|Publication number||USRE38039 E1|
|Application number||US 09/584,420|
|Publication date||Mar 18, 2003|
|Filing date||Jun 1, 2000|
|Priority date||Feb 1, 1996|
|Also published as||DE19603637C1, US5761236|
|Publication number||09584420, 584420, US RE38039 E1, US RE38039E1, US-E1-RE38039, USRE38039 E1, USRE38039E1|
|Inventors||Jürgen Kleinschmidt, Peter Heist|
|Original Assignee||Lambda Physik Ag|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (48), Non-Patent Citations (33), Referenced by (3), Classifications (12), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The instant invention relates to a laser for generating narrow-band radiation, comprising
a laser resonator which includes two reflecting elements and a laser active medium disposed between them,
a group of several refractive, wavelength selective elements each deflecting incident light at an angle which is specific of the wavelength of the incident light.
A laser of this kind is known from U.S. Pat. No. 5,150,370.
Lasers of the kind mentioned are applied particularly in the art of photographic lithography for the production of integrated circuits. Wavelengths below 200 nm are required for making structures in the dimension range of 0.18 μm by photographic lithography. Achromatic imaging optics for this wavelength range are difficult to produce. For this reason radiation of very narrow bandwidths is needed for the photolithographic production of structures of the above mentioned order of magnitude in order to keep errors caused by chromatic aberration in the structures obtained through photographic lithography within admissible tolerance limits. Acceptable bandwidths for refractive imaging optics lie in the range of 1 pm (refractive optics made of quartz alone: 0.3 pm, refractive optics of different materials: a few pm), the range extending from 10 pm to 100 pm for the catadioptrics which operate with a beam splitter and mirrors. In contrast thereto, an ArF excimer laser (λ=193 nm) has a bandwidth of 430 pm in the so-called free running operation so that optical elements must be provided inside the laser to limit the bandwidth if the above requirements are to be met.
It is known in the art to locate gratings providing beam expansion, prism assemblies, and/or Fabry-Perot etalons in the beam path of the resonator for narrowing the bandwidth.
As gratings and Fabry-Perot etalons are characterized by a high loss factor per round trip (transmission <70%) they are suited only conditionally for use in an ArF laser of which the resonator loss is much greater than in an XeCl or KrF laser, for instance. With Brewster prisms, on the other hand, and especially prisms with an antireflective coating the transmission is more than 95%.
Arrangements thus have been suggested with one or two dispersion prisms disposed in the resonator of the laser (1st International Symposium on 193 nm Lithography, Colorado Springs, Aug. 15-18, 1995). In this manner, bandwidths of approximately 10 pm can be achieved. The principle of such an arrangement is illustrated diagrammatically in FIG. 1 which depicts part of the beam path of the resonator. The incoming beam passes through an (optional) achromatic beam expander 1 and then is directed through a dispersion prism 2 to the highly reflective mirror 3 of the resonator which in turn reflects the incident light through the prism 2 and the beam expander 1 back to the second mirror of the resonator. The resonator mirror 3 is disposed at an angle with respect to the optical axis A of the laser, this angle corresponding to the deflection angle γ of the prism for the desired wavelength, e.g. λ=193 nm so that essentially only light of this wavelength is reflected and circulated in the resonator.
However, in excimer lasers including such prism assemblies time variations of the emission wavelength of the laser occur during burst operation, whereby the usefulness of the laser is limited as far as photographic lithography is concerned.
It is the object of the invention to improve a laser of the kind specified initially such that variations in radiation in response to temperature and, therefore, dependent on time during burst operation, are reduced as best as possible.
According to the solution proposed by the invention, in a laser for generating narrow-band radiation, comprising a laser resonator which includes two reflecting elements and a laser active medium disposed between them, as well as a group of several refractive, wavelength selective elements each deflecting incident light at an angle (γa, γb) which is specific of the wavelength of the incident light, at least one of the refractive, wavelength selective elements has a refractive index which rises as the temperature rises (dn/dT>0) and at least one of these elements has a refractive index which drops as the temperature rises (dn/dT<0). The laser may be an excimer laser, especially an ArF excimer laser. The group or refractive, wavelength selective elements preferably are arranged in the beam path of the resonator.
