JP2000151002A - Performance control method for gas discharge laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an efficient and sensitive method for deciding the condition of a laser mixed gas and degree of its aging or degradation. SOLUTION: A master data set, corresponding to a mixed gas wherein an output parameter such as output beam energy, is optimum to an input parameter such as a drive voltage applied to a discharge circuit of a discharge chamber by a power source is generally generated after the new filling at a factory. At another time, a current data set of output and input parameters corresponding to the current state of mixed gas is generated during the next start-up procedure (S4). The current state data set is then compared to the master data set (S5), so that the difference between the current state and the master data set is found (S6). Then, a followup procedure is performed automatically by a processor, based on the comparison (S9).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a method (and system) for determining the condition of a laser gas mixture in a discharge chamber of a gas discharge laser, and more particularly to an applied drive discharge voltage or other adjustable voltage. The parameters of the output laser beam relative to the input parameters are measured and the measured data is compared to a master set or a set of stored data to determine the condition of the laser gas mixture and / or electrical, mechanical or optical problems. A method (and system) for determining whether it is present within the system.

[0002]

BACKGROUND OF THE INVENTION Gas discharge lasers, such as excimer or molecular lasers, are well known as valuable tools for many industrial applications. There is a great demand for excimer laser applications in many areas, especially in electronics and photolithography processes, to have precise control over long durations and simultaneous stabilization of many laser parameters. The amount of "uptime" of the laser, or the time the laser is in operation and used for industrial use, is a key variable when discussing operating costs. It would be desirable to be able to tune, sensitively control, and stabilize various laser parameters continuously and efficiently.

The types and qualities of gas discharges include output power, energy stability, efficiency, bandwidth, long and short axis ray profiles, pulse widths in time and space, ray divergence and coherence. Affects many important laser parameters. The quality of the gas discharge depends on factors such as the composition of the gas mixture in the discharge chamber, the quality of the preionization used, the characteristics of the discharge circuit and the outer shape of the electrodes used. See R.S. S. Taylor's Journal of Applied Physics B41, PP. 1-24 (1986). Decomposition and contamination of the gas mixture and design of the gas exchange system (eg, flow rate) also strongly determine the limits of achievable laser parameters. Fast gas exchange between the electrodes may be achieved by using a laser discharge chamber design that includes fast blower gas circulation. Cryostatic devices and techniques may be used for additional gas purification. For further details, reference is made to DE 3212928.

[0004] Optimal gas mixtures for various gas discharge lasers are generally known. F ₂ : Kr: Ne is 0.
The ratio of 1: 1.0: 98.9 is sufficiently optimal for, for example, a KrF-excimer laser, and the ratio of F ₂ : Ne of 0.1: 99.9 is not sufficient. It is believed to be well suited for F ₂ -excimer lasers. Figure 1 is a plot of laser output power for F ₂ concentration and represents a method for determining what is actually optimal F ₂ concentration. Time has elapsed, as the laser is running, the gas mixture "ages" continuously degraded or results, via a chemical reaction between the metal dust F ₂ is diluted, F ₂ is consumed. In this regard, see U.S. Pat. No. 4,977,573 to Bittenson, assigned to the present assignee. After a certain amount of time, after a certain number of pulses, or after a certain amount of parameter change, such as a change in the discharge voltage to compensate for gas degradation and maintain a particularly constant output energy, the gas Partial gas replacement (PRG) of a replenishment or volume of gas mixture, such as halogen injection (HI), to restore the original distribution as closely as possible and fully restore and optimize laser parameters An overall fresh replenishment of the gas mixture is performed.

[0005] It is also desirable that the life of the laser mixed gas can be extended. Problems associated with changing the laser mixture from optimum as the laser gas decomposes significantly reduce laser output performance, resulting in processing errors and excessive laser downtime.

A mass spectrometer may be used for accuracy analysis of the composition of the gas mixture. See Bedwell U.S. Pat. No. 5,090,020 for details.
However, for continuous operation of excimer laser and molecular laser systems, mass spectrometers are undesirably large and expensive equipment components. Other methods of monitoring the condition of the laser gas mixture include measuring the spectral width or bandwidth of the laser emission (see US Pat. No. 5,450,436 to Mizoguchi et al.) And measuring the beam profile of the laser emission. (Wakabayashi's US Patent No. 5,
642,374) and measuring other properties such as the discharge width or the temporal pulse width of the output beam, where a rough assessment of the state of the gas mixture may be made. For further details, see U.S. Pat. No. 5,440,578 to Sandstrom. Another technique for measuring the aging of the laser gas mixture is to count the total number of laser pulses since the most recent new fill of the discharge chamber. See Das US Patent No. 5,646,954 for details.

