U.S. patent number RE40,009 [Application Number 10/922,783] was granted by the patent office on 2008-01-22 for methods and apparatus for adjusting beam parallelism in ion implanters.
This patent grant is currently assigned to Varian Semiconductor Equipment Associates, Inc.. Invention is credited to Joseph C. Olson, Anthony Renau.
United States Patent |
RE40,009 |
Olson , et al. |
January 22, 2008 |
Methods and apparatus for adjusting beam parallelism in ion
implanters
Abstract
Methods and apparatus for implanting ions in a workpiece, such
as a semiconductor wafer, include generating an ion beam, measuring
parallelism of the ion beam, adjusting the ion beam for a desired
parallelism based on the measured parallelism, measuring a beam
direction of the adjusted ion beam, orienting a workpiece at an
implant angle referenced to the measured beam direction and
performing an implant with the workpiece oriented at the implant
angle referenced to the measured beam direction. The implant may be
performed with a high degree of beam parallelism.
Inventors: |
Olson; Joseph C. (Beverly,
MA), Renau; Anthony (West Newbury, MA) |
Assignee: |
Varian Semiconductor Equipment
Associates, Inc. (Gloucester, MA)
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Family
ID: |
24603771 |
Appl.
No.: |
10/922,783 |
Filed: |
August 20, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09649183 |
Aug 28, 2000 |
06437350 |
Aug 20, 2002 |
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Current U.S.
Class: |
250/492.21;
250/492.3; 250/492.2; 250/396R |
Current CPC
Class: |
H01J
37/3171 (20130101); H01J 37/1471 (20130101) |
Current International
Class: |
H01J
37/08 (20060101) |
Field of
Search: |
;250/492.21,492.2,396R,492.3 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 926 699 |
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Jun 1999 |
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EP |
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0 975 004 |
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Jan 2000 |
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EP |
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03017949 |
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Jan 1991 |
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JP |
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20011229873 |
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Aug 2001 |
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JP |
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WO 99/13488 |
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Mar 1999 |
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WO |
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WO 01/04926 |
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Jan 2001 |
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WO |
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WO 01/27968 |
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Apr 2001 |
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WO |
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Other References
Olson J.C. et al., "Control of channeling uniformity for advanced
applications", 2000 International Conference on Ion Implantation
Technology Proceedings. Ion Implantation Technology--2000 (Cat. No.
00EX432), Alpbach, Aus., pp. 670-673, XP002200390, 2000,
Piscataway, NJ, IEEE, ISBN:0-7803-6462-7. cited by other .
International Search Report mailed Mar. 28, 2002 for International
Patent Application No. PCT/US01/22392 with an International filing
date of Jul. 13, 2001. cited by other.
|
Primary Examiner: Berman; Jack I.
Claims
What is claimed is:
1. A method for implanting ions into a workpiece, comprising the
steps of: generating an ion beam; adjusting the ion beam for a
desired measure of parallelism in a plane; measuring a beam
direction of the adjusted ion beam in said plane .Iadd.without
implanting any workpiece with the ion beam.Iaddend.; tilting a
workpiece about an axis perpendicular to said plane at an implant
angle referenced to the measured beam direction; and performing
.[.an.]. .Iadd.the .Iaddend.implant with the workpiece tilted at
the implant angle.
2. A method as defined in claim 1, wherein the step of adjusting
the ion beam comprises adjusting the ion beam for substantially
parallel ion trajectories.
3. A method as defined in claim 2, wherein the beam direction
differs from a reference direction by a beam angle.
4. A method as defined in claim 1, wherein the step of tilting a
workpiece comprises tilting a semiconductor wafer at the implant
angle referenced to the measured beam direction.
5. A method as defined in claim 1, wherein the implant angle is
zero degrees and the workpiece is tilted normal to the measured
beam direction.
6. A method as defined in claim 1, further comprising the step of
measuring an angle of non-parallelism of the ion beam, wherein the
step of adjusting the ion beam is based on the measured angle of
non-parallelism.
7. A method as defined in claim 6, wherein the beam direction and
the angle of non-parallelism of the ion beam are measured with a
movable beam profiler and one or more beam detectors.
