U.S. patent number RE44,240 [Application Number 12/189,817] was granted by the patent office on 2013-05-28 for electron beam exposure system.
This patent grant is currently assigned to Mapper Lithography IP B.V.. The grantee listed for this patent is Bert Jan Kampherbeek, Pieter Kruit, Alexander Hendrik Vincent Van Veen, Marco Jan-Jaco Wieland. Invention is credited to Bert Jan Kampherbeek, Pieter Kruit, Alexander Hendrik Vincent Van Veen, Marco Jan-Jaco Wieland.
United States Patent |
RE44,240 |
Wieland , et al. |
May 28, 2013 |
Electron beam exposure system
Abstract
The invention relates to an electron beam exposure apparatus for
transferring a pattern onto the surface of a target, comprising: a
beamlet generator for generating a plurality of electron beamlets;
a modulation array for receiving said plurality of electron
beamlets, comprising a plurality of modulators for modulating the
intensity of an electron beamlet; a controller, connected to the
modulation array for individually controlling the modulators, an
adjustor, operationally connected to each modulator, for
individually adjusting the control signal of each modulator; a
focusing electron optical system comprising an array of
electrostatic lenses wherein each lens focuses a corresponding
individual beamlet, which is transmitted by said modulation array,
to a cross section smaller than 300 nm, and a target holder for
holding a target with its exposure surface onto which the pattern
is to be transferred in the first focal plane of the focusing
electron optical system.
Inventors: |
Wieland; Marco Jan-Jaco (Delft,
NL), Kampherbeek; Bert Jan (Delft, NL), Van
Veen; Alexander Hendrik Vincent (Rotterdam, NL),
Kruit; Pieter (Delft, NL) |
Applicant: |
Name |
City |
State |
Country |
Type |
Wieland; Marco Jan-Jaco
Kampherbeek; Bert Jan
Van Veen; Alexander Hendrik Vincent
Kruit; Pieter |
Delft
Delft
Rotterdam
Delft |
N/A
N/A
N/A
N/A |
NL
NL
NL
NL |
|
|
Assignee: |
Mapper Lithography IP B.V.
(Delft, NL)
|
Family
ID: |
32230384 |
Appl.
No.: |
12/189,817 |
Filed: |
August 12, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10699246 |
Oct 30, 2003 |
6897458 |
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60422758 |
Oct 30, 2002 |
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Reissue of: |
11128512 |
May 12, 2005 |
7091504 |
Aug 15, 2006 |
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Current U.S.
Class: |
250/494.1;
250/396R; 250/306; 250/492.3; 250/492.22; 250/398 |
Current CPC
Class: |
B82Y
40/00 (20130101); H01J 3/02 (20130101); H01J
37/06 (20130101); H01J 37/3177 (20130101); B82Y
10/00 (20130101); H01J 2237/3045 (20130101); H01J
2237/06308 (20130101); H01J 2237/06375 (20130101); H01J
2237/0435 (20130101) |
Current International
Class: |
H01J
37/30 (20060101); H01J 37/304 (20060101) |
Field of
Search: |
;250/492.22,492.3,494.1,306,307,310,397,398 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1300870 |
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Apr 2003 |
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EP |
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1300870 |
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Sep 2003 |
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EP |
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2340991 |
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Mar 2000 |
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GB |
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2340991 |
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Jan 2002 |
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GB |
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2002110527 |
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Apr 2002 |
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JP |
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2002110527 |
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Dec 2002 |
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JP |
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0241372 |
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May 2002 |
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WO |
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0243102 |
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May 2002 |
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WO |
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WO 02/41372 |
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May 2002 |
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WO |
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WO 02/43102 |
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May 2002 |
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WO |
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2004040614 |
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May 2004 |
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WO |
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Other References
"Microstructures for Particle Beam Control", G.W., Journal of
Vacuum Science and Tech., Nov. 1, 1988, pp. 2023-2027, XP000001001.
cited by applicant .
Shimazu et al Jpn Appl. Phys. 34 p6689. An approach to a
High-Througput E-Beam Writer with a Single-Gun Multiple-Path
System. cited by applicant .
Journ. Vac Science B.18. New concept for High-throughput
multielectron beam direct write system. cited by applicant .
"Microstructures for Particle Beam Control", G.W., Journal of
Vacuum Science and Tech., Nov. 1, 1999, pp. 2023-2027, XP000001001.
cited by applicant.
|
Primary Examiner: Wells; Nikita
Attorney, Agent or Firm: Hoyng Monegier LLP Owen; David P.
Haitjema; Caroline J.
Parent Case Text
.Iadd.Notice: More than one reissue application has been filed for
the reissue of U.S. Pat. No. 7,091,504. The reissue applications
are application Ser. No. 12/189,817 (the present application), Ser.
Nos. 13/343,036, and 13/343,038, all of which are divisional
reissues of U.S. Pat. No. 7,091,504..Iaddend.
The present patent application is a Divisional of application Ser.
No. 10/699,246 filed Oct. 30, 2003, now U.S. Pat. No. 6,897,458
which is a Non-Provisional of Provisional Application No.
60/422,758 filed Oct. 30, 2002.
Claims
The invention claimed is:
1. A method for transferring a pattern onto a target exposure
surface with a multi-beam lithography system, comprising the steps
of: generating a plurality of beamlets; individually modulating the
intensity of each beamlet of said plurality of beamlets by means of
a modulator device .Iadd.for blanking or not blanking each beamlet
in whole or in part.Iaddend.; controlling said modulator device,
using control signals, by means of a controller operationally
coupled to said modulator; .Iadd.and .Iaddend. .[.individually.].
adjusting .Iadd.at least one of .Iaddend.said control signals.
2. The method according to claim 1 in which timing of said control
signals is adjusted.
3. The method of claim 1, in which timing of said control signals
is individually adjusted.
4. The method according to claim 1 in which modulation is performed
.[.as an "off" or "on" condition of a beamlet,.]. by either
deflecting said beamlet within the system, or by allowing free
passage of said beamlet at said modulator.[., the condition thereby
being controlled on the basis of available electronic pattern data,
in which timing is adjusted by correcting an instance of deflection
or passage of said beamlet, said correction being calculated by the
controller.]..
5. The method of claim 1, .Iadd.wherein .Iaddend.said control
signals .[.having.]. .Iadd.have .Iaddend.a timing base, and timing
of the control signal of at least one beamlet is adjusted.
6. The method of claim 1, further comprising the step of
determining a position of a beamlet, storing said position in a
memory and comparing said position with a desired position.
7. The method of claim 6, wherein said position of a beamlet is the
actual position of a beamlet on said exposure surface.
8. The method of claim 6, wherein said adjustment of said timing is
based on the result of said comparing.
9. The method of claim .[.1.]. .Iadd.2.Iaddend., wherein said
timing is adjusted locally.
10. The method of claim .[.1.]. .Iadd.2.Iaddend., wherein
.Iadd.said .Iaddend.adjusting .Iadd.of .Iaddend.timing .Iadd.of
said control signals .Iaddend.comprises correcting a timing
window.
11. The method of claim .[.1.]. .Iadd.2.Iaddend., wherein said
control signals have a timing base.
12. The method of claim 11, wherein said controller calculates a
corrected timing window, and applies said corrected timing window
to said timing base.
13. The method of claim 11, wherein said controller calculates a
corrected timing window, and applies said corrected timing window
to said timing base of an individual beamlet.
14. An electron beam exposure apparatus for transferring a pattern
onto the surface of a target using a plurality of electron
beamlets, comprising: a modulator array for receiving said
plurality of electron beamlets, comprising a plurality of
modulators for modulating the intensity of a beamlet of said
plurality of beamlets; a controller, operationally coupled to said
modulator array, for controlling each modulator of said plurality
modulators .Iadd.on the basis of electronic pattern data to write
the pattern.Iaddend., said controller producing a plurality of
control signals with at least one control signal for each
modulator, and an adjustor for allowing individual adjustment of a
control signal.
15. The electron beam exposure apparatus according to claim 14,
wherein said plurality of control signals .[.having.]. .Iadd.have
.Iaddend.a timing base.
16. The electron beam exposure apparatus according to claim 14,
wherein said adjustor is adapted for allowing individual adjustment
of timing of a control signal.
17. The electron beam exposure apparatus according to claim 14,
furthermore provided with a measuring device for measuring the
actual position of at least one of said beamlets, and wherein the
controller is provided with a memory for storing said actual
position and a desired position, a comparator for comparing the
desired position and the actual position of said at least one of
said beamlets, and wherein the adjustor is operationally coupled to
the controller for receiving instructions for adjusting a control
signal issued to a modulator to compensate for the difference
between said desired position and said actual position of said at
least one of said electron beamlets.
18. The electron beam exposure apparatus according to claim 14,
wherein the adjustor is operationally coupled to the controller for
receiving instructions indicating the amount of the
adjustments.
19. The electron beam exposure apparatus of claim 14, wherein the
adjustor is adapted for adjusting timing of each control
signal.
20. The electron beam exposure apparatus of claim 14, further
comprising a beamlet generator, said beamlet generator comprising:
a source for emitting at least one electron beam, .Iadd.and
.Iaddend. at least one beamsplitter for splitting said at least one
emitted electron beam into said plurality of electron beamlets.
21. The electron beam exposure apparatus according to claim 20,
further comprising a modulation array, comprising a beamlet blanker
array comprising a plurality of beamlet blankers for the deflection
of a passing electron beamlet and a beamlet stop array, having a
plurality of apertures aligned with said beamlet blankers of said
beamlet blanker array.
