Identifying gas leaks in laser systems

Abstract

The invention relates to a method (30) for detecting a gas leak in a gas line (24) of a laser system (10). In this case, after the laser beam (14) is guided through the gas-filled process chamber (20), the laser beam properties are determined by means of a detector. The gas of the process chamber (20) is replaced at different time points (Pi), the gas being present in the gas line (24) before a time period (Ri) between the time points (Pi), i.e. Within the age of the gas. After the gas replacement, a beam characteristic of the laser beam (14) is detected with a detector and a beam difference (Si) of the beam characteristic is associated with a gas age difference (Gi) to form a data pair (Di). Gas leaks in the gas line (24) can be inferred from changes in the beam difference (Si) with the gas age difference (Gi). In order to quantify gas leaks, the beam difference (Si) can be linearly fitted over the gas age difference (Gi). The calculation and analysis of the data pairs (Di) may be performed using the algorithm (28). Preferably, the time point (Pi) of the gas replacement can be determined automatically by the algorithm (28) by gas pressure analysis. The invention also relates to a laser system (10) for carrying out such a method (30).

Description

Technical Field

[0001] This invention relates to a method for identifying gas leaks, and more particularly for identifying changes in gas mixtures in a laser system. The invention also relates to a laser system for implementing this method. Background Technology

[0002] As is well known, gas needs to be supplied to laser systems discretely. Here, gas lines may become contaminated, leading to differences in laser beam characteristics. However, not all gas lines will experience this problem. Therefore, identifying the affected systems for priority treatment is crucial. Summary of the Invention

[0003] Therefore, the object of the present invention is to provide a method and an apparatus that can identify gas leaks or changes in gas composition in an extremely simple manner.

[0004] According to the present invention, the task can be accomplished by a method according to claim 1 and a laser system according to claim 13. The dependent claims describe preferred embodiments.

[0005] Therefore, the task described in this invention can be solved by a method for identifying gas leaks in a laser system, wherein the laser system has: a gas reservoir (especially in the form of a gas cylinder); a gas-filled process cavity for guiding and / or amplifying the laser beam; and a gas pipeline from the gas reservoir to the process cavity. Here, for the sake of simplicity, "gas leak" is broadly understood as a change in the gas mixture, such as a change caused by leakage, contamination, outward diffusion, and / or inward diffusion of other gases. A detector (especially a detector in the form of a camera device) determines the characteristics of the laser beam directly or indirectly after the (laser beam) passes through the process cavity. Furthermore, a computer exists with algorithms for evaluating the laser beam characteristics and, preferably, for determining whether a gas leak exists. The method comprises the following steps:

[0006] A) Introduce gas into the process chamber at multiple time points;

[0007] B) Obtain (Erfassen) these time points;

[0008] C) Obtain the laser beam characteristics over a time interval between the points in time when the gas is introduced into the process cavity;

[0009] D) Determine the differences in laser beam characteristics and gas age (differences in time periods in method step C);

[0010] E) Output data pairs, each consisting of beam differences related to gas age differences.

[0011] The algorithm can execute at least steps C) to E).

[0012] Beam difference occurs when the composition of the gas introduced during gas exchange differs from that of the gas previously present in the process chamber. In other words, the difference in gas composition before and after gas exchange is crucial. The magnitude of beam difference varies with the difference in gas composition. If the composition of the gas introduced in successive gas exchanges remains unchanged, no beam difference will occur; however, if the composition difference is significant, a large beam difference will result.

[0013] The deviation between the composition of the gas introduced during ventilation and the rated composition in the gas reservoir is proportional to the residence time of the gas in the gas line. This period of time can also be referred to as the "gas age".

[0014] Therefore, the magnitude of the beam difference during gas exchange (i) is proportional to the difference in gas age obtained from the gas age during gas exchange (i-1) and the gas age during gas exchange (i).

[0015] Preferably, step D can be performed directly after ventilation. Alternatively, the average value for the entire time period can be calculated in step D).

[0016] As a preferred option, the following additional method steps may be performed:

[0017] F) Fit a function, in particular a straight line, to multiple data pairs consisting of beam differences and gas age differences, where beam differences are plotted on the ordinate and gas age differences on the abscissa.

[0018] G) Determine and especially output the slope of the function, particularly the straight line.

[0019] As an alternative or additional option, the intercept in the fit can also be considered.

[0020] The vertical and horizontal axes can usually be interchanged.

[0021] In another preferred embodiment of the method, the correlation coefficient of the data pair consisting of beam difference and gas age difference is determined and output, in particular,.

[0022] As an alternative or additional option, a hypothesis parameter (p) can also be determined and output. This hypothesis parameter (p) can be used to classify lines.

