 382/294
• CPC Class Codes: G06T 2207/10061 from scanning electron microscope
• CPC Class Codes: G06T 2207/30148 Semiconductor; IC; Wafer
• CPC Class Codes: G06T 7/73 using feature-based methods
• CPC Class Codes: H01J 2237/31749 Focused ion beam
• CPC Class Codes: H01J 37/222 Image processing arrangements associated with the tube image data processing or generation, in general G06T
• CPC Class Codes: H01J 37/28 with scanning beams H01J37/268, H01J37/292, H01J37/2955 take precedence
• CPC Class Codes: H01J 37/3045 Object or beam position registration
• CPC Class Codes: H01L 22/12 for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions electrical measurement of diffusions H01L22/14
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

An improved method of high accuracy beam placement for local area navigation in the field of semiconductor chip manufacturing. This invention demonstrates a method where high accuracy navigation to the site of interest within a relatively large local area (e.g. an area 200 μm×200 μm) is possible even where the stage/navigation system is not normally capable of such high accuracy navigation. The combination of large area, high-resolution scanning, digital zoom and registration of the image to an idealized coordinate system enables navigation around a local area without relying on stage movements. Once the image is acquired any sample or beam drift will not affect the alignment. Preferred embodiments thus allow accurate navigation to a site on a sample with sub-100 nm accuracy, even without a high-accuracy stage/navigation system.

Claims

1. A method for high accuracy beam placement and navigation to a feature of interest within a local area on a sample surface, comprising:

loading a sample into a sample imaging system employing a moveable sample stage, and said sample imaging system including computer hardware and non-transitory computer memory storing computer instruction embodying a computer program;

acquiring a first image of a local area on the sample using the sample imaging system at a first field of view, the first field of view being large enough to insure that the location of a feature of interest is included in the image based considering the accuracy of the imaging system, the first image including the location of the feature of interest and one or more alignment points near the feature of interest, and said first image also having a resolution such that the image pixel size is equal to or smaller than the alignment points;

superimposing a coordinate system overlay on the first image, with the computer program, the coordinate system overlay representing idealized coordinates of features on the sample surface;

registering the first image with the coordinate system with the computer program using a plurality of alignment points in the first image and corresponding idealized elements in the coordinate system overlay;

after the image and the coordinate system have been registered, navigating the sample imaging system to the location of the feature of interest in the acquired first image using the known coordinates from the coordinate system;

identifying one or more transfer fiducials in the first image, wherein said transfer fiducials comprise unique visible features on the sample surface that can be easily identified;

recording the offset between the transfer fiducials and the feature of interest with the computer program;

acquiring a second image of the sample surface using the sample imaging system at a second field of view, said second field of view being smaller than the first field of view and including the feature of interest and the one or more transfer fiducials;

identifying the one or more transfer fiducials in the second image;

using the recorded offset between the transfer fiducials and the feature of interest to precisely navigate the sample of imaging system to the location of the feature of interest.

2. The method of claim 1, wherein the resolution of the first image yields a pixel size within the range of 10-60 nm.

3. The method of claim 1, wherein the coordinate system overlay includes idealized geometric shapes that represent the locations of features on a semiconductor surface and that are visually displayed superimposed over the first image.

4. The method of claim 3, wherein the alignment points comprise one or more visible features in the first image that correspond to geometric shapes in the coordinate system overlay, and wherein the step of registering the first image with the coordinate system includes matching the first image with the coordinate system overlay so that the alignment points in the first image and the corresponding geometric shapes are aligned.

5. The method of claim 4, wherein the step of registering the first image with the coordinate system includes selecting the alignment points interactively by using a computer pointing device to indicate an alignment point in the first image and also using the computer pointing device to indicate the corresponding position in the coordinate system overlay.

6. The method of claim 1 in which registering the first image with the coordinate system comprises locating the one or more alignment points and determining the offset errors between the one or more alignment points and the corresponding features in the coordinate overlay.

