CN114303059A

CN114303059A - Fluorine detection in gas discharge light sources

Info

Publication number: CN114303059A
Application number: CN202080060559.7A
Authority: CN
Inventors: O·祖里塔
Original assignee: Cymer LLC
Current assignee: Cymer LLC
Priority date: 2019-08-29
Filing date: 2020-08-21
Publication date: 2022-04-08
Also published as: TWI820776B; WO2021041224A1; JP2022545182A; TW202111321A; TW202242376A; TWI770568B; JP7360539B2

Abstract

One method comprises the following steps: receiving at least a portion of a mixed gas from a gas discharge chamber, wherein the mixed gas comprises fluorine; reacting fluorine in the portion of the mixed gas with the hydroxide to form a new gas mixture comprising oxygen and water; sensing a water concentration within the new gas mixture; and estimating a fluorine concentration within the portion of the mixed gas based on the sensed water concentration.

Description

Fluorine detection in gas discharge light sources

Cross Reference to Related Applications

This application claims priority to U.S. application No. 62/893,377 entitled "fluorine detection in gas discharge light source" filed on 29.8.2019, the entire contents of which are incorporated herein by reference.

Technical Field

The disclosed subject matter relates to the detection of fluorine in a mixed gas.

Background

One type of gas discharge light source used for photolithography is known as an excimer light source or laser. Excimer light sources typically use a combination of one or more noble gases (such as argon, krypton or xenon) and a reactive gas (such as fluorine or chlorine). Excimer light sources are known for the fact that under appropriate electrical stimulation (providing energy) and high voltage (gas mixture) conditions, a pseudo-molecule, called an excimer, is produced, which is present only in the energized state and produces amplified light in the ultraviolet range.

An excimer light source generates a beam of light having a wavelength in the Deep Ultraviolet (DUV) range and which is used to pattern a semiconductor substrate (or wafer) in a lithographic apparatus. The excimer light source can be constructed using a single gas discharge cell or using multiple gas discharge cells.

Disclosure of Invention

In some general aspects, a method comprises: at least a portion that receives a mixed gas from the gas discharge chamber, the mixed gas including fluorine; reacting fluorine in the portion of the mixed gas with the hydroxide to form a new gas mixture comprising oxygen and water; sensing a water concentration within the new gas mixture; and estimating a fluorine concentration within the portion of the mixed gas based on the sensed water concentration.

Implementations may include one or more of the following features. For example, the hydroxide may include an alkaline earth metal hydroxide. The hydroxide may be devoid of alkali metal and carbon.

The mixed gas may be an excimer laser gas comprising at least a mixture of the gain medium and the buffer gas.

The method may further comprise: adjusting the relative concentration of fluorine in the gas mixture from the set of gas supplies based on the estimated fluorine concentration in the portion of the mixed gas; and performing gas renewal by adding the adjusted gas mixture from the gas supply source to the gas discharge chamber. The gas refresh can be performed by filling the gas discharge cell with a mixture of gain medium and buffer gas and fluorine. By filling the gas discharge cell with a gain medium comprising a rare gas and a halogen and a buffer gas comprising an inert gas, the gas discharge cell can be filled with a mixture of the gain medium and the buffer gas. The noble gas may include argon, krypton, or xenon; the halogen may include fluorine; and the inert gas may include helium or neon. The gas discharge cell may be filled with a mixture of gain medium and buffer gas and fluorine in the following manner: adding a mixture of the gain medium and the buffer gas and fluorine to an existing mixed gas in the gas discharge chamber; alternatively, at least the mixture of gain medium and buffer gas and fluorine is used to replace the existing gas mixture in the gas discharge chamber. Gas renewal may be performed by performing one or more of a gas refill scheme or a gas injection scheme.

By receiving a portion of the mixed gas prior to performing gas renewal on the gas discharge chamber, a portion of the mixed gas may be received from the gas discharge chamber. Gas rejuvenation may include adding a gas mixture from a set of gas supplies to the gas discharge chamber, the gas mixture including at least some fluorine.

Gas renewal may be performed by performing one or more of a gas refill scheme or a gas injection scheme.