It was found that the variations in time of the emission wavelength, as observed with arrangements according to the state of the art, are due to the fact that the refractive index of the prisms used is dependent upon temperature and, therefore, the deflection angle for the desired radiation, e.g. light of 193 nm wavelength, varies during burst operation because of the radiation absorption in correspondence with the heating and cooling of the prisms. In accordance with the invention, this variation of the deflection angle at least is reduced by use of a combination of no less than two refractive elements which differ in sign of dn/dT.
If the elements are designed and arranged appropriately the temperature responsive changing of the deflection angle can be eliminated altogether. In particular, the angles of incidence at the refractive dispersive elements can be selected such that the sum of the individual deflection angles of the respective elements at a predetermined wavelength of the incident light is independent of temperature variations during operation of the laser.
For the ultraviolet range of the spectrum, quartz glass is the preferred material for at least one refractive dispersive element, especially quartz glass known under the tradename of Suprasil (dn/dT>0), while CaF2 (dn/dT<0) is the material for at least one refractive dispersive element.
A special embodiment of the invention comprises a beam splitter which is disposed between the laser active medium and one of the reflecting elements, the group of refractive, wavelength selective elements being arranged between the beam splitter and the reflecting element. In this way the assembly which confines the bandwidth is positioned in a part of the resonator which, in operation, has a relatively low light intensity as a consequence of which the service life of the assembly is prolonged.
The refractive, dispersive elements particularly may be dispersion prisms. At the same time, preferably at least one of these prisms is a Brewster prism. The surface of incidence of the other prisms may be given an antireflective coating.
The laser according to the invention especially may comprise a first dispersion prism and a second dispersion prism, the change in response to temperature of the refractive index of the first prism having a different sign than the change of the refractive index of the second prism, and the apex angle of the second prism being selected such that upon incidence of light radiating through the first prism on the second prism at the Brewster angle, the overall deflection angle as determined by the first and second prisms is independent of temperature variations during operation of the laser. This eliminates the need for an antireflective coating on the surface of incidence of the second prism.
Advantageously, the surfaces of incidence of the prisms are illuminated as completely as possible. To accomplish that, a beam expander may be arranged ahead of the first prism.
In another embodiment of the invention a Fabry-Perot etalon may be included in the beam path of the laser in front of or behind the group of refractive dispersive elements. Bandwidths of less than 1 pm are obtainable with this embodiment.
The invention will be described further, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 illustrates the principle of a prism assembly confining the bandwidth;
FIG. 2 diagrammatically shows a first embodiment of a laser arrangement according to the invention;
FIG. 3 shows the beam path through the two prisms confining the bandwidth in the laser arrangement shown in FIG. 2;
FIG. 4 presents the zero position function in dependence on the apex angle and the angle of incidence of the second prism for a first wavelength;
FIG. 5 presents the zero position function in dependence on the apex angle and the angle of incidence of the second prism for a second wavelength;
FIG. 6 depicts the assembly which confines the bandwidth in a second embodiment of the invention.
FIG. 2 is a diagrammatic presentation of the beam path of a first embodiment of the invention, an excimer laser being used as the example.
The laser resonator comprises two highly reflective mirrors 12, 14 with a laser active medium between them which is brought about by gas discharge caused by electrodes in an appropriate compartment 10. A polarizing beam splitter permitting approximately 98% of p-polarized light to pass while reflecting approximately 98% of s-p-polarized light is disposed between the laser active medium 10 and the mirror 12. At the other side, i.e. between the laser active medium 10 and the mirror 14, there is a rotary component 18 which rotates the polarization plane of the light, e.g. a λ/4 plate or a Faraday rotator. The polarizing beam splitter couples out essentially s-polarized light 15 from the resonator, while it passes essentially p-polarized light 16 which then is reflected by mirror 12 so as to run through another cycle in the resonator. Component 18 has the effect of coupling out a certain portion of the resonator radiation. The laser arrangement including the beam splitter 20 is advantageous in that only part of the radiation generated in the laser active medium is incident on optical elements which are arranged between the beam splitter 20 and the mirror 12, whereby their service life is prolonged.
