U.S. patent application number 14/048654 was filed with the patent office on 2014-02-06 for extreme ultraviolet light generation apparatus.
This patent application is currently assigned to GIGAPHOTON INC.. The applicant listed for this patent is GIGAPHOTON INC.. Invention is credited to Tooru ABE, Kouji KAKIZAKI, Osamu WAKABAYASHI.
Application Number | 20140034852 14/048654 |
Document ID | / |
Family ID | 44559059 |
Filed Date | 2014-02-06 |
United States Patent
Application |
20140034852 |
Kind Code |
A1 |
KAKIZAKI; Kouji ; et
al. |
February 6, 2014 |
EXTREME ULTRAVIOLET LIGHT GENERATION APPARATUS
Abstract
An extreme ultraviolet light generation apparatus may include: a
laser apparatus; a chamber provided with an inlet for introducing a
laser beam outputted from the laser apparatus to the inside
thereof; a target supply unit provided to the chamber for supplying
a target material to a predetermined region inside the chamber; a
collector mirror disposed in the chamber for collecting extreme
ultraviolet light generated when the target material is irradiated
with the laser beam in the chamber; an extreme ultraviolet light
detection unit for detecting energy of the extreme ultraviolet
light; and an energy control unit for controlling energy of the
extreme ultraviolet light.
Inventors: |
KAKIZAKI; Kouji;
(Hiratsuka-shi, JP) ; ABE; Tooru; (Hiratsuka-shi,
JP) ; WAKABAYASHI; Osamu; (Hiratsuka-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GIGAPHOTON INC. |
TOCHIGI |
|
JP |
|
|
Assignee: |
GIGAPHOTON INC.
Tochigi
JP
|
Family ID: |
44559059 |
Appl. No.: |
14/048654 |
Filed: |
October 8, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13042755 |
Mar 8, 2011 |
8569722 |
|
|
14048654 |
|
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Current U.S.
Class: |
250/504R |
Current CPC
Class: |
H01S 3/2316 20130101;
H01S 3/2232 20130101; H05G 2/003 20130101; H05G 2/008 20130101 |
Class at
Publication: |
250/504.R |
International
Class: |
H05G 2/00 20060101
H05G002/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 11, 2010 |
JP |
2010-055153 |
Jan 31, 2011 |
JP |
2011-018748 |
Claims
1. An extreme ultraviolet light generation apparatus, comprising: a
laser apparatus; a chamber provided with an inlet for introducing a
laser beam outputted from the laser apparatus to the inside
thereof; a target supply unit provided to the chamber for supplying
a target material to a predetermined region inside the chamber; a
collector mirror disposed in the chamber for collecting extreme
ultraviolet light generated when the target material is irradiated
with the laser beam in the chamber; an extreme ultraviolet light
detection unit for detecting energy of the extreme ultraviolet
light; and an energy control unit for controlling energy of the
extreme ultraviolet light.
2-21. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority from Japanese Patent
Application No. 2010-055153 filed Mar. 11, 2010, and Japanese
Patent Application No. 2011-018748 filed Jan. 31, 2011, the
disclosure of each of which is incorporated herein by reference in
its entirety.
BACKGROUND
[0002] 1. Technical Field
[0003] This disclosure relates to an apparatus for generating
extreme ultraviolet (EUV) light.
[0004] 2. Related Art
[0005] With recent increase in integration of semiconductor
process, transfer patterns for use in photolithography of the
semiconductor process have rapidly become finer. In the next
generation, microfabrication at 70 to 45 nm, and further,
microfabrication at 32 nm or less is to be demanded. Accordingly,
for example, to meet the demand for microfabrication at 32 nm or
less, an exposure apparatus is expected to be developed, where EUV
light of a wavelength of approximately 13 nm is combined with a
reduction projection reflective optical system.
[0006] There are mainly three types of known EUV light generation
apparatuses, namely, a laser produced plasma (LPP) type apparatus
using plasma produced as a target material is irradiated with a
laser beam, a discharge produced plasma (DPP) type apparatus using
plasma produced by discharge, and a synchrotron radiation (SR) type
apparatus using orbital radiation.
SUMMARY
[0007] An extreme ultraviolet light generation apparatus according
to one aspect of this disclosure may include: a laser apparatus; a
chamber provided with an inlet for introducing a laser beam
outputted from the laser apparatus to the inside thereof; a target
supply unit provided to the chamber for supplying a target material
to a predetermined region inside the chamber; a collector mirror
disposed in the chamber for collecting extreme ultraviolet light
generated when the target material is irradiated with the laser
beam in the chamber; an extreme ultraviolet light detection unit
for detecting energy of the extreme ultraviolet light; and an
energy control unit for controlling energy of the extreme
ultraviolet light.
[0008] According to another aspect of this disclosure, a method for
controlling an output of burst-outputted extreme ultraviolet light,
in an extreme ultraviolet light generation apparatus including a
laser apparatus, a chamber, a target supply unit, a collector
mirror for collecting extreme ultraviolet light, an extreme
ultraviolet light detection unit, and an energy control unit for
controlling energy of the extreme ultraviolet light, may include:
supplying a target material into the chamber; irradiating the
target material with a laser beam; detecting energy of an extreme
ultraviolet light pulse emitted when the target material is
irradiated with the laser beam; and controlling energy of an
extreme ultraviolet light pulse outputted following the extreme
ultraviolet light pulse, based on the detection result.
[0009] These and other objects, features, aspects, and advantages
of this disclosure will become apparent to those skilled in the art
from the following detailed description, which, taken in
conjunction with the annexed drawings, discloses preferred
embodiments of this disclosure.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG. 1 schematically illustrates an EUV light generation
system according to a first embodiment of this disclosure.
[0011] FIG. 2 illustrates change over time in ideal EUV pulse
energy at successive burst light emission.
[0012] FIG. 3 illustrates change over time in EUV pulse energy when
feedback control is not performed at burst light emission.
[0013] FIG. 4 is a flowchart showing overall control procedure
including energy control processing by an EUV light generation
controller.
[0014] FIG. 5 is a flowchart showing the energy control processing
procedure shown in FIG. 4.
[0015] FIG. 6 is a flowchart showing burst-lead control processing
procedure shown in FIG. 5.
[0016] FIG. 7 is a flowchart showing feedback control processing
procedure shown in FIG. 5.
[0017] FIG. 8 schematically shows change over time in signals at
successive burst light emission.
[0018] FIG. 9 is a time chart showing, in enlargement, the change
over time in signals between two burst light emission shown in FIG.
8.
[0019] FIG. 10 is a flowchart showing control amount read-out
processing procedure according to the first embodiment of this
disclosure.
[0020] FIG. 11 is a flowchart showing control amount update
processing procedure according to the first embodiment of this
disclosure.
[0021] FIG. 12 shows an example of a relation table according to a
second embodiment of this disclosure.
[0022] FIG. 13 is a flowchart showing control amount read-out
processing procedure according to a third embodiment of this
disclosure.
[0023] FIG. 14 is a flowchart showing control amount update
processing procedure according to the third embodiment of this
disclosure.
[0024] FIG. 15 is a flowchart showing control amount read-out
processing procedure according to a fourth embodiment of this
disclosure.
[0025] FIG. 16 is a flowchart showing control amount update
processing procedure according to the fourth embodiment of this
disclosure.
[0026] FIG. 17 is a flowchart showing control amount read-out
processing procedure according to a fifth embodiment of this
disclosure.
[0027] FIG. 18 is a flowchart showing control amount update
processing procedure according to the fifth embodiment of this
disclosure.
