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Timestamp: 2014-12-22 09:29:49
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Matched Legal Cases: ['application No. 60', 'application No. 60', 'application No. 60', 'application No. 60', 'art 1', 'application No. 02202776']

Patent US6727731 - Energy control for an excimer or molecular fluorine laser - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA method and gas replenishment algorithm for excimer and molecular fluorine lasers is based on parameters upon which gas aging more closely depends than pulse count, such as input energy to the electrical discharge, and also preferably time. A burst control method and algorithm includes measuring the...http://www.google.com/patents/US6727731?utm_source=gb-gplus-sharePatent US6727731 - Energy control for an excimer or molecular fluorine laserAdvanced Patent SearchPublication numberUS6727731 B1Publication typeGrantApplication numberUS 09/688,561Publication dateApr 27, 2004Filing dateOct 16, 2000Priority dateMar 12, 1999Fee statusLapsedPublication number09688561, 688561, US 6727731 B1, US 6727731B1, US-B1-6727731, US6727731 B1, US6727731B1InventorsUlrich Rebhan, Guenter NowinskiOriginal AssigneeLambda Physik AgExport CitationBiBTeX, EndNote, RefManPatent Citations (102), Non-Patent Citations (26), Referenced by (4), Classifications (28), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetEnergy control for an excimer or molecular fluorine laserUS 6727731 B1Abstract A method and gas replenishment algorithm for excimer and molecular fluorine lasers is based on parameters upon which gas aging more closely depends than pulse count, such as input energy to the electrical discharge, and also preferably time. A burst control method and algorithm includes measuring the energies of initial pulses of a first burst occurring after a long burst break, calculating values of input voltages for the initial pulses that would bring output energies of the individual laser pulses or groups of pulses to substantially the same values, and applying the calculated voltages in a subsequent first burst after a long burst break to achieve substantially same predetermined output energy values for the pulses or groups of pulses. Similar operations may be performed for one or more subsequent bursts following the first burst. The values for the first burst may be maintained in a first table of input voltage values to be read by a processor which signals a power supply circuit to apply the voltages according to the voltage values in the table. The values for subsequent bursts may be maintained in a second table, and a third table, etc. A final table such as the third table may be used for all subsequent bursts until another long burst break again occurs, after which the first table is again used for the first burst following the long burst break.
PRIORITY This application claims the benefit of priority to U.S. provisional patent application No. 60/159,525, filed Oct. 15, 1999, and No. 60/171,717, filed Dec. 22, 1999, and this application is a continuation-in-part of U.S. patent application Ser. No. 09/447,882, filed Nov. 23, 1999, which claims the benefit of U.S. provisional application No. 60/124,785, filed Mar. 17, 1999, and this application is a continuation-in-part of U.S. patent application Ser. No. 09/418,052, filed Oct. 14, 1999 now U.S. Pat. No. 6,243,406, which claims the benefit of U.S. provisional application No. 60/123,928, filed Mar. 12, 1999, and this application is a continuation-in-part of U.S. patent application Ser. No. 09/484,818, filed Jan. 18, 2000 now U.S. Pat. No. 6,243,405, which claims the benefit of U.S. provisional patent application No. 60/127,062, filed Mar. 31, 1999, all of the above application being hereby incorporated by reference.
Excimer and molecular fluorine lasers may be typically operated in burst mode. This means that the laser generates a �burst� of pulses, such as 100 to 500 pulses as mentioned above at a constant repetition rate, followed by a burst break or pause of from a few milliseconds up to a few seconds while the stepper/scanner does some wafer positioning. A burst break may be a short burst break such as may occur when the beam spot is moved to a different location on a same wafer, or may be a long burst break such as would occur when the stepper/scanner changes the wafer.
RECOGNIZED IN THE INVENTION There are short-term effects and long-term effects that influence the behavior associated with the energies of pulses during burst and from burst to burst. Short-term effects may last for only a few seconds or less. Long term effects include gas aging (several days), tube aging (several months) and maybe optical effects (years). These effects may be taken into account by changing controller parameters. The parameter adaptation may be advantageously performed automatically.
SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a gas replenishment algorithm that is based on parameters upon which gas aging more closely depends than pulse count, such as input energy to the electrical discharge, and also preferably time.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates energy versus pulse number for a burst of pulses from a pulsed gas discharge laser having the input high voltage kept constant during the burst.
INCORPORATION BY REFERENCE What follows is a cite list of references each of which is, in addition to those references cited above in the priority section, hereby incorporated by reference into the detailed description of the preferred embodiment below, as disclosing alternative embodiments of elements or features of the preferred embodiments not otherwise set forth in detail below. A single one or a combination of two or more of these references may be consulted to obtain a variation of the preferred embodiments described in the detailed description below. Further patent, patent application and non-patent references are cited in the written description and are also incorporated by reference into the preferred embodiment with the same effect as just described with respect to the following references:
Detailed Description of the Preferred Embodiment Gas Discharge Laser System
The laser resonator which surrounds the laser chamber 2 containing the laser gas mixture includes optics module 10 including line-narrowing optics for a line narrowed excimer or molecular fluorine laser, which may be replaced by a high reflectivity mirror or the like in a laser system wherein either line-narrowing is not desired, or if line narrowing is performed at the front optics module 12, or a spectral filter external to the resonator is used, or if the line-narrowing optics are disposed in front of the HR mirror, for narrowing the linewidth of the output beam. The laser chamber 2 is sealed by windows transparent to the wavelengths of the emitted laser radiation 14. The windows may be Brewster windows or may be aligned at another angle, e.g., 5�, to the optical path of the resonating beam. One of the windows may also serve to output couple the beam.
E=�*C*U 2 A gas replenishment action is preferably triggered when the accumulated input energy of a large number of laser pulses has reached a predetermined level. In a counter, the input energy of the laser pulses is added until a predetermined level Erepl is achieved. This level is preferably in the range of 0.1 to 10 MJ for lithography laser systems.
E repl =ΣE i=�*C*ΣU i 2, where is the standard symbol for taking a summation, and Ei and Ui and the energies and voltages corresponding to the ith particular pulse.
i =U+ΔU
i U i 2=(U+ΔU i)2 U 2+2*U*ΔU i, where the ΔUi 2 has been dropped according to this approximation. Then,
E repl�*C*Σ(U 2+2*U*ΔU i) This means the trigger level for gas replenishment Erepl is proportional to the accumulated variation in charging voltage.
E repl=[�*C*n*U 2] +[C*U*ΣU i] There may be many trigger levels such as Erepl 1, Erepl 2, etc. for performing different gas replenishment actions such as halogen injections or gas replacements of different amount or compositions of gases. As averred to above, the preferred gas replenishment algorithm may involve taking into consideration a combination of more just the accumulated energy applied to the discharge, such as including the time or charging voltage or other parameter that may be indicative of the halogen depletion in the laser tube 2.
If the pressure in the tube was, e.g., 3 bar prior to the injection and the tube has 40,000 cm3, and the injection is such that the pressure in the accumulator was reduced to 3 bar after the injection, then 2�20/40,000 bar would be the approximate pressure increase in the tube 2 as a result of the injection, or 1 mbar. If the premix A contains 1%F2:99%Ne, then the increase in partial pressure of the F2 in the laser tube as a result of the injection would be approximately 0.01 mbar.
After the new fill is performed, the halogen gas begins to react with components of the laser tube 2 that it comes into contact with, whether the laser is operating or not. �Gas replenishment� is a general term which includes gas replacement (PGRs and MGRs each subject to varying amounts and compositions of injected and released gases) and gas injections (HIs and enhanced HIs again each subject to varying amounts and compositions of injected gases), performed to bring the gas mixture status back closer to new fill status.
