U.S. patent application number 13/742276 was filed with the patent office on 2013-05-23 for extreme ultra violet light source apparatus.
This patent application is currently assigned to GIGAPHOTON INC.. The applicant listed for this patent is GIGAPHOTON INC.. Invention is credited to Takeshi ASAYAMA, Hiroshi KOMORI, Masato MORIYA.
Application Number | 20130126762 13/742276 |
Document ID | / |
Family ID | 41132400 |
Filed Date | 2013-05-23 |
United States Patent
Application |
20130126762 |
Kind Code |
A1 |
MORIYA; Masato ; et
al. |
May 23, 2013 |
EXTREME ULTRA VIOLET LIGHT SOURCE APPARATUS
Abstract
An extreme ultra violet light source apparatus in which debris
moving within a chamber are prevented from reducing reflectance or
transmittance of optical elements of an EUV collector mirror, etc,
and extreme ultra violet light can stably be generated in a long
period. The apparatus includes: a target supply unit for supplying
a target to a predetermined position within a chamber; a driver
laser for applying a laser beam to the target to generate first
plasma; a collector mirror provided within the chamber, for
collecting extreme ultra violet light radiated from the first
plasma; a gas supply unit for supplying a gas into the chamber; an
excitation unit for exciting the gas to generate second plasma
around a region where the first plasma is generated; and an exhaust
unit for exhausting the chamber and ejecting debris emitted from
the first plasma to outside of the chamber.
Inventors: |
MORIYA; Masato;
(Hiratsuka-shi, JP) ; KOMORI; Hiroshi;
(Hiratsuka-shi, JP) ; ASAYAMA; Takeshi;
(Hiratsuka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GIGAPHOTON INC.; |
Oyama-shi |
|
JP |
|
|
Assignee: |
GIGAPHOTON INC.
Oyama-shi
JP
|
Family ID: |
41132400 |
Appl. No.: |
13/742276 |
Filed: |
January 15, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12385245 |
Apr 2, 2009 |
|
|
|
13742276 |
|
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Current U.S.
Class: |
250/504R |
Current CPC
Class: |
H05G 2/005 20130101;
G03F 7/70916 20130101; H05G 2/003 20130101; H05G 2/008 20130101;
G03F 7/70033 20130101 |
Class at
Publication: |
250/504.R |
International
Class: |
H05G 2/00 20060101
H05G002/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 7, 2008 |
JP |
2008-099406 |
Claims
1-14. (canceled)
15. An extreme ultraviolet light source apparatus comprising: a
chamber; a target supply unit configured to supply a target
material, which is tin, into the chamber; a gas supply unit
configured to supply a hydrogen gas into the chamber; a CO.sub.2
laser configured to apply a laser beam to the target material
supplied from the target supply unit to generate plasma from which
extreme ultraviolet light is emitted, and excite the hydrogen gas
and an electrically neutral tin both existing in the chamber to
make the hydrogen gas and the tin chemically react with each other
and generate a gaseous product; a collector mirror configured to
collect the extreme ultraviolet light from the plasma, in the
chamber; and an exhaust unit configured to exhaust the hydrogen gas
and the gaseous product from the chamber.
16. The extreme ultraviolet light source apparatus according to
claim 15, wherein the gaseous product is SnH.sub.4.
17. The extreme ultraviolet light source apparatus according to
claim 15, wherein a surface of the collector mirror is coated with
a protective film containing at least one of ruthenium (Ru),
silicon carbide (SiC), carbon (C), silicon dioxide (SiO.sub.2), and
ruthenium oxide (RuO.sub.2).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an extreme ultra violet
(EUV) light source apparatus to be used as a light source of
exposure equipment.
[0003] 2. Description of a Related Art
[0004] Recent years, as semiconductor processes become finer,
photolithography has been making rapid progress to finer
fabrication. In the next generation, microfabrication of 100 nm to
70 nm, further, microfabrication of 50 nm or less will be required.
Accordingly, in order to fulfill the requirement for
microfabrication of 50 nm or less, for example, exposure equipment
is expected to be developed by combining an EUV light source
generating EUV light having a wavelength of about 13 nm and reduced
projection reflective optics.
