U.S. patent number 3,629,577 [Application Number 04/859,791] was granted by the patent office on 1971-12-21 for method and apparatus for producing a stereo image by electron microscopy.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Jurgen Gullasch, Ulrich Weber.
United States Patent |
3,629,577 |
Weber , et al. |
December 21, 1971 |
METHOD AND APPARATUS FOR PRODUCING A STEREO IMAGE BY ELECTRON
MICROSCOPY
Abstract
For producing a stereo image, for example of a crystalline
object, by electron beam microscopy, any chosen surface area of the
object is rotated about a central axis defined by the direction of
the electron beam. The amount of rotation is such that after a
subsequent tilting of the object about a second axis intersecting
the central axis, the image intensity of the surface area is the
same in the starting position as in the end position of the tilting
displacement. Respective individual pictures are taken in these two
object positions.
Inventors: |
Weber; Ulrich (Karlsruhe,
DT), Gullasch; Jurgen (Minderslachen, DT) |
Assignee: |
Siemens Aktiengesellschaft
(Berlin, DT)
|
Family
ID: |
5706761 |
Appl.
No.: |
04/859,791 |
Filed: |
September 22, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Sep 23, 1968 [DT] |
|
|
P 17 89 019.6 |
|
Current U.S.
Class: |
250/307; 250/310;
250/442.11 |
Current CPC
Class: |
H01J
37/20 (20130101) |
Current International
Class: |
H01J
37/20 (20060101); H01j 037/26 () |
Field of
Search: |
;250/49.5R,49.5A,49.5B,60,61 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Nelms; D. C.
Claims
We claim:
1. The method of producing electron-microscopic stereo images by
sequentially taking pairs of stereoscopically coordinated
individual pictures, which comprises exposing the object to be
imaged to a beam of electrons whose direction defines a central
axis, rotating the object surface area to be photographed about
said central axis, then tilting the object an angular amount equal
to the stereo angle about a second axis intersecting said central
axis, the rotation about said central axis being in an angular
amount at which the image brightness of said area is the same in
the starting and end positions respectively of the tilting, and
taking first and second pictures of the object when said
electron-irradiated surface area is in said two positions
respectively.
2. The method of producing electron-microscopic stereo images by
sequentially taking pairs of stereoscopically coordinated
individual pictures, which comprises exposing the objects to be
imaged to a beam of electrons whose direction defines a central
axis, adjusting an adjustable axis to be parallel to or in
coincident relation with the normal of the object surface area to
be photographed, said adjustable axis being noncoincident with said
central axis, and rotating said object surface area about said
adjustable axis an angular amount equal to the stereo angle, said
angular amount corresponding to the angle formed between said
central and said adjustable axes.
3. The method according to claim 1, which comprises rotationally
adjusting the object about a third axis for obtaining a surface
brightness intensity, sufficient to permit said pictures to record
a stereoscopic image before said object surface area is rotated
about said central axis, said third axis passing through the
intersection of said central and second axes and extending
transversely to each of said latter two axes.
4. The method according to claim 1, wherein said central axis and
said second axis are perpendicular to each other.
5. The method according to claim 4, which comprises mounting said
object on the intersection of said central and second axes.
6. The method according to claim 1, which comprises rotationally
adjusting the object about a third axis for obtaining a desired
surface brightness intensity, sufficient to permit said pictures to
record a stereoscopic image before said object surface area is
rotated about said central axis.
7. In apparatus for producing electron-microscopic stereo images by
sequentially taking pairs of stereoscopically coordinated
individual pictures having means for producing an electron beam in
a direction defining a central axis, a device for holding a
specimen object on said central axis, and means for
photographically taking individual pictures of the
electron-illuminated object, the improvement according to which
said device comprises a cardanic joint assembly, of gimbal
structures, having three cardanic journal axes of which one is
coincident with said central axis, said three axes having a common
intersection on said central axis, an object support mounted on
said assembly near said intersection for holding the object on said
intersection, whereby said device permits rotating any chosen
surface area of the object about said central axis and then tilting
the object through the stereo angle about one of said other axes
between two picture-taking positions in which the chosen area has
substantially the same brightness, said gimbal structures
comprising a quadrangular frame at whose center point said
intersection is located, said frame having two coaxial pivot pins
protruding from opposite frame sides, a first U-shaped gimbal
member on whose two legs said respective pivot pins are mounted to
permit rotation of said frame about one of said cardanic journal
axes, two further pivot pins protruding from the other two sides
respectively of said frame and defining another one of said journal
axes, a second U-shaped gimbal member fastened to said other pivot
pins for rotation about said other journal axis, said object
support being fastened to said second gimbal member, a slider
displaceable transversely of said central axis, an axle mounted on
said slider and having an axis perpendicular to the slider
displacement direction, said axle being rotatable about its axis,
said first gimbal member being fastened to said axle to rotate
together therewith, a second slider on which said first slider is
displaceable, and a third slider on which said second slider is
displaceable, the displacement directions of said three sliders
extending at an angle of 90.degree. to each other, whereby
respective translatory adjustments are applicable to said object
support relative to said central axis.