An assembly which narrows the bandwidth is arranged between the beam splitter 20 and the mirror 12. It consists of an achromatic beam expander 30, a Brewster prism 32 made of a quartz glass which is highly transparent to ultraviolet light, preferably Suprasil, and a prism 34 made of CaF2 which is coated to render it antireflecting on its surface of incidence. The beam path through the prisms 32 and 34 is shown schematically in FIG. 3. The temperature coefficient of the refractive index, i.e. the derivation of the refractive index according to temperature is 18.10−6 K−1 for Suprasil and −3.10−6 K−1 for CaF2 at λ=193 nm. The deflection angle Γa of prism 32 thus changes in opposite sense to the deflection angle γb of prism 34 when the temperature changes. Therefore, the variation of the total angle γ=γa+γb upon temperature variation is kept small or even caused to disappear entirely.
The condition for disappearance of the variation of the total deflection angle γ following a temperature change ΔTa at prism 32 and a temperature change ΔTb at prism 34 may be expressed as follows:
wherein index “a” designates values belonging to prism 32 and index “b” designates values belonging to prism 34, na, nb being the refractive indices of prisms 32 and 34, respectively.
The table below lists the values used in the calculations made here:
refractive index n
dispersion dn/dλ (μm−1)
dn/dT (10−4 K−1)
20 . . . 30
specific heat c (J/g · K)
heat conductivity (W/m · K)
Data taken from: Journal of Non-Crystalline Solids 135 (1991 86; Kohlraush (1968), Herzeus, Quartzglas für Optik - Daten und Eigenschaften, 1994.
The derivations dγa/dna and dγb/dnb, in general, depend on the refractive index, the geometry of the refractive element, and the direction of the incident ray. For prisms in particular, they are determined by the respective refractice indices na, the apex angles εa, εb of the prisms, and the angles of incidence βa and βb, respectively, the relationship between the deflection angle γ, the angle of incidence β, the apex angle ε, and the refractive index n being well known.
Where effects of heat conduction are negligible, the following applies to the temperature change due to radiation absorption ΔT;
α=absorption coefficient of the material of the prism
g=density of the material of the prism
c=specific heat of the material of the prism
F=total fluence of the laser radiation at the entry into the prism.
Due to the negligible absorption within prism 32, the total fluence Fb at the entry into prism 34 is nearly the same as Fa (the total fluence into prism 32). Thus ΔTa/ΔTb is not time-dependent. The solution of equation (1), consequently, always is possible by proper choice of dγa/dna and dγb/dnb, respectively. If one applies any common numerical zero position search method equation (1) can be resolved readily according to any one of the determining values βa. εa. βb, and εb, for example according to angle of incidence βb, with apex angle εb of prism 34, apex angle ε, and the angle of incidence βa or prism 32 being given. Also, the respective value e.g. an angle of incidence βb which renders the whole deflection independent of temperature when the other values are given can be determined easily by experiment.
Solution of equation (1) for two different wavelengths are given below for purposes of illustration. To this end, it is convenient to define a zero position function G as follows:
The zero positions of G correspond to the solutions of equation (1).
In the first example, prism 32 is a Brewster prism made of Suprasil with symmetric beam passage and an apex angle εa=67.08°. The apex angle of CaF2 prism 34 was given as 75°, 75.5°, 76°. . . 78.5°, and equation (1) was resolved for λ=248 nm by determining the zero position of function G with βb being the variable. In FIG. 4, function G is plotted above the angle of incidence βb for the various apex angles. It will seen that for each apex angle εb an angle of incidence βb may be found at which the thermally provoked changes of the deflection angles γA, γb are compensated, in other words G=0. Compensation occurs, for example, for εb=77° and βb=55.86° (0.975 rad). Compensation especially may be achieved at the Brewster's angle (βb=0.972 rad) if the apex angle εb=76.9°. In this case it is not necessary to provide the entry surface of prism 34 with an antireflective coating.