8. A method for implanting ions into a workpiece, comprising the
steps of: generating an ion beam; measuring parallelism of the ion
beam in a plane; adjusting the ion beam in said plane for a desired
parallelism based on the measured parallelism; measuring a beam
direction of the adjusted ion beam in said plane .Iadd.without
implanting any workpiece with the ion beam.Iaddend.; tilting a
workpiece about an axis perpendicular to said plane at an implant
angle referenced to the measured beam direction; and performing an
implant with the workpiece tilted at the implant angle referenced
to the measured beam direction.
9. A method as defined in claim 8, wherein the step of adjusting
the ion beam comprises adjusting the ion beam for substantially
parallel ion trajectories.
10. A method as defined in claim 8, wherein the implant angle is
zero degrees and the workpiece is tilted normal to the measured
beam direction.
11. A method as defined in claim 8, wherein the step of measuring
parallelism of the ion beam comprises the step of measuring an
angle of non-parallelism of the ion beam and wherein the step of
adjusting the ion beam is based on the measured angle of
non-parallelism.
12. A method as defined in claim 11 wherein the angle of
non-parallelism and the beam direction are measured with a movable
beam profiler and one or more beam detectors.
13. A method as defined in claim 8 wherein the step of tilting a
workpiece comprises tilting a semiconductor wafer.
14. Apparatus for implanting ions into a workpiece, comprising:
means for generating an ion beam; means for measuring parallelism
of the ion beam in a plane; means for adjusting the ion beam in
said plane for a desired parallelism based on the measured
parallelism; means for measuring a beam direction of the adjusted
ion beam in said plane .Iadd.without implanting any workpiece with
the ion beam.Iaddend.; means for tilting a workpiece about an axis
perpendicular to said plane at an implant angle referenced to the
measured beam direction; and means for performing an implant with
the workpiece tilted at the implant angle referenced to the
measured beam direction.
15. Apparatus as defined in claim 14, wherein said means for
adjusting the ion beam comprises means for adjusting the ion beam
for substantially parallel trajectories.
16. Apparatus as defined in claim 14, wherein the implant angle is
zero degrees and the workpiece is tilted normal to the measured
beam direction.
17. Apparatus as defined in claim 14, wherein said means for
measuring parallelism and said means for measuring the beam
direction comprises a movable beam profiler and one or more beam
detectors.
18. Apparatus as defined in claim 14, wherein said means for
tilting the workpiece comprises a tilt mechanism for tilting a
semiconductor wafer relative to the ion beam.
19. Apparatus for implanting ions into a workpiece, comprising: an
ion beam generator; an ion optical element for adjusting the ion
beam for a desired parallelism in a plane; a measuring system for
measuring a beam direction of the adjusted ion beam in said plane
.Iadd.without implanting any workpiece with the ion beam.Iaddend.;
and a tilt mechanism for tilting the workpiece about an axis
perpendicular to said plane at an implant angle referenced to the
measured beam direction, wherein an implant is performed with the
workpiece tilted at the implant angle referenced to the measured
beam direction.
20. Apparatus as defined in claim 19, wherein said ion optical
element comprises an angle corrector magnet for adjusting the ion
beam for substantially parallel ion trajectories.
21. Apparatus as defined in claim 18, wherein said measuring system
comprises a movable beam profiler and one or more beam
detectors.
22. Apparatus as defined in claim 18, wherein said tilt mechanism
is configured for tilting a semiconductor wafer.
23. A method as defined in claim 1, further comprising the step of
scanning the ion beam in said plane.
24. A method as defined in claim 8, further comprising the step of
scanning the ion beam in said plane.
25. Apparatus as defined in claim 14, further comprising means for
scanning the ion beam in said plane.
26. Apparatus as defined in claim 19, further comprising a scanner
for scanning the ion beam in said plane.
.Iadd.27. A method for implanting ions into a workpiece,
comprising: generating an ion beam; measuring a beam direction of
the ion beam without implanting any workpiece with the ion beam;
tilting a workpiece about an axis that is not parallel to the
measured beam direction at an implant angle referenced to the
measured beam direction; and performing an implant with the
workpiece tilted at the implant angle..Iaddend.
.Iadd.28. A method as defined in claim 27, wherein tilting the
workpiece comprises tilting a semiconductor wafer..Iaddend.