8. In apparatus for producing electron-microscopic stereo images by
sequentially taking pairs of stereoscopically coordinated
individual pictures having means for producing an electron beam in
a direction defining a central axis, a device for holding a
specimen object on said central axis, and means for
photographically taking individual pictures of the
electron-illuminated object, the improvement according to which
said device comprises a cardanic joint assembly of gimbal
structures, having three cardanic journal axes of which one is
coincident with said central axis, said three axes having a common
intersection on said central axis, an object support mounted on
said assembly near said intersection for holding the object on said
intersection, whereby said device permits rotating any chosen
surface area of the object about said central axis and then tilting
the object through the stereo angle about one of said other axes
between two picture-taking positions in which the chosen area has
substantially the same brightness, two sliders displaceable in
respective directions perpendicular to each other, one of said
sliders carrying said object support and being mounted and
displaceable upon the other slider, a rotatable circular disc
structure to which said other slider is fixedly attached to be
rotationally adjustable together therewith, said rotatable discs
being mounted on said cardanic assembly, said cardanic assembly
comprising a first U-shaped bracket on whose bottom said rotatable
disc structure is mounted, a second U-shaped bracket having two leg
portions with respective coaxial pivot pins, said first bracket
having two leg portions connnected with said respective pivot pins
to be rotatable about their common axis, and an angle piece (W) and
a pivot pin protruding from one leg of said angle piece and having
a pivot axis coincident with one of said two cardanic journal axes
other than said central axis, said second bracket (H3) being
journaled on said latter pivot pin to be rotatable about said one
journal axis.
9. In apparatus for producing electron-microscopic stereo images by
sequentially taking pairs of stereoscopically coordinated
individual pictures having means for producing an electron beam in
a direction defining a central axis, a device for holding a
specimen object on said central axis, and means for
photographically taking individual pictures of the
electron-illuminated object, the improvement according to which
said device comprises a cardanic joint assembly of gimbal
structures, having three cardanic journal axes of which one is
coincident with said central axis, said three axes having a common
intersection on said central axis, an object support mounted on
said assembly near said intersection for holding the object on said
intersection, whereby said device permits rotating any chosen
surface area of the object about said central axis and then tilting
the object through the stereo angle about one of said other axes
between two picture-taking positions in which the chosen area has
substantially the same brightness, two sliders displaceable in
respective directions perpendicular to each other, one of said
sliders carrying said object support and being mounted and
displaceable upon the other slider, a rotatable circular disc
structure to which said other slider is fixedly attached to be
rotationally adjustable together therewith, said rotatable discs
being mounted on said cardanic assembly, said cardanic assembly
comprising a first U-shaped bracket on whose bottom said rotatable
disc structure is mounted, a second U-shaped bracket having two leg
portions with respective coaxial pivot pins, said first bracket
having two leg portions connected with said respective pivot pins
to be rotatable about their common axis, a mounting structure, and
a pivot pin connected with said mounting structure and having an
axis defining one of said cardanic journal axes other than said
central axis, said second bracket (H3) being journaled on said
pivot pin for rotation about said one journal axis.
10. Apparatus according to claim 9, comprising slider means
displaceable in a direction transverse to said central axis, an
axle (A5) mounted on said slider means and extending therefrom in a
direction parallel to said central axis, said axle being adjustable
by said slider means to a position coaxial with said central axis,
said mounting structure being connected to said axle so as to be
rotatable about said central axis.
11. An apparatus according to claim 10, said slider means
comprising a top slider (S5) carrying said axle, and a bottom
slider (S4) on which said top slider is displaceable in a direction
perpendicular to the displacement direction of said top slider,
said bottom slider being operable to impart translatory
displacements to said axle (A5) relative to said central axis (Z).
Description
Our invention relates to a method for producing a stereo image
whose individual images, for example of a crystalline object, are
produced by means of electron microscopy.