[0005] As the EUV light source, there are three kinds of light
sources, which include an LPP (laser produced plasma) light source
using plasma generated by applying a laser beam to a target
(hereinafter, also referred to as "LPP type EUV light source
apparatus"), a DPP (discharge produced plasma) light source using
plasma generated by discharge, and an SR (synchrotron radiation)
light source using orbital radiation. Among them, the LPP light
source has advantages that extremely high intensity close to black
body radiation can be obtained because plasma density can be
considerably made larger, that light emission of only the necessary
waveband can be performed by selecting the target material, and
that an extremely large collection solid angle of 2.pi. steradian
can be ensured because it is a point light source having
substantially isotropic angle distribution and there is no
structure surrounding the light source such as electrodes.
Therefore, the LPP light source is considered to be predominant as
a light source for EUV lithography requiring power of more than
several tens of watts.
[0006] Here, a principle of generating EUV light in the LPP type
EUV light source apparatus will be explained. When a laser beam is
applied to a target material supplied into a vacuum chamber, the
target material is excited and plasmarized. Various wavelength
components including EUV light are radiated from the plasma. Then,
the EUV light is reflected and collected by using an EUV collector
mirror that selectively reflects a desired wavelength component
(e.g., a component having a wavelength of 13.5 nm), and outputted
to an exposure unit.
[0007] FIG. 5 shows an example of the conventional EUV light source
apparatus. As shown in FIG. 5, the EUV light source apparatus 61
includes a vacuum chamber 62 in which EUV light is generated, a
target supply unit 64 for supplying a target 63 to a predetermined
position within the vacuum chamber 62, a driver laser 66 for
generating an excitation laser beam 65 to be applied to the target
63, a laser beam focusing optics 67 for focusing the excitation
laser beam 65 generated by the driver laser 66, and an EUV
collector mirror 70 for collecting and outputting EUV light 69
emitted from plasma 68 generated when the excitation laser beam 65
is applied to the target 63, a magnetic field generating unit
including a magnetic field coil 77 for generating a magnetic field
that confines ionized debris included in debris generated from the
plasma 68, and an evacuating pump 80 for evacuating the vacuum
chamber 62.
[0008] In the LPP type EUV light source apparatus, there is a
problem that the debris emitted from the plasma 68 attach to the
surfaces of the optical elements of the EUV collector mirror 70,
the laser beam focusing optics 67, a laser beam entrance window 74,
an SPF (spectral purity filter) (not shown), an entrance window of
an optical sensor (not shown), and so on, and reduce the
reflectance or transmittance of EUV light, and thereby, reduce the
output of EUV light and/or sensitivity of the sensor. In order to
solve the problem, a technology of confining and ejecting the
ionized debris generated from plasma by using a magnetic field to
the outside of the vacuum chamber is known (Japanese Patent
Application Publication JP-P2005-197456A). The debris refers to
flying materials from plasma including neutral particles and ions
and waste target materials.
[0009] For example, when the tin metal target 63 is excited by the
excitation laser beam 65, most of tin becomes plasma 68 including
polyvalent positive ions and electrons. When a magnetic field is
applied to the region including the plasma 68 by the magnetic field
coil 77, the positive tin ions are constrained by the magnetic
field and moved in a direction along lines of magnetic force.
Thereby, the amount of the positive tin ions attaching to the
optical elements of the EUV collector mirror 70, the laser beam
focusing optics 67, the laser beam entrance window 74, the SPF (not
shown), the entrance window of the optical sensor (not shown), and
so on is reduced, and the positive tin ions are efficiently ejected
to the outside of the vacuum chamber 62 by the evacuating pump
80.
[0010] JP-P2005-197456A discloses protection of the EUV collector
mirror by trapping the ionized debris included in the debris
generated from the plasma by using the magnetic field within the
vacuum chamber of the EUV light source apparatus.
[0011] Further, Japanese Patent Application Publication
JP-P2006-210157A discloses generation of EUV light by cooling and
pressurizing tin hydride (SnH.sub.4) to release the tin hydride in
droplets or liquid jet and plasmarizing the tin hydride by using a
laser beam.
[0012] As explained above, in the conventional LPP type EUV light
source apparatus, since the ionized debris are constrained by the
magnetic field and moved in the direction of lines of magnetic
force and efficiently ejected by the evacuating pump, the ionized
debris can be prevented from attaching to the optical elements
within the chamber to deteriorate the performance of the EUV light
source apparatus.
