U.S. patent application number 10/159790 was filed with the patent office on 2003-12-04 for apparatus for tilting a beam system.
Invention is credited to Drainoni, Riccardo, Groholskiy, Alexander, Tanguay, Michael.
Application Number | 20030222221 10/159790 |
Document ID | / |
Family ID | 29419713 |
Filed Date | 2003-12-04 |
United States Patent
Application |
20030222221 |
Kind Code |
A1 |
Groholskiy, Alexander ; et
al. |
December 4, 2003 |
APPARATUS FOR TILTING A BEAM SYSTEM
Abstract
The present invention provides a column tilt apparatus and
method for providing an off-normal angle of incidence of a beam in
a scanned beam system onto a substrate passing through the
eucentric point that is electro-mechanically adjustable during
operation while maintaining vacuum integrity of the column and work
chamber, and without introducing significant vibrations.
Inventors: |
Groholskiy, Alexander;
(Salem, MA) ; Drainoni, Riccardo; (Woburn, MA)
; Tanguay, Michael; (Kennebunk, ME) |
Correspondence
Address: |
MICHAEL O. SCHEINBERG
P.O. BOX 164140
AUSTIN
TX
78716-4140
US
|
Family ID: |
29419713 |
Appl. No.: |
10/159790 |
Filed: |
May 31, 2002 |
Current U.S.
Class: |
250/442.11 |
Current CPC
Class: |
H01J 37/16 20130101;
H01J 37/28 20130101; H01J 37/023 20130101; H01J 37/3056 20130101;
H01J 2237/0245 20130101 |
Class at
Publication: |
250/442.11 |
International
Class: |
H01J 037/20 |
Claims
We claim as follows:
1. A method for moving a beam column of a beam system through an
interval of spatial displacement, comprising the steps of:
providing a first subassembly; and providing a second subassembly
to which the beam column is affixed that is electro-mechanically
drive-able through a path of spatial displacement with respect to
the first subassembly.
2. The method of claim 1, wherein a beam of the beam column passes
through a point that remains substantially fixed with respect to
the first subassembly throughout a range of spatial
displacement.
3. The method of claim 1, wherein the path of spatial displacement
is a circular arc.
4. The method of claim 1, wherein during spatial displacement a gas
seal is maintainable between a first region that includes a beam of
the beam column and a second region that excludes the beam.
5. The method of claim 1, further comprising the steps of:
providing a motor mounted to one of the two subassemblies with a
first gear mounted to a rotatable shaft of the motor; and providing
a second gear enmeshed with the first gear and mounted to the
opposite subassembly to which the motor is mounted; whereby
rotation of the shaft causes relative motion between the
subassemblies.
6. The method of claim 1, wherein the second subassembly to which
the beam column is affixed is electro-mechanically drive-able
through a sequence of incremental steps of spatial displacement
with respect to the first subassembly
7. The method of claim 1, further comprising the steps of:
providing a mechanism to limit the extent of displacement.
8. The method of claim 1, further comprising the steps of:
providing an air bearing between conformal opposing surfaces of the
two subassemblies.
9. An apparatus for moving a beam column of a beam system through a
path of spatial displacement, comprising: a first subassembly; and
a second subassembly to which the beam column is mounted; and an
electromechanical drive system to electro-mechanically drive the
second subassembly through a path of spatial displacement with
respect to a position of the first subassembly.
10. The apparatus of claim 9, wherein a beam of the beam column
passes through a point that remains substantially fixed with
respect to the first subassembly throughout a range of spatial
displacement.
11. The apparatus of claim 9, wherein during the spatial
displacement a gas seal is maintainable between a first region that
includes a beam of the beam column and a second region that
excludes the beam.
12. The apparatus of claim 9, further comprising a bellows
apparatus.
13. The apparatus of claim 9, wherein the electromechanical drive
system further comprises: a motor mounted to one of the two
subassemblies with a first gear mounted to a rotatable shaft of the
motor; and a second gear enmeshed with the first gear and mounted
to the opposite subassembly to which the motor is mounted; whereby
rotation of the shaft causes relative motion between the
subassemblies.
14. The apparatus of claim 13, wherein the motor is controllable to
drive the beam column through a sequence of incremental steps of
spatial displacement.