.Iadd.29. A method as defined in claim 27, wherein tilting the
workpiece comprises tilting a semiconductor wafer about an axis
that is substantially perpendicular to the measured beam
direction..Iaddend.
.Iadd.30. A method as defined in claim 27, further comprising
scanning the ion beam..Iaddend.
.Iadd.31. A method as defined in claim 27, wherein generating an
ion beam comprises generating a ribbon ion beam..Iaddend.
.Iadd.32. A method as defined in claim 27, further comprising
adjusting the ion beam for a desired parallelism..Iaddend.
.Iadd.33. Apparatus for implanting ions into a workpiece,
comprising: means for generating an ion beam; means for measuring a
beam direction of the ion beam without implanting any workpiece
with the ion beam; means for tilting a workpiece about an axis that
is not parallel to the measured beam direction at an implant angle
referenced to the measured beam direction, wherein the implant is
performed with the workpiece tilted at the implant
angle..Iaddend.
.Iadd.34. Apparatus as defined in claim 33, wherein said means for
tilting the workpiece comprises a tilt mechanism for tilting a
semiconductor wafer relative to the ion beam..Iaddend.
.Iadd.35. Apparatus as defined in claim 33, where said means for
tilting the workpiece comprises a tilt mechanism for tilting a
semiconductor wafer about an axis that is substantially
perpendicular to the measured beam direction..Iaddend.
.Iadd.36. Apparatus as defined in claim 33, further comprising
means for scanning the ion beam..Iaddend.
.Iadd.37. Apparatus as defined in claim 33, wherein said means for
generating comprises means for generating a ribbon ion
beam..Iaddend.
.Iadd.38. Apparatus as defined in claim 33, further comprising
means for adjusting the ion beam for a desired
parallelism..Iaddend.
.Iadd.39. Apparatus for implanting ions into a workpiece,
comprising: an ion beam generator; a measuring system for measuring
a beam direction of the ion beam without implanting any workpiece
with the ion beam; and a tilt mechanism for tilting the workpiece
about an axis that is not parallel to the measured beam direction
at an implant angle referenced to the measured beam direction,
wherein the implant is performed with the workpiece tilted at the
implant angle..Iaddend.
.Iadd.40. Apparatus as defined in claim 39, wherein said tilt
mechanism is configured for tilting a semiconductor
wafer..Iaddend.
.Iadd.41. Apparatus as defined in claim 39, wherein said tilt
mechanism is configured to tilt a semiconductor wafer about an axis
that is substantially perpendicular to the measured beam
direction..Iaddend.
.Iadd.42. Apparatus as defined in claim 39, further comprising a
scanner for scanning the ion beam..Iaddend.
.Iadd.43. Apparatus as defined in claim 39, where said ion beam
generator is configured to generate a ribbon ion beam..Iaddend.
.Iadd.44. Apparatus as defined in claim 39, further comprising an
ion optical element for adjusting the ion beam for a desired
parallelism..Iaddend.
.Iadd.45. A method for implanting ions into a workpiece, comprising
the steps of: generating an ion beam; adjusting the ion beam for a
desired measure of parallelism; measuring a beam direction of the
adjusted ion beam without implanting any workpiece with the ion
beam; tilting a workpiece about an axis that is not parallel to the
measured beam direction at an implant angle referenced to the
measured beam direction; and performing the implant with the
workpiece titled at the implant angle..Iaddend.
.Iadd.46. A method as defined in claim 45, wherein the step of
adjusting the ion beam comprises adjusting the ion beam for
substantially parallel ion trajectories..Iaddend.
.Iadd.47. A method as defined in claim 45, wherein tilting the
workpiece comprises tilting a semiconductor wafer..Iaddend.
.Iadd.48. A method as defined in claim 45, wherein tilting the
workpiece comprises tilting a semiconductor wafer about an axis
that is substantially perpendicular to the measured beam
direction..Iaddend.
.Iadd.49. A method for implanting ions into a workpiece, comprising
the steps of: generating an ion beam; measuring parallelism of the
ion beam; adjusting the ion beam for a desired parallelism based on
the measured parallelism; measuring a beam direction of the
adjusted ion beam without implanting any workpiece with the ion
beam; tilting a workpiece about an axis that is not parallel to the
measured beam direction at an implant angle referenced to the
measured beam direction; and performing the implant with the
workpiece tilted at the implant angle referenced to the measured
beam direction..Iaddend.
