U.S. patent application number 14/292606 was filed with the patent office on 2015-12-03 for method and apparatus for slice and view sample imaging.
This patent application is currently assigned to FEI Company. The applicant listed for this patent is FEI Company. Invention is credited to Valerie Brogden.
Application Number | 20150348751 14/292606 |
Document ID | / |
Family ID | 54698219 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150348751 |
Kind Code |
A1 |
Brogden; Valerie |
December 3, 2015 |
METHOD AND APPARATUS FOR SLICE AND VIEW SAMPLE IMAGING
Abstract
Methods, apparatuses, and systems for slice and view processing
of samples with dual beam systems. The slice and view processing
includes exposing a vertical wall of a trench formed in a sample
surface; capturing a first image of the wall by interrogating the
wall with an interrogating beam while the wall is at a first
orientation relative to the beam; capturing a second image of the
wall by interrogating the wall with the beam while the wall is at a
second orientation relative to the beam, wherein first distances in
the first image between a reference point and surface points on the
wall are different than second distances in the second image
between the reference point and the surface points; determining
elevations of the surface points using the first distances and the
second distances; and fitting a curve to topography of the wall
using the elevations.
Inventors: |
Brogden; Valerie; (Portland,
OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FEI Company |
Hillsboro |
OR |
US |
|
|
Assignee: |
FEI Company
Hillsboro
OR
|
Family ID: |
54698219 |
Appl. No.: |
14/292606 |
Filed: |
May 30, 2014 |
Current U.S.
Class: |
250/307 ;
250/310 |
Current CPC
Class: |
G01N 23/2208 20130101;
H01J 37/265 20130101; H01J 37/3056 20130101; H01J 2237/31749
20130101; G01N 23/2255 20130101; H01J 2237/31745 20130101; H01J
37/3023 20130101; H01J 2237/2611 20130101; H01J 2237/2814 20130101;
G01N 23/2251 20130101; H01J 37/26 20130101 |
International
Class: |
H01J 37/305 20060101
H01J037/305; H01J 37/26 20060101 H01J037/26 |
Claims
1. An apparatus for observing a feature using dual charged particle
beams, comprising: a focused ion beam column configured to
generate, focus, and direct a focused ion beam; an electron beam
column configured to generate, focus, and direct an electron beam;
one or more processors; and a computer-readable storage medium
coupled to at least one of the one or more processors, the
computer-readable storage medium comprising first executable
instructions and second executable instructions, wherein the first
executable instructions, when executed, cause the one or more
processors to direct the focused ion beam to mill a trench in a
surface of a substrate, the trench exposing a vertical wall having
an area around a feature to be observed, and wherein the second
executable instructions, when executed, cause the one or more
processors to: direct the electron beam to capture a first electron
beam image of the vertical wall while the electron beam column is
maintained at a first angle of incidence relative to a longitudinal
axis of the electron beam column; change the angle of incidence
between the longitudinal axis and the vertical wall from the first
angle of incidence to a second angle of incidence; direct the
electron beam to capture a second electron beam image of the wall
while the electron beam column is maintained at the second angle of
incidence; and approximate a topography of the vertical wall based
on differences between the first electron beam image and the second
electron beam image.
2. The apparatus of claim 1, wherein approximation of the
topography of the vertical wall comprises calculating
three-dimensional coordinates for a plurality of points on the
vertical wall using positions of the plurality of points in the
first electron beam image and the second electron beam image
relative to a reference point in the first electron beam image and
the second electron beam image.
3. The apparatus of claim 2, wherein approximation of the
topography of the vertical wall comprises fitting a curve to the
three-dimensional coordinates that approximates the topography of
the vertical wall.
4. The apparatus of claim 1, wherein approximation of the
topography of the vertical wall based on differences between the
first electron beam image and the second electron beam image
comprises: measuring in the first electron beam image first
distances between a plurality of points on the vertical wall and
one or more reference points on the vertical wall; and measuring in
the second electron beam image second distances between the
plurality of points and the one or more reference points.
5. The apparatus of claim 1, wherein the second executable
instructions, when executed, cause the one or more processors to
change the angle of incidence of between the longitudinal axis and
the vertical wall by directing a rotation of a stage.
6. The apparatus of claim 1, wherein the second executable
instructions, when executed, cause the one or more processors to
change the angle of incidence of between the longitudinal axis and
the vertical wall by directing a repositioning of the electron beam
column.
7. The apparatus of claim 1, further comprising third executable
instructions that, when executed, cause the one or more processors
to: direct the focused ion beam to sequentially remove a plurality
of slices from a volume of material located behind the vertical
wall, wherein the volume of material comprises a feature to be
observed and sequentially removing the plurality of slices
sequentially exposes a plurality of additional vertical walls; and
carry out the second executable instructions for each vertical wall
of the plurality of additional vertical walls.
8. The apparatus of claim 7, further comprising fourth executable
instructions that, when executed, cause the one or more processors
to construct a three-dimensional image of the feature to be
observed using the approximations of the topographies of the
vertical wall and the plurality of additional vertical walls.
9. A method of processing a sample by slice and view processing
with a dual beam system, comprising: exposing a vertical wall of a
trench formed in a surface of a sample by removing a first slice of
material from the sample using an etching beam; capturing a first
image of the vertical wall by interrogating the vertical wall with
an interrogating beam while the vertical wall is at a first
orientation relative to the interrogating beam; reorienting the
vertical wall relative to the interrogating beam; capturing a
second image of the vertical wall by interrogating the vertical
wall with the interrogating beam while the vertical wall is at a
second orientation relative to the interrogating beam, wherein
first distances in the first image between a reference point and
surface points on the vertical wall are different than second
distances in the second image between the reference point and the
surface points; determining elevations of the surface points using
the first distances and the second distances; and fitting a curve
to a topography of the vertical wall using the elevations.
10. The method of claim 9, wherein fitting the curve to the
topography of the vertical wall comprises generating
three-dimensional coordinates for the surface points, wherein the
three-dimensional coordinates comprise a vertical location, a
horizontal location, and an elevation for each of the surface
points.
11. The method of claim 10, wherein fitting the curve to the
topography of the vertical wall comprises applying a
three-dimensional Fourier fit to the three-dimensional
coordinates.
12. The method of claim 10, wherein fitting the curve to the
topography of the vertical wall comprises applying a least squares
regression to the three-dimensional coordinates.
13. The method of claim 9, wherein the vertical wall is a first
vertical wall and further comprising: exposing a subsequent
vertical wall behind the first vertical wall by applying the
etching beam to the first vertical wall such that a subsequent
slice of material is removed from a surface of the first vertical
wall; and applying the steps of capturing a first image,
reorienting, capturing a second image, determining elevations, and
fitting a curve to the subsequent vertical wall.
14. The method of claim 13, further comprising: carrying out the
steps of claim 13 a number of times in connection with a series of
successively exposed vertical walls to produce a number of fitted
curves representing the series of successively exposed vertical
walls; and generating a three-dimensional representation of a
feature of the sample using the number of fitted curves.
15. The method of claim 9, wherein reorienting the vertical wall
relative to the interrogating beam comprises changing an angle of
incidence between the interrogating beam and the vertical wall by
translating a source of the interrogating beam away from a
longitudinal axis of the interrogating beam during the capturing
the first image.
16. The method of claim 9, wherein reorienting the vertical wall
relative to the interrogating beam comprises rotating the
sample.
17. The method of claim 16, wherein the elevations are determined
according to the following formula: Z i = A ' B ' _ - A B _ cos
.theta. sin .theta. , ##EQU00003## wherein Z.sub.i is the elevation
of a point i of the surface points, A.sub.i is a position of the
reference point in the first image, A.sub.i' is a position the
reference point in the second image, B.sub.i is a position of point
i in the first image, B.sub.i' is a position of point i in the
second image, | A.sub.'B.sub.'| is the distance between A.sub.i'
and B.sub.i', | A.sub.B.sub.| is the distance between A.sub.i and
B.sub.i, and .theta. is the difference of the first angle of
incidence and the second angle of incidence.
18. A particle beam system for slice and view processing a volume
of a sample having a feature to be observed, comprising: an etching
beam column configured to emit an etching beam; an interrogating
beam column configured to emit an interrogating beam; one or more
processors; and a computer-readable storage medium coupled to at
least one of the one or more processors, the computer-readable
storage medium comprising executable instructions that, when
executed, cause the one or more processors to direct the etching
beam to sequentially remove slices of the sample across a thickness
of the volume, the removal of each slice exposing a surface of the
sample, and, for each surface exposed: direct the interrogating
beam to capture a first image of the surface exposed while
maintaining a first angle of incidence between a longitudinal axis
of the interrogating beam column and the surface exposed and a
second image of the surface exposed while maintaining a second
angle of incidence between the longitudinal axis and the surface
exposed, and record first positions of pairs of points in the first
image and second positions of the pairs of points in the second
image, wherein each of the pairs of points comprises a point on the
surface exposed and a reference point.
19. The particle beam system of claim 18, wherein the executable
instructions, when executed, direct the one or more processors to
determine an elevation for the point on the surface exposed of each
of the pairs of points according to the following formula: Z = A '
B ' _ - AB _ cos .theta. sin .theta. , ##EQU00004## wherein Z is
the elevation of the point on the surface exposed, A is a position
of the reference point in the first image, A' is a position of the
reference point in the second image, B is a position of point on
the surface exposed in the first image, B' is a position of the
point on the surface exposed in the second image, | A'B'| is the
distance between A' an B', | AB| is the distance between A and B,
and .theta. is the difference between the first angle of incidence
and the second angle of incidence.
20. The particle beam system of claim 18, wherein the reference
point of each of the pairs of points is a same reference point.
21. The particle beam system of claim 18, wherein the executable
instructions, when executed, cause the one or more processors to
direct the etching beam to mill machine-identifiable shapes on the
surface exposed, wherein the machine-identifiable shapes correspond
to the points on the surface exposed.
22. The particle beam system of claim 21, wherein the
machine-identifiable shapes comprise two or more different
shapes.
23. The particle beam system of claim 18, wherein the interrogating
beam comprises an electron beam and the etching beam comprises a
charged particle beam.
24. The particle beam system of claim 18, wherein each surface
exposed is a vertical wall of a trench formed in a surface of the
sample.
25. The dual charged particle beam system of claim 18, wherein the
etching beam column and the interrogating beam column are the same.
Description
TECHNICAL FIELD
[0001] The present invention relates to methods, apparatuses, and
systems for imaging samples in two and three dimensions using
beams, such as charged particle beams.