[0007] Many techniques are known in which the output beam energy or effectiveness is monitored and steps are taken to maintain the output beam at optimal energy. See Hotrich U.S. Pat. No. 3,899,750, Yoshida et al. U.S. Pat. No. 4,429,392, and Bittenson et al. U.S. Pat. No. 4,977,573. Noble and halogen gas concentrations have also been maintained by using a complex sequence of chemical reactions to determine mixed gas concentrations and replenishing exhausted gas. See U.S. Pat. No. 4,740,982 to Hakta et al.

[0008]

The parameters measured and monitored to determine the state of the laser gas mixture are each other than the gas mixture state, such as, for example, stabilized output energy, repetition rate, etc. Depends on other parameters. They are based on the generally well-known behavior of laser systems and general experience with the aging of the gas mixture in the discharge chamber. It is desirable to have a technique for monitoring a gas mixture without changing other parameters that affect the analysis. It is also desirable that the characteristics of the discharge chamber, optics and discharge circuit, etc., be taken into account in the procedure for monitoring the gas mixture to achieve greater integrity and accuracy.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an efficient and sensitive method and system for determining the state of a gas mixture and its aging or deterioration.

[0010]

SUMMARY OF THE INVENTION To solve the above-mentioned problems, in the method and system of the present invention, an internal computer control system preferably includes a laser mixture gas in the discharge chamber during a particular check subroutine. Determine the state of. For example, pulse energy, bandwidth, long or short axis ray profile, energy stability, energy efficiency,
Amplified spontaneous release (ASE (amplified spontaneous
emission)), discharge width, ray divergence, ray coherence,
Output light parameters, such as spatial or temporal pulse width, are measured and stored by an internal control system for input parameters, such as drive voltage. The measured data is then used to determine the master profile or master data set measured when an optimal gas mixture condition exists, such as after a new fill of the discharge chamber with the gas mixture. Is compared to Preferably, the plurality of master data sets are measured as respectively corresponding to different operating states of the laser independent of the gas mixture state.

Within the system, for example, output pulse energy, bandwidth, long or short axis ray profile, energy stability, energy efficiency, amplified spontaneous emission (AS)
E) an output beam having at least one measurable characteristic parameter such as discharge width, beam divergence, beam coherence, spatial or temporal pulse width, beam coherence, spatial pulse width or temporal pulse width. And a method for determining the condition of the gas mixture of a gas laser system comprising a discharge chamber containing the gas mixture. However, in the discharge chamber, energy is supplied to the mixed gas by applying a drive discharge voltage to the electrodes of the discharge circuit from a power supply. For a laser having a particular operating state, preferably comprising an optimal gas mixture depending on the operating state, a master distribution or master data set of output beam parameters is measured for input parameters such as drive voltage. This master data set is stored in the memory of the control system of the laser where it is desired to measure the state of the gas mixture at a later time. At another time, preferably during a check subroutine, such as during a start-up procedure, the current state data set of the measured output beam parameters in the master data set relative to the measured input parameters in the master data set is transmitted to the gas discharge laser. Measured. The current state data set is then compared to the master data set and the deviation is noted for numerical and / or derivative values, for example, for slopes or integrals at data points along a curve defined by the data set.

A small deviation, eg, in value or gradient, between the master status data and the current status data generally indicates that the laser gas mixture has aged or that the F ₂ concentration of the gas mixture has been somewhat depleted. Will be shown. Large deviations may indicate that new replenishment is needed, or significant mechanical,
It may indicate that an electrical or optical hardware problem exists in the system. A follow-up procedure is then performed, depending on whether there is a gap between the master state dataset and the current data state dataset, and what type of gap exists. Be executed.

[0013] The current data set may be measured after a new refill, and the data set is compared to a master data set obtained after a previous new refill. If a gap exists between the newly refilled master dataset and the current dataset, otherwise a hardware problem when the gas mixture has not yet aged, assuming that the operating conditions have not changed. Is suspected.

In a preferred embodiment, one or more calibration data sets corresponding to different gas mixture conditions and / or laser operating conditions are first measured and stored. The processor compares the current state data (status data) deviated from the master data set with the calibration data set to find a calibration data set that is most similarly deviated from the master data set. The processor then determines from the stored gas mixture data for the similarly offset calibration data what type of follow-up procedure should be performed. For example, follow-up procedures, F _2, or HCl, or active rare gas, or a mixture of halide molecules and the active noble gas, such as may include recruitment of molecules of a quantity comprising active halide species.