.Iadd.50. A method as defined in claim 49, wherein the step of
adjusting the ion beam comprises adjusting the ion beam for
substantially parallel ion trajectories..Iaddend.
.Iadd.51. A method as defined in claim 49, wherein tilting the
workpiece comprises tilting a semiconductor wafer..Iaddend.
.Iadd.52. A method as defined in claim 49, wherein tilting the
workpiece comprises tilting a semiconductor wafer about an axis
that is substantially perpendicular to the measured beam
direction..Iaddend.
.Iadd.53. Apparatus for implanting ions into a workpiece,
comprising: means for generating an ion beam; means for measuring
parallelism of the ion beam; means for adjusting the ion beam for a
desired parallelism based on the measured parallelism; means for
measuring a beam direction of the adjusted ion beam without
implanting any workpiece with the ion beam; means for tilting a
workpiece about an axis that is not parallel to the measured beam
direction at an implant angle referenced to the measured beam
direction; and means for performing the implant with the workpiece
tilted at the implant angle referenced to the measured beam
direction..Iaddend.
.Iadd.54. Apparatus as defined in claim 53, wherein said means for
adjusting the ion beam comprises means for adjusting the ion beam
for substantially parallel ion trajectories..Iaddend.
.Iadd.55. Apparatus as defined in claim 53, wherein said means for
tilting the workpiece comprises a tilt mechanism for tilting a
semiconductor wafer relative to the ion beam..Iaddend.
.Iadd.56. Apparatus as defined in claim 53, wherein said means for
tilting the workpiece comprises a tilt mechanism for tilting a
semiconductor wafer about an axis that is substantially
perpendicular to the measured beam direction..Iaddend.
.Iadd.57. Apparatus for implanting ions into a workpiece,
comprising: an ion beam generator; an ion optical element for
adjusting the ion beam for a desired parallelism; a measuring
system for measuring a beam direction of the adjusted ion beam
without implanting any workpiece with the ion beam; and a tilt
mechanism for tilting the workpiece about an axis that is not
parallel to the measured beam direction at an implant angle
referenced to the measured beam direction, wherein the implant is
performed with the workpiece tilted at the implant angle referenced
to the measured beam direction..Iaddend.
.Iadd.58. Apparatus as define in claim 57, wherein said ion optical
element comprises an angle corrector magnet for adjusting the ion
beam for substantially parallel ion trajectories..Iaddend.
.Iadd.59. Apparatus as define in claim 57, wherein said tilt
mechanism is configured for tilting a semiconductor
wafer..Iaddend.
.Iadd.60. Apparatus as define in claim 57, wherein said tilt
mechanism is configured to tilt a semiconductor wafer about an axis
that is substantially perpendicular to the measured beam
direction..Iaddend.
Description
FIELD OF THE INVENTION
This invention relates to systems and methods for ion implantation
of semiconductor wafers or other workpieces and, more particularly,
to methods and apparatus for adjusting beam parallelism in ion
implanters.
BACKGROUND OF THE INVENTION
Ion implantation is a standard technique for introducing
conductivity-altering impurities into semiconductor wafers. A
desired impurity material is ionized in an ion source, the ions are
accelerated to form an ion beam of prescribed energy, and the ion
beam is directed at the surface of the wafer. The energetic ions in
the beam penetrate into the bulk of the semiconductor material and
are embedded into the crystalline lattice of the semiconductor
material to form a region of desired conductivity.
Ion implantation systems usually include an ion source for
converting a gas or a solid material into a well-defined ion beam.
The ion beam is mass analyzed to eliminate undesired ion species,
is accelerated to a desired energy and is directed onto a target
plane. The beam is distributed over the target area by beam
scanning, by target movement or by a combination of beam scanning
and target movement. An ion implanter which utilizes a combination
of beam scanning and target movement is disclosed in U.S. Pat. No.
4,922,106 issued May 1, 1990 to Berrian et al.