In the second embodiment, prism 32 is a Brewster prism made of Suprasil with symmetric beam passage and an apex angle εa=65.3°. The apex angle of the CaF2 prism was given as 74°, 74.5°, 75°. . . 77.5°, and equation (1) was solved for λ=193 nm with βb as the variable. In FIG. 5, function G is plotted above the angle of incidence βb for the various apex angles. Here, compensation at the Brewster's angle (βb=0.973 rad) occurs at an apex angle εb=77.5°.
The principle described above may be applied readily also to assemblies which limit the bandwidth and contain more than two prisms. The corresponding generalization of equation (1) is as follows:
wherein indices c, d designate the respective values of the further prisms. Here, too, there always is a solution, provided at least one prism is made of a material having another sign of the temperature coefficient of the refractive index than that of the material of other prisms.
FIG. 6 illustrates an assembly narrowing the bandwidth in accordance with a second embodiment of the invention. This embodiment differs from the one shown in FIG. 1 in that the assembly narrowing the bandwidth includes a Fabry-Perot etalon 40 between prism 34 and mirror 12 in addition to the two prisms 32 and 34. Bandwidths of 1 pm and less are obtainable with this arrangement. Moreover, the apparatus according to the invention may comprise other elements to limit the bandwidth, such as a grating instead of mirror 14.
In the embodiments described above the narrowing prism assembly was located in the area between the beam splitter 20 and the mirror 12. This is advantageous in view of the fact that less radiation loading and less heating is suffered. In principle, a prism assembly with thermal compensation, as described above, may be positioned anywhere in the beam path of the laser. Thus the invention may realized also with other laser configurations than the one illustrated in FIG. 1, for instance, with those functioning without the polarizing beam splitter 20.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3611436||Jan 24, 1969||Oct 5, 1971||Bell Telephone Labor Inc||Mode-selective laser using resonant prisms|
|US3775699||Feb 3, 1971||Nov 27, 1973||Ferranti Ltd||Laser having a gas-filled fabry-perot etalon mode selector|
|US3868592||May 30, 1973||Feb 25, 1975||Coherent Radiation||Improved tuning apparatus for a dye laser|
|US4399540||Sep 22, 1980||Aug 16, 1983||Lamba Physik Gesellschaft Zur Herstellung Von Lasern Mbh & Co. Kg||Tunable laser oscillator|
|US4696012||Jun 11, 1985||Sep 22, 1987||Texas Instruments Incorporated||Tunable multiline/multiband laser|
|US4829536||Jun 9, 1987||May 9, 1989||Kabushiki Kaisha Komatsu Seisakusho||Multi-mode narrow-band oscillation excimer laser|
|US4856018||Jan 20, 1987||Aug 8, 1989||Kabushiki Kaisha Komatsu Seisakusho||Light source for reduced projection|
|US4873692||Aug 12, 1988||Oct 10, 1989||Spectra-Physics||Pulsed tunable solid state laser|
|US4905243||Dec 22, 1988||Feb 27, 1990||Lambda Physik Forschungs-Und Entwicklungs-Gmbh||Method and apparatus for stabilizing the frequency of a laser beam|
|US4942583||Jun 17, 1988||Jul 17, 1990||Hewlett-Packard Company||Misalignment-tolerant, grating-tuned external-cavity laser|
|US4972429||Nov 18, 1988||Nov 20, 1990||Spectra-Physics, Inc.||Achromatic prism beam expander for high magnification and tunable laser using same|
|US4975919||Mar 18, 1988||Dec 4, 1990||Kabushiki Kaisha Komatsu Seisakusho||Laser wavelength control apparatus|