[0028] FIG. 19 is a flowchart showing control amount read-out
processing procedure according to a sixth embodiment of this
disclosure.
[0029] FIG. 20 is a flowchart showing control amount update
processing procedure according to the sixth embodiment of this
disclosure.
[0030] FIG. 21 is a flowchart showing control amount read-out
processing procedure according to a seventh embodiment of this
disclosure.
[0031] FIG. 22 is a flowchart showing control amount update
processing procedure according to the seventh embodiment of this
disclosure.
[0032] FIG. 23 schematically shows change in signals at successive
burst light emission, in a case where a trigger signal is a signal
indicating a burst light emission period.
[0033] FIG. 24 is a time chart showing, in enlargement, the change
in signals between two burst light emission shown in FIG. 23.
[0034] FIG. 25 schematically illustrates a configuration of the EUV
light generation system according to a modification of this
disclosure.
[0035] FIG. 26 schematically illustrates an example of an
oscillator shown in FIG. 25.
[0036] FIG. 27 schematically illustrates another example of an
oscillator shown in FIG. 25.
[0037] FIG. 28 schematically illustrates an example of an
oscillator shown in FIG. 25, the oscillator being configured of
semiconductor lasers.
[0038] FIG. 29 schematically illustrates an example of an
oscillator shown in FIG. 25, the oscillator being provided with a
high-speed shutter on the exterior thereof.
[0039] FIG. 30 schematically illustrates another example of an
oscillator shown in FIG. 25, the oscillator being provided with a
high-speed shutter on the exterior thereof.
[0040] FIG. 31 schematically illustrates an EUV light generation
system according to a second modification of this disclosure, in
which a regenerative amplifier is provided between an oscillator
and a preamplifier.
[0041] FIG. 32 shows operation of the regenerative amplifier shown
in FIG. 31.
[0042] FIG. 33 schematically illustrates a configuration of an EUV
light generation system according to a third modification of this
disclosure.
[0043] FIG. 34 schematically illustrates the EUV light generation
system according to the first embodiment, to which a pre-pulse
laser is additionally provided.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0044] Hereinafter, embodiments of this disclosure will be
described in detail with reference to the accompanying drawings.
The embodiments described below merely show an example of this
disclosure and do not limit the scope of this disclosure. Further,
configurations and operation described in each embodiment may not
be required configurations and operation of this disclosure. It
should be noted that like elements are referenced by like reference
numerals, and duplicate description thereof will be omitted.
First Embodiment
[0045] First, an EUV light generation apparatus according to a
first embodiment of this disclosure will be described. FIG. 1 is a
schematic diagram illustrating a configuration of an EUV light
generation system according to the first embodiment. The EUV light
generation system may include a driver laser 1, an EUV light
generation apparatus 2 for generating EUV light L2 using CO.sub.2
pulsed laser beam L1 outputted from the driver laser 1, and an EUV
light source controller C capable of controlling the driver laser 1
and the EUV light generation apparatus 2.
[0046] The driver laser 1 may output the CO.sub.2 pulsed laser beam
L1 under the control of the EUV light source controller C. The
outputted CO.sub.2 pulsed laser beam L1 may be reflected by an HR
(high reflection) mirror M1 and an off-axis paraboloidal mirror M2,
and may enter an EUV chamber 10 through a window 15 of the EUV
light generation apparatus 2.
[0047] In the EUV light generation apparatus 2, a target generator
12 may output a target 13, which is a droplet of Sn, so that the
target 13 passes through a plasma generation region PL inside the
EUV chamber 10. The timing at which the target 13 is outputted from
the target generator 12 may be controlled with a droplet control
signal S4 sent from the EUV light source controller C to a droplet
controller 11. The droplet controller 11 may control the timing at
which the target 13 is generated in response to the droplet control
signal S4. Among the outputted targets 13, targets 13 that have not
contributed to the generation of EUV light may be collected into a
target collection unit 14 disposed so as to face the target
generator 12. Further, the EUV light generation apparatus 2 may
include an EUV light detector 16. The EUV light detector 16 may
detect the energy of EUV light emitted in the plasma generation
region PL, and may output an EUV pulse energy detection signal S2
to the EUV light source controller C.
[0048] Meanwhile, the CO.sub.2 pulsed laser beam L1, outputted from
the driver laser 1, having entered the EUV chamber 10 may be
focused in the plasma generation region PL through a through-hole
provided at the center of an EUV collector mirror M3. In the plasma
generation region PL, the target 13 may be irradiated with the
CO.sub.2 pulsed laser beam L1, whereby the target material 13 may
be turned into plasma. EUV light L2 with a wavelength of
approximately 13.5 nm may be emitted from this plasma. The emitted
EUV light L2 may be collected by the EUV collector mirror M3, and
focused at an intermediate focus IF. Further, the EUV light L2 may
enter an exposure apparatus 100 while diverging from the
intermediate focus IF.
[0049] Based on a trigger signal S1 from the exposure apparatus
100, the EUV light source controller C may control such that at
least the timing at which the target 13 is generated is
synchronized with the timing at which the CO.sub.2 pulsed laser
beam L1 is outputted from the driver laser 1, thereby controlling
the generation of the EUV light L2 in the plasma generation region
PL.
[0050] The EUV light source controller C may perform burst lead
control processing so that at least lead-side pulse energy is
stably at a desirable value at burst light emission. The EUV light
source controller C may include an energy control processing unit
20, a pulse history unit 21, a timer 22, and a control amount
storage unit 23. The pulse history unit 21 may store an EUV pulse
energy value within a predetermined time Tw together with a pulse
generation time. In this processing of the EUV pulse energy
history, a time at which an EUV pulse is generated may be
identified based on the trigger signal S1 from the exposure
apparatus 100, and an EUV pulse energy value may be identified
based on the EUV pulse energy detection signal S2 from the EUV
light detector 16. The EUV pulse energy detection signal S2 may,
instead of a detection signal from the EUV light detector 16, be an
EUV pulse energy detection signal from an EUV light detector (not
shown) provided to the exposure apparatus 100. Alternatively, the
configuration may be such that the EUV pulse energy detection
signals from both the exposure apparatus 100 and the EUV light
detector 16 are used as the EUV pulse energy detection signal S2.
The timer 22 may time a predetermined time, for example, a trigger
wait time T, which will be described later. The control amount
storage unit 23 may updatably store, as a parameter log, a control
amount of the lead-side pulse energy corresponding to an averaged
EUV pulse energy generated within the predetermined time Tw. The
energy control processing unit 20 may perform feedback control, and
in particular, the energy control processing unit 20 may learn and
update the control amount of the lead-side pulse energy based on
the parameter log stored in the pulse history unit 21. The energy
control processing unit 20 may perform the burst lead control
processing for stabilizing an output of lead-side pulse energy,
based on the control amount of the updated lead-side pulse
energy.
[0051] Here, an ideal burst light emission pattern will be
described. FIG. 2 is a time chart showing a case in which burst
light emission has been generated in order of B11, B12, B13, B14,
and B15, and burst light emission B to be controlled next is to be
generated. In this case, the burst light emission B12, B13, B14,
and B15 are generated within the above-mentioned predetermined time
Tw. Also, a burst-length time TB may be a period of the burst light
emission B15 immediately preceding the burst light emission B to be
controlled. Also, a burst-rest time Tr may be a light-emission-rest
time immediately preceding the burst light emission B to be
controlled. FIG. 2 shows an ideal burst light emission, in which
EUV pulse energy Ep is uniform for every burst light emission.