It is known that devices for producing stereo image pairs of
crystal specimens by scanning electron microscopes must be equipped
with devices which permit displacing each point of the specimen
with respect to its distance from the electron beam, and which also
permit tilting the specimen surface about an axis which is nearly
or precisely perpendicular to the electron beam direction. It is
further known that pairs of stereo images to be viewed with known
optical equipment, can be combined to a stereo image only if the
stereo angle remains limited in accordance with physiological
optics, for example the Luscher-parallax condition. The production
of stereo images further requires that the image brightnesses of
the object surfaces in the two individual images be not, or only
slightly, different from each other. The change in image brightness
when tilting the object is due to the fact that the number of
secondary electrons released by the primary electron beam out of a
specimen surface, and consequently the image brightness of the
object surface, greatly depends upon the inclination angle of the
surface normal of the object relative to the direction of the
primary electron beam. It may happen, therefore, that a stereo
effect of interesting object structures cannot, or only very
deficiently, be attained if at the mutually corresponding
localities of the individual images produced, the image intensities
differ so greatly from each other that no genuine stereo effect
will result. For the same reason, it may be difficult to measure
the local object height.
It is an object of our invention to provide a method and means for
the production of stereo images by electron microscopy which
minimize or virtually eliminate the above-mentioned difficulties.
More specifically, it is an object of the invention to readily
afford producing electron-optical stereo images which secures
substantial constancy of the image brightness with respect to given
object surfaces in the two individual images of a stereo pair.
According to our invention, we first rotate the chosen surface area
or face of the object about a central axis defined by the direction
of the electron beam, whereafter we tilt the object about a second
axis intersecting the central axis, the tilting being in an amount
corresponding to the stereo angle; and the rotation about the
central axis being such that the image brightness of the surface is
substantially the same in the starting position and in the end
position respectively of the tilting displacement. The individual
pictures of the stereo pair are taken as the object is in these two
positions respectively.
Preferably, the cented axis and the second axis are perpendicular
to each other, and the point of intersection is situated within the
object or specimen.
According to another feature of our invention, a third axis may be
provided which passes through the intersection of the first and
second axes and which extends perpendicularly or at a different
angle to each of these two axes, the specimen being rotatable about
the third axis for maintaining a given surface brightness intensity
of the object.
According to a further, alternative method of the invention, any
chosen surface of the object is rotated about an axis which is
noncoincident with the beam direction; and adjustable so as to be
parallel to, or identical with, the normal direction of the surface
(i.e., the direction perpendicular to the surface), the amount of
rotation, constituting the stereo angle, being dependent upon the
angle between the adjustable axis and the central axis defined by
the beam direction.
As a consequence of the object movements performed in accordance
with the above-described method of the invention, noninteresting
object faces or surface areas can be uniformly suppressed as
regards their brightness intensity on the corresponding localities
of the stereo image pair, thus more clearly imaging and emphasizing
the other structural features of the object. This is tantamount to
having the possibility of varying and/or improving the image
contrasts. For example, the intensity of a planar crystal surface
can be uniformly suppressed for more clearly imaging any individual
small etch pits located on the surface.
The invention will be further elucidated with reference to the
accompanying drawing in which:
FIG. 1 is an explanatory diagram;
FIG. 2 is a schematically perspective view of apparatus embodying
the invention by way of example; and
FIG. 3 is a schematically perspective view of another apparatus
also embodying the invention by way of example.
The diagram shown in FIG. 1 serves to permit a comparison of the
method according to the invention with those heretofore available.
The perspective representation indicates various axes. Among these
is the Z-axis (central axis) shown with an arrowhead opposed to the
direction of the primary beam of electrons. Also apparent is an
axial direction X which is perpendicular to the primary
electron-beam direction (Z-direction) and about which the specimen
surface, in the heretofore customary manner, was tilted in
opposition to the beam direction z about the angles .phi..sub.1 in
order to first obtain a given image brightness of the surface, and
thereafter is tilted through the stereo angle .DELTA..phi. to the
angular position .phi..sub.2. Also indicated in FIG. 1 is an axis Y
which is assumed to be perpendicular to the X-axis and to the
Z-axis, although it may also intersect these two axes at a
different angle. The Z-, Y- and X- axes are shown to intersect in a
single point P although this is not an indispensable requirement.
Further represented is a spherical surface O about the common
intersection P of the three axes with latitude circles A and B
concentric to the X-direction and Y-direction respectively.
For simplification, assume that the surface structure of the
specimen is composed of three areas conjointly forming a
triple-edged pyramid represented in central projection. The surface
normal (not shown) passes through the intersection point P of the
axes and intersects the surface O of the sphere at C, D and E.