BACKGROUND
[0002] Electron microscopy offers the opportunity to investigate
the ultrastructure of a wide range of biological and inorganic
specimens in 3-D at high resolution. In the field of biological
sciences, for example, electron microscopy allows the observation
of molecular mechanisms of diseases, the conformation of flexible
protein structures and the behavior of individual viruses and
proteins in their natural biological context. As another example,
electron microscopy plays an important quality control function in
the manufacture of semiconductors and electronic devices by
allowing for the detection and characterization of nanoscale
defects in electrical, optical, and micromechanical systems, which
may affect the performance of such products. Defects can include
contaminant particles that become embedded in a product during
fabrication or a manufacturing defect, such as a bridge creating a
short circuit between two closely spaced conductors that are
intended to be electrically separated from each other. One
technique employed with electron microscopy to carry out such
investigations is called Slice-and-View.TM. (hereafter "slice and
view"). This technique is typically performed with a dual beam
system, that is, a system combining a focused ion beam (FIB) device
and a scanning electron microscope (SEM) such as the DualBeam.RTM.
instruments commercially available from FEI Company, the assignee
of the present invention.
[0003] In the slice and view technique, as illustrated by FIG. 1,
the focused ion beam cuts and slices a sample with high precision
to reveal its 3D internal structures or features. Typically, the
focused ion beam cuts exposes a cross section, or face,
perpendicular to the top of the surface of the sample material
having the hidden feature to be viewed. Because the SEM beam axis
is typically at an acute angle relative to the focused ion beam
cuts axis, a portion of the sample in front of the face is
preferably removed so that the SEM beam can have access to image
the face. After obtaining an image of the face by the SEM, another
layer of substrate at the face may be removed using the focused ion
beam cuts, revealing a new, deeper face and thus a deeper
cross-section of the feature. Since only the portion of the feature
at the very surface of the face is visible to the SEM, sequential
repetition of cutting and imaging, or slicing and viewing, provides
the data needed to reconstruct the sliced sample into a 3D
representation of the feature. The 3D structure is then used to
analyze the feature.
[0004] During slicing, variations in the topography of the surface
exposed may occur as the focused ion beam traverses a sample. In
some circumstances, the exposed face may have a surface morphology
attributable to a phenomenon known colloquially as the "curtaining"
effect, which is schematically illustrated in FIGS. 2A and 2B. When
a sample 210 contains heterogeneous structures and/or compositions,
the material removal rate of focused ion beam 215 from FIB column
220 may vary locally as focused ion beam 215 carries out a line
mill 225 across face 230 in the direction of arrows 240. As a
result, the surface of the sample exposed by the focused ion beam
has a rippled face, or curtain. Local increases in the material
removal rate may form concave curtains, such as curtaining
artifacts 245A, 245B, and 245C, which penetrate into the face being
exposed. Local decreases in the material removal rate may form
convex curtains, such as curtaining artifact 250, which protrude
from the face being exposed.
[0005] Software algorithms for 3-D reconstruction from slice and
view imaging generally assume that surface of each slice imaged by
the SEM is flat. Applicant has found that the presence of
curtaining and other artifacts create topographical variations mean
that the surface is not flat and this lack of flatness manifests as
noise (e.g., decreased resolution) in the 3-D representation formed
from images of the exposed surfaces. Thus, applicant has discovered
that there is a need for methods, apparatuses, and systems that
take into account variations in the topography of surfaces
interrogated by an SEM during slice and view imaging of a sample,
such as topographical variations caused by the curtaining effect,
in order to improve the resolution of 3-D representations generated
therefrom.
SUMMARY
[0006] In some embodiments of the disclosure, a method of
processing a sample by slice and view processing with a dual beam
system is provided that includes: exposing a vertical wall of a
trench formed in a surface of a sample by removing a first slice of
material from the sample using an etching beam; capturing a first
image of the vertical wall by interrogating the vertical wall with
an interrogating beam while the vertical wall is at a first
orientation relative to the interrogating beam; reorienting the
vertical wall relative to the interrogating beam; capturing a
second image of the vertical wall by interrogating the vertical
wall with the interrogating beam while the vertical wall is at a
second orientation relative to the interrogating beam, wherein
first distances in the first image between a reference point and
surface points on the vertical wall are different than second
distances in the second image between the reference point and the
surface points; determining elevations of the surface points using
the first distances and the second distances; and fitting a curve
to a topography of the vertical wall using the elevations.
[0007] In some embodiments of the disclosure, an apparatus for
observing a feature using dual charged particle beams is provided
that includes a focused ion beam column configured to generate,
focus, and direct a focused ion beam; an electron beam column
configured to generate, focus, and direct an electron beam; one or
more processors; and a computer-readable storage medium coupled to
at least one of the one or more processors. The computer-readable
storage medium includes first executable instructions and second
executable instructions. The first executable instructions, when
executed, cause the one or more processors to direct the focused
ion beam to mill a trench in a surface of a substrate, the trench
exposing a vertical wall having an area around a feature to be
observed. The second executable instructions, when executed, cause
the one or more processors to direct the electron beam to capture a
first electron beam image of the vertical wall while the electron
beam column is maintained at a first angle of incidence relative to
a longitudinal axis of the electron beam column; to change the
angle of incidence of between the longitudinal axis and the
vertical wall from the first angle of incidence to a second angle
of incidence; to direct the electron beam to capture a second
electron beam image of the wall while the electron beam column is
maintained at the second angle of incidence; and to approximate a
topography of the vertical wall based on differences between the
first electron beam image and the second electron beam image.
[0008] In an embodiment of the apparatus, approximation of the
topography of the vertical wall includes calculating
three-dimensional coordinates for a plurality of points on the
vertical wall using positions of the plurality of points in the
first electron beam image and the second electron beam image
relative to a reference point in the first electron beam image and
the second electron beam image. In an embodiment of the apparatus,
approximation of the topography of the vertical wall includes
fitting a curve to the three-dimensional coordinates that
approximates the topography of the vertical wall. In an embodiment
of the apparatus, approximation of the topography of the vertical
wall based on differences between the first electron beam image and
the second electron beam image includes measuring in the first
electron beam image first distances between a plurality of points
on the vertical wall and one or more reference points on the
vertical wall; and measuring in the second electron beam image
second distances between the plurality of points and the one or
more reference points.
[0009] In an embodiment of the apparatus, the second executable
instructions, when executed, cause the one or more processors to
change the angle of incidence of between the longitudinal axis and
the vertical wall by directing a rotation of a stage. In an
embodiment of the apparatus, the second executable instructions,
when executed, cause the one or more processors to change the angle
of incidence between the longitudinal axis and the vertical wall by
directing a repositioning of the electron beam column.
[0010] In an embodiment of the apparatus, the apparatus includes
third executable instructions that, when executed, cause the one or
more processors to direct the focused ion beam to sequentially
remove a plurality of slices from a volume of material located
behind the vertical wall, wherein the volume of material includes a
feature to be observed and sequentially removing the plurality of
slices sequentially exposes a plurality of additional vertical
walls; and carry out the second executable instructions for each
vertical wall of the plurality of additional vertical walls. In an
embodiment, the apparatus includes the third executable
instructions and fourth executable instructions that, when
executed, cause the one or more processors to construct a
three-dimensional image of the feature to be observed using the
approximations of the topographies of the vertical wall and the
plurality of additional vertical walls.
[0011] In some embodiments of the disclosure, a particle beam
system for slice and view processing a volume of a sample having a
feature to be observed is provided. The particle beam system
includes an etching beam column configured to emit an etching beam;
an interrogating beam column configured to emit an interrogating
beam; one or more processors; and a computer-readable storage
medium coupled to at least one of the one or more processors. The
computer-readable storage medium includes executable instructions
that, when executed, cause the one or more processors to direct the
etching beam to sequentially remove slices of the sample across a
thickness of the volume, the removal of each slice exposing a
surface of the sample, and, for each surface exposed: direct the
interrogating beam to capture a first image of the surface exposed
while maintaining a first angle of incidence between a longitudinal
axis of the interrogating beam column and the surface exposed and a
second image of the surface exposed while maintaining a second
angle of incidence between the longitudinal axis and the surface
exposed, and record first positions of pairs of points in the first
image and second positions of the pairs of points in the second
image, wherein each of the pairs of points includes a point on the
surface exposed and a reference point.
[0012] The foregoing has outlined rather broadly the features and
technical advantages of the present invention in order that the
detailed description of the invention that follows may be better
understood. Additional features and advantages of the invention
will be described hereinafter. It should be appreciated by those
skilled in the art that the conception and specific embodiments
disclosed may be readily utilized as a basis for modifying or
designing other structures for carrying out the same purposes of
the present invention. It should also be realized by those skilled
in the art that such equivalent constructions do not depart from
the spirit and scope of the invention as set forth in the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] For a more thorough understanding of the present disclosure,
and advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0014] FIG. 1 is a diagram showing slice and view processing of a
sample.
[0015] FIG. 2A is a side view diagram of a sample undergoing slice
and view processing and exhibiting curtains.
[0016] FIG. 2B is a front elevated view diagram of the sample of
FIG. 2A.
[0017] FIG. 3 is a flow diagram of a method of processing a sample
by slice and view processing according to an embodiment of the
disclosure.
[0018] FIG. 4A is a simplified diagram of a sample provided with a
fiducial in accordance with an embodiment of the disclosure.
[0019] FIG. 4B shows an enlarged portion of the sample of FIG. 2A
in which a sloping trench has been formed in a surface of the
sample.
[0020] FIG. 5 is a simplified diagram showing the execution of a
line mill by a focused ion beam to expose a surface of a sample in
accordance with an embodiment of the disclosure.
[0021] FIG. 6A shows an SEM micrograph of a sample captured by an
electron beam while maintaining the sample at a first orientation
and having machine-recognizable shapes that can be etched at
various points into the face of the sample.
[0022] FIG. 6B shows an SEM micrograph of the sample of FIG. 6A
captured while maintaining the sample at a second orientation
different from the first orientation in accordance with an
embodiment of the disclosure.
[0023] FIGS. 7A-7C are diagrams illustrating the imaging of a
sample surface by a SEM device from two different orientations in
accordance with an embodiment of the disclosure.
[0024] FIGS. 8A and 8B are schematic illustrations of SEM images of
a sample surface captured by a SEM in accordance with an embodiment
of the disclosure.
[0025] FIG. 9A, is a diagram illustrating the reorientation of a
sample surface being imaged by an SEM from a first orientation to a
second orientation according to another embodiment of the
disclosure.
[0026] FIG. 9B is an illustration of a first image of the sample
surface of FIG. 9A captured by an SEM while the sample surface is
maintained at a first orientation relative to the SEM.
[0027] FIG. 9C is an illustration of a second image of the sample
surface of FIG. 9A captured by an SEM while the sample surface is
maintained at a second orientation relative to the SEM.
