JP2002094160A - F2 laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molecular fluorine (F2) laser wherein one of the plural emission lines around 157 nm is efficiently selected. SOLUTION: This molecular fluorine (F2) laser is provided wherein a gas mixture comprises molecular fluorine for generating a spectral emission including two or three closely spaced emission lines around 157 nm. An etalon provides emission line selection such that the output beam only includes one of these emission lines. The etalon also serves to outcouple the beam and/or narrow the selected emission line. Alternatively, a prism provides the emission line selection and the etalon narrows the selected emission line. The etalon may be a resonator reflector which also selects an emission line while another element outcouples the beam. The etalon plates comprise a material that is substantially transparent at 157 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to molecular fluorine (F ₂ ).
It relates laser, in particular, with improved efficiency, to F ₂ laser having a line narrowing of emission lines and the selected emission lines selected.

[0002]

BACKGROUND OF THE INVENTION Semiconductor manufacturers are currently using deep ultraviolet (DUV) lithography tools based on the KrF excimer laser system operating at about 248 nm, with next generation ArF operating at about 193 nm. The excimer laser system continues.
Vacuum UV (VUV) lithography is about 15
It can be used _{F 2} laser operating at 7 nm.

[0003] The release of the _{F 2} laser about λ ₁ = 157.6
At least two characteristic lines of 29 nm and λ ₂ = 157.523 nm are included.
Each emission line has a natural line width (natu) of about 15 pm (.015 nm).
ral linewidth). The ratio of the intensity between the two bright lines is | (λ ₁ ) / | (λ ₂ ) = 7. VNIshenko,
SAKochubel, and AMRazher, Sov. Journ. QE-16, 5
(1986). 1, _{F 2} laser spontaneous emission spectrum (spontaneous emission spectrum)
2 illustrates two closely spaced peaks described above.

[0004] With the advent of integrated circuit device technology in the submicron regime, fine lithography technology is required.
In KrF and ArF excimer laser systems, the narrow (> 100 pm) spontaneous emission spectrum requires line narrowing and tuning. The narrowing of the emission line width is most commonly achieved through the use of a wavelength selector consisting of one or more prisms and diffraction gratings (Littrow configuration).
nfiguration)). However, when the F ₂ laser operating at a wavelength of about 157 nm, the use of reflection type diffraction grating is its reflectivity is low at this wavelength is sometimes unsatisfactory because the oscillation threshold is high. In this regard, the two applicants of the present application have proposed a master oscillator-power amplifier design.
A tor-power amplifier design has been proposed (see US patent application Ser. No. 09 / 599,130, assigned to the same assignee as the present application and incorporated herein by reference), for example, each preferably The use of a diffraction grating and / or etalon in combination with a beam expander to improve the power of the output beam and a very narrow linewidth (<1 pm)
Is possible. F ₂ laser tunability (tunability) are shown using the laser resonator inside the prism. M.Kakehata, E.Hashimoto, F.Kannar
i, M.Obara, Keio University Minutes (U.Keio Proc.) CLEO
-90, 106 (1990).

[0005] F ₂ laser is also characterized by relatively the high cavity losses due to absorption and scattering of the gas and all of the optical elements, oxygen and water vapor which exhibit strong absorptive particularly about 157 nm. Short wavelength (157 nm) has become a cause of high absorption and scattering losses of the _{F 2} laser, whereas 24
KrF excimer lasers operating at 8 nm do not experience such losses. Therefore, it is recognized that it is advisable in the present invention to take measures to optimize the resonator efficiency. In addition, the output beam characteristics are more susceptible to temperature-induced changes when manufacturing smaller structures by lithography at 157 nm than for lithography at longer wavelengths such as 248 nm.

[0006]

Therefore, about 157 nm
One of the plurality of discharge emission line (emission line) of it is possible to provide an F ₂ laser is effectively selected is an object of the present invention.

[0007] To provide the F ₂ laser with an effective means for narrow linewidth selected bright line described above is yet another object of the present invention.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a
About 157 nm when used in a graphics system
One of the plurality of emission lines of the output emission spectrum, eg, λ
₁F (see above) is selected₂Provide a laser. Book
The invention also relates to the narrowing of the selected bright line.
g) and provide the means for doing so. Learn more
In other words, the present invention ₂Multiple brightness of about 157nm of laser
Use the first etalon to select one of the lines, which is
In addition, the above-mentioned selected bright line also serves to narrow the line width.
Also, the first etalon performs bright line selection and the second
Another optical element, such as an etalon,
The line width may be reduced. Alternatively, a second eta
Ron, prism, grating or birefringent plate (bire
Another element, such as a fringent plate, selects the emission line and
1 etalon narrows this selected emission line
There is also. Also, a first etalon, a second etalon,
Rhythm (s), birefringent plate or diffraction
A second optical element such as a grating is used in combination
And the primary emission line (ie, λ₁) And narrow the line width
Sometimes. The first and / or second etalon is resonant
With a reflector reflector component
Used in reflection mode, or a laser system
Used in transmission mode placed between the resonant reflectors of the
Is also good.

In a preferred arrangement, a transmissive etalon (transm
The issive etalon is located after the prism beam expander in the laser cavity. Highly reflective (HR)
ctive) A resonant reflector follows the etalon. Alternatively, the etalon may function as an HR resonant reflector instead. Also, the prism beam expander and etalon may be on the outcoupling side of the laser chamber, where the etalon is transmissive and has a partially reflecting outcoupling mirror.
rror) or the etalon is an output coupler (outcou
pler). Resonant reflector 1
For example, those that are also used to outcouple the beam may be used to seal the laser chamber as windows on the chamber, thereby providing a more efficient laser resonator. You. The line narrowing unit including the etalon and the prism beam expander is preferably a module purged with an inert gas substantially free of substances that absorb radiation of about 157 nm.
ed module).

If two etalons are used, preferably one etalon is used for line selection and the other etalon is used to narrow the selected line, or Both are used together for line selection and line narrowing of the selected line. Also, one of the etalons may be used for output coupling or as a high reflection resonant reflector, and one may be used for output coupling, as if configured for use in reflection mode. May be used as a high reflection resonant reflector, or one or both may be used in a transmission mode.

The pressure and composition of the gas mixture and its concentration are selected to improve the operation of the laser, the gas mixture preferably using neon as the sole buffer gas or a second gas. Including the use of neon as a buffer gas in combination with helium as a buffer gas, having a total pressure of less than 5 bar and a fluorine concentration in the range of 0.05% to 0.20%.
Optical interface in the cavity,
That is, the number of optical elements is reduced, and the materials and other properties that make up the optical elements and the laser gas are selected to provide improved output beam characteristics.

The etalon plate is preferably Ca
_{F 2, MgF 2, LiF 2} , BaF 2, SrF 2, such quartz and fluorine doped silica (fluorine doped quartz), comprises a material having a sufficient transmittance in 157 nm.
Etalon plates are available from invar®, zerodur, ultra low expansion glass (Ultra
one, two, or preferably three, including materials having a low coefficient of thermal expansion, such as lowexpansion glass) or quartz.
Separated by two spacers. A gas such as helium, another inert gas such as krypton, neon, argon or nitrogen, or a gas that generally does not strongly absorb radiation at 157 nm, or a solid such as those mentioned above for the plates may be interposed between the etalon plates. The gap is filled or the gap is evacuated. Etalon is tuned piezoelectrically (piezo-ellectrically tune)
d) or rotationally tune
d) or may be pressure tuned.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Priority) The present application is related to US Provisional Patent Application No. 60 / 212,18, filed on June 16, 2000.
Claim the benefit of priority 3

[0014] (Detailed Description of the Preferred Embodiment) FIG. 2 (a) and 2 (b) shows the first and second preferred embodiment of the F ₂ laser resonator according to the present invention. As will be appreciated, the entire F ₂ laser system in order to provide an output beam having a high energy stability and high wavelength stability and bandwidth stability, FIG. 2 (a) ~ FIG 2 (b) In addition to the components shown in the above, other components are also included. For example, a suitable F
_{The two-} laser system includes a power supply for applying a voltage to the laser gas filling the discharge chamber 2 and a solid-state pulser module.

Further, a gas processing and supply module is included for controlling the composition of the gas in the laser chamber 2. Additionally, a diagnostic module is included to monitor the energy of the laser pulse or the energy dose or moving average of the energy of the laser pulse and to monitor the wavelength and / or bandwidth of the beam. The diagnostic module is used to monitor a parameter indicative of the concentration of molecular fluorine in the laser chamber, so that the processor, together with the gas processing module, provides feedback to maintain the desired gas mixture composition.
arrangement).