[0013] However, part of the generated positive ions recombine with
electrons and become neutral particles, move without being
constrained by the magnetic field, and attach to the surfaces of
the optical elements within the chamber to reduce the reflectance
and transmittance of EUV light, and thereby, reduce the performance
of the EUV light source apparatus. Especially, polyvalent positive
ions of tin or the like easily recombine with electrons and reduce
the performance of the EUV light source apparatus.
[0014] Further, it is difficult to ionize all target materials by,
the excitation laser, and part of the target materials become
neutral debris, move without being constrained by the magnetic
field, and attach to the optical elements within the chamber to
reduce the reflectance or transmittance of EUV light, and thereby,
reduce the performance of the EUV light source apparatus.
SUMMARY OF THE INVENTION
[0015] The present invention has been achieved in view of the
above-mentioned circumstances. A purpose of the present invention
is to provide an extreme ultra violet light source apparatus in
which debris moving within a chamber are prevented from reducing
reflectance or transmittance of optical elements of an EUV
collector mirror and so on, and extreme ultra violet light can
stably be generated in a long period.
[0016] In order to accomplish the above-mentioned purpose, an
extreme ultra violet light source apparatus according to one aspect
of the present invention is an apparatus for generating extreme
ultra violet light by applying a laser beam to a target, including:
a chamber in which extreme ultra violet light is generated; a
target supply unit for supplying a target to a predetermined
position within the chamber; a driver laser for applying a laser
beam to the target supplied by the target supply unit to generate
first plasma; a collector mirror provided within the chamber, for
collecting the extreme ultra violet light radiated from the first
plasma to output the extreme ultra violet light; a gas supply unit
for supplying a gas into the chamber; an excitation unit for
exciting the gas supplied by the gas supply unit to generate second
plasma around a region where the first plasma is generated; and an
exhaust unit for exhausting the chamber and ejecting debris emitted
from the first plasma to outside of the chamber.
[0017] According to the one aspect of the present invention, the
gas is supplied into the chamber of the ultra violet light source
apparatus and excited to generate the second plasma around the
region where the first plasma, and the debris emitted from the
first plasma are gasified and ejected to the outside of the
chamber, and therefore, the debris are prevented from attaching to
the optical elements within the chamber. Thereby, the debris moving
within the chamber are prevented from reducing reflectance or
transmittance of the optical elements of the EUV collector mirror
and so on, and extreme ultra violet light can stably be generated
in a long period.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows an internal structure of an EUV light source
apparatus according to the first embodiment of the present
invention;
[0019] FIG. 2 shows an internal structure of an EUV light source
apparatus according to the second embodiment of the present
invention;
[0020] FIG. 3 shows an internal structure of an EUV light source
apparatus according to the third embodiment of the present
invention;
[0021] FIG. 4 shows an internal structure of an EUV light source
apparatus according to the fourth embodiment of the present
invention; and
[0022] FIG. 5 shows an internal structure of a conventional EUV
light source apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] Hereinafter, preferred embodiments of the present invention
will be explained in detail by referring to the drawings. The same
reference characters are assigned to the same component elements
and the description thereof will be omitted.
[0024] FIG. 1 is a schematic diagram showing an extreme ultra
violet (EUV) light source apparatus according to the first
embodiment of the present invention. The EUV light source apparatus
employs a laser produced plasma (LPP) type and is used as a light
source of exposure equipment.
[0025] As shown in FIG. 1, the EUV light source apparatus 1
includes a vacuum chamber 2 in which EUV light is generated, a
target supply unit 4 for supplying a target 3 to a predetermined
position within the vacuum chamber 2, a driver laser 6 for
generating an excitation laser beam 5 to be applied to the target
3, a laser beam focusing optics 7 for focusing the excitation laser
beam 5 generated by the driver laser 6, an EUV collector mirror 10
for collecting and outputting EUV light 9 emitted from plasma 8
(hereinafter, also referred to as "target plasma") generated when
the excitation laser beam 5 is applied to the target 3, a magnetic
field generating unit including a magnetic field coil 17 for
generating a magnetic field that confines ionized debris included
in debris generated from the plasma 8, and an evacuating pump 20
for evacuating the vacuum chamber 2.