[0028] FIG. 10 is a schematic diagram of an apparatus for observing
a feature using dual charged particle beams according to an
embodiment.
[0029] FIG. 11 is a block diagram of an embodiment of a slice and
view dual charged particle beam system 1102 according to an
embodiment.
DETAILED DESCRIPTION
[0030] In the following discussion and in the claims, the terms
"including" and "comprising" are used in an open-ended fashion, and
thus should be interpreted to mean "including, but not limited to .
. . . " To the extent that any term is not specially defined in
this specification, the intent is that the term is to be given its
plain and ordinary meaning. Furthermore, use of the term "and/or"
herein shall be construed as an "inclusive" or, and not an
"exclusive" or. For example, used herein the phrase "A and/or B"
would mean "A, B, or A and B." As another example, used herein the
phrase "A, B, and/or C" would mean "A, B, C, or any combination
thereof." Further, whenever the terms "automatic," "automated," or
similar terms are used herein, those terms will be understood to
include manual initiation of the automatic or automated process or
step.
[0031] As used herein, the terms "mill" and "etch" refer to the
removal of material of a sample, and the terms "slice," "slice
mill," and "etch a slice" refers to the removal of material from a
sample in the shape of a slice. As used herein, the term "slice,"
when used as a noun, refers to the body of material removed by the
FIB to expose a surface. The slice may be characterized, for
example by a width dimension, a height dimension, and a thickness
dimension, which correspond, respectively, to the edges of the
illustrative sample of FIG. 1 aligned with x, y, and z axes shown
therein.
[0032] An "image," as used herein, means an image displayed on a
display unit or on a disposable medium such as paper, as well as a
representation thereof in a computer memory, for example. As used
herein, the term "image plane" refers to the plane in which an
image generated by an interrogating beam system (e.g., a SEM) is
formed, whereas the "imaging plane" refers to the cross-section of
a sample exposed by removing a slice from the sample using an
ablating beam system (e.g., a FIB) device.
[0033] The accompanying drawings are intended to aid in
understanding various embodiments of the present invention. Unless
otherwise indicated, the accompanying drawings are not drawn to
scale.
[0034] Although other coordinate systems may be used to explain
and/or implement embodiments of the invention, for simplicity the
3-D coordinate system shown in FIG. 1 is used herein as the
coordinate system for the samples and sample environments described
in connection with the various illustrative embodiments of the
disclosure. Thus, unless indicated otherwise or in different
context, the terms "z-axis," "z-coordinate," "z-height,"
"elevation," "thickness direction," and the like are used herein
with reference to the z-axis of FIG. 1; the terms "x-axis",
"x-coordinate," "horizontal," "horizontal direction," "horizontal
alignment," "width direction," "sample width", "slice width," and
the like are used herein with reference to the x-axis of FIG. 1;
and the terms "y-axis", "y-coordinate," "vertical," "vertical
direction," "vertical alignment," "depth," "height," "height
direction," "sample height", "slice height," and the like are used
herein with reference to the y-axis of FIG. 1. Accordingly,
"height" and "vertical height" will be used synonymously herein to
refer to the distance measured from a point to the surface of the
sample directly beneath the point along a line parallel to and in
the direction of the y-axis of FIG. 1, whereas the "z-height" and
"elevation" will be used synonymously herein to refer to the
distance from a point to the imaging plane of the sample along an
axis parallel to the z-axis of FIG. 1 and intersecting both the
point and the imaging plane. Further, as used herein, the depth of
a point located in a trench formed in a top surface of the sample
(e.g., the surface directly beneath the "slicing direction" arrow
of FIG. 1) is measured from a plane overlapping the surface to the
point along a line parallel to the y-axis of FIG. 1 and
intersecting both the surface of the sample direction of the y-axis
of FIG. 1.
[0035] In some cases, it may be desirable to provide a method of
forming a 3-D representation of a feature by slice and view
processing of a sample, wherein the quality (e.g., resolution) of
the 3-D representation is improved by characterizing and correcting
for topographical variation in the profiles (i.e., deviation from a
flat profile) of surfaces imaged on which the 3-D representation is
based. In various embodiments, an interrogating beam captures at
least two images of each surface of a sample exposed after a slice
of material has been removed from the sample by an etching beam.
For each surface exposed, the interrogating beam captures a first
image of the exposed surface and then captures a second image of
the exposed surface after the exposed surface has been reoriented
relative to the interrogating beam. In some embodiments, the
etching beam is a focused ion beam of a FIB device and the
interrogating beam is an electron beam of a SEM. In some
embodiments, a sample is mounted on a stage, and the reorientation
of the exposed surface relative to the interrogating beam comprises
rotating the sample by an angle .theta.. In some embodiments, the
reorientation of the exposed surface relative to the interrogating
beam comprises changing an angle of incidence between the
interrogating beam and the exposed surface by repositioning a
source of the interrogating beam. By imaging each of the surfaces
of a sample exposed during slice and view processing from two
different perspectives (i.e., capturing the second image while
maintaining the exposed surface at an orientation, relative to the
interrogating beam, that is different from the orientation
maintained while capturing the first image), topographical
information about each of the exposed surfaces can be obtained and
used to generate a 3-D representation of a feature in the sample
having greater resolution than would have been otherwise been
achieved had the exposed surfaces been assumed to be flat.
[0036] Referring now to FIG. 3, a flow diagram of a method 300 of
processing a sample by slice and view processing with a dual beam
system in accordance with an embodiment of the disclosure is shown.
In order to remove material from the sample, the dual beam system
of method 300 utilizes an etching beam, such as a focused ion beam
from a FIB device or a laser beam from a laser. In order to image
surfaces of the sample exposed by the etching beam, the dual beam
system of method 300 utilizes an interrogating beam, such as an
electron beam from a SEM. In some embodiments, the sample is
mounted on a stage. In some such embodiments, the stage is
rotatable and/or translatable relative to the etching and
interrogating beams, and rotation of the stage allows reorientation
of the exposed surfaces such that images of the exposed surfaces
can be taken from different perspectives. It should be noted that
although the method 300 is explained using a focused ion beam from
an FIB device, an electron beam from an SEM, a rotatable stage, and
other specific elements, such selections are merely exemplary, and
components capable of equivalent functions may be used. It should
further be noted that while various embodiments of the disclosure
utilize focused ion beams and/or lasers to remove slices, other
tools, such as an ultramicrotome, could also be used for slice
removal. Such tools may also form exposed surfaces deviating from a
flat profile, which may be corrected for using one or more of the
techniques disclosed herein.
[0037] The method 300 may begin at Block 305 by loading a sample
onto the stage of the dual beam system. The stage of the dual beam
system is typically tilted to 52 degrees from the horizontal so
that the FIB impacts normal to the sample surface, and the electron
beam impacts the sample surface at 52 degrees. In some embodiments,
cross-sectional walls approximately perpendicular to the sample
surface are achieved by having the focused ion beam impact the
surface of the sample at a slight angle from the normal to account
for the Gaussian shape of the focused ion beam cross-section. A
stage tilt angle of 53 or 54 degrees can provide a more vertical
cross-section wall than a stage tilt of 52 degrees.
[0038] The method 300 may continue to Block 310 by forming fiducial
410 in surface 405 of a sample 400 in proximity to feature 412 to
be observed using the focused ion beam to facilitate accurate
positioning of the focused ion and electron beams during slice and
view processing. As shown in FIG. 4A, fiducial 410 is preferably of
a robust shape so that the centerline of fiducial 410 is readily
recognizable even after repeated scans by the focused ion beam,
which tends to erode fiducial 410. In some embodiments, fiducial
410 may be formed sufficiently close to the location of the sample
400 slicing so that the stage does not need to be moved to shift
the focused ion and electron beam positions from fiducial 410 to an
area being removed. That is, the electron beam can be shifted
sufficiently using beam deflection electrodes to image the fiducial
410 or to remove a cross section from the sample 400 without
requiring a stage movement. Fiducial 410 is used to ensure accurate
positioning of the focused ion beam and the electron beam in Blocks
315, 320, 325, 330, and 340. Beam position is obtained by
re-imaging fiducial 410 to obtain new coordinate offsets to adjust
the system for beam and stage drift. The coordinates of fiducial
410 are known, so any discrepancy between the known coordinates of
fiducial 410 and the measured coordinates of fiducial 410 produce
an offset that can be applied to the measured coordinates. In
machines that have no edge recognition capability, local beam
placement is performed solely using the fiducial 410 as a
reference. Feature 412 may be below the surface, as shown by the
dashed lines in FIG. 4A.
[0039] The method 300 may continue to Block 315 where sloping
trench 420 (FIG. 4B) in surface 405 of sample 400 is formed using
the focused ion beam. Sloping trench 420 may, for example, be
milled approximately 1 .mu.m from feature 412, have a width of
about 4 microns, and a depth in a range of from about 1.0 .mu.m to
about 3.0 .mu.m. The depth of the sloping trench 420 may depend on
the position of feature 412 below the surface. The angle of the
sloping trench 420 is sufficient so that both the focused ion beam
and the electron beam can scan a cross section 415 at the end of
sloping trench 420. Cross section 415 is typically normal to the
substrate surface and runs parallel to the direction of the line
mill. A thin, finishing cut may be made at cross section 415 to
provide a smoother surface than was provided by the focused ion
beam when the focused ion beam was removing the bulk of material to
form sloping trench 420. In some embodiments, sloping trench 420 is
dimensioned such that the electron beam may fully interrogate a
vertical wall exposed by the FIB from two or more different
orientations (of the SEM relative to the vertical wall to be
imaged), without obstruction of the electron beam by other surfaces
of the sample.
[0040] In various embodiments, the size and shape of the area to be
milled is determined through information gathered by machine
vision, which allows for accuracy and automation of the sample
processing. In machine vision, a computer is used to process image
information, usually obtained from the SEM image, to determine
physical properties of a feature such as a feature's edges, size,
and center of mass. Software used for machine vision may include,
for example, Cognex VisionPro software from Cognex Corporation,
Nantick, Mass. Typical machine vision software operates to identify
a feature in a sample region based on image properties such as
average gray level, contrast and texture. For instance, each pixel
in the image may be given an assigned value, such as a single
number, that represents a texture quality of that pixel with
respect to surrounding pixels. The feature of interest will
typically have different image properties, such as texture, from
the surrounding sample in which the feature is imaged. The feature
of interest therefore can be identified as the group of pixels
having an average texture within a certain parameter of value that
differs from the surrounding image. The machine vision software
preferably automatically locates and measures the feature of
interest in each imaged slice of the sample.