The processor also determines if the selected voltage is at the primary laser electrodes 3a and 3b and at the preionization electrode.
It is also used to control the power supply as applied to an ion electrode (not shown). The optics control module adjusts the optics of the laser resonator for wavelength and / or bandwidth tuning, for example, in a feedback device having a processor and a diagnostic module.
The processor also preferably has an imaging system
em) interface unit and / or communicate with the stepper / scanner module control computer (s).

[0017] By the above, the following references, when disclosing the preferred or alternative features of the whole F ₂ laser system described in this application, an alternative embodiment of elements or features in preferred resonator Example And incorporated herein by reference.

US patent application Ser. No. 09 / 317,527,
No. 09 / 343,333, No. 09 / 453,670
No., 09 / 447,882, 09 / 317,69
No. 5, No. 09 / 574,921, No. 09 / 559,1
No. 30, No. 60/122, No. 145, No. 60/140,
No.531, No.60 / 140,530, No.60 / 16
No. 2,735, No. 60 / 166,952, No. 60/1
No. 71,172, No. 09 / 453,670, No. 60 /
No. 184,705, No. 60 / 128,227, No. 60
No./141,678, No. 60 / 173,993, No. 6
No. 0 / 166,967, No. 60 / 172,674, No. 60 / 162,845, No. 60 / 160,182,
No. 60 / 127,237, No. 09 / 535,276
No. 09 / 247,887, No. 60 / 181,15
No. 6, No. 60 / 149,392, No. 60 / 198,0
No. 58, No. 09/390, 146, No. 09/131,
No. 580, No. 09 / 432,348, No. 60/20
No. 4,095, No. 09 / 172,805, No. 60/1
No. 72,749, No. 60 / 166,952, No. 60 /
No. 178,620, No. 09 / 416,344, No. 60
/ 186,003, 60 / 158,808, 0
No. 9 / 484,818, No. 09 / 317,526, No. 60 / 124,785, No. 09 / 418,052,
No. 09 / 379,034, No. 60 / 171,717
No., No. 60 / 159,525, No. 09 / 513,02
No. 5, No. 60 / 124,785, No. 60/160, 1
No. 26, No. 09 / 418,052, and No. 60/18
No. 6,096, and US Pat. No. 6,005,880,
Nos. 6,014,206, 4,393,405, 4,977,573, 4,905,243, 5,729,565, 4,860,300, and 6th Nos. 5,020,723; 5,396,514, each of which is assigned to the same assignee as the present invention, and U.S. Patent Nos. 5,901,163, 5,978,40.
No. 6, No. 6,014,398, No. 6,028,880
No. 5,559,584, No. 5,221,823
No. 5,763,855, No. 5,811,753
No. 4,616,908, 4,691,322
No. 5,535,233, No. 5,557,629
No. 5,337,330, 5,818,865
No. 5,991,324, No. 5,982,800
No. 5,982,795, No. 5,940,421
No. 5,914,974, No. 5,949,806
No. 5,936,988, No. 6,028,872
No. 5,729,562, 5,978,391
No. 5,450,207, No. 4,926,428
No. 5,748,346, 5,025,445
No. 5,978,394, and references cited in "Priority" or "Prior Art" of this application or other references mentioned in the detailed description below.

A general description of line narrowing optics used in the preferred embodiment, or alternatives and / or variations of its elements or features, will now be given. Line narrowing optics are provided on either side of the discharge chamber 2 and include, for example, one or more beam expanders, one or more etalons, one diffraction grating, and / or a birefringent plate. It is used with refractive or catadioptric (catadioptric) optical lithography imaging system or an F ₂ laser, which is line narrowed as used with total reflection imaging system. Line-narrowing packa
ge) may include a beam expander and one or more etalons, followed by an HR mirror as a resonant reflector.

Blocking stray light of the resonator,
1 to match and / or reduce divergence
One or more apertures may be included in the resonator. As mentioned above, the line narrowing optics is the output coupling side of the laser chamber 2.
g side) (Nos. 60 / 166,277, 60 / 173,993, each assigned to the same assignee as the present application and incorporated herein by reference).
No. 60 / 166,967), including or in addition to output coupling elements.

[0021] The beam expander of the line narrowing optics preferably includes one or more prisms. The beam expander may include other beam expansion optics such as a lens assembly or a converging / diverging lens pair. The diffraction grating, etalon (s) or highly reflective mirrors may be rotatable so that wavelengths propagating within the acceptance angle of the resonator can be selected or tuned. Alternatively, the diffraction grating, etalon (s), or other optical device (s), or the entire line narrowing module, may each be assigned to the same assignee as the present application and incorporated by reference. Nos. 60 / 178,445 and 09 /, which are incorporated herein by reference.
The pressure may be adjusted as described in the '317,527 patent application. If a diffraction grating is used,
It is preferred to use an amplifier after the laser oscillator to increase the power of the beam. One or more dispersing prisms may be used, and more than one etalon may be used.

There are many alternative optical configurations that can be used, depending on the type and degree of narrowing and / or the desired selection and tuning, and the particular laser on which the narrowing optics is to be installed. I do. For this purpose, U.S. Pat.
No. 399,540, No. 4,905,243, No. 5,2
No. 26,050, No. 5,559,816, No. 5,65
9,419, 5,663,973, 5,76
Nos. 1,236, and 5,946,337, and U.S. Patent Application Nos. 09 / 317,695, 09/130,
No. 277, No. 09 / 244,554, No. 09/31
No. 7,527, No. 09 / 073,070, No. 60/1
No. 24, 241, No. 60/140, 532, No. 60 /
No. 147,219, and Nos. 60 / 140,531, 60 / 147,219, 60 / 170,342,
No. 60 / 172,749, No. 60 / 178,620
No., No. 60 / 173,983, No. 60 / 166,27
No. 7, No. 60 / 166,967, No. 60 / 167,8
No. 35, No. 60/170, 919, No. 60/186,
096, each of which is assigned to the same assignee as the present application, and U.S. Patent Nos. 5,095,492, 5,6.
No. 84,822, No. 5,835,520, No. 5,85
No. 2,627, 5,856,991, 5,89
No. 8,725, No. 5,901,163, No. 5,91
No. 7,849, No. 5,970,082, No. 5,40
No. 4,366, No. 4,975,919, No. 5,14
No. 2,543, No. 5,596,596, No. 5,80
No. 2,094, No. 4,856,018, No. 5,97
No. 0,082, 5,978,409, 5,99
9,318, 5,150,370, and 4,8
29,536 and German patent DE 298 2
No. 20090.3 is incorporated herein by reference.

In all of the above and below embodiments, the materials used for the beam expander prism, etalon, laser window and output coupler are preferably such as the 157 nm output emission wavelength of a molecular fluorine laser. It is highly transparent at a wavelength of 200 nm or less. This material can also withstand prolonged exposure to UV radiation with minimal degradation. An example of such a material is Ca
F ₂ , MgF ₂ , BaF, BaF ₂ , LiF, LiF ₂
And SrF ₂ , and in some cases, quartz or fluorine-doped quartz may be used. Also, in all embodiments, many optical surfaces, particularly prism optical surfaces, preferably have anti-reflective coatings (anti-reflective coatings) on one or more optical surfaces to minimize their return loss and extend life. ref
lective coating). A highly reflective dielectric coating (e.g., a highly reflective dielectric reflector or etalon) on the inner surface of the surface where it is desired to have a high degree of reflection is required.
ive dielectric coating) may be used.

A power amplifier may be followed by a narrowed oscillator, such as those described above, to increase the power of the beam output by the oscillator. Preferred features of the oscillator-amplifier setup are described in U.S. patent application Ser. No. 09 / 599,130, assigned to the same assignee as the present application and incorporated herein by reference. The amplifier may be the same as or separate from the discharge chamber 2. Optical or electrical delays may be used to time the discharge at the amplifier with the time at which the light pulse arrives from the oscillator to the amplifier.

Referring to FIG. 2A, the F ₂ laser of the first embodiment is filled with a laser gas containing molecular fluorine.
Main electrodes 3a and 3 coupled to a power supply circuit such that a voltage is applied across electrodes 3a, 3b to generate a pulsed discharge.
b is included. Also provided is UV pre-ionization of the discharge laser, which is located near the solid electrode of at least one main discharge of the laser, by an array of spark gaps or other source of UV radiation. (Surface (surfac
e), barrier or corona gas discharge). Suitable pre-ionization units are described in US patent application Ser. No. 09 / 247,887, each assigned to the same assignee as the present application and incorporated herein by reference.
No. 60 / 162,845.