The delivery of a parallel ion beam to the semiconductor wafer is
an important requirement in many applications. A parallel ion beam
is one which has parallel ion trajectories over the surface of the
semiconductor wafer. In cases where the ion beam is scanned, the
scanned beam is required to maintain parallelism over the wafer
surface. The parallel ion beam prevents channeling of incident ions
in the crystal structure of the semiconductor wafer or permits
uniform channeling in cases where channeling is desired. Typically,
a serial ion implanter is utilized when a high degree of beam
parallelism is required.
In one approach, the beam is scanned in one dimension so that it
appears to diverge from a point, referred to as the scan origin.
The scanned beam then is passed through an ion optical element
which performs focusing. The ion optical element converts the
diverging ion trajectories to parallel ion trajectories for
delivery to the semiconductor wafer. Focusing can be performed with
an angle corrector magnet or with an electrostatic lens. The angle
correction magnet produces both bending and focusing of the scanned
ion beam. Parallelism may be achieved with an electrostatic lens,
but energy contamination can be a drawback.
The output ion beam from the angle corrector magnet or other
focusing element may be parallel or may be converging or diverging,
depending on the parameters of the ion beam and the parameters of
the focusing element. When an angle corrector magnet is utilized,
parallelism can be adjusted by varying the magnetic field of the
angle corrector magnet. The angle corrector magnet typically has a
single magnetic field adjustment which varies both parallelism and
bend angle, or beam direction. It will be understood that the ion
implanter is often required to run a variety of different ion
species and ion energies. When the beam parameters are changed,
readjustment of the angle corrector magnet is required to restore
beam parallelism.
In prior art ion implanters, the angle corrector magnet is
typically adjusted so that the ion beam has normal incidence on a
wafer plane of the ion implanter end station. However, the angle
corrector adjustment which achieves normal incidence on the wafer
plane may result in less than optimum parallelism. In particular,
an ion beam that is adjusted for normal incidence on the wafer
plane may be somewhat diverging or converging. As shown in FIG. 8,
the angle corrector magnet is adjusted such that the center ray of
ion beam 200 is normal to wafer plane 202. However, when the beam
200 is adjusted to be normal to wafer plane 202, the parallelism of
beam 200 may be degraded such that the beam converges or diverges.
The lack of parallelism is unacceptable in highly critical
applications.
In another approach, the angle corrector magnet is designed for
best parallelism under typical conditions, and the ion implanter
end station is positioned for normal incidence of the ion beam on
the wafer. However, beam parallelism and normal incidence are not
maintained over a wide range of beam parameters, and changing the
position of the end station is very difficult.
Accordingly, there is a need for improved methods and apparatus for
adjusting beam parallelism in ion implanters.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, a method is provided
for implanting ions into a workpiece. The method comprises the
steps of generating an ion beam, adjusting the ion beam for a
desired measure of parallelism, measuring a beam direction of the
adjusted ion beam, orienting a workpiece at an implant angle
referenced to the measured beam direction, and performing an
implant with the workpiece oriented at the implant angle.
The step of adjusting the ion beam may comprise adjusting the ion
beam for substantially parallel ion trajectories. In general, the
beam direction may differ from the beam axis of the ion implanter.
The implant angle may be zero degrees, in which case the workpiece
is oriented normal to the measured beam direction.
The workpiece may comprise a semiconductor wafer, and the step of
orienting the workpiece may comprise tilting the semiconductor
wafer at the implant angle referenced to the measured beam
direction.
The method may further comprise the step of measuring an angle of
non-parallelism of the ion beam. The step of adjusting the ion beam
may be based on the measured angle of non-parallelism. The beam
direction and the angle of non-parallelism of the ion beam may be
measured with a movable beam profiler and one or more beam
detectors.
According to another aspect of the invention, apparatus is provided
for implanting ions into a workpiece. The apparatus comprises means
for generating an ion beam, means for measuring parallelism of the
ion beam, means for adjusting the ion beam for a desired
parallelism based on the measured parallelism, means for measuring
a beam direction of the adjusted ion beam, means for tilting a
workpiece at an implant angle referenced to the measured beam
direction, and means for performing an implant with the workpiece
tilted at the implant angle referenced to the measured beam
direction.
