Excitation laser system, method of operating excitation laser system, and method of operating an excitation laser system of an extreme ultraviolet (EUV) photolithography apparatus

Abstract

A method for operating an excited laser system includes measuring the operating power of a laser beam, determining whether the operating power is below a threshold power value, optically measuring the spectrum emitted from a gain medium of the laser beam to determine the composition of the gain medium, and adjusting the composition of the gain medium based on the optical measurement. An apparatus includes: an optical emission spectrometer configured to capture the spectrum emitted from the gain medium of the laser beam, and a gas supply unit configured to control the gas supply to the gain medium based on the composition of the gain medium determined from the spectrum.

Description

Technical Field

[0001] none. Prior Technology

[0002] With advancements in semiconductor device technology, photolithography processes have continuously evolved, resulting in increasingly smaller and denser device structures. One such photolithography technique is extreme ultraviolet (EUV) lithography. EUV lithography utilizes laser irradiation of the target material to generate ultraviolet light. However, the power of the laser used in EUV lithography decreases over time, leading to inconsistent process fabrication. Summary of the Invention

[0003] none. Simple Explanation of the Diagram

[0004] When read in conjunction with the illustrations, the appearance of one embodiment of this disclosure is readily understood from the following detailed description. It is worth noting that, in accordance with industry standard practice, the various features are not drawn to scale. In fact, for clarity of discussion, the dimensions of the various features have been arbitrarily increased or decreased. Figures 1 and 2 illustrate an EUV lithography apparatus according to an embodiment of the present disclosure. Figure 3 illustrates an excitation laser system according to an embodiment of this disclosure. Figure 4 illustrates a laser generator according to an embodiment of this disclosure. Figure 5 illustrates a laser amplifier according to an embodiment of this disclosure. Figure 6 illustrates an optical emission spectrometer for capturing light emitted from a laser generator according to an embodiment of this disclosure. Figure 7 illustrates the components of an optical emission spectrometer for capturing light emitted from a laser generator according to an embodiment of this disclosure. Figures 8A, 8B and 9 illustrate the optical emission spectra according to embodiments disclosed herein. Figure 10 illustrates a laser power diagram emitted by a laser generator according to one embodiment over a period of time, which overlaps with an optical emission spectrum emitted by the laser generator over the same period of time. Figure 11 illustrates a flowchart of the operation method of the excitation laser system according to an embodiment. Figure 12 illustrates a flowchart of the operation method of the excitation laser system according to an embodiment. Figure 13 illustrates a computing system according to one embodiment. Implementation

[0005] The following disclosure provides many different implementations, for example, different features for implementing the subject matter. Specific examples of elements and arrangements are described below to simplify one implementation of this disclosure. These are, of course, merely examples and not intended to be limiting. For example, in the description, the formation of a first feature on or over a second feature includes an implementation in which the first and second features are formed in direct contact, and may also include an implementation in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact. Furthermore, one implementation of this disclosure may repeat reference numerals and / or letters in various examples. This repetition is for the purpose of simplification and clarity and does not itself define the relationship between the various implementations and / or configurations discussed.

[0006] Furthermore, spatially related terms such as "below," "below," "lower part," "above," and "upper part" may be used herein for the sake of simplicity in describing the relationship between another element or feature and another element or feature shown in the diagram. In addition to describing orientation in the diagram, spatially related terms are intended to include different orientations of the apparatus in use or operation. The instrument may be oriented in other ways (rotated 90 degrees or otherwise), and the spatially relative descriptions used herein may also be interpreted accordingly. Unless otherwise explicitly stated, each element having the same reference numerals is assumed to have the same material composition and thickness within the same thickness range.

[0007] Furthermore, in the methods and processes described herein, one or more additional operations may exist between the described operations, and the order of operations may be changed. In one embodiment of this disclosure, the phrase "one of A, B, and C" means "A, B, and / or C (A, B, C, A and B, A and C, B and C, or A, B, and C)", and does not imply an element from A, an element from B, and an element from C, unless otherwise stated. In the following embodiments, the materials, configurations, dimensions, processes, and / or operations described for one embodiment (e.g., one or more figures) may be used in other embodiments, and their detailed description may be omitted.

[0008] Figure 1 is a schematic diagram of an EUV lithography apparatus 2 according to some embodiments of the present disclosure. The EUV lithography apparatus 2 includes an EUV radiation source 100 for generating EUV radiation, an exposure device 200 such as a scanner, and an excitation laser system 300. The EUV radiation source 100 and the exposure device 200 are mounted on the main floor (MF) of the cleanroom, while the excitation laser system 300 is mounted on the base floor (BF) below the main floor. The EUV radiation source 100 and the exposure device 200 are positioned above base plates PP1 and PP2, respectively, via dampers DP1 and DP2. The EUV radiation source 100 and the exposure device 200 are coupled to each other by a coupling mechanism, which may include a focusing unit.

[0009] The EUV lithography apparatus 2 is designed to expose a photoresist layer to EUV light (which may also be referred to interchangeably herein as EUV radiation). The photoresist layer comprises a material sensitive to EUV light. The EUV lithography apparatus employs an EUV radiation source 100 to generate EUV light, for example, EUV light with wavelengths ranging from about 1 nm to about 100 nm. In one particular example, the EUV radiation source 100 generates EUV light with a wavelength centered at about 13.5 nm. In some embodiments, the EUV radiation source 100 utilizes a laser-generated plasma (LPP) mechanism to generate EUV radiation.

[0010] Exposure apparatus 200 includes various reflective optical elements, such as convex / concave / plane mirrors, a mask holding mechanism including a mask stage, and a wafer holding mechanism. EUV radiation generated by EUV radiation source 100 is guided by the reflective optical elements onto a mask fixed on the mask stage. In some embodiments, the mask stage includes an electrostatic chuck to hold the mask.