[0026] Further, in order to generate plasma 21 (hereinafter, also
referred to as "secondary reaction plasma") for ionizing
electrically neutral debris of the debris generated from the plasma
8, the EUV light source apparatus 1 includes a gas supply unit 23
for supplying a gas for secondary reaction plasma, and an RF (radio
frequency) antenna 25 as an RF excitation unit for exciting the gas
for secondary reaction plasma to generate the secondary reaction
plasma 21. In the embodiment, hydrogen chloride (HCl) gas is used
as the gas for secondary reaction plasma, and a coil is used as the
RF antenna 25.
[0027] In the embodiment, the target supply unit 4 heats and melts
solid tin (Sn), and supplies the tin target 3 in a form of a solid
state or liquid droplets into the vacuum chamber 2. As the drive
laser 6, a carbon dioxide (CO.sub.2) pulse laser that can generate
light having a relatively long wavelength is used. For example, the
output of the carbon dioxide pulse laser is 20 kW, the pulse
repetition frequency is 100 kHz, and the pulse width is 20 ns.
However, in the present invention, the kinds of target materials
and laser light sources are not limited to these and various kinds
of target materials and laser light sources may be used.
[0028] The excitation laser beam 5 is introduced into the vacuum
chamber 2 through an entrance window 14 provided in the vacuum
chamber 2. The laser beam focusing optics 7 includes at least one
lens and/or at least one mirror. The laser beam focusing optics 7
may be located inside the vacuum chamber 2 as shown in FIG. 1, or
outside the vacuum chamber 2.
[0029] The EUV collector mirror 10 is a collective optics for
collecting light by selectively reflecting a predetermined
wavelength component (e.g., EUV light near 13.5 nm) of the various
wavelength components radiated from the target plasma 8. The EUV
collector mirror 10 has a concave reflection surface, and a
multilayer film of molybdenum (Mo) and silicon (Si) for selectively
reflecting EUV light having a wavelength near 13.5 nm is formed on
the reflection surface and the reflectance of EUV light of about
60% is obtained.
[0030] The EUV light 9 radiated from the target plasma 8 is
reflected by the EUV collector mirror 10 and guided out to an
exposure unit through an intermediate focusing point (IF). An SPF
(spectral purity filter) may be provided at the upstream or
downstream of the intermediate focusing point (IF). The SPF removes
unwanted light (light having longer wavelengths than that of EUV
light, e.g., ultraviolet light, visible light, infrared light, and
so on) of the light radiated from the target plasma 8 and transmits
only desired light, for example, the EUV light having a wavelength
of 13.5 nm. Further, a gate valve 19 for separating the exposure
unit and the EUV light source apparatus 1 may be provided for
maintenance. In FIG. 1, the EUV light generated from the target
plasma 8 is reflected leftward by the EUV collector mirror 10,
focused on the EUV intermediate focusing point (IF), and then,
outputted to the equipment unit.
[0031] The tin target 3 supplied from the target supply unit 4 is
excited by the excitation laser beam 5, and part of the target
becomes the target plasma 8. The target plasma 8 contains
electrons, polyvalent positive tin ions (Sn.sup.+), and tin
radicals (Sn*). Among them, the positive tin ions (Sn.sup.+) are
subjected to Lorentz force (F=qv.times.B) when the magnetic field
is provided, and move in a direction of lines of magnetic force
while twining around the lines of magnetic force. Here, "q" is
charge of a charged particle, "v" is a velocity of the charged
particle, and "B" is magnetic flux density.
[0032] Thereby, the movement of ions in the direction orthogonal to
the direction of the lines of magnetic force is restricted and the
ions are confined by the magnetic field. Since the positive tin
ions (Sn.sup.+) are confined by the magnetic field, in the case
where optical element such as the EUV collector mirror 10, the
entrance window 14, the SPF (not shown), an entrance window of an
optical sensor (not shown) is provided in the direction orthogonal
to the direction of the lines of magnetic force, the amount of the
positive tin ions (Sn.sup.+) attaching to the surfaces of the
optical element can be reduced.
[0033] However, the generated positive tin ions (Sn.sup.+) easily
recombine with electrons, and part of the positive tin ions
(Sn.sup.+) may recombine with electrons and be neutralized, and
attach to the optical elements as neutral tin debris (Sn) without
being constrained by the magnetic field. Further, it is difficult
to ionize all target materials by the target excitation laser, and
part of the target materials may attach to the optical elements as
neutral particles without being constrained by the magnetic field.
Furthermore, the tin radicals (Sn*) generated from the plasma are
also neutral, and may attach to the optical elements without being
constrained by the magnetic field.