The dispersing prism 4 has a high-reflection coating on its rear surface, and functions as a high-reflection resonant reflector. The etalon 6 serves as an output coupler for the beam. Prism 4 also serves to seal one end of discharge chamber 2, while etalon 6 may also serve to seal the other end of discharge chamber 2. Also, one of the etalon 6 and the prism 4 may serve to seal one end of the discharge chamber 2, while the other end may be sealed by a window. A partially reflecting resonant reflecting mirror may seal one end of the discharge chamber 2.

An energy monitoring device 8 is included in the first embodiment and measures the energy of the output beam of the laser. A beam splitter 10 is also shown. In addition, prism 4
And the reflectance maximum of the etalon 6 and the sideband of the dispersion spectrum of
₂ Superposition with selected emission line of laser
One or more apertures (not shown) may be inserted into the resonator to cut the sideband of n). The aperture may have dimensions approximately equal to the diameter of the laser beam (see US patent application Ser. No. 09 / 130,277 and US Pat. No. 5,161,238). The opening is an amplified spontane generated in the gas discharge chamber 2.
ous emission). It is advantageous to cut off the otherwise resulting parasitic emissions, which generally do not have the desired lasing characteristics. Therefore,
Such parasitic emissions, if not excluded by the aperture, can degrade the output beam, including its spectral purity and divergence. In general, any of the embodiments described in this application may be modified by adding one or more apertures that exclude this parasitic emission.

The power supply voltage applied between the main electrodes 3a and 3b in the discharge chamber 2 and the laser voltage are based in part on the energy measured using the energy monitoring device 8.
The concentrations of the components of the gas mixture are controlled by adjusting the characteristics of the output beam, including energy. In a first preferred embodiment, bright line selection is achieved through the use of a dispersing prism 4.

The prism 4 is preferably rotatable or tiltable to adjust the range of wavelengths that it reflects within the acceptance angle of the resonator. Prisms can be directed to include only one of a number of discharge emission line F ₂ laser (e.g., see FIGS. 1 and 6 (a) ~ FIG 6 (b)). 1
More than one dispersing prism may be included, and a beam expander may be provided in front of dispersing prism 4.
Also, the dispersion prism 4 may be arranged in front of the high reflection or partial reflection mirror of the resonance reflector.

Due to the wavelength dependence of the refractive index of the material of the prism 4, the light entering the prism 4 is refracted at various angles according to the wavelength. Only emission lines having wavelengths within a certain wavelength range that exit the prism 4 within the acceptance angle of the laser cavity will then be outcoupled as an output laser beam. In other words, retroreflection (retr) from a highly reflective surface behind the prism 4 or a highly reflective mirror placed after the prism.
After oreflecting, the different wavelength emission lines enter the discharge chamber at different angles with respect to the optical axis of the resonator. A bright line having a wavelength within the wavelength range reflected within the acceptance angle of the resonator is selected, and all other bright lines are not selected or suppressed. The prism is tuned so that the desired center wavelength is aligned parallel to the optical axis and experiences minimal optical loss, and therefore that wavelength is dominant in output. This center wavelength is at or near the center wavelength of the F ₂ emission line desired to be selected.

The narrowing is provided by an etalon 6 which can also serve as an output coupler. The etalon 6 is also a high reflection or partial reflection resonance reflection mirror (resonato
r reflector mirror). Etalon 6 preferably has a low finesse. The reflective inner surface of the plate of the etalon 6 exhibits a reflectivity of, for example, about 4-6%, so that the maximum reflectivity of the etalon can be 16% -24%. However, the reflectivity, somewhat increased / reduced as required, it is possible to increase / decrease the overall gain of the F ₂ laser.

Also, alternative embodiments may be implemented using one or more apertures, preferably having dispersive elements, such as prisms and, alternatively, diffraction gratings. Opening, a prism is used for the bright line selection time to distribute the release of the F ₂ laser. Selected bright lines pass through the aperture, and unselected bright lines are blocked by the aperture. An etalon or prism is then used to narrow the selected bright line.

Referring back to the first embodiment of FIG. 2A, a single-spectrum bright line is selected by the prism 4, and the selected bright line is narrowed by the optical etalon 6. FIGS. 3A and 3B illustrate a method for achieving the narrowing of the line width. The reflectance function of the etalon 6 for the light wavelength of the incident light, in this case about 157 nm (refl
ectivity function) R is shown in FIG.
This reflectance function is represented by a sine function substantially as follows. R (v) 〜1 + sin (2Bv / v ₀ ) where v ₀ is the free spectral range of the etalon 6 (FS
R: free spectral range, where n is the refractive index of the material in the gap between the plates of the etalon 6 and L is the spacing of the etalon plates in centimeters, v ₀ = ｖ nL [cm ^−1] ]. These spectral components having a frequency close to the minimum value of the refractive index R of the etalon 6 have a maximum loss in the resonator and are suppressed. Therefore, the etalon's FSR is a free running laser.
If the line width of the selected bright line in er) is approximately equal to, but somewhat smaller than, the output line width is narrowed. The FSR must not be much smaller than the free running linewidth in order to prevent the gradual generation of sidebands in the adjacent interference order.

[0034] FIG. 3 (b) shows a solid line representing the selected emission lines of the free-running line width of F ₂ laser. The etalon reflectance function of FIG. 3 (a) is superimposed on the selected bright line. The resulting narrowed bright line is indicated by the dashed line in FIG. 3 (b). As noted above, if the FSR is too small, the outer peak of the reflectance spectrum of FIG. 3 (a) will greatly overlap the selected bright line. Allowing the "parasitic" sidebands to resonate degrades the beam quality. If there is a dispersive element such as a prism 4 or other prism (s) or diffraction grating in the resonator, the selected emission line reduces the width of the etalon 6's reflectivity maxima. As a result, the etalon 6 does not suppress the sidebands, since the etalon 6 does not suppress the sidebands, while an aperture is arranged in the resonator to cut off the sidebands, and finally becomes very narrow. A linewidth, high quality output beam is obtained.

FIG. 4 is a sectional view of the first embodiment shown in FIGS. 2 (a) and 2 (b).
And a pressure-tuned outcoupler used with any of the second embodiments.
alon) 6 showing an enlarged and more detailed view. Alternatively, a solid etalon may be used instead, but the etalon reflectance spectrum of the etalon in FIG. 4 may be used to adjust the gas pressure between the etalon plates (see below) or to adjust the gap spacing. The etalon shown in FIG. 4 with two plates separated by an air gap is preferred because it can be adjusted by Any of these etalons can be tuned rotationally. As FIG. 4 shows, the etalon 6 is preferably
In order to eliminate the lossy optical interface of the additional optical window that seals the chamber 2, it serves both as a seal and a window for the discharge chamber 2 and serves to reduce the overall size of the resonator mechanism. Fulfill. In the illustrated embodiment, the etalon 6 comprises a bellows 14 and an O-
The chamber 2 can be sealed via the ring 16.

The etalon 6 is shown housed within a jacket 18. A gas inlet 20 is preferably provided, and one or more gases such as helium (preferred), neon, krypton, argon, nitrogen, another inert gas or another gas that does not absorb strongly around 157 nm are selected at a selected pressure. Can be filled in the jacket 18. The jacket is equipped with conventional means for measuring the pressure of the gas inside. The gas inlet 20 may also be used to evacuate the envelope, including the gap between the plates 22 of the etalon 6, to a low pressure using a mechanical pump. CaF ₂ , Mg
Solid materials, such as F ₂ , LiF ₂ , BaF ₂ , SrF ₂ , quartz and fluorine-doped quartz, or another solid material that does not absorb strongly around 157 nm, may fill the gap between the plates of the etalon 6. The reflective inner surface of the plate 22 of the etalon 6 is a reflective film
And may be left uncoated. The spacer 26 may be made of Invar®, Zerodur, Ultra Low Expansion (ULE®) glass or quartz, or another material having a low coefficient of thermal expansion such that the temperature sensitivity of the gap thickness L is minimal. Contains. This is advantageous because the reflectivity function of the etalon 6 depends on the gap spacing.