[0011] Figure 2 is a simplified schematic diagram of the details of an EUV lithography apparatus according to an embodiment, showing the exposure of a photoresist layer 211 coated on a substrate 210 using a patterned EUV beam. The exposure apparatus 200 is an integrated circuit lithography apparatus, such as a stepper, scanner, step-scanning system, direct write system, or device using contact and / or proximity to a photomask, etc., equipped with one or more optical elements 205a, 205b, for example, to illuminate a mask 205c (also called a photomask or photomask) with an EUV beam to generate a patterned beam, and one or more reduction projection optical elements 205d, 205e for projecting the patterned beam onto the substrate 210 disposed on the photoresist layer 211. In some embodiments, the mask 205c is a reflective mask. Mechanical components (not shown) may be provided to generate controlled relative movement between the substrate 210 and the mask 205c. EUV radiation source 100 includes an EUV light radiator ZE that emits EUV light in chamber 105. This EUV light is reflected by mirror collector 110 and travels along a path into exposure apparatus 200 to irradiate photoresist layer 211 on substrate 210. In some embodiments, substrate 210 is a semiconductor substrate. In some embodiments, the semiconductor substrate is a semiconductor wafer, such as a silicon wafer or other type of wafer to be patterned.

[0012] In some embodiments, the mask 205c includes a reflective multilayer stack disposed on a substrate formed of a low thermal expansion material. In some embodiments, the reflective multilayer stack includes multiple film pairs, such as molybdenum-silicon (Mo / Si) film pairs (e.g., a layer of molybdenum above or below a silicon layer in each film pair) or molybdenum-beryllium (Mo / Be) film pairs. In some embodiments, a capping layer is disposed above the reflective multilayer stack, and an absorption layer is disposed above the capping layer. Patterns can be formed in the absorption layer such that the pattern of the mask reflecting light exposes the photoresist.

[0013] As shown in Figure 1, the EUV radiation source 100 includes a target droplet generator 115 and a mirror collector 110, enclosed by a chamber 105. In some embodiments, the target droplet generator 115 includes a reservoir for containing source material and a nozzle 120, through which target droplets DP of the source material are supplied into the chamber 105. In some embodiments, the target droplets DP are tin (Sn), lithium (Li), or an alloy of Sn and Li. In some embodiments, the diameter of each target droplet DP ranges from about 10 micrometers (μm) to about 100 μm. For example, in one embodiment, the target droplet DP is a tin droplet with a diameter of about 10 μm to about 100 μm. In other embodiments, the target droplet DP is a tin droplet with a diameter of about 25 μm to about 50 μm. In some embodiments, the target droplets DP are supplied through nozzle 120 at a rate of approximately 50 droplets per second (i.e., a jetting frequency of approximately 50 Hz) to approximately 50,000 droplets per second (i.e., a jetting frequency of approximately 10 Hz, approximately 50 kHz). Droplet catcher 125 is used to catch excess target droplets. For example, some target droplets may be intentionally missed by the laser pulse.

[0014] In some embodiments, the excitation laser beam LR2 generated by the excitation laser system 300 is a pulsed laser beam. In some embodiments, the excitation laser system includes a laser generator comprising a carbon dioxide (CO2) laser source with a wavelength in the infrared region of the electromagnetic spectrum. For example, in one embodiment, the laser generator emits laser light with a wavelength of approximately 9.4 μm or approximately 10.6 μm. The laser beam LR1 generated by the excitation laser system 300 is guided by the laser light guide element 320, focused by the focusing device 330 into the excitation laser beam LR2, and then introduced into the EUV radiation source 100.

[0015] In some embodiments, the excitation laser beam LR2 comprises a preheating laser beam and a main laser beam. In such embodiments, a preheating laser beam pulse (which may be interchangeably referred to herein as a "prepulse") is used to heat (or preheat) a given target droplet to create a low-density target plume having multiple smaller droplets, which is then heated (or reheated) by a pulse of the main laser beam, thereby producing increased EUV optical emission. In some embodiments, the spot size of the preheating laser beam pulse is about 100 μm or smaller, and the spot size of the main laser beam pulse is in the range of about 150 μm to about 300 μm. In some embodiments, the preheating laser beam and the main laser beam pulse have pulse durations in the range of about 10 ns to about 50 ns, and pulse frequencies in the range of about 1 kHz to about 100 kHz. In some embodiments, the preheating laser beam and the main laser beam have an average power in the range of about 1 kilowatt (kW) to about 50 kW. In one embodiment, the pulse frequency of the excitation laser LR2 corresponds to the ejection frequency of the target droplet DP.

[0016] In some embodiments, the excitation laser beam LR2 is guided to the excitation region ZE via a window (or lens). The window is made of a suitable material that is substantially transparent to the laser beam. The generation of the pulsed laser beam is synchronized with the ejection of the target droplet DP via nozzle 120. As the target droplet passes through the excitation region, the pre-pulsed laser beam heats the target droplet and transforms it into a low-density target plume. The delay between the pre-pulsed and main-pulsed laser beams is controlled to allow the target plume to form and expand to an optimal size and geometry. In some embodiments, the pre-pulsed and main-pulsed laser beams have the same pulse duration and peak power. When the main pulse heats the target plume, a high-temperature plasma is generated. The plasma emits EUV radiation, which is collected by a mirror collector 110. The mirror collector 110 also reflects and focuses the EUV radiation for use in a photolithography exposure process performed by the exposure apparatus 200. In some embodiments, the mirror collector 110 is designed to have an elliptical geometry. In some embodiments, the mirror collector 110 is designed with a suitable coating material and shape to serve as a mirror for collecting, reflecting, and focusing EUV.

[0017] In some embodiments, the coating material of the mirror collector 110 is similar to the reflective multilayer of an EUV shield. In some examples, the coating material of the mirror collector 110 includes a reflective multilayer (e.g., multiple Mo / Si film pairs) and may also include a capping layer (e.g., Ru) coated on the reflective multilayer to substantially reflect EUV light. In some embodiments, the mirror collector 110 may also include a grating structure designed to efficiently scatter laser beams directed onto the mirror collector 110. For example, a silicon nitride layer may be coated on the mirror collector 110 and patterned to have a grating pattern.

[0018] In such an EUV radiation source 100, plasma generated by laser application produces physical debris, such as ions, gases, and atoms of droplets, as well as the required EUV radiation. Material buildup on the mirror collector 110 must be prevented, as well as physical debris leaving the chamber 105 and entering the exposure apparatus 200. Since gas molecules absorb EUV light, the lithography system used for EUV lithography patterning can be maintained in a vacuum or low-pressure environment to avoid EUV intensity loss. In some embodiments, a buffer gas is supplied by a first buffer gas supply source 130 through an aperture in the mirror collector 110 through which the pulsed laser is delivered to the tin droplets. In some embodiments, the buffer gas is H2, He, Ar, N2, or other inert gases. Buffer gas may also be supplied to the mirror collector 110 and / or around its edges by one or more second buffer gas supply sources 135. Furthermore, the chamber 105 includes one or more gas outlets 140, allowing the buffer gas to be discharged outside the chamber 105. Hydrogen (H2) has a low absorption rate to EUV radiation. In some embodiments, hydrogen can be excited by EUV radiation to generate hydrogen (H*) radicals. These hydrogen radicals can be used for cleaning purposes. Hydrogen radicals reaching the coated surface of the mirror collector 110 can chemically react with metallic contaminants in the droplets to form hydrides, such as metal hydrides. When tin (Sn) is used as the droplet, the hydrogen radicals can react with tin to form stanane (SnH4), a gaseous byproduct of the EUV generation process. The gaseous SnH4 can then be pumped out through outlet 140.

