Enhanced FIB-SEM systems for large-volume 3D imaging

Patent metadata

Field	Value
Publication number	US-10600615-B2
Application number	US-201815883025-A
Country	US
Kind code	B2
Filing date	Jan 29, 2018
Priority date	Jan 27, 2017
Publication date	Mar 24, 2020
Grant date	Mar 24, 2020

Abstract

A microscopy system for imaging a sample can include a scanning electron microscope system configured for imaging a surface layer of the sample and a focused ion beam system configured for generating an ion beam for milling the surface layer away from a sample after it has been imaged. A movable mechanical shutter can be configured to be moved automatically into a position between the sample and the scanning electron microscope system, so that when the electron beam is not imaging the sample the movable mechanical shutter is positioned between the sample and the scanning electron microscope system.

First claim

What is claimed is:

1. A microscopy system for imaging a sample, the microscopy system comprising:
a focused ion beam system configured to direct a focused ion beam onto a sample;
a scanning electron microscope system configured to direct an electron beam onto the sample; and
a plurality of charged-particle detectors, each detector being configured to monitor an electrical current on the detector, wherein the plurality of charged particle detectors includes a movable shutter located between the sample and the scanning electron microscope system, the shutter being configured to be moved automatically into a position between the sample and the scanning electron microscope system, so that when the electron beam is not irradiating the sample the shutter is positioned between the sample and the scanning electron microscope system and blocks sputtered ions produced by the focused ion beam directed onto the sample from entering a column of the scanning electron microscope system; and
a control computer configured to receive a plurality of signals indicative of the electrical currents on the plurality of charged particle detectors and configured to control automatically properties of a focused ion beam produced by the focused ion beam system in response to the received signals when the shutter is positioned between the sample and the scanning electron microscope system.

2. The system of claim 1 , wherein the control computer is configured to automatically prevent a focused ion beam produced by the focused ion beam system from striking the sample in response to at least one of the signals of the plurality of signals having a value that is outside a range of predetermined values.

3. The system of claim 1 , wherein the control computer is configured to automatically control the focused ion beam milling rate in response to at least one of the signals from the plurality of charged particle detectors.

4. The system of claim 1 , wherein the plurality of charged particle detectors includes an inner Faraday cup configured to capture non-scattered ions produced by the focused ion beam system, and an annular Faraday cup configured to capture ions produced by the focused ion beam system and scattered by the sample.

5. The system of claim 1 , wherein the plurality of charged particle detectors includes the sample.

6. The system of claim 5 , wherein the sample is maintained at a positive voltage bias that is selected to reject electrons below an energy threshold from entering the scanning electron microscope system.

7. The system of claim 1 , further comprising a switch configured to control a movement of a mechanical stop into a path of the electron beam or into a path of the ion beam to prevent the electron beam or the ion beam from reaching the sample, wherein the switch is configured to control the movement of the mechanical stop in response to a signal from the control computer.

8. The system of claim 1 , further comprising a plurality of switches, each of the switches being configured to control a movement of a mechanical stop into a path of the electron beam or into a path of the ion beam to prevent the electron beam or the ion beam from reaching the sample, wherein each of the switches is configured to control the movement of the mechanical stop in response to a signal from the control computer.

9. The system of claim 1 , wherein the scanning electron microscope system includes a focusing lens and a detector located between the focusing lens and the sample.

10. The system of claim 1 , wherein the scanning electron microscope system includes:
an electron accelerator configured for generating a primary electron beam for irradiating the sample;
an aperture in a mask, wherein the primary electron beam passes through the aperture when irradiating the sample;
a lens configured for focusing the primary electron beam on the sample;
a detector configured for detecting a signal of electrons emitted from the sample in response to the irradiation by the primary electron beam; and wherein the system includes:
one or more processors configured to:
control a parameter of the primary electron beam while the primary electron beam irradiates the sample and while the detector detects the signal of electrons,
generate a plurality of images of different surface layers of the sample based on the detected signal from the different surface layers,
vary the parameter when irradiating different surface layers of the sample, including surface layers for which an image is generated based on the detected signal, and
select, based on the plurality of images, a fixed value of the parameter to use for irradiation of subsequent surface layers of the sample by the primary electron beam.

11. The system of claim 10 , wherein the one or more processors are further configured to:
fit a curve of an image quality metric for the plurality of images as a function of the varied parameter; and
select the fixed value of the parameter to use for subsequent irradiation of the sample based on the fitted curve.

12. The system of claim 11 , wherein the image quality metric includes a focus index (FI) expressed as:

FI
=

[

∑

i
=
0

n
-
1

⁢

(

I
*

S
1

-

I
*

S
2

)

2

]

/
n

,

where I represents an image of the sample, S 1 and S 2 represent 2D Gaussian functions of shorter and longer length scales, respectively, than a resolution limit of the scanning electron microscope system, i represents a pixel in the image, and n represents a total number of pixels considered in the image.

13. The system of claim 10 , wherein different values of the parameter are selected for different tiles of an image of a surface of the sample.

14. The system of claim 10 , wherein the parameter is a focus of the primary electron beam.

15. The system of claim 10 , wherein the parameter is one of an astigmatism of the primary electron beam, or an aperture alignment of the primary electron beam.

Assignees

• Hughes Howard Med Inst

Inventors

• Xu C Shan
• Hayworth Kenneth J
• Hess Harald F

Classifications

• H01J37/28 Primary

  with scanning beams {(H01J37/268, H01J37/292, H01J37/2955 take precedence)} · CPC title

• H01J2237/2067

  Surface alteration · CPC title

• H01J2237/0262

  electrostatic · CPC title

• H01J37/31

  for cutting or drilling · CPC title

• H01J2237/024

  Moving components not otherwise provided for · CPC title