[0023] Therefore, for evaluation, the determined beam differences can be expressed as a function of gas age differences. Fitting curves (especially linear fitting curves) can be matched to the data cloud, particularly using the least squares method.

[0024] If certain conditions are met, such as an absolute correlation coefficient (abs(R)) > 0.6 and a null hypothesis parameter (P < 0.05), then a practical analysis can be performed. For this, the slope (m) of the fitted curve, or the so-called extrapolation difference height (m) * typical ventilation time period (e.g., 14 days), can be evaluated. That is, the slope of the fitted curve can be multiplied by the gas age difference (here, 14 days). This value reflects the maximum expected beam difference during the typical ventilation time period.

[0025] To obtain the beam difference more accurately, the beam difference can be determined in a first direction and a second direction perpendicular to it on the detector.

[0026] Furthermore, the beam difference can be defined as a combination of the beam difference in the first direction and the beam difference in the second direction. Preferably, the beam differences in the first and second directions can be squared, added together, and then, in particular, their square roots can be obtained.

[0027] The ventilation time point can be automatically obtained. Therefore, it is preferable to evaluate the measured gas pressure.

[0028] When determining the characteristics of a laser beam, the preheating time of the laser system can be considered.

[0029] In step D), a beam difference can be replaced by another beam difference with a corresponding gas age difference. This significantly improves the significance of the data pair. Therefore, when calculating beam differences, it is not necessary to use the beam characteristics of successive gas exchanges. If a beam characteristic cannot be used due to a specific gas exchange, such as (i-1), unsuitable system conditions, or gas exchange execution errors, the beam difference between gas exchanges (i-2) and (i) can be calculated using their beam characteristics. To calculate beam differences, the algorithm can automatically search for possible gas exchange pairs, and it should be particularly noted that beam differences are not repeatedly included in the evaluation.

[0030] In another preferred embodiment of the method, erroneous / faulty system states can be identified, and data collected under erroneous states can be excluded. For example, before accepting data, it can be checked whether the laser beam has been correctly directed to the target, whether the laser system has been properly preheated, whether the beam size is correct, whether the laser beam has been correctly directed to the camera device, and / or whether the camera device is functioning properly. These can be identified, for example, by analyzing its background noise.

[0031] The advantages of this invention are particularly evident when using a laser beam to generate extreme ultraviolet radiation. Here, the laser beam can irradiate a target, especially a target in the form of a tin droplet, to generate plasma within the target that emits extreme ultraviolet radiation.

[0032] Laser beam characteristics can exist in the form of laser beam size, laser power, and / or other parameters. However, it is known that ensuring the characteristics of a laser beam is the most practical and simplest method when they exist in the form of laser beam position and beam differences exist in the form of beam jumps.

[0033] Additionally, the objective of the invention is also achieved by a laser system for performing the methods described herein, wherein the laser system has a gas reservoir, a process cavity for guiding a laser beam, a gas pipeline guiding the gas reservoir to the process cavity, a detector for determining the characteristics of the laser beam, and a computer equipped with an algorithm for evaluating the characteristics of the laser beam, wherein the algorithm is at least designed to perform method steps C) through E). Furthermore, the laser system may also be designed to automatically perform method steps A) and / or B).

[0034] Further advantages of the invention can be seen from the specification and drawings. Similarly, the features described above, as well as those further elaborated below, can be used alone or in any combination according to the invention. The illustrated and described embodiments should not be construed as exhaustive, but rather as exemplary features for the description of the invention. Attached Figure Description

[0035] Figure 1 A laser system and a method for identifying gas leaks in a laser system are illustrated schematically.

[0036] Figure 2 The graph shows the variation of the laser beam characteristic S with time t, especially when based on Figure 1 The curves showing the changes in laser beam characteristics over time during gas exchange in a laser system.

[0037] Figure 3a The gas age difference G represents the beam difference S of the laser beam in the first direction.

[0038] Figure 3b The difference in gas age G illustrates the difference in laser beam S in the second direction.

[0039] Figure 3c The gas age difference G illustrates the beam difference S of the laser beam, determined by the first and second directions.

[0040] Figure 4 A schematic diagram of the method is shown. Detailed Implementation

[0041] Figure 1A laser system 10 is shown, equipped with an amplifier 12 for a laser beam 14. The laser beam 14 is used in particular to generate extreme ultraviolet radiation 18 by irradiating a target 16 (in the form of a tin droplet).

[0042] Amplifier 12 has a gas-filled process cavity 20 through which the laser beam 14 is guided. Amplifier 12 also has a gas reservoir 22, in the form of a gas cylinder, which is connected to the process cavity 20 via a gas line 24.