[0041] The method 300 may continue to Block 320 where, as shown in
FIG. 5, a vertical wall 505 having curtaining artifacts 545 and 550
is exposed by removing a slice of material from sloping trench 420
across cross-section 415. The slice of material may be removed from
sloping trench 420 using a focused ion beam 515 from FIB column
520. In some embodiments, the slice of material is removed by
executing a "line mill," as is shown in FIG. 5. A line mill
involves milling an essentially one dimensional line running
substantially parallel to the plane of a cross-section 415 (and
vertical wall 505). The execution of a line mill is A line mill is
also illustrated in FIGS. 2A and 2B, wherein focused ion beam 220
of FIB column 220 carrying out line mill 225 by traversing face 230
of sample 210 from left to right in a straight line in the
direction of arrows 240, focused ion beam 215 being substantially
parallel to face 230. In other embodiments, the slice of material
is removed by executing a rectangle mill with focused ion beam 515.
In one such embodiment, FIB column 520 is part of a system
configured to receive input from a user specifying a slice
thickness and remove slices of material of the specified thickness
by executing a line mill with a focused ion beam from FIB column
520.
[0042] In various embodiments, the thickness of slice removed by
the etching beam (focused ion beam 515 in the case of FIG. 5) is in
a range of from about 20 nm to about 100 nm, such as in a range of
from about 30 nm to about 60 nm, alternatively from about 35 nm to
about 45 nm, alternatively from about 35 nm to about 40 nm. In some
embodiments, thickness of the milled slice removed may be less than
about 300 nm. The width and height dimensions of the slice removed
may be, for example, in a range of from about 10 .mu.m to about 100
.mu.m.
[0043] In some embodiments, the method 300 may initially skip Block
320. In such embodiments, Blocks 325-355 are first carried out with
respect to the surface of the sample exposed at cross-section 415
in Block 315. In such embodiments, the first iteration of Block 320
will be carried out on the second surface imaged in the slice and
view processing of sample 400.
[0044] The method 300 may optionally include Block 325 where the
surface of vertical wall 505 is decorated. As used herein, the term
"decorating" refers to the light preferential etching of portions
of a surface of the sample, such as vertical wall 505, to delineate
interfaces between layers, as described, for example, in U.S. Pat.
No. 7,858,936 to Castagna and Bray for "Slice and View with
Decoration," which is owned by the application of the present
invention.
[0045] In step 328, machine-identifiable shapes are optionally
etched into the vertical wall to mark or flag the location of
surface points 555 on vertical wall 505. In some embodiments,
forming the machine-identifiable shapes may be carried out by an
electron beam directed toward vertical wall 505 in the presence of
an etch-enhancing gas, such as xenon difluoride. The electron beam
and gas preferentially etches some of the materials present on
vertical wall 505, so that the same surface points 555 can be
identified in images of the vertical wall 505 captured from
different viewing angles (e.g., at a different angle of incidence
of the interrogating beam). For example, xenon difluoride etches
silicon oxides faster than it etches silicon nitrides and so leaves
a small stair-step edge at the oxide-nitride boundary. The
thickness of material removed may, for example, be less than about
30 nm, alternatively less than about 20 nm. In some embodiments,
the depths of the machine-identifiable shapes are preferably
smaller than the slice thickness, so that the shapes are milled
away with each slice. In other embodiments, the shapes may be
milled deeper that the slice thickness so that the points are
visible from slice-to-slice to make the same points on different
slices. The shapes can be re-milled at each slice, optionally to a
depth greater than the slice thickness to propagate the point
through a series of slices.
[0046] Machine identifiable shapes can be formed at positions on
the vertical wall that appear from the image to have different
elevations, as determined either manually by an operator or
automatically using image recognition software. Alternatively,
machine-identifiable shapes could be milled in a regular pattern,
such as a rectangular rid across the surface. In some embodiments,
rather than using a milled machine-identifiable shapes, existing
sample features can be used, or a combination of existing features
and milled shaped. A pattern of points to form an elevation map of
the vertical face can be determined by using offsets from one or
more machine identifiable features or fiducials, without each of
the measurement points being individually marked. For example, a
positioning and orienting fiducial can be milled in one corner of
the sample, and then the elevation can be determined at points in a
grid pattern, with the points spaced at known distances from the
fiducial in an x-ray array, or other pattern.
[0047] The presence of machine-identifiable shapes on vertical wall
505 improves the ability of machine vision software to identify the
position of specific surface points 555 on vertical wall 505 in
images of the sample captured by the SEM at different angles of
incidence. Referring to FIGS. 6A and 6B, SEM micrographs of a face
of a sample exposed by a focused ion beam have been captured by an
electron beam while maintaining the exposed vertical wall at
different orientations relative to the electron beam. To illustrate
how machine-identifiable shapes may be used to identify the
location of specific surface points 555 on the face in different
images captured at different orientations, graphics of six
different machine-identifiable shapes have been superimposed over
each micrograph at positions corresponding to specific locations on
the sample face. The machine-identifiable shapes of FIG. 6B have
further been edited to show how the machine-identifiable shapes
would appear if rotated and imaged with the actual sample of the
micrograph. Although the degree of orientation has distorted the
images of FIG. 6B, the specific positions marked by the
machine-identifiable shapes are instantly identifiable to the human
eye. By comparison, points surrounding some of the
machine-identifiable shapes (e.g., the and machine-identifiable
shapes) lie on relatively featureless planes of the sample, and are
considerably more difficult to track between images captured at
different orientations and to distinguish from nearby points that
are also located on the relatively featureless plane.
[0048] Machine-identifiable shapes suitable for various embodiments
of the disclosure typically comprise substantially 2-D shapes
identifiable by pattern recognition algorithms of machine vision
software. Examples of suitable machine-identifiable shape shapes
include, but are not limited to, basic geometric shape, such as
circles, squares, triangles, and rectangles, and simple symbols,
such those shown in FIGS. 6A-6B, 8A-8B, and 9B-9C. Varying the
shape of machine-identifiable shapes used for surface points 555
reduces or eliminates the likelihood that a decorated point shown
in a first image of vertical wall 505 will be mistaken for a
different point marked with a machine-identifiable shape having an
identical or similar shape as the decorated point in a second image
captured after reorienting the beam relative to vertical wall 505.
A greater diversity of shapes used to mark surface points 555 will
result in a lower likelihood of misidentification. In an
embodiment, machine-identifiable shapes used to identify surface
points 555 on vertical wall 505 comprise at least two shapes.
[0049] From Block 325, the method 300 may continue to Block 330 by
capturing and storing a first image of vertical wall 505 with an
electron beam of an SEM while vertical wall is maintained at a
first orientation relative to the electron beam and/or the SEM. As
shown in FIG. 7A, a first image of vertical wall 505 may be
generated by interrogating vertical wall 505 of sample 400 with
electron beam 705 from SEM 530 as vertical wall 505 is held at a
first orientation "O" relative to electron beam 705. The electron
beam 705 is typically operated at 5 kV and uses a through-the-lens
detector. Storage of images capture by electron beam 705 may be
implemented on a computer-readable storage medium such as a
computer hard drive.
[0050] From Block 330, the method 300 may continue to Block 535 by
reorienting the vertical wall 505 relative to electron beam 705
and/or SEM 530 from the first orientation O to a second orientation
"O'." Reorientation of vertical wall 505 relative to electron beam
705 may be carried out by rotating or tilting sample 400.
Additionally or alternatively, reorientation of vertical wall 505
relative to electron beam 705 may be carried out by changing an
angle of incidence between electron beam 705 and the vertical wall
505 by translating the SEM 530 away from the longitudinal axis 710
of the SEM 530 maintained during the capturing of the first image.
In both orientation O and O', SEM 530 is aligned such that
longitudinal axis 710 intersects vertical wall 505.
[0051] Referring now to FIG. 7B, a diagram illustrating a
reorientation of vertical wall 505 relative to SEM 530 according to
an embodiment of the disclosure is shown. Reorientation of vertical
wall 505 is carried out by tilting sample 400 by an angle
.theta..sub.1 in the direction of arrow R.sub.P about an axis
normal to the viewing plain (shown as point P). The reorientation
changes the orientation of sample 400 from orientation O to
orientation O'. After reorientation of vertical wall 505, the
method 300 may continue to Block 340 by capturing and storing a
second image of vertical wall 505 at orientation O'. As shown in
FIG. 7C, the second image of vertical wall 505 may be generated by
interrogating vertical wall 505 of sample 400 with electron beam
705 from SEM 530 as vertical wall 505 is held at a first
orientation O' relative to electron beam 705.
[0052] In various embodiments, imaging of vertical walls 505 is
carried out using focused ion beam 515 of FIB column 520. In some
embodiments, the imaging steps of method 300 are carried out using
the FIB column 520, and a SEM is not used to capture the images of
vertical walls 505. In one such embodiment, a single charged
particle beam may be used instead of a dual charged particle beam
system. In other embodiments, both FIB column 520 and SEM 530 are
used to capture the images of vertical walls 505. In some
embodiments, one or more of the vertical walls may be imaged by
both FIB column 520 and SEM 530. In some embodiments, one or more
vertical walls are imaged by both FIB column 520 and SEM 530 while
one or more other vertical walls are imaged by only one of FIB
column 520 and SEM 530. In some embodiments, one or more vertical
walls are imaged by both FIB column 520 and SEM 530 while the other
vertical walls are imaged by FIB column 520 but not SEM 520, or by
SEM 530 but not FIB column 520.
[0053] From Block 340, the method 300 may continue to Block 345,
wherein 3-D coordinates corresponding to surface points 555 are
generated. In an embodiment, the 3-D coordinates for a given
surface point p.sub.i of surface points 555 comprise the x and y
coordinates of the point p.sub.i on the imaging plane (see e.g.,
FIG. 1) of vertical wall 505, as measured from an arbitrary origin,
and the elevation of the point p.sub.i.
[0054] Differences in elevations of surface points 555 on vertical
wall 505 may be determined using the first and second images
captured by SEM 530 at orientations O and O', respectively. One
point can be designated being positioned in a reference plane from
which other elevations are measured. An elevation Z.sub.i for a
given surface point p.sub.i of surface points 555 may be determined
by measuring the distances between surface point p.sub.i and a
fixed reference point in each of the first and second images, and
inputting the measured distances into the following Formula
(1):
Z i = A ' B ' _ - A B _ cos .theta. sin .theta. , Formula ( 1 )
##EQU00001##
Wherein
[0055] A.sub.i is a position of the reference point in the first
image, A.sub.i' is a position the reference point in the second
image, B.sub.i is a position of point i in the first image,
B.sub.i' is a position of point i in the second image, Z.sub.i is
the elevation relative to the height at reference point A.sub.i of
surface point i, at position B.sub.i, | A.sub.'B.sub.'| is the
distance between A.sub.i' and B.sub.i', | A.sub.B.sub.| is the
distance between A.sub.i and B.sub.i, and .theta. is the difference
of the first angle of incidence and the second angle of
incidence.