[0052] FIG. 3 shows change over time in EUV pulse energy in the
case where the feedback control is not performed for burst light
emission. In this burst light emission, 31 successive EUV pulses P1
through P31 are generated, for example. Here, EUV pulses subject to
the burst lead control processing by the energy control processing
unit 20 may be EUV pulses within a learning control region E1. To
be more specific, the EUV pulses subject to the burst lead control
processing may be the first m EUV pulses; that is, seven EUV pulses
of EUV pulses P1 through P7. Further, EUV pulses within a feedback
region E2 may be k EUV pulses of the (m+1)-th pulse through the
(m+k)-th pulse, which is the last pulse; that is, 24 EUV pulses of
EUV pulses P8 through P31. In this feedback control, the EUV pulse
energy of an EUV pulse may be controlled based on the EUV pulse
energy of an immediately preceding EUV pulse within the burst light
emission.
[0053] In general, an EUV light generation system is used as a
light source for an exposure apparatus in which an irradiation
object, such as a semiconductor wafer, is exposed to light, and
which repeats light emission operation with step and scan system.
In other words, the EUV light generation apparatus repeats such
operation pattern that successive pulsed light emission, i.e.,
burst light emission at a predetermined operating frequency is
performed during scanning exposure and the pulsed light emission is
paused during step movement. In order to have this operation
pattern repeated, burst oscillation operation is performed, where
successive pulse oscillation for a predetermined time in which the
burst light emission is performed and pulse oscillation pause are
repeated.
[0054] Here, when the feedback control is not performed for the EUV
pulse energy at the burst light emission, a burst light emission
pattern may be such that a value of the EUV pulse energy is not
constant, as shown in FIG. 3. In particular, with an existing EUV
light generation system, each EUV pulse energy is detected at burst
light emission, or an averaged EUV pulse energy within a
predetermined period is detected, whereby the feedback control is
performed for each EUV pulse energy.
[0055] However, as shown in FIG. 3, the value of the lead-side
pulse energy of burst light emission, in particular, the value of
lead pulse energy tends to be a large value, and in many cases, the
energy value may exceed the range of values which can be controlled
with the feedback control. That is, it is difficult to generate an
ideal burst light emission in which values of the EUV pulse energy
in a burst light emission period are uniform as shown in FIG. 2. It
is contemplated that this is because a burst rest period is
provided between burst light emission and a thermal condition in
the EUV light generation system may change between the burst light
emission period and the burst rest period. Hence, even if the
feedback control is performed, it is difficult to stably control
the lead-side pulse energy to be a predetermined pulse energy
value. Further, when the burst light emission period, the burst
rest period, and so forth vary, or when a desirable value of EUV
pulse energy varies for each burst light emission period, it is
even more difficult to stably control the value of the lead-side
pulse energy.
[0056] In controlling to stabilize the lead-side pulse energy, even
if burst oscillation by the driver laser of the EUV light
generation system is stabilized, it is highly likely that the EUV
pulse energy cannot be stabilized. That is, the change in thermal
condition in the EUV light generation system is a thermal change in
an optical element such as a mirror in the EUV light generation
system, and this optical element may also be used for the output of
the EUV light.
[0057] In the first embodiment, in order to control such that the
lead-side pulse energy value at the burst light emission is
stabilized at a desirable value, the energy control processing unit
20 is configured to perform the burst lead control processing. In
this specification, "burst output" is defined as a case in which a
successive pulse output of EUV light for a predetermined time and
pulse output pause are alternately repeated.
[0058] Next, energy control processing including the burst lead
control processing by the energy control processing unit 20 will be
described with reference to the drawings. FIG. 4 is a flowchart
showing the overall control procedure including the energy control
processing by the EUV light source controller C. FIG. 5 is a
flowchart showing the energy control processing procedure shown in
FIG. 4. FIG. 6 is a flowchart showing the burst lead energy control
processing procedure shown in FIG. 5. FIG. 7 is a flowchart showing
the feedback control processing procedure shown in FIG. 5. FIG. 8
is a time chart schematically showing change over time in signals
during successive burst light emission. FIG. 9 is a time chart
showing, in enlargement, change over time in signals between two
burst light emission shown in FIG. 8.
[0059] First, as shown in FIG. 4, the EUV light source controller C
may perform initialization (step S101). This initialization may
include setting an initial value of a trigger wait time T so as to
be larger than a burst start threshold Tth, setting an initial
value for a control amount to be used in the burst lead control
processing, and so forth. Then, the EUV light source controller C
may perform energy control processing for stabilizing each pulse
energy value at the burst light emission at a desirable value (step
S102). Then, the EUV light source controller C may determine
whether or not processing for stopping laser oscillation is
performed (step S103). If the laser oscillation is stopped (step
S103, Yes), this processing is ended, and if the laser oscillation
is not stopped (step S103, No), this processing shifts to step
S102, and the energy control processing may be performed.
[0060] As shown in FIG. 5, in the energy control processing in step
S102, it may first be determined whether or not the energy control
processing unit 20 has detected the trigger signal S1 inputted from
the exposure apparatus 100 (step S111). If the energy control
processing unit 20 detects the trigger signal S1 (step S111, Yes),
it may be determined whether or not the trigger wait time T is
larger than the burst start threshold Tth (step S112). As shown in
FIG. 9, this trigger wait time T may be a time between trigger
signals S1, and may be a value set in the initialization or a time
timed by the timer 22. The burst start threshold Tth may be a
predetermined value, and may, for example, be 20 ms. As shown in
FIG. 9, this burst start threshold Tth may be a value larger than
an EUV pulse interval Tp in a burst light emission period.
[0061] If the trigger wait time T is equal to or larger than the
burst start threshold Tth (step S112, Yes), the energy control
processing unit 20 may set a burst pulse number Pb, which is a
variable and is counted from the burst lead, to Pb=1 (step S113).
Then, the processing shifts to the burst lead control processing in
step S116. If the trigger wait time T is not larger than the burst
start threshold Tth (step S112, No), the burst pulse number Pb may
be incremented to be Pb+1 (step S114). Further, it may be
determined whether or not the burst pulse number Pb is equal to or
smaller than a predetermined burst lead control pulse number m
(step S115). The burst lead control pulse number m may be the
number of pulses subject to the burst lead control processing. If
the burst pulse number Pb is equal to or smaller than a burst lead
control pulse number m (S115, Yes), the processing may shift to
step S116, in which the burst lead control processing may be
performed. If the burst pulse number Pb is larger than the burst
lead control pulse number m (S115, No), the feedback control
processing may be performed (step S117). Then, after the burst lead
control processing in step S116 or the feedback control processing
in step S117 is performed, the processing may return to step
S102.
[0062] As shown in FIG. 6, in the burst lead control processing in
step S116, control amount read-out processing may first be
performed (step S201). This control amount may be an EUV pulse
energy control amount of the order corresponding to a burst pulse
number Pb within the learning control region E1, and may be stored
updatably in the control amount storage unit 23 by the energy
control processing unit 20. In the first embodiment, this control
amount may be determined based on an averaged output of the EUV
pulse energy within the predetermined period Tw and the value of
the burst pulse number Pb, and may be held in a relation table.
Further, in step S201, the control amount read-out processing may
be performed, in which the control amount of the EUV pulse energy
corresponding to the averaged output at a given time tm0 is read
out with reference to this relation table.
[0063] As shown in FIG. 10, in this control amount read-out
processing, EUV pulse energy E for a count value of the number of
pulses (the number of EUV pulses) within the predetermined time Tw
obtained based on the history in the pulse history unit 21 may be
added and an averaged output, in which the sum is divided by the
predetermined time Tw, may be calculated (step S301). The averaged
output W may be a parameter log, and may be calculated with the
following Expression (1).