[0015] A gas discharge laser system is also provided. The laser system includes a discharge chamber containing a laser gas mixture and a resonator to generate a laser beam. The power supply circuit supplies energy to the gas mixture by applying a drive voltage to a discharge circuit that ultimately provides a potential difference via electrodes in the discharge chamber. The system further comprises means for measuring input parameters, such as, for example, drive voltage, and means for measuring output beam parameters, which have already been mentioned, such as, for example, the output power of the laser, that vary with the state of the gas mixture. Prepare. The processor is
It then receives the input and output parameter measurements as the current state data set. The current state data set is compared to a master data set representing a fully optimal gas mixture and laser operating state. The master data set used may vary between other operating conditions, such as laser systems of different ages or repetition rates. The current state data set may be, for example, following a halogen refill procedure, during an initial start-up procedure, during one or more subsequent start-up procedures, after a subsequent new refill, or under conditions other than optimal gas mixture conditions. , Measured, may also be compared with one or more calibration data sets. The follow-up procedure may be performed depending on the type of deviation known from the comparison, such as a numerical value, a derivative value, or an integral value at a point along the curve defined by the data set.

[0016]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

According to the invention, the output and input parameters are measured under optimal gas laser conditions and under various other conditions of the gas mixture and the laser system, and are preferably associated with at least one master data set. Is set with one or more calibration data sets. During the continuous operation of the laser, the same parameters are measured and a current data set relating to the current gas mixture state and the laser operating state is set. The current data set may be measured using the same or a different laser as the master data set. One or more calibration data sets may also be measured and stored using the same or different lasers as the current data set. The master data set and the calibration data set may also be measured using the same or different lasers. The current data set is compared to the master data set, and is also preferably compared to at least one of the one or more calibration data sets, especially when a deviation is found between the master data set and the current data set.

In the preferred embodiment of the present invention described below with reference to the accompanying drawings, the output light parameter is pulse energy and the input parameter is drive voltage. Bandwidth or spectral width, long or short ray contour, ray divergence, temporal or spatial ray coherence, energy stability, energy efficiency, discharge width and spatial or temporal pulse width, or excimer or molecular laser Other parameters, such as the other parameters that vary with the gas mixture of the gas laser, may be used as output beam parameters to be measured. The input parameter may be another parameter that changes as the laser system is operated and / or statically ages.

FIG. 2 shows a qualitative plot of the output energy of a gas laser as a function of the drive voltage of the laser drive circuit. The measured drive voltage is preferably that applied to the discharge circuit from the laser power supply. The power supply generally charges a charging capacitor connected to a step-up transformer. The connection is controlled by a switch. Voltage from the step-up transformer is applied to a set of electrodes in the discharge chamber. Another voltage, such as the voltage on the electrodes or the voltage of the charging or peaking capacitor, may be measured instead.

In this manner, energy is imparted to the laser gas and excites the molecules of the laser gas to higher energy states where relaxation of the molecules from that state is a source of lasing action. In some lasers, this voltage is applied to the pump medium, not to the laser active gas itself, but the drive voltage (or current) is still present in almost every known laser system. As shown, the slope of the laser output energy curve versus drive voltage of FIG. 2 is everywhere positive,
Increases with voltage. This graph is generated using experimentally measured data values for a wide variety of gas discharge lasers. That is, in general, the graph of FIG.
KrF, ArF, F ₂ , XeCl, XeF, and Kr
It shows features common to gas discharge lasers such as excimer lasers such as Cl lasers and molecular lasers.

The graph of FIG. 2 represents a data set stored in an internal computer control system (hereinafter "processor") of the laser system. Computer
Preferably, data representative of the value of the drive voltage applied to the main discharge circuit from the power supply is received, while at the same time preferably the output energy or power of the laser beam is received from an energy meter or power meter. Several data points of the output energy with respect to the drive voltage are measured and stored. Preferably, a graph as shown in FIG. 2 is generated and produced by the processor. Data is preferably taken during a particular subroutine executed during the startup subroutine of the gas laser system, and a graph is generated. However, it is desirable to check the quality of the laser mixed gas in the discharge chamber.

In practice, the relationship between drive voltage and laser output energy has a unique dependence on the particular characteristic curve of the laser gas mixture. Examination of the graphs generated during the start-up procedure reveals the relative distribution of the individual gases in the mixture, the total pressure, and the aging and degradation of the mixture
The quantity associated with the laser mixture is known. It can be seen that a comparison of the two graphs generated at different times, such as two different startup procedures, reveals a difference in the state of the laser gas mixture at the two times the graph was generated. By comparing the two graphs, other differences in hardware and system can be distinguished between the two startups at two different times.