15. The apparatus of claim 9, further comprising: a mechanism to
limit the extent of displacement.
16. The apparatus of claim 15, wherein the mechanism further
comprises a sensor to detect an extent of displacement.
17. The apparatus of claim 9, further comprising: an air bearing
between conformal opposing surfaces of the two subassemblies.
18. A beam system for interacting with a work piece, comprising: a
first subassembly; a second subassembly; an electro-mechanical
drive system to electro-mechanically drive the second subassembly
through a path of spatial displacement with respect to a position
of the first subassembly; and a beam column mounted to the second
subassembly for generating a beam to interact with the work
piece.
19. The system of claim 21, wherein during the displacement a gas
seal is maintainable between a first region that includes the beam
and a second region that excludes the beam.
20. The system of claim 21, wherein the beam column is drive-able
through a pre-determinable sequence of spatial displacements.
21. The system of claim 21, further comprising a processor for
controlling the rate of spatial displacement of the beam column.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to the field of scanned beam
systems, and in particular, to a method and apparatus for tilting a
beam column.
BACKGROUND OF THE INVENTION
[0002] Scanned beam microscopy systems, including charged particle
beam systems such as electron beam and focused ion beam (FIB)
systems, are widely used in characterization or treatment of
materials on a microscopic scale. For example, focused ion beam
systems are used in manufacturing operations because of their
ability to image, etch, mill, deposit and analyze with great
precision. Ion columns in FIB systems using gallium liquid metal
ion sources (LMIS), for example, can provide five to seven
nanometer lateral imaging resolution.
[0003] The beam of a scanning beam system typically scans the
surface of a target specimen in a raster pattern. This raster
pattern may be used to produce an image of the surface of the
target. When the scanned beam strikes the target, particles or
photons are emitted from the immediate vicinity of beam impact. A
portion of these emissions are measured or collected using a
suitable detector or collector that produces an output signal
indicative of the intensity of the emission. This output signal is
then processed to produce an observable image displayed on a
conventional video monitor.
[0004] A typical application of scanning beam systems is for
analysis and treatment of integrated circuits (IC). In this
application, a focused ion beam is used to produce an image of the
circuit. This image is then used in conjunction with circuit layout
information to navigate the ion beam over the surface of the
circuit to locate a specific element or feature of interest. When
the beam is scanned to the local area of interest, the beam current
can be increased to cut into the circuit die and expose circuit
features buried in layers. The FIB system can then alter the
exposed circuit by cuffing conductive traces to break electrical
connections or by depositing conductive material to provide new
electrical connections. This etching or deposition is caused by a
physical or chemical reaction of the beam ions with the specimen
and occurs at a rate that is largely dependent upon the constituent
ions of the beam, the presence and type of etch enhancing or
deposition precursor gases, and the beam current.
[0005] Although the typical focused beam system configuration
provides a beam that impinges normal to the substrate, focused beam
systems may be used in tilt orientations, in which the beam
impinges at an off-normal angle of incidence with respect to the
plane of the substrate to perform ion beam milling or electron beam
viewing at a specified angle. Although this could be accomplished
by tilting the stage that contains the working piece to be viewed
or etched, there is difficulty in maintaining coincidence between
the center point of beam impact and the axis of stage rotation for
all desired angles of incidence.
[0006] Alternatively, a change in angle of incidence could be
obtained by tilting the beam column about an axis of rotation
passing through the working piece at the desired center point of
beam impact. But prior art methods do not provide a satisfactory
way to provide a change in column tilt angle without interrupting
system operation. Prior art methods for providing column tilt to
produce an off-normal angle of incidence include the use of fixed
tapered spacers in conjunction with vacuum seals to set the
incidence angle of the beam. To expose the working piece to
successive incidence angles, one must iteratively change the
spacers used to set the angle of column tilt. Changing the tapered
spacers required exposing the sample chamber, thereby requiring
additional time to evacuate the chamber and restart and stabilize
the emitter after the tilt angle is changed. An alternative prior
art method employs a bellows that purportedly enables the system to
remain sealed while the column is mechanically tilted, but the
change in tilt angle must be performed manually and is difficult to
rapidly set to a precise angle of tilt.