The following is the preferred etalon gap thickness L
This is an estimated value. Self-propelled F₂The line width of the laser is about 1 pm
Since its wavelength is about 157 nm, the FSR is about 0.4
cm ^-1Should be. This is the gap between the plates.
(MgF₂, CaF₂, LiF₂, BaF₂, Sr
F₂, Crystalline quartz or fluoride
Solid material with a refractive index of about 1.5 (such as silica quartz)
Etalon spacing L is 8.3 mm
Means that it should. In addition,
As discussed in detail in etalon 6, etalon 6 is
Can have a gap filled with an inert gas such as
In this case, the thickness should be about 12.5 mm
You. Both of these intervals L can be easily achieved. Eta
For Ron plates and / or to fill gaps
To MgF₂, CaF₂, LiF₂, LiF, BaF₂,
SrF₂Or crystal or fluorine-doped crystal quartz
The use of solid materials that are
It is almost transparent to light near the wavelength of m
Indeed partially.

As suggested above, etalon design considerations include etalon frequency reflectivity to changes in ambient conditions such as temperature.
Is a requirement for the stability of the maximum and minimum values of For example, MgF ₂ has a linear expansion coefficient of 13.7 × 10 ⁻⁶ K ⁻¹ along the c-axis and a temperature of 1.47 × 10 ⁻⁵ K ⁻¹ for a normal beam. It has a refractive index (temperature indexcoefficient). this is,
Centering of the spectral emission line with respect to the maximum value of the reflectance function R (v), for example 10% of FSR
Means that the temperature must be stabilized to within 0.06K to maintain within. CaF
_{If 2} is used, this stability must be within 0.05K.

The present invention provides this stability by using a low thermal expansion material as the spacer. Also in accordance with the present invention, two separated by a gap in the above mentioned envelope, preferably filled with an inert gas such as one or a combination of the above mentioned gases.
2 (a) or 2 respectively with two plates
This is also achieved by providing an outcoupler etalon 6 of the first or second embodiment of (b), wherein the gas pressure controls the gas's refractive index and thus the etalon's reflection. Controlled to control the center wavelength of the aligned peak of the rate function. For an inert gas such as nitrogen, the refractive index changes by about 300 ppm per bar of pressure. Thus, with spacing L = 12.5 mm between reflective surfaces, frequency control within 10% of the FSR requires pressure control within a resolution of 2 mbar. As discussed, the first reason for using helium, and alternatively nitrogen, argon or other inert gas or vacuum, in the pressure regulated etalon 6 is primarily due to the fact that oxygen, water vapor and Air is not transparent at the 157 nm wavelength of interest because carbon is present and each strongly absorbs about 157 nm.

Further, the inner surface of the output coupling etalon 6 may or may not be coated with a partially reflective coating. In the latter case, the reflectivity of each surface is about 4-6%
Which results in a maximum reflectivity of the etalon of 16% to 24%.
%. Alternatively, a dielectric coating may be provided for high reflectivity such that each surface exhibits a high reflectivity of greater than 50%, perhaps 90% or more, for example up to 97%. Similar considerations apply to solid etalons.

The second embodiment shown in FIG. 2B is the same as the first embodiment shown in FIG. 2A, except that the prism 4 shown in FIG. The difference is that they have been replaced. The high reflection mirror 12 may seal one end of the discharge chamber, and / or the etalon 6 may seal the other end of the discharge chamber. In the second embodiment, the etalon 6 provides a bright line selection function, and eliminates the need for the prism 4 of the first embodiment in FIG. The advantage of the second embodiment over the first embodiment is simplicity, with fewer elements in the resonator and fewer optical interfaces for the beam to traverse, reducing optical losses and extending life. is there. However, the suppression of the secondary bright line is not as effective in the second embodiment as in the first embodiment.

In the second embodiment, the etalon 6 reduces the line width of the selected single bright line simultaneously with the bright line selection in the same manner as described above in connection with the first embodiment. Used for both. Line selection is achieved by adjusting the etalon's FSR and the wavelength of maximum reflectance such that the reflectance at the desired wavelength is maximized and the reflectance at the wavelengths of the other unselected lines is minimized. This bright line selection is described in further detail below. The etalon 6 also couples out the beam as done in the first embodiment.

FS of etalon 6 of the first and second embodiments
R, or more generally, the etalon 6 of FIGS. 8 (a), 8 (b) or 9 (a) or 9 (a) -9.
F _{2 of the} invention, such as etalon 34 of (b) (below)
The FSR of any gas-filled etalon used with the laser can be adjusted in the following manner. The pressure of the gas filling the etalon jacket 18 (see FIG. 4), and in particular the gas between the plates 22 of the etalon 6, can be changed to adjust the refractive index of the gas. Alternatively, for example, using a piezoelectric element as the etalon spacer 26,
The distance L between the plates 22 can be changed. FS
Since R depends on both the refractive index of the gas and the spacing L between the plates 22, the FSR
Can be adjusted. By adjusting the FSR of the etalon 6, aligned to the desired emission lines to be selected to the maximum value in the reflectance spectrum of the etalon 6, at the same time the non-selection of the free-running F ₂ laser the minimum value of the reflectance spectrum of the etalon 6 By aligning the bright lines, the bright lines can be selected accurately. Any etalon used in the preferred embodiment can also be tuned piezoelectrically or rotationally to adjust the FSR.

FIGS. 5A and 5B show the etalon 6
An example of a method of narrowing the line width by the method will be described below. As discussed quantitatively below, the FSR of etalon 6
Is adjusted by either changing the gap spacing or changing the pressure of the gas in the gap, as described above. The requirements for pressure resolution derived above apply here as well. The advantage of this configuration is that it is simpler because no prism is required for bright line selection. However, this system is inefficient at suppressing unwanted emission lines and can result in residual emission at such wavelengths.

A self-propelled F ₂ laser emission line λ of about 157 nm
The reflectance spectra of etalon 6 near ₂ (left part) and λ ₁ (right part) are shown in FIG. Preferably, the pressure of the gas filling the gap of the etalon 6 is changed to align the maximum and minimum reflectivity to λ ₂ and λ ₁ respectively. Alternatively, the gap spacing may be changed or both the pressure and the gap spacing may be changed to produce the same effect. FIG. 5 (b)
Is, lambda _{2 (part} on the left) and lambda _{1 (right} part) of the free-running F ₂ laser (solid line), and F ₂ laser having an emission line selection (lambda ₁₎ and the line narrowing of the selected emission lines 2 shows the output emission spectrum (broken line). That is, Figure 5 a broken line in FIG. 5 (b) is the output emission spectra of the free-running F ₂ laser
FIG. 5A of the etalon 6 superimposed on the solid line of FIG.
Represents a reflectance spectrum.

In addition to the molecular fluorine, a F ₂ laser gas mixture in the discharge chamber of the present invention further includes one or more other gases including at least one buffer gas. FIGS. 6 (a) and 6 (b) show free-running F ₂ having helium and neon as buffer gases, respectively.
3 shows a spectrum of a laser.

FIG. 6A shows a helicopter as a buffer gas.
Self-propelled F of about 157 nm with ₂Laser Spect
Show Two bright lines are observed. FIG.
Self-propelled about 157nm with neon as buffa gas
F₂3 shows a laser spectrum. In this case, three bright lines
Is observed. About 157.6 of the spectrum of FIG.
The corresponding emission lines at 2 nm and 157.52 nm are clearly visible
6 (a). This is shown in FIG.
F that released the creature₂The laser is powered by a neon buffer
Helium as a buffer gas
F that emits the spectrum of FIG.₂From laser
This is because it showed a long pulse duration.

[0048] In any embodiment of the F ₂ laser of the present invention, as the pulse duration is long, achievable spectral linewidth narrower. Each time the laser beam makes one round trip in the resonator, spectral filtering of the beam is performed. After each reflection from the etalon output coupler 6, the intensity spectrum I ^{(j + 1)} (v) of the reflected beam is the etalon's reflectance function R (v) and the incident spectrum I ^{(j + 1).
(j)} The product of (v), that is, I ^{(j + 1)} (v) = R (v) I ^(j) (v) where j is the number of round trips. For example, if the reflectance function can be approximated by a Gaussian function, the width of the beam spectrum decreases with the reciprocal of the square root of the number of round trips. That is, the following equation. The Δv ~ j ^-1/2 preferred embodiment also includes means for increasing the pulse length of the molecular fluorine laser by utilizing neon as a buffer gas. FIGS. 7 (a), 7 (b) and 7 (c) show the time pulse shapes for the gas mixtures shown in Table 1. FIG.