In the conventional method for producing a stereo image, the two
individual images of the stereo pair differ from each other in that
the tilting angle .phi., denoting the angular displacement about
the X-axis, after first taking a picture at an angle .phi..sub.1,
is changed by the stereo angle .DELTA..phi. to assume the angular
position .phi..sub.2, this being represented at point C. Relative
to this tilting displacement, the .phi.-tilting axis perpendicular
to the cented axis Z is designated as the X-axis. Due to the
tilting displacement, the surface normal directions passing through
C, D, E change to directions passing through C', D', E'
respectively. The Y-direction which is assumed to be fixed with the
specimen, changes along the latitude circles A to the Y'-direction.
In the following, the points C, C', C", C.sub.1, C.sub.2, D, D', E,
E' where the surface normal directions passing through the sphere
center point intersect the surface O of the sphere, are used to
denote the surface normal directions as well as the surfaces C, D
and E themselves.
As a consequence of the tilting displacement, the corresponding
surfaces C and C', D and D', E and E' in the two individual
pictures are imaged in respectively different sizes and also with
different image brightnesses. Thus, for example, it may happen that
the increased inclination of the surfaces C' and E' will result in
a higher image intensity relative to C and E, whereas the
brightness at the surface D in the second picture D' is reduced.
For similar reasons, an inversion in contrast of the area
brightness may take place and may weaken or obviate the stereo
effect.
The method according to the invention minimizes or eliminates these
difficulties at least with respect to any surface area of interest
to the observer. In lieu of the additional tilting about the X-axis
by the angle .DELTA..phi., we provide for other displacing
movements of the specimen. That is, we provide for a rotary
displacement about the central axis and tilting movement about the
Y-axis which extends at an angle, for example perpendicularly, to
the Z-beam direction (central axis) as well as to the X-axis. For
explaining the method steps, let it be assumed that the surface
area denoted by C is the one which, with respect to image
structure, intensity and characteristic limitation, is of
particular importance. This arbitrarily selected surface area C is
inclined by the tilting angle .phi..sub.1 relative to the beam
direction Z. It is not necessary that the surface C be first
rotated about the X-axis an angular amount .phi..sub.1, since the
surface structure of the specimen object is almost always such that
from the outset the surfaces occupy a given angle relative to the
plane defined by the Z- and X-axes.
One of the applicable ways of turning the face C to the positions
C" or C.sub.1 for taking the stereo pictures is as follows. The
face C is rotated about the Z-axis into a second position C" in
such a manner that a subsequent tilting to the position C.sub.1
about the Y-axis by the stereo angle .DELTA..theta. does not cause
a change in image brightness intensity for the face C". The face
direction C" is determined by the fact that, upon tilting the face
C" one half of the stereo angle .DELTA..theta./2, it no longer
possesses a component in the X-axis direction. When displacing the
face C to C" and taking the electron-optical pictures, no stereo
effect is at first produced since the face normals C and C" do not
change the angle relative to the beam direction Z, i.e., their
projections in the beam direction remain unchanged. Consequently,
their image intensity also remains unchanged. With this rotation,
the other faces of the specimen P likewise do not change their
intensity.
The subsequent .DELTA..theta. tilting about the Y-axis, which
transfers the face C from the position C" to the position C.sub.1,
does not change the image brightness, at least of the face C,
because the directions C" and C.sub.1 of the face normals form the
same angle .alpha. relative to the Z-axis as the face normal
direction C.
The face positions C" and C.sub.1 differ from each other, with
respect to tilting about the Y-axis, by the stereo angle
.DELTA..theta. and result in obtaining a pair of stereo pictures on
which the face C has the same brightness intensities
respectively.
The second method according to the invention provides as a first
step that an axis be moved in such a manner that it becomes
identical with or parallel to the face normal direction on the
chosen face of the specimen. Thereafter the chosen face is rotated
about this axis and brought into two positions differing from each
other by the stereo angle which is now dependent upon the angle
defined by the central axis, i.e., the electron-beam axis on the
one hand, and the adjustable axis on the other hand. The latter
angle can be computed or the positions can be determined
experimentally.
The embodiments of apparatus according to the invention illustrated
in FIGS. 2 and 3 are designed for performing the first-described
method according to the invention.
The device shown in FIG. 2 comprises three sliders S1, S2 and S3
arranged one above the other and serving to impart translatory
displacements to the specimen P shown situated on the central axis
Z in the path of the electron beam. The slider S1 is used for the
first horizontal translatory motion of the specimen, the slider S2
for the second horizontal specimen motion perpendicular to that of
the slider S1, and the slider S3 permits a vertical translatory
movement of the specimen in the direction of the electron beam
which is along the central axis Z. Mounted on the slider S1 is a
fixed axle MA which can be turned by means of a spur gear Z1.