[0007] It is desirable to have the beam remain focused at the same
point on the work piece throughout a range of column tilt angles.
This can be achieved by tilting the beam about the point at which
the beam is focused to maintain a constant "eucentric point." A
"eucentric point" is defined as an arbitrary point through which
the beam passes when it is not being deflected and that is a
specified distance from the axis of beam deflection. The eucentric
point is preferably chosen to coincide with the center point of
beam impact and the eucentric point preferably stays at the same
location in space for all angles of column tilt. Prior art methods
do not provide a satisfactory method of achieving this constant
eucentric point. Further, prior art methods do not provide a
satisfactory way to provide a change in tilt angle without
interrupting system operation. It would therefore be desirable to
provide a system and method that enables column tilt over a range
of tilt angles during system operation while maintaining a constant
eucentric point that overcomes prior art limitations.
SUMMARY OF THE INVENTION
[0008] The present invention overcomes prior art limitations by
providing a method and apparatus for automated adjustment of the
tilt angle of a beam column during operation of a scanned beam
system over a continuous angular sector, while maintaining a
constant eucentric point, maintaining vacuum integrity of the
column and work chamber, and without introducing significant
vibrations.
[0009] According to the present invention, a beam column can be
driven electro-mechanically throughout a range of angular
displacement to enable precise control of the angle of tilt while
maintaining a constant eucentric point. The electro-mechanical
drive system can be controlled by computer to provide a desired
sequence of angular displacements through which the column is
tilted during operation of the beam system. Air bearing support is
provided to minimize friction and vibration in the system and a
unique bellows is employed to maintain a vacuum or low-pressure
environment as the column is tilted
[0010] 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 disclosure provided herein may be
readily utilized as a basis for modifying or designing other
structures for carrying out the same purposes of the present
invention. Persons of skill in the art will realize that such
equivalent constructions do not depart from the spirit and scope of
the invention as set forth in the appended claims, and that not all
objects attainable by the present invention need be attained in
each and every embodiment that falls within the scope of the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] For a more complete understanding of the present invention,
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0012] FIG. 1 is a diagram of a focused ion beam system.
[0013] FIG. 2 is a perspective view of an embodiment of a column
tilt apparatus of the present invention.
[0014] FIG. 3A is a side view of the column tilt apparatus shown in
FIG. 2.
[0015] FIG. 3B is a detail view of meshed gears employed in an
embodiment of the present invention.
[0016] FIG. 4 is a cross-sectional view of a gear unit employed in
an embodiment of the present invention.
[0017] FIG. 5 is a perspective view of an embodiment of a column
tilt apparatus of the present invention.
[0018] FIG. 6 is a perspective view of a bellows assembly.
[0019] FIG. 7 is cross-section view of a bellows assembly.
[0020] FIG. 8A shows a non-uniform current distribution of a
focused ion beam. FIG. 8B shows an area etched by a focused ion
beam oriented perpendicular to work piece surface and having the
current distribution shown in FIG. 8A. FIG. 8C shows an area etched
by a focused ion beam tiled approximately five degrees from the
vertical and having the current distribution shown in FIG. 8A.
[0021] FIG. 9 is an illustration of a tilt geometry.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The present invention provides a method and apparatus for
automated adjustment of the tilt angle of a beam column during
operation of a scanned beam system over a continuous angular
sector, while maintaining a constant eucentric point, maintaining
vacuum integrity of the column and work chamber, and without
introducing significant vibrations.
[0023] The present invention will be discussed in the context of
use in a focused ion beam system for demonstrative purposes.
However, it will be understood that the methods of the present
invention may also be employed in other scanned systems, such as
electron beam systems including scanning electron microscopes and
scanning transmission electron microscopes.
[0024] In FIG. 1, a focused ion beam system 8 includes an evacuated
envelope 10 having an upper neck portion 12 within which are
located a liquid metal ion source 14 and a focusing column 16
including extractor electrodes and an electrostatic optical system.
Ion beam 18 passes from source 14 through column 16 and between
electrostatic deflection mechanism schematically indicated at 20
toward specimen 22, which comprises, for example, a semiconductor
device positioned on movable X-Y stage 24 within lower chamber 26.