[0049]

[Table 1]

[0050] If the concentration of neon _{F 2} laser gas mixture is increased, the pulse length as a result increases from approximately 8n sec (0% neon) to 25n seconds (for 96.8% neon).

(Total pressure and fluorine concentration considerations) The gas mixture is optimized for pulse energy (gain) and pulse energy stability. Higher energy results are achieved at higher pressures and higher fluorine concentrations, respectively.
Energy fluctuations also increase. The preferred device balances these considerations. That is, about 5 bar
And a fluorine concentration in the range of 0.05% to 0.2% are preferred.

In an embodiment utilizing neon as the sole buffer gas, there are three bright lines in the free running spectrum. The following three conditions should be met.

Mv ₀ = v ₁ ; (k + ／) v ₀ = v ₂ ; (j + ／) v ₀ = v ₃ , where m, j, and k are integers, and v ₀ is the optical frequency domain ( optical frequency domain) is the free spectral range of the etalon in, v ₁ is the optical frequency of the emission line to be selected, v ₂ and v ₃ are the optical frequency of the spectral emission lines to be suppressed. If only two emission lines are present, such as when helium is used as a buffer gas,
This set of equations is reduced to the following two equations:

Mv ₀ = v ₁ ; (k + ／) v ₀ = v ₂ , where v ₁ is the optical frequency of the bright line to be selected.

FIGS. 8A and 8B schematically show third and fourth preferred embodiments of a resonator apparatus for a molecular fluorine laser. To increase the wavelength separation effect, FIG.
Multiple (two or more) prisms 28, 30 may be used as shown in (a). The second prism 30 may have a high-reflectance coating on its back surface, or may be placed in front of a high-reflection resonant reflection mirror. Prism 3
The use of such a separate high-reflection mirror 32 in place of the high-reflection coating on the back of 0 is shown in FIG. 8 (b).
Such a separate high reflection mirror 32 could be used in combination with multiple prisms. An advantage of the separate mirror 32 is that it can be more easily manufactured than the prism 30. At the same time, the use of separate mirrors 32 increases both the optical loss and wavelength dispersion as the number of optical surfaces traversed by the beam increases. Thus, the number of prisms and the decision whether to use separate mirrors depends on the total amount of dispersion desired to achieve a reliable selection of a single emission line. As noted above, one or more apertures are inserted into the resonators of any of the systems of FIGS. 8 (a) and 8 (b) to provide sidebands of the dispersion spectrum of prisms 28, 30 and / or to cut the sidebands overlap between the maximum value and the F ₂ laser of selected emission lines of the reflectance of the etalon 6.

FIG. 9A and FIG. 9B show about 157n.
The schematic representations of the fifth and sixth preferred embodiments, respectively, of a molecular fluorine laser resonator device emitting at m. In the fifth embodiment of FIG. 9A, the high finesse etalon 34 is
(A) It replaces the prism 4 of the first embodiment. FIG.
In the sixth embodiment of FIG. 9B, a high finesse etalon 34 is also used, and the output coupling mirror 35 replaces the output coupling etalon 6 of the fifth embodiment of FIG. In general, any of the embodiments described in this application may be modified to include the high finesse etalon shown in FIGS. 9 (a) and 9 (b).

In either the fifth or sixth embodiment, bright line selection is preferably achieved through the use of an etalon 34 having a relatively high finesse. 9 (a) and 9
The etalon 34 in (b) operates in a reflection mode and has a high reflectivity surface of the previously described embodiment, ie, the high reflectivity back surface of the prism 4 of the first embodiment or the prism 30 of the third embodiment. It can serve as an alternative to the high reflectivity mirror 12 of the second embodiment or the high reflectivity mirror 32 of the third embodiment. Alternatively, the etalon 34 operates in a transmission mode and may be located in front of the high reflection resonant reflecting mirror. In addition, the etalon 34 can replace the prism 12, 30 or the entire prism 28 and reflector 28 due to its bright line selection characteristics combined with its high reflectivity characteristics.

FIG. 10A shows the reflectance R of the etalon 34 versus the optical frequency v of the laser beam. This is represented by the following function: R (v) -Fsin ² (πv / v ₀ ) / (1 + Fsin
² (πv / v ₀ )) where F = 4R / (1-R) ² is the finesse factor of the etalon 34, v ₀ is the free spectral range (FSR) of the etalon, and n is the etalon V ₀ = １ ／ nL [cm ^-1 ] where L is the refractive index of the gap material and L is the etalon spacing in centimeters. The finesse coefficient F is the finesse and F = π (F / 2)
Related as ^1/2 . Spectral components having frequencies near the minimum of the reflectivity function of the etalon 34 suffer the greatest loss in the resonator and are therefore suppressed. If the finesse of the etalon 34 is sufficiently high, any light having a frequency outside the narrow spectral region corresponding to the condition v = kv ₀ when k = integer, as shown in FIG. 10 (a). It will be almost completely reflected by the etalon 34 which shows a reflectance close to 1 at the frequency. Thus, except for these narrow areas of minimal reflection at v = kv ₀ , etalon 34 serves exactly as a highly reflective surface. Preferably, the etalon 34 is configured to suppress such unwanted spectral emission lines by setting the minimum value (s) of the etalon 34 reflectivity at the center of the unwanted spectral emission lines. . The etalon 34 according to either the fifth or sixth embodiment may be a solid etalon (solid etalon) as described above.
d-state etalon, evacuated etalon
alon) or an inert gas-filled etalon,
Here, the inert gas can again be helium, argon, neon, krypton, nitrogen, or any one or combination of other gases that do not strongly absorb light at about 157 nm. Further, in the gap between the plates of the etalon 34, CaF ₂ , MgF ₂ , LiF ₂ ,
Solid materials such as BaF ₂ , SrF ₂ , quartz or fluorine-doped quartz, or other solid materials that do not strongly absorb light at about 157 nm are included.

FIGS. 10 (a) to 10 (c) correspond to FIG.
9A and 9B illustrate the characteristics of the bright line selection of the high finesse etalon 34. FIG. FIG. 10A shows the wavelength dependence of the reflectance of the high finesse etalon 34. FIG.
(B) shows an emission spectrum of the free-running _{F 2} laser. F ₂ with high finesse etalon 34 in its resonator mechanism
The resulting power emission of the laser is shown in FIG. Figure 10 (a) As can be observed from the through Figure 10 (c), one of the two bright lines as desired but is selected as the output of the F ₂ laser.

The wavefront curvature of the beam (wavefront curv
is compensated for by using a cylindrical lens in the resonator (see US Pat. No. 6,061,382, incorporated herein by reference). The etalons 6 and 34 of the present invention are generally susceptible to beam front curvature. Thus, one or more cylindrical lenses located within the resonator can provide a collimated beam with the etalons 6,34. In addition, wavefront curvature compensation can be achieved via one or more curved resonator mirrors.

Other variations are possible in promoting the goals and objectives of the present invention. For example, the prism 4 in FIG.
9 (a), the high reflection mirror 12, the etalon 6 of any embodiment, the prism 28 or prism 30 of FIG. 8 (a), the prism 28 or high reflection surface 32 of FIG. 8 (b), and FIGS. Any of the high finesse etalons in FIG. 9B can seal the laser discharge chamber 2. This advantageously reduces the number of optical interfaces that the beam must traverse, thus reducing optical losses. In particular, no extra laser window (s) is needed after being replaced by one or more of the optical elements just mentioned. If the etalons 6, 34 are used to seal the discharge chamber, the pressure of the gas in the etalons 6, 34 is increased to approach the pressure of the gas mixture;
It may be advantageous to prevent distortion of the etalons 6, 34 due to pressure differences, but only if the etalon is still performing bright line selection and / or line narrowing.

FIG. 11 shows a molecular fluorine (F) including a line narrowing module 50 having a prism beam expander 46 and an etalon 48 for bright line selection and / or line narrowing.
₂ ) A seventh preferred embodiment of the laser resonator device is shown. Seventh
In the resonator device of the embodiment, molecular fluorine, neon and / or
Or a discharge chamber 2 filled with a gas mixture comprising one or more buffer gases, such as helium. A pair of main discharge electrodes 3a and 3b are located in the discharge chamber and connected to a pulser circuit (not shown) to apply a voltage to molecular fluorine. One or more pre-ionization units are also in the discharge chamber (not shown, but see the above referenced 60 / 162,845 patent application). Another embodiment of the discharge chamber 2 is 09 / 453,6.
No. 70 patent application, otherwise as described above and / or as understood by those skilled in the art.