7. The method of claim 6 in which registering the first image with the coordinate system comprises includes matching the alignment points in the first image with the corresponding elements in the coordinate system overlay and aligning the coordinate system overlay with the first image.

8. The method of claim 7 in which aligning the coordinate system overlay with the first image comprises shifting, rotating, stretching, or resizing the coordinate system overlay in order to match the first image with the coordinate system overlay.

9. The method of claim 1 further comprising, after registering the first image with the coordinate system using a plurality of alignment points in the first image and corresponding idealized features in the coordinate system overlay, re-imaging one or more additional sites with other alignment points near the feature of interest and averaging the offset error indicated by the different images.

10. The method of claim 1, wherein the step of registering the first image with the coordinate system is performed by automated computer script executed on a computer machine.

11. The method of claim 1 wherein the step of identifying one or more transfer fiducials in the first image comprises creating one or more suitable transfer fiducials on the sample near the location of the feature of interest.

12. The method of claim 11 in which creating one or more suitable transfer fiducials on the sample near the location of the feature of interest comprises milling a trench in the sample surface to use as a fiducial, said trench forming a frame completely surrounding the location of the feature of interest.

13. The method of claim 1 in which identifying one or more transfer fiducials in the magnified first image comprises creating one or more desired transfer fiducials within the local area but separated from the feature of interest.

14. The method of claim 13 in which the one or more desired transfer fiducials are created by ion beam sputtering or surface staining, gas-assisted etching or deposition, or electron beam induced gas-assisted etching or deposition.

15. The method of claim 13 further comprising, after creating the one or more desired transfer fiducials, re-imaging the local area and repeating the steps of:

superimposing a coordinate system overlay on the first image, the coordinate system overlay representing idealized coordinates of features on the sample surface;

registering the first image with the coordinate system using a plurality of alignment points in the first image and corresponding idealized features in the coordinate system overlay; and

after the image and the coordinate system have been registered, navigating the sample imaging system to the location of the feature of interest in the acquired first image using the known coordinates from the coordinate system.

16. The method of claim 1 in which the first field of view is at least 100 μ

m×

100 μ

m.

17. The method of claim 1 in which the second field of view is 10% of the size of the first field of view or less.

18. The method of claim 6 in which the offset errors are used to position the particle beam before acquiring the second image.

19. A charged particle system including a non-transitory memory storing computer instructions to perform the step of claim 1.

26. The method of claim 1 wherein the step of locating within the first image one or more unique visible sample features on the surface of the sample to serve as transfer fiducials comprises creating one or more suitable transfer fiducials on the sample near the location of the feature of interest.

27. The method of claim 26 in which creating one or more suitable transfer fiducials on the sample near the location of the feature of interest comprises milling a trench in the sample surface to use as a fiducial, said trench forming a frame completely surrounding the location of the feature of interest.

20. A method for accurately locating a feature of interest on a sample in a particle beam system, comprising:

loading a sample into a particle beam system employing a movable sample stage, and using the particle beam system to carry of the steps of;

imaging a target area of the sample with a particle beam to obtain a first image, the target area including the location of a feature of interest and one or more additional visible alignment features having known coordinates, said first image being of a high enough resolution that the first image pixel size is no more than twice the size of any of said alignment features;

superimposing a graphical representation of a coordinate system over the first image, the coordinate system using idealized geometric shapes to represent the locations of visible features within the target area;

locating the one or more alignment features having known coordinates within the first image;

determining an offset error between the superimposed coordinate system and the first image;

aligning the coordinate system with the first image;

locating within the first image one or more unique visible sample features on the surface of the sample to serve as transfer fiducials;

recording the offset between the transfer fiducials and the location of the feature of interest;

acquiring a second image of the sample with a particle beam at the location of the feature of interest, the second image having a smaller field of view than the first image;

locating the transfer fiducials in the second image;

locating the feature of interest within the second image using the recorded offset between the transfer fiducials and the feature of interest;

using the location of the feature of interest to control the placement of a particle beam; and

processing the sample using the particle beam.

