U.S. patent application number 10/087265 was filed with the patent office on 2002-09-05 for high repetition rate uv excimer laser.
Invention is credited to Sparrow, Robert W..
Application Number | 20020122450 10/087265 |
Document ID | / |
Family ID | 23041411 |
Filed Date | 2002-09-05 |
United States Patent
Application |
20020122450 |
Kind Code |
A1 |
Sparrow, Robert W. |
September 5, 2002 |
High repetition rate UV excimer laser
Abstract
The invention relates to an High Repetition Rate UV Excimer
Laser which includes a source of a laser beam and one or more
windows which include magnesium fluoride. Another aspect of the
invention relates to an excimer laser which includes a source of a
laser beam, one or more windows which include magnesium fluoride
and a source for annealing the one or more windows. Another aspect
of the invention relates to a method of producing a predetermined
narrow width laser beam.
Inventors: |
Sparrow, Robert W.;
(Sturbridge, MA) |
Correspondence
Address: |
CORNING INCORPORATED
SP-TI-3-1
CORNING
NY
14831
|
Family ID: |
23041411 |
Appl. No.: |
10/087265 |
Filed: |
March 1, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60272814 |
Mar 2, 2001 |
|
|
|
Current U.S.
Class: |
372/57 |
Current CPC
Class: |
H01S 3/08004 20130101;
C30B 11/00 20130101; C30B 29/12 20130101; H01S 3/225 20130101; H01S
3/034 20130101; H01S 3/0346 20130101; H01S 3/1055 20130101; H01S
3/106 20130101 |
Class at
Publication: |
372/57 |
International
Class: |
H01S 003/22; H01S
003/223 |
Claims
What is claimed is:
1. A method of producing a .gtoreq.4 kilohertz repetition rate
excimer laser beam comprising: oscillating a laser beam whereby the
laser beam exits a first magnesium fluoride crystal window of a
chamber and passing the laser beam through a second magnesium
fluoride crystal window of the chamber to provide a .gtoreq.4
kilohertz repetition rate excimer laser beam.
2. A method as claimed in claim 1 wherein the .gtoreq.4 killohertz
repetition rate excimer laser beam has a power of greater than or
equal to 10 mJ.
3. A method as claimed in claim 1 wherein the magnesium fluoride
crystal windows maintain durability over 500 million pulses of the
laser beam.
4. A .gtoreq.4 kilohertz repetition rate excimer laser comprising:
a .gtoreq.4 kilohertz repetition rate excimer laser beam source for
producing a .gtoreq.4kilohertz repetition rate excimer laser beam
and one or more magnesium fluoride crystal windows for transmitting
said .gtoreq.4 kilohertz repetition rate excimer laser beam.
5. An excimer laser according to claim 4, wherein the laser beam
has a power of greater than or equal to 10 mJ.
6. An excimer laser according to claim 4, wherein said .gtoreq.4
kilohertz repetition rate excimer laser beam source is an argon
fluoride excimer laser beam source.
7. An excimer laser according to claim 4, wherein said .gtoreq.4
kilohertz repetition rate excimer laser beam source is a krypton
fluoride excimer laser beam source.
8. An excimer laser according to claim 6 further comprising: a
source for annealing the one or more windows.
9. An excimer laser according to claim 4 wherein the windows
maintain durability over 500 million pulses of the laser beam.
10. An excimer laser comprising: a source for a laser beam; one or
more windows comprising magnesium fluoride crystal; and a source
for annealing the one or more comprising magnesium fluoride crystal
windows.
11. An excimer laser according to claim 10, wherein the laser beam
has a power of greater than or equal to 10 mJ.
12. An excimer laser according to claim 10, wherein the laser beam
has a repetition rate of greater than or equal to 4 KHz.
13. An excimer laser according to claim 10, wherein the laser beam
source is argon fluoride.
14. An excimer laser according to claim 10, wherein the laser beam
source is krypton fluoride.
15. An .gtoreq.4 kilohertz repetition rate argon fluoride excimer
laser window comprising a magnesium fluoride crystal.
16. A method of producing a predetermined narrow width laser beam
comprising: oscillating a laser beam whereby the laser beam exits a
first window of a chamber; widening the laser beam through one or
more prisms; controlling the widened laser beam to a predetermined
narrow width; and passing the predetermined narrow width laser beam
through a second window of the chamber, wherein the first and
second windows of the chamber are comprised of magnesium
fluoride.