An ion pump 28 is employed for evacuating neck portion 12. The
chamber 26 is evacuated with turbo-molecular and mechanical pumping
system 30 under the control of vacuum controller 32. The vacuum
system provides within chamber 26 a vacuum of between approximately
1.times.10.sup.-7 Torr and 5.times.10.sup.-4 Torr. If an
etch-assisting or an etch-retarding gas is used, the chamber
background pressure is typically about 1.times.10.sup.-5 Torr.
[0025] High voltage power supply 34 is connected to liquid metal
ion source 14 as well as to appropriate electrodes in focusing
column 16 for forming an approximately 1 keV to 60 keV ion beam 18
and directing the same downwardly. Deflection controller and
amplifier 36, operated in accordance with a prescribed pattern
provided by pattern generator 38, is coupled to deflection plates
20 whereby beam 18 may be controlled to trace out a corresponding
pattern on the upper surface of specimen 22. In some systems the
deflection plates are placed before the final lens, as is well
known in the art.
[0026] The source 14 typically provides a metal ion beam of
gallium, although other ion sources, such as a multi-cusp or other
plasma ion source, can be used. The source typically is capable of
being focused into a sub-one-tenth micron wide beam at specimen 22
for either modifying the surface 22 by ion milling, enhanced etch,
material deposition, or for the purpose of imaging the surface 22.
A charged particle multiplier 40 used for detecting secondary ion
or electron emission for imaging is connected to video circuit and
amplifier 42, the latter supplying drive for video monitor 44 also
receiving deflection signals from controller 36. The location of
charged particle multiplier 40 within chamber 26 can vary in
different embodiments. For example, a preferred charged particle
multiplier 40 can be coaxial with the ion beam and include a hole
for allowing the ion beam to pass. A scanning electron microscope
41, along with its power supply and controls 45, are optionally
provided with the FIB system 8.
[0027] A fluid delivery system 46 optionally extends into lower
chamber 26 for introducing and directing a gaseous vapor toward
sample 22. 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 fluid
delivery system 46.
[0028] A door 60 is opened for inserting specimen 22 on stage 24
which may be heated or cooled, and also for servicing the reservoir
50. The door is interlocked so that it cannot be opened if the
system is under vacuum. The high voltage power supply provides an
appropriate acceleration voltage to electrodes in ion beam column
16 for energizing and focusing ion beam 18. When it strikes
specimen 22, material is sputtered, that is physically ejected,
from the sample. Focused ion beam systems are commercially
available, for example, from FEI Company, Hillsboro, Oreg., the
assignee of the present application. Signals applied to deflection
controller and amplifier 36 cause the focused ion beam to move
within a target area to be imaged or milled according to a pattern
controlled by pattern generator 38.
[0029] A preferred embodiment of the present invention is shown in
perspective view in FIG. 2. A column tilt apparatus 2000 comprises
a first assembly 2100 and a second assembly 2200. First assembly
2100 remains stationary, whereas second assembly 2200 moves with
respect to first assembly 2100. A beam column is inserted into a
cylindrical bore 2800 that passes through both subassemblies to
enable the beam generated by the beam column to propagate to a
substrate located below column tilt apparatus 2000. The beam column
is mounted to assembly 2200 so that the beam column moves with
assembly 2200. FIG. 1 shows schematically the relationship between
first assembly 2100, lower chamber 26, FIB column housing 12, and
second assembly 2200. As will be described more fully below,
cylindrical bore 2800 is the interior of a bellows assembly that
has an upper portion mounted to movable subassembly 2200 and a
lower portion that is stationary.
[0030] Attached to assembly 2200 is a motor 2220 and a gear unit
2240. A side view of column tilt apparatus 2000 is shown in FIG.
3A. Motor 2220 is attached to a gear 2212. Gear 2212 is enmeshed
with a gear 2215. Gear 2215 is attached to a smaller gear 2216, as
shown in FIG. 3B, and is also attached to gear unit 2240. As shown
in FIG. 3B, gear 2216 is enmeshed with a gear segment 2111 that is
attached to stationary assembly 2100.