[0019] In some implementations, the EUV lithography apparatus may also include other modules, or be integrated (or coupled) with other modules in some implementations.

[0020] Lasers emitted from excited laser systems in EUV equipment may exhibit power decay over time due to the degradation of the gain medium, which includes carbon dioxide. In EUV lasers, up to 60% of carbon dioxide molecules decompose into carbon monoxide when excited by plasma. The power of the laser beam emitted from the gain medium decreases with a relative increase in carbon monoxide concentration and a decrease in carbon dioxide concentration. Catalysts (such as gold) can contact the gain medium to catalyze the recombination of carbon monoxide and oxygen radicals into carbon dioxide. While this catalytic reaction can mitigate carbon dioxide decomposition, a significant amount of carbon monoxide may still remain in the gain medium. Furthermore, the effectiveness of the catalyst decreases over time due to contamination. For example, silica in the quartz tube containing the gain medium may contaminate or coat the catalyst and reduce its effectiveness.

[0021] The presence of carbon monoxide in the gain medium reduces laser efficiency and the efficiency of EUV lithography equipment used in semiconductor device fabrication. Directly monitoring the gain medium composition by removing the quartz tube module of the laser generator or amplifier leads to inaccurate measurements because the composition of the gain medium may differ between the measurement state and the operating state of the laser generation or amplification. Furthermore, direct sampling of gain media containing carbon monoxide is hazardous to personnel due to its toxicity. The topics presented herein allow for non-invasive, real-time monitoring of the gain medium composition using emission spectroscopy analysis. These topics also provide control over the gain medium composition to improve the power output of excited laser systems.

[0022] Figure 3 schematically illustrates an excitation laser system 300 according to an embodiment of the present disclosure. The excitation laser system 300 includes a laser generator 6, a first laser amplifier 8, a second laser amplifier 10, and a third laser amplifier 12. More or fewer laser amplifiers and corresponding components may be provided. The laser generator 6 is connected to the first laser amplifier 8 via a channel 14 through which a laser beam generated by the laser generator can pass. The first laser amplifier 8 is connected to the second laser amplifier 10 via a channel 16 through which the laser beam amplified by the first laser amplifier can pass. The second laser amplifier 10 is connected to the third laser amplifier 12 via a channel 18 through which the laser beam amplified by the second laser amplifier can pass. The third laser amplifier 12 is connected to an optical guide element 320 through which a laser beam amplified by the third laser amplifier can pass. Power sensors 15, 17, 19, and 21 are configured to measure the lower portion of the laser emitted through channels 14, 16, 18, and the optical guide element 320.

[0023] The excitation laser system 300 also includes a first optical emission spectrometer 20 configured to optically capture a first spectrum from a first gain medium of the laser generator 6, a second optical emission spectrometer 22 configured to optically capture a second spectrum from a second gain medium of the first laser amplifier 8, a third optical emission spectrometer 24 configured to optically capture a third spectrum from a third gain medium of the first laser amplifier 8, and a fourth optical emission spectrometer 26 configured to optically capture a fourth spectrum from a fourth gain medium of the third laser amplifier 12. In some embodiments, the first, second, third, and fourth optical emission spectrometers are wirelessly connected to a computing system. In some embodiments, the first, second, third, and fourth optical emission spectrometers are wired to the computing system. In some embodiments, the optical emission spectrometers are connectable to and movable between the laser generator and the first, second, and third amplifiers.

[0024] In some embodiments, the gas supply unit 74 controls the gas supply, pressure, and flow of the gain medium in the laser generator 6 and laser amplifiers 8, 10, and 12 via gas manifolds 76, 78, 80, and 82. The gas manifolds are connected to the gas supply unit 74 via gas and control lines 84, 86, 88, and 90. These gas and control lines include gas supply lines for any amount of gas contained in the gain medium, and control lines for operating any one or more unit devices (e.g., valves, pumps, vents, and blowers) to control gas flow and pressure to obtain gain. Each gas manifold is connected to gas inlets 84, 86, 88, and 90 for supplying gas to the gain medium, and gas outlets 85, 87, 89, and 91 for receiving gas from the gain medium in the laser generator 6 and laser amplifier 8. The gas supply unit 74 and gas manifolds 76, 78, 80, and 82 can be controlled by a computing system.

[0025] Figure 4 schematically illustrates an embodiment of a laser generator 27 including a quartz tube 28 containing a gain medium 30. In some embodiments, the laser generator is a carbon dioxide laser, and the gain medium 30 includes carbon dioxide, nitrogen, helium, and any byproduct gases, such as carbon monoxide. A catalyst 43, such as a gold catalyst, is located inside the quartz tube to convert carbon monoxide back into carbon dioxide. The laser generator includes a reflector 34 and an output coupler 32 with a partially reflective surface. A power supply 36 is configured to apply a high voltage between electrodes 38 and 40 to stimulate the gain medium 30. When power is applied to the gain medium, the molecules of the gain medium enter an excited state and emit photons. The photons are reflected between the reflector 34 and the output coupler 32 and ultimately exit the quartz tube as a laser beam 42. The composition, flow rate, and pressure of the gain medium in the quartz tube are controlled by an inlet 46 and an outlet 44. An optical emission spectrometer 48 is configured to capture the operating spectrum of light emitted from the excited gain medium 30 in the quartz tube 28. A power sensor 50 (e.g., a thermoelectric sensor) measures the operating power of the laser beam 42. The laser generator 27, the optical emission spectrometer 48, and the power sensor 50 can be controlled by a computing system.