17. A method according to claim 16, wherein the laser beam has a
power of greater than or equal to 10 mJ.
18. A method according to claim 16, wherein the laser beam has a
repetition rate of greater than or equal to 4 KHz.
19. A method according to claim 16, further comprising pulsing the
laser beam over 500 million pulses.
20. A method according to claim 19, wherein the first and second
window maintain durability.
21. A method according to claim 19, wherein the laser beam is
pulsed over 900 million pulses and the first and second window
maintain durability.
22. A method according to claim 16, further comprising: annealing
the first window.
23. A method according to claim 22, further comprising: annealing
the second window.
24. A method according to claim 16, wherein the laser beam source
is argon fluoride.
25. A method according to claim 16, wherein the laser beam source
is krypton fluoride.
Description
[0001] The present application claims priority to U.S. Provisional
Patent Application No. 60/272,814, filed Mar. 2, 2001, which is
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The subject invention is directed generally to an High
Repetition Rate UV Excimer Laser.
BACKGROUND OF THE INVENTION
[0003] Throughout this application various publications are
referenced. The disclosures of each of these publications in their
entireties are hereby incorporated by reference in this
application.
[0004] Excimer lasers have been conventionally developed for
commercial use as a light source of a reducing projection and
exposure device for a semiconductor manufacturing apparatus,
because an excimer laser enables extremely precise work.
[0005] Light oscillating from the excimer laser has various
wavelength components and the central wavelength varies. As a
result, if the light is in the as-is status, an aberration will
occur when the light passes through an external optical element,
such as a lens, thereby reducing the accuracy of the work. For this
reason, there is a widely used art of making a narrow band, in
which an excimer laser is equipped with a wavelength selecting
element, such as a grating, to narrow the spectral width of the
laser oscillation wavelength and to stabilize the central
wavelength as a central value of the oscillation wavelength.
[0006] U.S. Pat. No. 6,181,724 discloses an excimer laser. Laser
gas is sealed in a laser chamber and energy is supplied as a result
of an electrical discharge in a discharge electrode, causing the
laser beam to oscillate. The oscillating laser beam exits through a
rear window, the beam size is widened while passing through a first
prism and a second prism, and then the laser beam enters a grating.
In the grating, an angle relative to the light path of the laser
beam is controlled by an actuator and by oscillating the laser beam
at a predetermined wavelength, a narrow band is achieved. A group
of optical components, which are the first prism, the second prism,
and the grating, is collectively called the narrow-band optics. The
laser beam, with the wavelength being controlled by the narrow-band
optics, passes through a front window and a front mirror, which is
a partial reflecting mirror, and part of the laser beam exits the
laser chamber.
[0007] Typically, synthetic fused silica or calcium fluoride is
used as the material of the optical components for the excimer
lasers, however, there are significant disadvantages in using these
materials. In order to manufacture semiconductors efficiently in
large quantities, there has been a demand to increase the power of
a laser by increasing the laser oscillation pulse numbers per unit
time (also called the repetition frequency or repetition rate).
However, the energy density is high in the resonator of the laser,
and moreover, a laser beam reciprocates in the resonator and passes
through the optical components many times. For this reason, as the
power of a laser becomes higher, the optical components are
deteriorated as a result of even minor distortion or unevenness
inside the material. Even minor deterioration of the optical
components exerts a great influence on the quality of the
oscillating laser beam. Thus, the optical components of synthetic
fused silica or calcium fluoride are insufficient in durability
when the power of an excimer laser is increased, and a highly
accurate control of the wavelength of an High Repetition Rate UV
Excimer Laser is difficult when these optical components are
used.
SUMMARY OF THE INVENTION
[0008] The present invention relates to an High Repetition Rate
(.gtoreq.4 kilohertz) UV Excimer Laser which includes a source of a
laser beam and one or more windows which include magnesium
fluoride.
[0009] Another aspect of the present invention includes an High
Repetition Rate UV Excimer Laser which includes a source for a
laser beam, one or more windows which include magnesium fluoride,
and a source for annealing the one or more windows.
[0010] Yet another aspect of the present invention includes an High
Repetition Rate UV Excimer Laser window which includes magnesium
fluoride.
