JP2003503860A - Molecular fluorine laser having a spectral line width of less than 1 pm - Google Patents

Abstract

SUMMARY A narrow band molecular fluorine laser system includes an oscillator and an amplifier, the oscillator generating a 157 nm beam having a linewidth of less than 1 pm, wherein the amplifier reduces the power of the beam by one or more. Increase more than predetermined like watts. The oscillator includes a discharge chamber filled with a laser gas containing fluorine molecules and a buffer gas, connected to a discharge circuit that supplies energy to the fluorine molecules, an electrode in the discharge chamber, and the discharge chamber. A resonator for generating a laser beam having a wavelength of about 157 nm. A line narrowing optical system for reducing the line width of the laser beam to less than 1 pm is included in the resonator and / or outside the resonator. The amplifier may be the same or a separate discharge chamber, using optical and / or electronic delays to time the pulses from the oscillator to reach the amplifier at a maximum in the amplifier discharge current. Good.

Description

Detailed Description of the Invention

PRIORITY This application relates to US provisional patent application 60 / 140,5, filed June 23, 1999.
No. 31, and US provisional patent application 60 / 204,0 filed May 15, 2000
No. 95 and US provisional patent application 60/162, filed October 29, 1999.
735 and US Provisional Patent Application 60/166 filed November 23, 1999.
, 967 and US provisional patent application 60/17 filed December 13, 1999
Claim priority to No. 0,342. This application gives priority to US provisional patent application 60 / 120,218 filed February 12, 1999 and US provisional patent application 60 / 119,486 filed February 10, 1999. Claim,
It is a continuation-in-part application of U.S. patent application Ser. No. 09 / 317,527 filed May 24, 1999. This application also claims priority to US provisional patent application 60 / 130,392 filed April 19, 1999, US patent application 09 / 550,558 filed April 17, 2000. It is a partial continuation application of the issue. All of the above-referenced priority applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION The present invention relates to a molecular fluorine laser system including a line enhancement element and a method of generating a VUV laser beam having a spectral linewidth of less than about 1 pm.

2. 2. Description of Related Art Vacuum UV microlithography is based on the short wavelength (157.6) of molecular fluorine lasers.
nm) to enable the formation of structures of 0.1 pm or less by photolithographic exposure in a semiconductor substrate. TFT annealing and micromachining applications can also be advantageously performed at this wavelength.

Given the limited selection of high quality optical materials available for manufacturing imaging lenses in this wavelength range, the minimum chromatic aberration requirement is that of laser sources for refractive and partially achromatic imaging systems. Limit the spectral linewidth to less than 1 pm. The possibility is that the spectral linewidth is between 0.1 pm and 0.2 pm and possibly even below 0.1 pm in the future. A conventional molecular fluorine laser emits a VUV beam with a spectral linewidth greater than 1 pm.

The drawback of narrowing the spectral linewidth in a laser is that it generally leads to a significant reduction in efficiency and output power. Thus, in the present invention, the desired high throughput for 157 nm wafer steppers or wafer scanners is achieved,
It will be appreciated that it would be advantageous to have a line-narrowed fluorine molecular laser emitting an output beam of less than 1 pm with an average high output power in the range of a few watts to 10 watts or more.

SUMMARY OF THE INVENTION Accordingly, a first object of the present invention is to provide a VUV laser system having a narrow linewidth, ie, a linewidth of less than about 1 pm, which forms small structures on a silicon wafer.

A second object of the invention is a VUV laser enabling sufficient throughput for VUV lithographic applications at 157 nm with a sufficient output power, ie a linewidth of 1 pm or less, exhibiting an output power of at least a few watts. Is to provide.

According to the above object, an oscillator and an amplifier are included, said oscillator generating a 157 nm beam having a linewidth of less than 1 pm, said amplifier predetermining the power of the beam to be greater than 1 or a few watts. Methods and apparatus are provided, such as narrow-band molecular fluorine laser systems, that scale above a specified amount. The oscillator comprises a discharge chamber filled with a laser gas containing fluorine molecules and a buffer gas, electrodes in the discharge chamber connected to a discharge circuit for supplying energy to the fluorine molecules, the discharge chamber and a line narrowing optical device. A resonator for generating a laser beam having a wavelength of about 157 nm and a linewidth of less than 1 pm.

The amplifier is preferably a discharge chamber filled with a laser gas containing molecular fluorine and a buffer gas, and the same or similar discharge that energizes the molecular fluorine, for example using an electrical delay circuit. An electrode connected to the circuit. The discharge of the amplifier is set to have a discharge current that is at or near maximum when the pulse from the oscillator reaches the amplifier discharge chamber.

The line narrowing optics is preferably tuned with respect to the maximum transmission of selected portions of the spectral distribution of the beam and the relatively low transmission of outer portions of the spectral distribution of the beam. Contains one or more etalons. A prism beam expander is preferably provided after the etalon that expands the beam incident on the etalon. Two etalons may be used and adjusted so that only a single interference order is selected.

The line narrowing optics may further include a diffraction grating selecting a single interference order of the etalon corresponding to a selected portion of the spectral distribution of the beam. The resonator further preferably comprises a gap within the resonator and in particular between the discharge chamber and the beam expander. The second gap may be provided outside the discharge chamber.

The line narrowing optical system may not include an etalon. For example, the line narrowing optics may instead only include a beam expander and a diffraction grating. The beam expander preferably comprises 2, 3 or 4 VUV transparent prisms in front of the diffraction grating. Said diffraction grating preferably has a high reflectivity surface which acts as a resonator reflector in addition to its role of diffracting the beam.

The line narrowing optics comprises an etalon output coupler tuned for maximum transmission of selected portions of the spectral distribution of the beam and relatively low transmission of outer portions of the spectral distribution of the beam. May be included. The system also preferably includes an optical system, such as a diffraction grating, a scattering prism or an etalon, that follows the beam expander and selects the single interference order of the etalon output coupler. The resonator preferably has one or more gaps that reduce stray light and divergence within the resonator.

In any of the above configurations including a diffraction grating, a high-reflectance mirror may be arranged after the diffraction grating, and the diffraction grating and the high-reflectance mirror may form a Littman arrangement. Alternatively, the diffraction grating may serve to retroreflect and scatter the beam in a Littrow arrangement. A transmission grating or grism may be used.

The buffer gas preferably regulates the pressure of the gas mixture sufficiently to increase the output energy for a given input energy, energy stability, gas and tube life, and / or pulse duration. It contains neon and / or helium. The laser system more particularly cooperates with the gas supply system to move the fluorine molecules into the discharge chamber, thereby replenishing the fluorine molecules into the discharge chamber, and in the discharge chamber. A processor for controlling the fluorine molecule concentration and keeping the fluorine molecule concentration within a predetermined range of optimum performance of the laser.

The laser system may further include a spectral filter between the oscillator and the amplifier, which further narrows a line width of an output beam of the oscillator. The spectral filter may include an etalon following the beam expander. Alternatively, the spectral filter may include a diffraction grating that scatters and narrows the beam. In the diffraction grating embodiment, the spectral filter may include a lens that focuses the beam onto a collimating optics through a slit before striking the beam expander-grating combination.

INCORPORATION BY REFERENCE The following is a citation list of references, each of which is in addition to those references cited above in the Priority Section, in the detailed description of the preferred embodiments below. Are disclosed by way of reference and disclose alternative embodiments of the elements or features of the preferred embodiments. Reference may be made to these references alone or in combinations of two or more to obtain variations of the preferred embodiments described in the detailed description below. Other patents, patent applications and non-patent references are cited in the description and, with the same effect as just described for the following references, are included in the preferred embodiment by reference. 1-U. Stams "Status of 157 nm 157 excimer laser" International Sematech 15
7 Workshop, February 15-17, 1999, Litchfield, Arizona, USA. 2-T. Hoffman, J. M. Huber, P.H. Das, S. Shora "micro lithography for high repetition rate _F 2 (157nm) prospects of the laser" International Sematech 157 workshop, February 15-17, 1999, the United States, Arizona,
Litchfield. 3-1-U. Stamm, I. Braggin, S.M. Gobokov, J. Klein Schmid, R.A. Patzel, E. Slovodchikov, K.K. Vogler, F.M. Boss and D. Busching "Excimer Laser for 157 nm Lithography" 24th International Microlithography Symposium, March 14-19, 1999, Santa Clara, CA, USA. 4-T. Hoffman, J. M. Huber, P.H. Das, S. Scholar “Revisiting F ₂ Laser for DUV Microlithography” 24th International Microlithography Symposium, March 14-19, 1999, Santa Clara, California, USA. 5-W. Mukenheim, B.C. Rukuru "Excimer Laser with Narrow Linewidth and Large Internal Beam Divergence" J. Phys. E: Sci. Instrum. 20 (1987) 1
394. 6-G. Grunefeld, H .; Schulter, P. Andersen, E. W. Rote “Operation of KrF and ArF Tunable Excimer Laser without Cassegrain Optics” Applied Physics B62 (1996) 241. 7-US patent application 09/3175, each of which is assigned to the same assignee as the present application
26, 09/343333, 60/122145, 60/140531, 60/162735, 60/166952, 60/171172, 60
/ 141678, 60/173993, 60/166967, 60/17
Nos. 2674 and 60/181156, and Kleinschmidt serial numbers not yet assigned, filed May 18, 2000, entitled "Laser speckle in photolithography due to controlled divergence of the spatial coherence of the laser beam. Patent application for "removal" and US patent specification No. 6005880. 8-Laser Focus / Electronic Optics, W. Reprinted from August 1987 Edition. Muequenheim “Seven ways to combine two excimer lasers”.

Detailed Description of the Preferred Embodiments Referring to FIG. 1, a VUV laser system, preferably a Fluorine Molecular Laser for Deep Ultraviolet (DUV) or Vacuum Ultraviolet (VUV) lithography, is shown schematically. TFT
Alternative configurations for laser systems used in other industrial applications such as annealing and / or micromachining are similar to and / or modified from the system shown in FIG. 1 and meet the requirements of the present application. As will be appreciated by those skilled in the art. To this end, alternative VUV laser systems and component arrangements are each assigned to the same assignee as the present application.
317695, 09/317526, 09/317527, 09/343
333, 60/122145, 60/140531, 60/162735
No. 60/166952, 60/171172, 60/141678, 6
0/1739393, 60/166967, 60/172674 and 60 /
No. 1811156 and a patent application for “Removal of laser speckle in photolithography by controlled divergence of spatial coherence of laser beam” filed May 18, 2000, to which Kleinschmidt serial numbers have not yet been assigned. And U.S. Pat. No. 6,0058,880.

The system shown in FIG. 1 generally comprises a laser chamber 2 having one or several pairs of main discharge electrodes 3 connected to a solid pulser module 4, and a gas treatment module 6. The solid-state pulser module 4 is powered by a high voltage power supply 8. The laser chamber 2 is surrounded by the optical module 10 and the optical module 12 to form a resonator. The optical modules 10 and 12 are connected to the optical control module 14
Controlled by.

The laser control computer 16 receives various inputs and controls various operating parameters of the system. The diagnostic module 18, as shown, preferably passes various parameters of the separated portion of the main beam 20 via an optical system, such as a beam splitter module 21, which deflects the small beam portion towards the module 18. Receive and measure. Beam 20 is preferably the laser output to an imaging system (not shown) and ultimately to a workpiece (not shown). Laser control computer 16 communicates with stepper / scanner computer 26 and other control units 28 via interface 24.

The laser chamber 2 contains a laser gas mixture and comprises one or several pairs of main discharge electrodes 3 and one or more preionization electrodes (not shown). Suitable main electrodes 3 are U.S. patent application Ser. Nos. 09 / 453,670, 60 / 184,705 and 60/1.
No. 28227, each of which is assigned to the same assignee as the present application and hereby incorporated by reference. Other electrode configurations are described in US Pat. Nos. 5,729,565 and 4,860,300,
Each of these is assigned to the same assignee, and other embodiments are described in US Pat. Nos. 4,691,322, 5,535,233 and 5,557,629, all of which are hereby incorporated by reference. included. The laser chamber 2 also includes a preionizer (not shown). Suitable preionization units are described in US patent application Nos. 60162845, 60/160182, 60/1.
27237, 09/535276 and 09/247887, each of which is assigned to the same assignee as the present application, and other embodiments are described in US Pat. Nos. 5,337,330, 5,818,865. Issue and 599
All of the above mentioned patents and patent applications, which are described in US Pat. No. 13,324, are hereby incorporated by reference.

The solid-state pulser module 14 and the high voltage power supply 8 supply the electrical energy of the compressed electrical pulse to the preionization electrode and the main electrode 3 in the laser chamber 2 and to the gas mixture. Suitable pulser modules and high voltage power supplies are described in US patent applications 60/149392, 60/198058 and 09.
/ 390146, and Osmanou et al., US Pat. No. and 602072
No. 3, each of which is assigned to the same assignee as the present application and is hereby incorporated by reference. Other alternative pulser modules have been described in US Pat.
0421, 5914974, 5949806, 5936988,
No. 6,028,872 and 5,729,562, each of which is hereby incorporated by reference. Conventional pulser modules can generate electrical pulses in excess of 3 Joules of electrical power (see the '988 patent, supra).

The laser cavity surrounding the laser chamber 2 containing the laser gas mixture comprises line-narrowing excimers or line-narrowing optics for molecular fluorine lasers, which line-narrowing is not desired, or , The line narrowing can be done in the front optics module 12 or if a spectral filter outside the resonator is used to narrow the linewidth of the output beam, it can be replaced by a high reflectivity mirror or the like in the laser system. Some modifications of the line narrowing optical system will be described in detail later.

The laser chamber 2 is sealed by a window transparent to the wavelength of the emitted laser radiation 14. The window may be a Brewster window or it may be aligned at different angles to the optical path of the resonant beam. The laser chamber,
A beam path to and from each of the optics modules 10 and 12 is defined by an enclosure 17
And 19 and from inside the enclosure, otherwise V
Practically removes water vapor, oxygen, hydrocarbons, fluorocarbons, etc. that strongly absorb UV laser radiation.

After a part of the output beam 20 has passed through the out coupler of the optical module 12, this output part impinges on a beam splitter module 21, which part of the beam is diagnosed by the diagnostic module 18. Or an optical system that allows a small portion of the outcoupled beam to reach the diagnostic module 18 and a main beam portion 20 to follow as the output beam of the laser system. Including. Suitable optics include beam splitters or partially reflective surface optics. One or more beamsplitters and / or HR mirrors and / or dichroic mirrors may be used to direct a portion of the beams to components of diagnostic module 18. Small for detection in diagnostic module 18 using holographic beam samplers, transmission gratings, partially transmissive reflective diffraction gratings, grisms, prisms, or other refractive, scattering and / or transmissive optics Beam part 22 to main beam 2
It may be separated from 0 so that most of the main beam 20 reaches the application process either directly or via the imaging system or otherwise. The output beam 20 may be transmitted at the beam splitter module and the reflected beam portion 22 may be directed at the diagnostic module 18, or the main beam 20 may be reflected and a small portion 22 transmitted to the diagnostic module 18. . The portion of the outcoupled beam that persists past the beamsplitter module 21 is the output beam 20 of the laser, which output beam 20 is for industrial or experimental applications such as workpieces for imaging systems or photolithographic applications. Propagate toward.