The master data set is optimally structured,
And it is preferably measured using a laser system that has not yet aged. That is, a new replenishment of the laser gas mixture is preferably performed just before measuring the data of the master data set. At this time, the laser mixed gas has not yet changed over time, and the distribution of each gas constituting the laser mixed gas or the percentage of each gas is optimal. In addition, the hardware of the system, including electronics and optics, along with the optical configuration of each optical module in the system, is measured along with a master data set that may be represented by a master graph generated from the master data set. Sometimes the best. This master data set is then stored as a master data set to be compared to each subsequently measured data set after all of the above has been verified. The master data set is preferably measured using data taken after the first fresh refill and warm-up of the laser mixture to operating equilibrium temperature. Preferably, prior to generating the master graph from the master data set, following measurement of the master data set, the master data set is preferably automatically transferred and stored in a memory accessible by the processor. The master data set may generally be measured at the factory after manufacturing a new laser. The master data set may be generated with the same laser or a different laser from which it is desired to learn its gas mixture state at a later time.

The two or more master data sets may be generated using lasers of various ages (age), provided that one master data set is preferably generated by one new laser. As the gas laser itself ages, the data set measured when other than the gas mixture and other system components are optimal will generally change. Therefore, it is preferable to have one or more master data sets, each corresponding to a different age range of the laser itself. For example, three master data sets are measured, preferably from which a master graph is generated, which are used in the present invention. The first master data set is, for example, 10 ⁹
One laser pulse corresponds to the optimal state of the laser below the age. The second master data set is, for example, 1 to 2.5 ×
This corresponds to the optimal state of 10 ⁹ laser pulse age lasers. The third master data set is, for example, 2.5 × 1
It corresponds to the optimal state of the laser older than ⁰⁹ laser pulse ages.

Preferably, several "calibration" data sets are also measured and stored in memory accessible by the processor. Each calibration data set corresponds to a different state of the gas mixture. Including F ₂ concentration, the bank of data sets corresponding to the mixed gas of various aging conditions (bank) is thereafter a mixed gas processor is not exactly known state of what is determined to be deviated from the optimum It can be used to compare with the corresponding subsequently generated data set. Calibration data corresponding to other laser system conditions in which the user knows and learns the evolution with time, pulse counting, or other parameters that evolve when the laser is on and / or off, or in an intermediate mode. The set may be measured and stored.

In this manner, the processor preferably analyzes a number of values related to several previously measured data sets of output light energy versus drive voltage and preferably plots a graph or curve from the data. Generate and compare them to the current data set to determine the current state of the gas mixture. Electrical and mechanical hardware problems, optical placement problems, and degradation problems can also occasionally occur, and can be noticed during the previously described check subroutines, and another advantage of the invention is recognized.

It is, however, a general and regular aging of the laser gas mixture. However, it is a comparison between the master data set and / or other previously measured and stored calibration data sets and the current data set measured at a particular time after measuring the master data set and other graphs. Observable by In particular, differences in magnitude and slope between, for example, the curves or graphs representing the master data set and the current data set indicate important characteristics of the laser gas mixture. One such feature is the degree to which the gas mixture generally ages and degrades at the time the second data set is measured.
Another feature is the reduction of the latest from the time of the new supplement to the second data set is generated, for example, the specific gas in the mixture as a F _2.

For example, the magnitude, slope, etc., of a data set of output beam parameters, eg, laser energy, for a given value of an input parameter, eg, drive voltage, may vary with age or age of the laser gas mixture. Dependent and preferably measured in terms of time or pulse count since the last new replenishment, but may refer to other events important to the laser system. FIG. 3 shows how the magnitude of the output energy decreases as the laser gas mixture ages over time. Three curves are shown in FIG. The highest curve is the master curve generated using the new or near-new laser and the data taken just after or almost immediately after the new refill, for example one million pulses. The middle curve shows that sometime after a new replenishment, for example 2 days or after 5,000 pulses,
Generated using data collected. The lowest curves were generated using data taken sometime later, for example, 5 days after new replenishment or 100 million pulses later.

As the laser gas mixture ages,
It can be observed from FIG. 3 that the curve shifts downward at the expected rate. For example, after one or more new refills,
Based on experience following previous fresh refills, it is possible to evaluate how much the laser gas has aged. As the gas mixture ages, the halogen concentration decreases,
Many changes, including increased pollutants such as CF ₄ or dust occurs. This information is important because appropriate follow-up actions that may be used in accurate industrial use can be taken to ensure the reliability of the output beam.