[0011] Yet another aspect of the present invention includes a
method of producing a predetermined narrow width laser beam. The
method includes oscillating a laser beam whereby the laser beam
exits a first window of a chamber, widening the laser beam through
one or more prisms, controlling the laser beam to a predetermined
narrow width, and passing the predetermined narrow width laser beam
through a second window of the chamber, where the first and second
windows of the chamber include magnesium fluoride.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] These and other features and advantages of this invention
will be evident from the following detailed description of
preferred embodiments when read in conjunction with the
accompanying drawings in which:
[0013] FIG. 1 illustrates an High Repetition Rate UV Excimer Laser
according to one embodiment of the present invention.
[0014] FIG. 2 illustrates an High Repetition Rate UV Excimer Laser
according to an alternative embodiment of the present
invention.
[0015] FIG. 3 illustrates an High Repetition Rate UV Excimer Laser
according to an alternative embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present invention relates to an excimer laser which
includes a source of a laser beam and one or more windows which
include magnesium fluoride.
[0017] Excimer laser devices are described in U.S. Pat. Nos.
6,181,724, 6,282,221, 6,067,311 and 6,014,398, which are hereby
incorporated by reference.
[0018] Typically, an excimer laser operates as follows. Laser gas
is sealed in a laser chamber and energy is supplied to the gas by
an electrical discharge in a discharge electrode. This causes the
laser beam to oscillate. The oscillating laser beam exits the laser
chamber through a rear window, the size of the laser beam is
widened while passing through prisms, and the laser beam enters a
grating. In the grating, an angle relative to the light path of the
laser beam is controlled by an actuator and by oscillating a
predetermined wavelength a narrow band width is achieved. The laser
beam, with the controlled wavelength passes through a front window
and a front mirror and part of the laser beam exits the laser
chamber.
[0019] With this general view of the operation of an excimer laser
in mind, FIG. 1 illustrates one embodiment of an High Repetition
Rate UV Excimer Laser of the present invention. As shown in FIG. 1,
High Repetition Rate UV Excimer Laser device 10 includes a
plurality of prisms such as first and second (and optionally third)
prisms 12, first mirror 13, second mirror 15, a grating 14, and
first 16 and second 18 windows. First window 16 and second window
18 in laser chamber 17 form an ordinary Brewster angle relative to
a laser beam 11 in order to reduce energy loss. Components, such as
plurality of prisms 12, first mirror 13 and second mirror 15, and
first window 16 and second window 18 are made of a fluoride optical
material, such as calcium fluoride, barium fluoride or magnesium
fluoride. In one embodiment, these components are made of magnesium
fluoride. In an alternative embodiment, first window 16 and second
window 18 are made of magnesium fluoride and other components, such
as plurality of prisms 12, first mirror 13 and second mirror 15 are
made of other materials, such as calcium fluoride.
[0020] Another aspect of the present invention includes a method of
producing a predetermined narrow width laser beam. The method
includes oscillating a laser beam where the laser beam exits a
first window of a chamber, widening the laser beam through one or
more prisms, controlling the laser beam to a predetermined narrow
width, and passing the predetermined narrow width laser beam
through a second window of the chamber, where the first and second
windows of the chamber include magnesium fluoride.
[0021] In use, referring to FIG. 1, laser gases (such as Ar, Kr, Ne
and/or F) are sealed in laser chamber 17 and energy is supplied to
the laser gas by an electrical discharge in a discharge electrode
(not shown). This causes laser beam 11 to oscillate. Oscillating
laser beam 11 exits the laser chamber 17 through a rear window 16.
Laser beam 11 passes through prisms 12, is reflected by second
mirror 15 and grating 14. In first mirror 15, an angle relative to
the light path of laser beam 11 is controlled by an actuator. By
oscillating laser beam 11 at predetermined wavelength, a narrow
band width is achieved for laser beam 11. Laser beam 11 is totally
reflected by grating 14 and second mirror 15 causing laser beam 11
to reverse its original path and exit chamber 17 from front window
18 and exit from first mirror 13.