According to a further aspect of the invention, apparatus is
provided for implanting ions into a workpiece. The apparatus
comprises an ion beam generator, an ion optical element for
adjusting the ion beam for a desired parallelism, a measuring
system for measuring a beam direction of the adjusted ion beam, and
a tilt mechanism for tilting a workpiece at an implant angle
referenced to the measured beam direction. An implant is performed
with the workpiece tilted at the implant angle referenced to the
measured beam direction.
The ion optical element may comprise an angle corrector magnet for
adjusting the ion beam for substantially parallel ion trajectories.
The measuring system may comprise a movable beam profiler and one
or more beam detectors. Where the implant angle is zero degrees,
the workpiece is tilted normal to the measured beam direction.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, reference is
made to the accompanying drawings, which are incorporated herein by
reference and in which:
FIG. 1 is a schematic diagram of an ion implanter suitable for
implementing the present invention;
FIG. 2 is a schematic diagram that illustrates the operation of an
angle corrector magnet for the case of a relatively large bend
angle and converging ion trajectories;
FIG. 3 is a schematic diagram that illustrates the operation of an
angle corrector magnet for the case of a relatively small bend
angle and diverging ion trajectories;
FIG. 4 is a flow chart of a process for adjusting an ion implanter
in accordance with an embodiment of the invention;
FIG. 5 is a schematic diagram of a parallel ion beam incident on a
tilted wafer in accordance with an embodiment of the invention;
FIGS. 6A-6C are schematic diagrams that illustrate operation of a
device for measuring beam parallelism and beam direction;
FIGS. 7A-7C are graphs of beam detector output as a function of
beam profiler position for the beam conditions illustrated in FIGS.
6A-6C, respectively; and
FIG. 8 is a schematic diagram that illustrates the prior art method
of adjusting beam parallelism.
DETAILED DESCRIPTION
A simplified block diagram of an example of an ion implanter
suitable for incorporating the present invention is shown in FIG.
1. An ion beam generator 10 generates an ion beam of a desired
species, accelerates ions in the ion beam to desired energies,
performs mass/energy analysis of the ion beam to remove energy and
mass contaminants and supplies an energetic ion beam 12 having low
level of energy and mass contaminants. A scanning system 16, which
includes a scanner 20 and an angle corrector 24, deflects the ion
beam 12 to produce a scanned ion beam 30 having parallel or nearly
parallel ion trajectories. An end station 32 includes a platen 36
that supports a semiconductor wafer 34 or other workpiece in the
path of scanned ion beam 30 such that ions of the desired species
are implanted into the semiconductor wafer 34. The ion implanter
may include additional components well known to those skilled in
the art. For example, the end station 32 typically includes
automated wafer handling equipment for introducing wafers into the
ion implanter and for removing wafers after implantation, a dose
measuring system, an electron flood gun, etc. It will be understood
that the entire path traversed by the ion beam is evacuated during
ion implantation.
The principal components of ion beam generator 10 include an ion
beam source 40, a source filter 42, an acceleration/deceleration
column 44 and a mass analyzer 50. The source filter 42 is
preferably positioned in close proximity to ion beam source 40. The
acceleration/deceleration column 44 is positioned between source
filter 42 and mass analyzer 50. The mass analyzer 50 includes a
dipole analyzing magnet 52 and a mask 54 having a resolving
aperture 56.
The scanner 20, which may be an electrostatic scanner, deflects ion
beam 12 to produce a scanned ion beam having ion trajectories which
diverge from a scan origin 60. The scanner 20 may comprise
spaced-apart scan plates connected to a scan generator. The scan
generator applies a scan voltage waveform, such as a sawtooth
waveform, for scanning the ion beam in accordance with the electric
field between the scan plates.
Angle corrector 24 is designed to deflect ions in the scanned ion
beam to produce scanned ion beam 30 having parallel ion
trajectories, thus focusing the scanned ion beam. In particular,
angle corrector 24 may comprise magnetic pole pieces 26 which are
spaced apart to define a gap and a magnet coil (not shown) which is
coupled to a power supply 28. The scanned ion beam passes through
the gap between the pole pieces 26 and is deflected in accordance
with the magnetic field in the gap. The magnetic field may be
adjusted by varying the current through the magnet coil. Beam
scanning and beam focusing are performed in a selected plane, such
as a horizontal plane.