One window 40 is a plano-parallel optical window that serves as an output coupler. A partially reflective mirror may alternatively be used separately from the chamber window 40 to couple the beam out, which window 40 serves the dual purpose of sealing the chamber 2 and coupling out the beam, and The number of optical surfaces of the optical fiber, thereby advantageously improving its efficiency. Window 40
Is preferably aligned perpendicular to the optic axis, but at an angle such as 5E or Brewster angle or other choice to achieve the desired reflectivity and transmissivity properties and / or prevent parasitic oscillations It may be oriented at a given angle.

The vacuum bellows 56 or similar device provides flexibility in terms of freedom of adjustment and a vacuum tight seal. Another window 44 is preferably a plano-convex lens (plano-convex
U.S. Pat. No. 6,0,067, each assigned to the same assignee as the present application and incorporated herein by reference.
61,382 and European Patent Application EP 0095570
6 serves to compensate for wavefront curvature as described in A1. Seal confidentiality is ensured by seal 42. Lens 44 may or may not be adjustable. Lens 44 may be slightly (about 5 degrees) tilted from the normal to the beam to avoid parasitic oscillations. Preferably, the lens 44 is anti-reflective coated.

The resonator of the F ₂ laser according to the seventh embodiment shown in FIG. 11 includes a bright line selection and / or narrowing unit coupled to the chamber 2 via the bellows 56 and the seal 42. The beam is preferably expanded by one or more beam expanding prisms 46 to reduce beam divergence. Several prisms 46 may be used, and a converging diverging lens pair may be used.
A lens pair) or other beam expanding means known to those skilled in the art may be used.

A transmission etalon is preferably placed after the beam expander prism 46 and serves as a wavelength selector. Finally, the highly reflective mirror 32 returns the beam through the resonator.

Since the line narrowing unit is in the enclosure 50 which is coupled to the laser chamber 2 using the bellows 56 and the seal 42, the laser resonator line narrowing unit is sealed from the outside air. Inert purge gas is flowed through the enclosure 50 through inlet and outlet ports 52,54. A vacuum port may be included, or a pump may be connected via either port 52 or 54. Methods of controlling the atmosphere in the enclosure include maintaining the enclosure under evacuation conditions using a pump, or flushing purge gas through the enclosure 50, and preferably first evacuating the enclosure, then The purge gas flows at a low flow rate. The evacuation is followed by a backfill of the purge gas, and this procedure is repeated several times, for example 3 to 10 times, before the purge gas is flowed at a low speed. The alternative treatment for maintaining Prepare atmosphere for further details and enclosure, with each beam delivery path enclosure for which incorporated by (F ₂ laser of the present application by reference and assigned to the same assignee as the present application U.S. patent application Ser. Nos. 09 / 343,333, 09 / 594,944 (for diagnostic beam splitter modules).
892 and 09 / 598,522.

The entire beam path between the chamber 2 and the highly reflective mirror 32 is actually enclosed in an enclosure 50 which is preferably purged with nitrogen or some inert gas such as helium, argon, krypton or the like. It is suitable. High-purity nitrogen is preferably used for this purpose.

The pressure of the nitrogen in the enclosure 50 is adjustable, and the transmission spectrum of the etalon 48 can be adjusted by changing the pressure of the nitrogen (for example, a narrow line including a diffraction grating and a beam expander). (See US patent application Ser. No. 09 / 178,445, assigned to the same assignee as the present application and incorporated herein by reference for pressure regulation of the widthening unit). Maximum value of the transmission of the etalon 48 is suitably, in a free-running F ₂ of the spontaneous emission spectrum of the laser, a large number of emission lines in the vicinity of 157nm which preferably also includes a secondary emission lines around 157.52nm is suppressed, Fifteen
The adjustment is made so as to coincide with the maximum value of the primary emission line at λ ₁ near 7.62 nm.

[0070] FIG. 12 (a) ~ FIG. 12 (c), the bright line that is selected by adjusting the etalon, for example, narrow linewidth primary emission line of approximately 157.62nm of _{F 2} laser of the embodiment of FIG. 11 An example of a method for converting the data will be described. 12 (a) is illustrates spontaneous emission spectrum of the primary emission line of approximately 157.62nm of _{F 2} laser. The transmission of the etalon 48 is a periodic function of the wavelength, as illustrated in FIG. The solid line in FIG. 12B represents the first tuning position of the etalon 48, and the broken line represents the second tuning position of the etalon 48. Etalon 48 may be piezoelectric, rotary and / or by adjusting the pressure in the gap between its plates as described above in connection with either the discussion of FIG. 11 or the discussion of FIG. Tuned. One way to change the pressure is to use needle valves 52 and 54 to control the inlet and outlet rates of the nitrogen purge gas shown in FIG. For example, the pressure may be increased by closing the outlet valve 54 and / or opening the inlet valve 52, and vice versa.

The width of each transmission peak is approximately the free spectral range of the etalon divided by its finesse, and since the finesse is limited by the quality of the optical surface, it is as free as possible to minimize the width of the transmission peak. It is preferred to reduce the spectral range. The minimum free spectral range is determined by the requirement that the peak adjacent to the central peak be substantially free of oscillation. FIG.
Since the approximate natural bandwidth of the emission peak illustrated in (a) is approximately 0.6-1.0 pm, a preferred optimal free spectral range is approximately 1.0 pm. FIG. 12 (b) and FIG.
The solid line shown in FIG. 2 (c) illustrates a preferred spectral alignment, where FIG. 12 (c) shows a single narrowed peak. The dashed lines in FIGS. 12B and 12C indicate the second in the laser output when the transmission spectrum of the etalon 48 deviates from the optimum value indicated by the solid line.
An undesired spectral alignment is illustrated because two peaks are shown, including the occurrence of a peak.

A variant of the seventh embodiment includes having an output coupler as an optical element independent of the window 40, in which case the output window 40 of the chamber 2 is a plane-planar window.
o window). This offers the opportunity to place the resonator optics on a mechanically stable structure separate from the chamber 2. However, this increases the optical losses and reduces the efficiency of the laser. A second etalon, diffraction grating and / or one or more dispersive prisms may be included with the line narrowing unit of FIG. Etalon 48
May be replaced by a reflective etalon and, as in the high or low finesse etalons such as those etalons 6, 34 described above, serve a dual role as a bright line selection element and as a resonant reflector. .

The described laser oscillator typically produces lower output power compared to a free-running resonator. Thus, as described in the above part of the present application and in the 09 / 599,130 patent application incorporated by reference herein above, as in any of the first to sixth embodiments. In the seventh embodiment, an amplifier can be used.

The preferred material for all optical elements is CaF ₂ , but among the few materials known to be sufficiently transparent at 157 nm, MgF ₂ , BaF ₂ , Sr
F ₂ , LiF ₂ or LiF can alternatively be used. Etalon 48 is preferably greater than 50%,
The etalon 48 preferably has an anti-reflective coating on its outer surface, while its inner surface is preferably coated with a thin film dielectric coating having a reflectivity of 90% to 97%.

While illustrative drawings and specific embodiments of the present invention have been described and illustrated, it should be understood that the scope of the present invention is not limited to the specific embodiments discussed herein. . That is, the examples should be considered as illustrative rather than restrictive, and as will be appreciated, by those skilled in the art, the scope of the invention as set forth in the appended claims and their scope Variations on these embodiments may be made without departing from the equivalents.

Further, the method claims (me
In a thod claim, the steps are provided in a selected order, but this is for printing convenience only and does not imply any particular order of performing the steps. That is, the steps can be performed in a variety of orders within the scope of these claims, unless a specific order is explicitly indicated or understood by one of ordinary skill in the art to be necessary. For example, in some method claims, the step of selecting one of the plurality of emission lines and narrowing the selected emission line includes the step of causing the beam to traverse the narrowing and / or emission line selection element and cause a laser resonance. This can be done in any of the temporal sequences coupled out of the vessel or in any combination thereof.

[Brief description of the drawings]

FIG. 1 is a diagram showing an emission spectrum of an F ₂ laser without bright line selection or line narrowing.

2 (a) is a diagram showing a first preferred embodiment of the F ₂ laser according to the present invention. (B) is a diagram showing a second preferred embodiment of the present invention.

FIG. 3 (a) illustrates the periodic wavelength dependence of the reflectivity function of the output coupled etalon according to the present invention.
FIG. 3B is a diagram illustrating a feature of additional narrowing of the output coupling etalon of FIG.