[0026] Figure 5 schematically illustrates an embodiment of a laser amplifier 51 including a quartz tube 52 containing a gain medium 54. In some embodiments, the laser amplifier is used in conjunction with a carbon dioxide laser, and the gain medium 54 includes carbon dioxide, nitrogen, helium, and any byproduct gases, such as carbon monoxide. A catalyst 67, such as a gold catalyst, is located within the quartz tube to convert carbon monoxide back into carbon dioxide. In some embodiments, the laser amplifier receives a laser beam 56 from a laser generator or another laser amplifier. In some embodiments, the laser amplifier includes multiple mirrors or other reflective surfaces (not shown) to internally reflect the laser beam by the gain medium 54 before it leaves the laser amplifier. A power supply 58 is configured to apply a high voltage between electrodes 60, 62 to stimulate the gain medium 54. When power is applied to the gain medium, the molecules of the gain medium enter an excited state and emit photons, which add power to the laser beam 56 to produce an amplified laser beam 64 exiting the laser amplifier 51. The composition, flow rate, and pressure of the gain medium in the quartz tube are controlled by inlet 66 and outlet 68. An optical emission spectrometer 70 is configured to capture the operating spectrum of light emitted from the excitation gain medium 54 in the quartz tube 52. A power sensor 72 (e.g., a thermoelectric sensor) measures the operating power of the laser beam 64 emitted from the laser amplifier 51. The laser amplifier 51, optical emission spectrometer 70, and power sensor 72 can be controlled by a computing system. In some embodiments, multiple laser amplifiers are arranged in series to progressively amplify the laser beam emitted from the laser generator.

[0027] Figure 6 schematically illustrates an optical emission spectrometer 150 according to one embodiment, which captures the spectrum 152 emitted from the excitation gain medium within the quartz tube 92 of a laser generator or laser amplifier 93. In some embodiments, the optical emission spectrometer 150 captures the spectrum of light emitted from the excitation gain medium inside the quartz tube 92. According to one embodiment, the optical emission spectrometer 150 is connected to a computing system 156. In some embodiments, the optical emission spectrometer is a photodetector. An example of an optical emission spectrometer is the CCS200 compact spectrometer from Thorlabs, Inc.

[0028] Figure 7 schematically illustrates the components of an optical emission spectrometer 158 according to one embodiment. An emission-collecting optics element 160 transmits a spectrum 162 emitted from an excitation gain medium 164. The spectrum 162 passes through the emission-collecting optics element 160 and is detected by a spectrometer assembly 166. A signal processor 168 processes the spectral signal generated by the spectrometer assembly 166. In some embodiments, one or more emission-collecting optics elements and a signal processor are located external to the optical emission spectrometer and are not included within it. In some embodiments, the signal processor is integrated into a computing system configured to receive and process spectral signals. In some embodiments, the emission-collecting optics element is integrated into a laser generator or laser amplifier. In some embodiments, the emission optics element includes an optical fiber cable configured to transmit light emitted from the gain medium to the spectrometer assembly. In some embodiments, the emission optics element includes one or more lenses configured to transmit or otherwise modify the light emitted from the gain medium to the spectrometer assembly. In some embodiments, the emission optics element includes an optical fiber cable and a lens.

[0029] Figure 8A shows the optical emission spectrum indicating the abundance of carbon dioxide, while Figure 8B shows a graph of the optical emission spectrum, including peak 170 at approximately 470 nm, corresponding to the abundance of carbon monoxide. Figure 9 shows the optical emission spectrum including peak 171, which corresponds to the presence of carbon monoxide. Because carbon dioxide and carbon monoxide have different characteristic emission spectra, optical emission spectroscopy can be used to monitor the carbon monoxide content in the gain medium.

[0030] Figure 10 shows a graph 172 representing the operating power of the laser beam emitted by the laser generator over a period of time, according to an embodiment. Graph 172 overlaps with graphs 174 and 176, showing the ratio (expressed as a percentage) of carbon monoxide to carbon dioxide in the gain medium of the laser generator over the same time period. This ratio is determined based on the peak values ​​representing carbon monoxide at two different wavelengths in the optical emission spectrum obtained from the gain medium. The series in graph 174 represents the percentage of carbon monoxide in the gain medium determined based on the peak at 520 nm in the spectrum, while the series in graph 176 represents the percentage of carbon monoxide determined based on the peak at 466 nm in the spectrum. The horizontal axis represents time, starting from T0 when the laser generator operates at high power or the target power, and ending at time T1 elapsed after T0. Line 178 represents the threshold power value of the laser generator. Figure 10, showing the operating status of the laser generator over time, is similar to Figure 10 shown in the figure and can be obtained from the laser amplifier.

[0031] In some embodiments, the operation of the laser generator or laser amplifier is controlled such that the power of the laser beam emitted from it is maintained above a threshold power value of 178. In some embodiments, the operation of the laser generator or laser amplifier is adjusted when the laser power falls below the threshold power value of 178. In some embodiments, the operation of the laser generator or laser amplifier is adjusted such that the power of the laser beam emitted from it returns to the power conditions at time T0, or to the power conditions at any time between time T0. In some embodiments, when the laser beam reaches the desired target power, the amount of carbon monoxide or its average value in either of Figures 174 and 176 represents a reference spectrum. The reference spectrum may represent a reference amount of carbon monoxide in the gain medium corresponding to a laser beam previously operating at a higher target power. The carbon monoxide reference amount may be compared with the amount of carbon monoxide determined by the spectrum emitted from the gain medium at the time of measurement (e.g., when the laser power is below the threshold power value). In some implementations, the flow rate of carbon dioxide entering the gain medium and the carbon dioxide pressure in the gain medium are adjusted to reduce the amount of carbon monoxide in the gain medium to approach a reference amount of carbon monoxide, thereby increasing the laser beam emitted from the gain medium.

[0032] Figure 11 illustrates a method of operating an excitation laser system of an EUV lithography apparatus according to some embodiments. This method includes operation 1101, measuring the operating power of the laser beam in the excitation laser system. In some embodiments, a power sensor is used to measure the operating power. In some embodiments, the laser beam is maintained in a gain medium comprising carbon dioxide. In some embodiments, the gain medium is located in a laser generator. In some embodiments, the gain medium is located in laser generator 6 shown in Figure 3. In some embodiments, the gain medium is maintained in laser generator 27 shown in Figure 4. In some embodiments, the gain medium is located in a laser amplifier. In some embodiments, the gain medium is located in any one or more of laser amplifiers 8, 10, and 12 shown in Figure 3. In some embodiments, the gain medium is located in laser amplifier 51 shown in Figure 5. In some embodiments, the laser beam is maintained by the gain medium of one or more of the laser generator and laser amplifier.