Seated on top of the axle MA is a cardanic joint assembly of
several gimbal members. One of these members, a U-shaped bracket
member H1, is fastened to the axle MA and has its lateral legs SH1
and SH2 provided with inwardly directed journal pins A1, A2. A
frame R is secured to the ends of the pins A1 and A2. The frame is
composed of four lateral parts 1, 2, 3, 4 of which the parts 1 and
3 are connected with the pins A1 and A2. Each of the lateral parts
2 and 4 carries in its middle another axle pin A3 or A4 which
protrudes inwardly in the plane defined by the frame R. Another
U-shaped gimbal member H2 has its lateral legs SH3 and SH4 joined
with the pins A3 and A4 respectively. The bottom BO of member H2
carries the specimen support PT on whose point the specimen P
itself is fastened. The member H1, the frame R and the member H2
are angularly displaced 90.degree. from each other so as to jointly
form a cardanic or universal-joint suspension for the specimen P.
The electron-beam direction identical with the Z-axis passes
through the specimen P and the axle MA. The X-axis for the angular
rotation about the angle .phi. (see FIG. 1) extends through the
journal pins A3 and A4; and the Y-axis extends through the pins A1
and A2 of the gimbal member H1.
Before a stereo picture of the specimen P can be taken, the
specimen P must be brought into the focal point of the electron
beam by applying translatory displacements with the aid of the
sliders S1, S2, S3. For taking a stereo picture with the imprecise
known method, it suffices to tilt the member H2 about the X-axis,
i.e., about the journal pins A3 and A4. For taking stereo pictures
by the method according to the invention, the .phi. tilting is
first used alone for adjusting a desired brightness of the image,
and is not changed once this adjustment is made. After suitable
rotation of the specimen P about the beam direction (Z-axis) the
stereo tilting is performed by tilting the specimen about the
Y-axis. The rotation about the Z-axis is transmitted to the
specimen P through the axle MA and the gimbal member H1 fastened to
that axle. The tilting about the Y-axis is effected by the journal
pins A1 and A2 whose rotation is transferred to the specimen P
through the frame R and the member H2.
The apparatus shown in FIG. 3 resembles that of FIG. 2 in
comprising two sliders S4 and S5 which are fastened one above the
other and are displaceable at an angle of 90.degree. relative to
each other. An axle A5 is mounted on the slider S5 and rotatable by
means of a spur gear Z2. A mounting structure W-shaped as an angle
piece is fastened to the top end of the axle A5. The sliders S5 and
S4 serve to shift the object P into the center axis Z. A gimbal
bracket member H3 is fastened by a pivot pin A6 to the upper end of
the leg W1 of the angle piece W. The lateral legs SH5 and SH6 of
the likewise U-shaped member H3 carry coaxial pins A7 and A8
between which a U-shaped gimbal bracket H4 is attached. The pins A7
and A8 engage the lateral legs SH7 and SH8. The bottom BD of member
H4 carries on a further axle (not visible) a circular disc KS whose
surface OB is perpendicular to the common axis of pins A7 and A8. A
slider S6 mounted on the disc surface carries another slider S7
displaceable perpendicularly to the sliding direction of slider S6.
The displacement of slider S7 is along the common axis of pins A7
and A8. The specimen carrier PT with the specimen P is fastened on
the sliding member SC of the slider S7.
The sliders S6 and S7 and the disc KS serve to place selected
localities of the specimen P into the focal point of the electron
beam Z without requiring each time a new focusing of the electron
beam onto the specimen P situated parallel to the plane SC. The two
sliders S4 and S5 serve to bring the specimen P into the electron
beam Z. The coarse displacement of the specimen P in the direction
of the central axis (coincident with the direction of the electron
beam Z) is effected by means of the sliders S4 to S7.
For taking stereo pictures in accordance with the conventional
imprecise method, a rotation of the specimen about the X-axis
coincident with the common axis of the pins A7 and A8 may be used.
This possibility of rotation is also applicable for the purpose of
the method according to the invention, namely for improving the
inclination of individual crystal faces of the specimen P relative
to the center axis Z and hence relative to the electron beam
direction. In this manner the brightness of these faces can be
varied. The tilting of the specimen about the Z-axis is effected by
turning the angle piece W with the aid of the axle A5 fastened on
the slider S5. The subsequent tilting about the Y-axis, important
for taking stereo pictures, is effected with the aid of the bracket
members H3 and the pivot pin A6.
* * * * *