The slope of the curve of the output energy of the gas laser with respect to the drive voltage also depends on the F ₂ percentage concentration in the laser gas mixture. FIG. 4 shows how this slope decreases as the F ₂ percentage concentration in the laser mixture decreases. The curve of FIG. 4 differs from the curve of FIG. 3 since only the F ₂ concentration changes between the curves of FIG. 4, while, as already mentioned, the contamination and the contaminants generated as the laser gas mixture ages. Other factors, such as dust build-up, affect the slope of the curve in FIG.

Three curves are shown in FIG. The highest curve is the master curve generated using the master data set from a laser having a first F ₂ concentration. The middle curve was generated using data from a laser having a _second F2 concentration lower than the first concentration. The lowest curve was generated using data from a laser having a third F ₂ concentration lower than either the first or _second concentration. As F ₂ percentage concentration decreases, that decreases at a rate gradient of the curve is expected is observed from FIG. For example, after a new replenishment of more than one, it can be based on the subsequent previously experienced a new refill, to evaluate how much F ₂ concentration was decreased. By performing appropriate follow-up action such as to cause the case to restore the optimal F ₂ percentage concentration that is used in the precise industrial use, it is possible to ensure the reliability of the output beam, this information is important is there. Comparing curves such as the curves in FIG. 4 may also provide unique signs of the time-dependent percentage decrease of other gases in the laser gas mixture.

Referring to FIGS. 3 and 4, the aging of the laser gas mixture is observed from the drop in laser output energy with respect to the drive voltage at a given voltage. However, this drop is evident by the downward shift of the curve as in FIG. Such as F _2, there is a lack of a specific gas component can be observed from a decrease in the slope of the curve of the laser output energy for driving voltage as shown in FIG. A master graph generated using the master data set measured immediately or almost immediately after a new refill of the laser is generated using data measured during the laser system check subroutine, such as during the laser start-up procedure. Analyzing the deviation between the two graphs over a wide range of voltages, as compared to the second graph generated, plays a delicate technique to characterize the deviation of the characteristics of the laser gas mixture. The same may be done with other input parameters other than voltage, affecting important output parameters such as pulse energy, and other output parameters that change as the gas mixture degrades.

In addition, graphs generated using data collected during the subroutine some time after the last new refill, and a laser generated with optimal hardware and optical alignment arrangement. Comparison with a master graph generated using data taken immediately after a new refill may or may not result in a discrepancy. If no deviation is found, then the gas mixture and system hardware are determined to be satisfactory under the subroutine of the present invention. Any deviations observed may have been observed in previous comparisons, so whether follow-up actions should be performed and what type of follow-up actions should be performed And / or any follow-up action may then be performed quickly and efficiently and empirically, either automatically or by a user initiated action. For example, the gas handling procedure may compare measured data sets and / or graphs generated from the data sets, observe any deviations, and indicate experience and / or otherwise observed deviations. Depending on the required knowledge of the substance, the gas mixture can be refilled or performed by injecting one or more gases, or by gas replacement or fresh refilling, or otherwise restored to the initial state. can do.

Preferably, the output energy with respect to the drive voltage is measured. However, the measurement result may be represented by a graph or a table generated by the processor representing the current state of the gas mixture. Instead of graphs or tables, other database configurations may be used. The processor then compares the current dataset table or graph with the stored dataset graph or table according to the flowchart of FIG. 5, where the graph is used as an example. In general, the processor will analyze any deviation between the current state and the optimal state or state of the other known gas mixture and store the current graph in a master graph and / or a bank of graphs stored by the processor. After comparing all of the (sets), determine what type of shift exists and what follow-up should be performed. The preferred procedure is particularly illustrated by the flowchart of FIG.

The general procedure shown in FIG. 5 begins with a user initiated system power-up signal. Alternatively, a warm-up period is started, which otherwise maximizes the emission of output light from the laser chamber and the optics of the laser system (step S1). Next, it is determined whether a new replenishment is required (step S2). If a new replenishment is required, then a new replenishment is performed (step S3). After a new replenishment has been performed in step S3, or if no new replenishment is required, a measurement is then made and then a graph is generated (step S4). The measurement is preferably made at the output beam energy relative to the drive voltage. Next, including the data measured in step S4, which may be in the form of the current graph generated in step S4, and at least a table or graph of the master data set,
A comparison is made of one or more stored data sets with a table or graph (step S5). In a preferred embodiment, the current age of the laser is checked first. Then, in step S5, the master data set table or graph, preferably of a stored master data set table or graph group, corresponding to the age range including the current age of the laser, is read in step S5. Selected to be used as a graph.