[0056] The relationship between the capturing of the first image of
vertical wall 505 of Block 330, the reorienting of vertical wall
505 of Block 335, the capturing of the second image of vertical
wall 505 of Block 340, and the variables of Formula (1) may be
better understood from the embodiments of the disclosure shown in
FIGS. 8A-9C. It the outset, it should be understood and observed by
comparing FIG. 9C to FIG. 9B and FIG. 8A to FIG. 8B, that the
distances between one or more pairs of points on a vertical wall
405 measured in the first image of the vertical wall 405 differ
from distances measured for the same pairs of points when measured
in the second image of vertical wall 405.
[0057] In FIGS. 8A and 8B, SEM images have been captured for
vertical wall 505 after being decorated by focused ion beam 515. In
FIG. 8A, SEM image 800A shows vertical wall 505 imaged by SEM 530
from the orientation O shown in FIG. 7A. Machine-identifiable
shapes B.sub.1, B.sub.2, B.sub.3, B.sub.4, B.sub.5, and B.sub.6
mark the location of points P.sub.1, P.sub.2, P.sub.3, P.sub.4,
P.sub.5, and P.sub.6, respectively. Each of distances D.sub.1,
D.sub.2, D.sub.3, D.sub.4, D.sub.5, and D.sub.6 correspond to the
values for the expression | A.sub.B.sub.| of Formula (1) for points
P.sub.1, P.sub.2, P.sub.3, P.sub.4, P.sub.5, and P.sub.6,
respectively. As described above, various embodiments of the
disclosure utilize machine vision to locate features of images
captured in method 300, and, when used in combination with
machine-identifiable shapes such as the machine-identifiable shapes
B.sub.1, B.sub.2, B.sub.3, B.sub.4, B.sub.5, and B.sub.6, the
accuracy of tracking surface points can be improved. For image
800A, machine vision may be used in combination with
machine-identifiable shapes B.sub.1, B.sub.2, B.sub.3, B.sub.4,
B.sub.5, and B.sub.6 to precisely determine the positions of points
P.sub.1, P.sub.2, P.sub.3, P.sub.4, P.sub.5, and P.sub.6, allowing
the x-y coordinates of points P.sub.1, P.sub.2, P.sub.3, P.sub.4,
P.sub.5, and P.sub.6 and the distances D.sub.1, D.sub.2, D.sub.3,
D.sub.4, D.sub.5, and D.sub.6 between P.sub.1, P.sub.2, P.sub.3,
P.sub.4, P.sub.5, and P.sub.6 and reference point A to be precisely
determined. Further, as discussed above, machine vision improves
the tracking of points between images of vertical wall 505 taken at
different orientations, such as between image 800A and 800B, by
reducing the probability of mistaking the identity of one surface
point for another.
[0058] Turning to FIG. 8B, SEM image 800B shows vertical wall 505
imaged by SEM 530 from the orientation O' shown in FIG. 7A.
Machine-identifiable shapes B.sub.1', B.sub.2', B.sub.3', B.sub.4',
B.sub.5', and B.sub.6' mark the location of points P.sub.1',
P.sub.2', P.sub.3', P.sub.4', P.sub.5', and P.sub.6', respectively.
Each of distances D.sub.1', D.sub.2', D.sub.3', D.sub.4', D.sub.5'
and D.sub.6' corresponds to the values for the expression |
A.sub.B.sub.| of Formula (1) for points P.sub.1, P.sub.2, P.sub.3,
P.sub.4, P.sub.5, and P.sub.6, respectively. Similar to FIG. 800A,
machine vision may be used to more precisely ascertain the values
of D.sub.1', D.sub.2', D.sub.3', D.sub.4', D.sub.5' and D.sub.6'.
Machine vision, used in combination with the five uniquely shaped
machine-identifiable shapes B.sub.1, B.sub.2, B.sub.3, B.sub.4,
B.sub.5, and B.sub.6 may also be used to identify the points
P.sub.1', P.sub.2', P.sub.3', P.sub.4', P.sub.5', and P.sub.6 so
that elevations Z.sub.1, Z.sub.2, Z.sub.3, Z.sub.4, Z.sub.5, and
Z.sub.6 are not inadvertently calculated using distances from the
wrong points. It should be noted that points P.sub.1-P.sub.6 and
P.sub.1'-P.sub.6' correspond to the same locations on vertical wall
505 exposed by focused ion beam 515 and imaged by SEM 530 and that
points P.sub.1-P.sub.6 and P.sub.1'-P.sub.6' are the
representations of those locations as viewed in SEM images 800A and
800B. Likewise, reference points A and A' also correspond to the
same location on sample 400. Referring again to FIGS. 7A-7C, the
angle .theta. of Formula (1) used for calculating the elevations
Z.sub.1, Z.sub.2, Z.sub.3, Z.sub.4, Z.sub.5, and Z.sub.6 is angle
.theta..sub.1 shown in FIG. 7B.
[0059] In some embodiments, to facilitate unobstructed access of
electron beam 705 to vertical wall 505 at larger values of angle
.theta., side trenches 825A and 825B may be milled by focused ion
beam 515 in Block 315 or as part of any one of Blocks 330, 335, and
340. For example, if reorientation of vertical wall 505 results in
an orientation O' wherein access to vertical wall 505 is blocked be
an obstructing portion of the sample, focused ion beam may be
utilized to remove the obstruction to allow imaging of the entire
vertical surface 505.
[0060] The orientation of vertical wall 505 relative to the
electron beam 705 and/or the SEM 530 is not limited to the
rotations shown in FIGS. 7A and 7B, and the method 300 contemplates
the use of any translation of vertical wall 505 relative to SEM 530
whereby topographical information can be extracted from images of
vertical wall 505 obtained in accordance with Blocks 330 and 340.
One such embodiment is illustrated in FIGS. 9A-9C. FIG. 9A shows a
decorated vertical wall 505 situated at an orientation o'. In FIG.
9A vertical wall 505 is rotated from orientation o' about axis 900
by an angle .theta..sub.2 in the direction of rotation indicated by
arrow R.sub.A to an orientation o''. Axis 900 overlaps or runs
parallel to the longitudinal beam axis of FIB column 520.
Illustrations of SEM images captured by SEM 530 at orientation o'
and o'' are shown in FIGS. 9B and 9C, respectively.
[0061] In FIG. 9B, SEM image 900A shows vertical wall 505 imaged by
SEM 530 while vertical wall 505 is maintained at orientation o'
relative to SEM 530. Machine-identifiable shapes b.sub.1, b.sub.2,
b.sub.3, b.sub.4, b.sub.5, and b.sub.6 mark the location of points
p.sub.1, p.sub.2, p.sub.3, p.sub.4, p.sub.5, and p.sub.6 on
vertical wall 505, respectively. Each of distances d.sub.1,
d.sub.2, d.sub.3, d.sub.4, d.sub.5, and d.sub.6 correspond to the
values for the expression | A.sub.B.sub.| of Formula (1) for points
P.sub.1, p.sub.2, p.sub.3, p.sub.4, p.sub.5, and p.sub.6,
respectively. In FIG. 9C, SEM image 900C shows vertical wall 505
imaged by SEM 530 from the orientation o'' shown in FIG. 9A.
Machine-identifiable shapes b.sub.1', b.sub.2', b.sub.3', b.sub.4',
b.sub.5', and b.sub.6' mark the location of points p.sub.1',
p.sub.2', p.sub.3', p.sub.4', p.sub.5', and p.sub.6' on vertical
wall 505, respectively. Each of distances d.sub.1', d.sub.2',
d.sub.3', d.sub.4', b.sub.5', and d.sub.6' corresponds to the
values for the expression | A.sub.B.sub.| of Formula (1) for points
p.sub.1, p.sub.2, p.sub.3, p.sub.4, p.sub.5, and p.sub.6,
respectively. Machine vision may be used to more precisely
ascertain the values of d.sub.1', d.sub.2', d.sub.3', d.sub.4',
d.sub.5' and d.sub.6'. Referring again to FIG. 9A, the angle
.theta. of Formula (1) used for calculating the elevations z.sub.1,
z.sub.2, z.sub.3, z.sub.4, z.sub.5, and z.sub.6 is angle
.theta..sub.2.
[0062] Although all of the surface points of FIGS. 8A-9C are
measured with respect to a single reference point, embodiments of
the disclosure are not so limited. Distances may be measured for
all of surface points 555 using a single reference, a different
reference point for each of surface points 555, or distances for
some of surface points 555 may be calculated from one or more
common reference points and distances for other surface points may
be calculated from unique reference points. Positions for the
reference points may be any location on or above the sample that is
visible in both the first image and the second image of the surface
point 555 being imaged. In various embodiments, reference points
and the surface points 555 are located on vertical surface 505. In
one such embodiment, a single reference point located in corner of
vertical wall 555 is used to calculate all of the elevations for
surface points 555.
[0063] In Block 345, the references points, surface points 555, or
both the reference points and surface points 555 may be randomly
generated by system 1102, selected by a human operator, selected to
facilitate more precise curve fittings, selected to satisfy a
desired balance between speed of sample processing and precision of
curve fittings, or any combination thereof. Unless prohibited by
the constraints of a particular application, selection and/or
machine-identifiable shape of the reference points and the surface
points 555 may be carried out at any time after formation of the
trench in Block 315 and before the destruction of vertical wall 505
by removal of the next slice of material in the next iteration of
method 300. Selection and machine-identifiable shape of either of
the reference points of surface points 555 may be carried out at
the same time or at different times.
[0064] From Block 345, the method may proceed to Block 350 wherein
curves are fitted to the 3-D coordinates to approximate a
topography of vertical wall 505. In an embodiment, a topography of
vertical wall 505 is approximated by applying a three-dimensional
Fourier fit to the three-dimensional coordinates of surface points
555. In another embodiment, a topography of vertical wall 505 is
approximated by applying a least squares regression to the
three-dimensional coordinates.
[0065] From Block 350, the method may proceed to Block 355 by
determining whether to carry out another iteration of slice and
view processing of sample 400 (e.g., by repeating Block 315 through
Block 350) or continue to Block 360 by terminating slice and view
processing of sample 400 and generating a 3-D image of feature 412.
To generate a 3-D image of a feature 412, it is desirable to obtain
many images, depending on the size of the feature 412 or the
desired detail of the 3-D image. In Block 355 the iterations of the
slice and view technique are counted as processing of sample 400
progresses. In an embodiment, slice and view processing is carried
out until a predetermined number of slice and view iterations have
been carried out. In another embodiment, termination of slice and
view iterations is initiated in response to the occurrence of a
particular trigger event. In yet another embodiment, termination of
slice and view processing depends on whether additional input is
received by the slice and view processing system after a certain
number of slice and view iterations have been carried out. In any
case, if it is determined that slice and view processing of sample
400 should continue, the method 300 proceeds from Block 355 to
Block 360 along the "No" path. If it is determined that the
reiterative slicing process has concluded, the method 300 proceeds
from Block 355 to Block 360 along the "Yes" path.