21. The method of claim 20, wherein the alignment features comprise one or more visible features in the first image that correspond to geometric shapes in the superimposed coordinate system, and wherein the step of aligning the coordinate system with the first image includes matching the first image with the superimposed coordinate system so that the alignment features in the first image and the corresponding geometric shapes are aligned.

22. The method of claim 20 in which aligning the coordinate system with the first image comprises shifting, rotating, stretching, or resizing the superimposed coordinate system in order to match the first image with the superimposed coordinate system.

23. The method of claim 20 further comprising, after aligning the coordinate system with the first image using a plurality of alignment features in the first image and corresponding idealized features in the superimposed coordinate system, re-imaging one or more additional sites with other alignment features near the feature of interest and averaging the offset error indicated by the additional images.

24. The method of claim 20, wherein the steps of determining an offset error between the superimposed coordinate system and the first image and aligning the coordinate system with the first image are performed by automated computer script executed on a computer machine.

25. The method of claim 20, wherein the steps of locating the feature of interest within the second image using the recorded offset between the transfer fiducials and the feature of interest and using the location of the feature of interest to control the placement of a particle beam are performed by automated computer script executed on a computer machine.

28. The method of claim 20 in which the first image has a field of view that is at least 100 μ

m×

100 μ

m.

29. The method of claim 28 in which the second image has a field of view that is 10% or less of the size of the field of view of the first image.

30. A charged particle system including a non-transitory memory storing computer instructions to perform the step of claim 20.

31. A method for navigating a sample without relying on stage movements, the sample having a target area with a feature of interest and one or more alignment points, the method comprising loading the sample into a sample imaging system, said sample imaging system including a computer program embodied in computer instructions stored in non-transitory computer memory and executed on a computer hardware system for carrying out the following steps:

acquiring a first image of the target area;

overlaying the image with an idealized coordinate system of alignment points within the target area;

locating one or more of the alignment points within the image near the feature of interest;

aligning the idealized coordinate system with the image;

locating one or more unique features on the sample within the target area but separated from the sample;

recording the offset between the feature of interest and the unique features in the first image;

acquiring a new image of the sample with a smaller field of view, the new image including the feature of interest; and

locating the feature of interest in the new image.

32. The method of claim 31, wherein the steps of acquiring a first image of the target area;

overlaying the image with an idealized coordinate system of alignment points within the target area;

locating one or more of the alignment points within the image near the feature of interest;

aligning the idealized coordinate system with the image;

locating one or more unique features on the sample within the target area but separated from the sample;

recording the offset between the feature of interest and the unique features in the first image;

acquiring a new image of the sample with a smaller field of view, the new image including the feature of interest; and

locating the feature of interest in the new image are performed by automated computer script executed on a computer machine, said computer machine operably connected to a particle beam system.

33. An apparatus for accurately locating a feature of interest on a sample, comprising:

a moveable sample stage for supporting the sample;

a particle beam column for producing a beam of particles to image the sample; and

a computer-readable memory storing computer instructions, the instructions including a program for controlling the apparatus and causing the apparatus to carry out the steps of;

(i) acquiring a first image of the target area;

(ii) overlaying the image with an idealized coordinate system of alignment points within the target area;

(iii) precisely locate one or more of the alignment points within the image near the feature of interest;

(iv) aligning the idealized coordinate system with the image;

(v) locating one or more unique features on the sample within the target area but separated from the sample;

(vi) recording the offset between the feature of interest and the unique features in the first image;

(vii) acquiring a new image of the sample with a smaller field of view, the new image including the feature of interest;

(viii) locating the feature of interest in the new image; and

(ix) using the location of the feature of interest to control the placement of a particle beam relative to the sample.

34. The apparatus of claim 33 in which the sample stage has positional error of ±

500 nm or greater and in which the particle beam can be positioned relative to sample with a positional error of ±

100 nm or smaller.

35. The apparatus of claim 33 in which the particle beam can be positioned relative to the sample with a positional error of ±

30 nm or smaller.