If it is determined that the table or graph of the current data set and the table or graph of the master data set are identical or nearly identical (within a specified tolerance) (step 6), then the laser Is in a ready state that can be used for industrial use such as photolithography (step S10), and steps S7 to S
9 and steps S11 to S13 are not necessary. The procedure of the preferred embodiment according to the invention shown in FIG. 5 thus ends for this run.

If the tables or graphs of the master data set and the current data set are not the same, it is determined whether a large deviation exists or a small deviation exists (step S7). If small deviations or deviations outside the specified tolerances are observed, then preferably the user will be notified via a message, for example on a computer display, or a message such as an audio or visual alarm signal. Is notified (step S8). The follow-up procedure is performed automatically, such as by user input in response to receiving a message or signal, or as initiated by the processor using a pre-programmed software routine (step S9). Follow-up procedures are performed, such as halogen injection, partial gas replacement, gas replenishment, and total pressure correction (eg, by adjusting gas temperature). As a result of the follow-up procedure, the gas mixture is preferably returned to a state that is minimally deviated from the initial starting state, so that fully optimal laser system performance is again possible and industrial use of the laser system may be promoted. (Step S10).

If a large deviation has been determined to exist or has been observed that far exceeds the specified tolerances as described above and may be outside the second set of tolerances ( At this time, it is determined whether or not new replenishment has been executed (step S1).
1). If the new replenishment has not been executed, a new replenishment of follow-up is executed at that time (step S3).

After a new replenishment of follow-up has been performed, the data set is measured, and preferably a graph or table of output energy versus drive voltage may be generated (step S4), following the procedure already described. Done. If a new refill was just performed and the current data set was measured immediately after the latest new refill, then the gas mixture is assumed to be optimal. In this case, where the current data set is measured immediately after the latest fresh refill and the gas mixture is assumed to be optimal, it is assumed that no deviation is the result of the aged gas mixture.

The fact that an electrical, mechanical or optical hardware problem exists somewhere in the system is therefore indicated by the presence of a large deviation (step S12). Some possible problems include problems with gas delivery systems, optical modules in systems such as optical windows or line narrowing and / or adjusting elements, laser discharge chambers themselves, and trouble with electrical components such as power supplies and optical path cleaning systems. is there. Some gas delivery problems include leaks, fouling of gas cylinders, partial pressure changes of fluorine from cylinder to cylinder, and contamination from almost empty cylinder walls. The user then preferably follows clear instructions for locating the problem and, if possible, requests a repair (step S13). These serious problems, indicated by the large deviations observed when comparing the current dataset table or graph with the master dataset table or graph, are easily distinguished from gas aging. This is because large deviations of the current graph from the master graph are generally much greater than due to aging and are not eliminated by performing a new replenishment.

In the method of FIG. 6, step S8 of FIG.
The method differs from the method of FIG. 5 in that the steps S8a and S8b of b are replaced. According to the method of FIG. 6, sometime a bank of calibration data sets (not shown) is preferably stored in the memory of the processor before the current state is measured. In general, calibration data sets are measured at the factory and they define the response of a laser system (or similar laser system) when operating with different gas mixtures of a common aging type. Following step S7, after it has been determined that there is a small deviation between the table or graph of the current dataset and the table or graph of the master dataset, one or more of the tables or graphs of the current dataset or A comparison of all calibration data sets to a table or graph is performed (step S8a), and one or more calibration data sets that are similarly offset from the master data set are found. Thereafter, the processor determines from the stored gas mixture data for one or more similarly offset calibration data sets what type of follow-up procedure to perform to return the gas mixture to a more desirable state. I do. For example, a follow-up procedure may include gas injection, partial replacement, or other replenishment of an amount of F ₂ , HCl, active noble gas or a mixture thereof, or (eg, gas temperature or total gas volume in the discharge chamber). (By adjusting the total pressure). The processor may initiate the follow-up procedure such that the follow-up procedure is automatically initiated and / or performed with or without user assistance.

Using the preferred method of the present invention, it is possible to determine gas quality and distribution composition. It is also easy to schedule new refills and follow-up procedures for refills. Furthermore, the method is very sensitive so that F ₂ concentrations up to 3 × 10 ⁻⁴ absolute units can be resolved. That is, 0.3 percent or possibly less deviation can be detected using the sensitive method of the present invention. This method is also efficiently performed by a processor that uses special check subroutines that do not require additional hardware to be added to existing systems, and the benefits of the present invention are realized at low cost. In addition, the processor will automatically re-adjust the actual laser performance to the level of the master data set,
A system with a laser gas mixture which operates a gas handling system and thus has an infinite lifetime is in principle possible.