[0043] The gas exchange in process chamber 20 is not continuous, but rather occurs at intervals of several days. Here, changes in gas composition lead to changes in laser beam characteristics (not shown). Leaks in the gas line 24, used to store gas between gas exchanges, are particularly critical. If the gas in gas line 24 becomes contaminated, the contaminated gas will be introduced into process chamber 20 during the next gas exchange.

[0044] To determine whether the laser system 10 has a leak, the laser system 10 has a computer 26 with algorithm 28. The basic idea of ​​the method 30 according to the invention is that the longer the gas remains in the gas line 24, the more severe the contamination. Therefore, different residence times in the gas line 24 result in differences in the characteristics of the laser beam, which are detectable, and leaks can be determined based on these differences.

[0045] The characteristics of a laser beam can be detected using a detector (not shown), especially a detector in the form of a camera device.

[0046] Figure 2 A graph showing the variation of the laser beam characteristic S with time t is presented. The following will combine... Figure 1 right Figure 2 The following explanation is provided. Time points (Pi-2), (Pi-1), (Pi), (Pi+1), and (Pi+2) represent the time points, shown by dashed lines, when the gas is introduced into process chamber 20. The dotted lines represent the laser beam characteristics S. The solid lines represent measurements taken at time points (Pi-1), (Pi), (Pi+1), and (Pi+2), taking into account the preheating time of amplifier 12.

[0047] from Figure 2It can be seen that the gas introduced into process chamber 20 previously resided in gas line 24 for different durations. Specifically, when the gas is introduced into process chamber 20 at time point (Pi), its presence time in gas line 24 is time period (Ri). When the gas is introduced into process chamber 20 at time point (Pi-1), it has previously resided in gas line 24 for time period (Ri-1), and when the gas is introduced into process chamber 20 at time point (Pi+1), it has previously resided in gas line 24 for time period (Ri+1). Since the lengths of time periods (Ri-1), (Ri), and (Ri+1) are different, the gas composition of the gas introduced into process chamber 20 will also differ in the event of a leak in gas line 24. This will result in beam differences, such as beam differences (Si) and (Si+1).

[0048] Therefore, the gas age difference (Gi) caused by the differences in time periods (Ri-1), (Ri), and (Ri+1) will lead to a beam difference (Si). Gas age difference (Gi) = (Ri-1) - (Ri), gas age difference (Gi+1) = (Ri) - (Ri+1).

[0049] Figure 3a , 3b Figure 3c shows a schematic diagram of multiple data pairs (Di) (as unlabeled data points), where the horizontal axis represents the gas age difference G (in days) and the vertical axis represents the beam difference S (in millimeters).

[0050] Figure 3a The record of the beam difference S in the first direction on the detector is shown. Figure 3b The record of the beam difference S in the second direction is shown. Figure 3c Both the first and second directions were considered.

[0051] Figure 3a The linear fit of the data point (Di) has an R-value of 0.99. Figure 3b The value is -0.31. Figure 3c The mean is 0.96. Extrapolating to 14 days yields... Figure 3a The beam difference is 76 μm. Figure 3b The beam difference is -5μm. Figure 3c The beam difference is 79 μm. Based on the slope of the fitted data points (Di) and taking into account the correlation coefficient (R value), although... Figure 3b No, but Figure 3a and 3c This indicates that there is a leak in gas line 24.

[0052] Figure 4 Method 30, which includes the following method steps, is illustrated schematically:

[0053] A) Perform ventilation in process chamber 20.

[0054] B) Determine the timestamp for ventilation.

[0055] C) Measure the laser beam characteristics (S) after air exchange.

[0056] D) Determine the beam difference (Si) and gas age difference (Gi). To improve the information content, new assignments can be made to the gas exchange pairs. Data that may contain errors can be discarded or replaced.

[0057] E) Outputs a data pair (Di) consisting of beam difference (Si) and gas age difference (Gi).

[0058] F) Fit a straight line using multiple data pairs (Di).

[0059] G) Determine and / or output the slope of the straight line.

[0060] Then you can perform the following steps:

[0061] H) Evaluate the straight line and its correlation coefficient.