[0031] A side view of gear unit 2240 is shown in FIG. 4. Gear unit
housing 2242 is attached to, and moves with, assembly 2200. Passing
through gear unit housing 2242, and free to rotate there within
against ball bearings 2244, is a shaft 2246 to which gears 2215 and
2216 are attached at one end. When motor 2220 is caused to rotate,
gear 2212 rotates. The rotation of gear 2212 causes gear 2215 and
2216 to also rotate. Since gear 2216 is enmeshed with gear segment
2111, which is attached to stationary assembly 2100, assembly 2200
is forced to move.
[0032] Referring again to FIG. 2, assembly 2100 and assembly 2200
each have facing surfaces 2150 and 2250, respectively, that exhibit
a radius of curvature that is the same as the radius of curvature
exhibited by gear segment 2111, shown in FIG. 3B, so that the
angular rotation of gear 2216 defines the angular displacement of
assembly 2200. Since, the beam column is attached to assembly 2200,
it moves with assembly 2200, and thus, the angular rotation of the
motor transmitted to gear 2216 controls and defines the angular
displacement of the beam column. The radius of curvature of the
surfaces 2150 and 2250 are preferably such that the angular
displacement of assembly 2200 causes the beam to rotate about an
axis passing through the eucentric point of the beam system.
[0033] Motor 2220 is controlled by electrical signals that
correspond to a desired angular displacement of the beam column.
Thus, while the beam system is in operation, the angular
displacement of the beam column can be adjusted by a controlled
changed in the electrical signals driving motor 2220. When gears
2215 and 2216 are caused to rotate, shaft 2246 is also thereby
caused to rotate. At the end of shaft 2246 that is opposite to the
end that gears 2215 and 2216 are mounted, is mounted a flag 2248,
shown in FIG. 4. Flag 2248 rotates with shaft 2246. Referring to
FIG. 2, optical sensors 2250, preferably infrared sensors, are
mounted in a position such that flag 2248 will obstruct an optical
path of sensors 2250 when assembly 2200 is rotated to an extreme of
angular displacement clockwise or counterclockwise. When
obstruction of the optical path occurs, a sensor 2250 generates an
electrical signal that causes motor 2220 to stop rotating, thereby
causing assembly 2200, and consequently, the beam column, to stop
its angular displacement. Moreover, in conjunction with optical
gratings, a stepper motor, and encoder, the stepper motor can be
controlled to produce angular displacement with a resolution
{fraction (1/30,000)} of a degree or better, subject to the
mechanical tolerances that can be minimized to the limits of
machining precision.
[0034] Friction between surfaces 2150 and 2250 is preferably
eliminated, or at least minimized, by an air bearing; that is,
pressurized air is applied to cause assembly 2200 to be lifted
above assembly 2100 by a small amount, e.g., 10 microns, and even
less than 2 micrometers, to prevent frictional contact between
surfaces 2150 and 2250 and further to minimize vibration. Persons
of ordinary skill in the art will recognize other methods for
reducing vibration and friction between assemblies 2100 and 2200,
given the disclosure herein.
[0035] FIG. 5 is another perspective view of column tilt apparatus
2000 showing motor 2220 connected to gear 2212, which is enmeshed
with gear 2215. Gear unit 2240 is located behind a cover plate 2290
that provides support for electrical connections to electronics
assembly 2270. Electronics assembly 2270 enables control signals to
be transmitted to motor 2220 and sensor signals to be received from
sensors 2250.
[0036] Inserted and mounted within cylindrical bore 2800 is a
bellows that enables motion between assemblies 2100 and 2200 while
maintaining vacuum in the focused beam system. A perspective view
of a bellows assembly 2300 is shown in FIG. 6. A first mounting
flange 2320 is provided for mounting bellows assembly 2300 to
second assembly 2200 with holes 2322 aligned with the holes 2222
shown in FIG. 5 for securing bellows 2300 to assembly 2200 with
bolts or other suitable mechanism. A second mounting flange 2340 is
also provided for mounting bellows assembly 2300 to a fixed
structural support assembly to which subassembly 2100 is mounted.
Thus, an upper portion of the bellows assembly moves with
subassembly 2200 and the lower portion of the bellows assembly
remains stationary.