|US4977563||Sep 22, 1988||Dec 11, 1990||Mitsubishi Denki Kabushiki Kaisha||Laser apparatus|
|US4985898||Mar 1, 1990||Jan 15, 1991||Matsushita Electric Industrial Co., Ltd.||Narrow-band laser apparatus|
|US5081635||Aug 25, 1988||Jan 14, 1992||Kabushiki Kaisha Komatsu Seisakusho||Apparatus for controlling output from an excimer laser device|
|US5095492||Jul 17, 1990||Mar 10, 1992||Cymer Laser Technologies||Spectral narrowing technique|
|US5142543||Jan 27, 1989||Aug 25, 1992||Kabushiki Kaisha Komatsu Seisakusho||Method and system for controlling narrow-band oscillation excimer laser|
|US5150370||Dec 12, 1990||Sep 22, 1992||Matsushita Electric Industrial Co., Ltd.||Narrow-band laser apparatus|
|US5226050||Jan 25, 1991||Jul 6, 1993||Lambda Physik Forschungs - Und Entwicklungsgesellschaft - Gmbh||Small line width tunable laser|
|US5404366||Feb 14, 1994||Apr 4, 1995||Kabushiki Kaisha Komatsu Seisakusho||Narrow band excimer laser and wavelength detecting apparatus|
|US5414723||Feb 14, 1992||May 9, 1995||Krapchev; Vladimir B.||Infrared laser system|
|US5559816||May 30, 1995||Sep 24, 1996||Lambda Physik Gesellschaft Zur Herstellung Von Lasern Mbh||Narrow-band laser apparatus|
|US5596456||Feb 25, 1994||Jan 21, 1997||New Focus, Inc.||Achromatic anamorphic prism pair|
|US5596596||Dec 15, 1995||Jan 21, 1997||Kabushiki Kaisha Komatsu Seisakusho||Narrow band excimer laser|
|US5646954||Feb 12, 1996||Jul 8, 1997||Cymer, Inc.||Maintenance strategy control system and monitoring method for gas discharge lasers|
|US5657334||Feb 15, 1996||Aug 12, 1997||Cymer, Inc.||External high voltage control for a laser system|
|US5659419||Jul 11, 1995||Aug 19, 1997||Lambda Physik Gesellschaft Zur Herstellung Von Lasern Mbh||Tunable narrowband optical parametrical oscillator|
|US5663973||Jun 10, 1996||Sep 2, 1997||Lambda Physik Gesellschaft Zur Herstellung Von Lasern Mbh||Tunable narrowband source of a coherent radiation|
|US5684822||Nov 17, 1994||Nov 4, 1997||Cymer, Inc.||Laser system with anamorphic confocal unstable resonator|
|US5748316||Oct 20, 1994||May 5, 1998||Komatsu, Ltd.||Detector for wavelength of excimer laser|
|US5761236||Jul 18, 1996||Jun 2, 1998||Lambda Physik Gesellschaft Zur Herstellung Von Lasern Mbh||Laser for generating narrow-band radiation|
|US5802094||Oct 10, 1996||Sep 1, 1998||Kabushiki Kaisha Komatsu||Narrow band excimer laser|
|US5835520||Apr 23, 1997||Nov 10, 1998||Cymer, Inc.||Very narrow band KrF laser|
|US5852627||Sep 10, 1997||Dec 22, 1998||Cymer, Inc.||Laser with line narrowing output coupler|
|US5856991||Jun 4, 1997||Jan 5, 1999||Cymer, Inc.||Very narrow band laser|
|US5898725||Jan 21, 1997||Apr 27, 1999||Cymer, Inc.||Excimer laser with greater spectral bandwidth and beam stability|
|US5901163||Dec 8, 1997||May 4, 1999||Cymer, Inc.||Narrow band laser with etalon based output coupler|
|US5917849||Sep 10, 1997||Jun 29, 1999||Cymer, Inc.||Line narrowing device with double duty grating|
|US5946337||Apr 29, 1998||Aug 31, 1999||Lambda Physik Gmbh||Hybrid laser resonator with special line narrowing|
|US5970082||Jul 1, 1997||Oct 19, 1999||Cymer, Inc.||Very narrow band laser|
|US5978409||Sep 28, 1998||Nov 2, 1999||Cymer, Inc.||Line narrowing apparatus with high transparency prism beam expander|
|US5999318||Mar 9, 1999||Dec 7, 1999||Cymer, Inc.||Reflective overcoat for replicated diffraction gratings|
|EP0395717A1||Jan 11, 1989||Nov 7, 1990||Ardenne Stiftung||Device for ablative photodecomposition of organic and inorganic substances, in particular hard dental materials.|