To compensate for the various depletion rates of the gases in the discharge chamber, the laser system of the preferred embodiment performs a variety of separate and cross-linked gas replenishment procedures, which take into account the variety of individual degradation rates by referring to a comprehensive database of different laser operating conditions. A preferred technique is disclosed in the Ser. No. 09/379,034 application already mentioned above. The behavior of the particular laser in operation and related experiences with gas degradation under different operating conditions are stored in that database and are used by a processor-controlled �expert system� to determine the current conditions in the laser and manage the gas replenishment or refurbishment operations. A history of gas actions performed during the current operation of the laser may also be used in accord with the present invention.
As mentioned above, series of small gas injections (referred to as enhanced and ordinary micro gas or halogen injections, or HI) can be used to return any constituent gas of an excimer or molecular laser, particularly the very active halogen, to its optimal concentration in the discharge chamber without disturbing significant output beam parameters. However, the gas mixture also degrades over time as contaminants build up in the discharge chamber 2. Therefore, mini gas replacements (mGR) and partial gas replacements (PGR) are also performed in the preferred methods. Gas replacement generally involves releasing some gas from the discharge chamber, including expelling some of the contaminants. mGR involves replacement of a small amount of gas periodically at longer intervals than the small HIs are performed. PGR involves still larger gas replacement and is performed at still longer periodic intervals generally for �cleaning� the gas mixture. The precise intervals in each case depend on consulting current laser operating conditions and the expert system and comprehensive database. The intervals are changes of parameters which vary with a known relationship to the degradation of the gas mixture. As such, the intervals may be one or a combination of time, pulse count, accumulated energy input to the discharge, charging or driving voltage or variations in charging voltage, pulse shape, pulse duration, pulse stability, beam profile, coherence, discharge width or bandwidth. In addition, the accumulated pulse energy dose may used as such an interval. Each of HI, mGR and may be performed while the laser system is up and running, thus not compromising laser uptime.
FIGS. 5 and 6 are graphs of driving voltage versus time also illustrating the intervals of periodic HI and periodic HI and mGR, respectively, for a fully operating system in accord with the present invention. FIG. 5 includes a plot of driving voltage versus time (A) wherein HIs are performed about every 12 minutes, as indicated by the vertical lines (some of which are designated for reference with a �B�) on the graph, for a narrowband laser running in 2000 Hz burst mode at 10 mJ output beam energy. The vertical axis only corresponds to graph A. As is shown by graph A, the small HIs produce no noticeable discontinuities in the driving voltage. The top horizontal axis shows the increasing accumulated energy to the discharge.
FIG. 6 is a plot (labelled �A�) of driving voltage versus time wherein HIs are performed about every 12 minutes, as indicated by the short vertical lines on the graph (again, some of which are designated for reference with a �B� and the vertical axis doesn't describe the halogen injections in any way), and mGR is performed about every 90 minutes, as indicated by the taller vertical lines on the graph (some of which are designated with a �C� for reference and again the vertical axis is insignificant in regard to the mGRs shown), for a narrowband laser running in 2000 Hz burst mode at 10 mJ output beam energy. Again, the driving voltage is substantially constant around 1.8 KV and no major changes, e.g., more than 5%, are observed. As with FIG. 5, the top horizontal axis shows the increasing accumulated energy to the discharge.
FIG. 7 includes a graph (labelled �A�) of pulse energy stability versus time of the laser pulses by values of standard deviation (SDEV) and moving average stabilities (�MAV) as percentages of the absolute pulse energy for a system in accord with the present invention. The graphs labelled �B� and �C� show the moving average for groups of 40 pulses each. During this run, micro-halogen injections were performed resulting in very stable continuous laser operation without any detectable deviations caused by the gas replenishment actions.
The overall calculation depends also on the amount of depletion that the halogen gas has undergone (or will undergo) between injections. Such depletion is, in principal, known as a function of many factors, e.g., including time and accumulated energy to the discharge (and possibly any of the parameters enumerated above or others). For example, a change in halogen partial pressure (or, alternatively, the number of halogen molecules) in the laser tube 2 in the interval between injections can be calculated to depend on kt�t and on kp�Einput, wherein kt and kEinput are constants that depend on the rate of halogen depletion with time and accumulated energy input to the discharge, respectively, and t and Einput are the amount of time and the accumulated energy input to the discharge, respectively, in the interval under consideration. The amount of accumulated energy to the discharge itself depends on the repetition rate and pulse energy, taking into account also the number of pulses in a burst and the pause intervals between bursts for a laser operating in burst mode. Again, other parameters may have an effect and may be additive terms included with this calculation.