[0066] In Block 360, a 3-D representation of feature 412 is
generated from data generated during slice and view processing of
sample 400. In various embodiments, the 3-D image of feature 412 is
constructed from a stack of modified slice images of vertical walls
505. In one such embodiment, a single slice image for each of
vertical walls 505 is selected for modification. The single slice
images may be selected from one of the first and second images
captured by SEM 530 for each of the vertical walls 505, or other
SEM images of the vertical walls 505 may be used. Each of the
single slice images are modified by bending the slice image to
conform to the 3-D curve fitted to the vertical surface 405
represented by the slice image. That is, each of the single slice
images assumes a 3-dimensional curvature corresponding to the
topography of the vertical wall 505 represented by the single slice
image. Each of the modified slice images are then arranged in the
stack according to the position of the vertical surface 405
represented by the slice image in sample 400 relative to the other
slices. Alternatively, the slice images may be arranged in the
stack and then modified. After modification and arrangement of the
slice images, the 3-D image of feature 412 is formed from the
modified and arranged slice images. By modeling sample 400 using
the modified slice images having 3-D curvatures representative of
the topography of the slice images rather than assuming each image
represents a flat 2-D plane, the effects of curtaining on the
resolution and/or image quality of 3-D representation may be
reduced or eliminated because more accurate representations of the
imaged surfaces are being used to model the 3-D image of the
slice-and-viewed feature (e.g., feature 412).
[0067] The modeling of feature 412 may be carried out by
commercially available software in conjunction with supplemental
computer-executable instructions that, when executed, bend the
slice images used by the commercially available software to
generate the 3-D representation into the shapes of the fitted
curves corresponding to the slice images. Alternatively, the
supplemental computer-executable instructions may modify the
commercially available software to accept as input slice images
already bent into the shapes of the fitted curves corresponding to
the slice images. Software for 3-D construction may preferably
include, for example, Amira three-dimensional imaging software from
Visage Imaging, Inc. San Diego, Calif., or Avizo three-dimensional
visualization software from VSG, Visualization Sciences Group, Inc.
Burlington, Mass.
[0068] An apparatus for performing the methods described above is
shown in FIG. 3. illustrating a typical dual beam system 1010 with
a vertically mounted SEM column and a focused ion beam (FIB) column
mounted at an angle of approximately 52 degrees from the vertical.
Such dual beam systems are commercially available, for example,
from FEI Company, Hillsboro, Oreg., the assignee of the present
application. While an example of suitable hardware is provided
below, the invention is not limited to being implemented in any
particular type of hardware.
[0069] A scanning electron microscope 1041, along with power supply
and control unit 1045, is provided with the dual beam system 1010.
An electron beam 1043 is emitted from a cathode 1052 by applying
voltage between cathode 1052 and an anode 1054. Electron beam 1043
is focused to a fine spot by means of a condensing lens 1056 and an
objective lens 1058. Electron beam 1043 is scanned
two-dimensionally on the specimen by means of a deflection coil
1060. Operation of condensing lens 1056, objective lens 1058, and
deflection coil 1060 is controlled by power supply and control unit
1045.
[0070] Electron beam 1043 can be focused onto substrate 1022, which
is on movable X-Y stage 1025 within lower chamber 1026. When the
electrons in the electron beam strike substrate 1022, secondary
electrons are emitted. These secondary electrons are detected by
secondary electron detector 1040 as discussed below. STEM detector
1062, located beneath the TEM sample holder 1024 and the stage
1025, can collect electrons that are transmitted through the sample
mounted on the TEM sample holder as discussed above.
[0071] Dual beam system 1010 also includes focused ion beam (FIB)
system 1011 which comprises an evacuated chamber having an upper
neck portion 1012 within which are located an ion source 1014 and a
focusing column 1016 including extractor electrodes and an
electrostatic optical system. The axis of focusing column 1016 is
tilted 52 degrees from the axis of the electron column. The ion
column 1012 includes an ion source 1014, an extraction electrode
1015, a focusing element 1017, deflection elements 1020, and a
focused ion beam 1018. Focused ion beam 1018 passes from ion source
1014 through focusing column 1016 and between electrostatic
deflection means schematically indicated at 1020 toward substrate
1022, which comprises, for example, a semiconductor device
positioned on movable X-Y stage 1025 within lower chamber 1026.
[0072] Stage 1025 can preferably move in a horizontal plane (X and
Y axes) and vertically (Z axis). Stage 1025 can also tilt
approximately sixty (60) degrees and rotate about the Z axis. In
some embodiments, a separate TEM sample stage (not shown) can be
used. Such a TEM sample stage will also preferably be moveable in
the X, Y, and Z axes. A door 1061 is opened for inserting substrate
1022 onto X-Y stage 1025 and also for servicing an internal gas
supply reservoir, if one is used. The door is interlocked so that
it cannot be opened if the system is under vacuum.
[0073] An ion pump 1028 is employed for evacuating neck portion
1012. The chamber 1026 is evacuated with turbomolecular and
mechanical pumping system 1030 under the control of vacuum
controller 1032. The vacuum system provides within chamber 1026 a
vacuum of between approximately 1.times.10.sup.-7 Torr and
5.times.10.sup.-4 Torr. If an etch assisting, an etch retarding
gas, or a deposition precursor gas is used, the chamber background
pressure may rise, typically to about 1.times.10.sup.-5 Torr.
[0074] The high voltage power supply provides an appropriate
acceleration voltage to electrodes in focusing column 1016 for
energizing and focusing ion beam 1018. When it strikes substrate
1022, material is sputtered, that is physically ejected, from the
sample. Alternatively, ion beam 1018 can decompose a precursor gas
to deposit a material.
[0075] High voltage power supply 1034 is connected to liquid metal
ion source 1014 as well as to appropriate electrodes in ion beam
focusing column 1016 for forming an approximately 1 keV to 60 keV
ion beam 1018 and directing the same toward a sample. Deflection
controller and amplifier 1036, operated in accordance with a
prescribed pattern provided by pattern generator 1038, is coupled
to deflection plates 1020 whereby ion beam 1018 may be controlled
manually or automatically to trace out a corresponding pattern on
the upper surface of substrate 1022. In some systems the deflection
plates are placed before the final lens, as is well known in the
art. Beam blanking electrodes (not shown) within ion beam focusing
column 1016 cause ion beam 1018 to impact onto blanking aperture
(not shown) instead of substrate 1022 when a blanking controller
(not shown) applies a blanking voltage to the blanking
electrode.
[0076] The liquid metal ion source 1014 typically provides a metal
ion beam of gallium. The source typically is capable of being
focused into a sub one-tenth micrometer wide beam at substrate 1022
for either modifying the substrate 1022 by ion milling, enhanced
etch, material deposition, or for the purpose of imaging the
substrate 1022.
[0077] A charged particle detector 1040, such as an Everhart
Thornley or multi-channel plate, used for detecting secondary ion
or electron emission is connected to a video circuit 1042 that
supplies drive signals to video monitor 1044 and receiving
deflection signals from a system controller 1019. The location of
charged particle detector 1040 within lower chamber 1026 can vary
in different embodiments. For example, a charged particle detector
1040 can be coaxial with the ion beam and include a hole for
allowing the ion beam to pass. In other embodiments, secondary
particles can be collected through a final lens and then diverted
off axis for collection.
[0078] A micromanipulator 1047, such as the AutoProbe 1000.TM. from
Omniprobe, Inc., Dallas, Tex., or the Model MM3A from Kleindiek
Nanotechnik, Reutlingen, Germany, can precisely move objects within
the vacuum chamber. Micromanipulator 1047 may comprise precision
electric motors 1048 positioned outside the vacuum chamber to
provide X, Y, Z, and theta control of a portion 1049 positioned
within the vacuum chamber. The micromanipulator 1047 can be fitted
with different end effectors for manipulating small objects. In the
embodiments described herein, the end effector is a thin probe
1050.
[0079] A gas delivery system 1046 extends into lower chamber 1026
for introducing and directing a gaseous vapor toward substrate
1022. U.S. Pat. No. 5,851,413 to Casella et al. for "Gas Delivery
Systems for Particle Beam Processing," assigned to the assignee of
the present invention, describes a suitable gas delivery system
1046. Another gas delivery system is described in U.S. Pat. No.
5,435,850 to Rasmussen for a "Gas Injection System," also assigned
to the assignee of the present invention. For example, iodine can
be delivered to enhance etching, or a metal organic compound can be
delivered to deposit a metal.
[0080] System controller 1019 controls the operations of the
various parts of dual beam system 1010. Through system controller
1019, a user can cause ion beam 1018 or electron beam 1043 to be
scanned in a desired manner through commands entered into a
conventional user interface (not shown). Alternatively, system
controller 1019 may control dual beam system 1010 in accordance
with programmed instructions stored in a memory 1021. In some
embodiments, dual beam system 110 incorporates image recognition
software, such as software commercially available from Cognex
Corporation, Natick, Mass., to automatically identify regions of
interest, and then the system can manually or automatically extract
samples in accordance with the invention. For example, the system
could automatically locate similar features on semiconductor wafers
including multiple devices, and take samples of those features on
different (or the same) devices.
[0081] It various embodiments, it may be desirable to carry out
method 300 with a beam system. In some such embodiments, the beam
system is a dual charged particle beam system comprising an etching
beam column, configured to expose surfaces of the sample by
emitting an etching beam that removes material from the sample, and
an interrogating beam column, configured to image the surfaces
exposed by emitting an interrogating beam.
[0082] Referring now to FIG. 11, a block diagram of an embodiment
of a slice and view dual charged particle beam system 1102 is
shown. System 1102 comprises a control sub-system 1104, an etching
beam sub-system 1130, an interrogating beam sub-system 1140, and a
stage 1150 configured to work in cooperation to carry out slice and
view processing of a sample such as, for example, sample 1160.
Sample 1160 comprises a sample volume 1161 containing all or part
of a feature 1170 to be observed by removing slices 1168 of sample
volume 1161 and imaging surfaces 1162 exposed by removal of slices
1168. The slices may be cut such that each of the slices 1168 is a
vertical wall 1164 (i.e., normal the base plane of sample 1160 in
contact with stage 1150) of a trench 1180 formed in a surface of
sample 1160. By carrying out a slice and view processing of sample
1160 using system 1102, a 3-D representation (e.g., a 3-D image) of
feature 1170 may be formed.