|EP0402570A2||Mar 1, 1990||Dec 19, 1990||Matsushita Electric Industrial Co., Ltd.||Narrow-band laser apparatus|
|EP0472727A1||May 18, 1990||Mar 4, 1992||Kabushiki Kaisha Komatsu Seisakusho||Narrow-band oscillation excimer laser|
|JPS60205420A||Title not available|
|JPS61139950A||Title not available|
|WO1996016455A1||Nov 16, 1995||May 30, 1996||Cymer Laser Technologies||Laser system with anamorphic confocal unstable resonator|
|1||A. Bloom, "Modes of a Laser Resonator Containing Tilted Birefringent Plates," J. of the Optical Society of America, vol. 64, No. 4, Lancaster Press, Inc., Lancaster PA, Apr. 1974, pp. 447-452.|
|2||Abstract and handouts of an Aug. 15-18, 1995 conference in Colorado Springs, Colorado, from First International Symposium on 193nm Lithography. "ArF Excimer Laser with High Repetition Rate for DUV Lithography," by R. Pätzel et al., 21 pages.|
|3||Abstract and handouts of and Aug. 15-18, 1995, conference, in Colorado Springs, Colorado, from First International Symposium on 193nm Litography, "ArF Excimer Laser with High Reptition Rate for DUV Lithography," by R. Pätzel, I. Bragin, U. Rebhan & d. Basting, 21 pages in length.|
|4||D. Basting et al., "Processing of PTFE with High Power VUV Laser Radiation," 3 pages. [No Date].|
|5||D. Basting, "Industrial Excimer Lasers," pp. 40-41. [No Date].|
|6||D.J. Krajnovich et al., "Testing of the durability of single-crystal calcium fluoride with and without antireflection coatings for use with high-power KrF excimer lasers," Applied Optics, vol. 31, No. 28, Oct. 1, 1992, pp. 6062-6075.|
|7||E. Armandillo et al., "Simple, compact, high-repetiton rate XeCI laser," Review of Scientific Instruments, Vo. 56, No. 5, Part 1, May 1985, pp. 674-676.|
|8||Irving J. Bigio et al., "Injection-Locking Unstable Resonator Excimer Lasers," IEEE J. of Quantum Electronics, vol. QE-19, No. 9, Sep. 1983, pp. 1426-1436.|
|9||J.H.C. Sedlacek et al., "Optical materials for use with excimer lasers," SPIE, vol. 1835, Excimer Lasers, Nov. 1992, pp. 80-88.|
|10||J.H.C. Sedlacek et al., "Performance of Excimer Lasers As Light Sources for 193-nm Lithography," Proceedings of SPIE, Optical Microlithography X, Mar. 12-14, 1997, Santa Clara, CA vol. 3051, pp. 874-881.|
|11||K. Wani et al., "Narrow-band KrF Excimer laser-tunable and wavelength stabilized," SPIE-The International Society for Optical Engineering, Excimer Beam Applications, vol. 998, Sep. 6, 1988, Boston, MA, 10 pages.|
|12||K. Wani et al., "Narrow-band KrF excimer laser-tunable and wavelength stabilized," SPIE-The International Society for Optical Engineering, Excimer Beam Applicatons, vol. 998, Sep. 6, 1988, Boston, MA, 10 pages.|
|13||K. Wani et al., "Narrow-band KrF Excimer laser—tunable and wavelength stabilized," SPIE—The International Society for Optical Engineering, Excimer Beam Applications, vol. 998, Sep. 6, 1988, Boston, MA, 10 pages.|
|14||K. Wani et al., "Narrow-band KrF excimer laser—tunable and wavelength stabilized," SPIE—The International Society for Optical Engineering, Excimer Beam Applicatons, vol. 998, Sep. 6, 1988, Boston, MA, 10 pages.|
|15||M. Kakehata et al., "Experimental Study of Tunability of a Discharge Pumped Molecular Fluorine Laser," Conference on Lasers and Electro-optics, vol. 7, Optical Society of America, May 1990.|
|16||M. Mizoguchi et al., "100-fs, 10-Hz, terawatt KrF laser," J. Opt. Soc. Am B, vol. 9, No. 4, Apr. 1992, pp. 560-564.|