A preferred arrangement of a gas discharge laser system with internal laser parameter control is shown in FIG. The system comprises a gas discharge chamber 1 containing a gas mixture and a discharge circuit comprising electrodes 9 for causing a discharge using the gas mixture. The resonator constitutes an optical path through a laser tube 1 comprising, for example, a high-reflectance reflective grating, a prism or a high-reflectivity backside of a rear mirror 2 and an output-coupling beam splitter or front mirror 3, respectively. The outcoupled portion of the beam is a beam splitter 4
, So that the outer coupling portion is reflected toward the internal energy monitor 5. The internal computer control system 6 or processor receives data from the internal energy monitor 5.

The laser system further includes a power supply 7 for applying a driving voltage to the electrode 9 or the discharge circuit of the discharge chamber 1 to give energy to the mixed gas. The value of the drive voltage, preferably corresponding to the detected value of the output light energy, measured by the internal energy monitor 5 and also received by the internal computer control system 6, is preferably received by the internal computer control system 6. Computer control system 6 preferably stores and retrieves the previously described master and calibration data sets in memory. Control system 6
Will then generate a table or graph for any dataset, or store the dataset in any form, including a database format that uses at least a range or portion of the dataset. The control system 6 preferably performs many other functions as described above. The gas compartment 8 is connected to the discharge chamber 1 by a gas pipe and has an internal computer control system 6.
Or manual flow control. The portion of the out-coupling ray not reflected by the beam splitter 4 is the output ray 10 of the system.

The specific embodiments described in this specification, the accompanying drawings, and the abstract are not intended to limit the scope of any claims, but rather to embody the spirit of the invention. It only has the meaning of explaining with a typical embodiment. It is understood that the scope of the present invention is covered by the words of the claims and their structural and functional equivalents.

[0046]

As described above, according to the present invention, it is possible to provide an efficient and sensitive method and system for determining the state of a mixed gas and the degree of its aging or deterioration.

[Brief description of the drawings]

FIG. 1 is a diagram showing a graph of laser output energy with respect to an F ₂ partial pressure in a KrF-excimer laser, showing that a maximum value of the output energy exists at an F ₂ partial pressure at which the output energy can be determined.

FIG. 2 is a graph showing a qualitative dependence of laser output energy on a driving voltage of a discharge chamber of a gas discharge laser.

3 shows how the graph of laser output energy versus drive voltage of FIG. 2 shifts down with the age of the laser gas mixture.

FIG. 4 is a diagram showing how the gradient of laser output energy with respect to the drive voltage curve of FIG. 2 depends on the F ₂ concentration in the laser mixed gas.

FIG. 5 is a flowchart illustrating a step-by-step procedure for monitoring the state of the laser gas mixture and other components of the laser system according to the present invention.

FIG. 6 illustrates a step-by-step procedure for monitoring the state of the laser gas mixture and other components of the laser system according to the present invention, including comparing the current state data set with one or more calibration data sets. It is a flowchart for the.

FIG. 7 is a layout diagram of a laser system according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser tube (discharge chamber) 2 Rear mirror 3 Front mirror 4 Beam splitter 5 Internal energy monitor 6 Internal computer control unit 7 Power supply 8 Gas compartment and gas pipe 9 Electrode 10 Output light

 ──────────────────────────────────────────────────続 き Continuation of the front page (71) Applicant 591283936 Germany, 37079 Göttingen, Hans-Beckler-Strasse 12 (72) Inventor Klaus Wolfgang Forgler Germany, 37085 Göttingen, Liechtenstein Walder Strasse 13 (72) Inventor Peter Heist, Germany 07743 Jena, Kro -Seewitzer Strasse 2a

Claims (30)