The enclosure 23 confines the beam paths of the beams 22 and 20 and keeps the beam paths free of light absorbing species. The smaller enclosures 17 and 19 confine the beam path between the chamber 2 and the optical modules 10 and 12. A preferred enclosure 23 and beam splitting module 21 is described in US patent application Ser. Nos. 09 / 343,333 and 6, incorporated herein by reference above.
0/140530 and US patent application 09/1 assigned to the same assignee
No. 31580 and US Pat. Nos. 5,559,584, 5,221,823, 5,763,855, 5,817,753 and 4,616,908, all of which are hereby incorporated by reference. For example, the beam splitting module 21 preferably also includes optics for filtering visible red light from the beam 22 so that practically only VUV light is received at the detector of the diagnostic module 18. Filtering optics may be included to filter red light from the output beam 20. Also, the inert gas purification is preferably flowed to the enclosure 23.

The diagnostic module 18 preferably includes at least one energy detector. This detector measures the total energy of said beam portion, which corresponds directly to the energy of the output beam 20. An optical configuration such as an optical attenuator, eg a plate or coating, or other optical system is formed in or near the detector or beam splitter module 21 and the intensity of the radiation impinging on the detector. , May control spectral distribution and / or other parameters (each of which is assigned to the same assignee as the present application, which is hereby incorporated by reference in US patent application Ser.
172805, 60 / 172,749, 60/166952 and 60/17
8620).

Certain other components of diagnostic module 18 are preferably wavelength and / or bandwidth detection components, such as monitor etalons or grating spectrometers (each assigned to the same assignee as the present application). United States Patent Application 09/416344, 6
0/186003, 60/158808 and 60/186960 and Rokai et al., Using "multi-element or tandem see-through hollow cathode lamps, filed May 10, 2000, with no serial number assigned yet. Absolute Wavelength Calibration of Lithography Lasers "US Pat. No. 490
No. 5243, No. 5978391, No. 5450207, No. 4926428,
See 5748346, 5025445 and 5978394. The wavelength and / or bandwidth detection and monitoring components are hereby included by reference).

Other components of the diagnostic module, such as those relating to gas control and / or output beam energy stability, are each assigned to the same assignee, which is hereby incorporated by reference in US patent application Ser. 484818 and 09/418
It may also include a pulse shape detector or an ASE detector as described in each of the '052 patents. For example, there may be a beam alignment monitor, such as that described in US Pat. No. 6,014,206, incorporated by reference.

The processor or control computer 16 determines, among other input or output parameters of the laser system and output beam, pulse shape, energy, spontaneous emission amplified light (ASE), energy stability, energy over burst mode operation. Receive and process some values of shoot, wavelength, spectral purity and / or bandwidth. The processor 16 also controls the line narrowing module to adjust wavelength and / or bandwidth, or spectral purity, and controls the power supply and pulser modules 4 and 8, preferably moving average pulse power. Alternatively, the energy is controlled so that the amount of energy at the point on the workpiece stabilizes around a desired value. In addition, the computer 16 controls the gas processing module 6 including gas supply valves connected to various gas sources.

The laser gas mixture is initially filled into the laser chamber 2 during a fresh fill. The gas mixture for the highly stable excimer laser according to the preferred embodiment uses helium or neon or a mixture of helium and neon as buffer gas, depending on the laser. Suitable gas mixtures are described in US Pat. Nos. 4,393,405 and 4,977,573 and US patent application Ser. No. 09/3317526.
No. 09/513025, 60/12785, 09/418052, 6
0/159525 and 60/160126, each of which is assigned to the same assignee and is hereby incorporated by reference. The concentration of fluorine in the gas mixture is 0.003% to 1.0.
It may range up to 0%, preferably about 0.1%. Additional gas additives such as noble gases may be added for increased energy stability and / or as an attenuator as described in the '025 application mentioned above. Xenon and / or argon additives may be used, especially for F2 lasers. The concentration of xenon and / or argon in the gas mixture may range from 0.0001% to 0.1%. For ArF lasers, a xenon or krypton additive having a concentration between 0.0001% and 0.1% may be used.

The halogen and noble gas injection procedure, the total pressure regulation procedure and the gas exchange procedure are preferably carried out using a gas treatment module 6 comprising a vacuum pump, a valve network and one or more gas compartments. . The gas treatment module 6 receives gas via gas lines connected to gas containers, tanks, cans and / or bottles. Suitable gas treatment and / or replacement procedures for the preferred embodiments other than those specifically described herein are disclosed in U.S. Pat. Nos. 4,977,573 and 5,396,514, each of which is assigned to the same assignee as the present application. / 124785, 09/41805
2, 09/3799034, 60/171717 and 60/159525 and U.S. Pat. Nos. 5,978,406, 6014398 and 602888.
No. 0, each of which is hereby incorporated by reference. The Xe gas supply may be included either inside or outside the laser system according to the '025 application mentioned above.

A general description of the line narrowing features of some embodiments of the present invention will now be given first, followed by a detailed discussion with reference to FIGS. 2a-6b. Example line narrowing optics that provide a relatively high degree of dispersion for narrow band lasers such as for use with catadioptric optical lithographic imaging systems are included in an optical module 10 that includes a beam expander, an optional etalon and a diffraction grating. . As mentioned above, the front optics module may include similar line narrowing optics (each assigned to the same assignee, which is hereby included by reference 60/166).
See 277, 60/1739393 and 60/166967 applications). For semi-narrow band lasers that are not the subject of the invention, such as used with total internal reflection imaging systems, the diffraction grating may be replaced by a high reflectance mirror and a low degree of dispersion may be generated by a dispersive prism. . Semi-narrow band lasers typically have an output beam linewidth of greater than 1 pm, depending on the unique free-running band of the laser, and in some laser systems, may be as high as 100 pm.

The beam expander of the exemplary line narrowing optics of the optics module described above preferably includes one or more prisms. The beam expander may include lens assemblies or other beam expanding optics such as a convergent / divergent lens pair. The diffraction grating or high-reflectance mirror is preferably rotatable so that the wavelength reflected during the acceptance angle of the resonator can be selected or adjusted. Instead, the diffraction grating or other optics or the entire line narrowing module is each assigned to the same assignee, which is hereby incorporated by reference into 60/178445 and 09/3.
The pressure may be adjusted as described in the 17527 application. The diffraction grating may be used both to disperse the beam to achieve a narrow bandwidth and, preferably, to retroreflect the beam towards the laser tube. Alternatively, a high-reflectivity mirror that receives the reflection from the diffraction grating and reflects the beam back towards the diffraction grating to doubly disperse the beam is placed after the diffraction grating or the diffraction grating. The grating may be a transmission diffraction grating. One or more dispersive prisms may be used and one or more etalons may be used.

Many can be used depending on the type and degree of line narrowing desired and / or the choice and adjustment, and in particular depending on the particular laser in which the line narrowing optics are to be installed. Alternative optical arrangements exist. To this end, U.S. Pat. Nos. 4,399,540, 4,905,243 and 52, each assigned to the same assignee as the present application.
26050, 5559816, 5659419, 5663973, 5761236 and 5946337 and U.S. patent application Ser. No. 09/3176.
95, 09/130277, 09/244554, 09/317527, 09/073070, 60/124241, 60/140532, 60.
/ 147219, 60/140531, 60/147219, 60/17
0342, 60 / 172,749, 60/178620, 60/17399
No. 3, 60/166277, 60/166967, 60/167835,
60/170919 and 60/186096 and U.S. Pat. No. 5,095.
No. 492, No. 5648822, No. 5835520, No. 5852627, No. 5856991, No. 5898725, No. 5901163, No. 591784.
No. 9, 5790082, No. 5404366, No. 4975919, No. 51
No. 42543, No. 5596596, No. 5802094, No. 4856018, No. 59700082, No. 5978409, No. 5999318, No. 5150.
370 and 4829536 and German patent specification DE 29822090.3.
, Respectively, which are hereby incorporated herein by reference.

The optics module 12 is preferably a beam 2 such as a partially reflective resonator reflector.
Includes means to outcouple 0s. The beam 20 may otherwise be outcoupled, such as by an intra-cavity beam splitter, or a partially reflective surface of another optical element, the optical module 12 in this case including a high reflectance mirror. . The optical control module 14 connects the optical modules 10 and 12 to the processor 1
6 and receives and interprets the signal from 6 and controls it to initiate the realignment or relocation procedure (see the '241,' 695, 277, 554 and 527 applications referenced above).

A detailed description of the line narrowing configuration of the oscillator element of the laser system according to the preferred embodiment will now be described with reference to FIGS. 2a-2f. Some embodiments of laser system oscillators using line narrowing techniques for molecular fluorine lasers that meet, or nearly meet, the first object of the present invention are shown in Figures 2a-2f.

FIG. 2 a comprises a discharge chamber 2 comprising preferably fluorine molecules and a buffer gas comprising neon, helium or a mixture thereof (see application 09/317526), in which the main discharge is located. 1 shows an oscillator of a laser system according to the first embodiment with an electrode pair 3 (not shown) and a preionization arrangement (not shown). Figure 2a
The system shown in also includes a prism beam expander 30 and a diffraction grating 32 in a Littrow configuration. The beam expander 30 may include one or more prisms, preferably several prisms. The beam expander serves to reduce the divergence of the beam incident on the diffraction grating and thus improve the wavelength resolution of the wavelength selector. The diffraction grating is preferably a high blaze angle echelle diffraction grating (see 60/170342 application, incorporated by reference).

The illustrated system removes stray light, reduces broadband background, and serves to reduce the linewidth of the beam by lowering the acceptance angle of the resonator 34. In the resonator. Alternatively, one gap 34 may be included on either side of the chamber 2 or the gap 34
Need not be included. An exemplary gap 34 is described in US Pat. No. 5,161,238, which is assigned to the same assignee and is hereby incorporated by reference (see also the 09/130277 application incorporated by reference). Want).

The system of FIG. 2 a also includes a partially reflective outcoupling mirror 36. The outcoupling mirror 36 may be replaced by a high reflectivity mirror and the beam may otherwise be polarized, or otherwise within the resonator, such as the surface of a prism, window or beam splitter. Optical surface may be used (see, eg, US Pat. No. 5,150,370, incorporated by reference).

The system of FIG. 2b includes the chamber 2 described above with respect to FIG. 2a, a gap 34, a partially reflective outcoupling mirror 36, and a beam expander 30. The system of FIG. 2b also includes a diffraction grating 38 and a high reflectance mirror 40. Diffraction grating 38 preferably differs from diffraction grating 32 of FIG. 2a either in its orientation with respect to the beam, its arrangement such as its blaze angle, etc., or both. The laser beam is incident on the diffraction grating 38 at an angle closer to 90E with respect to the diffraction grating 32. This angle of incidence is, in practice, preferably very close to 90E. This is an arrangement referred to here as the Littman arrangement. The Littman arrangement increases the chromatic dispersion of the diffraction grating 38. After passing through or being reflected by the diffraction grating 38, the diffracted beam is reflected by the high reflectance mirror 40. The adjustment of the wavelength is preferably achieved by tilting the high-reflecting mirror 40. As described above with respect to the exemplary arrangement, adjustment may otherwise be accomplished by rotating other optics or pressure adjusting one or more optics, or otherwise. , May be accomplished as will be appreciated by those skilled in the art.

FIG. 2 c shows another embodiment of an oscillator, preferably having a laser chamber 2, a gap 34, an outcoupler 36, a beam expander 30, and a Littrow diffraction grating 34, as described above. It is shown diagrammatically. In addition, the system of FIG. 2c includes one or more etalons 42, for example two, which provide high resolution line narrowing, and the diffraction grating 32 serves to select a single interference order of etalons 42. Etalon 42
May be arranged at various positions in the resonator, that is, at positions other than those shown. For example, the prism of the beam expander 30 may be arranged between the etalon 42 and the diffraction grating. The etalon 42 may be used as an output coupler, as described in more detail below with reference to Figures 2e-2f. Etalon 4
The arrangement of Figure 2c, including 2 (as well as later Figure 2d), is each assigned to the same assignee, and is hereby incorporated by reference, US Patent Application No. 60/162735, 60.
No. 178445 or 60/158808.

FIG. 2d shows another embodiment of a laser system having more than one etalon, for example two etalons are illustrated. The system of FIG. 2d replaces the grating 32 with a high reflectivity mirror and the etalon 43 is not available to select the single interference order of the etalon 43 as in the system of FIG. 2c except that it is configured differently by omitting The free spectral range of the etalon 43 is instead set so that one of the etalons 43, preferably the first etalon after the beam expander 30, selects a single order of the other etalon 43, eg the second etalon 43. Adjust to. The suitably arranged second etalon 43 can thus have a smaller free spectral range and a higher wavelength resolution. Several further variations of the etalon 43 of the system of FIG. 2d are hereby incorporated by reference into US Pat. No. 4,856,018.
Can be used as described in the issue.

2e and 2f each show an embodiment similar to the arrangement described above with reference to FIGS. 2a and 2b, which differs in that the partially reflective outcoupler mirror 36 is replaced by a reflective etalon outcoupler 46. The etalon out coupler 46 is shown in FIG.
And a 2f grating 32 or 38 in combination with the beam expander 30, the grating 32 or 38 selecting a single interference order for the etalon outcoupler 46. Alternatively, one or more dispersive prisms or other etalons may be used in combination with the etalon outcoupler 46 to select the single interference order of the etalon 46. The diffraction grating 32 or 38 limits the wavelength range to the single interference order of the out-coupler etalon 46. 2e and / or 2f
2e, which can be used in combination with the system described above in FIG.
And 2f system variants are described in US Pat. Nos. 6,028,879, 360.
No. 9586, No. 3471800, No. 3546622, No. 5901163,
No. 5856991, No. 5440574 and No. 5479431; Leng Ferner, Generation of Tunable Pulsed Microwave Radiation by Nonlinear Interaction of Nd: YAG Laser Radiation in GaP Crystals, Optics Letter, Vo
l. 12, No. 3 (March 1987) and S. Marcus, Cavity Damping and Coupling Modulation of Etalon-Coupled CO ₂ Lasers, J. Am. Appl. Phys
． , Vol. 53, No. 9 (September 1982) and the physics and technology of laser cavities, author D.M. R. Hall and P. E. Jackson, page 244, each of which is hereby incorporated by reference.

The materials used for the prisms of the beam expander 30, the etalons 42, 43, 46, and the laser window in all of the above-described embodiments shown and described with reference to FIGS. 2a-2f are preferably It should be highly transparent at wavelengths below 200 nm, such as at the 157 nm output radiation wavelength of molecular fluorine lasers. The material is also capable of withstanding long-term exposure to UV light with minimal degradation effects.
Examples of materials such as these include CaF ₂ , MgF ₂ , BaF, BaF ₂ , LiF,
LiF ₂ and SrF ₂ . Also, in all of the above embodiments of Figures 2a-2f, many optical surfaces, particularly those of the prisms, are preferably used to minimize reflection losses and increase their life. One or more of which have antireflective coatings.

Further, as described in the above general description, the gas component relating to the F ₂ laser in the above configuration uses helium, neon, or a mixture of helium and neon as a buffer gas. The concentration of fluorine in the buffer gas is preferably in the range of 0.003% to about 1.0%, preferably about 0.1%. Xenon, and / or argon, and / or oxygen, and / or krypton,
And / or minor additions of other gases may be used to increase the energy stability, burst control or output energy of the laser beam. The concentration of xenon, argon, oxygen, or krypton in the mixture is 0.0001% to 0.
． It may range up to 1%. Some alternative gas components, including trace gas additives, are described in US patent application Ser. Nos. 09/513025 and 09/317526, each of which is assigned to the same assignee and is hereby incorporated by reference. Included by.