[0033] This method also includes operation 1102, which determines whether the operating power of the laser beam is below a threshold power value. In some embodiments, the calculation system is configured to compare the operating power measured by a power sensor with a threshold power value. In one embodiment, one or more of the power sensors 15, 17, 19, and 21 in FIG. 3 are used to determine the operating power of the laser beam emitted from the laser generator 6 or the laser amplifiers 8, 10, and 12. In one embodiment, the power sensor 50 shown in FIG. 4 is used to determine the operating power of the laser beam emitted from the laser generator 27. In one embodiment, the power sensor 72 shown in FIG. 5 is used to determine the operating power of the laser beam emitted from the laser amplifier 51.

[0034] This method also includes operation 1103, whereby, when the operating power of the laser beam is determined to be below a threshold, an optical measurement is performed on the spectrum emitted from the gain medium. In some embodiments, optical emission spectroscopy is used to perform optical measurements on the spectrum of the laser beam. In some embodiments, an optical emission spectrometer is used to perform optical measurements on the spectrum. In some embodiments, the optical emission spectrometer is connected to a computing system. In some embodiments, any one or more of the first, second, third, and fourth optical emission spectrometers 20, 22, 24, and 26 shown in FIG. 3 may be heterogeneous and used to optically measure the spectrum of light emitted from the gain medium. In some embodiments, the optical emission spectrometer 48 shown in FIG. 4 is used for optical spectral measurements. In some embodiments, the optical emission spectrometer 70 shown in FIG. 5 is used for optical spectral measurements.

[0035] This method also includes operation 1104, which determines that the difference between the amount of carbon monoxide in the gain medium shown in the optical measurement spectrum and the reference amount of carbon monoxide shown in the reference spectrum emitted from the gain medium under conditions corresponding to the operation of the laser beam is where the target power is higher than the operating power. In one embodiment, the amount of carbon monoxide in the gain medium shown in the optical measurement spectrum is measured at any time after time T0 in FIG. 10, and the reference amount of carbon monoxide shown in the reference spectrum of the gain medium corresponds to the carbon monoxide concentration at time T0 or any time between T0 and the measurement time. In some embodiments, the operating power and carbon monoxide concentration depicted at time T0 are considered to be the gold standard for the gain medium of the laser generator or laser amplifier.

[0036] This method also includes operation 1105, which involves adjusting at least one of the carbon dioxide flow rate to the gain medium and the carbon dioxide pressure in the gain medium to reduce the amount of carbon monoxide reference in the gain medium. In some embodiments, the method includes increasing the carbon dioxide flow rate to the gain medium. In some embodiments, the method includes decreasing the carbon dioxide pressure in the gain medium. In some embodiments, the method includes increasing the carbon dioxide flow rate to the gain medium and decreasing the carbon dioxide pressure in the gain medium. In some embodiments, the method includes adjusting at least one of the carbon dioxide flow rate to the gain medium and the carbon dioxide pressure in the gain medium to increase the operating power of the laser beam to a target power, such as a gold standard.

[0037] According to some embodiments, increasing the flow rate of carbon dioxide to the gain medium increases the amount of carbon dioxide relative to carbon monoxide in the gain medium, thereby allowing more photons to be generated by the excitation of carbon dioxide molecules. Greater photon generation can increase the power of the laser beam. According to some embodiments, reducing the pressure of carbon dioxide in the gain medium increases the mean free path between molecules in the gain medium and slows down the rate at which carbon dioxide decomposes into carbon monoxide through collisions of carbon dioxide molecules. Slowing down the rate of carbon dioxide decomposition into carbon monoxide can be achieved by using a catalyst to catalytically convert carbon monoxide into carbon dioxide, thereby increasing the carbon dioxide concentration in the gain medium.

[0038] In some embodiments, adjusting at least one of the carbon dioxide flow rate to the gain medium and the carbon dioxide pressure in the gain medium to reduce the amount of carbon monoxide in the gain medium to a reference carbon monoxide level is achieved using gas supply unit 74, gas and control lines 84, 86, 88, and 90, and gas manifolds 76, 78, 80, and 82, as shown in FIG3. In some embodiments, adjusting at least one of the carbon dioxide flow rate to the gain medium and the carbon dioxide pressure in the gain medium to reduce the amount of carbon monoxide in the gain medium to a reference carbon monoxide level is achieved using inlet 46 and outlet 44, as shown in FIG4. In some embodiments, adjusting at least one of the carbon dioxide flow rate to the gain medium and the carbon dioxide pressure in the gain medium to reduce the amount of carbon monoxide in the gain medium to a reference carbon monoxide level is achieved using inlet 66 and outlet 68, as shown in FIG6.

[0039] Figure 12 illustrates a method of operating an excited laser system according to some embodiments. This method includes operation 1201, which measures a first operating power of a laser beam emitted from a laser generator of the excited laser system. The laser generator includes a first gain medium comprising carbon dioxide, which sustains the laser beam. The method also includes operation 1202, which determines whether the first operating power is below a first threshold power value. The method further includes operation 1203, which, upon determining that the first operating power is below the first threshold power value, optically acquires a first operating spectrum emitted from the first gain medium. The method also includes operation 1204, which determines the amount of carbon monoxide in the first gain medium from the first operating spectrum. The method further includes operation 1205, which adjusts at least one of the carbon dioxide flow rate to the first gain medium and the carbon dioxide pressure in the first gain medium to a level sufficient to reduce the amount of carbon monoxide in the first gain medium to the amount shown in a first reference spectrum corresponding to a target power of the laser generator. The operations in the figure are according to various embodiments, and Figure 12 can be applied independently to a laser generator, a laser amplifier, or a combination of a laser generator and one or more laser amplifiers.

[0040] Figure 13 is a block diagram illustrating an example of a computing system 710 for controlling the operation of one or more of the EUV lithography apparatus 2, the excitation laser system 300, the laser generator 27, and the laser amplifier 51, and optionally, any one or more optical emission spectrometers, gas supply units, gas manifolds, and other components explicitly or implicitly described herein according to various embodiments. In some embodiments, the computing system 710 is implemented using hardware or a combination of hardware and software, in a dedicated server, integrated into another entity, or distributed across multiple entities, such as via a cloud or wired network. According to various embodiments, the computing system 710 can communicatively connect to one or more of the EUV lithography apparatus 2, the excitation laser system 300, the laser generator 27, and the laser amplifier 51, and any other components explicitly or implicitly described herein, using a wireless or wired network 740 to allow data exchange between them.