22. The electron beam exposure apparatus according to claim
.[.20.]. .Iadd.21.Iaddend., further comprising a second
electrostatic lens array located between said beamsplitter and said
beamlet blanker array to focus said plurality of electron
beamlets.
23. The electron beam exposure apparatus according to claim 22,
wherein said beamlet blanker array is located in the focal plane of
said second electrostatic lens array.
24. An electron beam exposure apparatus for transferring a pattern
onto the surface of a target using a plurality of electron
beamlets, comprising: a modulator array for receiving said
plurality of electron beamlets, comprising a plurality of
modulators for modulating the intensity of a beamlet of said
plurality of beamlets; .Iadd.and .Iaddend. a controller,
operationally coupled to said modulator array, for controlling each
modulator of said plurality modulators .Iadd.on the basis of
electronic pattern data to write the pattern.Iaddend., said
controller producing a plurality of control signals with at least
one control signal for each modulator, said controller comprising
an adjustor allowing individual adjustment of at least one control
signal.
25. The electron beam exposure apparatus of claim 24, wherein said
plurality of control signals .[.having.]. .Iadd.have .Iaddend.a
timing base.
26. The electron beam exposure apparatus of claim 24, said adjustor
allowing individual adjustment of timing of at least one control
signal.
27. An electron beam exposure apparatus for transferring a pattern
onto the surface of a target using a plurality of electron
beamlets, comprising: .Iadd.a modulator array comprising a
plurality of modulators for modulating the intensity of a beamlet
of said plurality of beamlets;.Iaddend. a scanning deflector for
scanning said plurality of electron beamlets over said surface of
said target, comprising at least one array of electrostatic
deflectors having at least one electrostatic deflector for each
beamlet; a controller, operationally coupled to said scanning
deflector, for controlling each electrostatic deflector
.Iadd.individually .Iaddend.using a control signal; .Iadd.and
.Iaddend. an adjustor for .[.adusting.]. .Iadd.adjusting
.Iaddend.said control signal.
28. The electron electron beam exposure apparatus of claim 27,
wherein said control signal has a timing base, and said adjustor
being adapted for adjusting timing of said control signal.
29. An electron beam exposure apparatus for transferring a pattern
onto the surface of a target using a plurality of electron
beamlets, comprising: a scanning deflector for scanning said
plurality of electron beamlets over said surface of said
target.Iadd.; a beamlet blanking array.Iaddend., comprising at
least one array of electrostatic deflectors having at least one
electrostatic deflector for each beamlet .Iadd.for blanking
beamlets on the basis of electronic pattern data.Iaddend.; a
controller, operationally coupled to said .[.scanning deflector.].
.Iadd.beamlet blanking array.Iaddend., for controlling each
electrostatic deflector using a control signal, said controller
being adapted for adjusting at least one .Iadd.of the
.Iaddend.control .[.signal.]. .Iadd.signals.Iaddend..
30. The electron beam exposure apparatus of claim 29, wherein said
controller is operationally coupled to said .[.scanning
deflector.]. .Iadd.beamlet blanking array .Iaddend.for controlling
each electrostatic deflector using a control signal having a timing
base.
31. The electron beam exposure apparatus of claim 29, wherein said
controller being adapted for adjusting timing of at least one
control signal .Iadd.so that said pattern data is applied when the
corresponding beamlet enters a desired area to be written by the
beamlet.Iaddend..
32. The electron beam exposure apparatus of claim 29, wherein said
controller generates a plurality of control signals, at least one
control signal for each electrostatic deflector.
33. The electron beam exposure apparatus of claim 32, wherein said
controller is adapted for adjusting timing of each control
signal.
34. The electron beam exposure apparatus of claim 32, wherein said
controller is adapted for adjusting timing of each control signal
individually.
35. An electron beam exposure apparatus for transferring a pattern
onto the surface of a target using a plurality of electron
beamlets, comprising: a blanking deflection means for effectively
realising an off/on condition for individual beamlets at said
target surface, by deflecting such individual beamlets within the
system; a controller, operationally coupled to said blanking
deflection means, for individually controlling electrostatic
deflectors of said blanking deflection means, said controller using
an individual control signal for each deflector of said deflection
means, thereby determining said on and off condition for individual
beamlets; correction means, part of, or operationally associated
with said controller for individually correcting a timing window of
a beamlet adjusting the control signal of the blanking deflector
for said beamlet.
36. An electron beam exposure apparatus for transferring a pattern
onto the surface of a target using a plurality of electron
beamlets, comprising: a blanking deflection device for effectively
realising an off/on condition for individual beamlets at said
target surface, comprising a plurality of deflectors for deflecting
such individual beamlets within the system for realising said
off/on condition; a controller, operationally coupled to said
blanking deflection device, for individually controlling
electrostatic deflectors of said blanking deflection device, said
controller using an individual control signal for each deflector of
said deflection device, thereby determining said on and off
condition for individual beamlets; a correction device, part of, or
operationally associated with said controller for individually
correcting a timing window of a beamlet adjusting the control
signal of the blanking deflector for said beamlet.
.Iadd.37. The method according to claim 4, wherein said modulation
is controlled on the basis of available electronic pattern data in
which timing is adjusted by correcting an instance of deflection or
passage of said beamlet, said correction being calculated by the
controller..Iaddend.
.Iadd.38. A maskless lithography system for transferring a pattern
onto the surface of a target, comprising: an electron beam
generator for generating an electron beam; an optical system and
beam splitter for generating a plurality of separate beamlets from
the electron beam; a modulation array for modulating individual
beamlets on the basis of electronic pattern data to write the
pattern; and a focusing electron optical system for projecting the
beamlets onto the target and reducing the cross section of the
individual beamlets; wherein said beamlets projected onto the
target are maintained separate to each other until projection of
said beamlets on to said target..Iaddend.
.Iadd.39. The system according to claim 38, wherein said system
further includes, downstream of said beam splitter, a condensor
lens array for focusing individual beamlets within said plurality
of beamlets..Iaddend.
.Iadd.40. The system according to claim 39, wherein said individual
beamlets are focused to a diameter in a range from about 0.1 to 1
.mu.m..Iaddend.
.Iadd.41. The system according to claim 39, wherein the condensor
lens array comprises two aligned plates with holes..Iaddend.
.Iadd.42. The system according to claim 41, wherein the thickness
of the plates is within a range from about 10 to 500
.mu.m..Iaddend.
.Iadd.43. The system according to claim 41, wherein the condensor
lens array comprises a plate with holes of a diameter within a
range from 50 to 200 .mu.m, and a pitch within a range from about
50 to 500 .mu.m..Iaddend.
.Iadd.44. The system according to claim 41, wherein the system
further comprises insulators for supporting said
plates..Iaddend.
.Iadd.45. The system according to claim 38, wherein said modulation
array includes a beamlet blanker array and a beamlet stop
array..Iaddend.
.Iadd.46. The system according to claim 45, wherein said modulation
means is included between said beam splitter and said projection
lenses..Iaddend.
.Iadd.47. The system according to claim 45, wherein the beam
diameter is within the range from about 0.1 to 5 .mu.m at the
beamlet blanker array..Iaddend.
.Iadd.48. The system according to claim 45, wherein the transversal
energy at said beamlet blanker array is within the range from about
1 to 20 meV..Iaddend.
.Iadd.49. The system according to claim 45, wherein the beamlet
blanker array comprises an array of electrostatic deflectors, each
electrostatic deflector comprising a first electrode connected to
ground and a second electrode connected to a circuit receiving
control data..Iaddend.
.Iadd.50. The system according to claim 49, wherein each
electrostatic deflector is controlled individually..Iaddend.
.Iadd.51. The system according to claim 45, wherein the beamlet
blanker array is located in an electrostatic focal plane of the
plurality of beamlets..Iaddend.
.Iadd.52. The system according to claim 51, wherein the beamlet
stop array is positioned outside an electrostatic focal plane of
the plurality of beamlets..Iaddend.
.Iadd.53. The system according to claim 38, wherein the focusing
electron optical system comprises an array of electrostatic lenses
for focusing each individual beamlet within said plurality of
beamlets with a corresponding electrostatic lens..Iaddend.
.Iadd.54. The system according to claim 53, wherein the array of
electrostatic lenses comprises two or more plates, each plate
having a thickness within a range from about 10 to 500
.mu.m..Iaddend.
.Iadd.55. The system according to claim 53, wherein the array of
electrostatic lenses comprises two or more plates, the distance
between consecutive plates being within a range from 50 to 800
.mu.m..Iaddend.
.Iadd.56. The system according to claim 53, wherein the array of
electrostatic lenses comprises three or more plates, the distance
between consecutive plates being different from plate to
plate..Iaddend.
.Iadd.57. The system according to claim 38, wherein the focusing
electron optical system comprises a lens array of the magnetic
type..Iaddend.
.Iadd.58. The system according to claim 45, wherein the focusing
electron optical system comprises a lens array of the magnetic type
and an array of electrostatic lenses, the lens array of the
magnetic type being located between the beamlet stop array and the
array of electrostatic lenses..Iaddend.
.Iadd.59. The system according to claim 57, wherein the lens array
of the magnetic type is included for enhancing the focusing
properties of the projection system..Iaddend.
.Iadd.60. The system according to claim 38, wherein the beam
splitter is formed by a spatial filter..Iaddend.