[0034] Accordingly, in the embodiment, the hydrogen chloride (HCl)
gas is supplied near the target within the vacuum chamber 2 by the
gas supply unit 23, and a radio-frequency electric field (e.g.,
13.56 MHz) is applied to the hydrogen chloride gas by the RF
antenna 25. By exciting the neutral tin (Sn) tin radicals (Sn*),
and the hydrogen chloride (HCl) gas around the region where the
plasma of the tin target material (target plasma 8) is generated,
the secondary reaction plasma (RF plasma) 21 is generated.
[0035] In the secondary reaction plasma 21, the neutral tin (Sn)
and/or tin radicals (Sn*), that have not been excited until being
ionized by the excitation laser beam 5, are ionized or the neutral
tin (Sn), that has been excited to be the positive tin ions
(Sn.sup.+) by the excitation laser beam 5 and then recombined with
electrons to be neutralized, is ionized. The positive tin ions
(Sn.sup.+) ionized in the secondary reaction plasma 21 are
constrained by the magnetic field, and ejected by the evacuating
pump 20 provided on extended lines of the lines of magnetic
force.
[0036] Further, in the secondary reaction plasma 21, gaseous
products of tin hydride (SnH.sub.4), tin chloride (SnCl.sub.4), and
so on are generated by chemical reaction, and those gaseous
products are also ejected by the evacuating pump 20. Thereby, the
attachment of debris of neutral tin (Sn) and so on to the optical
elements, which attachment was impossible to be prevented only by
the conventional magnetic confinement system, can be effectively
reduced. Further, the same effect may be obtained by exciting
helicon wave plasma by using a radio-frequency electric field and a
magnetic field so as to generate the secondary reaction plasma
21.
[0037] In order to prevent the attachment of debris of tin (Sn)
etc. to the optical elements, it is effective that the ions
constrained by the magnetic field are efficiently attracted to the
evacuating pump 20 and efficiently ejected by the evacuating pump
20. For the purpose, when a conductive mesh 27 is provided near the
inlet of the evacuating pump 20, a bias is applied to the mesh 27
by using an RF power supply 29, and current is blocked by a
blocking capacitor 28, a cathode fall (sheath) occurs on the
surface of the mesh 27. Thereby, the mesh 27 is negatively charged
and the positive ions such as the positive tin ions (Sn.sup.+) are
attracted through the mesh 27 to the evacuating pump 20 and
efficiently ejected by the evacuating pump 20. Alternatively, by
providing the magnetic coil 17 configured such that the magnetic
flux density at the evacuating pump 20 side is lower, the ions
constrained by the Lorentz force gradually move to the evacuating
pump 20 side and are efficiently ejected by the evacuating pump
20.
[0038] As the gas used for generation of the secondary reaction
plasma 21, argon gas (Ar), nitrogen gas (N.sub.2) hydrogen gas
(H.sub.2), halogen gas (F.sub.2, Cl.sub.2, Br.sub.2, I.sub.2),
halogenated hydrogen gas (HF, HCl, HBr, HI), or a mixed gas
containing at least two of them is preferable. Especially, the
hydrogen gas (H.sub.2), chlorine gas (Cl.sub.2), bromine gas
(Br.sub.2), hydrogen chloride gas (HCl), and hydrogen bromide gas
(HBr) react with tin (Sn) in the secondary reaction plasma 21, and
generate reaction products at low vapor pressure such as tin
hydride (SnH.sub.4) tin chloride (SnCl.sub.4), tin bromide
(SnBr.sub.4), and so on, and those reaction products are gasified
in the vacuum chamber 2. The gasified reaction products are easily
ejected from the vacuum chamber 2 by the evacuating pump 20.
[0039] Here, by coating the surface of the EUV collector mirror 10
with ruthenium (Ru), silicon carbide (SiC), carbon (C), silicon
dioxide (SiO.sub.2), or ruthenium oxide (RuO.sub.2) as a protective
coating film 12, the corrosion of the surface of the EUV collector
mirror 10 by the gas used for generation of the secondary reaction
plasma 21, especially, the halogen gas or halogenated hydrogen gas
can be prevented without significant reduction of the reflectance
of EUV light. In this case, if the gas used for generation of the
secondary reaction plasma 21 is supplied around the EUV collector
mirror 10, the surface of the EUV collector mirror 10 is hardly
corroded by the gas.