All of the oscillator configurations shown in FIGS. 2a-2f can be advantageously used to generate a VUV beam 20 having a wavelength of about 157 nm and a linewidth of about 1 pm or less. Some of these configurations with an output line width of less than 1 pm already fulfill the first object of the invention with respect to said line width. These oscillators are shown in FIG.
It may be used with other elements, such as amplifiers, as described below in -6b, to meet the second objective of the invention, ie to achieve sufficient output power for practical throughput in 157 nm lithography. Other oscillators that generate line widths of 1 pm or more can be used advantageously in combination with other line narrowing elements, as will be described below in FIGS. 3a-4b, to meet the first objective,
It may be used with an amplifier as described in embodiments a-4b to meet the second objective.

FIG. 3 a shows diagrammatically in block form a laser system according to a preferred embodiment of the present invention in which a narrower linewidth than the output by the oscillator 48 is desired and a higher power than the output by the oscillator 48 is desired. In order to reduce the line width, the oscillator 48
Of the output beam 20 is directed through a spectral filter 50. Beam 20 is directed through amplifier 52 to increase the output power.

The system of FIG. 3 a includes a line narrowing oscillator 48, a spectral filter 50, and an amplifier 52. Various preferred configurations of spectral filter 50 are shown in Figures 3b-3d.
Will be described later. Oscillator 48 of FIG. 3a is an electric discharge molecular fluorine laser that produces a spectral linewidth of about 1 pm, preferably one of the configurations described above with respect to FIGS. 2a-2f, or a variation thereof as described above, or , As would be understood by one of ordinary skill in the art as found in one or more references incorporated by reference above. The oscillator 48 is followed by a spectral filter 50 which transmits light in a narrower spectral region, ie below the linewidth of the output beam 20 from said oscillator, ie below about 1 pm. Finally, the transmitted beam is amplified in an amplifier 52 in response to the separate discharge chambers to produce an output beam 54 that meets the first and second objectives of the present invention. Preferably, the oscillator and amplifier discharges are each assigned to the same assignee, thereby delaying circuits and advantages as described in US patent application 60/204095 and US patent specification No. 6005880, each of which is hereby incorporated by reference. Synchronize using a solid-state pulser circuit.

The spectral filter 50 preferably comprises one of the arrangements shown in Figures 3b-3d. A prism, a diffraction grating, a grism, a holographic beam sampler, an etalon, a lens, a gap, a beam extract, preferably for narrowing the line width of the input beam 20 without consuming a substantial portion of the energy of the input beam 20. Those skilled in the art will appreciate that variations using any of a number of combinations of pandas, collimating optics, etc. would be advantageous.

FIG. 3b includes a beam expander followed by one or more etalons 58, resulting in an output beam having a linewidth practically narrower than the linewidth of the input beam 20 of, for example, about 1 pm or less, 1 illustrates an embodiment of a first spectral filter 50 that meets a first objective. Each etalon 58 comprises two partially reflective surfaces of reflectivity R separated by a gap, preferably of gas filled, of thickness D. Etalon T (λ)
The transmission spectrum of is described by a periodic function of wavelength λ. ^{T (λ) = (1+ (} 4F 2 / B 2) sin (2BnDcos (l) / λ)) - 1 (1) where, n, the refractive index of preferably an internal gas material satisfying etalon 58 Where l is the tilt angle of the etalon 58 with respect to the beam, and F is the finesse of the etalon 58 defined as follows. F = BR ^1/2 / (1-R) (2)

The reflectivity R and the spacing D of the etalon are chosen such that only a single maximum transmission overlaps the emission spectrum of the broadband oscillator. For example, if the finesse of the etalon 58 is selected to be 10, the spectral width of the highest transmittance is approximately 1/10 of the free spectral range (FSR) of the etalon 58. Therefore, the selection of the free spectral region of 1 pm is such that the line width of the oscillator (48) output (about 1 pm) is
Slightly narrower than twice SR, it produces a transmitted beam with a spectral linewidth of 0.1 pm without sidebands.

The use of multiple etalons 58 allows for a higher contrast ratio,
This contrast ratio is defined as the ratio between the maximum transmittance and the transmittance at a wavelength intermediate between the maximum transmittances. This contrast ratio for one etalon is (1
Almost equal to + 4F ² / B ² ). Higher finesse values lead to higher contrast. For several etalons 58, the total contrast ratio is (1 + 4F ² /
B ² ) ⁿ , where n is the number of etalons 58. In addition, the spectral width of the maximum transmission decreases as the number of etalons 58 used increases. Disadvantages of using some etalons 58 include high cost and complexity of the device and increased optical loss.

The beam expander 56 shown in FIG. 3 b acts to reduce the divergence of the beam incident on the etalon 58. From equation (1), it follows that a change in the beam incidence angle I causes a wavelength shift at which maximum transmission occurs. Assuming an FSR of 1 pm, the etalon spacing is D = 1.2 cm. If the transmission interference spectrum of the etalon 58 is its maximum at normal incidence (l = 0), the angle 1 at which the transmission spectrum again reaches a maximum is 1 to (8 / nD) ^1/2 = 3. 6
It is mrad. Therefore, the spectral filter 50 shown in FIG. 3b is preferably configured such that the divergence of the beam is below l, preferably by a factor comparable to the finesse F of the etalon 58. Since the output of the oscillator 48 is less than 1 because a typical molecular fluorine laser is a few milliliters, the beam expander 56 is used to reduce this dispersion from the above-described typical 1. Understand the benefits. It is also suitable to use one or more gaps 34 in the oscillator 48 to reduce its power dispersion (see the 09/130277 application referenced above).

The gap between the plates of the etalon 58 is preferably filled with internal gas. Tuning the transmission wavelength is accomplished by varying the pressure of the gas, as described in the 09/317527 application referenced above. In addition to pressure and rotational adjustments of the etalon's output transmission spectrum, the etalon 58 may be piezoelectrically adjusted to geometrically change the gap spacing.

FIG. 3c shows the spectral filter 5 of FIG. 3a, which generally uses a diffraction grating 60.
2 schematically shows a second embodiment of No. 0. There are other ways of constructing the spectral filter 50 according to the second embodiment using a diffraction grating 60, but one example is shown in FIG. 3c and is described here. The spectral filter 50 shown in FIG. 3c is a Cerny tuner spectrometer modified to achieve high resolution. Lens 6
The input beam 20 focused by 1a passes through the input slit 62a and then enters the collimating mirror 64. After being reflected from the mirror 64, the beam enters the beam expander 66 and then the diffraction grating 60. The beam is dispersed and reflected from diffraction grating 60, after which the beam traverses beam expander 66 again, through output slit 62b and from collimating mirror 64 at or near the focal point of lens 62b. To be done. At this time,
The output beam 59 has a line width that is practically narrower than the line width of the input beam 20, which is, for example, about 1 pm, i.

The diffraction grating 60 is preferably a high-blaze echelle diffraction grating 60. The chromatic dispersion of this preferred diffraction grating 60 is described by the following equation. λ / dl = (2 / λ) tanl (3) where l is the incident angle. The spectral width Δλ of the transmitted beam is defined by the diffraction grating 6
Zero dispersion dλ / dl, magnification M of the prism expander 66, focal length L of the collimating mirror 64, and width d of the slits 62a, 62b of the spectrometer.
Determined by and. Δλ = d (LMdλ / dl) -1 (4)

For example, using an Echelle grating 60 with an incident angle 1 of 78.6E, L = 2m and M = 8, the slit width d that achieves a resolution of 0.1 mm for the spectral filter 50 of FIG. d = about 0.1 mm. Therefore, it is preferable to reduce the divergence of the oscillator 48 in order to increase the transmission of the beam 20 through the input slit 61a. This can be advantageously achieved using a gap in the resonator of oscillator 48 (see again the 09/130277 application mentioned above).

A third example of a spectral filter 50 that can be used is shown in FIG. 3d. The spectral filter 50 of FIG. 3d is similar to the spectral filter shown in FIG.
Instead of the collimating mirror 64 used in the embodiment of FIG.
8 is used in the embodiment of FIG. 3d. The advantage of the embodiment of Figure 3d is its simplicity and the absence of astigmatism introduced by the mirror 64 of Figure 3c at non-zero angles of incidence.

At the moment when the gain of the amplifier 52 is at or near its maximum value, the amplifier 52
It is now repeated that synchronization of the electrical discharge pulses in chamber 2 of oscillator 48 and amplifier 52 is preferred to ensure that the line narrowing optical pulse from oscillator 48 arrives in chamber 2 of It is useful. In addition, this preferred synchronization timing should be replicable between pulses, giving high energy stability of the output pulse. A preferred embodiment of the electronic circuitry that enables this precise timing control is described in the above-mentioned US Pat. No. 6,0058,80 and US patent application 60/204095.

FIG. 4 a illustrates the use of a single discharge chamber 70 to provide gain media for both oscillator and amplifier. The arrangement of FIG. 4a includes a discharge chamber 70 within a resonator that includes a high reflectivity mirror 72 and a partially reflective outcoupling mirror 74. A pair of gaps 34 are also included as described above to match the divergence of the resonator of oscillator 48.
A small portion of the discharge voltage cross section is used to generate a non-narrowed beam 76 with this oscillator configuration. It may also include one or more line narrowing components having this oscillator configuration, or the oscillator according to the description above with respect to Figures 2a-2f may be modified.

Similar to the embodiment shown and described with respect to FIG. 3a, this non-narrowed output is preferably a spectral filter 5 which is one of the embodiments described in FIGS. 3b-3d.
Aim through 0. Given the significant time it takes for the beam to traverse the spectral filter 50 (eg, a few nanoseconds), it is preferable to adjust the arrival time of the filtered pulse with respect to a second maximum of discharge current. is there. To achieve this temporal adjustment, an optical delay line is preferably inserted after the spectral filter 50. One of those described in US patent application 60/130392, the delay line being assigned to the same assignee and hereby incorporated by reference.
You can choose one.

4b (i)-(iii) show the current through the discharge gap and the non-narrowed beam 76.
, And the output 59 of the oscillator-amplifier system, each as a function of time. The current exhibits several cycles of oscillation, as shown in Figure 4b (i). Figure 4
The optical pulse shown in b (ii) evolves towards the end of the first maximum of current (a). The second maximum of the current separates from the first maximum by about 20 nanoseconds, thus providing sufficient time for beam 76 to traverse spectral filter 50 and additional optical delay line 78. This discussion of maximum continuous timing in the electrical discharge current shows how an additional optical delay line 78 can be used to advantage to precisely adjust the arrival time of the pulse in chamber 70 (amplifier). .. The line-narrowed beam from the spectral filter 50, whose temporal pulse shape is shown in FIG. 4b (iii), is therefore the same as in FIG.
A beam 59 that overlaps with and is amplified by the second maximum b of the current shown in b (i) and is thus line narrowed, ie, sufficiently narrower than 1 pm, is output with sufficient power,
The first and second objects of the present invention are satisfied.

FIG. 5 a shows the use of a line narrowing oscillator followed by a power amplifier formed in a separate discharge chamber. Any of the embodiments shown and described, including those discussed with respect to the exemplary embodiments, patents and publications included by reference, and the embodiments described with respect to FIGS. Can be used to narrow the An example of a suitable line narrowing oscillator 48 is described in Figures 5b-5f.

The line-narrowing oscillator 48 shown diagrammatically in FIG. 5 (b) is preferably US Pat. No. 5,559,816, DE 2982, each of which is incorporated by reference.
2090.3, U.S. Pat. No. 4,985,898, U.S. Pat. No. 515.
The prism beam expander 30 and the diffraction grating 32 described in any of 0370 and U.S. Pat. No. 5,852,627 are used. Alternatively, a Littman arrangement may be used (see above discussion regarding FIG. 2b). 2a-4a
, The additional gap 34 in the resonator is
It reduces the divergence of the beam and thus advantageously increases the resolution of the wavelength selector (see again the 09/130277 application for details).

The embodiment shown in FIG. 5c utilizes multiple etalons 43 as wavelength selective elements (see FIG. 2d). The prism beam expander 30 in combination with the gap 34 helps reduce the beam divergence at the etalon 43,
Therefore, the resolution of the wavelength selector is improved. In addition, the prism beam expander 30 reduces the intensity of the beams in certain areas of the surface of the etalon 43, thus extending their life.

5d-5e show alternative arrangements, each including an RF or microwave pumped optical waveguide laser as the oscillator. The arrangement of Figure 5d is preferably a pair of RF electrodes 80.
And an optical waveguide 82, which preferably comprises a ceramic capillary filled with a laser active gas mixture. Any of the resonator arrangements shown in Figures 2a-5c may be used in this embodiment, in which the discharge chamber 2 is shown in Figure 5d.
The RF excitation optical waveguide arrangement shown in FIG. Features of optical waveguide lasers that can be used in the arrangements of FIGS. P. Kristenson, Small Self-Contained ArF Laser, Performing Organization Report No. AFOSR IR 95-
0370; Ishihara and S.M. C. Lin, Microwave Pump High Pressure Gas Laser, Applied Physics, B48, 315-326 (1989); and Ohmi, Tadahiro and Tanaka, Nobuyoshi, Excimer Laser Oscillation Device and Method, Excimer Laser Exposure Device, and Laser Tube, European Patent Application Publication See in specification 0820132A2, each of which is hereby incorporated by reference. RF-pumped lasers are generally discussed, for example, in Kirt Bondery, "Shielded Carbon Dioxide Laser Achieves New Power Levels," thereby incorporated by reference, Laser Focus World, August 1996, pages 95-100. Operating with a carbon dioxide gas medium as described above.

The particular arrangement shown in FIG. 5d includes the prism beam expander 30 and the diffraction grating 32 in a Littrow arrangement. A Littman arrangement including a diffraction grating 38 and an HR mirror 40 may be used here (see Figures 2b and 2f). In particular,
Also included is a pair of gaps 34 that coordinate the oscillations of the resonator. The partially reflective mirror 365 outcouples the output beam 20. An etalon outcoupler 46 may be used in place of mirror 36 (see Figures 2e-2f).

The arrangement shown diagrammatically in FIG. 5e is such that the diffraction grating comprises one or more etalon 4
3 and the same as in FIG. 5d, except that the HR mirror 44 was replaced. Diffraction gratings 32 or 38 may be used with etalon 43 and etalon outcoupler 46 may be used in place of partially reflecting mirror 36.

The advantage of this RF excitation optical waveguide type laser is its long pulse which enables more efficient line narrowing because the line width is almost inversely proportional to the number of round trips of the beam in the resonator. In addition, the RF pumped optical waveguide laser has a small discharge width (about 0.
5 mm), which allows a high angular resolution of the wavelength selector depending on the prism of the beam expander 30 and the diffraction grating 32. This is shown in Figures 5d-5e.
Both of the embodiments shown in are applicable.