W=(.SIGMA.E)/Tw (1)
[0064] If the predetermined time Tw is not obtained by the time
tm0, it is preferable that EUV pulse energy for a count value of
the number of pulses by the time tm0 may be added and an averaged
output obtained by dividing the sum by a time by the time tm0 may
be calculated as the averaged output W. However, the averaged
output W may be directly calculated based on Expression (1).
[0065] Then, based on the calculated averaged output W and the
value of the burst pulse number Pb, the corresponding control
amount may be read out from the control amount storage unit 23
(step S302), and the processing may return to step S201.
[0066] For example, in the relation table stored in the control
amount storage unit 23, in its initial state, control amounts
preset for each EUV pulses up to the m-th pulse from the lead of
the burst light emission within the range of averaged outputs W
divided into n stages may be stored in a matrix, as shown in a
relation table Ta in FIG. 10. For example, if a value of an
averaged value W is within the range of "W.sub.1 to W.sub.2" for
the lead EUV pulse (burst pulse number Pb=1), the control amount
C.sub.(2,1) may be read out.
[0067] Referring again to FIG. 6, the energy control processing
unit 20 may output an EUV pulse energy control signal S3 indicating
the read-out control amount to the driver laser 1, and the CO.sub.2
pulsed laser beam L1 may be outputted to have the EUV pulsed light
emitted (step S202).
[0068] Subsequently, the energy control processing unit 20 detects
the emitted EUV pulse energy based on the EUV pulse energy
detection signal S2 (step S203), and updates the history in the
pulse history unit 21 based on the detected EUV pulse energy (step
S204). Then, control amount update processing for updating the
relation table Ta in the control amount storage unit 23 may be
performed based on the updated history in the pulse history unit 21
(step S205).
[0069] As shown in FIG. 11, in the control amount update
processing, the energy control processing unit 20 may first
calculate a difference .DELTA.E between an EUV pulse energy Es
detected in step S203 and a desirable EUV pulse energy Et (step
S311).
[0070] Then, to reduce the difference .DELTA.E, the energy control
processing unit 20 may calculate an optimal control amount
C.sub.new as indicated by Expression (2) given below (step S312).
C.sub.new may be calculated with Expression (2).
C.sub.new=C+.DELTA.E*dC/dE*Gain (2)
[0071] Then, the energy control processing unit 20 may update, to
the calculated control amount C.sub.new, a corresponding control
amount C in the control amount storage unit 23 (step S313), and the
processing may return to step S205. For example, if the value of
the averaged output W as the parameter log is in "W.sub.1 to
W.sub.2," and the pulse is the lead EUV pulse (burst pulse number
Pb=1), the control amount C.sub.(2,1) in the relation table Ta may
be updated to the optimal control amount C.sub.new.
[0072] Referring back to FIG. 6, the energy control processing unit
20 may reset the trigger wait time T timed by the timer 22 to T=0
(step S206), and the processing may return to step S116.
[0073] As shown in FIG. 8, in this burst lead control processing,
based on the averaged output W, which is the parameter log for the
EUV pulse energy within the predetermined time Tw, the optimal
control amount for the EUV pulse energy corresponding to the
averaged output W may be selected for the each EUV pulse within the
learning control region E1, and an EUV pulse may be emitted.
Further, in the burst lead control processing, the energy control
processing unit 20 may calculate such optimal control amount that
would reduce the difference .DELTA.E between a predetermined
emitted EUV pulse energy Es and the desirable EUV pulse energy Et
to update the control amount, and the energy control processing
unit 20 may learn so that the EUV pulse, which should emit light
when the averaged output W is in the same range, may be at the
desirable EUV pulse energy Et.
[0074] Next, the feedback control processing in step S117 shown in
FIG. 5 will be described with reference to the drawings. As shown
in FIG. 7, the energy control processing unit 20 may first read out
the control amount calculated based on the immediately preceding
EUV pulse energy from the control amount storage unit 23 (step
S211). Then, the energy control processing unit 20 may output the
EUV pulse energy control signal S3 indicating the read-out control
amount to the driver laser 1, to cause the CO.sub.2 pulsed laser
beam L1 to be oscillated and to have the EUV pulsed light emitted
(step S212).
[0075] Then, the energy control processing unit 20 may detect the
emitted EUV pulse energy based on the EUV pulse energy detection
signal S2 (step S213), calculate a control amount based on the
detected EUV pulse energy (step S214), and store the calculated
control amount in the control amount storage unit 23.
[0076] Then, the energy control processing unit 20 may reset the
trigger wait time T timed by the timer 22 to T=(step S215), and the
processing may return to step S117.
[0077] As described above, in this feedback control processing, the
output of the EUV pulse energy may be controlled so that the
difference between the immediately preceding EUV pulse energy and
the predetermined EUV pulse energy is reduced. To be more specific,
as shown in FIG. 8, the processing may be performed for the EUV
pulses within a feedback control region E2.
[0078] The history held in the pulse history unit 21 may be a time
history of EUV pulse energy detection signals S2, as shown in FIG.
8(e). The history held in the pulse history unit 21 may be a time
history from the time tm0 to the start of the predetermined time
Tw, and the history before then may successively be deleted.
[0079] The averaged output W calculated in step S301 is a time
average; however, since the predetermined time Tw is preset, the
calculated value may not be divided by the predetermined time Tw,
and an integrated value of EUV pulse energy within the
predetermined time Tw may be used. Alternatively, an averaged value
of EUV pulse energy may be used. Further, the number of EUV pulses
may serve as the parameter log.
[0080] In the first embodiment, the configuration is such that the
energy control processing unit 20 performs the energy control for
one or more lead-side pulse energy including at least the first
pulse of EUV pulses to be emitted subsequently based on the
parameter log of the immediately preceding burst light emission,
lead-side pulse energy at burst light emission can stably be
controlled at a desirable value.
Second Embodiment
[0081] In the second embodiment, the burst lead control pulse
number m may be 1. This is because the EUV pulse of the burst lead
may vary largely from the value of the desirable EUV pulse energy
according to the parameter log. FIG. 12 shows a relation table Tb
stored in the control amount storage unit 23 in this case. In the
relation table Tb, a control amount corresponding to a range of an
averaged output W may be stored and updated only for an EUV pulse
of a burst lead Accordingly, the feedback control processing in
step S117 may be performed for the second and the subsequent EUV
pulses counted from the burst lead.
Third Embodiment
[0082] In the above-described first embodiment, the configuration
is such that the control amount is read out using the relation
table stored in the control amount storage unit 23, and the control
amount is updated; however, in the third embodiment, the
configuration may be such that the burst lead control processing is
performed by having the control amount read out using a relational
expression indicative of the control amount corresponding to an
averaged output W and having the control amount updated.
[0083] FIG. 13 is a flowchart showing control amount read-out
processing procedure in the burst lead control processing according
to the third embodiment. Also, FIG. 14 is a flowchart showing the
control amount update processing procedure in the burst lead
control processing according to the third embodiment.
[0084] In the control amount read-out processing shown in FIG. 13,
similarly to step S301, an averaged output W may be calculated as a
parameter log (step S401). Then, the obtained averaged output W may
be applied to the relational expression indicated by Expression (3)
for the control amount C with the averaged output W serving as a
variable, whereby the control amount may be calculated (step S402),
and the processing may return to step S201.