[0062] Based on all the accompanying drawings, the present invention generally relates to a method 30 for identifying gas leaks in a gas line 24 of a laser system 10. Here, after a laser beam 14 is guided through a gas-filled process cavity 20, a detector is used to determine the characteristics of the laser beam. The gas in the process cavity 20 is replaced at different time points Pi, wherein the gas was previously present in the gas line 24 during the time period Ri between said time points Pi, i.e., the gas age. After the gas replacement / exchange, the beam characteristics of the laser beam 14 are detected by a detector, and the beam difference Si of the beam characteristics is correlated with the gas age difference Gi to form a data pair Di. Gas leaks in the gas line 24 can be inferred from the change in beam difference Si with the gas age difference Gi. To quantify the gas leak, the beam difference Si can be linearly fitted to the gas age difference Gi. The data pair Di can be calculated and analyzed using algorithm 28. Preferably, the time point Pi of the exchange can be automatically determined by algorithm 28 through gas pressure analysis. The present invention also relates to a laser system 10 for implementing this method 30.

[0063] List of reference numerals

[0064] 10 Laser Systems

[0065] 12 Amplifiers

[0066] 14 Laser beam

[0067] 16 targets

[0068] 18. Extreme ultraviolet radiation

[0069] 20 Process Chambers

[0070] 22 Gas storage tank

[0071] 24 Gas pipelines

[0072] 26 Computers

[0073] 28 Algorithm

[0074] 30 methods

Claims

1. A method (30) for identifying gas leaks in a laser system (10), wherein, The laser system (10) has the following components: -Gas storage unit (22); - A process cavity (20) filled with gas, in which a laser beam (14) is guided at least temporarily; - Gas line (24) from the gas reservoir (22) to the process chamber (20); - A detector for determining the characteristics of the laser beam (14) after it passes through the process cavity (20); - A computer (26) equipped with an algorithm (28) for evaluating the characteristics of the laser beam; Furthermore, the method (30) comprises the following method steps to be executed multiple times at different time points (Pi): A) At time points (Pi-2), (Pi-1), and (Pi), gas is introduced from the gas reservoir (22) into the process chamber (20), and the gas flow is interrupted during the time periods (Ri-1) and (Ri) between the time points (Pi-2), (Pi-1), and (Pi); B) Obtain the time points (Pi-2), (Pi-1), and (Pi); C) Determine the laser beam characteristics within the time periods (Ri-1) and (Ri); D) Determine the beam difference (Si) based on the difference between the laser beam characteristics within the time period (Ri-1) and (Ri), and determine the gas age difference (Gi) based on the difference between the time period (Ri-1) and (Ri); E) Output a data pair (Di) consisting of the beam difference (Si) and the gas age difference (Gi); 2. The method according to claim 1, wherein, The method (30) further comprises the following additional method steps after the multiple executions of method steps A) to E): F) Fit a function to multiple data pairs (Di), where the vertical axis represents beam difference (Si) and the horizontal axis represents gas age difference (Gi); G) Determine the slope of the function.

3. The method according to claim 2, wherein, In method step F), the correlation coefficient (R) of the data pair (Di) is determined and output.

4. The method according to claim 3, further comprising the following additional method steps: H) Classify the function based on its slope and its correlation coefficient (R).

5. The method according to any one of the preceding claims, wherein, In method step D), the beam difference (Si) in a first direction on the detector and the beam difference (Si) in a second direction perpendicular to the first direction are determined.

6. The method according to claim 5, wherein, The beam difference (Si) is also determined by defining the hypotenuse with the first direction as the first right-angle side and the second direction as the second right-angle side.

7. The method according to any one of the preceding claims, wherein, In step B), the measured gas pressure is taken into account to determine the time points (Pi-2), (Pi-1), and (Pi).

8. The method according to any one of the preceding claims, wherein, In method step C), the preheating time of the laser system (10) is taken into account when determining the characteristics of the laser beam.

9. The method according to any one of the preceding claims, wherein, In method step D), one beam difference (Si) is replaced by another beam difference (Si) with a corresponding gas age difference (Gi).

10. The method according to any one of the preceding claims, wherein, Identify erroneous system states, and data collected at these points in time are not considered for determining data pairs (Di).

11. The method according to any one of the preceding claims, wherein, The laser beam (14) is used to generate extreme ultraviolet radiation (18).

12. The method according to any one of the preceding claims, wherein, The laser beam characteristics exist in the form of laser beam position, and the beam difference (Si) exists in the form of beam jump.

13. A laser system (10) for performing the method (30) according to any one of the preceding claims, wherein, The laser system (10) has the following components: -Gas storage unit (22); - A process cavity (20) filled with gas, in which a laser beam (14) can be guided at least temporarily; - Gas line (24) from the gas reservoir (22) to the process chamber (20); - A detector for determining the characteristics of the laser beam (14) after it passes through the process cavity (20); - A computer (26) equipped with an algorithm (28) for evaluating the characteristics of the laser beam; The algorithm (28) is designed to execute at least steps C) to E).

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