[0083] Etching beam sub-system 1130 comprises an etching beam
column 1131 configured to emit an emit etching beam 1139 and to
remove slices 1168 by emitting etching beam 1139. In an embodiment,
etching beam column 1131 is a FIB column 1132 configured to emit a
focused ion beam 1134. In another embodiment, etching beam column
1131 is a laser 1136 comprising laser beam 1138. Still other
embodiments comprise multiple etching beam columns and/or types of
etching beam columns. Etching beam sub-system is configured to
carry out removal of material in accordance with material removal
instructions 1109 stored on computer-readable storage medium
1106.
[0084] Interrogating beam sub-system 1140 comprises interrogating
beam column 1141, which is configured to emit interrogating beam
1143 to capture images of surfaces 1162 of sample 1160 exposed by
etching beam sub-system 1130. In an embodiment, interrogating beam
column 1141 is a SEM 1142 and interrogating beam 1143 is an
electron beam 1144. In another embodiment, interrogating beam
column 1141 is a FIB device and interrogating beam 1143 is a
focused ion beam. Embodiments of system 1102 are not limited to a
single interrogating beam column, a single type of interrogating
beam column, or a single type of interrogating beam. In various
embodiments, interrogating beam 1141 is configured to interrogate
surfaces 1162 from different angles of incidence such that images
of the surfaces may be captured from different perspectives as
described above.
[0085] In various embodiments, a single beam column is used in both
etching beam sub-system 1130 and interrogating beam sub-system
1140. That is, some embodiments of the disclosure comprise a beam
column configured to emit etching beam 1131 for removing slices
1168 from sample 1160, decorating surfaces 1162, and/or forming
trench 1180 and also an interrogating beam 1141 for imaging
surfaces 1162 exposed by etching beam 1131. In some embodiments,
the slice and view beam system comprises a single charged particle
beam column capable of removing material from a sample and imaging
surfaces exposed by removing material from the sample. In one such
embodiment, the single charged particle beam column is an FIB
device, configured to emit both etching beams and interrogating
beams. In other embodiments, the slice and view beam system
comprises a dual charged particle beam system 1102 comprising an
etching beam column 1131 and a separate interrogating beam column
1140, wherein the etching beam column 1131 is capable of emitting
both etching beam 1139 and interrogating beam 1143. In such
embodiments, the dual charged particle beam system 1102 is
configured to operate in at least two of the following three modes.
In the first mode, etching beam column 1131 carries out etching
tasks (e.g., removing slices, decorating surfaces, forming
trenches) and the interrogating tasks (e.g., capturing the first
images and the second images), and interrogating beam column 1141
carries out neither etching tasks nor interrogating tasks. In the
second mode, etching beam column 1131 carries out etching tasks and
interrogating tasks, and interrogating beam column 1141 also
carries out interrogating tasks but not etching tasks. In the third
mode, etching beam column 1131 carries out etching tasks but not
interrogating tasks, and interrogating beam column 1141 carries out
interrogating tasks but not etching tasks. In one such dual charged
particle beam system 1102, the etching beam column 1131 is a FIB
device and the interrogating beam column 1141 is a SEM. The FIB
device can also be used to form an image and so can function as
both the etching beam and the interrogating beam. An electron beam
can etch in the presence of an etch precursor gas, as well as
forming an image.
[0086] Stage 1150 supports sample 1150 during slice and view
processing. In various embodiments, stage 1150 is rotatable and
configured to rotate in directions and to degrees allowing an
surface 1163 of sample 1162 to be imaged from different angles of
incidence by interrogating beam 1143. Stage 1025, as described
above, is an example of a stage suitable for use in system
1102.
[0087] Control sub-system 1104 comprises a computer-readable
storage medium 1106, a display device 1118, human interface 1120,
and one or more processors 1123. Computer-readable storage medium
1104 stores processor accessible information comprising executable
instructions 1108, 2-D images captured by interrogating beam system
1140, such as SEM images 1116 captured by SEM column 530, and 3-D
representations 1117 of feature 412 generated by information (e.g.,
SEM images of exposed samples surfaces, 3-D coordinates of points
on the exposed surfaces) obtained via slice and view processing of
sample 1160. Computer-readable storage medium 1104 is coupled to
one or more processors 1123 such that one or more processors 1123
can read and execute executable instructions 1108, process data
acquired from at least one of sub-systems 1130 and 1140, human
interface 1120, and stage 1150 in accordance with executable
instructions 1108, direct the writing of data acquired from at
least one of sub-systems 1130 and 1140, human interface 1120, and
stage 1150 to computer-readable storage medium 1106.
Computer-readable storage medium may be a device capable of storing
information for a period of time in a format readable by a
computer, such as a hard drive. Examples of suitable
computer-readable storage mediums include, but are not limited to,
PATA, SATA, SCSI, and SSD hard drives.
[0088] Display device 1118 may be configured to display information
from one or more of sub-systems 1104, 1130, 1150, and stage 1150.
Display device 1118 projects electronically generated images, which
may include, for example, 3-D representations 1117 generated from
the slice and view processing of sample 1160, SEM images 1116
captured with respect to surfaces 1162, 3-D representations of
curves fitted to topographies of surfaces 1162, or any combination
thereof. Examples of suitable display devices include, but are not
limited to, LCD displays, plasma displays, cathode rays tube
displays, and wall projectors.
[0089] Human interface 1120 comprises devices 1121 configured to
enable human interaction with sub-systems 1104, 1130,1140, and
1150. Human interaction with sub-systems 1104, 1130,1140, and 1150
may include, for example, the inputting by a human operator of
instructions and/or data 1122 for controlling slice and view
processing of a sample and/or for manipulating experimental data
produced therefrom. Examples of devices suitable for human
interface 1120 include, but are not limited to, keyboards, computer
mice, touch interfaces such as tablet computers, or any combination
thereof. Human interface 1120 also comprises executable
instructions for managing the interactions of human operators with
system 1102.
[0090] One or more processors 1123 carry out executable
instructions 1108 stored on computer-readable storage medium 1106,
thereby controlling sub-systems 1131 and 1140. One or more
processors 1123 also read and send information to display device
1118 for viewing by a human operator and/or observer. For example,
in various embodiments one or more processors 1123 access 3-D
representations 1117 and/or SEM images 1116 stored on
computer-readable storage medium 1106. In such embodiments, one or
more processors 1123 also direct display device 1118 to display 3-D
representations 1117 and/or SEM images 11116. One or more
processors 1123 further process instructions and/or data 1122 in
accordance with executable instructions 1108 and direct the storage
of data acquired from sub-systems 1130 and 1140, human interface
1120, and stage 1150 on computer-readable storage medium 1106.
[0091] Embodiments of slice and view processing of the disclosure,
such as method 300 described above, may be carried out by system
1102 according to executable instructions 1108 stored on
computer-readable storage medium 1106 of system 1102. Executable
instructions 1108 comprise material removal instructions 1109,
machine vision software 1110, image capture instructions 1112,
reorienting instructions 1113, topography characterization
instructions 1114, and 3-D imaging software 1115.
[0092] Material removal instructions 1109 include instructions for
removing slices 1168 to expose surfaces 1162. Material removal
instructions 1109, when executed, cause one or more processors 1123
to direct etching beam 1139 to remove slices 1168 in sequential
order across a thickness of sample volume 1161, the removal of each
slice 1169 exposing a surface 1163 of surfaces 1162.
[0093] In various embodiments, material removal instructions 1109
include additional instructions that, when executed, cause the one
or more processors 1123 to direct etching beam 1139 to carry out
one or more other material removal tasks. The other material
removal tasks include, but are not limited to, milling sloping
trench 1190 such that interrogating beam 1144 can interrogate an
exposed surface 1163 without being obstructed by other portions of
sample 1160; milling a fiducial near sample 1160 to facilitate
accurate positioning of etching beam 1139; milling side trenches
1120 such that interrogating beam 1144 can capture second images of
surfaces 1162 at greater degrees of stage rotation and/or beam
repositioning (e.g., steps 335 and 340 of method 300, supra)
without being obstructed by other portions of sample 1160; milling
machine-identifiable shapes on surfaces 1162 (e.g., steps 335 and
340 of method 300, supra); and any combination thereof.
[0094] For each exposed surface 1163, the one or more processors
1123 direct components of system 1102 to carry out one or more
image capture instructions 1110. Image capture instructions 1110,
when executed, cause one or more processors 1123 to direct
interrogating beam 1143 to interrogate an exposed surface 1163
while substantially maintaining a first angle of incidence between
a longitudinal axis of the interrogating beam column 1141 and
exposed surface 1163, thereby capturing a first image of exposed
surface 1163. Image capture instructions 1110, when executed, cause
one or more processors 1123 to direct interrogating beam 1143 to
interrogate exposed surface 1163 while substantially maintaining a
second angle of incidence between a longitudinal axis of the
interrogating beam column 1141 and exposed surface 1163, thereby
capturing a second image of exposed surface 1163. The image
information recorded by interrogating beam 1142 is processed by the
one or more processors 1123 using machine vision software 1112, and
one or more processors 1123 may direct the captured images to be
stored in the machine-readable storage medium 1106. Additional
information, including examples of machine vision software suitable
for embodiments of system 1102 is described in more detail
above.
[0095] The changing of the first angle of incidence to the second
angle of incidence is carried out by executing reorienting
instructions 1113. Reorienting instructions 1113 include
instructions for changing the angle of incidence of interrogating
beam 1143 on exposed surface 1163 after the first image of exposed
surface 1163 has been captured by interrogating beam 1143.
Additionally or alternatively, reorienting instructions 1113
include instructions for changing the angle of incidence of
interrogating beam 1143 on exposed surface 1163 by directing a
translation of interrogating beam column 1141 away from a
longitudinal axis of interrogating beam column during interrogation
of exposed surface 1163 at the first angle of incidence. The degree
of reorientation should be such that values of distances between
pairs of points 1165 measured in the second image of exposed
surface 1163 are different than values of distances measured
between the same pairs of points 1165 in the first image of exposed
surface 1163. Executable instructions 1108, when executed, cause
one or more processors 1123 to carry out the image capture
instructions 1110 for capturing the second image after an execution
of reorienting instructions reorientation 1113 has taken place and
before a removal of a slice 1168.
[0096] Topography characterization instructions 1114 include
instructions that, when executed, cause the one or more processors
1123 to generate curves 1111 fitted to topographies of surfaces
1162. Topography characterization instructions 1114 include
instructions to record first positions of pairs of points 1165 in
the first image and second positions of pairs of points 1165 in the
second image, wherein each pair of points 1165 comprises a
reference point 1167 and a point 1166 on exposed surface 1163.
[0097] For each pair of points 1165, reference point 1167 refers to
a fixed position relative to point 1166 on exposed surface 1163.