ΔP(F 2)intrval ≈P(F2)injection −k t �Δt−k Ei �ΔEi,
ΔN(F 2)interval ≈N(F 2)injection −k t �Δt−k Ei �ΔE i, where the constants kt and kEi would differ from the partial pressure calculation by a units conversion.
50 ms to 20�50 ms=1 s corresponding to a short break; and
During a long burst break, the power supply charges to the HV value that is provided in the first position, i.e., HV1, of Table 1 to prepare for the first pulse. When the first pulse is triggered, and the HV1 value from Table 1 is applied and causes the first pulse to occur, the resulting pulse energy is measured. If the energy is too low or too high, i.e., the measured pulse energy is different from a target energy, then the HV value for the first pulse in Table 1 is increased or decreased depending on the degree of variance with the target energy, and possibly some other factors such as results of previous measurements of first pulses after previous long burst breaks. That is, the power supply is charged to HV1 and the measured energy of the resulting first pulse is E1 M. Then, the measured energy E1 M is subtracted from the target energy E1 T to get �E1=E1 T−E1 M. Then, �HV1=HV1 new−HV1 is used, wherein �HV1 is calculated from �E1, and �HV1 is added to or subtracted from HV1, such as to replace HV1 with HV1 new in the first position of Table 1. As a result, the first pulse of the first burst of the next burst sequence following a long burst break will be closer to the target energy, and the controller preferably continues to learn the optimal HV settings by successive iterations.
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Physik, 63, 54, 1930.25Wakabayashi et al., "Billion Level Durable ArF Excimer Laser with Highly Stable Energy," SPIE 24<th >Annual International Symposium on Microlithography, May 14-19, 1999.26Wakabayashi et al., "Billion Level Durable ArF Excimer Laser with Highly Stable Energy," SPIE 24th Annual International Symposium on Microlithography, May 14-19, 1999.Referenced byCiting PatentFiling datePublication dateApplicantTitleUS6822977 *Jun 6, 2002Nov 23, 2004Lambda Physik AgMethod and apparatus for compensation of beam property drifts detected by measurement systems outside of an excimer laserUS8518030Mar 10, 2006Aug 27, 2013Amo Manufacturing Usa, LlcOutput energy control for lasersUS8767791Apr 29, 2011Jul 1, 2014Cymer, LlcSystem and method for controlling gas concentration in a two-chamber gas discharge laser systemWO2012148613A1 *Mar 27, 2012Nov 1, 2012Cymer, Inc.System and method for controlling gas concentration in a two-chamber gas discharge laser system* Cited by examinerClassifications U.S. Classification327/25, 372/29.015, 372/38.02, 372/25, 372/30, 372/38.07International ClassificationH01S3/036, H01S3/225, H01S3/22, G03F7/20, H01S3/038, H01S3/134Cooperative ClassificationG03F7/70041, H01S3/036, H01S3/134, G03F7/70025, H01S3/225, H01S3/22, H01S3/038, H01S3/2258, G03F7/70575European ClassificationG03F7/70B8, G03F7/70L4F, G03F7/70B4, H01S3/22, H01S3/036, H01S3/134, H01S3/225Legal EventsDateCodeEventDescriptionJun 17, 2008FPExpired due to failure to pay maintenance feeEffective date: 20080427Apr 27, 2008LAPSLapse for failure to pay maintenance feesNov 5, 2007REMIMaintenance fee reminder mailedMay 5, 2003ASAssignmentOwner name: LAMBDA PHYSIK AG, GERMANYFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:REBHAN, ULRICH;NOWINSKI, GUENTER;REEL/FRAME:014019/0227;SIGNING DATES FROM 20030415 TO 20030417Owner name: LAMBDA PHYSIK AG HANS-BOECKER-STRASSE 12D-37079 GORotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google