[0037] Also partially shown in FIG. 6 are a first bellows
subassembly 2350 and second bellows subassembly 2360. These
subassemblies are shown more fully in FIG. 7, which provides a
cross-section view of bellows assembly 2300. First and second
bellows subassemblies 2350 and 2360 are preferably formed of a
plurality of flat cylindrical rings each formed of stainless steel
of nominal thickness 0.05 inches with an inner diameter of about
3.2 inches and an outer diameter of about 4.2 inches. To form the
bellows, a first and second adjacent ring are welded at their inner
diameter. The second and a third adjacent ring are welded at their
outer diameter. The third and a fourth adjacent ring are welded at
their inner diameter, and so forth, to form the accordion-like
structures, 2350 and 2360, shown in FIG. 7.
[0038] The upper end of bellows subassembly 2350 is welded to
flange structure 2320 and the lower end of bellows subassembly 2350
is welded to a cylindrical structure 2370. Similarly, the lower end
of bellows subassembly 2360 is welded to flange structure 2340 and
the upper end of bellows subassembly 2360 is welded to cylindrical
structure 2370. When subassembly 2200 is caused to move with
respect to subassembly 2100, bellows subassemblies 2350 and 2360
expand and contract in accordion-like manner. Cylindrical structure
2370, which may be formed of thin steel, prevents any particulate
matter from entering into its interior, thereby preventing
contamination within the system.
[0039] O-rings are also employed to maintain a vacuum seal between
the bellows assembly and the beam column on one side and the system
vacuum chamber on the other side. In particular, an O-ring groove
2380 shown in FIG. 6 is provided to form a pressure seal at the
mating surfaces of flange 2390, also shown in FIG. 6, and a mating
flange of the beam column (not shown). This prevents leakage
between the low pressure region interior to bellows assembly 2300
and the environment exterior to the tilt apparatus. A similar
O-ring (not shown) forms a seal between flange 2340 and the system
vacuum chamber. As previously noted, the end of the beam column
through which the beam is emitted is inserted into the central bore
of the bellows assembly and vacuum sealed with the bellows,
enabling the beam to travel in the vacuum to the work piece. The
beam column can then be tilted through an angular displacement
while maintaining the vacuum seal. The bellows described herein can
withstand 10,000 full stroke cycles, although full stroke cycles
are not used in practice. As such, the bellows can exceed the life
of the beam system in which it is employed. Alternatively, the
bellows can be replaced in less than two hours by service
personnel.
[0040] The bellows 2300 can be constructed to provide at least 5
degrees and preferably 10 degrees of angular displacement of
assembly 2200. This is advantageous when the contour of a feature
etched into a substrate is important. For example, during the
fabrication of integrated circuits, it is common to etch a part of
a circuit using a focused ion beam system to expose a cross section
of the various layers of the circuit. If the etched wall is curved
or not perpendicular to the surface, a cross sectional view of the
exposed surface will be distorted. To maximize resolution of the
imaged cross section, the etching is preferably straight down,
perpendicular to the surface of the wafer on which the integrated
circuit is formed.
[0041] Because the current distribution across the focused ion beam
in not uniform, a vertical focused ion beam does not etch an edge
that is perpendicular to the surface. FIG. 8A shows a graph of the
intensity distribution 2705 of a focused ion beam, showing that the
ion current does not fall instantly to zero, but trails off at the
edge of the beam. FIG. 8B shows a typical wall 2710 of a cross
section etched by a focused ion beam having the intensity
distribution shown in FIG. 8A. Wall 2710 is not perpendicular to a
wafer surface 2720. By etching using a tilted focused ion beam,
preferably tilted about 4 degrees from the vertical, the etched
wall can be made vertical. FIG. 8C shows a typical wall 2730 etched
using a tilted focused ion beam. Wall 2730 is approximately
perpendicular to a wafer surface 2740.
[0042] Thus, tilting a charged particle beam column provides a
method for producing an etched wall that is approximately
perpendicular to a work piece surface so that a high-resolution
image of the exposed wall be obtained. Although the same effect
could be accomplished by tilting the stage, tilting stages have
several disadvantages as described in U.S. Pat No. 6,039,000,
"Focused Particle Beam System and Methods Using a Tilt Column,"
which is assigned to the assignee of the present application.