C=(dC/dW)*(A/exp(B.times.W)+D) (3)
[0085] In Expression (3), A and B are constants, and D is an offset
amount. The relational expression for the control amount C may be
set for each EUV pulse from the lead within the learning control
region E1. In other words, the relational expressions may be set
for the number of pulses corresponding to the burst lead control
pulse number m.
[0086] Also, in the control amount update processing shown in FIG.
14, similarly to step S311, the difference .DELTA.E between the
detected EUV pulse energy Es and the desirable EUV pulse energy Et
may be calculated (step S411). Then, an optimal offset amount
D.sub.new for reducing the difference .DELTA.E may be calculated
using the following Expression (4) (step S412).
D.sub.new=D+.DELTA.E*dC/dE*Gain (4)
[0087] Then, an offset amount D in the relational expression may be
updated to the calculated optimal offset amount D.sub.new (step
S413), and the processing may return to step S205.
Fourth Embodiment
[0088] In the above-described first embodiment, the configuration
is such that the control amount is read out using the averaged
output W within the predetermined time Tw as the parameter log and
the control amount is updated, whereby the burst lead control
processing is performed; however, in the fourth embodiment, the
configuration may be such that a control amount is read out using
the immediately preceding burst-length time TB shown in FIG. 8 as
the parameter log and the control amount is updated. In other
words, in the fourth embodiment, when the burst light emission is
performed, the burst-length time TB of the immediately preceding
burst light emission that may affect the burst light emission to be
controlled may be used as the parameter log.
[0089] FIG. 15 is a flowchart showing the control amount read-out
processing procedure in the burst lead control processing according
to the fourth embodiment. FIG. 16 is a flowchart showing the
control amount update processing procedure in the burst lead
control processing according to the fourth embodiment.
[0090] In the control amount read-out processing shown in FIG. 15,
the immediately preceding burst-length time TB may be acquired from
the history in the pulse history unit (step S501). Then, based on
the value of the acquired burst-length time TB, the corresponding
control amount may be read out from a relation table Tc stored in
the control amount storage unit 23 (step S502), and the processing
may return to step S201.
[0091] Here, in the relation table Tc, control amounts C.sub.1,
C.sub.2, . . . , C.sub.n-1, C.sub.n may be set respectively, for
example, for an n number of ranges (0 to T.sub.1, T.sub.1 to
T.sub.2, . . . , T.sub.n-1 to T.sub.n) of the burst-length time TB
for the burst lead pulses. Then, for example, if the acquired
burst-length time TB is within the range of T.sub.1 to T.sub.2, the
control amount C.sub.2 may be read out.
[0092] Further, in the control amount update processing shown in
FIG. 16, similarly to step S311, the difference .DELTA.E between
the detected EUV pulse energy Es and the desirable EUV pulse energy
Et may be calculated (step S511). Then, to reduce the difference
.DELTA.E, an optimal control amount C may be calculated using the
difference .DELTA.E with Expression (2) (step S512).
[0093] The corresponding control amount C may be updated to the
calculated optimal control amount C.sub.new (step S513), and the
processing may return to step S205. For example, when the optimal
control amount C.sub.new corresponding to the control amount
C.sub.2 is calculated, overwriting processing for updating the
control amount C.sub.2 to the optimal control amount C.sub.new may
be performed.
Fifth Embodiment
[0094] In the above-described first embodiment, the configuration
is such that the control amount is read out using the averaged
output W within the predetermined time Tw as the parameter log and
the control amount is updated, whereby the burst lead control
processing is performed. In the fifth embodiment, the configuration
may be such that the control amount is read out using the
immediately preceding burst-rest time Tr shown in FIG. 8 as the
parameter log, and the controlled amount is updated. In other
words, in the fifth embodiment, when the burst light emission is
performed, the burst-rest time Tr, which is a light emission rest
time since the completion of the immediately preceding burst light
emission that may affect the burst light emission to be controlled,
may be used as the parameter log.
[0095] FIG. 17 is a flowchart showing the control amount read-out
processing procedure in the burst lead control processing according
to the fifth embodiment. FIG. 18 is a flowchart showing the control
amount update processing procedure in the burst lead control
processing according to the fifth embodiment.
[0096] In the control amount read-out processing shown in FIG. 17,
the immediately preceding burst-rest time Tr may first be acquired
from the history in the pulse history unit 21 (step S601). Then,
based on the value of the acquired burst-rest time Tr, the
corresponding control amount may be read out from a relation table
Td stored in the control amount storage unit 23 (step S602), and
the processing may return to step S201.
[0097] In the relation table Td, control amounts C.sub.1, C.sub.2,
. . . , C.sub.n-1, C.sub.n may be set respectively, for example,
for an n number of ranges (0 to Tr.sub.1, Tr.sub.1 to Tr.sub.2, . .
. , Tr.sub.n-1 to Tr.sub.n) of the burst-rest time Tr for the burst
lead pulses. Then, for example, if the acquired burst-rest time Tr
is within the range of Tr.sub.1 to Tr.sub.2, the control amount
C.sub.2 may be read out.
[0098] Also, in the control amount update processing shown in FIG.
18, similarly to step S311, the difference .DELTA.E between the
detected EUV pulse energy Es and the desirable EUV pulse energy Et
may be calculated (step S611). Then, to reduce the difference
.DELTA.E, an optimal control amount C.sub.new may be calculated
using the difference .DELTA.E with Expression (2) (step S612).
[0099] Then, the corresponding control amount C may be updated to
the calculated optimal control amount C.sub.new (step S613), and
the processing may return to step S205. For example, if the optimal
control amount C.sub.new corresponding to the control amount
C.sub.2 is calculated, overwriting processing for updating the
control amount C.sub.2 to the optimal control amount C.sub.new may
be performed.
Sixth Embodiment
[0100] In the above-described fourth embodiment, the configuration
is such that the control amount is read out from the relation table
Tc using the immediately preceding burst-length time TB as the
parameter log and the control amount is updated. In the sixth
embodiment, instead of the relation table Tc, similarly to the
third embodiment, the configuration may be such that the control
amount may be read out using the relational expression indicative
of the control amount corresponding to the immediately preceding
burst-length time TB, and the control amount may be updated.
[0101] FIG. 19 is a flowchart showing the control amount read-out
processing procedure in the burst lead control processing according
to the sixth embodiment. FIG. 20 is a flowchart showing the control
amount update processing procedure in the burst lead control
processing according to the sixth embodiment.
[0102] In the control amount read-out processing shown in FIG. 19,
the immediately preceding burst-length time TB may be acquired from
the history in the pulse history unit (step S701). Then, the
acquired burst-length time TB may be inputted to a relational
expression indicative of the relationship of the control amount
with respect to the burst-length time TB, the relational expression
being shown in Expression (5) stored in the control amount storage
unit 23; the corresponding control amount may be calculated (step
S702); and the processing may return to step S201.
C=(dC/dT)*(A/exp(B.times.TB)+D) (5)
[0103] In Expression (5), A and B are constants, and D is an offset
amount. The relational expression for the control amount C may be
set for each EUV pulse from the lead within the learning control
region E1. In other words, the relational expressions may be set
for the number of pulses corresponding to the burst lead control
pulse number m.
[0104] Also, in the control amount update processing shown in FIG.
20, similarly to step S311, the difference .DELTA.E between the
detected EUV pulse energy Es and the desirable EUV pulse energy Et
may be calculated (step S711). Then, the optimal offset amount
D.sub.new for reducing the difference .DELTA.E may be calculated
with Expression (4) (step S712). Then, the offset amount D in the
relational expression may be updated to the calculated optimal
offset amount D.sub.new (step S713), and the processing may return
to step S205.