.Iadd.61. The system according to claim 58, wherein the spatial
filter is formed by an aperture array..Iaddend.
.Iadd.62. The system according to claim 61, wherein the apertures
of the aperture array are arranged in a hexagonal
structure..Iaddend.
.Iadd.63. The system according to claim 61, wherein each aperture
of the aperture array has an area inversely proportional to the
current density of a beamlet that is, in use, transmitted through
said aperture..Iaddend.
.Iadd.64. The system according to claim 38, wherein the beam
splitter comprises an electrostatic quadruple lens
array..Iaddend.
.Iadd.65. The system according to claim 38, wherein the beam
splitter comprises a number of aperture arrays in series along the
path of the electron beam or plurality of beamlets, the aperture
arrays having mutually aligned apertures, each subsequent aperture
array along the path from electron beam generator to target having
apertures being smaller than corresponding apertures of the
previous array..Iaddend.
.Iadd.66. The system according to claim 38, wherein, along a
beamlet path from electron beam generator to target, an
electrostatic lens array is located immediately after said beam
splitter..Iaddend.
.Iadd.67. The system according to claim 38, the system further
comprising: a beamlet blanker array for controllably deflecting
individual beamlets of said plurality of beamlets; and a beamlet
stop array for obstructing deflected beamlets and letting through
undeflected beamlets..Iaddend.
.Iadd.68. The system according to claim 67, wherein the beamlet
blanker array is located in a focal plane of an electrostatic lens
array for focusing said plurality of beamlets..Iaddend.
.Iadd.69. The system according to claim 38, wherein said beamlets
projected onto the target are maintained parallel to one
another..Iaddend.
.Iadd.70. A deflection system for deflecting a plurality of
electron beamlets with respect to a target surface, the deflection
system comprising: a first deflector array for deflecting the
beamlets in a first direction; and a second deflector array for
deflecting the beamlets in a second direction, the second direction
being opposite to the first direction..Iaddend.
.Iadd.71. The deflection system according to claim 70, wherein, in
use, combined deflection of a beamlet by said first deflector array
and said second deflector array results in displacement of the
beamlet at the target surface without changing an orientation of
the beamlet with respect to the target surface..Iaddend.
.Iadd.72. The deflection system according to claim 71, wherein said
orientation of the beamlet is perpendicular to the target
surface..Iaddend.
.Iadd.73. A maskless lithography system for transferring a pattern
onto a surface of a target, comprising: a beamlet generator for
generating a plurality of electron beamlets; a modulation array for
modulating an intensity of electron beamlets of the plurality of
electron beamlets; a deflection system according to claim 70 for
deflecting the modulated electron beamlets; a target holder for
holding a target having a surface for receiving the pattern to be
transferred..Iaddend.
.Iadd.74. The system according to claim 73, wherein the system
further comprises an electron optical system for focusing the
modulated electron beamlets on the surface of the
target..Iaddend.
.Iadd.75. The system according to claim 73, wherein the deflection
system is positioned within the electron optical system such that
deflection occurs in a front focal plane of the electron optical
system..Iaddend.
.Iadd.76. An electron-optical arrangement for use in a maskless
lithography system, the arrangement comprising: a deflector system
according to claim 70 for deflecting a plurality of beamlets; and
an electrostatic lens array for focusing said plurality of
deflected beamlets; wherein the deflector array is positioned in a
front focal plane of the electrostatic lens array..Iaddend.
.Iadd.77. The arrangement according to claim 76, wherein the
electrostatic lens array comprises two or more plates, and the
deflector array is formed by deposition of electrostatic scan
deflectors on a target surface side of one of the two or more
plates of the electrostatic lens array..Iaddend.
.Iadd.78. The arrangement according to claim 76, wherein the
electrostatic lens array comprises two or more plates, each plate
having a thickness within a range from about 10 to 500
.mu.m..Iaddend.
.Iadd.79. The arrangement according to claim 76, wherein the
electrostatic lens array comprises two or more plates, the distance
between consecutive plates being within a range from about 50 to
800 .mu.m..Iaddend.
.Iadd.80. The arrangement according to claim 76, wherein the
electrostatic lens array comprises three or more plates, the
distance between consecutive plates being different from plate to
plate..Iaddend.
.Iadd.81. A method of displacement of a plurality of beamlets with
respect to a target surface, the method comprising: deflecting the
beamlets in a first direction by means of a first deflector array;
deflecting the beamlets in a second, opposite direction by means of
a second deflector array..Iaddend.
.Iadd.82. The method according to claim 81, wherein the combined
deflection in the first direction and the second direction results
in displacement of the beamlet at the target surface without
changing an orientation of the beamlet with respect to the target
surface..Iaddend.
.Iadd.83. The method according to claim 82, wherein the orientation
of the beamlet after the combined deflection is perpendicular to
the target surface..Iaddend.
.Iadd.84. The method according to claim 81, wherein the plurality
of beamlets are parallel with respect to each other before the
first deflecting step and after the second deflecting
step..Iaddend.
.Iadd.85. The method according to claim 81, further comprising
providing an electrostatic lens array positioned so that the
deflector arrays are in a front focal plane of the electrostatic
lens array; and focusing the plurality of beamlets with the
electrostatic lens array..Iaddend.
.Iadd.86. A maskless lithography system for transferring a pattern
onto the surface of a target, comprising: an electron beam
generator for generating an electron beam; a beam splitter for
splitting the electron beam into a plurality of electron beamlets;
a modulation array for modulating the plurality of beamlets on the
basis of electronic pattern data in accordance with the pattern to
be transferred; an array of electrostatic scan deflectors for
deflecting electron beamlets to scan the target surface, wherein
the array of electrostatic scan deflectors comprise scan deflection
electrodes, each scan deflection electrode being arranged to
deflect a group of electron beamlets in the same direction; an
optical system for focusing the plurality of beamlets; a target
holder for holding a target with its surface onto which the pattern
is to be transferred in a focal plane of the optical
system..Iaddend.
.Iadd.87. The maskless lithography system according to claim 86,
wherein the deflection electrodes are electrodes deposited on a
plate..Iaddend.
.Iadd.88. The maskless lithography system according to claim 87,
wherein the deflection electrodes are deposited on the side of the
plate facing the target holder..Iaddend.
.Iadd.89. The maskless lithography system according to claim 86,
wherein the deflection electrodes comprise strips..Iaddend.
.Iadd.90. The maskless lithography system according to claim 86,
wherein the modulation array comprises an array of apertures, and
the deflection electrodes are positioned close to said
apertures..Iaddend.
.Iadd.91. The maskless lithography system according to claim 90,
wherein the deflection electrodes are positioned in a front focal
plane of the electrostatic lenses..Iaddend.
.Iadd.92. The maskless lithography system according to claim 86,
wherein the scan deflection electrodes comprise a first group of
strips and a second group of strips, the first group of strips
being arranged to scan in a first direction, the second group of
strips being arranged to scan in a second direction..Iaddend.
.Iadd.93. The system according to claim 86, wherein the deflection
electrodes are in the form of strips..Iaddend.
.Iadd.94. The system according to claim 93, wherein alternating
voltages are located on consecutive strips..Iaddend.
.Iadd.95. The maskless lithography system according to claim 92,
wherein the direction is opposite to the second
direction..Iaddend.
.Iadd.96. A maskless lithography system for transferring a pattern
onto the surface of a target, comprising: an electron beam
generator for generating an electron beam; an electron-optical
arrangement; and a target holder for holding a target provided with
a surface for receiving the pattern to be transferred; wherein the
electron-optical arrangement comprises: a beam splitter for
splitting the electron beam into a plurality of beamlets; a first
electrostatic lens array for focusing the beamlets; a modulation
array comprising a plurality of modulators for modulating the
beamlets on the basis of electronic pattern data to write the
pattern; a deflector array comprising a plurality of electrostatic
deflectors for deflecting a portion of the beamlets in a
predetermined direction; a second electrostatic lens array for
focusing the deflected beamlets..Iaddend.
.Iadd.97. The maskless lithography system according to claim 96,
wherein the beam splitter comprises an aperture array having
apertures arranged in a hexagonal pattern..Iaddend.
.Iadd.98. The maskless lithography system according to claim 96,
wherein said beam splitter comprises an aperture array having about
5,000 to 30,000 apertures..Iaddend.
.Iadd.99. The maskless lithography system according to claim 96,
wherein said beam splitter comprises an aperture array having
apertures with a size adjusted to compensate for non-uniform
current density of said electron beam..Iaddend.
.Iadd.100. The maskless lithography system according to claim 99,
wherein each aperture has an area inversely proportional to a
current density based on the respective beamlet to be transmitted
through said aperture..Iaddend.
.Iadd.101. The maskless lithography system according to claim 96,
wherein said beam splitter comprises a number of aperture arrays in
series along a path of the electron beam or plurality of beamlets,
the aperture arrays having mutually aligned apertures, each
subsequent aperture array along the path towards the first
electrostatic lens array having apertures that are smaller than the
apertures of a previous aperture array..Iaddend.
.Iadd.102. The maskless lithography system according to claim 96,
wherein said first electrostatic lens array is arranged to focus
individual beamlets within the plurality of beamlets to a diameter
in a range from about 0.1 to 1 .mu.m..Iaddend.
.Iadd.103. The maskless lithography system according to claim 102,
wherein the first electrostatic lens array comprises two aligned
plates with holes..Iaddend.