[0043] The geometry of motion provided by the above-described
system is illustrated in FIG. 9. A reference axis A passes through
a first subassembly 2810 that is fixed with respect to the
reference axis. A tilt axis B passes through a second assembly 2820
to which the beam column is mounted and is coincident with the beam
axis of the column. Second subassembly 2820 is fixed with respect
to the tilt axis but may move with respect to first subassembly
2810 through a path of spatial displacement, S. Tilt axis B may
coincide with reference axis A or may rotate about an axis of
rotation C perpendicular to A and B to form an angle of
displacement, .theta.. To the extent that the radius of curvature R
is constant with respect to .theta., the path of spatial
displacement, S is a circular arc. This causes the beam to pass
through a point that remains substantially unchanged with respect
to the first subassembly during spatial displacement of the beam
column, thereby enabling the system to maintain a substantially
constant eucentric point for all angles of tilt. This angular
displacement is achieved by the preferred embodiment of the present
invention described above. Moreover, it is achieved with minimal
vibration for a continuous range of tilt angles without
interruption of system operation.
[0044] As noted above, motor 2220 is controlled by electrical
signals that correspond to a desired angular displacement of the
beam column. Thus, while the beam system is in operation, the
angular displacement of the beam column can be adjusted by a
controlled changed in the electrical signals driving motor 2220.
Motor 2220 and associated electrical signals can be implemented to
continuously--or in steps, in the case of a stepping motor--drive
the moveable subassembly electro-mechanically through a desired
angular displacement from its current position or to a particular
desired angle of tilt.
[0045] A desired sequence of angular displacements through which
the column is tilted during an interval of time can be implemented
in software to program a microprocessor, or other programmable
machine, to cause electronic circuitry within a motor control
subsystem to generate the electrical signals required to drive the
column through the desired sequence. A user of the system can
program the sequence by way of an information display apparatus and
an information entry apparatus such as, for example, a video
monitor and keyboard.
[0046] The system user controls the tilt of the column by entering
information through a keyboard that can be displayed on a video
monitor, and transmitted to a computer. The computer can be caused
by information transmitted to it to initiate a sequence of outputs
that cause the motor control subsystem to generate signals that
drive subassembly 2200 through a desired sequence of angular
displacements.
[0047] The beam column of the system is mounted to subassembly 2200
in an orientation that aligns the axis of the beam emitted by the
beam column with the tilt axis of subassembly 2200. The emitted
beam therefore passes through an interior region of the chamber to
impact the work piece affixed to the work station in the chamber at
the currently desired angle of incidence. Embeddable in the
computer is a software program that enables control of, not only
tilt angle, but also the rate at which angular displacement occurs.
The computer be programmed to control the dwell time at a fixed
angle of tilt between successive changes in tilt angle.
[0048] Further, the computer can be programmed to control movement
and rate of movement of the work station. Thus, control of the
relative orientation and relative rate of motion between the work
station and the beam of the beam column is provided. Additionally,
the emission of the beam can be caused to cease for a controllable
and specifiable interval of time. Therefore, the beam can be
"turned off" if desired when, for example, relative motion between
the beam column and the work station occurs.
[0049] The system of the present invention may further comprise an
imaging subsystem comprising an imaging beam source and a detector.
The imaging beam source and detector are disposed at such angles
and distances with respect to the work station as to enable imaging
of the work piece, without interfering with the beam emitted by the
beam column. In an alternative embodiment, the imaging beam source
may be the beam column mounted to subassembly 2200 to enable
imaging at selectable desired tilt angles. A detector generates
signals in response to emissions received from the work piece.
These signals may then be processed and sent to a video monitor to
display an image of the work piece.
[0050] Thus, the present invention provides an automate-able
electromechanical drive system to drive a beam column through a
pre-determinable sequence of displacements. 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 herein without departing from the spirit
and scope of the invention as defined by the appended claims. For
example, and without limitation, persons of ordinary skill in the
art will readily see that the electro-mechanical drive system
described herein could also include hydraulic elements. A linear
motor could be used in substitution of the rotary motor described
above. A mechanically activated disconnect switch could be used
instead of or in addition to the sensors employed to limit the
extent of displacement of the apparatus.
[0051] The invention achieves multiple objectives and because the
invention can be used in different applications for different
purposes, not every embodiment falling within the scope of the
attached claims will achieve every objective. 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.
* * * * *