The reference point 1167 of pairs of points 1165 may be the same
reference point (e.g., points B.sub.1-B.sub.6 in FIGS. 8A-8B and
9B-9C all refer to a common reference point A), a different
reference point may be used for each pair of points 1165, or some
of pairs of points 1165 may share common reference points while the
reference points of other pairs of points 1165 are unique.
Positions for the reference points 1167 may be any location on or
above the sample visible in both the first image and the second
image of the exposed surface 1163 being imaged. In various
embodiments, both the reference points 1167 and pairs of points
1165 are located on the exposed surface 1163. In one such
embodiment, a reference point 1167 is selected for each of pairs of
points 1165 at a position on exposed surface 1163 near or
overlapping a corner of exposed surface 1163.
[0098] The quantity of pairs of points 1165 and the position of at
least one of reference point 1167 and point 1166 for each of the
pair of points 1165 may be generated, randomly or otherwise,
according to topography characterization instructions 1114 executed
by one or more processors 1123, input via human interface 1120 by a
human operator, or a combination thereof. The quantity of pairs of
points 1165 and the position of at least one of reference point
1167 and point 1166 for each of the pair of points 1165 may be
selected to facilitate the generation of more precise fitted curves
1111, selected to satisfy a desired balance between speed of sample
processing and precision the fitted curves 1111 generated, or any
combination thereof.
[0099] In various embodiments, the system 1102 utilizes machine
vision software 1112 to ascertain the positions of reference points
1167 and points 1166. Machine vision software 1112 may determine
positions of the reference points 1167 and points 1166 immediately
by immediately processing the image information as it is obtained
by interrogating beam 1143, or processing may occur at a later
time, such as after the imaging of the last surface 1162.
[0100] In various embodiments, the execution of topography
characterization instructions 1114 may be facilitated by milling
machine-identifiable shapes on the exposed surface 1163 at
positions corresponding to points of pairs of points 1165. In such
embodiments, the material removal instructions 1109 comprise
instructions for milling machine-identifiable shapes on one or more
of surfaces 1162 at positions corresponding to reference points
1167, points 1166, or both the reference points 1167 and points
1166 of pairs of points 1165. The presence of machine-identifiable
shapes on surfaces 1162 improves the ability of machine vision
software 1112 to track the position of the reference points 1167
and points 1166 on an exposed surface 1163 from the first image to
the second image (i.e., find the same positions on the surface
exposed in both images). The machine-identifiable shapes may
comprise one or more substantially 2-dimensional shapes
identifiable by pattern recognition algorithms of machine vision
software 1112. Examples of suitable machine-identifiable shape
shapes include, but are not limited to basic geometric shape, such
as circles, squares, triangles, and rectangles, and simple symbols,
such as the symbols shown in FIGS. 6A-6B, 8A-8B, and 9B-9C. In
various embodiments, material removal instructions 1109 comprises
instructions for providing surfaces 1162 with differently-shaped
machine-identifiable shapes. Varying the shape of
machine-identifiable shapes used for points on an exposed surface
1163 reduces or eliminates the likelihood that points shown in the
first image of the exposed surface 1163 will be mistaken for
different points having the same or a similar shape of
machine-identifiable shape in the second image of the exposed
surface 1163. The likelihood of misidentification of misidentifying
points on exposed surface 1163 decreases as the diversity of
machine-identifiable shape shapes employed increases. In an
embodiment, the machine-identifiable shapes used to identify points
on an exposed surface 1163 comprise at least two shapes. In another
embodiment, a different machine-identifiable shape is used to mark
each of points 1166 on an exposed surface 1163.
[0101] Topography characterization instructions 1114 include
instructions to determine elevations for each of points 1166 using
the following Formula (2):
Z = A ' B ' _ - AB _ cos .theta. sin .theta. , Formula ( 2 )
##EQU00002##
wherein Z is the elevation of the point 1166, A is a position of
the reference point 1167 in the first image, A' is a position of
the reference point 1167 in the second image, B is a position of
point 1166 on exposed surface 1163 in the first image, B' is a
position of the point 1166 on exposed surface 1163 in the second
image, | A.sub.B.sub.| is the distance between A' an B', |
A.sub.B.sub.| is the distance between A and B, and .theta. is the
difference between the first angle of incidence and the second
angle of incidence.
[0102] Topography characterization instructions 1114 further
include instructions to generate 3-D coordinates for each of points
1166. In an embodiment, the coordinates of each point 1166
comprises the x and y coordinates of the point 1166 on the imaging
plane (see FIG. 1), as measured from an arbitrary origin, and the
elevation of the point 1166, as determined by Formula (1).
Topography characterization instructions 1114 further comprises
executable algorithms for fitting 3-D curves to the 3-D
coordinates. Examples of algorithms suitable for fitting 3-D curves
to the 3-D coordinates include, but are not limited to, least
squares regression and Fourier Transform analysis.
[0103] System 1102 utilizes 3-D imaging software 1115 to generate
3-D representations of features 1170 processed by system 1102. The
executable instructions 1108 of system 1102 may comprise
instructions for generating 3-D representations of feature 1170
after slice and view processing feature 1170 according to
executable instructions 1108 using system 1102. 3-D imaging
software 1115 may include executable instructions that, when
executed, use the 3-D fitted curves 1111 to eliminate or reduce the
effect of curtaining on the resolution and/or image quality of 3-D
representation 1117. In an embodiment, system 1102 comprises 3-D
imaging software 1115 that, when executed by one or more processors
1123, generates 3-D representations of a feature 1170 processed
according to slice and view processing using images of surfaces
1163 and assuming that surfaces 1163 are flat. System 1102 further
comprises supplemental executable instructions that, when executed
by one or more processors 1123, modify execution of 3-D imaging
software 1115 by bending the images of surfaces 1163 to correspond
to fitted curves 1111, and then using the bent images of surfaces
1163 (instead of the flat images of surfaces 1163) to generate the
3-D representation of feature 1170.
[0104] In various embodiments, system 1102 is configured to carry
out the steps of method 300. In some embodiments, system 1102 is
configured to coordinate the execution of executable instructions
1109, 1110, 1112, 1113, 1114, and 1115 (e.g., via a set of
executable coordinating instructions). In one such embodiment,
system 1102 is configured to carry out image capture instructions
1110 before and after reorienting instructions 1113 for each
surface 1163 exposed by removal of a slice 1168. In said
embodiment, system 1102 is also configured to execute topography
characterization instructions 1114 on the sets of 3-D coordinates
generated for one or more of surface 1162. In embodiments utilizing
machine-identifiable shapes, system 1102 is configured to execute
material removal instructions for decorating surfaces 1162 after
exposure of each exposed surface 1163 and before the first
execution of image capture instructions 1110 for the same exposed
surface 1163. System 1102 may be configured to carry out executable
instructions 1108 automatically, semi-automatically, by
instructions manually entered into human interface 1120 by a human
operator, or any combination thereof. System 1102 may be configured
to determine the appropriate number of surfaces to be sliced and
viewed given one or more parameters (e.g., desired resolution, time
available to complete processing, sample characteristics, etc.),
which may be stored on computer-readable storage medium 1106, input
by a human operator via human interface 1120, or a combination
thereof. System 1102 may be configured to iteratively slice and
view the sample 1160 a number of times determined by system 1102 to
be appropriate for a given set of parameters, each slice and view
iteration carried out via execution of executable instructions
1109, 1110, 1112, 1113, 1114, and 1115. It should be understood
that executable instructions 1109-1115 are illustrated in FIG. 11
as discrete blocks to facilitate understanding of various
embodiments of the disclosure, and do not imply limitations of
functionality for system 1102.
[0105] System 1102 may be utilized in sample processing environment
1100. Examples of sample processing environment 1100 include, but
are not limited to, laboratories and other experimental facilities
for carrying out analysis of biological samples, failure analysis
of mechanical components, quality control in material manufacture,
and defect testing of electronic components such as silicon wafers
and other semiconductor components.
[0106] While embodiments of the invention have been shown and
described, modifications thereof can be made by one skilled in the
art without departing from the spirit and teachings of the
invention. The embodiments described herein are exemplary only, and
are not intended to be limiting. Many variations and modifications
of the invention disclosed herein are possible, and alternative
embodiments that result from combining, integrating, and/or
omitting features of the embodiments disclosed herein are also
within the scope of the invention. Where numerical ranges or
limitations are expressly stated, such express ranges or
limitations should be understood to include iterative ranges or
limitations of like magnitude falling within the expressly stated
ranges or limitations (e.g., from about 1 to about 10 includes, 2,
3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For
example, whenever a numerical range with a lower limit, R.sub.1 and
an upper limit, R.sub.u, is disclosed, any number falling within
the range is specifically disclosed. In particular, the following
numbers within the range are specifically disclosed:
R=R.sub.1+k*(R.sub.u-R.sub.1), wherein k is a variable ranging from
1 percent to 100 percent with a 1 percent increment, i.e., k is 1
percent, 2 percent, 3 percent, 4 percent, 5 percent, 50 percent, 51
percent, 52 percent, 95 percent, 96 percent, 97 percent, 98
percent, 99 percent, or 100 percent. Moreover, any numerical range
defined by two R numbers as defined in the above is also
specifically disclosed. Use of the term "optionally" with respect
to any element of a claim is intended to mean that the subject
element is required, or alternatively, is not required. Both
alternatives are intended to be within the scope of the claim. Use
of broader terms such as "comprises," "includes," "having," etc.
should be understood to provide support for narrower terms such as
"consisting of," "consisting essentially of," "comprised
substantially of," etc.
[0107] Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made to the embodiments
described herein without departing from the spirit and scope of the
invention as defined by the appended claims. Moreover, the scope of
the present application is not intended to be limited to the
particular embodiments of the process, machine, manufacture,
composition of matter, means, methods and steps described in the
specification. As one of ordinary skill in the art will readily
appreciate from the disclosure of the present invention, processes,
machines, manufacture, compositions of matter, means, methods, or
steps, presently existing or later to be developed that perform
substantially the same function or achieve substantially the same
result as the corresponding embodiments described herein may be
utilized according to the present invention. Accordingly, the
appended claims are intended to include within their scope such
processes, machines, manufacture, compositions of matter, means,
methods, or steps.
[0108] Accordingly, the scope of protection is not limited by the
description set out above but is only limited by the claims which
follow, that scope including all equivalents of the subject matter
of the claims. Each and every claim is incorporated into the
specification as an embodiment of the present invention. Thus, the
claims are a further description and are an addition to the
embodiments of the present invention. The discussion of a reference
in the Detailed Description of the Embodiments is not an admission
that it is prior art to the present invention, especially any
reference that may have a publication date after the priority date
of this application.
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