FIG. 5f schematically illustrates another source of a narrow linewidth beam that can be used in accordance with the present invention and act as the oscillator 48 in the embodiment of FIG. 5a. Figure 5f
Of a diode, for example, as described in US Pat. No. 6,0026,979, which is assigned to the same assignee and is hereby incorporated by reference, or otherwise known to those skilled in the art. It includes a solid-state laser 85, such as a pumped Nd: YAG laser or other such type of laser, having a third harmonic output at 355 nm. The fixed laser 85 pumps a narrow linewidth tunable laser 86, such as a die laser or an optical parametric oscillator, for example about 472.
Radiate 9 nm. This 472.9 nm radiation is focused into a gas cell 88 containing a mixture of metal halide and an inert gas to generate a third harmonic beam at 157.6 nm. The third harmonic generation in such gases is described by Kang A. et al., Each of which is hereby incorporated by reference. H. Young J. et al. F. Bjoklung G. C. Harris S. E. , A physical review letter, v. 29,
985 (1972) and Kung A. H. Young J. et al. F. Harris S. E. Applied Physics Letter, v. 22, page 301 (1973).

6 a and 6 b schematically show another embodiment in which part of the discharge volume of the discharge chamber 2 is used as part of the oscillator for line narrowing and the same discharge chamber is used as the amplifier 52. . The arrangement of Fig. 6a is similar to that shown in Fig. 4a, except that the line width of the beam 30 is narrowed within the resonator of the oscillator and preferably no spectral filter 50 is used. Alternatively, the spectral filter 50 may be used in addition to the line narrowing optics of the oscillator of Figure 6a. Again, the line-narrowing arrangement of the oscillator may be configured as described in any of the above descriptions (see in particular FIGS. 2a-2f, 5c and 5f), or any patents, Generate an output beam 20 that is narrow enough to meet the first object of the invention, as described in any of the applications or publications, or otherwise modified as understood by one of ordinary skill in the art. You may. The output beam 20 from the oscillator is expanded by an external beam expander 90, which preferably comprises one or more prisms and, alternatively, a lens arrangement.

The expanded beam 92 is then directed through the delay line 78 ('392
(See application), the pulse is synchronized with the amplification maximum of chamber 70, as described above. The optical delay line 78 serves to fine tune the arrival time of the light pulse at the amplifier portion, similar to the embodiment shown and described with respect to Figures 4a-4b (iii). The expanded beam 20 then advantageously fills the remaining practical part of the discharge cross section.

In the above embodiment, the gas mixture in the discharge chamber 2, 70 of the oscillator is adjusted to obtain the longest possible pulse. In addition, the discharge current waveform can be modified by carefully introducing impedance mismatches in the pulse forming network and the discharge gap. The impedance mismatch results in longer discharge times and thus longer light pulses. The lower gain resulting from such a modification implies a lower efficiency of the oscillator. However, in the embodiments discussed above, the amount of reduction in the output power of the oscillator recovers in the amplification stage.

While exemplary drawings of the invention and particular embodiments have been described and illustrated, it should be understood that the scope of the invention is not limited to the particular embodiments discussed. Therefore, the above embodiments should be considered as illustrative rather than limiting, and variations on these embodiments may be departed by those skilled in the art from the scope of the invention described in the claims and their equivalents. It should be understood that it can be formed without.

In addition, in the method claims, steps have been arranged in selected typographical columns. However, steps are performed except for those steps in which the columns are selected and arranged for typographical convenience and the particular order of the steps is clearly stated or understood to be necessary by one of ordinary skill in the art. It is not intended to imply any particular order.

[Brief description of drawings]

FIG. 1 schematically illustrates a molecular fluorine laser system according to a preferred embodiment.

2a-f schematically show some other embodiments according to the first aspect of the invention, including various line narrowing resonators and techniques utilizing a line narrowing oscillator of a molecular fluorine laser. .

FIG. 3 a schematically shows a preferred embodiment according to the second aspect of the invention including an oscillator, a spectral filter in various configurations and an amplifier, and b-d a spectral filter according to the second aspect of the invention. Figure 6 schematically shows another embodiment of.

FIG. 4 a schematically shows another embodiment according to the second aspect of the invention comprising a single discharge chamber providing a gain medium for both the oscillator and the amplifier and having a spectral filter in between, b ( i)-(iii) respectively show waveforms of discharge current, non-narrowed beam intensity, and output beam intensity according to another embodiment of FIG. 3a.

FIG. 5 a schematically shows a preferred embodiment according to the third aspect of the invention, including a line narrowing oscillator followed by a power amplifier, and b-f, a line narrowing oscillator according to the third aspect of the invention. Figure 6 schematically shows another embodiment of.

6 a-b schematically show another embodiment according to the fourth aspect of the invention, including a single discharge chamber providing a gain medium for both the oscillator for line narrowing and the amplifier.

[Procedure amendment]

[Submission date] January 17, 2002 (2002.17)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Contents of correction]

Title: Fluorine molecular laser having a spectral linewidth of less than 1 pm

[Claims]

Detailed Description of the Invention

PRIORITY This application relates to US provisional patent application 60 / 140,5, filed June 23, 1999.
No. 31, and US provisional patent application 60 / 204,0 filed May 15, 2000
No. 95 and US provisional patent application 60/162, filed October 29, 1999.
735 and US Provisional Patent Application 60/166 filed November 23, 1999.
, 967 and US provisional patent application 60/17 filed December 13, 1999
Claim priority to No. 0,342. This application gives priority to US provisional patent application 60 / 120,218 filed February 12, 1999 and US provisional patent application 60 / 119,486 filed February 10, 1999. Claim,
It is a continuation-in-part application of U.S. patent application Ser. No. 09 / 317,527 filed May 24, 1999. This application also claims priority to US provisional patent application 60 / 130,392 filed April 19, 1999, US patent application 09 / 550,558 filed April 17, 2000. It is a partial continuation application of the issue.

BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION The present invention relates to a molecular fluorine laser system including a line narrowing element and a method of generating a VUV laser beam having a spectral linewidth of less than about 1 pm.

2. 2. Description of Related Art Vacuum UV microlithography is based on the short wavelength (157.6) of molecular fluorine lasers.
nm) to enable the formation of structures of 0.1 pm or less by photolithographic exposure in a semiconductor substrate. TFT annealing and micromachining applications can also be advantageously performed at this wavelength.

Given the limited selection of high quality optical materials available for manufacturing imaging lenses in this wavelength range, the minimum chromatic aberration requirement is that of laser sources for refractive and partially achromatic imaging systems. Limit the spectral linewidth to less than 1 pm. The possibility is that the spectral linewidth is between 0.1 pm and 0.2 pm and possibly even below 0.1 pm in the future. A conventional molecular fluorine laser emits a VUV beam with a spectral linewidth greater than 1 pm.

T. M. Bloomstein et al., "Critical Issues in 157 nm Lithography," Journal of Vacuum Science and Technology: Part B, American Institute of Physics, New York, USA.
vol. 16, No. 6. According to May 26, 1998, pages 3154-3157, the typical linewidth of a 157 nm laser is 10-15 pm, ie,
It is at least an order of magnitude smaller than the normal linewidth of a 193 nm laser. Therefore, in 157 nm lasers less line narrowing is required compared to what has already been done in 248 and 193 nm based projection systems.

Several methods of line narrowing are known in the art. For example, US Pat. No. 5,835,520 discloses a KrF excimer laser capable of producing laser pulses having a bandwidth on the order of 0.5 pm. According to US Pat. No. 5,835,520, three types of dispersive elements can be used for line narrowing: prisms, etalons and diffraction gratings. Moreover, according to US Pat. No. 5,835,520, a small beam divergence is required to obtain a narrow linewidth. For this purpose, a slit and a beam expander are inserted in the laser cavity.

The drawback of narrowing the spectral linewidth in a laser is that it generally leads to a significant reduction in efficiency and output power. Thus, in the present invention, the desired high throughput for 157 nm wafer steppers or wafer scanners is achieved,
It will be appreciated that it would be advantageous to have a line-narrowed fluorine molecular laser emitting an output beam of less than 1 pm with an average high output power in the range of a few watts to 10 watts or more.

Line narrowing excimer lasers with high output power are described, for example, in US Pat.
It is known from 881231. In US Pat. No. 4,881,231,
A narrow bandwidth is disclosed for excimer laser systems suitable as sources in high resolution lithography. This system includes a discharge pump excimer laser oscillator 44 that includes an intracavity Fabry-Perot or other resonator for bandwidth narrowing.
Equipped with. In addition, absorption cells can be provided in the laser oscillator that pass a limited bandwidth for further bandwidth narrowing. The line-narrowed beam that excites the laser oscillator is amplified by an excimer laser amplifier. 1
The combination of said laser oscillator and laser amplifier in a discharge pump F ₂ laser emitting at a wavelength of 57.6 nm (without line narrowing) is described by Masayuki Kakehata et al., “Gain of discharge pump F ₂ laser at high pumping rate”. And saturation intensity measurement ", Applied Physics Letters, Vol. 61, No. 26, 1992 12
It is known from the 28th of the month, pages 3089-3091.

SUMMARY OF THE INVENTION Accordingly, a first object of the present invention is to provide a VUV laser system having a narrow linewidth, ie, a linewidth of less than about 1 pm, that forms small structures on a silicon wafer.

A second object of the invention is a VUV laser enabling sufficient throughput for VUV lithographic applications at 157 nm with a sufficient output power, that is to say an output power of at least several watts, with a linewidth of 1 pm or less. Is to provide.

In accordance with the above object, an oscillator and an amplifier are included, the oscillator generating a 157 nm beam having a linewidth of less than 1 pm, the amplifier predetermining the power of the beam to be greater than one or a few watts. Methods and apparatus are provided, such as narrow-band molecular fluorine laser systems, that scale above a specified amount. The oscillator comprises a discharge chamber filled with a laser gas containing fluorine molecules and a buffer gas, electrodes in the discharge chamber connected to a discharge circuit for supplying energy to the fluorine molecules, the discharge chamber and a line narrowing optical device. A resonator for generating a laser beam having a wavelength of about 157 nm and a linewidth of less than 1 pm.

According to the invention, the amplifier comprises, with respect to the electrodes, the same or a similar discharge circuit, for example the same discharge chamber, which uses an electrical delay circuit to energize the molecular fluorine. . The amplifier discharge is timed to be at or near the maximum in discharge current when the pulse from the oscillator reaches the amplifier discharge chamber.

According to the invention, the same discharge chamber acts as both an oscillator and an amplifier, so that the beam emitted from the oscillator and coupled out is at or near the maximum discharge current in the discharge chamber. In, extra-cavity optics are needed to redirect into the discharge chamber.

The line narrowing optics is preferably tuned with respect to the maximum transmission of selected portions of the spectral distribution of the beam and the relatively low transmission of outer portions of the spectral distribution of the beam. Contains one or more etalons. A prism beam expander is preferably provided after the etalon that expands the beam incident on the etalon. Two etalons may be used and adjusted so that only a single interference order is selected.

The line narrowing optics may further include a diffraction grating that selects a single interference order of the etalon corresponding to a selected portion of the spectral distribution of the beam. The resonator further preferably comprises an opening in the resonator and in particular between the discharge chamber and the beam expander. A second opening may be provided outside the discharge chamber.

The line narrowing optical system may not include an etalon. For example, the line narrowing optics may instead only include a beam expander and a diffraction grating. The beam expander preferably comprises 2, 3 or 4 VUV transparent prisms in front of the diffraction grating. Said diffraction grating preferably has a high reflectivity surface which acts as a resonator reflector in addition to its role of diffracting the beam.

The line narrowing optics includes an etalon output coupler tuned for maximum transmission of selected portions of the spectral distribution of the beam and relatively low transmission of outer portions of the spectral distribution of the beam. May be included. The system also preferably includes an optical system, such as a diffraction grating, a scattering prism or an etalon, that follows the beam expander and selects the single interference order of the etalon output coupler. The resonator preferably has one or more apertures that reduce stray light and divergence within the resonator.

In any of the above configurations including a diffraction grating, a high reflectance mirror may be arranged after the diffraction grating, and the diffraction grating and the high reflectance mirror may form a Littman arrangement. Alternatively, the diffraction grating may serve to retroreflect and scatter the beam in a Littrow arrangement. A transmission grating or grism may be used.

The buffer gas preferably regulates the pressure of the gas mixture sufficiently to increase output energy for a given input energy, energy stability, gas and tube life, and / or pulse duration. It contains neon and / or helium. The laser system more particularly cooperates with the gas supply system to move the fluorine molecules into the discharge chamber, thereby replenishing the fluorine molecules into the discharge chamber, and in the discharge chamber. A processor for controlling the fluorine molecule concentration and keeping the fluorine molecule concentration within a predetermined range of optimum performance of the laser.

The laser system may further include a spectral filter that further narrows the linewidth of the output beam of the oscillator. The spectral filter may include an etalon following the beam expander. Alternatively, the spectral filter may include a diffraction grating that scatters and narrows the beam. In the diffraction grating embodiment, the spectral filter may include a lens that focuses the beam onto a collimating optics through a slit before striking the beam expander-grating combination.

INCORPORATION BY REFERENCE The following is a citation list of references, each of these references, in addition to those references cited above in the Priority Section, in place of the elements or features of the preferred embodiment: Is disclosed. Reference may be made to these references alone or in combinations of two or more to obtain variations of the preferred embodiments described in the detailed description below. Other patents, patent applications and non-patent references are cited in this description. 1-U. Stams "Status of 157 nm 157 excimer laser" International Sematech 15
7 Workshop, February 15-17, 1999, Litchfield, Arizona, USA. 2-T. Hoffman, J. M. Huber, P.H. Das, S. Shora "micro lithography for high repetition rate _F 2 (157nm) prospects of the laser" International Sematech 157 workshop, February 15-17, 1999, the United States, Arizona,
Litchfield. 3-1-U. Stamm, I. Braggin, S.M. Gobokov, J. Klein Schmid, R.A. Patzel, E. Slovodchikov, K.K. Vogler, F.M. Boss and D. Busching "Excimer Laser for 157 nm Lithography" 24th International Microlithography Symposium, March 14-19, 1999, Santa Clara, CA, USA. 4-T. Hoffman, J. M. Huber, P.H. Das, S. Scholar “Revisiting F ₂ Laser for DUV Microlithography” 24th International Microlithography Symposium, March 14-19, 1999, Santa Clara, California, USA. 5-W. Mukenheim, B.C. Rukuru "Excimer Laser with Narrow Linewidth and Large Internal Beam Divergence" J. Phys. E: Sci. Instrum. 20 (1987) 1
394. 6-G. Grunefeld, H .; Schulter, P. Andersen, E. W. Rote “Operation of KrF and ArF Tunable Excimer Laser without Cassegrain Optics” Applied Physics B62 (1996) 241. 7-US patent application 09/3175, each of which is assigned to the same assignee as the present application
26, 09/343333, 60/122145, 60/140531, 60/162735, 60/166952, 60/171172, 60
/ 141678, 60/173993, 60/166967, 60/17
Nos. 2674 and 60/181156, and Kleinschmidt serial numbers not yet assigned, filed May 18, 2000, entitled "Laser speckle in photolithography due to controlled divergence of the spatial coherence of the laser beam. Patent application for "removal" and US patent specification No. 6005880. 8-Laser Focus / Electronic Optics, W. Reprinted from August 1987 Edition. Muequenheim “Seven ways to combine two excimer lasers”.