[0105] In the sixth embodiment, the configuration is such that the
control amount is obtained based on the relational expression using
the burst-length time TB as the parameter log; however, the
configuration may be such that the control amount may be obtained
with a relational expression using the burst-rest time Tr, instead
of the burst-length time TB, as the parameter log.
Seventh Embodiment
[0106] In the seventh embodiment, the configuration may be such
that a control amount is read out from a relation table Te for
control amounts set based on a matrix of the averaged output W and
the burst-length time TB, with the averaged output W within the
predetermined time Tw and the burst-length time TB being used as
the parameter logs, and the control amount is updated, whereby
burst lead control processing is performed. If the burst lead
control pulse number m is plural, a plurality of relation tables
may be used.
[0107] FIG. 21 is a flowchart showing the control amount read-out
processing procedure in the burst lead control processing according
to the seventh embodiment. FIG. 22 is a flowchart showing the
control amount update processing procedure in the burst lead
control processing according to the seventh embodiment.
[0108] In the control amount read-out processing shown in FIG. 21,
the averaged output W and the immediately preceding burst-length
time TB may be acquired from the history in the pulse history unit
21 (step S801). Then, the corresponding control amount may be read
out from the relation table Te stored in the control amount storage
unit 23, based on the acquired averaged output W and the
burst-length time TB (step S802), and the processing may return to
step S201.
[0109] Further, in the control amount update processing shown in
FIG. 22, the difference .DELTA.E between the detected EUV pulse
energy Es and the desirable EUV pulse energy Et may be calculated
(step S811). Then, to reduce the difference .DELTA.E, an optimal
control amount C.sub.new may be calculated using the difference
.DELTA.E with Expression (2) (step S812).
[0110] Then, the corresponding control amount C may be updated to
the calculated optimal control amount C.sub.new (step S813), and
the processing may return to step S205. For example, if the value
of the control amount C set when the value of the averaged output W
is within the range of W.sub.1 to W.sub.2 and the value of the
burst-length time TB within the range of T.sub.1 to T.sub.2 is
C.sub.(2,2), when an optimal control amount C.sub.new corresponding
to this control amount C.sub.(2,2) is calculated, overwriting
processing for updating the control amount C.sub.(2,2) to the
optimal control amount C.sub.new may be performed.
[0111] If a control amount is calculated using a relational
expression instead of a relation table, this relational expression
may be a function in which the control amount C is determined with
the averaged output W and the burst-length time TB being used as
variables. If the burst lead control pulse number m is plural, a
plurality of relation tables may be used. The burst-rest time Tr
may be used instead of the burst-length time TB, or a relation
table of a three-dimensional matrix with the burst-rest time Tr
added or a function in which a control amount C is determined by a
relational expression determined by three variables including the
averaged output W, the burst-length time TB, and the burst-rest
time Tr may be used.
[0112] In these first through seventh embodiments, the
configuration is such that the control amount C of at least a
single lead-side EUV pulse determined by one of the averaged output
W of the EUV pulse energy within the predetermined time Tw, the
burst-length time TB, and the burst-rest time Tr or a combination
of at least two of these may be read out and updated, and the burst
lead control processing is performed in which the learning control
is performed for the at least single lead-side EUV pulse energy to
be burst-emitted next. Accordingly, the value of the lead-side EUV
pulse energy does not become a value largely deviated from the
desirable EUV pulse energy, and stable burst light emission can be
performed.
[0113] In the above-described first through seventh embodiments,
the configuration is such that the trigger signal S1 is indicated
on each pulse in burst light emission. In contrast, as shown in
FIGS. 23 and 24, a trigger signal S1a indicated on each burst may
be used instead of the trigger signal S1 from the exposure
apparatus 100. In this case, the energy control processing unit 20
may be configured to generate an EUV pulse energy control signal S3
based on rising timing of the trigger signal S1a. A repetition rate
within the burst of the EUV pulse energy control signal S3 may be
held in the EUV light source controller C in advance or may be
designated by the exposure apparatus 100. The generated EUV pulse
energy control signal S3 may be inputted to the driver laser 1 and
to the pulse history unit 21 and the timer 22 as well. The pulse
history unit 21 may treat the EUV pulse energy control signal S3 as
the trigger signal S1 and may save the history of the EUV pulse
energy. Also, the timer 22 may treat the EUV pulse energy control
signal S3 as the trigger signal S1 and may perform timing
processing. In other words, even with the trigger signal S1a
indicative of each burst light emission period, as long as the
energy control processing unit 20 generates EUV pulse energy
control signals S3 corresponding to second and later trigger
signals S1a (or first and later trigger signals S1a), processing
similar to any of the above-described first through seventh
embodiments can be performed.
First Modification
[0114] In the first modification, a detailed control configuration
of a driver laser 1 that is controlled by the EUV light source
controller C according to any of the above-described first through
seventh embodiments will be described. As shown in FIG. 25, the
driver laser 1 may include an oscillator 25 including a master
oscillator MO such as a semiconductor laser that oscillates a
longitudinal-mode pulsed laser beam in gain bandwidths of a
preamplifier PA and a main amplifier MA, and the preamplifier PA
and the main amplifier MA that successively amplify the pulsed
laser beam outputted from the oscillator 25. Also, the driver laser
1 may include a driver laser controller C1. The driver laser
controller C1 may output to the oscillator 25 a trigger signal S11
and a laser pulse energy control signal S13 that control the
oscillation of the CO.sub.2 pulsed laser beam L1 from the
oscillator 25, based on a trigger signal S1 and an EUV pulse energy
control signal S3 outputted from an EUV light source controller
C.
[0115] The preamplifier PA may be a slab amplifier. The laser beam
outputted from the oscillator 25 may be incident on an input window
of the preamplifier PA. The preamplifier PA may include an
amplification region, amplify the inputted laser beam through
multipass-amplification with mirrors M31 and M32 in the
amplification region, and output the amplified laser beam through
an output window toward an HR (high reflection) mirror M11. In this
way, the single longitudinal-mode pulsed laser beam may pass
through the amplification region filled with a gain medium within
the preamplifier PA to be further amplified efficiently, and be
outputted therefrom.
[0116] The amplified pulsed laser beam outputted from the
preamplifier PA may be reflected by the HR mirrors M11 and M12, and
may enter a relay optical system R2. The relay optical system R2
may expand a beam width or diameter of the amplified pulsed laser
beam so that the amplified pulsed laser beam enters an
amplification region of the main amplifier MA filled with mixed gas
serving as a gain medium for the CO.sub.2 laser beam so as to have
the space filled with the amplified pulsed laser beam. With this,
the amplified pulsed laser beam may pass through the amplification
region filled with the gain medium within the main amplifier MA to
be further amplified efficiently, and be outputted.
[0117] Then, the amplified pulsed laser beam outputted from the
main amplifier MA may be collimated by a relay optical system R3.
The collimated laser beam may be reflected with high reflectivity
by the HR mirror M1 and the off-axis paraboloidal mirror M2, and
may enter the EUV chamber 10 of the EUV light generation apparatus
2 through the window 15.
[0118] Here, an optical element M21, which is configured of a
partial reflection mirror or a beam splitter for detecting the
output of the CO.sub.2 pulsed laser beam L1, may be provided
between the HR mirror M1 and the off-axis paraboloidal mirror M2.
The laser beam reflected by the optical element M21 may be focused
by a focusing lens R21, and thereafter the output of the CO.sub.2
pulsed laser beam L1 may be detected by a laser beam detector 24.