By discharging the mixed gas from the gas discharge chamber and guiding the discharged mixed gas to the reaction vessel containing the hydroxide, a portion of the mixed gas from the gas discharge chamber can be received. The method may further include transferring the new gas mixture from the reaction vessel to a measurement vessel, wherein sensing the water concentration within the new gas mixture includes sensing the water concentration within the new gas mixture within the measurement vessel. The water concentration within the new gas mixture may be sensed by exposing a sensor within the measurement vessel to the new gas mixture.

The method may further comprise, after the fluorine concentration within the portion of the mixed gas has been estimated, venting a new gas mixture from the measurement vessel.

The water concentration within the new gas mixture may be sensed by sensing the water concentration within the new gas mixture without diluting the portion of the mixed gas with another material.

By adding water to form the inorganic fluoride, a portion of the mixed gas can be reacted with the hydroxide to form a new gas mixture comprising water. The hydroxide may comprise calcium hydroxide and the inorganic fluoride may comprise calcium fluoride.

The water concentration in the new gas mixture may be sensed by sensing the water concentration in the new gas mixture only after a predetermined period of time has elapsed after the reaction has started.

The portion of the mixed gas may be the effluent gas, and the portion of the mixed gas may react with the hydroxide by removing fluorine from the effluent gas to form a new gas mixture comprising water.

By estimating based only on the sensed water concentration and the chemical reaction between fluorine and hydroxide in the portion of the mixed gas, the fluorine concentration within the portion of the mixed gas may be estimated based on the sensed water concentration.

The concentration of fluorine in the portion of the mixed gas may be about 500-2000ppm (parts per million).

The reaction of fluorine in the portion of the mixed gas with the hydroxide to form a new gas mixture comprising water may be stable.

By performing a reaction that is linear and provides a direct relationship between the concentration of fluorine in the portion of the mixed gas and the concentration of water in the new gas mixture, the fluorine in the portion of the mixed gas can react with the hydroxide to form a new gas mixture comprising water.

The method may further include sensing an oxygen concentration within the new gas mixture, and may additionally estimate a fluorine concentration within the portion of the mixed gas based on the sensed oxygen concentration.

In other general aspects, a method comprises: performing a first gas refresh by adding a first gas mixture from a set of gas supplies to the gas discharge chamber: removing at least a portion of the mixed gas from the gas discharge chamber after the first gas refresh, the mixed gas comprising fluorine; reacting a portion of the removed fluorine of the mixed gas with a reactant to form a new gas mixture comprising oxygen and water; sensing a water concentration within the new gas mixture; estimating a fluorine concentration within the portion of the removed mixed gas based on the sensed water concentration; adjusting a relative concentration of fluorine in the second gas mixture from the set of gas supplies based on the estimated fluorine concentration in the portion of the mixed gas removed; and performing a second gas refresh by adding the adjusted second gas mixture from the gas supply source to the gas discharge chamber.

Implementations may include one or more of the following features. For example, the reactant may comprise a hydroxide. The mixed gas in the gas discharge cell may comprise an excimer laser gas comprising at least a mixture of a gain medium and a buffer gas.

By estimating the fluorine concentration within the portion of the removed mixed gas without measuring the fluorine concentration within the portion of the removed mixed gas, the fluorine concentration within the portion of the removed mixed gas may be estimated based on the sensed concentration of water.

In other general aspects, the apparatus includes a detection device fluidly connected to each gas discharge cell of the excimer gas discharge system, and a control system connected to the detection device. Each detection device includes: a vessel defining a reaction chamber containing a hydroxide and fluidly connected to the gas discharge chamber for receiving a mixed gas containing fluorine from the gas discharge chamber in the reaction chamber; and a water sensor. The vessel causes a reaction between the fluorine and hydroxide in the received mixed gas to form a new gas mixture comprising oxygen and water. The water sensor is configured to be fluidly connected to the new gas mixture and to sense an amount of water within the new gas mixture when fluidly connected to the new gas mixture. The control system is configured to: receiving an output from the water sensor and estimating a fluorine concentration in the mixed gas received from the gas discharge chamber; determining whether a fluorine concentration within a gas mixture from a gas supply system of a gas maintenance system should be adjusted based on the estimated fluorine concentration in the mixed gas; and sending a signal to the gas maintenance system instructing the gas maintenance system to adjust the relative concentration of fluorine in the gas mixture supplied to the gas discharge chamber from the gas supply system of the gas maintenance system during gas renewal to the gas discharge chamber.