.Iadd.104. The maskless lithography system according to claim 103,
wherein the thickness of the plates is within a range from about 10
to 500 .mu.m..Iaddend.
.Iadd.105. The maskless lithography system according to claim 103,
wherein the holes have a diameter within a range from about 50 to
200 .mu.m, and a pitch within a range from 50 to 500
.mu.m..Iaddend.
.Iadd.106. The maskless lithography system according to claim 103,
wherein the first electrostatic lens array further comprises
insulators for supporting said plates..Iaddend.
.Iadd.107. The maskless lithography system according to claim 96,
wherein the modulation array comprises: a beamlet blanker aperture
array provided with said modulators, said modulators being further
electrostatic deflectors for deflecting beamlets in a further
predetermined direction; a beamlet stop array for terminating
beamlets deflected by the further electrostatic deflectors of the
beamlet blanker array..Iaddend.
.Iadd.108. The maskless lithography system according to claim 107,
wherein the first electrostatic lens array is arranged to focus
individual beamlets within the plurality of beamlets to a diameter
in a range from about 0.1 to 5 .mu.m at the beamlet blanker
array..Iaddend.
.Iadd.109. The maskless lithography system according to claim 107
wherein the beamlet blanker array is located in an electrostatic
focal plane of the plurality of electron beamlets..Iaddend.
.Iadd.110. The maskless lithography system according to claim 109,
wherein the beamlet stop array is positioned outside a focal plane
of the plurality of electron beamlets..Iaddend.
.Iadd.111. The maskless lithography system according to claim 107,
wherein each further electrostatic deflector comprises a first
electrode connected to ground, and a second electrode connected to
a circuit for receiving control data..Iaddend.
.Iadd.112. The maskless lithography system according to claim 96,
wherein the second electrostatic lens array comprises two or more
plates, each plate having a thickness within a range from about 10
to 500 .mu.m..Iaddend.
.Iadd.113. The maskless lithography system according to claim 96,
wherein the second electrostatic lens array comprises two or more
plates, the distance between consecutive plates being within a
range from 50 to 800 .mu.m..Iaddend.
.Iadd.114. The maskless lithography system according to claim 96,
wherein the second electrostatic lens array comprises three or more
plates, the distance between consecutive plates being different
from plate to plate..Iaddend.
.Iadd.115. A method of cleaning an electron optical system
comprising an electron beam generator for generating an electron
beam, a target holder for holding a target on to which one or more
beamlets are to be projected, and at least one of: a beam splitter
for splitting the electron beam into a plurality of beamlets; one
or more electrostatic lens arrays for focusing the beam or
beamlets; a modulation array comprising a plurality of modulators
for modulating the beam or beamlets; a deflector array comprising a
plurality of electrostatic deflectors for deflecting the beam or a
portion of the beamlets in a predetermined direction; and a second
electrostatic lens array for focusing the deflected beamlets; the
system further comprising a power supply connected to at least one
of the beam splitter, the first electrostatic lens array, the
modulation array, the deflector array, and the second electrostatic
lens array; wherein the method comprises: admitting a gas into the
electron optical system; supplying power by means of the power
supply to the electron optical system for creating a plasma
therein; terminating said supplying of power; and removing said gas
from the electron optical system..Iaddend.
.Iadd.116. The method according to claim 115, wherein said gas
comprises oxygen..Iaddend.
.Iadd.117. The method according to claim 116, the method further
comprising: adding a further gas for removal of oxides into the
maskless lithography system; resupplying power to the maskless
lithography system; terminating said resupplying of power; and
removing said further gas from the maskless lithography
system..Iaddend.
.Iadd.118. The method according to claim 117, wherein said further
gas comprises HF..Iaddend.
.Iadd.119. A method for transferring a pattern onto the surface of
a target, comprising: generating a plurality of electron beamlets;
modulating the plurality of beamlets on the basis of electronic
pattern data in accordance with the pattern to be transferred;
providing an array of electrostatic scan deflectors having
electrodes in the form of strips; deflecting the electron beamlets
using the array of electrostatic scan deflectors to scan the target
surface; and focusing the plurality of beamlets onto the target
surface onto which the pattern is to be transferred..Iaddend.
.Iadd.120. The method according to claim 119, further comprising:
creating relative movement in a first direction between the
plurality of beamlets and the target; and wherein the step of
providing an array of electrostatic scan deflectors comprises
providing strips oriented in a direction corresponding to the first
direction..Iaddend.
.Iadd.121. The method according to claim 119, further comprising:
creating relative movement in a first direction between the
plurality of beamlets and the target; and wherein the step of
deflecting the electron beamlets comprises deflecting the beamlets
in a direction different from the first direction..Iaddend.
.Iadd.122. The method according to claim 119, wherein the step of
deflecting the electron beamlets comprises applying alternating
voltages on consecutive strips of the electrostatic scan deflector
electrodes..Iaddend.
.Iadd.123. The method according to claim 119, wherein the step of
providing an array of electrostatic scan deflectors comprises
providing a first group of strips and a second group of strips, the
first group of strips being arranged to scan in a first direction,
the second group of strips being arranged to scan in a second
direction..Iaddend.
.Iadd.124. The method according to claim 123, wherein the first
direction is opposite to the second direction..Iaddend.
.Iadd.125. A method of operating an electron optical system
comprising an electron beam generator for generating an electron
beam, a target holder for holding a target on to which one or more
beamlets are to be projected, and at least one of: a beam splitter
for splitting the electron beam into a plurality of beamlets; one
or more electrostatic lens arrays for focusing the beam or
beamlets; a modulation array comprising a plurality of modulators
for modulating the beam or beamlets; a deflector array comprising a
plurality of electrostatic deflectors for deflecting the beam or a
portion of the beamlets in a predetermined direction; and a second
electrostatic lens array for focusing the deflected beamlets; the
method comprising operating the system at an elevated
temperature..Iaddend.
.Iadd.126. The method according to claim 125, wherein oxygen is
admitted to the system..Iaddend.
.Iadd.127. The method according to claim 125, wherein operating the
system is performed at a temperature above 150 C..Iaddend.
.Iadd.128. The method according claim 125, wherein operating the
system is performed at a temperature below 400 C..Iaddend.
.Iadd.129. The method according to claim 125, wherein the operating
temperature is elevated sufficiently to effect a reduction of
contamination of the system..Iaddend.
.Iadd.130. The method according to claim 129, further comprising
preheating the electron optical system at a temperature between
1000 and 1500 C..Iaddend.
.Iadd.131. A method of operating an electron optical system
comprising an electron beam generator for generating an electron
beam, a target holder for holding a target on to which one or more
beamlets are to be projected, and at least one of: a beam splitter
for splitting the electron beam into a plurality of beamlets; one
or more electrostatic lens arrays for focusing the beam or
beamlets; a modulation array comprising a plurality of modulators
for modulating the beam or beamlets; a deflector array comprising a
plurality of electrostatic deflectors for deflecting the beam or a
portion of the beamlets in a predetermined direction; and a second
electrostatic lens array for focusing the deflected beamlets; the
method comprising the step of admitting oxygen to the system during
operation..Iaddend.
Description
BACKGROUND
Several kinds of electron beam exposure systems are known in the
art. Most of these systems are provided to transfer very precise
patterns onto an exposure surface of a substrate. Since lithography
features are pushed to become smaller and smaller following Moore's
law, the high resolution of electron beams could be used to
continue the drive to even smaller features than today.
A conventional electron beam exposure apparatus has a throughput of
about 1/100 wafer/hr. However, for lithography purposes a
commercially acceptable throughput of at least a few wafers/hr is
necessary. Several ideas to increase the throughput of an electron
beam exposure apparatus have been proposed.
U.S. Pat. No. A1-5,760,410 and U.S. Pat. No. A1-6,313,476, for
instance, disclose a lithography system using an electron beam
having a cross section, which is modified during the transferring
of a pattern to an exposure surface of a target. The specific cross
section or shape of the beam is established during operation by
moving the emitted beam inside an aperture by using electrostatic
deflection. The selected aperture partially blanks and thereby
shapes the electron beam. The target exposure surface moves under
the beam to refresh the surface. In this way a pattern is written.
The throughput of this system is still limited.
In US A1-20010028042, US-A1-20010028043 and US-A1-20010028044 an
electron beam lithography system is disclosed using a plurality of
electron beams by using a plurality of continuous wave (CW)
emitters to generate a plurality of electron beamlets. Each beamlet
is then individually shaped and blanked to create a pattern on the
underlying substrate. As all these emitters have slightly different
emission characteristics, homogeneity of the beamlets is a problem.
This was corrected by levelling every individual beam current to a
reference current. Correction values for the mismatch are extremely
difficult to calculate and it takes a significant amount of time,
which reduces the throughput of the system.
In Journal of Vacuum Science and Technology B18 (6) pages 3061
3066, a system is disclosed which uses one LaB.sub.6-source for
generating one electron beam, which is subsequently, expands,
collimated and split into a plurality of beamlets. The target
exposure surface is mechanically moved relatively to the plurality
of beamlets in a first direction, the beamlets are switched on and
off using blanking electrostatic deflectors and at the same time
scanning deflectors sweep the beamlets which have passed the
blanker array over the target exposure surface in a direction
perpendicular to the first direction, thus each time creating an
image. In this known system, electrostatic and/or magnetic lenses
are used to reduce the image before it is projected on the target
exposure surface. In the demagnification process at least one
complete intermediate image is created, smaller than the one
before. When the entire image has the desired dimensions, it is
projected on the target exposure surface. A major disadvantage of
this approach is that the plurality of electron beamlets together
has to pass through at least one complete crossover. In this
crossover, Coulomb interactions between electron in different
beamlets will disturb the image, thus reducing the resolution.