The pulse energy of the CO.sub.2 pulsed laser beam L1 detected by
the laser beam detector 24 may be inputted as a laser pulse energy
detection signal S5 to the EUV light source controller C and to the
driver laser 1.
[0119] The driver laser controller C1 may output a trigger signal
S11 and a laser pulse energy control signal S13 to the oscillator
25, and thus perform energy control for the pulsed laser beam to be
inputted into the preamplifier PA. At this time, the driver laser
controller C1 may control the driver laser 1 based on the inputted
laser pulse energy detection signal S5. The control for the EUV
pulse energy outputted from the EUV light generation apparatus 2
may be performed by the high-order EUV light source controller
C.
[0120] That is, in the first modification, the configuration may be
such that oscillation timing, an oscillation wavelength, and an
oscillation waveform of the pulsed laser beam inputted to the
preamplifier PA are controlled.
[0121] As shown in FIG. 26, the master oscillator MO, for example,
may be configured such that a Pockels cell 34, a polarizer 35, and
a CO.sub.2 gain medium 33 are arranged between a pair of resonator
mirrors 31 and 32 in that order from the resonator mirror 31 side.
The CO.sub.2 gain medium 33 may be excited in a predetermined state
with voltage of a constant frequency being applied from a laser
power supply 37. The polarizer 35, for example, may transmit
P-polarized component of a laser beam with respect thereto. A
Pockels cell control power supply 36 may output to the Pockels cell
an oscillation control signal S30 for generating a predetermined
pulse shape at predetermined timing based on the trigger signal S11
and the laser pulse energy control signal S13. The Pockels cell 34
with voltage being applied thereto may rotate the polarization of
the laser beam incident thereon while predetermined voltage or
higher is applied thereto. First, in a state in which voltage is
not applied to the Pockels cell 34 based on the oscillation control
signal S30, the linearly polarized CO.sub.2 laser beam is
transmitted through the Pockels cell 34 without having the
polarization thereof rotated; thus, the CO.sub.2 laser beam is
incident on the polarizer 35 as the P-polarized component and is
not outputted toward the preamplifier PA. Here, when predetermined
or higher voltage is applied to the Pockels cell 34 for a
predetermined period based on the oscillation control signal S30,
the amplified CO.sub.2 laser beam incident on the Pockels cell 34
may be converted to a laser beam of S-polarized component with
respect to the polarizer 35 by the Pockels cell 34, and be
reflected by the polarizer 35 to be outputted toward the
preamplifier PA. The laser pulse energy outputted from the
polarizer 35 toward the preamplifier PA may be controlled by
adjusting the length of the predetermined period during which
voltage is applied by the Pockels cell control power supply 36.
[0122] In the oscillator shown in FIG. 26, the configuration is
such that the laser pulse energy is controlled by controlling the
predetermined period during which the voltage is applied from the
Pockels cell control power supply 36 to the Pockels cell 34. In
contrast, as shown in FIG. 27, the Pockels cell control power
supply 36 may apply to the Pockels cell 34 a control signal S31 for
applying voltage for a predetermined period based only on the
trigger signal S11, and the laser power supply 37 may output a
voltage control signal S32 for controlling the excited state of the
CO.sub.2 gain medium 33 based on the pulse energy control signal
S13 inputted to the laser power supply 37. As a result, the laser
pulse energy outputted from the polarizer 35 toward the
preamplifier PA may be controlled.
[0123] Also, as shown in FIG. 28, a semiconductor laser may be used
as the master oscillator MO. The semiconductor laser may preferably
be a quantum-cascade laser. An output coupling mirror 42 may be
provided at the front side of the master oscillator MO, and a rear
optical module 43 may be provided at the rear side. The output
coupling mirror 42 and the rear optical module 43 may form an
optical resonator with a semiconductor device 41 having an optical
amplification region arranged therebetween. This optical resonator
may be controlled by a semiconductor laser controller C2. The
semiconductor laser controller C2 may output an oscillation
wavelength signal S41 to a longitudinal-mode control actuator 45
through a longitudinal-mode controller 44. This longitudinal-mode
control actuator 45 may control a wavelength of a laser beam
outputted from the optical resonator. Also, the semiconductor laser
controller C2 may output an oscillation pulse shape signal S42 to a
current control actuator 46 based on the trigger signal S11 and the
laser pulse energy control signal S13. This current control
actuator 46 may control a current waveform that is applied to the
semiconductor device 41, and may control a pulse shape of the
pulsed laser beam outputted from the optical resonator and the
timing at which the pulsed laser beam is outputted. This pulsed
laser beam of which the pulse shape and the output timing are
controlled may be inputted to the preamplifier PA. The pulse shape
may include a pulse width and a pulse peak value, and hence by
controlling the pulse shape, the pulse energy can be
controlled.
[0124] It is to be noted that the output coupling mirror 42 may be
a mirror treated with partial reflection mirror coating. The output
coupling mirror 42 may output a laser beam, and may also return
part of the laser beam into the optical resonator for resonant
amplification. The rear optical module 43 may include a collimator
lens and a grating with the Littrow arrangement for selecting a
predetermined wavelength of the laser beam. The laser beam
outputted from the rear side of the semiconductor device 41 is
collimated by the collimator lens, and outputted as a collimated
beam toward the grating, and the laser beam the wavelength of which
is selected by the grating is returned to the semiconductor device
41 through the collimator lens. With this, the desirable single
longitudinal-mode laser beam can be outputted from the output
coupling mirror 42 toward the preamplifier PA.
[0125] Further, in the above-described first modification, the
laser pulse energy is controlled by having the master oscillator MO
being controlled; however, the configuration may be such that the
laser pulse energy inputted to the preamplifier PA may be
controlled in the oscillator 25 but outside the master oscillator
MO. In this case, a laser beam with predetermined laser pulse
energy may be outputted from the master oscillator MO.
[0126] For example, as shown in FIG. 29, the Pockels cell 34 and
the polarizer 35 shown in FIG. 26 may be provided outside the
master oscillator MO. In particular, the Pockels cell 34 and the
polarizer 35 may be provided outside the front-side resonator
mirror 31 and 32 in that order toward the preamplifier PA. The
Pockels cell control power supply 36 may cause the Pockels cell 34
to function as a shutter by controlling the voltage applied to the
Pockels cell 34, and may control the laser pulse energy outputted
from the master oscillator MO by controlling duration and degree of
opening of the shutter.
[0127] Also, as shown in FIG. 30, the Pockels cell control power
supply 36 may apply voltage, which causes the Pockels cell 34 to be
open, for a predetermined period and the voltage applied from the
laser power supply 37 to the CO.sub.2 gain medium 33 may be
controlled, whereby the intensity of the laser beam outputted from
the master oscillator MO may be controlled.
Second Modification
[0128] In the above-described first modification, the configuration
is such that the laser pulse energy inputted to the preamplifier PA
is controlled by controlling the oscillator 25. In contrast, in the
second modification, a regenerative amplifier 50 may be provided
between the oscillator 25 and the preamplifier PA. The driver laser
controller C1 may control the regenerative amplifier 50, and hence
the laser pulse energy of the laser beam inputted to the
preamplifier PA may be controlled. If the regenerative amplifier 50
is used, a pulsed laser beam with a small output such as a laser
beam outputted from a semiconductor laser can efficiently be
amplified in a state in which the pulse shape thereof is
maintained, and be outputted to the preamplifier PA. The pulsed
laser beam outputted from the regenerative amplifier 50 may
efficiently be amplified by the preamplifier PA and the main
amplifier MA.