Detailed Description of the Preferred Embodiments Referring to FIG. 1, a VUV laser system, preferably a Fluorine Molecular Laser for Deep Ultraviolet (DUV) or Vacuum Ultraviolet (VUV) lithography, is shown schematically. TFT
Alternative configurations for laser systems used in other industrial applications such as annealing and / or micromachining are similar to and / or modified from the system shown in FIG. 1 and meet the requirements of the present application. As will be appreciated by those skilled in the art. To this end, alternative VUV laser systems and component arrangements are each assigned to the same assignee as the present application.
317695, 09/317526, 09/317527, 09/343
333, 60/122145, 60/140531, 60/162735
No. 60/166952, 60/171172, 60/141678, 6
0/1739393, 60/166967, 60/172674 and 60 /
No. 1811156 and a patent application for “Removal of laser speckle in photolithography by controlled divergence of spatial coherence of laser beam” filed May 18, 2000, to which Kleinschmidt serial numbers have not yet been assigned. And U.S. Pat. No. 6,0058,880.

The system shown in FIG. 1 generally comprises a laser chamber 2 having one or several pairs of main discharge electrodes 3 connected to a solid pulser module 4 and a gas treatment module 6. The solid-state pulser module 4 is powered by a high voltage power supply 8. The laser chamber 2 is surrounded by the optical module 10 and the optical module 12 to form a resonator. The optical modules 10 and 12 are connected to the optical control module 14
Controlled by.

The laser control computer 16 receives various inputs and controls various operating parameters of the system. The diagnostic module 18, as shown, preferably passes various parameters of the separated portion of the main beam 20 via an optical system, such as a beam splitter module 21, which deflects the small beam portion towards the module 18. Receive and measure. Beam 20 is preferably the laser output to an imaging system (not shown) and ultimately to a workpiece (not shown). Laser control computer 16 communicates with stepper / scanner computer 26 and other control units 28 via interface 24.

The laser chamber 2 contains a laser gas mixture and comprises one or several pairs of main discharge electrodes 3 and one or more preionization electrodes (not shown). Suitable main electrodes 3 are U.S. patent application Ser. Nos. 09 / 453,670, 60 / 184,705 and 60/1.
No. 28227, each of which is assigned to the same assignee as the present application. Other electrode configurations are described in US Pat. Nos. 5,729,565 and 4,860,300, each of which is assigned to the same assignee, and other embodiments are US Pat. No. 4,691,322. , 55th
35233 and 5557629. The laser chamber 2 also includes a preionizer (not shown). A suitable preionization unit is
U.S. Patent Applications 60162845, 60/160182, 60/127237
No. 09 / 535,276 and 09/2447887,
Each of these is assigned to the same assignee as the present application, and other embodiments are described in US Pat. Nos. 5,337,330, 5,818,865 and 5,991,324.

The solid-state pulser module 14 and the high voltage power supply 8 supply the electrical energy of the compressed electrical pulse to the preionization electrode and the main electrode 3 in the laser chamber 2 and to the gas mixture. Suitable pulser modules and high voltage power supplies are described in US patent applications 60/149392, 60/198058 and 09.
/ 390146, and Osmanou et al., US Pat. No. and 602072
No. 3, each of which is assigned to the same assignee as the present application and is hereby incorporated by reference. Other alternative pulser modules have been described in US Pat.
0421, 5914974, 5949806, 5936988,
No. 6,028,872 and 5,729,562. Conventional pulser modules can generate electrical pulses in excess of 3 Joules of electrical power (see the '988 patent, supra).

The laser cavity surrounding the laser chamber 2 containing the laser gas mixture comprises line-narrowing excimers or line-narrowing optics for molecular fluorine lasers, which are not desired to be line-narrowed, or , Line narrowing can be done in the front optics module 12, or if a spectral filter outside the resonator is used to narrow the linewidth of the output beam, it can be replaced by a high reflectivity mirror or the like in the laser system. Some modifications of the line narrowing optical system will be described in detail later.

The laser chamber 2 is sealed by a window transparent to the wavelength of the emitted laser radiation 14. The window may be a Brewster window or it may be aligned at different angles to the optical path of the resonant beam. The laser chamber,
A beam path to and from each of the optics modules 10 and 12 is defined by an enclosure 17
And 19 and from inside the enclosure, otherwise V
Practically removes water vapor, oxygen, hydrocarbons, fluorocarbons, etc. that strongly absorb UV laser radiation.

After a portion of the output beam 20 has passed through the out coupler of the optics module 12, this output portion impinges on a beam splitter module 21, which causes a portion of the beam to be diagnosed by the diagnostic module 18. Or an optical system that allows a small portion of the outcoupled beam to reach the diagnostic module 18 and a main beam portion 20 to follow as the output beam of the laser system. Including. Suitable optics include beam splitters or partially reflective surface optics. One or more beamsplitters and / or HR mirrors and / or dichroic mirrors may be used to direct a portion of the beams to components of diagnostic module 18. Small for detection in diagnostic module 18 using holographic beam samplers, transmission gratings, partially transmissive reflective diffraction gratings, grisms, prisms, or other refractive, scattering and / or transmissive optics Beam part 22 to main beam 2
It may be separated from 0 so that most of the main beam 20 reaches the application process either directly or via the imaging system or otherwise. The output beam 20 may be transmitted at the beam splitter module and the reflected beam portion 22 may be directed at the diagnostic module 18, or the main beam 20 may be reflected and a small portion 22 transmitted to the diagnostic module 18. . The portion of the outcoupled beam that persists past the beamsplitter module 21 is the output beam 20 of the laser, which output beam 20 is for industrial or experimental applications such as workpieces for imaging systems or photolithographic applications. Propagate toward.

The enclosure 23 confines the beam paths of the beams 22 and 20 so that the beam paths are free of light absorbing species. The smaller enclosures 17 and 19 confine the beam path between the chamber 2 and the optical modules 10 and 12. A preferred enclosure 23 and beam splitting module 21 is described in US patent application Ser. Nos. 09 / 343,333 and 60/140530 mentioned above, US patent application Ser. No., 5221823, No. 5763855, No. 5811
753 and 4616908. For example, the beam splitting module 21 preferably also includes optics for filtering visible red light from the beam 22 so that practically only VUV light is received at the detector of the diagnostic module 18. Filtering optics may be included to filter red light from the output beam 20. Also, the inert gas purification is preferably flowed to the enclosure 23.

The diagnostic module 18 preferably includes at least one energy detector. This detector measures the total energy of said beam portion, which corresponds directly to the energy of the output beam 20. An optical configuration such as an optical attenuator, eg a plate or coating, or other optical system is formed in or near the detector or beam splitter module 21 and the intensity of the radiation impinging on the detector. , Spectral distribution and / or other parameters may be controlled (US patent application Ser. No. 09/172805, 60/1727, each assigned to the same assignee as the present application).
49, 60/166952 and 60/178620).

Certain other components of the diagnostic module 18 are preferably wavelength and / or bandwidth detection components, such as monitor etalons or grating spectrometers (each assigned to the same assignee of the present application). United States Patent Application 09/416344, 6
0/186003, 60/158808 and 60/186960 and Rokai et al., Using "multi-element or tandem see-through hollow cathode lamps, filed May 10, 2000, with no serial number assigned yet. Absolute Wavelength Calibration of Lithography Lasers "US Pat. No. 490
No. 5243, No. 5978391, No. 5450207, No. 4926428,
See 5748346, 5025445 and 5978394. ).

Other components of the diagnostic module are US patent application 0, each assigned to the same assignee, such as for gas control and / or output beam energy stability.
Pulse shape detectors or ASE detectors such as those described in each of 9/484818 and 09/418052 may be included. For example, there may be a beam alignment monitor, such as that described in US Pat. No. 6,014,206, incorporated by reference.

The processor or control computer 16 determines pulse shape, energy, spontaneous emission amplified light (ASE), energy stability, energy over burst mode operation among other input or output parameters of the laser system and output beam. Receive and process some values of shoot, wavelength, spectral purity and / or bandwidth. The processor 16 also controls the line narrowing module to adjust wavelength and / or bandwidth, or spectral purity, and controls the power supply and pulser modules 4 and 8, preferably moving average pulse power. Alternatively, the energy is controlled so that the amount of energy at the point on the workpiece stabilizes around a desired value. In addition, the computer 16 controls the gas processing module 6 including gas supply valves connected to various gas sources.

The laser gas mixture is initially filled into the laser chamber 2 during a fresh filling. The gas mixture for the highly stable excimer laser according to the preferred embodiment uses helium or neon or a mixture of helium and neon as buffer gas, depending on the laser. Suitable gas mixtures are described in US Pat. Nos. 4,393,405 and 4,977,573 and US patent application Ser. No. 09/3317526.
No. 09/513025, 60/12785, 09/418052, 6
0/159525 and 60/160126, each of which is assigned to the same assignee. The concentration of fluorine in the gas mixture may range from 0.003% to 1.00%, preferably
It is about 0.1%. Additional gas additives such as noble gases may be added for increased energy stability and / or as an attenuator as described in the '025 application mentioned above. Xenon and / or argon additives may be used, especially for F2 lasers. The concentration of xenon and / or argon in the gas mixture is
It may range from 0.0001% to 0.1%. For ArF lasers, a xenon or krypton additive having a concentration between 0.0001% and 0.1% may be used.

The halogen and noble gas injection procedure, the total pressure regulation procedure and the gas exchange procedure are preferably carried out using a gas treatment module 6 comprising a vacuum pump, a valve network and one or more gas compartments. . The gas treatment module 6 receives gas via gas lines connected to gas containers, tanks, cans and / or bottles. Suitable gas treatment and / or replacement procedures for the preferred embodiments other than those specifically described herein are disclosed in U.S. Pat. Nos. 4,977,573 and 5,396,514, each of which is assigned to the same assignee as the present application. / 124785, 09/41805
2, 09/3799034, 60/171717 and 60/159525 and U.S. Pat. Nos. 5,978,406, 6014398 and 602888.
No. 0 is described. The Xe gas supply may be included either inside or outside the laser system according to the '025 application mentioned above.

A general description of the line narrowing features of some embodiments of the present invention will now be given first, followed by a detailed discussion with reference to FIGS. 2a-6b. Example line narrowing optics that provide a relatively high degree of dispersion for narrow band lasers such as for use with catadioptric optical lithographic imaging systems are included in an optical module 10 that includes a beam expander, an optional etalon and a diffraction grating. . As mentioned above, the front optics module may include similar line narrowing optics (see 60/166277, 60/1739393 and 60/166967 applications, each assigned to the same assignee). I want to be). For semi-narrow band lasers that are not the subject of the invention, such as used with total internal reflection imaging systems, the diffraction grating may be replaced by a high reflectance mirror and a low degree of dispersion may be generated by a dispersive prism. . Semi-narrow band lasers typically have an output beam linewidth of greater than 1 pm, depending on the unique free-running band of the laser, and in some laser systems, may be as high as 100 pm.

The beam expander of the exemplary line narrowing optics of the optics module described above preferably includes one or more prisms. The beam expander may include lens assemblies or other beam expanding optics such as a convergent / divergent lens pair. The diffraction grating or high-reflectance mirror is preferably rotatable so that the wavelength reflected during the acceptance angle of the resonator can be selected or adjusted. Instead, the diffraction grating or other optics, or the entire line narrowing module, is pressure adjusted as described in the 60/178445 and 09/317527 applications, each assigned to the same assignee. Good. The diffraction grating may be used both to disperse the beam to achieve a narrow bandwidth and, preferably, to retroreflect the beam towards the laser tube. Alternatively, a high-reflectivity mirror that receives the reflection from the diffraction grating and reflects the beam back towards the diffraction grating to doubly disperse the beam is placed after the diffraction grating or the diffraction grating. The grating may be a transmission diffraction grating. More than one dispersive prism may be used, 1
More than one etalon may be used.

Many types can be used depending on the type and degree of line narrowing desired and / or the selection and adjustment, and in particular depending on the particular laser in which the line narrowing optics should be installed. Alternative optical arrangements exist. To this end, U.S. Pat. Nos. 4,399,540, 4,905,243 and 52, each assigned to the same assignee as the present application.
26050, 5559816, 5659419, 5663973, 5761236 and 5946337 and U.S. patent application Ser. No. 09/3176.
95, 09/130277, 09/244554, 09/317527, 09/073070, 60/124241, 60/140532, 60.
/ 147219, 60/140531, 60/147219, 60/17
0342, 60 / 172,749, 60/178620, 60/17399
No. 3, 60/166277, 60/166967, 60/167835,
60/170919 and 60/186096 and U.S. Pat. No. 5,095.
No. 492, No. 5648822, No. 5835520, No. 5852627, No. 5856991, No. 5898725, No. 5901163, No. 591784.
No. 9, 5790082, No. 5404366, No. 4975919, No. 51
No. 42543, No. 5596596, No. 5802094, No. 4856018, No. 59700082, No. 5978409, No. 5999318, No. 5150.
370 and 4829536 and German patent specification DE 29822090.3.
Note these as seen in issues.

The optics module 12 is preferably a beam 2 such as a partially reflective resonator reflector.
Includes means to outcouple 0s. The beam 20 may otherwise be outcoupled, such as by an intra-cavity beam splitter, or a partially reflective surface of another optical element, the optical module 12 in this case including a high reflectance mirror. . The optical control module 14 connects the optical modules 10 and 12 to the processor 1
6 and receives and interprets the signal from 6 and controls it to initiate the realignment or relocation procedure (see the '241,' 695, 277, 554 and 527 applications referenced above).

A detailed description of the line narrowing configuration of the oscillator element of the laser system according to the preferred embodiment will now be described with reference to FIGS. 2a-2f. Some embodiments of laser system oscillators using line narrowing techniques for molecular fluorine lasers that meet, or nearly meet, the first object of the present invention are shown in Figures 2a-2f.

FIG. 2 a comprises a discharge chamber 2 which preferably comprises molecular fluorine and a buffer gas comprising neon, helium or mixtures thereof (see the 09/317526 application), in which the main discharge 1 shows an oscillator of a laser system according to the first embodiment with an electrode pair 3 (not shown) and a preionization arrangement (not shown). Figure 2a
The system shown in also includes a prism beam expander 30 and a diffraction grating 32 in a Littrow configuration. The beam expander 30 may include one or more prisms, preferably several prisms. The beam expander serves to reduce the divergence of the beam incident on the diffraction grating and thus improve the wavelength resolution of the wavelength selector. The diffraction grating is preferably a high blaze angle echelle diffraction grating (see the 60/170342 application referenced above).

The illustrated system removes stray light, reduces broadband background, and serves to reduce the linewidth of the beam by lowering the acceptance angle of the resonator 34. In the resonator. Alternatively, one opening 34 may be included on either side of the chamber 2 or the opening 34
Need not be included. An exemplary opening 34 is described in US Pat. No. 5,161,238, which is assigned to the same assignee (0 above).
See also the 9/130277 application).

The system of FIG. 2 a also includes a partially reflective outcoupling mirror 36. The out-coupling mirror 36 may be replaced by a high reflectance mirror and the beam may otherwise be polarized, or otherwise within the resonator, such as the surface of a prism, window or beam splitter. May be outcoupled as by using an optical surface of the same type (see, eg, US Pat. No. 5,150,370, cited above).

The system of FIG. 2b includes the chamber 2 described above with respect to FIG. 2a, an aperture 34, a partially reflective outcoupling mirror 36, and a beam expander 30. The system of FIG. 2b also includes a diffraction grating 38 and a high reflectance mirror 40. Diffraction grating 38 preferably differs from diffraction grating 32 of FIG. 2a either in its orientation with respect to the beam, its arrangement such as its blaze angle, etc., or both. The laser beam is incident on the diffraction grating 38 at an angle closer to 90 ° with respect to the diffraction grating 32. This angle of incidence is actually very close to 90 °. This is an arrangement referred to here as the Littman arrangement. The Littman arrangement increases the chromatic dispersion of the diffraction grating 38. After passing through or being reflected by the diffraction grating 38, the diffracted beam is reflected by the high reflectance mirror 40. The adjustment of the wavelength is preferably achieved by tilting the high-reflecting mirror 40. As described above with respect to the exemplary arrangement, adjustment may otherwise be accomplished by rotating other optics or pressure adjusting one or more optics, or otherwise. , May be accomplished as will be appreciated by those skilled in the art.