Moreover, due to the strong demagnification of the image, the area
that is exposed at one time is rather small, so a lot of wafer
scans are needed to expose a die: 16 scans are needed to expose one
die, requiring a very high stage speed for reaching a commercially
acceptable throughput.
In GB-A1-2.340.991, a multibeam particle lithography system is
disclosed having an illumination system, which produces a plurality
of ion sub-beams. The illumination systems use either a single ion
source with aperture plates for splitting a beam in sub-beams, or a
plurality of sources. In the system using a single ion source, the
aperture plate is projected (demagnified) on a substrate using a
multibeam optical system. The system furthermore uses a deflection
unit of electrostatic multipole systems, positioned after the
multibeam optical system, for correcting individual imaging
aberrations of a sub-beam and positioning the sub-beam during
writing. The publication does not disclose how each sub-beam is
modulated. Furthermore, controlling individual sub-beams is a
problem, and maintaining inter-sub-beam uniformity.
In Jpn. J. Appl. Phys. Vol. 34 (1995) 6689 6695, a multi-electron
beam (`probes`) lithography system is disclosed having a specific
ZrO/W-TFE thermal emission source with an emitter tip immersed in a
magnetic field. A disadvantage of such a source is its limited
output. Furthermore, this source needs a crossover. The mutual
homogeneity of the `probes` is not further discussed. Furthermore,
the intensity of the source is a problem.
The article furthermore in a general way mentions a writing
strategy in which a stage is moved in one direction, and deflectors
move the `probes` concurrently through the same distance
perpendicular to the direction of the stage movement. A further
problem, not recognised in this publication, is correction of
deviation of electron beamlets from their intended positions.
SUMMARY OF THE INVENTION
It is an objective of the current invention to improve the
performance of known electron beam exposure apparatus.
Another objective is to improve the resolution of known electron
beam exposure apparatus.
Yet another objective of the current invention is to improve
throughput of known electron beam exposure apparatus.
Yet another objective of the current invention is to overcome the
problems related to Coulomb interactions and the demagnification
methods in the prior art.
Another objective of the current invention is to simplify
controlling uniformity of beamlets, especially during writing.
The invention relates to an electron beam exposure apparatus for
transferring a pattern onto the surface of a target, comprising:
beamlet generator for generating a plurality of electron beamlets;
a modulation array for receiving said plurality of electron
beamlets, comprising a plurality of modulators for modulating the
intensity of an electron beamlet; a controller, operationally
connected to the modulation array for individually controlling the
modulators using control signals; an adjustor, operationally
connected to each modulator, for individually adjusting the control
signal of each modulator; a focusing electron optical system
comprising an array of electrostatic lenses wherein each lens
focuses a corresponding individual beamlet, which is transmitted by
said modulation array, to a cross section smaller than 300 nm, and
a target holder for holding a target with its exposure surface onto
which the pattern is to be transferred in the first focal plane of
the focusing electron optical system.
In this apparatus, electron crossover could be avoided, as it does
not demagnify a complete (part of) an image. In this way,
resolution and writing speed increases. Furthermore, it avoids the
needs to control the current in each individual beamlet. The
apparatus is less complex as the position correction and modulation
are integrated.
In an embodiment of an electron beam exposure apparatus according
to the present invention, said modulation array comprises: a
beamlet blanker array comprising a plurality of beamlet blankers
for the deflection of a passing electron beamlet, a beamlet stop
array, having a plurality of apertures aligned with said beamlet
blankers of said beamlet blanker array.
In this way, it is possible to avoid crossover of electron beamlets
in one single focal point, and make high-speed modulation possible.
In an embodiment, substantially every beamlet blanker is aligned
with an electron beamlet, in order to make it possible to
individually modulate every beamlet. Furthermore, the beamlet stop
array comprises at least one plane of apertures, substantially
every aperture being aligned with one beamlet, preferably with an
aperture centred with respect to a beamlet. In this way, a beamlet
passes an aperture when an electron beamlet is not deflected, and a
beamlet is blocked or stopped when the beamlet is deflected. In an
embodiment of this modulation array, the controller is
operationally connected to said beamlet blankers.
In an embodiment, the electron beam exposure apparatus is
furthermore provided with measuring means for measuring the actual
position of at least one of said beamlets, and the controller is
provided with memory means for storing said actual position and a
desired position, a comparator for comparing the desired position
and the actual position of said beamlets, and wherein the adjustor
is operationally connected to the controller for receiving
instructions for adjusting the control signals issued to the
modulators to compensate for the measured difference between said
desired position and said actual position of said electron
beamlets. In this way, by adjusting control signals, positioning of
the beamlets can be corrected in an easy way. Measurement of the
actual positions can for instance be done as described in U.S. Pat.
No. A1-5,929,454.
In an embodiment, the controller is operationally connected to the
beamlet blankers, in an embodiment via the adjustor.
In an embodiment, the adjustor is operationally connected to the
controller for receiving instructions indicating the amount of the
adjustments. The amount of the adjustments can be determined based
a resulting value of the above-mentioned comparator.
In a further embodiment, the adjustor is adapted for individually
adjusting timing of each control signal. In this very easy way,
correction can be accomplished.
In an embodiment of the electron beam exposure apparatus according
to the present invention, the beamlet generating means comprise: a
source for emitting at least one electron beam, at least one
beamsplitter for splitting said at least one emitted electron beam
into said plurality of electron beamlets
In this way, a uniform intensity distribution among the beamlets is
easily achieved if the source emits uniformly in all relevant
directions. In an embodiment, the electron beam exposure apparatus
further comprising a second electrostatic lens array located
between said beam splitting means and said beamlet blanker array to
focus said plurality of electron beamlets. In this embodiment,
substantially every electrostatic lens is aligned and focuses one
electron beamlet. In a further embodiment thereof, the beamlet
blanker array is located in the focal plane of said second
electrostatic lens array.
In an embodiment of the electron beam exposure apparatus of the
current invention with beamsplitter, the beamsplitter comprise a
spatial filter, preferably an aperture array. In this way, one
source with one beam, or, when source intensity is insufficient or
intensity fluctuates across the beam, several sources, are easily
split into a plurality of beamlets.
When source intensities are high, the splitting means can comprise
a number of aperture arrays in a serial order along the path of the
electron beam or plurality of beamlets, the aperture arrays having
mutually aligned apertures, each next aperture array along the path
from the source to the target having apertures that are smaller
than the apertures of the previous aperture array. This reduces
heat load.
In an embodiment of the aperture array, the apertures of each
aperture array are arranged in a hexagonal structure, which makes
it possible to obtain close integration.
In a further embodiment of the electron beam exposure apparatus
comprising splitting means comprising an aperture array, each
aperture of the aperture array has an area inversely proportional
to the current density based on the beamlet that is transmitted
through that same aperture.
In a further embodiment of the electron beam exposure apparatus
comprising a beamsplitter, the beamsplitter comprises an aperture
array, wherein the aperture sizes in the aperture array are adapted
to create a discrete set of predetermined beamlet currents.
These embodiments improve the uniformity of the electron
beamlets.
In yet a further embodiment of the electron beam exposure apparatus
comprising the beamsplitter, the beamsplitter comprises an
electrostatic quadrupole lens array.
In an embodiment, the electron beam exposure apparatus according to
the present invention comprises a thermionic source. In an
embodiment, the thermionic source is adapted for being operated in
the space charge limited regime. It was found that space charge has
a homogenising effect, which is favourable in this specific
application. Furthermore, in certain settings, the space charge may
have a negative lens effect.
In a further embodiment with the thermionic source, the thermionic
electron source has a spherical cathode surface. In an embodiment,
the thermionic source comprises at least one extractor electrode.
In another embodiment, the extractor electrode is a planar
extractor electrode. In an embodiment thereof, the extractor is
located after the space charge region and provided with a positive
voltage for inducing a negative lens effect. These voltages can be
set at a predefined value for creating a negative lens effect for
the emitted electron beam.
In an alternative embodiment, the extractor electrode has a
spherical surface with through holes. All these embodiments serve
to create a negative lens influence on the electron beam, thus
avoiding a crossover in the electron beam.
In another embodiment of the electron beam exposure apparatus of
the current invention, the apparatus further comprises an
illumination system that transforms the electron beam, emitted by
said source, into a collimated electron beam before it reaches said
splitting means.
In yet another embodiment of the electron beam exposure apparatus
said beamlet generator comprises an array of sources of which each
source is responsible for the generation of an electron beamlet. In
a further embodiment thereof, the electron beam exposure apparatus
further comprising a second electrostatic lens array located
between said array of sources and said beamlet blanker array to
focus said plurality of electron beamlets.
In an embodiment of the electron beam exposure apparatus with
beamlet blanking means, said beamlet blanker comprise electrostatic
deflectors.
In yet another embodiment of the electron beam exposure apparatus
according to the invention, it further comprising scanning
deflection means provided between the modulation array and the
focusing electron optical system for deflecting the electron
beamlets to scan said target exposure surface. In an embodiment
thereof, the scanning deflection means comprises electrostatic scan
deflectors. In a further embodiment thereof, the electron beam
exposure apparatus is further provided with actuating means for
moving said electrostatic scan deflectors and said means for
holding the target relatively to each other in the plane of the
surface onto which the pattern is to be transferred in a direction
that differs from the direction of the deflection performed by said
electrostatic scan deflectors.