Is a diagram showing an etalon as an output coupler and window F ₂ laser according to the invention; FIG.

FIG. 5 (a) shows the vicinity of a free-running F ₂ laser emission line λ ₂ (left part) and λ ₁ (right part) of about 157 nm.
FIG. 4 is a diagram showing the wavelength dependence of the reflectance of the output coupling etalon according to the present invention. (B) Self-propelled F ₂ when there is no bright line selection or narrowing (solid line) and when there is bright line selection and narrowing (dashed line) performed by the output coupling etalon of FIG. 5 (a). FIG. 3 is a diagram illustrating an emission spectrum of a laser.

FIG. 6A is a diagram showing a free-running output emission spectrum of an F ₂ laser using helium as a buffer gas. (B) shows F using neon as a buffer gas.
FIG. 3 is a diagram showing a free-running output emission spectrum of _two lasers.

7 (a) is a diagram showing a temporal pulse shape of the F ₂ laser having only helium as the buffer gas. (B) is a diagram showing a temporal pulse shape of the F ₂ laser with a helium and neon as the buffer gas. (C) is a diagram showing a temporal pulse shape of the F ₂ laser with a helium neon with very small concentrations of most as the buffer gas.

8 (a) is a diagram showing a third embodiment of the F ₂ laser according to the present invention. (B) is a diagram showing a fourth embodiment of the present invention.

FIG. 9 (a) shows a fifth embodiment of the present invention including a high finesse etalon. (B) is a diagram showing a sixth embodiment of the present invention including a high finesse etalon.

FIG. 10 (a) shows the reflectance spectrum of the high finesse etalon of either FIG. 9 (a) or FIG. 9 (b) according to the present invention. (B) is a diagram showing a self-propelled output emission spectra of F ₂ laser. FIG. 10C shows a free-running output emission spectrum of the F ₂ laser whose reflectance spectrum is selected by the high finesse etalon shown in FIG. FIG. 4 is a diagram showing an output emission spectrum.

11 is a diagram showing a preferred resonator arrangement for the F ₂ laser including line narrowing module inert gas has been purged with a beam expander and the etalon for the bright line selection and / or line narrowing It is.

FIGS. 12 (a) to 12 (c) show etalons adjusted to FIG.
The F ₂ laser selected emission lines of the first embodiment illustrates a method of line narrowing.

[Explanation of symbols]

 2 Laser discharge chamber 3a, 3b Main discharge electrode 4, 28, 30 Dispersion prism 6, 48 Etalon 8 Energy monitoring device 10 Beam splitter 12, 32 High reflection mirror 14, 56 Bellow 16 O -Ring 18 ... Etalon jacket 20 ... Gas inlet 22 ... Wedge type mirror substrate 24 ... Reflective surface 26 ... Spacer 34 ... High finesse etalon 40,44 ... Window 42 ... Seal 46 ... Beam expander prism 50 ... Enclosure 52 ... Inlet Port 54: Exit port

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Sergey V. Goborkov, USA 33433, Boca Raton, Lacosta Drive 6315 Nambaem (72) Inventor Ube Stamm, Göttingen 37085, Germany, Heinholzbeek 29 F term (reference) 5F071 AA06 BB01 DD05 DD06 HH02 HH05 HH07 JJ05 5F072 AA06H02 HH07 JJ05 JJ13 KK02 KK06 KK08 KK15 KK16 KK18 MM20

Claims (46)