[0041] The computing system 710 includes a display 711, a processor 712, memory 713, an input / output interface 714, a network interface 715, and a memory 716 storing an operating system 717, a program, or an application program 718, such as an application program for controlling the EUV lithography equipment 2, the excitation laser system 300, the laser generator 27, the laser amplifier 51, and any other components explicitly or implicitly described herein. The processor 712 may be a general-purpose microprocessor, a microcontroller, etc. The memory 716 may be random access memory (RAM), flash memory, read-only memory (ROM), a hard disk or optical disk, or any other suitable storage device for storing information and instructions to be executed by the processor 712. The processor 712 and memory 716 may be supplemented or incorporated therein by dedicated logic circuitry.

[0042] Network interface 715 may include a network interface card, such as an Ethernet card and a modem. In some embodiments, input / output interface 714 is configured to connect to multiple devices, such as input devices and / or output devices. Example input devices include a keyboard and pointing devices (such as a mouse or trackball) that a user can use to provide input to computing system 710. Example output devices include display devices, such as an LED (light-emitting diode) or LCD (liquid crystal display) screen for displaying information to a user.

[0043] Application 718 may contain instructions that, when executed by computing system 710 (or its processor 712), cause computing system 710 (or its processor 712) to control EUV lithography equipment 2, excitation laser system 300, laser generator 27, laser amplifier 51, and any other components expressly or implicitly described herein, and to perform other operations, methods, and / or processes expressly or implicitly described herein.

[0044] Data 719 may include parameters used in control operations, received data, such as data transmitted via input / output interface 714 or via network interface 715 from EUV lithography equipment 2, excitation laser system 300, laser generator 27 and laser amplifier 51 and any other components explicitly or implicitly described herein, data for display on display 711, data transmitted via network to or from EUV lithography equipment 2, excitation laser system 300, laser generator 27, laser amplifier 51 and any other components explicitly or implicitly described herein via wired network 740, or data generated during operation of computing system 710.

[0045] In some embodiments, the computing device is configured to control one or more power sensors to measure the operating power of one or more laser generators and one or more laser amplifiers. In some embodiments, the computing device is programmed to determine whether the measured operating power is below a threshold power value. In some embodiments, the computing device is configured to control one or more optical emission spectrometers to optically capture spectra from one or more laser generators and one or more laser amplifiers when the corresponding operating power is determined to be below the threshold power value. In some embodiments, the computing device is configured to determine the amount of carbon monoxide in the gain medium of one or more laser generators and one or more laser amplifiers based on the corresponding measured spectra. In some embodiments, the computing device is configured to control a gas supply unit to adjust at least one of the flow rate of carbon dioxide to the gain medium and the pressure of carbon dioxide in the gain medium, reducing the amount of carbon monoxide in the gain medium to the amount of carbon monoxide shown in a corresponding reference spectrum corresponding to the target power of one or more laser generators and one or more laser amplifiers.

[0046] The subject matter of one embodiment of this disclosure is for improving the performance, maintenance, and operation of EUV lithography systems. The subject matter of one embodiment of this disclosure can be used to non-invasively measure the composition of a laser gain medium and control or otherwise adjust the composition of the gain medium to maintain laser power or return the laser to a target power state. The subject matter of one embodiment of this disclosure avoids the need to obtain a physical sample of the gain medium, which may otherwise contain hazardous materials such as carbon monoxide. The subject matter of one embodiment of this disclosure also avoids compositional inaccuracies caused by removing physical gas samples from the gain medium. The subject matter of one embodiment of this disclosure also avoids the need to shut down the laser device to obtain a gain medium sample.

[0047] According to one embodiment, a method of operating an extreme ultraviolet (EUV) lithography apparatus to excite a laser system includes measuring the operating power of a laser beam in the excitation laser system, wherein the laser beam is maintained in a gain medium comprising carbon dioxide. The method further includes determining whether the operating power of the laser beam is below a threshold power value. The method further includes, when the operating power of the laser beam is determined to be below the threshold power value, optically measuring the spectrum of light emitted from the gain medium. The method further includes determining the difference between the amount of carbon monoxide in the gain medium in the optically measured spectrum and a reference amount of carbon monoxide depicted in a reference spectrum of light emitted from the gain medium corresponding to a state where the laser beam operates at a power higher than the target power. The method further includes adjusting at least one of the flow rate of carbon dioxide to the gain medium and the pressure of carbon dioxide in the gain medium to reduce the amount of carbon monoxide in the gain medium. In one embodiment, the gain medium is located in a laser generator. In one embodiment, the gain medium is located in a laser amplifier. In one embodiment, optical emission spectroscopy is used to perform the optical measurement of the spectrum. In one embodiment, the method includes increasing the flow rate of carbon dioxide to the gain medium. In one embodiment, the method includes reducing the pressure of carbon dioxide in the gain medium. In one embodiment, the method includes increasing the flow rate of carbon dioxide to the gain medium and decreasing the carbon dioxide pressure in the gain medium.

[0048] According to another embodiment, a method of operating an excited laser system includes measuring a first operating power of a laser beam emitted from a laser generator of the excited laser system, wherein the laser generator includes a first gain medium containing carbon dioxide, and the first gain medium sustains the laser beam. The method further includes determining whether the first operating power is lower than a first threshold power value. The method further includes, when the first operating power is determined to be lower than the first threshold power value, optically measuring a first operating spectrum of light emitted from the first gain medium and determining the amount of carbon monoxide in the first gain medium shown in the first operating spectrum. The method further includes adjusting at least one of the flow rate of carbon dioxide to the first gain medium and the pressure of carbon dioxide in the first gain medium to be sufficient to reduce the amount of carbon monoxide in the first gain medium. In one embodiment, the method includes increasing the flow rate of carbon dioxide to the first gain medium. In one embodiment, the method includes decreasing the pressure of carbon dioxide in the first gain medium. In one embodiment, the method further includes measuring a second operating power of a laser beam emitted from a laser amplifier of an excitation laser system, wherein the laser amplifier receives a laser beam from a laser generator, the laser amplifier including a second gain medium containing carbon dioxide, the second gain medium sustaining the laser beam; determining whether the second operating power is below the second threshold power value; when the second operating power is determined to be below the second threshold power value, optically obtaining a second operating spectrum emitted from the second gain medium, and determining the amount of carbon monoxide in the second gain medium based on the second operating spectrum; and adjusting at least one of the flow rate of carbon dioxide to the second gain medium and the pressure of carbon dioxide in the second gain medium to be sufficient to reduce the amount of carbon monoxide in the second gain medium. In one embodiment, the method includes increasing the flow rate of carbon dioxide to the second gain medium. In one embodiment, the method includes decreasing the pressure of carbon dioxide in the second gain medium.