In an embodiment, the adjustor or a time shifter are adapted for
shifting a timing base of the scanning deflection means and the
actuators with respect to each other. In an embodiment thereof, the
control signals of the modulators have a timing base and the
actuators of the target holder have a second timing base, and there
timing bases can be shifted with respect to one another. This can
for instance be used to have a critical component, which has to be
written on the target surface and which would lay between two
beamlets, written using only one beamlet.
In a further embodiment thereof, the electron beam exposure
apparatus furthermore comprises an additional aperture plate
between the modulation array and the focussing electron optical
system, the additional aperture plate having one surface directed
to and substantially parallel to the exposure surface of the
target, wherein said electrostatic scan deflectors are conducting
strips deposited on the side of the additional aperture plate
facing the exposure surface of the target located between said
blanker array and the electrostatic lens array of the focusing
electron optical system. In another embodiment thereof, the
electrostatic scan deflectors are conducting strips deposited at
the target exposure surface side of any of the lens plates present
in the focusing electron optical system. In an embodiment thereof,
the conducting strips alternatively have a positive or negative
potential.
In an embodiment of the electron beam exposure apparatus with the
blanking electrostatic deflectors, these deflectors deflect the
electron beamlets in such a way that a predetermined section of the
beamlet is stopped by the beamlet stop array.
In a further embodiment of the electron beam exposure apparatus
according to the present invention, it further comprises a
post-reduction acceleration stage, located between the
electrostatic lens array of the focusing electron optical system
and said protective means, for accelerating the electrons in the
plurality of transmitted electron beamlets.
In an embodiment of the controller, it is furthermore provided with
correction means to compensate for the incorrect positioning of the
electron beamlets on the target exposure surface by comparing the
theoretical position and the actual position of said beamlets
adjusting the control signals to compensate for the measured
difference between said theoretical position and said actual
position of said electron beamlets
In an embodiment of the electron beam exposure apparatus according
to the present invention, it further comprising protective means to
prevent particles released by impinging electrons to reach any one
of the aperture arrays, lens arrays or blanker arrays, preferably
located between the electrostatic lens array of the focusing
electron optical system and the exposure surface of a target,
preferably comprising an aperture array wherein the apertures have
a size smaller than 20 .mu.m.
In an embodiment of the electron beam exposure apparatus according
to the present invention, all lens arrays, aperture arrays and
blanker arrays are connected to a power supply, which, when gas is
admitted into the system, creates a plasma that cleans the plates
and removes all contaminants.
In a further embodiment, the electron beam exposure apparatus
according to the present invention, the system is operated at an
elevated temperature of about 200 600.degree. C. to keep the
apparatus clean.
The invention further relates to an electron beam exposure
apparatus for transferring a pattern onto the surface of a target,
comprising: a beamlet generator for generating a plurality of
electron beamlets; a modulation array for receiving said plurality
of electron beamlets, comprising a plurality of modulators for
modulating the intensity of an electron beamlet; a controller,
operationally connected to the modulation array, for individually
controlling the modulators using control signals; a focusing
electron optical system comprising an array of electrostatic lenses
wherein each lens focuses a corresponding individual beamlet, which
is transmitted by said modulation array, to a cross section smaller
than 300 nm, and a target holder for holding a target with its
exposure surface onto which the pattern is to be transferred in the
first focal plane of the focusing electron optical system, wherein
said beamlet generator comprises at least one thermionic source,
said source comprising at least one extractor electrode adapted for
being operated in a space charge limited region, said source
adapted for generating an electron beam, and said beamlet generator
furthermore provided with a beamsplitter for splitting said
electron beam up into a plurality of electron beamlets.
Using such a specific beamlet generator makes it possible to
provide uniform beamlets with a sufficient current to provide a
high throughput.
In an embodiment thereof, said extractor electrode is located after
said space charge region and is provided with a positive voltage
for inducing a negative lens effect to said electron beam.
The invention furthermore pertains to an electron beam generator
for generating a plurality of electron beamlets, wherein said
beamlet generator comprises at least one thermionic source, said
source comprising at least one extractor electrode adapted for
being operated in a space charge limited region, said source
adapted for generating an electron beam, and said beamlet generator
furthermore provided with a beamsplitter for splitting said
electron beam up into a plurality of electron beamlets.
The invention furthermore pertains to an electron beam exposure
apparatus for transferring a pattern onto the surface of a target,
comprising a beamlet generator for generating a plurality of
electron beamlets, a plurality of modulators for modulating each
electron beamlet, and a controller for providing each modulator
with a control signal, said control signal having a timing base,
wherein the controller is adapted for individually adjusting the
timing base of a control signal with respect to the other control
signals.
In this apparatus, the problem of positioning and modulating is
solved in a very simple and elegant way, reducing the number of
components and providing a robust apparatus.
The invention further pertains to a method for transferring a
pattern onto a target exposure surface with an electron beam, using
an electron beam exposure apparatus described above, and to a wafer
processed using the apparatus of the current invention. The
apparatus can furthermore be used for the production of mask, like
for instance used in state-of-the-art optical lithography
systems.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further elucidated in the following
embodiments of an electron beam exposure apparatus according to the
current invention, in which:
FIG. 1 shows an apparatus according to the present invention,
FIG. 2A shows a detail of a known electron beam exposure
apparatus,
FIG. 2B shows a detail of the electron beam exposure apparatus,
FIG. 3 shows an electron source with a spherical outer surface,
FIG. 3A shows a source with a space charge region,
FIG. 4 shows an embodiment of a electron beam exposure apparatus
starting from the beamlets,
FIG. 5A, 5B show embodiments of scan deflection arrays of the
current invention,
FIG. 6A, 6B show scan trajectories of the present invention,
FIG. 7A 7D show adjustment of modulation timing, and
FIG. 8A, 8B show effects of adjustment of modulation timing.
DESCRIPTION OF EMBODIMENTS
An embodiment of the present invention is schematically shown in
FIG. 1. Electrons are emitted from a single, stable electron source
1. An illumination system focuses and collimates the emitted
electron beam 5 to illuminate a desired area on an aperture plate 6
uniformly. This can for instance be established by using lenses 3
and 4. Due to the aperture plate 6 the electron beam 5 is split in
a plurality of electron beamlets, two of which 5a and 5b, are
shown. An alternative way to create a plurality of electron
beamlets is to use an array of electron sources. Each electron
source generates an electron beamlet, which is modulated in the
same way as the one created with a combination of a single source
and splitting means. Since the emission characteristics of each
source are slightly different, a single source 1 with beamsplitter
6 is preferred. An array of electrostatic lenses 7 focuses each
beamlet to a desired diameter. A beamlet blanker array 8 is
positioned in such a way that each individual beamlet coincides
with an aperture in the plate of beamlet blanker array 8. The
beamlet blanker array 8 comprises beamlet-blankers, for instance
blanking electrostatic deflectors. When a voltage is applied on a
blanking deflector an electric field across the corresponding
aperture is established. The passing electron beamlet, for example
beamlet 9, deflects and terminates at the beamlet stop array 10,
located behind the beamlet blanker array 8 following the electron
beamlet trajectory. When there is no voltage applied to the
blanking deflector the electron beamlet will pass the beamlet stop
array 10, and reach the focusing electron optical system comprising
an array of electrostatic lenses 13. This array 13 focuses each of
the transmitted beamlets 12 individually on the target exposure
surface 14. Finally scanning deflection means, most often
electrostatic scan deflectors, move the beamlets together in one
direction over the target exposure surface 14. In the embodiment
shown in FIG. 1 the scan deflectors are located on the target
exposure surface side 11a of beamlet stop array 10, thus forming an
additional scan deflection array 11. However, other locations are
also possible. During the scanning the target exposure surface 14
and the scan deflectors moves relatively to one another in a
direction different from the direction of the scan deflection.
Usually the target is a wafer or a mask covered with a resist
layer.
A remarkable aspect of the configuration shown in FIG. 1 is that
the entire image that is created by the combination of beamlet
blanker array 8 and beamlet stop array 10 is not demagnified as a
whole. Instead, each individual beamlet is individually focused on
the target exposure surface 14 by the focusing electron optical
system 13. The difference between these two approaches is shown in
FIGS. 2A and 2B. In FIG. 2A an entire image comprising 2 electron
beamlets 5a and 5b is demagnified to acquire the desired
resolution. To demagnify an image requires at least one crossing X.
In this crossing, all the electrons have to pass a small area.
Coulomb interactions deteriorate the resolution at that crossing
X.
In the present invention the method shown in FIG. 2B is used.
Consider two adjacent beamlets 5a, 5b that are projected on the
target exposure surface 14. Using the demagnification approach the
distance between the two beamlets also becomes smaller. The
focusing approach of the current invention, however, does not
change this distance between two beamlets. Only the cross section
of each beamlet is reduced.
The electron source 1 of FIG. 1 typically delivers 100 A/cm.sup.2
from an area of about 30 300 micron squared. In an embodiment, a
thermionic source is used. The electrons are preferably emitted in
the space charge limited emission regime in order to benefit from a
homogenizing effect of the space charge. Examples of such a source
are a LaB.sub.6 crystal, a dispenser source comprising Barium
Oxide, or a dispenser source comprising a layer of Barium or
Tungsten covered with Scandium Oxide.