[0129] The regenerative amplifier 50 may amplify a seed pulsed beam
SA outputted from the oscillator 25, and output the seed pulsed
beam SA to the preamplifier PA. In the regenerative amplifier 50,
for example, as shown in FIG. 31, a Pockels cell 53, a polarizer
58, a CO.sub.2 laser amplification unit EA, a Pockels cell 54, and
a quarter waveplate 57 may be arranged between a pair of resonator
mirrors 51 and 52 in that order from the resonator mirror 51 side.
The seed pulsed beam SA outputted from the oscillator 25 may be
made to enter the regenerative amplifier 50 through the polarizer
58, and the seed pulsed beam SA may be reciprocated between the
resonator mirrors 51 and 52 to be amplified, and outputted as an
amplified pulsed laser beam SB to the preamplifier PA through the
polarizer 58.
[0130] Now, the operation of the regenerative amplifier 50 will be
described with reference to a timing chart shown in FIG. 32. The
pulsed laser beam outputted from the oscillator 25 may be incident
on the polarizer 58 as the seed pulsed beam SA at timing t0, for
example. The S-polarized component of this incident beam, for
example, may be reflected by the polarizer 58 and introduced into a
resonator in the regenerative amplifier 50. The laser beam
introduced into the regenerative amplifier 50 may be amplified as
it passes through an amplification region of the CO.sub.2 laser
amplification unit EA, transmitted through the Pockels cell 54, to
which voltage is not applied, without a phase shift, converted to a
circularly polarized laser beam as it is transmitted through the
quarter waveplate 57, reflected with high reflectivity by the
resonator mirror 52, and converted to a linearly polarized laser
beam that would be incident on the polarizer 58 as the P-polarized
component. This laser beam may further be amplified as it passes
through the amplification region of the CO.sub.2 laser
amplification unit EA. The amplified laser beam may be incident on
the polarizer 58 as a laser beam of the P-polarized component,
transmitted through the polarizer 58, transmitted through the
Pockels cell 53, to which voltage is not applied, without a phase
shift, and reflected with high reflectivity by the resonator mirror
51. The laser beam reflected with high reflectivity may be
transmitted again through the Pockels cell 53 without a phase
shift, transmitted through the polarizer 58, and further amplified
as it passes again through the amplification region of the CO.sub.2
laser amplification unit EA.
[0131] Then, the voltage is applied to the Pockels cell 54 at
timing t1, the phase of the laser beam may change by a quarter
wavelength as it passes through the Pockels cell 54, whereby the
laser beam may be converted to a circularly polarized laser beam.
The circularly polarized laser beam may be transmitted through the
quarter waveplate 57, whereby it is converted to a linearly
polarized laser beam that would be incident on the polarizer 58 as
the S-polarized component. The laser beam reflected by the
resonator mirror 52 may be converted into the circularly polarized
laser beam as it is transmitted again through the quarter waveplate
57. Thereafter, the laser beam may be converted into a linearly
polarized laser beam that would be incident on the polarizer 58 as
the P-polarized component as it is transmitted through the Pockels
cell 54 to which voltage is applied. The laser beam may further be
amplified as it passes through the amplification region of the
CO.sub.2 laser amplification unit EA, transmitted through the
polarizer 58, transmitted through the Pockels cell 53 to which the
voltage is applied without a phase shift, reflected with high
reflectivity by the resonator mirror 51, transmitted again through
the Pockels cell 53 to which the voltage is not applied, and
transmitted through the polarizer 58. In the state in which voltage
is applied to the Pockels cell 54, the laser beam may be amplified
as it is reciprocated between the resonator mirrors 51 and 52.
[0132] The voltage may be applied to the Pockels cell 53 at timing
t2 at which the amplified pulsed laser beam SB is outputted
outside, and the laser beam may be converted into the circularly
polarized laser beam as it is transmitted through the Pockels cell
53 to which the voltage is not applied. The circularly polarized
laser beam may be reflected with high reflectivity by the resonator
mirror 51, and converted into a linearly polarized laser beam which
would be incident on the polarizer 58 as the S-polarized component
as it is transmitted again through the Pockels cell 53 to which the
voltage is applied. The laser beam may be reflected with high
reflectivity by the polarizer 58, and outputted as the amplified
pulsed laser beam SB toward the external preamplifier PA.
[0133] Here, for the Pockels cells 53 and 54 of the regenerative
amplifier 50, ON and OFF of voltage application may be performed by
Pockels cell control power supplies 55 and 56. A regenerative
amplifier controller C3 may control the Pockels cell control power
supplies 55 and as described above based on the laser pulse energy
control signal S13. That is, the laser pulse energy of the
amplified pulsed laser beam SB can be controlled by increasing or
decreasing the period during which voltage is applied to the
Pockels cell 54. It is to be noted that the trigger signal S11 may
be inputted to the semiconductor laser controller C2, and hence
timing at which the seed pulsed beam SA is oscillated may be
controlled.
Third Modification
[0134] In the above-described first modification, the oscillator 25
is controlled. In the second modification, the laser pulse energy
is controlled by controlling the regenerative amplifier 50. In
contrast, in the third modification, the laser pulse energy may be
controlled by controlling at least one of the preamplifier PA and
the main amplifier MA.
[0135] In particular, as shown in FIG. 33, the driver laser
controller C1 may output a laser pulse energy control signal S14 to
an amplifier power supply controller 60 that controls a
preamplifier power supply 61, which is a laser power supply for the
preamplifier PA, and a main amplifier power supply 62, which is a
laser power supply for the main amplifier MA. The amplifier
controller 60 performs the laser pulse energy control by
controlling the excitation intensity of the preamplifier PA and the
main amplifier MA based on the laser pulse energy control signal
S14.
[0136] Also, as shown in FIG. 34, in the case where a pre-pulse
laser 101 is used for irradiating the target 13 with pre-pulsed
laser beam before the target 13 is irradiated with the CO.sub.2
pulsed laser beam L1, the configuration may be such that EUV pulse
energy may be controlled by controlling laser pulse energy of the
laser beam outputted from the pre-pulse laser 101. If the
pre-pulsed laser beam is used, when the target 13 is irradiated
with the CO.sub.2 pulsed laser beam L1, the target 13 may be turned
into plasma more efficiently, whereby the EUV pulsed light can
efficiently be emitted.
[0137] The pre-pulsed laser beam may strike the target 13 via an
off-axis paraboloidal mirror M102. An optical element M121
configured of a partial reflection mirror or a beam splitter may be
provided at the upstream side of the off-axis paraboloidal mirror
M102. The pre-pulsed laser beam may be incident on a pre-pulsed
laser beam detector 121 through the optical element M121 and a
focusing lens R121, and the pre-pulsed laser beam detector 121 may
detect the pulse energy of the pre-pulsed laser beam, and output a
pre-pulsed laser pulse energy detection signal S6 to the pre-pulse
laser 101 and the EUV light source controller C. The EUV light
source controller C may output a control signal S60 to the
pre-pulse laser 101 and control the laser pulse energy.
[0138] It is to be noted that the laser pulse energy of only the
pre-pulse laser 101 may be controlled. Alternatively, the laser
pulse energy of both the pre-pulse laser 101 and the driver laser 1
may be controlled.
[0139] The above-described embodiments and the modifications
thereof are merely examples for embodying this disclosure, and this
disclosure is not limited thereto. Making various modifications
according to the specifications or the like is within the scope of
this disclosure, and it is apparent from the above description that
other various embodiments can be made within the scope of the
disclosure. For example, it is needless to mention that the
modifications indicated for each embodiment may be applied to
another embodiment as well.
* * * * *