In the embodiment of FIG. 1, end station 32 includes a beam
parallelism and direction measuring system 80. System 80 measures
beam parallelism and direction as described below. In addition, end
station 32 includes a tilt mechanism 84 for tilting wafer support
platen 36 with respect to the scanned ion beam 30. In one
embodiment, tilt mechanism 84 may tilt wafer support platen 36 with
respect to two orthogonal axes.
Examples of operation of angle corrector 24 are shown in FIGS. 2
and 3. As shown, the pole pieces 26 of angle corrector 24 may be
wedged shaped or similarly shaped so that different ion
trajectories have different path lengths through the gap between
the pole pieces. In FIG. 2, a relatively high intensity magnetic
field is applied. The ion trajectories have a relatively large bend
angle and may be converging as they exit from angle corrector 24.
In the example of FIG. 3, a relatively low intensity magnetic field
is applied. The ion trajectories have a relatively small bend angle
and may be diverging as they exit from angle corrector 24. Thus,
scanned ion beam 30 is incident on a wafer plane 70 at a positive
angle 72 with respect to a normal to wafer plane 70 in the example
of FIG. 2 and is incident on wafer plane 70 at a negative angle 74
with respect to a normal to wafer plane 70 in the example of FIG.
3. It will be understood that parallel or nearly parallel ion
trajectories can be produced by appropriate adjustment of the
magnetic field in angle corrector 24. However in general, the
magnetic field that provides the best parallelism does not
necessarily result in normal incidence of scanned ion beam 30 on
wafer plane 70.
A flow chart of a process for adjusting an ion implanter and
performing ion implantation in accordance with an embodiment of the
invention is shown in FIG. 4. In step 100, an ion beam is generated
and is transported through the beamline of an ion implanter. As
shown in FIG. 1, ion beam 12 is generated by ion beam generator 12
and is transported through scanner 20 and angle corrector 24 to end
station 32.
In step 102, the parallelism of the ion beam is measured at or near
the plane where the ion beam is incident on the semiconductor wafer
or other workpiece. An example of a technique for measuring ion
beam parallelism is described below in connection with FIGS. 6A-6C
and 7A-7C. The parallelism measurement typically provides an angle
of non-parallelism of the ion beam and, in particular, provides a
half angle of convergence or divergence of the ion beam. The
measured angle of non-parallelism represents the maximum excursion
of the ion beam trajectories from the center ray of the ion
beam.
In step 104, the ion beam is adjusted for a desired measure of
parallelism, typically near zero divergence or convergence. As
shown in FIG. 5, the parallelism of the ion beam may be changed by
adjusting the current supplied by power supply 28 to the magnet
coil. The adjusted current causes a change in the magnetic field of
angle corrector 24, which in turn changes the ion trajectories in
the ion beam. The adjustment is made by monitoring the measured
parallelism of scanned ion beam 30 as power supply 28 is adjusted.
When the best parallelism is achieved, the adjustment process of
step 104 is terminated. Typically, the ion beam may be adjusted
within 0.1.degree. half angle of divergence or convergence.
The magnetic field which provides the best parallelism is, in
general, not the same magnetic field which directs scanned ion beam
30 normal to wafer plane 70 of the ion implanter end station.
Instead, parallel ion beam 30 is incident on wafer plane 70 at an
angle 120 relative to a normal to wafer plane 70, as shown in FIG.
5. It will be understood that the angle 120 is exaggerated in FIG.
5 for purposes of illustration.
In step 106, the direction of the adjusted ion beam is measured. In
particular, the angle 120 of the adjusted ion beam relative to the
normal to wafer plane 70 is measured. An example of a technique for
measuring ion beam direction is described below in connection with
FIGS. 6A-6C and 7A-7C. Beam parallelism and beam direction are
measured in the plane of scanning and focusing of the ion beam.
In step 108, the implant angle is set relative to the direction of
the adjusted ion beam and, in particular, referenced to angle 120.
The implant angle is set by tilting wafer support platen 36
relative to the wafer plane 70 of the implanter using tilt
mechanism 84. Where normal incidence of the parallel scanned ion
beam 30 on the wafer 34 is desired, wafer support platen 36 is
tilted by an angle 122 that is equal to angle 120. Thus, the wafer
support surface of platen 36 is normal to parallel scanned ion beam
30. Where non-zero implant angles are desired, wafer support platen
36 is tilted relative to the measured beam direction. The measured
beam direction is thus the reference for setting the implant angle.