|17||M. Okada et al., "Electronic Tuning of Dye Lasers by an Electrooptic Birefringent Fabry-Perot Etalon," Optics Communications, vol. 14, No. 1, North-Holland Publishing Co., Amsterdam, May 1975, pp. 4-7.|
|18||M. Rothschild et al., "193-nm Lithography," Proceedings of SPIE, Lasers as Tools for Manufacturing of Durable Goods and Microelectronics, Jan. 29-Feb. 2, 1996, San Jose, CA vol. 2703, pp. 398-404.|
|19||M. Rothschild et al., "Optical Materials for 193-nm Lithography," First Intl. Symp. on 193nm Lithography, Digest of Abstracts, Aug. 15-18, 1995, 1 page.|
|20||Nagia, et al. "Development of High-Power Narrow Spectrum Tunable Excimer Laser", Mitsubishi Heavy Industries Report, vol. 30, No. 5 (1993-9) pp. 443-446 "Translated".|
|21||Press release entitled: "Lambda Physik shows readiness for the future challenges of microlithography," Fort Lauderdale, FL, Dec. 1997, 2 pages.|
|22||R.K. Brimacombe et al., "Line-narrowed industrial excimer laser for microlithography," Conference on Lasers and Electro-Optics, 1989 Technical Digest Series, vol. 11, Apr. 24-29, 1989, Baltimore, MD, 24 pages.|
|23||R.L. Sandstrom, "Measurements of beam characteristics relevant to DUV microlithography on KrF excimer laser," SPIE vol. 1264, Optical/Laser Microlithography III (Mar. 1990), pp. 505-519.|
|24||S. Saikan, "Nitrogen-Laser-Pmped Single-Mode Dye Laser," Applied Physics, 1978, 4 pages.|
|25||S.A. Myers, "An Improved Line Narrowing Technique for a Dye Laser Excited by a Nitrogen Laser," Optics Communications, vol. 4, No. 2, Oct. 1971, pp. 187-189.|
|26||Shintaro Kawata et al., "Spatial coherence of KrF excimer lasers," Applied Optics, vol. 31, No. 3, Jan. 20, 1992, pp. 387-396.|
|27||T.J. McKee, "Spectral-narrowing techniques for excimer laser oscillators," Canadian J. of Physics, vol. 63, No. 2, Feb. 1985, pp. 214-219.|
|28||T.W. Hänsch, "Repetitively Pulsed Tunable Dye Laser for High Resolution Spectroscopy," Applied Optics, Apr. 1972, vol. 11, No. 4, pp. 895-898.|
|29||Technology World Briefs, "Laser Could Extend Optical Lithography into VUV," Photonics Spectra, Jan. 1998, p. 48.|
|30||V.N. Ischenko et al., "High-Power Efficient Vacuum Ultraviolet F2 Laser Excited by an Electric Discharge," Soviet J. of Quantum Electronics, vol. 16, No. 5, American Institute of Physics, May 1986, pp. 707-709.|
|31||Y. G. Basov, "Telescopic and dispersive prism devices for laser technology," J. Opt. Technol., vol. 62 (3), Mar. 1995, pp. 141-152.|
|32||Y.G. Basov, "Telescopic and dispersive prism devices for laser technology," J. Opt. Technol., vol. 62(3), Mar. 1995, pp. 141-152.|
|33||Z. Haixing et al., "Some problems in 1:1 broadband excimer laser lithography," Proceedings, SPIE, Optical/Laser Microlithography V, Mar. 11-13, 1992, vol. 1674, pp. 701-706.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US6594301 *||Mar 21, 2001||Jul 15, 2003||Coherent, Inc.||Tunable modelocked ultrafast laser|
|US7899095 *||Mar 1, 2011||Cymer, Inc.||Laser lithography system with improved bandwidth control|
|US20080253413 *||Apr 9, 2008||Oct 16, 2008||Cymer, Inc.||Laser lithography system with improved bandwidth control|
|U.S. Classification||372/100, 372/20, 372/102, 372/32|
|International Classification||H01S3/225, H01S3/134, H01S3/08, H01S3/137|
|Cooperative Classification||H01S3/225, H01S3/137, H01S3/08004|
|Oct 31, 2005||FPAY||Fee payment|
Year of fee payment: 8
|Nov 4, 2009||FPAY||Fee payment|
Year of fee payment: 12