The extractor electrodes 2 usually, but not necessarily, focus the
beam. The illumination lenses 3 4 create a parallel beam of
electrons 5 on the aperture array 6. The lenses 3 4 are optimised
to limit the beam energy spread as a result of Coulomb
interactions, i.e. the opening angle of the beam is made as large
as possible. Furthermore lenses 3 4 are optimised to limit the beam
blur created by chromatic and spherical aberration effects. For the
latter it may be advantageous to use the aperture array 6 as a lens
electrode, because this may create negative chromatic and spherical
aberrations, resulting in a compensation of the aberrations of
lenses 3 4. Furthermore, it is possible to use lens 4 for
magnification of the pattern by slightly focusing or defocusing
it.
In such an embodiment, however, the electron beam emitted from the
single emitter is focussed in a small crossover x before it is
expanded. Within this crossover x there is a large energy spread
due to electron-electron interactions in this crossover x. In the
end the crossover x will be imaged demagnified on the target
exposure surface. Due to the Coulomb interactions the desired
resolution is not achieved. A method to expand and collimate the
expanded beam without a crossover is therefore desirable.
In a first embodiment, shown in FIG. 3, crossover in the
illumination electron optics is avoided by using an electron source
1 with a spherical or a hemispherical outer surface 15. In this
configuration a large opening angle .alpha. is formed, which
reduces the blur due to electron-electron interactions in the
emitted electron beam 5. Additionally the electron beams are
forming a spherical wave front, which results in a virtual
crossover 16 located in the centre of the source. There are no
electrons present in the virtual crossover; so disturbing
electron-electron interactions are absent.
The electrons can be extracted with a spherical extractor that
comprises large holes. The main advantage of the spherical shape of
the extractor is the more homogeneous field that is created.
In an alternative embodiment, shown in FIG. 3A, crossover is
avoided by extracting the electrons from the source/cathode 1 which
is at a voltage Vs and has a distant planar extractor 11. The
planar extractor has a positive voltage +V.sub.1 with respect to
the source 1. The combination of source and extractor now serves as
a negative lens. The extracted electrons passing the extractor
1.sub.1 thus expand due to the diverging electric field. Again, a
virtual crossover is created, which reduces the loss of resolution
due to Coulomb interactions to a great extent. Between source 1 and
extractor 1.sub.1 a space charged region S is present as is shown
in FIG. 3A. The presence of this space charge enhances the negative
lens effect created by the source-extractor combination.
By tuning V.sub.1 it is possible to let the source 1 operate in its
space charge limited emission mode. The main advantage of this
emission mode is the significant increase of homogeneity of the
emission. The increase of the total current can be limited by
selecting a source with a confined emission area.
The aperture array 6 has apertures of typically 5 150 .mu.m in
diameter with a pitch of about 50 500 .mu.m. The apertures are
preferably arranged in a hexagonal pattern. The aperture array 6
splits the incoming parallel beam of electrons 5 in a plurality of
electron beamlets, typically in the order of about 5,000 30,000.
The size of the apertures is adjusted to compensate non-uniform
current density of the illumination. Each aperture has an area
inversely proportional to the current density based on the
individual beamlets that is transmitted through that same aperture.
Consequently the current in each individual beamlet is the same. If
the heat load on the aperture plate becomes too large, several
aperture arrays are arranged in a serial order with decreasing
aperture diameters along the path of the electron beam or plurality
of electron beamlets. These aperture arrays have mutually aligned
apertures.
Another possible way to split the collimated electron beam 5 into a
plurality of electron beamlets is the use of a quadrupole lens
array. A possible configuration of such an array is disclosed in
U.S. Pat. No. 6,333,508, which document is referenced here as if
fully set forth.
FIG. 4 shows a detail closer image of the lithography system in one
of the embodiments of the present invention starting from the
plurality of beamlets. Condensor lens array 7 focuses each beamlet
to a diameter of about 0.1 1 .mu.m. It comprises two aligned plates
with holes. The thickness of the plates is typically about 10 500
.mu.m, while the holes are typically about 50 200 .mu.m in diameter
with a 50 500-.mu.m pitch. Insulators (not shown), which are
shielded from the beamlets, support the plates at typical distances
of 1 10 millimetres from each other.
The modulation array comprises a beamlet blanker array 8 and a
beamlet stop array 10. At the beamlet blanker array 8, the typical
beam diameter is about 0.1 5 .mu.m while the typical transversal
energy is in the order of a 1 20 meV. Beamlet blanking means 17 are
used to switch the electron beamlets on and off. They include
blanking electrostatic deflectors, which comprise a number of
electrodes. Preferably at least one electrode is grounded. Another
electrode is connected to a circuit. Via this circuit control data
are sent towards the blanking electrostatic deflectors. In this
way, each blanking deflector can be controlled individually.
Without the use of the beamlet blanking means 17 the electron
beamlet will pass the beamlet stop array 10 through the apertures.
When a voltage is applied on a blanking electrostatic deflector
electrode in the beamlet blanker array 8, the corresponding
electron beamlet will be, deflected and terminate on the beamlet
stop array 10.
In an embodiment, the beamlet blanker array 8 is located in the
electrostatic focal plane of the electron beamlets. With the
blanker array in this position, the system is less sensitive for
distortions. In this embodiment, the beamlet stop array is
positioned outside a focal plane of the electron beamlets.
The transmitted beamlets now have to be focused on the target
exposure surface 14. This is done by a focusing electron optical
system 13 comprising at least one array with electrostatic lenses.
Each individually transmitted electron beamlet is focused on the
target exposure surface by a corresponding electrostatic lens. The
lens array comprises two or more plates 13a and 13b, both having a
thickness of about 10 500 .mu.m and apertures 13c with a diameter
of about 50 250 .mu.m. The distance between two consecutive plates
is somewhere between 50-800 .mu.m and may be different from plate
to plate. If necessary, the focusing electron optical system may
also comprise a lens array of the magnetic type. It is then located
between the beamlet stop array 10 and the objective lens array of
the electrostatic type 13, to further enhance the focusing
properties of the electron optical system.
A major problem in all electron beam lithography systems patterning
a wafer or a mask is contamination. It reduces the performance of
the lithography system significant due to the interaction between
electrons and particles in the resist layer, the resist degrades.
In a polymeric resist, molecules are released due to cracking. The
released resist particles travel through the vacuum and can be
absorbed by any of the structures present in the system.
In order to cope with the contamination problem, in a particular
embodiment protective means are located in close proximity of the
target exposure surface, i.e. between the target exposure surface
and the focusing electron optical system. Said protective means may
be a foil or a plate. Both options are provided with apertures with
a diameter smaller than 20 .mu.m. The protective means absorb the
released resist particles before they can reach any of the
sensitive elements in the lithography system. In some cases it is
necessary to refresh the protective means after a predetermined
period, e.g. after every processed wafer or mask. In the case of a
protective plate the whole plate can be replaced. In a particular
embodiment, the foil is wound around the coil winders. A small
section of the foil is tightened just above the entire target
exposure surface 14. Only this section is exposed to the
contaminants. After a certain period the protective capacity of the
foil rapidly degrades due to the absorbed particles. The exposed
foil section then needs to be replaced. To do this the foil is
transported from one coil winder to the other coil winder, thus
exposing a fresh foil section to the contamination particles.
The entire system that is described above operates at relatively
low voltages. In operations in which high-energy electrons are
needed, an additional acceleration stage is positioned between the
electrostatic lens array of the focusing electron optical system 13
and the protective means. This acceleration stage adds energy to
the passing electrons. The beam may be accelerated additional tens
of kiloelectronvolts, e.g. 50 keV.
As explained earlier in FIG. 1, the beamlets 12 that have
successfully passed the beamlet stop array 10 are directed towards
the desired position on the target exposure surface 14 by two
means. First of all actuation means move the target exposure
surface 14 and the rest of the system in a certain mechanical scan
direction relatively to each other. Secondly scan deflection means
scan the transmitted beamlets 12 electrostatically in a direction
that differs from the mechanical scan direction. The scan
deflection means comprise electrostatic scan deflectors 18. In
FIGS. 1 and 3 these scan deflectors 18 are located on an additional
aperture array 11, and are depicted in FIG. 4.
In one embodiment, the electrostatic scan deflectors 18 are
deposited on the target exposure surface side of one of the plates
of the objective electrostatic lens array 13, such that the
deflection essentially occurs in the front focal plane of the
objective lenses. The desired result is that the deflected beamlets
impinge perpendicularly on the target surface.
In another embodiment there are two deflector arrays, one
deflecting in a first direction and the other deflecting in a
second, opposite direction. The combined deflection causes
displacement of the beamlets a displacement of the beamlets at the
target surface location, without changing the perpendicular axis of
a beamlet with respect to the target surface.
In a second embodiment, the electrostatic scan deflectors 18 are
located on the protective means.
The electrostatic scan deflectors 18 comprise scan deflection
electrodes, which are arranged to deflect an assembly of electron
beamlets in the same direction. The scan deflection electrodes may
be deposited in the form of strips 19 on a suitable plate 20 at the
target exposure surface side as is shown in FIG. 5A. The best yield
can be established when the strips 19 are deposited close to the
beamlet, thus close to the aperture 21, since this reduces
d.sub.b-sd. Moreover, it is preferable to position the scan
deflection electrodes outside an individual beamlet crossover
plane.