[Claims] 1. F₂A 157 nm and 158 nm laser including a primary emission line and a secondary emission line.
Specs with multiple closely spaced emission lines in the wavelength range between
Filled with a gas mixture containing molecular fluorine that generates tor emissions
And a pulse discharge for applying a voltage to the molecular fluorine
Electrodes coupled to a power supply circuit for a laser beam having a bandwidth of about 1 pm or less.
The discharge chamber for generating a system;
A resonator including a etalon and a pair of resonant reflectors.
The etalon is outside the secondary emission line and the primary emission line.
The transmittance of the primary emission line is reduced to substantially suppress the side portion.
To the maximum, the secondary emission line and the outer portion of the primary emission line
Is configured to have a relatively low transmission,
And said F ₂Laser provides narrowband VUV laser beam
Self-propelled F₂From the line width of the primary emission line of the laser
Single wavelength laser beam with narrow spectral linewidth
Select and narrow the primary emission line to emit light
A resonator comprising:₂laser. 2. The method according to claim 1, further comprising a second etalon that further narrows the primary emission line, wherein the second etalon is transmitted by the first etalon to suppress the outer portion. _2. The F2 laser of claim 1, wherein the F2 laser is arranged to maximize the transmittance of a central portion of a selected one of the primary emission lines and to make the transmittance of the outer portion of the selected emission line relatively low. 3. The apparatus according to claim 1, further comprising a second etalon for further narrowing the line width of the primary emission line, wherein the second etalon is transmitted by the first etalon to suppress the outer portion. 2. The arrangement of claim 1 wherein the primary emission line is arranged as a resonant reflector to maximize the reflectance of a central portion of a selected portion of the primary emission line and to relatively reduce the reflectance of the outer portion of the selected emission line. _{F 2} laser. Wherein said F ₂ laser according to claim 3 the second etalon is part of the resonator for further outcoupling a laser beam. 5. The F ₂ laser according to claim 3 wherein the second etalon is part of the resonator for reflecting the laser beam as a highly reflective resonator reflector. 6. The first etalon includes two plates, and at least one outer surface of the two plates has an anti-reflective coating thereon to minimize the reflectivity of the beam. _{F 2} according to any one of to 3
laser. 7. The method of claim 1, wherein only the primary emission line is within the acceptance angle of the resonator, and any other emission lines including the secondary emission line are dispersed outside the acceptance angle of the resonator. F ₂ laser according to claim 1, further comprising a prism disposed toward a specific direction for dispersing emission lines of the plurality of tight spacing, including the primary and secondary emission lines. 8. The prism beam expansion in front of the etalon for expanding the cross-sectional dimension of the beam incident on the etalon, such that the divergence of the beam is reduced before it is incident on the etalon. Claim 1 comprising a vessel
_2. The F2 laser according to 1. 9. An F ₂ laser, comprising molecular fluorine that produces a spectral emission that includes a plurality of closely spaced emission lines in a wavelength range between 157 nm and 158 nm, including a primary emission line and a secondary emission line. A discharge chamber filled with a gas mixture; a plurality of electrodes coupled to a power supply circuit for generating a pulsed discharge for applying a voltage to the molecular fluorine; including the discharge chamber; and further including a prism and a first etalon. A resonator, wherein only the primary emission line is within an acceptance angle of the resonator so that only the primary emission line is amplified among the plurality of closely-spaced emission lines, and the secondary emission line is The prism in a particular direction to disperse the plurality of closely spaced emission lines, including the primary and secondary emission lines, such that any other emission lines including the emission lines are dispersed outside the acceptance angle of the resonator. For Wherein the etalon is arranged to maximize transmittance of a selected portion of the primary emission line and to relatively reduce transmittance of an outer portion of the primary emission line to substantially suppress the outer portion. , Whereby said F
₂ laser, narrow in order to provide a band VUV laser beams, the primary to emit a single wavelength laser beam having a free-running F ₂ laser the primary emission line narrow spectral line width than the line width of the F ₂ laser including a resonator for line narrowing the emission line, a. Wherein said prism, F ₂ laser according to claim 9 having a highly reflective back for reflecting the laser beam as a highly reflective resonator reflector. 11. The prism is disposed between the resonant reflective elements of the resonator and has at least one anti-reflective coating on a beam entrance / exit surface for reducing reflection of the beam from the surface. _{F 2} laser according to claim 9. 12. The anti-reflection means for reducing reflection of said beam from each said beam entrance / exit surface on each beam entrance / exit surface, said prism being located between the resonant reflecting elements of said resonator. An F according to claim 9 having a coating.
₂ lasers. 13. The F of claim 9, wherein the etalon comprises two substantially parallel plates, the inner surface of each of which has a dielectric coating thereon to increase the reflectivity of the inner surface. ₂ lasers. 14. The etalon according to claim 9 or 13, wherein the etalon comprises two substantially parallel plates, the outer surface of each of which has an anti-reflective coating thereon to reduce the reflectivity of the outer surface. F ₂ laser. 15. The F _{2 according} to claim 1, wherein the gas mixture further comprises a buffer gas comprising neon.
laser. 16. The first etalon includes two plates separated by a gap, and wherein the first etalon is in an envelope filled with an inert gas.
_2. The F2 laser according to 1. 17. The gas in the envelope having a controlled pressure to regulate the etalon.
_{F 2} laser according to 6. 18. F ₂ laser according to claim 1 or 9 configured to be rotated for rotating tuning of the etalon is said etalon. 19. The etalon is coupled to a piezo element for piezoelectrically tuning the etalon.
Or _{F 2} laser according to 9. 20. The first etalon comprises two plates separated by a gap, the plates comprising CaF ₂ , MgF ₂ , LiF ₂ , LiF, Ba.
F _2, SrF _2, F 2 laser according to claim 1 or 9 including quartz and fluorine of doped silica material selected from the group of materials. 21. The first etalon comprises Invar®, Zerodur®, ultra low expansion glass,
And F ₂ laser according to claim 1 or 9 comprising two plates separated by one or more spacers including one or more materials selected from a group of materials consisting of quartz. 22. Further, F ₂ laser according to claim 1 or 9 along the optical path of the beam comprising an opening into said cavity. 23. The F _{2 according} to claim 22, wherein the aperture has a dimension approximately equal to but smaller than the beam dimension.
laser. 24. The method according to claim 24, wherein the aperture selects one of the plurality of closely spaced emission lines, wherein the aperture propagates the selected intensity line of maximum intensity within the acceptance angle of the resonator. can, and F ₂ laser according to claim 22 which is arranged to block any non-selected emission lines. 25. The semiconductor device according to claim 25, further comprising a second etalon for further narrowing the line width of the primary bright line, wherein the second etalon is provided in the first etalon.
The outer portion is arranged to maximize the transmittance of a central portion of the selected portion of the primary emission line transmitted by the etalon and to make the transmittance of the outer portion of the selected emission line relatively low. F ₂ laser according to suppress claim 9. 26. The semiconductor device according to claim 26, further comprising a second etalon for further narrowing the line width of the primary bright line, wherein the second etalon is provided in the first etalon.
Arranged as a resonant reflector for maximizing the reflectance of a central portion of a selected portion of the primary emission line transmitted by the etalon, and making the reflectance of an outer portion of the selected emission line relatively low. F ₂ laser according to suppress claim 9 wherein the outer portion Te. 27. The second etalon is part of the resonator that further couples the laser beam.
_2. The F2 laser according to 1. 28. The F _{2 of} claim 26, wherein the second etalon includes two plates, one of the two plates having a highly reflective internal surface for reflecting a laser beam as a highly reflective resonant reflector. laser. 29. _{F 2} laser according to any one of the preceding claims 1～3,9 or 25-26 second etalon is high finesse etalon. 30. The first etalon has a low finesse etalon, F ₂ laser according to claim 29. 31. The first etalon has a low finesse etalon, _{F 2} laser according to any one of claims 1～3,9 or 25-26. 32. Furthermore, in order to expand the beam prior to entering the etalon, F ₂ laser according to claim 9 including a beam expander in front of the etalon. 33. An F ₂ laser, comprising molecular fluorine that produces a spectral emission comprising a plurality of closely spaced emission lines in a wavelength range between 157 nm and 158 nm, including a primary emission line and a secondary emission line. A discharge chamber filled with a gas mixture; a plurality of electrodes coupled to a power supply circuit for generating a pulsed discharge for applying a voltage to the molecular fluorine; and a resonator including the discharge chamber; And wherein only the primary emission line is within the acceptance angle of the resonator and includes the secondary emission line so that only the primary emission line is amplified among the plurality of closely spaced emission lines. The above-mentioned 1 is set so that the bright line of the
A dispersive element arranged in a specific direction to disperse the plurality of closely-spaced bright lines including the secondary bright line and the secondary bright line; and An opening for selecting the primary emission line of the emission line,
An aperture that allows the selected emission line of maximum intensity to propagate within the acceptance angle of the resonator and is arranged to block any non-selected emission lines, including the secondary emission line; _{F 2} laser, including. 34. The apparatus of claim 34, further comprising means for narrowing the selected primary luminescent line, wherein the means for narrowing the selected primary luminescent line comprises a selected portion of the selected primary luminescent line having a maximum intensity. F ₂ laser according to claim 33 which is able, and arranged to suppress the outer portion of said selected primary emission line propagating within the acceptance angle of the resonator. 35. An arrangement in which the transmittance of a selected portion of the primary bright line is substantially maximized and the transmittance of an outer portion of the primary bright line is relatively low to substantially suppress the outer portion. whereby said _{F 2} laser, narrowband VU
To provide a V laser beam, line narrowed the primary emission line to emit a single wavelength laser beam having a narrow spectral line width than the line width of the free-running F ₂ laser the primary emission line F ₂ laser according to claim 33, further comprising an etalon to. 36. An arrangement wherein the reflectance of selected portions of the primary luminescent line is substantially maximized and the reflectance of the outer portion of the primary luminescent line is relatively low to substantially suppress the outer portion. whereby said _{F 2} laser, narrowband VU
To provide a V laser beam, line narrowed the primary emission line to emit a single wavelength laser beam having a narrow spectral line width than the line width of the free-running F ₂ laser the primary emission line F ₂ laser according to claim 33, further comprising an etalon to. 37. The method of claim 31, wherein only the primary emission line is within the acceptance angle of the resonator, and any other emission lines, including the secondary emission line, are dispersed outside the acceptance angle of the resonator. F ₂ laser according to any one of claims 33 to 36, further comprising a prism disposed toward the specific direction in order to disperse the emission lines of the plurality of tight spacing, including primary and secondary emission lines . 38. A method as claimed in any one of claims 34 to 35, further comprising a prism beam expander in front of the etalon to expand the beam before entering the etalon and reduce the divergence of the beam. _{F 2} laser according. 39. An F ₂ laser, comprising molecular fluorine that produces a spectral emission that includes a plurality of closely spaced emission lines in a wavelength range between 157 nm and 158 nm, including a primary emission line and a secondary emission line. A discharge chamber filled with a gas mixture, a plurality of electrodes coupled to a power supply circuit for generating a pulsed discharge for applying a voltage to the molecular fluorine, and a laser beam having a bandwidth of about 1 pm or less. A resonator including a discharge chamber, a transmission etalon, and a pair of resonant reflectors for generating, wherein the etalon substantially reduces the secondary emission line, The secondary emission line is configured to have a maximum transmittance and a relatively low transmittance of the secondary emission line, and thereby the F ₂
Laser, in order to provide a narrow-band VUV laser beams, said to emit a single wavelength laser beam having a narrow spectral line width than the bandwidth of the free-running F ₂ laser 1
F ₂ laser comprising: a resonator for selecting the next bright line. 40. The image forming apparatus further includes a second etalon for reducing the line width of the primary bright line, wherein the second etalon is provided with the first etalon.
The etalon is arranged so as to maximize the transmittance of a selected portion of the primary emission line transmitted by the etalon and to make the transmittance of an outer portion of the selected primary emission line relatively low to suppress the outer portion. _{F 2} laser according to claim 39. 41. The image forming apparatus further includes a second etalon for reducing the line width of the primary bright line, wherein the second etalon includes the first etalon.
The outer portion is arranged to maximize the reflectance of a selected portion of the selected primary emission line transmitted by the etalon and to relatively reduce the reflectance of an outer portion of the selected primary emission line. 40. The F of claim 39, wherein the portion is suppressed.
₂ lasers. 42. wherein for the second etalon further coupling out the laser beam, F ₂ laser according to claim 41 which is a part of the resonator. 43. The second etalon, for further reflecting the laser beam as a highly reflective resonator reflector, F ₂ laser according to claim 41 wherein a part of the resonator. 44. The first etalon comprises two plates, at least one outer surface of which has an anti-reflective coating thereon to minimize the reflectivity of the beam. _{F 2} laser according to any one of 41. 45. The method of claim 1, wherein only the primary emission line is within the acceptance angle of the resonator, and any other emission lines including the secondary emission line are dispersed outside the acceptance angle of the resonator. F ₂ laser according to claim 39, further comprising a prism disposed toward a particular direction in order to disperse the emission lines of the plurality of tight spacing, including primary and secondary emission lines. 46. A prism beam expander in front of said etalon for enlarging the cross-sectional dimension of said beam incident on said etalon, such that the divergence of said beam is reduced before entering said etalon. Claim 39 further comprising
_2. The F2 laser according to 1.