[0040] Next, the second embodiment of the present invention will be
explained.
[0041] FIG. 2 shows an internal structure of an EUV light source
apparatus according to the second embodiment of the present
invention. As shown in FIG. 2, the EUV light source apparatus 31
includes the same configuration as that of the EUV light source
apparatus according to the first embodiment, however, excites a
secondary reaction plasma 32 by using a magnetic field and
microwaves in place of the radio-frequency electric field. The
magnetic field is generated by the magnetic field coil 17, for
example, and the microwaves are generated by a microwave generating
unit (excitation unit) 35 for exciting a gas by generating
microwaves.
[0042] Here, the case of using hydrogen bromide gas (HBr) as the
secondary reaction plasma 32 will be explained as an example. By
the influence of the magnetic field and the microwaves, the
electrons in the hydrogen bromide gas molecules are accelerated by
cyclotron resonance, the accelerated electrons collide with the
gas, and the gas is excited. Thereby, electron cyclotron resonance
(ECR) plasma is generated. For example, when the intensity of the
magnetic field is 0.5 T, the ECR plasma is efficiently generated by
the microwaves having a frequency of about 14 GHz. The same effect
as that in the first embodiment of the present invention is also
obtained in the EUV light source apparatus according to the second
embodiment of the present invention.
[0043] Next, the third embodiment of the present invention will be
explained.
[0044] FIG. 3 shows an internal structure of an EUV light source
apparatus according to the third embodiment of the present
invention. As shown in FIG. 3, the EUV light source apparatus 41
includes a target supply unit 44 that can liquefy (or freeze and
solidify) tin hydride (SnH.sub.4) or halogenated tin (SnCl.sub.4,
SnBr.sub.4) as disclosed in JP-P2006-210157A, for example. Further,
the EUV light source apparatus shown in FIG. 3 may include a
replenishment gas supply unit 46.
[0045] As below, the case where the target supply unit 44 supplies
the liquefied (or frozen and solidified) tin chloride (SnCl.sub.4)
as a target will be explained as an example. The liquefied (or
frozen and solidified) tin chloride (SnCl.sub.4) supplied from the
target supply unit 44 is excited by the excitation laser beam 5,
and thereby, the target plasma 8 for generation of EUV light and
the secondary reaction plasma 21 are generated at the same
time.
[0046] However, in practice, only by the excitation with the
excitation laser beam 5, it is difficult to continuously generate
the secondary reaction plasma 21 because the energy necessary for
continuous excitation of the secondary reaction plasma 21 becomes
insufficient. Accordingly, by providing the RF (radio frequency)
excitation unit used in the first embodiment or the microwave
generating unit used in the second embodiment as well, the
secondary reaction plasma 21 can stably be generated.
[0047] In the secondary reaction plasma 21, the neutral tin (Sn)
and/or tin radicals (Sn*), that have not been excited until being
ionized by the excitation laser beam 5, are ionized or the neutral
tin (Sn), that has been excited to be the positive tin ions
(Sn.sup.+) by the excitation laser beam 5 and then recombined with
electrons to be neutralized, is ionized. The positive tin ions
(Sn.sup.+) ionized in the secondary reaction plasma 21 are
constrained by the magnetic field, and ejected by the evacuating
pump 20 provided on extended lines of the lines of magnetic force.
Further, in the secondary reaction plasma 21, gaseous products of
tin chloride (SnCl.sub.4) and so on are generated by chemical
reaction, and those gaseous products are also ejected by the
evacuating pump 20. Thereby, the attachment of debris of neutral
tin (Sn) to the optical elements, which attachment was impossible
to be prevented only by the conventional magnetic confinement
system, can be effectively reduced.
[0048] Furthermore, in order to continuously generate the secondary
reaction plasma 21, the EUV light source apparatus 41 may include
the replenishment gas supply unit 46, and the replenishment gas
supply unit 46 may supply chlorine gas (Cl.sub.2), hydrogen
chloride gas (HCl), and/or hydrogen gas (H.sub.2) as a
replenishment gas for secondary reaction plasma into the vacuum
chamber 2.