Implementations may include one or more of the following features. For example, each gas discharge cell of an excimer gas discharge system can contain an energy source and can contain a gas mixture that includes an excimer laser gas that includes a gain medium and fluorine.

The detection device may further comprise a measurement vessel fluidly connected to the reaction chamber of the reaction vessel and defining a measurement chamber configured to receive the new gas mixture. The wafer sensor may be configured to sense the amount of water within the new gas mixture in the measurement chamber.

The fluorine concentration in the portion of the mixed gas removed may be about 500-2000 ppm.

The excimer gas discharge system may comprise a plurality of gas discharge cells, and the detection apparatus may be fluidly connected to each of the plurality of gas discharge cells. The detection apparatus may comprise a plurality of containers, each container defining a reaction chamber containing a hydroxide and each container being fluidly connected to one of the gas discharge chambers, and a plurality of water sensors, each wafer sensor being associated with one container. The detection apparatus may comprise a plurality of containers, each container defining a reaction chamber containing the hydroxide and each container being fluidly connected to one of the gas discharge chambers, and the detection apparatus comprises a single water sensor fluidly connected to all containers.

Drawings

FIG. 1 is a block diagram of an apparatus including a detection device configured to measure a fluorine concentration within a gas mixture within a chamber;

FIG. 2 is a block diagram of the apparatus of FIG. 1, implemented as part of a Deep Ultraviolet (DUV) light source that generates a beam of light directed at a lithographic apparatus;

FIG. 3 is a block diagram of an implementation of a detection device of the apparatus of FIG. 1, wherein the detection device includes a fluorine sensor;

FIG. 4 is a block diagram of an implementation of the apparatus of FIG. 1, wherein the detection apparatus includes a buffer container;

FIG. 5 is a block diagram of an implementation of the apparatus of FIG. 1, wherein the detection apparatus comprises a plurality of reaction vessels, each reaction vessel being associated with one of a plurality of chambers;

FIG. 6 is a block diagram of an implementation of the apparatus of FIG. 2, showing details of an exemplary DUV light source;

FIG. 7 is a block diagram of an implementation of a control system that is part of the DUV light source shown in FIG. 2 or FIG. 6;

FIG. 8 is a block diagram of another implementation of the apparatus of FIG. 1, wherein the apparatus is implemented in conjunction with a fluorine scrubber;

FIG. 9 is a flow chart of a routine for detecting the fluorine concentration in the gas mixture of the chamber by the detection device;

FIG. 10 is a flow chart of a routine performed by the apparatus once the fluorine concentration is estimated and upon completion of the routine of FIG. 9; and

fig. 11 is a flowchart of a routine executed by the detection device to estimate the fluorine concentration in the gas mixture in the chamber, instead of the routine of fig. 9.

Detailed Description

Referring to fig. 1, the apparatus 100 includes a detection device 105, the detection device 105 being configured to measure or estimate the fluorine (F) concentration in the gas mixture 107 within the chamber 110, without directly measuring the fluorine concentration in the gas mixture 107 using a commercially available fluorine sensor. At room temperature, fluorine is a diatomic molecular gas consisting of its molecular structure F₂And (4) showing. The term "fluoro", as used herein, thus refers to molecular fluorine F₂. Fluorine molecules F in the chamber 110₂Is in a range too high to directly detect fluorine. For example, the fluorine concentration in chamber 110 is greater than about 500ppm (parts per million) and may be about 1000ppm or up to about 2000 ppm. However, commercially available fluorine sensors typically saturate at 10ppm, so it is not practical to directly measure the fluorine concentration in chamber 110 using commercially available fluorine sensors. Rather, the detection device 105 is capable of performing a chemical reaction that converts fluorine from the chamber 110 into one or more components (including water), each of which can be detected and measured with the sensor 115 of a commercially available sensing device 116. The detection device 105 may calculate or estimate the presence of water prior to the start of the chemical reaction based on the amount of water present after the chemical reaction (as provided from the sensor 115) and based on information about the chemical reactionAt what level of fluorine.