In one embodiment the first assembly is scanned in one direction
while the next one is scanned in the opposite direction, by putting
alternating voltages on the consecutive strips 19 as is shown in
FIG. 5B. The first strip has for instance a positive potential, the
second one a negative potential, the next one a positive etc. Say
the scan direction is denoted y. One line of transmitted electron
beamlets is then scanned in the -y-direction, while at the same
time the next line is directed towards +y.
As already mentioned there are two scan directions, a mechanical
scan direction M and a deflection scan direction S, both depicted
in FIGS. 6A and 6B. The mechanical scan can be performed in three
ways. The target exposure surface moves, the rest of the system
moves or they both move in different directions. The deflection
scan is performed in a different direction compared to the
mechanical scan. It is preferably perpendicular or almost
perpendicular to the mechanical scan direction, because the scan
deflection length .DELTA.x is then larger for the same deflection
scan angle .alpha..sub.sd. There are two preferable scan
trajectories, both shown in FIG. 6 for clarity. The first one is a
triangular shaped scan trajectory (FIG. 6A), the second one a saw
tooth shaped scan trajectory (FIG. 6B).
When the mechanical scan length is a throughput-limiting factor, an
assembly of electron beam exposure apparatuses as described above
is used to expose the entire wafer at the same time.
It is assumed that an ideal grid exists on the wafer and that the
electron beamlets can be positioned exactly on the grid
coordinates. Say that a correct pattern is created when the
electron beamlet can be positioned within 1/30.sup.th of the
minimum feature size. Then to write one pixel, 30 scan lines and
thus 30*30=900 grid points are needed. For the 45 nm-mode the
positioning should be controllable within a range of 1.5 nm. The
data path should therefore be able to handle an enormous amount of
data.
The writing strategy described above is based on the assumption
that the beamlet can only be switched on or off. To reduce the
amount of data by less grid lines, and thus less grid cells seems a
logical approach. However, the dimension control of the desired
pattern suffers considerably. An approach to circumvent this
problem is to pattern the target exposure surface 14 with discrete
dose control. Again the pattern is divided according to a
rectangular grid. However, the number of grid lines is much smaller
e.g. 2 5 per dimension, which results in a number of grid points of
about 4 25. In order to get the same pattern reliability as for the
finer grid, the intensity of each grid cell is variable. The
intensity is represented by a so-called gray value. In case of a 3
bit gray value representation, the values are 0, 1/7, 2/7, 3/7,
4/7, 5/7, 6/7 and 1 times the maximum dose. The number of data
required for the position of the beamlet reduces, although each
cell is represented with more information due to the controlled
dose variation.
In the present invention gray scale writing can be introduced in
several ways. First of all the deflection of the beams may be
controlled in such a way that part of the beam passes the beamlet
stop array 10, while part of the beam continues traveling towards
the target exposure surface 14. In this way for instance 1/3 or 2/3
of the beam can be stopped, resulting in 4 possible doses on the
target exposure surface, namely 0, 1/3, 2/3 and 1 times the maximum
dose, corresponding to a 2 bit gray value representation.
Another method to create gray levels is to deflect the beamlets in
such a way that they do not move with respect to the target surface
for a predetermined amount of time T, which amount of time T is
longer than a minimum on/off time of the blankers. During time T,
the modulator can now deposite 1, 2, 3, etc. shots on one position,
thus creating gray levels.
Another method to create these 4 so-called gray values is to change
the aperture size in the aperture array 6. If there are for
instance three aperture sizes, the original size, a size that
permits half the original current to pass and apertures with an
area such that only a fourth of the original current passes, the
same discrete dose values as mentioned before an be created. By
switching the beamlets on and off with the deflection electrodes 17
of the beamlet blanker array 8 the desired dose can be deposited on
the target exposure surface 14. A disadvantage of the latter method
is the fact that more beamlets are needed to write one pixel. Most,
including aforementioned methods for discrete dose control can also
be used to create more than 4 gray values, e.g. 8, 16, 32 or
64.
The positions of the beamlets on the target exposure surface most
often do not exactly correspond with the desired positions. This is
for instance due to misalignment of the different arrays with
respect to each other. Additionally, manufacturing errors may also
contribute to the offset of the individual beamlets. To transfer
the correct pattern from the controller onto the exposure surface
of the target, corrections have to be made. To this end, in a
particular embodiment, first the position of all beamlets is
measured and stored. Each position is then compared to the position
the beamlet should have. The difference in position is then
integrated in the pattern information that is sent to the
modulation means.
Since changing the signal sequence that is sent towards the
modulation means takes a lot of time, the measured difference in
position is integrated in the pattern information by transforming
it into a corresponding difference in timing in the beamlet
modulation control. FIGS. 7A 7D and 8A 8B explain how the
adjustments are implemented. As already mentioned the beamlet scan
is performed by combining two scan mechanisms: a mechanical scan
and a deflection scan. All pattern data, which is sent to each
beamlet, is supplied per deflection scan line. The desired
deflection scan width on the exposure surface of the target that is
patterned, W.sub.scan, is smaller than the deflection scan width
the apparatus can handle, W.sub.overscan, as is shown in FIGS. 7A
AND 7B. The overscan ability enables a correction in the deflection
scan direction. In FIG. 7A the beamlet is positioned correctly. In
FIG. 7B, however, the beamlet has shifted to the right. By
adjusting the timing in such a way that the pattern data is applied
when the beamlet enters the desired area, the offset can be
compensated for. The adjustment in the mechanical scan direction is
less precise than depicted in FIG. 7B. Since the pattern data is
written per scan line, only a discrete time delay is possible, i.e.
pattern generation can be postponed or accelerated per scan line. A
random time delay would result in a completely new control data
sequence. A calculation of such a new sequence takes a lot of time
and is therefore not desirable. In FIGS. 7C AND 7D is depicted what
the consequence is. In FIG. 7C again the desired location of the
beamlet is shown together with its first five corresponding scan
lines. In FIG. 7D the real position of the beamlet and its
trajectories is shown. For clarity the desired beamlet and scan
lines are also depicted with an empty circle and dashed lines,
respectively. It can be seen that the first scan line in the
desired situation does not cover the area that needs to be
patterned by the beamlet. So the beamlet start patterning halfway
the second scan line. Effectively the delay of information has
taken a time period that is necessary to scan one deflection scan
line.
FIGS. 8A and 8B show an example of how a change in the timing
corrects for the initial incorrect position of a structure written
by a not ideally positioned beamlet. FIG. 8A depicts the situation
without any timing correction. The empty dot represents the beamlet
at the correct position, while the filled one represents the real
location of the beamlet. The beamlet is scanned along the drawn
line to write a pattern. The line is dashed in the ideal case and
solid in the real case. In this example the written structure is a
single line. Consider a black and write writing strategy, i.e. the
beamlet is "on" or "off". The pattern is written when the "on"
signal is sent towards the modulation means. In order to write the
single line a certain signal sequence like the one shown in the
upper curve is sent towards the modulation means. When the same
signal sequence is sent in reality, the line is written at a
different position than desired. The offset of the beamlet leads to
an offset of the written structure.
FIG. 8B shows the situation wherein timing correction is applied.
Again the theoretical and actual spots and trajectories are
depicted with dashed and solid lines and dots respectively. The
signal sequence in the real situation is different than the
theoretical pattern information, in the fact that the signal
sequence in the real situation (lower curve) is sent at a different
time than the same sequence is sent in the idea configuration
(upper curve). As a result the single line is now written at the
correct location in the deflection scan direction. Moreover the
pattern processing started one scan line earlier resulting in a
better positioning of the single line in the mechanical scan
direction as well. Note that the single line is not precisely
positioned at the correct location. This is due to the slight
offset between the scan lines in the ideal and the real
situation.
The current electron beam exposure system is thus capable of
dynamically adjusting the position of a scanned line using timing
corrections. This allows for critical components in a pattern to be
written in one scan line instead of using two halves of two scan
lines, which would spread the critical component over two scan
lines. This correction can also be done locally, i.e. the timing
can be corrected over a small time window. The controller should
thus identify critical components, which would normally be spread
over two scan lines. Subsequently, the controller should calculated
a corrected timing window, and apply the corrected timing window to
the timing base used for scanning an electron beamlet. FIG. 7D
shows the adjustment principle, which could be used for this.
All lens plates, aperture plates and blanker plates can be
connected to a power supply, which, when gas is admitted into the
system, creates a plasma. The plasma cleans the plates and removes
all contamination. If one plasma does not clean thorough enough,
two gases may be admitted into the system in series. For instance
oxygen may be admitted first to remove all hydrocarbons residing in
the system. After the removal of the oxygen plasma, a second
plasma, for instance comprising HF, is created to remove all
present oxides.
Another possibility to reduce the contamination is to perform all
operations at elevated temperatures, i.e. 150 400.degree. C. A
pretreatment at 1000 1500.degree. C. may be necessary. At these
temperatures hydrocarbons get no chance to condense on any of the
elements in the system. Allowing a fraction of oxygen into the
system can further enhance the cleaning process.
It is to be understood that the above description is included to
illustrate the operation of the preferred embodiments and is not
meant to limit the scope of the invention. The scope of the
invention is to be limited only by the following claims. From the
above discussion, many variations will be apparent to one skilled
in the art that would yet be encompassed by the spirit and scope of
the present invention.
* * * * *