The non-zero implant angle may be set by tilting the wafer in a
direction parallel to the plane of scanning and focusing or may be
set by tilting the wafer in a direction orthogonal to the plane of
scanning and focusing. In each case, the non-zero implant angle is
referenced to the measured beam direction.
In step 110, the implant is performed with the wafer support platen
at the desired implant angle referenced to the measured beam
direction and with the scanned ion beam 30 adjusted for best
parallelism. Thus, the best parallelism is achieved at the desired
implant angle.
An example of a technique for measuring ion beam parallelism and
direction is described with reference to FIGS. 6A-6C and 7A-7C.
FIGS. 6A-6C are schematic diagrams which illustrate the measurement
of different ion beams with a beam profiler and two beam detectors.
FIGS. 7A-7C are graphs that illustrate the outputs of the beam
detectors as a function of profiler position.
As shown in FIGS. 6A-6C, ion beam parallelism and direction are
measured using a moving beam profiler 150 and spaced-apart beam
detectors 152 and 154, which correspond to beam parallelism and
direction measuring system 80 (FIG. 1). Beam profiler 150 may be
any element that partially blocks the ion beam and is laterally
movable relative to the ion beam. Detectors 152 and 154, for
example, may be Faraday cups which produce an electrical output
signal in response to an incident ion beam. As the profiler 150 is
moved across the ion beam, it blocks a portion of the ion beam and
produces an ion beam shadow. The beam shadow moves across detectors
152 and 154 and produces output signals in the form of
negative-going output current pulses.
As shown in FIG. 6A, a parallel scanned ion beam 160 has normal
incidence on a wafer plane 170. Detectors 152 and 154 produce
output pulses as shown in FIG. 7A when the profiler 150 is
positioned in alignment with each detector. The profiler positions
at which detector output pulses are generated can be used to
determine that ion beam 160 has parallel trajectories and is normal
to wafer plane 170.
Referring to FIG. 6B, a diverging ion beam 162 has normal incidence
on wafer plane 170. In this case, detector 152 produces an output
pulse as shown in FIG. 7B when profiler 150 is positioned to the
right of detector 152, and detector 154 produces an output pulse
when profiler 150 is positioned to the left of detector 154. The
profiler positions at which detector output pulses are generated
can be used to determine the angle of divergence of ion beam 162.
In response to a converging ion beam (not shown), detector 152
produces an output pulse when profiler 150 is positioned to the
left of detector 152, and detector 154 produces an output pulse
when profiler 150 is positioned to the right of detector 154. The
profiler positions at which detector output pulses are generated
can be used to determine the angle of convergence of the ion
beam.
As shown in FIG. 6C, a parallel ion beam 164 is incident on wafer
plane 170 at an angle 166. In this case, detectors 152 and 154
produce output pulses as shown in FIG. 7C when the profiler 150 is
positioned to the left of the respective detectors 152 and 154. The
profiler positions at which detector output pulses are generated
can be used to determine the direction and parallelism of ion beam
164.
In general, the ion beam may be converging or diverging and may
have a non-zero beam angle relative to the wafer plane. The
profiler positions when detector outputs pulses are generated can
be analyzed to determine both the parallelism and direction of the
ion beam. The parallelism may be specified as the half angle of
divergence or convergence, and the beam direction may be specified
relative to a normal to a wafer plane 170. Additional details
regarding techniques for measuring ion beam parallelism and
direction are provided in U.S. application Ser. No. 09/588,419,
filed Jun. 6, 2000, which is hereby incorporated by reference.
It will be understood that different techniques may be used for
measuring beam parallelism and direction within the scope of the
invention. In addition, the invention is not limited to use with a
scanned ion beam. For example, the invention may be used with a
ribbon ion beam as disclosed in U.S. Pat. No. 5,350,926, issued
Sep. 27, 1994 to White et al.
While there have been shown and described what are at present
considered the preferred embodiments of the present invention, it
will be obvious to those skilled in the art that various changes
and modifications may be made therein without departing from the
scope of the invention as defined by the appended claims.
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