[0049] In addition, a conductive mesh 27 may be provided near the
inlet of the evacuating pump 20 in the EUV light source apparatus
41. A direct-current high voltage is applied as a bias to the
conductive mesh 27 by using direct-current high voltage source 48,
for example, and thereby, the conductive mesh 27 is negatively
charged and the positive ions such as the positive tin ions
(Sn.sup.+) constrained by the magnetic field are attracted to the
inlet of the evacuating pump 20 and efficiently ejected from the
evacuating pump 20.
[0050] In the EUV light source apparatuses according to the first
to third embodiments of the present invention, the case where the
ion confinement effect by the magnetic field, the ionization
promotion effect by the secondary reaction plasma, and the
generation promotion effect of gaseous reaction products are
utilized in combination has been explained. However, in the EUV
light source apparatuses according to the first to third
embodiments of the present invention, without providing the
magnetic field generating unit, only with the secondary reaction
plasma, the reaction products having a low vapor pressure to be
gasified within the vacuum chamber such as tin hydride (SnH.sub.4),
tin chloride (SnCl.sub.4), tin bromide (SnBr.sub.4), and so on can
be generated, and the effect that the gasified reaction products
are ejected to the outside of the vacuum chamber 2 without
attaching to the optical elements within the vacuum chamber 2 is
obtained.
[0051] Next, the fourth embodiment of the present invention will be
explained.
[0052] FIG. 4 shows an internal structure of an EUV light source
apparatus according to the fourth embodiment of the present
invention. As shown in FIG. 4, the EUV light source apparatus 51
includes a charged particle flow generating unit 53 for flowing a
charged particle flow 52 in a curtain form along lines of magnetic
force of a magnetic field that confines charged particles contained
in debris.
[0053] For example, the charged particle flow generating unit 53
generates RF (radio frequency) excitation plasma by exciting a gas
with a radio-frequency electric field, or generates ECR (electron
cyclotron resonance) wave excitation plasma by exciting a gas with
a magnetic field and microwaves, or generates HWP (helicon wave
plasma) by applying a radio-frequency electric field and a magnetic
field to a gas. The charged particle flow generating unit 53
extracts ions from the plasma and generates an ion flow along the
lines of magnetic force.
[0054] As the gas used in the charged particle flow generating unit
53, argon gas (Ar), nitrogen gas (N.sub.2), hydrogen gas (H.sub.2),
halogen gas (F.sub.2, Cl.sub.2, Br.sub.2, I.sub.2), halogenated
hydrogen gas (HF, HCl, HBr, HI), or a mixed gas containing at least
two of them is preferable.
[0055] As below, the case of using an ion source unit (ion gun) for
generating chlorine (Cl.sup.+) ions as the charged particle flow
generating unit 53 will be explained. The curtain flow of the
chlorine ions generated by the charged particle flow generating
unit 53 flows between the target plasma 8 and the EUV collector
mirror 10 as the charged particle flow. The neutral tin debris
emitted from the excited target plasma 8 are trapped by the ion
curtain flow.
[0056] In the ion curtain flow, the neutral tin (Sn) and/or tin
radicals (Sn*) are ionized by charge exchange with chlorine ions,
or the neutral tin (Sn), that has been excited to be the positive
tin ions (Sn.sup.+) and then recombined with electrons to be
neutralized, are ionized by charge exchange with chlorine ions.
Thus ionized positive tin ions (Sn.sup.+) are constrained by the
magnetic field, and ejected by the evacuating pump 20 provided on
extended lines of the lines of magnetic force. Further, in the ion
curtain flow, the gaseous products of tin chloride (SnCl.sub.4) and
so on are generated as chemical reaction products of the neutral
tin debris emitted from the excited target plasma 8 and the
chlorine ions, and those gaseous products are also ejected by the
evacuating pump 20.
[0057] Alternatively, a plasma gun may be used as the charged
particle flow generating unit 53 and generate a plasma flow such
that the generated plasma flow may be introduced as the charged
particle flow 52 into the vacuum chamber 2. Further, the particles
generated by recombination of the charged particle flow 52 within
the vacuum chamber 2 may be ionized again by application of
radio-frequency or microwaves. Furthermore, the replenishment gas
for generation of secondary reaction plasma may be introduced into
the vacuum chamber 2 by the replenishment gas supply unit 46, the
secondary reaction plasma is generated by application of
radio-frequency or microwaves, and thereby, the effect of charged
particle flow 52 generated by the charged particle flow generating
unit 53 and the effect of the secondary reaction plasma generated
by the radio-frequency or microwaves may be used in
combination.
* * * * *