[0049] In another embodiment, the excitation laser system includes a laser generator configured to generate a laser beam from a first gain medium comprising carbon dioxide. The excitation laser system also includes a first power sensor configured to measure a first operating power of the laser beam exiting the laser generator. The excitation laser system further includes a first optical emission spectrometer configured to optically capture a first spectrum from the first gain medium. The excitation laser system also includes a gas supply unit configured to control the supply of carbon dioxide to the first gain medium. The excitation laser system also includes a computing system programmed to perform the following operations: controlling the first power sensor to measure the first operating power; determining whether the first operating power is below the first threshold power value; when the first operating power is determined to be below the first threshold power value, controlling the first optical emission spectrometer to optically capture the first spectrum; determining the amount of carbon monoxide in the first gain medium based on the first spectrum; and controlling the gas supply unit to adjust at least one of the carbon dioxide flow rate to the first gain medium and the carbon dioxide pressure in the first gain medium to reduce the amount of carbon monoxide in the first gain medium. In one embodiment, the computing system is programmed to control the gas supply unit to increase the carbon dioxide flow rate to the first gain medium. In one embodiment, the computing system is programmed to control a gas supply unit to reduce the pressure of carbon dioxide in a first gain medium. In another embodiment, the excitation laser system further includes a first laser amplifier configured to amplify a laser beam using a second gain medium comprising carbon dioxide, a second power sensor configured to measure a second operating power of the laser beam exiting the first laser amplifier, and a second optical emission spectrometer configured to optically capture a second spectrum from the second gain medium. The computing system is also programmed to perform the following operations: controlling the second power sensor to measure the second operating power; determining whether the second operating power is below a second threshold power value; when the second operating power is determined to be below the second threshold power value, controlling the second optical emission spectrometer to optically capture the second spectrum; determining the amount of carbon monoxide in the second gain medium based on the second spectrum; and controlling the gas supply unit to adjust at least one of the carbon dioxide flow rate to the second gain medium and the carbon dioxide pressure in the second gain medium to reduce the amount of carbon monoxide in the second gain medium.In one embodiment, the excitation laser system further includes a second laser amplifier configured to amplify a laser beam using a third gain medium comprising carbon dioxide; a third power sensor configured to measure a third operating power of the laser beam exiting the second laser amplifier; and a third optical emission spectrometer configured to optically capture a third spectrum from the third gain medium, wherein the computing system is also programmed to perform the following operations: controlling the third power sensor to measure the third operating power, determining whether the third operating power is lower than a third threshold power value, and when the third operating power is determined to be lower than the third threshold power value, controlling the third optical emission spectrometer to optically capture the third spectrum, determining the amount of carbon monoxide in the third gain medium based on the third spectrum, and controlling the gas supply unit to adjust at least one of the flow rate of carbon dioxide to the third gain medium and the pressure of carbon dioxide in the third gain medium to reduce the amount of carbon monoxide in the third gain medium. In one embodiment, the excitation laser system further includes a third laser amplifier configured to amplify a laser beam using a fourth gain medium comprising carbon dioxide; a fourth power sensor configured to measure a fourth operating power of the laser beam exiting the third laser amplifier; and a fourth optical emission spectrometer configured to optically capture a fourth spectrum from the fourth gain medium, wherein the computing system is further programmed to perform operations including: controlling the fourth power sensor to measure the fourth operating power; determining whether the fourth operating power is lower than a fourth threshold power value; when the fourth operating power is determined to be lower than a third threshold power value, controlling the fourth optical emission spectrometer to optically capture the fourth spectrum; determining the amount of carbon monoxide in the fourth gain medium based on the fourth spectrum; and controlling a gas supply unit to adjust at least one of the flow rate of carbon dioxide to the fourth gain medium and the pressure of carbon dioxide in the fourth gain medium to reduce the amount of carbon monoxide in the fourth gain medium. In one embodiment, at least one of the laser generator, the first laser amplifier, the second laser amplifier, or the third laser amplifier includes a quartz tube configured to contain a first gain medium in an excited state. In one embodiment, at least one of the first, second, third, or fourth optical emission spectrometers is configured to capture the first, second, or fourth spectrum of light emitted from the quartz tube, respectively. In one embodiment, the extreme ultraviolet (EUV) lithography apparatus includes an excitation laser system.

[0050] The foregoing outlines the features of various embodiments or examples to enable those skilled in the art to better understand the orientation of one embodiment of this disclosure. Those skilled in the art should understand that they can readily use this disclosure as a basis to design or modify other processes and structures to achieve the same purpose and / or the same advantages as the embodiments or examples described herein. Those skilled in the art should also recognize that such equivalent constructions do not depart from the spirit and scope of one embodiment of this disclosure, and various changes, substitutions, and modifications can be made without departing from the spirit and scope of one embodiment of this disclosure.

[0051] 2: EUV lithography equipment 6: Laser Generator 8, 10, 12: Laser amplifiers 14, 16, 18: Channels 15, 17, 19, 21: Power Sensors 20, 22, 24, 26: Emission spectrometer 27: Laser Generator 28: Quartz Tube 30: Gain Medium 32: Coupler 34: Reflector 36: Power supply 38, 40: Electrodes 42: Laser Beam 43: Catalyst 44: Exports 46: Entrance 48: Optical emission spectrometer 50: Power Sensor 51: Laser Amplifier 52: Quartz Tube 54: Gain Medium 56: Laser Beam 58: Power Supply 60, 62: Electrodes 64: Laser Beam 66: Entrance 67: Catalyst 68: Exports 70: Emission Spectrometer 72: Power Sensor 74: Gas Supply Unit 76, 78, 80, 82: Gas manifold 84, 86, 88, 90: Pipelines, Inlets 85, 87, 89, 91: Exports 92: Quartz Tube 93: Laser Amplifier 100: EUV radiation source 105: Chamber 110: Mirror Collector 115: Target Droplet Generator 120: Nozzle 125: Droplet trap 130: First buffer gas supply source 140: Export 150: Emission Spectrometer 152: Spectrum 156: Computing System 158: Emission Spectrometer 160: Optical Components 162: Spectrum 164: Gain Medium 166: Spectrometer Components 168: Processor 170, 171: Peak 172, 174, 176: Charts 178: Line, Threshold Power Value 200: Exposure device 205a, 205b, 205d, 205e: Optical elements 205c: Mask 210:Substrate 211: Photoresist layer 300: Excited Laser System 320: Optical guiding element 330: Focusing device 710: Computing System 711: Monitor 712: Processor 713: Memory 714: Input / Output Interface 715: Network Interface 716: Memory 717: Storage Operating System 718: Application 719: Data 740: Wired Network 1101,1102,1103,1104,1105,1201,1202,1203,1204,1205: Operations DP: Target droplet LR1, LR2: Excited laser, excited laser beam ZE: Excitation Region