FIG. 2 c shows another embodiment of an oscillator, preferably having a laser chamber 2, an aperture 34, an outcoupler 36, a beam expander 30 and a Littrow diffraction grating 34, as described above. It is shown diagrammatically. In addition, the system of FIG. 2c includes one or more etalons 42, for example two, which provide high resolution line narrowing, and the diffraction grating 32 serves to select a single interference order of etalons 42. Etalon 42
May be arranged at various positions in the resonator, that is, at positions other than those shown. For example, the prism of the beam expander 30 may be arranged between the etalon 42 and the diffraction grating. The etalon 42 may be used as an output coupler, as described in more detail below with reference to Figures 2e-2f. Etalon 4
The arrangement of FIG. 2c, including 2 (as well as later FIG. 2d), is assigned to the same assignee, respectively, US Pat.
It may be modified as described in any of 8808.

FIG. 2d shows another embodiment of a laser system having more than one etalon, for example two etalons are illustrated. The system of FIG. 2d replaces the grating 32 with a high reflectivity mirror and the etalon 43 is not available to select the single interference order of the etalon 43 as in the system of FIG. 2c except that it is configured differently by omitting The free spectral range of the etalon 43 is instead set so that one of the etalons 43, preferably the first etalon after the beam expander 30, selects a single order of the other etalon 43, eg the second etalon 43. Adjust to. The suitably arranged second etalon 43 can thus have a smaller free spectral range and a higher wavelength resolution. Some other variations of the etalon 43 of the system of Figure 2d can be used as described in US Pat. No. 4,856,018.

2e and 2f each show an embodiment similar to the arrangement described above with reference to FIGS. 2a and 2b, which differs in that the partially reflective outcoupler mirror 36 is replaced by a reflective etalon outcoupler 46. The etalon out coupler 46 is shown in FIG.
And a 2f grating 32 or 38 in combination with the beam expander 30, the grating 32 or 38 selecting a single interference order for the etalon outcoupler 46. Alternatively, one or more dispersive prisms or other etalons may be used in combination with the etalon outcoupler 46 to select the single interference order of the etalon 46. The diffraction grating 32 or 38 limits the wavelength range to the single interference order of the out-coupler etalon 46. 2e and / or 2f
2e, which can be used in combination with the system described above in FIG.
And 2f system variants are described in 09/317527 and 60/166 described above.
277 application and U.S. Pat. Nos. 6,028,879, 3,609,586 and 3,
No. 471800, No. 3546622, No. 5901163, No. 5856991.
Nos. 5440574 and 5479431; Leng Ferner, G
Generation of Tunable Pulsed Microwave Radiation by Nonlinear Interaction of Nd: YAG Laser Radiation in aP Crystals, Optics Letter, Vol. 12, No.
3 (March 1987) and S. Marcus, Cavity Damping and Coupling Modulation of Etalon-Coupled CO ₂ Lasers, J. Am. Appl. Phys. , Vol. 53
, No. 9 (September 1982) and the physics and technology of laser cavities, author D.M. R.
Hall and P. E. Jackson, page 244.

The materials used for the prisms of the beam expander 30, the etalons 42, 43, 46, and the laser window in all of the above-described embodiments shown and described with reference to FIGS. 2a-2f are preferably It should be highly transparent at wavelengths below 200 nm, such as at the 157 nm output radiation wavelength of molecular fluorine lasers. The material is also capable of withstanding long-term exposure to UV light with minimal degradation effects.
Examples of materials such as these include CaF ₂ , MgF ₂ , BaF, BaF ₂ , LiF,
LiF ₂ and SrF ₂ . Also, in all of the above embodiments of Figures 2a-2f, many optical surfaces, particularly those of the prisms, are preferably used to minimize reflection losses and increase their life. One or more of which have antireflective coatings.

As described in the above general description, the gas component for the F ₂ laser in the above configuration uses helium, neon, or a mixture of helium and neon as a buffer gas. The concentration of fluorine in the buffer gas is preferably in the range of 0.003% to about 1.0%, preferably about 0.1%. Xenon, and / or argon, and / or oxygen, and / or krypton,
And / or minor additions of other gases may be used to increase the energy stability, burst control or output energy of the laser beam. The concentration of xenon, argon, oxygen, or krypton in the mixture is 0.0001% to 0.
． It may range up to 1%. Some alternative gas components, including trace gas additives, are described in US patent application Ser. Nos. 09/513025 and 09/317526, each of which is assigned to the same assignee.

All of the oscillator configurations shown in FIGS. 2a-2f can be advantageously used to generate a VUV beam 20 having a wavelength of about 157 nm and a linewidth of about 1 pm or less. Some of these configurations with an output line width of less than 1 pm already fulfill the first object of the invention with respect to said line width. These oscillators are shown in FIG.
It may be used with other elements, such as amplifiers, as described below in -6b, to meet the second objective of the invention, ie to achieve sufficient output power for practical throughput in 157 nm lithography. Other oscillators that generate line widths of 1 pm or more can be used advantageously in combination with other line narrowing elements, as will be described below in FIGS. 3a-4b, to meet the first objective,
It may be used with an amplifier as described in embodiments a-4b to meet the second objective.

FIG. 3 a schematically illustrates, in block form, a laser system according to a preferred embodiment of the present invention in which a narrower linewidth than the output by oscillator 48 is desired and a higher power than the output by oscillator 48 is desired. In order to reduce the line width, the oscillator 48
Of the output beam 20 is directed through a spectral filter 50. Beam 20 is directed through amplifier 52 to increase the output power.

The system of FIG. 3 a includes a line narrowing oscillator 48, a spectral filter 50, and an amplifier 52. Various preferred configurations of spectral filter 50 are shown in Figures 3b-3d.
Will be described later. Oscillator 48 of Figure 3a is an electric discharge fluorine molecular laser generating a spectral linewidth of about 1 pm, preferably one of the configurations described above with respect to Figures 2a-2f, or a variation thereof as described above, or , As would be appreciated by one of ordinary skill in the art, as found in one or more of the references cited above. The oscillator 48 is followed by a spectral filter 50 which transmits light in a narrower spectral region, ie below the linewidth of the output beam 20 from said oscillator, ie below about 1 pm. Finally, the transmitted beam is transmitted to the amplifier 52 by
It produces an output beam 54 which is amplified in response to a separate discharge chamber and which fulfills the first and second objects of the invention. Preferably, the oscillator and amplifier discharges use a delay circuit and an advantageous solid state pulser circuit as described in US patent application 60/204095 and US Pat. No. 6,0058,80 assigned to the same assignee respectively. To synchronize.

The spectral filter 50 preferably comprises one of the arrangements shown in FIGS. 3b-3d. Preferably, prisms, diffraction gratings, grisms, holographic beam samplers, etalons, lenses, apertures, beam extracts to reduce the linewidth of the input beam 20 without consuming a substantial portion of the energy of the input beam 20. Those skilled in the art will appreciate that variations using any of a number of combinations of pandas, collimating optics, etc. would be advantageous.

FIG. 3b includes a beam expander followed by one or more etalons 58, resulting in an output beam having a linewidth that is substantially narrower than the linewidth of the input beam 20, for example less than about 1 pm, 1 illustrates an embodiment of a first spectral filter 50 that meets a first objective. Each etalon 58 comprises two partially reflective surfaces of reflectivity R separated by a gap, preferably of gas filled, of thickness D. Etalon T (λ)
The transmission spectrum of is described by a periodic function of wavelength λ. ^{T (λ) = (1+ (} 4F 2 / B 2) sin (2BnDcos (l) / λ)) - 1 (1) where, n, the refractive index of preferably an internal gas material satisfying etalon 58 Where l is the tilt angle of the etalon 58 with respect to the beam, and F is the finesse of the etalon 58 defined as follows. F = BR ^1/2 / (1-R) (2)

The reflectivity R and the spacing D of the etalon are chosen such that only a single maximum transmission overlaps the emission spectrum of the broadband oscillator. For example, if the finesse of the etalon 58 is selected to be 10, the spectral width of the highest transmittance is approximately 1/10 of the free spectral range (FSR) of the etalon 58. Therefore, the selection of the free spectral region of 1 pm is such that the line width of the oscillator (48) output (about 1 pm) is
Slightly narrower than twice SR, it produces a transmitted beam with a spectral linewidth of 0.1 pm without sidebands.

The use of multiple etalons 58 allows for a higher contrast ratio,
This contrast ratio is defined as the ratio between the maximum transmittance and the transmittance at a wavelength intermediate between the maximum transmittances. This contrast ratio for one etalon is (1
Almost equal to + 4F ² / B ² ). Higher finesse values lead to higher contrast. For several etalons 58, the total contrast ratio is (1 + 4F ² /
B ² ) ⁿ , where n is the number of etalons 58. In addition, the spectral width of the maximum transmission decreases as the number of etalons 58 used increases. Disadvantages of using some etalons 58 include high cost and complexity of the device and increased optical loss.

The beam expander 56 shown in FIG. 3 b acts to reduce the divergence of the beam incident on the etalon 58. From equation (1), it follows that a change in the beam incidence angle I causes a wavelength shift at which maximum transmission occurs. Assuming an FSR of 1 pm, the etalon spacing is D = 1.2 cm. If the transmission interference spectrum of the etalon 58 is its maximum at normal incidence (l = 0), the angle 1 at which the transmission spectrum again reaches a maximum is l- (λ / nD) ^1/2 = 3. 6
It is mrad. Therefore, the spectral filter 50 shown in FIG. 3b is preferably configured such that the divergence of the beam is below l, preferably by a factor comparable to the finesse F of the etalon 58. Since the output of the oscillator 48 is less than 1 because a typical molecular fluorine laser is a few milliliters, the beam expander 56 is used to reduce this dispersion from the above-described typical 1. Understand the benefits. It is also suitable to use one or more apertures 34 in the oscillator 48 to reduce its power dispersion (see the 09/130277 application referenced above).

The gap between the plates of the etalon 58 is preferably filled with internal gas. Tuning the transmission wavelength is accomplished by varying the pressure of the gas, as described in the 09/317527 application referenced above. In addition to pressure and rotational adjustments of the etalon's output transmission spectrum, the etalon 58 may be piezoelectrically adjusted to geometrically change the gap spacing.

FIG. 3c shows the spectral filter 5 of FIG. 3a, which generally uses a diffraction grating 60.
2 schematically shows a second embodiment of No. 0. There are other ways of constructing the spectral filter 50 according to the second embodiment using a diffraction grating 60, but one example is shown in FIG. 3c and is described here. The spectral filter 50 shown in FIG. 3c is a Cerny tuner spectrometer modified to achieve high resolution. Lens 6
The input beam 20 focused by 1a passes through the input slit 62a and then enters the collimating mirror 64. After being reflected from the mirror 64, the beam enters the beam expander 66 and then the diffraction grating 60. The beam is dispersed and reflected from diffraction grating 60, after which the beam traverses beam expander 66 again, through output slit 62b and from collimating mirror 64 at or near the focal point of lens 62b. To be done. At this time,
The output beam 59 has a line width that is practically narrower than the line width of the input beam 20, which is, for example, about 1 pm, i.

The diffraction grating 60 is preferably a high-blaze echelle diffraction grating 60. The chromatic dispersion of this preferred diffraction grating 60 is described by the following equation. λ / dl = (2 / λ) tanl (3) where l is the incident angle. The spectral width Δλ of the transmitted beam is defined by the diffraction grating 6
Zero dispersion dλ / dl, magnification M of the prism expander 66, focal length L of the collimating mirror 64, and width d of the slits 62a, 62b of the spectrometer.
Determined by and. Δλ = d (LMdλ / dl) -1 (4)

For example, using an Echelle grating 60 with an incident angle 1 of 78.6 °, L = 2 m and M = 8, the slit width d that achieves a resolution of 0.1 mm for the spectral filter 50 of FIG. , D = about 0.1 mm. Therefore, it is preferable to reduce the divergence of the oscillator 48 in order to increase the transmission of the beam 20 through the input slit 61a. This can be advantageously achieved using an aperture in the resonator of oscillator 48 (see again the 09/130277 application mentioned above).

A third example of a spectral filter 50 that can be used is shown in FIG. 3d. The spectral filter 50 of FIG. 3d is similar to the spectral filter shown in FIG.
Instead of the collimating mirror 64 used in the embodiment of FIG.
8 is used in the embodiment of FIG. 3d. The advantage of the embodiment of Figure 3d is its simplicity and the absence of astigmatism introduced by the mirror 64 of Figure 3c at non-zero angles of incidence.

At the moment when the gain of the amplifier 52 is at or near its maximum value, the amplifier 52
It is now repeated that synchronization of the electrical discharge pulses in chamber 2 of oscillator 48 and amplifier 52 is preferred to ensure that the line narrowing optical pulse from oscillator 48 arrives in chamber 2 of It is useful. In addition, this preferred synchronization timing should be replicable between pulses, giving high energy stability of the output pulse. A preferred embodiment of the electronic circuitry that enables this precise timing control is described in the above-mentioned US Pat. No. 6,0058,80 and US patent application 60/204095.

FIG. 4 a illustrates the use of a single discharge chamber 70 to provide gain media for both oscillator and amplifier. The arrangement of FIG. 4a includes a discharge chamber 70 within a resonator that includes a high reflectivity mirror 72 and a partially reflective outcoupling mirror 74. A pair of apertures 34 is also included as described above to match the divergence of the resonator of oscillator 48.
A small portion of the discharge voltage cross section is used to generate a non-narrowed beam 76 with this oscillator configuration. It may also include one or more line narrowing components having this oscillator configuration, or the oscillator according to the description above with respect to Figures 2a-2f may be modified.

Similar to the embodiment shown and described with respect to FIG. 3a, this non-narrowed output is preferably a spectral filter 5 which is one of the embodiments described in FIGS. 3b-3d.
Aim through 0. Given the significant time it takes for the beam to traverse the spectral filter 50 (eg, a few nanoseconds), it is preferable to adjust the arrival time of the filtered pulse with respect to a second maximum of discharge current. is there. To achieve this temporal adjustment, an optical delay line is preferably inserted after the spectral filter 50. United States patent application 60 / assigned the same delay line to the same assignee
It may be one of those described in No. 130392.

FIGS. 4 b (i)-(iii) show the current through the discharge gap and the non-narrowed beam 76.
, And the output 59 of the oscillator-amplifier system, each as a function of time. The current exhibits several cycles of oscillation, as shown in Figure 4b (i). Figure 4
The optical pulse shown in b (ii) evolves towards the end of the first maximum of current (a). The second maximum of the current separates from the first maximum by about 20 nanoseconds, thus providing sufficient time for beam 76 to traverse spectral filter 50 and additional optical delay line 78. This discussion of maximum continuous timing in the electrical discharge current shows how an additional optical delay line 78 can be used to advantage to precisely adjust the arrival time of the pulse in chamber 70 (amplifier). .. The line-narrowed beam from the spectral filter 50, whose temporal pulse shape is shown in FIG. 4b (iii), is therefore the same as in FIG.
A beam 59 that overlaps with and is amplified by the second maximum b of the current shown in b (i) and is thus line narrowed, ie, sufficiently narrower than 1 pm, is output with sufficient power,
The first and second objects of the present invention are satisfied.