[Claims] 1. A method for determining the state of a laser gas mixture of a gas discharge laser comprising a discharge chamber for producing an output light beam and energizing components of the gas mixture contained therein by a power supply. Measuring and storing a master data set of the relationship of output light parameters to input parameters known to vary with mixed gas conditions; and measuring a second data set at a subsequent time. And determining the state of the mixed gas by comparing the master data set with the second data set. 2. A method for determining the state of a laser gas mixture of a gas discharge laser comprising a discharge chamber for producing an output light beam and energizing a component of the gas mixture contained therein by a power supply. Generating a master data set by changing input parameters to the laser, monitoring changes in output parameters, and storing the parameter information; and a method of generating the master data set. Generating a second data set after generating the master data set in the same manner as above, and determining the state of the mixed gas by comparing the master data set with the second data set. And a method for controlling the performance of a gas discharge laser. 3. The performance control of a gas discharge laser according to claim 1, further comprising the step of adjusting the gas replenishment so as to minimize the difference between the current gas replenishment and the initial state. Method. 4. A method for generating one or more calibration data sets corresponding to one or more states of the gas mixture in addition to the master data set, wherein each of the master data set and the second data set is generated. Measuring and storing in a similar manner; and comparing the one or more calibration data sets to the second data set to determine a state of the gas mixture. The method for controlling the performance of a gas discharge laser according to claim 1. 5. The method according to claim 1, wherein the comparing step determines whether there is a shift between the master data set and the second data set, and determines whether the master data set and the second data set are offset.
5. The method of claim 4, wherein when it is determined that there is a deviation between the second data set and the one or more calibration data sets. A method for controlling the performance of the gas discharge laser according to the above. 6. The current state of the gas mixture is the second state.
6. The method of claim 5, wherein the data set is determined based on a comparison of the data set with the one or more calibration data sets. 7. The performance control of a gas discharge laser according to claim 1, wherein the master data set and the second data set are generated using different gas lasers of the same model. Method. 8. The method according to claim 1, wherein the master data set and the second data set are generated using the same gas laser. 9. The measured output parameters are: pulse energy, bandwidth, spectral width, long axis ray contour, short axis ray contour, ray divergence, energy stability, energy efficiency, discharge width, temporal ray coherence, The method of claim 1 or 2, wherein the method is selected from the group consisting of spatial light coherence, spatial pulse width, amplified spontaneous emission, and temporal pulse width. 10. The method according to claim 9, wherein the input parameter to be measured is a characteristic of energy applied to the gas mixture. 11. The method according to claim 9, wherein the measured input parameter is a drive voltage. 12. The performance control method for a gas discharge laser according to claim 1, wherein the measured input parameter is a characteristic of energy applied to the mixed gas. 13. The method according to claim 1, wherein the input parameter to be measured is a drive voltage. 14. A follow-up procedure is performed depending on whether there is a shift between the second data set and the master data set, and what type of shift exists. The method according to claim 1 or 2, further comprising a step. 15. The performance of the gas discharge laser according to claim 1, further comprising a step of determining whether there is a deviation between the current data set and the master data set. Control method. 16. The method according to claim 15, further comprising transmitting a message to a user of the laser system based on a result of the determining step. 17. The method of claim 15, further comprising adjusting a total pressure of the gas mixture. 18. A method for automatically replenishing said gas mixture by injecting halogen into said discharge chamber when it is determined that said deviation is due to a decrease in halogen concentration in said gas mixture. The method of controlling a performance of a gas discharge laser according to claim 15, further comprising: 19. The method according to claim 18, wherein the refilling step includes discharging a part of the mixed gas from the discharge chamber. 20. The method according to claim 18, wherein the refilling step is started by a command from the processor. 21. The replenishing step is started by a command from the user when the user is notified of the mixed gas state.
3. The method for controlling the performance of a gas discharge laser according to item 1. 22. The method as recited in claim 21, wherein the comparing step includes determining whether a shift between the master data set and the second data set exceeds a predetermined shift threshold. Item 3. The performance control method for a gas discharge laser according to item 1 or 2. 23. The method according to claim 22, further comprising a step of starting a new replenishment when the determining step determines that a large deviation exists. 24. The master data set and the second
Under the same conditions as when the dataset was generated,
Generating a third data set immediately after the new replenishment; and comparing the third data set with the master data set to determine a state of hardware components of the laser system. The method for controlling the performance of a gas discharge laser according to claim 23, comprising: 25. Perform a follow-up procedure depending on whether there is a gap between the third data set and the master data set, and what type of gap exists. The method of claim 24, further comprising the step of: 26. The method according to claim 1, further comprising: generating a master graph from the master data set; and generating a second graph from the second data set. Control method of gas discharge laser. 27. The method of claim 2, wherein the comparing step compares the measured values of the output ray parameters for a range of data points of the input parameters.
7. The performance control method for a gas discharge laser according to item 6. 28. The method of claim 1, wherein the comparing step compares the output ray parameter measurements to a range of data points of the input parameter.
Or the performance control method of the gas discharge laser according to 2. 29. The gas discharge laser according to claim 26, wherein the comparing step compares a gradient of the master graph and the second graph for a range of data points of an input parameter. Performance control method. 30. The performance control method for a gas discharge laser according to claim 1, wherein the master data set corresponds to a state when the laser is initialized.