[0052] Domestic storage information (please note in order of storage institution, date, and number) none Overseas storage information (please note in the order of storage country, institution, date, and number) none

Claims

1. A method for operating an extreme ultraviolet (EUV) lithography apparatus to excite a laser system, comprising: The method involves measuring the operating power of a laser beam in an excitation laser system, wherein the laser beam is held in a gain medium comprising carbon dioxide; determining whether the operating power of the laser beam is below a threshold power value; when the operating power of the laser beam is determined to be below the threshold power value, optically measuring a spectrum emitted from the gain medium; and determining the difference between the amount of carbon monoxide in the gain medium shown in the optically measured spectrum and a reference amount of carbon monoxide shown in a reference spectrum emitted by the gain medium under a state corresponding to the laser beam operating at a target power higher than the operating power. And adjust at least one of the carbon dioxide flow rate to the gain medium and the carbon dioxide pressure in the gain medium to reduce the amount of carbon monoxide in the gain medium.

2. The method as described in claim 1, wherein the method includes increasing the flow rate of the carbon dioxide toward the gain medium.

3. The method as described in claim 1, wherein the method includes reducing the carbon dioxide pressure in the gain medium.

4. A method for operating an excitation laser system, comprising: Measuring a first operating power of a laser beam emitted by a laser generator of the excitation laser system, wherein the laser generator includes a first gain medium having a carbon dioxide, the first gain medium maintaining a laser beam; determining whether the first operating power is lower than a first threshold power value; when the first operating power is determined to be lower than the first threshold power value, optically measuring a first operating spectrum of light emitted from the first gain medium and determining the amount of carbon monoxide in the first gain medium shown in the first operating spectrum; and adjusting at least one of a carbon dioxide flow rate to the first gain medium and a carbon dioxide pressure in the first gain medium to sufficiently reduce the amount of carbon monoxide in the first gain medium.

5. The method as claimed in claim 4, further comprising: measuring a second operating power of the laser beam emitted from a laser amplifier of the excitation laser system, wherein the laser amplifier receives the laser beam from the laser generator, the laser amplifier comprising a second gain medium including the carbon dioxide, the second gain medium maintaining the laser beam; determining whether the second operating power is lower than a second threshold power value; when the second operating power is determined to be lower than the second threshold power value, optically obtaining a second operating spectrum emitted from the second gain medium, and determining the amount of carbon monoxide in the second gain medium based on the second operating spectrum; and adjusting at least one of a carbon dioxide flow rate to the second gain medium and a carbon dioxide pressure in the second gain medium to sufficiently reduce the amount of carbon monoxide in the second gain medium.

6. A laser excitation system, comprising: A laser generator configured to generate a laser beam from a first gain medium comprising a carbon dioxide; A first power sensor configured to measure a first operating power of the laser beam exiting the laser generator; a first optical emission spectrometer configured to optically capture a first spectrum from the first gain medium; A gas supply unit configured to control the supply of carbon dioxide to the first gain medium; a computing system programmed to perform operations including: controlling the first power sensor to measure the first operating power; determining whether the first operating power is lower than the first threshold power value; when the first operating power is determined to be lower than the first threshold power value, controlling the first optical emission spectrometer to optically capture the first spectrum; determining the amount of carbon monoxide in the first gain medium from the first spectrum; and controlling the gas supply unit to adjust a carbon dioxide flow rate to flow to at least one of the first gain medium and a carbon dioxide pressure in the first gain medium to reduce the amount of carbon monoxide in the first gain medium.

7. The excitation laser system as described in claim 6, further comprising: A first laser amplifier configured to amplify the laser beam using a second gain medium including the carbon dioxide; a second power sensor configured to measure a second operating power of the laser beam exiting the first laser amplifier; The system also includes a second optical emission spectrometer configured to optically capture a second spectrum from a second gain medium, wherein the computing system is further programmed to perform the following operations: controlling the second power sensor to measure the second operating power; determining whether the second operating power is lower than a second threshold power value; when the second operating power is determined to be lower than the second threshold power value, controlling the second optical emission spectrometer to optically capture the second spectrum; determining the amount of carbon monoxide in the second gain medium from the second spectrum; and controlling the gas supply unit to adjust a carbon dioxide flow rate to flow to at least one of the second gain medium and a carbon dioxide pressure in the second gain medium to reduce the amount of carbon monoxide in the second gain medium.

8. The excitation laser system as described in claim 7, further comprising: A second laser amplifier configured to amplify a laser beam using a third gain medium including the carbon dioxide; a third power sensor configured to measure a third operating power of the laser beam exiting the second laser amplifier; and a third optical emission spectrometer configured to optically capture a third spectrum from the third gain medium, wherein the computing system is further programmed to perform the following operations: controlling the third power sensor to measure the third operating power; determining whether the third operating power is lower than the third threshold power value; when the third operating power is determined to be lower than the third threshold power value, controlling the third optical emission spectrometer to optically capture the third spectrum; determining the amount of carbon monoxide in the third gain medium based on the third spectrum; and controlling the gas supply unit to adjust a carbon dioxide flow rate to at least one of the third gain medium and a carbon dioxide pressure in the third gain medium to reduce the amount of carbon monoxide in the third gain medium.

9. The excitation laser system as claimed in claim 6, wherein the laser generator includes a quartz tube configured to contain the first gain medium in an excited state.

10. The excitation laser system as claimed in claim 9, wherein the first optical emission spectrometer is configured to capture the first spectrum of light emitted from the quartz tube.

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