FIG. 5 a shows the use of a line narrowing oscillator followed by a power amplifier formed in a separate discharge chamber. 2a-2 with the exemplary embodiments, patents and publications mentioned above.
Any of the embodiments shown and described, including those discussed with respect to the embodiments described with respect to f, can be used to reduce the bandwidth of the oscillator. An example of a suitable line narrowing oscillator 48 is described in Figures 5b-5f.

The line-narrowing oscillator 48 shown diagrammatically in FIG. 5 (b) is preferably the above-mentioned US Pat. No. 5,559,816, German Patent Specification No. 29822090.3, US Pat. No. 5,150,370 and US Pat. No. 5,852,627, using a prism beam expander 30 and a diffraction grating 32. Alternatively, a Littman arrangement may be used (see above discussion regarding FIG. 2b). As discussed above with respect to the embodiments of FIGS. 2a-4a, the additional aperture 34 in the resonator reduces the divergence of the beam and thus advantageously increases the resolution of the wavelength selector (for details, see Again, see the 09/130277 application).

The embodiment shown in FIG. 5c utilizes multiple etalons 43 as wavelength selective elements (see FIG. 2d). The prism beam expander 30 in combination with the aperture 34 helps reduce the beam divergence at the etalon 43,
Therefore, the resolution of the wavelength selector is improved. In addition, the prism beam expander 30 reduces the intensity of the beams in certain areas of the surface of the etalon 43, thus extending their life.

Excimer-type gas lasers that use an open optical waveguide and move an excimer medium into and through the open optical waveguide in a direction intersecting the optical axis are described, for example, in US Pat. It is known from No. 5,255,282. Figure 5d
-5e shows an alternative arrangement, each including an RF or microwave pumped optical waveguide laser as the oscillator. The arrangement of FIG. 5d preferably includes a pair of RF electrodes 80 and an optical waveguide 82, which preferably includes a ceramic capillary filled with a laser active gas mixture. Any of the resonator arrangements shown in Figures 2a-5c can be used in this embodiment, in which the discharge chamber 2 is R shown in Figure 5d.
It was replaced with an F-excited optical waveguide arrangement. Features of optical waveguide lasers that can be used in the arrangements of FIGS. P. Kristenson, Small Self Contained ArF Laser, Performing Organization Report No. AFOSR IR 95-0370
T .; Ishihara and S.M. C. Lin, microwave pump high pressure gas laser, applied physics, B48, 315-326 (1989); and Ohmi, Tadahiro and Tanaka, Nobuyoshi, excimer laser oscillation device and method, excimer laser exposure device, and laser tube, European Patent Application Publication See specification 0820132A2. RF-pumped lasers are commonly used, for example, Kurt Bondery “Shielded Carbon Dioxide Laser Achieves New Power Levels”, Laser Focus World, 1
It operates with a carbon dioxide gas medium, as discussed in August 996, pages 95-100.

The particular arrangement shown in FIG. 5d includes a prism beam expander 30 and a diffraction grating 32 in a Littrow arrangement. A Littman arrangement including a diffraction grating 38 and an HR mirror 40 may be used here (see Figures 2b and 2f). In particular,
Also included is a pair of apertures 34 that coordinate the oscillations of the resonator. The partially reflective mirror 365 outcouples the output beam 20. An etalon outcoupler 46 may be used in place of mirror 36 (see Figures 2e-2f).

The arrangement shown diagrammatically in FIG. 5e is such that the diffraction grating comprises one or more etalon 4
3 and the same as in FIG. 5d, except that the HR mirror 44 was replaced. Diffraction gratings 32 or 38 may be used with etalon 43 and etalon outcoupler 46 may be used in place of partially reflecting mirror 36.

The advantage of this RF excitation optical waveguide type laser is its long pulse which enables more efficient line narrowing because the line width is almost inversely proportional to the number of round trips of the beam in the resonator. In addition, the RF pumped optical waveguide laser has a small discharge width (about 0.
5 mm), which allows a high angular resolution of the wavelength selector depending on the prism of the beam expander 30 and the diffraction grating 32. This is shown in Figures 5d-5e.
Both of the embodiments shown in are applicable.

FIG. 5f schematically illustrates another source of a narrow linewidth beam that can be used in accordance with the present invention and act as the oscillator 48 in the embodiment of FIG. 5a. Figure 5f
For example, U.S. Patent Specification No. 600269, assigned to the same assignee.
Third harmonic at 355 nm, such as a diode-pumped Nd: YAG laser or other such type of laser, as described in No. 7 or otherwise known to those skilled in the art. It includes a solid state laser 85 having an output. The fixed laser 85 pumps a narrow linewidth tunable laser 86, such as a die laser or an optical parametric oscillator, and emits, for example, about 472.9 nm. This 472.
The 9 nm radiation is focused into a gas cell 88 containing a mixture of metal halide and an inert gas to generate a third harmonic beam at 157.6 nm. Third harmonic generation in such gases is described by Kang A. et al. H. Young J. et al. F. ,
Bjoklang G. C. Harris S. E. , Physical Review Letter, v
． 29, page 985 (1972) and Kang A .; H. Young J. et al. F
． Harris S. E. Applied Physics Letter, v. 22, page 301 (1973).

6 a and 6 b diagrammatically show another embodiment in which part of the discharge volume of the discharge chamber 2 is used as part of the oscillator for line narrowing and the same discharge chamber is used as the amplifier 52. . The arrangement of Fig. 6a is similar to that shown in Fig. 4a, except that the line width of the beam 30 is narrowed within the resonator of the oscillator and preferably no spectral filter 50 is used. Alternatively, the spectral filter 50 may be used in addition to the line narrowing optics of the oscillator of Figure 6a. Again, the line-narrowing arrangement of the oscillator may be arranged as described in any of the above descriptions (see in particular FIGS. 2a-2f, 5c and 5f) or any of the patents, patent applications or publications mentioned in this application. Any of the above or otherwise modified as will be appreciated by those skilled in the art to produce an output beam 20 that is narrow enough to meet the first object of the invention. Good. The output beam 20 from the oscillator is expanded by an external beam expander 90, which preferably comprises one or more prisms and, alternatively, a lens arrangement.

The expanded beam 92 is then directed through the delay line 78 ('392
(See application), the pulse is synchronized with the amplification maximum of chamber 70, as described above. The optical delay line 78 serves to fine tune the arrival time of the light pulse at the amplifier portion, similar to the embodiment shown and described with respect to Figures 4a-4b (iii). The expanded beam 20 then advantageously fills the remaining practical part of the discharge cross section.

In the above embodiment, the gas mixture in the discharge chamber 2, 70 of the oscillator is adjusted to obtain the longest possible pulse. In addition, the discharge current waveform can be modified by carefully introducing impedance mismatches in the pulse forming network and the discharge gap. The impedance mismatch results in longer discharge times and thus longer light pulses. The lower gain resulting from such a modification implies a lower efficiency of the oscillator. However, in the embodiments discussed above, the amount of reduction in the output power of the oscillator recovers in the amplification stage.

While exemplary drawings of the invention and specific embodiments have been described and illustrated, it should be understood that the scope of the invention is not limited to the particular embodiments discussed. Therefore, the above embodiments should be considered as illustrative rather than limiting, and variations on these embodiments may be departed by those skilled in the art from the scope of the invention described in the claims and their equivalents. It should be understood that it can be formed without.

In addition, in the method claims, steps have been arranged in selected typographical columns. However, steps are performed except for those steps in which the columns are selected and arranged for typographical convenience and the particular order of the steps is clearly stated or understood to be necessary by one of ordinary skill in the art. It is not intended to imply any particular order.

[Brief description of drawings]

FIG. 1 schematically illustrates a molecular fluorine laser system according to a preferred embodiment.

2a-f schematically show some other embodiments according to the first aspect of the invention, including various line narrowing resonators and techniques utilizing a line narrowing oscillator of a molecular fluorine laser. .

FIG. 3 a schematically shows a preferred embodiment according to the second aspect of the invention including an oscillator, a spectral filter in various configurations and an amplifier, and b-d a spectral filter according to the second aspect of the invention. Figure 6 schematically shows another embodiment of.

FIG. 4 a schematically shows another embodiment according to the second aspect of the invention comprising a single discharge chamber providing a gain medium for both the oscillator and the amplifier and having a spectral filter in between, b ( i)-(iii) respectively show waveforms of discharge current, non-narrowed beam intensity, and output beam intensity according to another embodiment of FIG. 3a.

FIG. 5 a schematically shows a preferred embodiment according to the third aspect of the invention, including a line narrowing oscillator followed by a power amplifier, and b-f, a line narrowing oscillator according to the third aspect of the invention. Figure 6 schematically shows another embodiment of.

6 a-b schematically show another embodiment according to the fourth aspect of the invention, including a single discharge chamber providing a gain medium for both the oscillator for line narrowing and the amplifier.

─────────────────────────────────────────────────── ─── Continued front page    (31) Priority claim number 60 / 166,967 (32) Priority date November 23, 1999 (November 23, 1999) (33) Priority claiming countries United States (US) (31) Priority claim number 60/170, 342 (32) Priority date December 13, 1999 (December 13, 1999) (33) Priority claiming countries United States (US) (31) Priority claim number 09 / 550,558 (32) Priority date April 17, 2000 (April 17, 2000) (33) Priority claiming countries United States (US) (31) Priority claim number 60 / 204,095 (32) Priority date May 15, 2000 (May 15, 2000) (33) Priority claiming countries United States (US) (31) Priority claim number 09 / 599,130 (32) Priority date June 22, 2000 (June 22, 2000) (33) Priority claiming countries United States (US) (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE), DE, JP, K R F-term (reference) 5F071 AA04 BB01 JJ04 JJ10                 5F072 AA04 HH02 HH07 HH09 JJ04                       JJ13 KK01 KK03 KK07 KK08                       KK09 KK15 KK18 KK30 MM08                       MM11 PP10 SS06 YY09

Claims (130)