[0022] FIG. 2 is a second embodiment of the present invention. High
Repetition Rate UV Excimer Laser device 20 includes a plurality of
prisms such as first and second prisms 22, mirror 25, grating 24,
and first 26 and second 28 windows. First window 26 and second
window 28 in laser chamber 27 form an ordinary Brewster angle
relative to a laser beam 21 in order to reduce energy loss. In this
embodiment, laser beam 21, is partially reflected by mirror 25,
which is a partially reflecting mirror, and part of laser beam 21
exits laser chamber 27. Components, such as plurality of prisms 22,
second mirror 25, and first window 26 and second window 28 are made
of a fluoride optical material, such as calcium fluoride, barium
fluoride or magnesium fluoride. In one embodiment, these components
are made of magnesium fluoride. In an alternative embodiment, first
window 26 and second window 28 are made of magnesium fluoride and
other components, such as plurality of prisms 22 and mirror 25 are
made of other materials, such as calcium fluoride.
[0023] Another aspect of the present invention includes an High
Repetition Rate UV Excimer Laser window made of magnesium
fluoride.
[0024] The laser windows of the present invention made of magnesium
fluoride maintain durability over a long operational life of the
High Repetition Rate UV Excimer Laser. As used herein, "maintain
durability" means that the magnesium fluoride windows have no
perceptible induced absorption. The magnesium fluoride windows
maintain durability for a laser having a output of greater than or
equal to 10 mJ and a repetition rate of greater than or about 4
KHz. Further, the magnesium fluoride windows of the present
invention maintain durability for a laser having a output of
greater than or equal to 10 mJ and a repetition rate of greater
than or about 4 KHz for over 500 million pulses and, optionally,
for over 900 million pulses.
[0025] Another aspect of the present invention includes an excimer
laser which includes a source for a laser beam, one or more windows
which include magnesium fluoride, and a source for annealing the
one or more windows.
[0026] FIG. 3 shows an embodiment of the present invention which
includes a source for annealing the windows of the laser chamber.
As shown in FIG. 3, excimer laser device 30 includes a plurality of
prisms such as first and second (and optionally third) prisms 32,
first mirror 33, second mirror 35, a grating 14, and first 16 and
second 18 windows. First window 36 and second window 38 in laser
chamber 37 form an ordinary Brewster angle relative to a laser beam
31 in order to reduce energy loss. Components, such as plurality of
prisms 32, first mirror 33 and second mirror 35, and first window
36 and second window 38 are made of a fluoride optical material,
such as calcium fluoride, barium fluoride or magnesium fluoride. In
one embodiment, these components are made of magnesium fluoride. In
an alternative embodiment, first window 36 and second window 38 are
made of magnesium fluoride and other components, such as plurality
of prisms 32, first mirror 33 and second mirror 35 are made of
other materials, such as calcium fluoride.
[0027] Typically, a first laser beam (as described above) and a
second laser beam are generated by discharge electrode in laser
chamber 37. In use, referring to FIG. 3, a second laser gas (such
as Ar, Kr, Ne and/or F) is sealed in laser chamber 37 and energy is
supplied to the second laser gas by a second electrical discharge
in a second discharge electrode (not shown). This causes a second
laser beam 31 to oscillate. Oscillating laser beam 31 exits the
laser chamber 37 through a rear window 36. Laser beam 31 passes
through prisms 32, is reflected by second mirror 35 and grating 34.
In second mirror 35, an angle relative to the light path of laser
beam 31 is controlled by an actuator. By oscillating laser beam 31
at predetermined wavelength, a narrow band width is achieved for
laser beam 31. Laser beam 31 is totally reflected by grating 34 and
second mirror 35 causing laser beam 31 to reverse its original path
and exit chamber 37 from front window 38 and exit from first mirror
33.
[0028] Second laser beam 31 is used to anneal first and second
windows 38 and 36 concurrently with operation of the excimer laser.
The windows are irradiated with second laser beam 31 with light
having a wavelength of about 250 nm. This wavelength corresponds to
the wavelength of the induced absorption band. Alternately, second
laser beam 31 is used either before or after operation of the
excimer laser to anneal first and second windows 36 and 38 while
the eximer laser is not in use.
[0029] Alternately, windows 36 and 38 are thermally annealed.
Thermal annealing is accomplished by heating first and/or second
windows in an environment such as an inert gas or under vacuum.
Although the temperature to which the windows are heated is
dependent on the level of induced absorption, a temperature of from
about 200 to about 800.degree. C. is typical.
[0030] Although preferred embodiments have been depicted and
described in detail herein, it will be apparent to those skilled in
the relevant art that various modifications, additions,
substitutions and the like can be made without departing from the
spirit of the invention and these are therefore considered to be
within the scope of the invention as defined in the claims which
follow.
* * * * *