[Claims] 1. A discharge chamber filled with a laser gas containing fluorine molecules and a buffer gas, a plurality of electrodes in the discharge chamber connected to a discharge circuit for supplying energy to the laser gas, and a wavelength of about 157 nm. Generate a laser beam having a linewidth of less than 1 pm,
A narrow band fluorine molecular laser system comprising an oscillator comprising a resonator comprising the discharge chamber and a line narrowing optics, and an amplifier, wherein a laser beam generated by the oscillator is increased in power of the beam. A laser system for directing through the amplifier for. 2. The laser system according to claim 1, wherein the line narrowing optics compares the maximum transmission of a selected portion of the spectral distribution of the beam with another portion of the spectral distribution of the beam. A laser system comprising one or more etalons tuned for relatively low transmission. 3. The laser system according to claim 2, wherein the line narrowing optical system includes a beam expander for expanding a beam incident on the one or more etalons before the one or more etalons. A laser system further comprising: 4. The laser system according to claim 3, wherein the beam expander includes a plurality of beam expansion prisms. 5. The laser system of claim 4, wherein the line narrowing optics further comprises a diffraction grating that selects a single coherence order of the one or more etalons.
The laser system of claim 1, wherein the selected interference order comprises the selected portion of the spectral distribution of the beam. 6. The laser system according to claim 4 or 5, further comprising a gap in the resonator. 7. The laser system according to claim 6, wherein the gap is arranged between the discharge chamber and the beam expander. 8. A laser system according to claim 4 or 5, wherein a first gap is provided on one side of the discharge chamber and a second gap is provided on the other side of the discharge chamber.
A laser system characterized by further comprising a gap. 9. The laser system according to claim 8, wherein the first gap is arranged between the discharge chamber and the beam expander. 10. The laser system according to claim 1, wherein the line narrowing optics compares the maximum transmission of a selected portion of the spectral distribution of the beam with another portion of the spectral distribution of the beam. A laser system comprising two etalons, each tuned for relatively low transmission. 11. The laser system of claim 10, wherein the line narrowing optics further comprises, prior to the etalon, a beam expander for expanding a beam incident on the etalon. system. 12. The laser system according to claim 11, wherein the beam expander includes a plurality of beam expanding prisms. 13. The laser system according to claim 12, wherein the line narrowing optics further comprises a diffraction grating selecting a single interference order of the etalon, the selected interference order of the beam. A laser system including the selected portion of the spectral distribution. 14. A laser system according to claim 12, further comprising a gap in the resonator. 15. The laser system according to claim 14, wherein the gap is arranged between the discharge chamber and the beam expander. 16. The laser system according to claim 12 or 13, further comprising a first gap on one side of the discharge chamber and a second gap on the other side of the discharge chamber. Laser system. 17. The laser system according to claim 16, wherein the first gap is arranged between the discharge chamber and the beam expander. 18. The system of claim 1, wherein the line narrowing optics has a maximum transmission of a selected portion of the spectral distribution of the beam and a relatively high portion of the other portion of the spectral distribution of the beam. A laser system including an etalon output coupler tuned for low transmission. 19. The laser system of claim 18, wherein the line narrowing optics further comprises optics for selecting a single interference order of the etalon output coupler. 20. The laser system of claim 18, wherein the line narrowing optics further comprises a diffraction grating selecting a single interference order of the etalon output coupler. 21. The laser system of claim 18, wherein the line narrowing optics further comprises a dispersive prism that selects a single interference order of the etalon output coupler. 22. The laser system of claim 18, wherein the line narrowing optics further comprises an etalon selecting a single interference order of the etalon output coupler. 23. The laser system according to claim 19, wherein the line narrowing optical system further includes a beam expander. 24. The laser system of claim 23, wherein the beam expander comprises one or more prisms. 25. The laser system of claim 23, further comprising a gap within the resonator. 26. The laser system of claim 25, further comprising a second gap, wherein the first and second gaps are located on opposite sides of the discharge chamber. 27. The laser system of claim 5, 13 or 20 further comprising a high reflectivity mirror after the diffraction grating, the diffraction grating comprising a Littman diffraction grating. Laser system. 28. The laser system of claim 5, 13 or 20 wherein the diffraction grating comprises a Littrow diffraction grating. 29. The laser system according to claim 1, wherein the buffer gas comprises neon which pressure-regulates the gas mixture and sufficiently increases output energy for a given input energy to deplete the fluorine molecules. A laser supply system that moves fluorine molecules into the discharge chamber, thereby replenishing the fluorine molecules into the discharge chamber; and a gas supply system that cooperates with the gas supply system to A laser system further comprising: a processor for controlling a fluorine molecule concentration and for keeping the fluorine molecule concentration within a predetermined range of the optimum performance of the fluorine molecule laser. 30. The laser system of claim 1, wherein the buffer gas comprises neon that pressure-regulates the gas mixture and sufficiently increases the energy stability of the laser, depleting the fluorine molecules, The laser system moves a fluorine molecule into the discharge chamber and thereby replenishes the fluorine molecule into the discharge chamber; and a gas supply system that cooperates with the gas supply system to provide fluorine in the discharge chamber. A laser system further comprising: a processor for controlling the molecular concentration and for maintaining the fluorine molecular concentration within a predetermined range of optimum performance of the molecular fluorine laser. 31. The laser system of claim 1, further comprising a spectral filter between the oscillator and the amplifier that further narrows the linewidth of the output beam of the oscillator. 32. The laser system according to claim 31, wherein the spectral filter has a maximum transmission of a selected portion of the spectral distribution of the beam and a relatively low transmission of another portion of the spectral distribution of the beam. A laser system comprising one or more etalons tuned for sex. 33. The laser system of claim 32, wherein the one or more etalons comprises two etalons. 34. The laser system of claim 32 or 33, wherein the spectral filter further comprises a bean expander before the one or more etalons. 35. The laser system of claim 31, wherein the spectral filter comprises a beam expander and a diffraction grating. 36. The laser system of claim 35, wherein the spectral filter further comprises collimating optics in front of the beam expander and diffraction grating. 37. The laser system of claim 36, further comprising a lens and a slit, the lens concentrating a beam passing through the slit before impinging on the collimating optics. system. 38. The laser system of claim 37, further comprising a second lens and a second slit, wherein the beam is retroreflected from the collimating optics, the beam expander and the diffraction grating before the second beam. A laser system characterized by focusing through a slit and the lens. 39. A discharge chamber filled with a laser gas containing a fluorine molecule and a buffer gas, which functions as both an oscillator and an amplifier, and a plurality of discharge chambers connected to a discharge circuit for supplying energy to the laser gas. An electrode, a resonator including the discharge chamber for generating a laser beam having a wavelength of about 157 nm, line narrowing optics for reducing the linewidth of the beam to less than 1 pm, and the generated and outcoupled beam. And an extra-cavity optical system that redirects from the oscillator into the discharge chamber at or near the maximum discharge current in the discharge chamber as an amplifier to increase the power of the beam. Narrow-band fluorine molecular laser system. 40. The laser system according to claim 39, wherein the extracavity optics time the incidence of the beam into the discharge chamber with respect to amplification at or near the maximum discharge current. A laser system comprising a line. 41. The laser system of claim 40, wherein the line narrowing optics is optical such that the beam traverses after being coupled out of the oscillator and before being re-injected into the chamber and amplified. A laser system including a spatially disposed off-cavity spectral filter. 42. The laser system of claim 41, wherein the spectral filter has a maximum transmission of a selected portion of the spectral distribution of the beam and a relatively low transmission of another portion of the spectral distribution of the beam. A laser system comprising one or more etalons tuned for sex. 43. The laser system of claim 42, wherein the one or more etalons comprises two etalons. 44. The laser system of claim 42 or 43, wherein the spectral filter further comprises a bean expander before the one or more etalons. 45. The laser system of claim 41, wherein the spectral filter comprises a beam expander and a diffraction grating. 46. The laser system of claim 45, wherein the spectral filter further comprises collimating optics in front of the beam expander and diffraction grating. 47. The laser system of claim 46, further comprising a lens and a slit, the lens concentrating a beam passing through the slit prior to impinging on the collimating optics. system. 48. The laser system of claim 47, further comprising a second lens and a second slit, the beam being retroreflected from the collimating optics, the beam expander and the diffraction grating before the second beam. A laser system characterized by focusing through a slit and the lens. 49. The laser system according to claim 39, wherein the line narrowing optical system includes an intracavity optical system. 50. The laser system of claim 49, wherein the intracavity optics compares the maximum transmission of a selected portion of the spectral distribution of the beam with another portion of the spectral distribution of the beam. A laser system comprising one or more etalons tuned for relatively low transmission. 51. The laser system of claim 50, wherein the intracavity optics comprises, prior to the one or more etalons, a bean expander that expands a beam incident on the one or more etalons. A laser system further comprising: 52. The laser system of claim 51, wherein the beam expander includes a plurality of beam expanding prisms. 53. The laser system of claim 52, wherein the intracavity optics further comprises a diffraction grating selecting a single coherence order of the one or more etalons, the coherence order being selected. A laser system including the selected portion of the spectral distribution of the beam. 54. The laser system of claim 52 or 53, further comprising a gap in the cavity. 55. The laser system according to claim 54, wherein the gap is disposed between the discharge chamber and the beam expander. 56. The laser system of claim 52 or 53, further comprising a first gap on one side of the discharge chamber and a second gap on the other side of the discharge chamber. Laser system. 57. The laser system according to claim 56, wherein the first gap is disposed between the discharge chamber and the beam expander. 58. The laser system of claim 49, wherein the intracavity optics compares the maximum transmission of a selected portion of the spectral distribution of the beam with another portion of the spectral distribution of the beam. A laser system comprising two etalons, each tuned for relatively low transmission. 59. The laser system of claim 58, wherein the intracavity optics further comprises, prior to the etalon, a bean expander that expands a beam incident on the etalon. system. 60. The laser system of claim 59, wherein the beam expander comprises a plurality of beam expanding prisms. 61. The laser system of claim 60, wherein the intracavity optics further comprises a diffraction grating selecting a single interference order of the etalon, the selected interference order of the beam. A laser system including the selected portion of the spectral distribution. 62. The laser system according to claim 60 or 61, further comprising a gap in the resonator. 63. The laser system of claim 62, wherein the gap is located between the discharge chamber and the beam expander. 64. The laser system of claim 60 or 61, further comprising a first gap on one side of the discharge chamber and a second gap on the other side of the discharge chamber. Laser system. 65. The laser system according to claim 64, wherein the first gap is disposed between the discharge chamber and the beam expander. 66. The system of claim 49, wherein the intra-cavity optics is configured such that the maximum transmission of a selected portion of the spectral distribution of the beam and the relative transmission of other portions of the spectral distribution of the beam. A laser system including an etalon output coupler tuned for low transmission. 67. The laser system of claim 66, wherein the intracavity optics further comprises optics for selecting a single interference order of the etalon output coupler. 68. The laser system of claim 66, wherein the intracavity optics further comprises a diffraction grating selecting a single interference order of the etalon output coupler. 69. The laser system of claim 66, wherein the intracavity optics further comprises a dispersive prism that selects a single interference order of the etalon output coupler. 70. The laser system of claim 66 wherein the intracavity optics further comprises an etalon selecting a single interference order of the etalon output coupler. 71. The laser system of any one of claims 67-70, wherein the intracavity optical system further comprises a beam expander. 72. The laser system of claim 71, wherein the beam expander comprises one or more prisms. 73. The laser system of claim 71, further comprising a gap within the resonator. 74. The laser system of claim 73, further comprising a second gap, wherein the first and second gaps are located on opposite sides of the discharge chamber. 75. A laser system according to claim 53, 61 or 68,
A laser system further comprising a high-reflectance mirror after the diffraction grating, wherein the diffraction grating comprises a Littman diffraction grating. 76. A laser system according to claim 53, 61, or 68,
A laser system, wherein the diffraction grating comprises a Littrow diffraction grating. 77. The laser system of claim 39, wherein the buffer gas comprises neon which pressure-regulates the gas mixture and sufficiently increases output energy for a given input energy to deplete the fluorine molecules. A laser supply system that moves fluorine molecules into the discharge chamber, thereby replenishing the fluorine molecules into the discharge chamber; and a gas supply system that cooperates with the gas supply system to A laser system further comprising: a processor for controlling a fluorine molecule concentration and for keeping the fluorine molecule concentration within a predetermined range of the optimum performance of the fluorine molecule laser. 78. The laser system of claim 39, wherein the buffer gas comprises neon that pressure-regulates the gas mixture and sufficiently increases the energy stability of the laser, depleting the fluorine molecules. The laser system moves a fluorine molecule into the discharge chamber and thereby replenishes the fluorine molecule into the discharge chamber; and a gas supply system that cooperates with the gas supply system to provide fluorine in the discharge chamber. A laser system further comprising: a processor for controlling the molecular concentration and for maintaining the fluorine molecular concentration within a predetermined range of optimum performance of the molecular fluorine laser. 79. The laser system of any one of claims 39-40, 49-53, 58-59, or 61, wherein the extra-cavity optics directs the beam back into the discharge chamber. A laser system comprising a beam expander that expands before entering and increases the amplification of the amplifier. 80. The laser system of claim 57, wherein the extra-cavity optics includes a beam expander that expands the beam before re-entering the discharge chamber to increase amplification of the amplifier. Laser system characterized by. 81. The laser system of claim 65, wherein the extra-cavity optics includes a beam expander that expands the beam before re-entering the discharge chamber to increase amplification of the amplifier. Laser system characterized by. 82. The laser system of claim 74, wherein the extra-cavity optics includes a beam expander that expands the beam before re-entering the discharge chamber to increase amplification of the amplifier. Laser system characterized by. 83. An optical waveguide filled with a laser gas containing fluorine molecules, and a pair of RFs connected to an RF power supply circuit for supplying energy to the laser gas.
Generating a laser beam having a wavelength of about 157 nm and a line width of less than 1 pm, and a plurality of electrodes surrounding the optical waveguide, including electrodes.
A narrow band fluorine molecular laser system comprising an oscillator comprising a resonator including the optical waveguide and a line narrowing optical system, and an amplifier, wherein a laser beam generated by the oscillator is increased in power of the beam. A laser system for directing through the amplifier for. 84. The laser system of claim 1, wherein the line narrowing optics compares a maximum transmission of a selected portion of the spectral distribution of the beam with another portion of the spectral distribution of the beam. A laser system comprising one or more etalons tuned for relatively low transmission. 85. The laser system of claim 84, wherein the line narrowing optics comprises, prior to the one or more etalons, a beam expander for expanding a beam incident on the one or more etalons. A laser system further comprising: 86. The laser system of claim 85, wherein the beam expander includes a plurality of beam expanding prisms. 87. The laser system of claim 86, wherein the line narrowing optics further comprises a diffraction grating selecting a single coherence order of the one or more etalons, the coherence order being selected. A laser system including the selected portion of the spectral distribution of the beam. 88. The laser system of claim 86 or 87, further comprising a gap within the resonator. 89. The laser system of claim 88, wherein the gap is located between the discharge chamber and the beam expander. 90. The laser system of claim 86 or 87, further comprising a first gap on one side of the discharge chamber and a second gap on the other side of the discharge chamber. Laser system. 91. The laser system of claim 90, wherein the first gap is located between the discharge chamber and the beam expander. 92. The system of claim 83, wherein the line narrowing optics comprises
A laser system comprising an etalon output coupler tuned for maximum transmission of selected portions of the spectral distribution of the beam and relatively low transmission of other portions of the spectral distribution of the beam. 93. The laser system of claim 92, wherein the line narrowing optics further comprises optics for selecting a single interference order of the etalon output coupler. 94. The laser system of claim 92 wherein the line narrowing optics further comprises a diffraction grating that selects a single interference order of the etalon output coupler. 95. The laser system of claim 92, wherein the line narrowing optics further comprises a dispersive prism selecting a single interference order of the etalon output coupler. 96. The laser system of claim 92, wherein the line narrowing optics further comprises an etalon selecting a single interference order of the etalon output coupler. 97. The laser system of any one of claims 93 through 96, wherein the line narrowing optics further comprises a beam expander. 98. The laser system of claim 97, wherein said beam expander comprises one or more prisms. 99. The laser system of claim 97, further comprising a gap within the resonator. 100. The laser system of claim 99, further comprising a second gap, wherein the first and second gaps are located on opposite sides of the discharge chamber. 101. A laser system according to claim 87 or 94, further comprising a high reflectance mirror after the diffraction grating, the diffraction grating comprising a Littman diffraction grating. system. 102. A laser system according to claim 87 or 94, wherein the diffraction grating comprises a Littrow diffraction grating. 103. A method of producing a laser beam at about 157 nm having a linewidth of less than 1 pm using a molecular fluorine gas discharge laser system, the step of producing a laser beam having a wavelength of about 157 nm; Narrowing the linewidth to less than 1 pm, outcoupling the beam from the resonator, and amplifying the outcoupled beam to increase the power of the beam. how to. 104. The method of claim 103, wherein the narrowing step comprises
A method comprising the steps of expanding and diverging the beam prior to the outcoupling step. 105. The method of claim 104, wherein the narrowing step comprises
A method comprising: passing the beam through one or more intracavity gaps. 106. The method according to claim 104 or 105, wherein the narrowing step comprises the step of interfering the beam with one or more elaton prior to the outcoupling step, The method, wherein the dispersing step comprises the step of selecting a spectral band remaining in the resonator that includes a single interference maximum of the one or more etalons. 107. The method of claim 106, wherein the outcoupling and interfering steps are performed simultaneously using an etalon output coupler. 108. The method of claim 103, wherein the narrowing step comprises
A method comprising expanding the beam using a beam expander and one or more etalons and interfering. 109. The method of claim 103, wherein the narrowing step comprises
A method comprising: interfering the beams, wherein the interfering step and the output combining step are performed simultaneously using an etalon output coupler. 110. The method of any one of claims 103-105 or 108-109, wherein between the output combining step and the amplifying step.
The method further comprising spectrally filtering the beam to further reduce the linewidth of the beam before amplification. 111. The method of claim 109 wherein the spectral filtering step comprises expanding and interfering the beam with one or more etalons. 112. The method of claim 109, wherein the spectral filtering step comprises expanding and interfering the beam. 113. The method of claim 103, wherein between the outcoupling step and the amplifying step, the amplification is timed and is performed at a predetermined time associated with the generating step. The method further comprising the step of optically delaying the beam. 114. In a narrow band fluorine molecular laser system, means for generating a laser beam having a wavelength of about 157 nm, means for narrowing the linewidth of the beam to less than 1 pm, and outputting the beam from a resonator. A laser system comprising means for combining and means for amplifying the out-combined beam to increase the power of the beam. 115. The laser system of claim 114, wherein said narrowing means includes means for expanding and diverging said beam. 116. The laser system of claim 115, wherein the narrowing means includes means for clipping the beam using one or more intracavity gaps. 117. The laser system of claims 115 or 116,
The narrowing means includes means for interfering the beams using one or more etalons, and the diverging means includes a spectral band remaining in the resonator including a single interference maximum of the one or more etalons. A laser system including means for selecting. 118. The laser system of claim 117, wherein said outcoupling means and interfering means comprise a single etalon output coupler. 119. The laser system of claim 114 wherein said narrowing means includes means for expanding and interfering said beam using a beam expander and one or more etalons. Laser system. 120. The laser system of claim 114, wherein said narrowing means comprises means for interfering said beams, said interfering and outcoupling means comprising a single etalon output coupler. Laser system. 121. The laser system of any one of claims 114-116 or 119-120, wherein said means for spectrally filtering said beam to further reduce the linewidth of said beam prior to amplification. A laser system further comprising means external to the laser system. 122. The laser system of claim 121 wherein said spectral filtering means includes means for expanding and interfering said beam with a beam expander and one or more etalons. Laser system. 123. The laser system of claim 121, wherein said spectral filtering means includes means for expanding and interfering with said beam. 124. The laser system of claim 114, further comprising means for optically delaying the beam to time the amplification of the beam and to perform the beam at a predetermined time. And laser system. 125. The laser system of claim 1, wherein the line narrowing optics includes a diffraction grating. 126. The laser system of claim 125, wherein the line narrowing optics further comprises a beam expander in front of the diffraction grating. 127. The laser system of claim 126, wherein the beam expander comprises one or more VUV transparent prisms. 128. The laser system of claim 127, further comprising a gap in the resonator between the discharge chamber and a prism beam expander. 129. The laser system of claim 128, further comprising a second gap on the other side of the discharge chamber. 130. The laser system of claim 127, further comprising a high reflectance mirror after the diffraction grating, the diffraction grating comprising a Littman diffraction grating.