To make this estimate accurate, the detection device 105 may assume that the chemical reaction that converts fluorine from the chamber 110 into a constituent is a linear reaction, where there is a direct correlation between the fluorine concentration before the chemical reaction begins and the water concentration at the end of the chemical reaction. Alternatively, the detection device 105 may assume that the conversion of fluorine has been completed (and therefore that there is no residual molecular fluorine F2 in the gas after the chemical reaction).

The apparatus 100 is in communication with a gas maintenance system 120, the gas maintenance system 120 comprising at least a gas supply system fluidly connected to the chamber 110 via a conduit system 127. As discussed in detail below, the gas maintenance system 120 includes one or more gas supply sources and a control unit (also including a valve system) for controlling which gases from the supply sources are transferred into the chamber 110 or out of the chamber 110 via the conduit system 127.

The apparatus 100 includes a controller 130, the controller 130 receiving the output from the water sensor 115 and calculating how much fluorine is present before the chemical reaction begins to estimate the amount of fluorine in the gas mixture 107. The controller 130 uses this information to determine whether the fluorine concentration in the gas mixture 107 needs to be adjusted. The controller 130 thus determines how to adjust the relative amount of gas in the supply of the gas maintenance system 120 that is transferred into the chamber 110 or out of the chamber 110 based on the determination. The controller 130 sends a signal to the gas maintenance system 120 instructing it to adjust the relative concentration of fluorine in the gas mixture 107 during the gas refresh to the chamber 110.

The detection device 105 includes a reaction vessel 135, the reaction vessel 135 defining a reaction chamber 140, the reaction chamber 140 containing a hydroxide sigma (-OH)145, where sigma is a metal. The reaction chamber 140 is fluidly connected to the chamber 110 via a conduit 137 to receive a mixed gas 150 including fluorine from the chamber 110. Although not shown, one or more fluid control devices, such as valves, may be placed in the conduit 137 to control when the mixed gas 150 is directed to the reaction chamber 140 and to control the flow rate of the mixed gas 150 into the reaction vessel 135. In this manner, the reaction chamber 140 chemically reacts fluorine in the received mixed gas 150 with the hydroxide 145 to form a new gas mixture 155. The interior of the reaction vessel 135 defining the reaction chamber 140 should be made of a non-reactive material so as not to interfere with or alter the chemical reaction between the received fluorine of the mixed gas 150 and the hydroxide 145. For example, the interior of the reaction vessel 135 may be made of a non-reactive metal such as stainless steel or monel metal.

The water sensor 115 is fluidly connected to receive the new gas mixture 155 and to sense the amount of water within the new gas mixture 155. The water sensor 115 may be a commercially available water sensor capable of detecting water concentrations within a range of concentrations expected due to chemical reactions. For example, the water sensor 115 senses water in the range of 200-1000ppm within the new gas mixture 155.

The water sensor 115 (and optionally the oxygen sensor 117) may be within the measurement cavity 175 of the measurement vessel 170. The measurement lumen 175 is fluidly connected to the reaction lumen 140 via a conduit 177. Although not shown in fig. 1, one or more fluid control devices (such as valves) may be placed in the conduit 177 to control when the new gas mixture 155 is directed to the measurement cavity 175 and to control the flow rate of the new gas mixture 155 into the measurement vessel 170.

In some implementations, the water sensor 115 can be a hygrometer that measures the amount of water vapor or humidity in the cavity 175. Instruments that measure humidity also typically measure mechanical or electrical changes in temperature, pressure, mass, and even moisture-absorbing substances, as these factors can also affect humidity. These measured quantities can result in humidity measurements through calibration and calculation. A hygrometer may be an electronic device that uses the condensation temperature (also known as the dew point), i.e., the full vapor saturation point of a substance. A hygrometer may be a device that detects and measures a change in capacitance or resistance of a substance to determine humidity. The hygrometer may be a resistance hygrometer that measures the change in the ability of a substance to hold an electrostatic charge. The hygrometer may be a capacitor-based hygrometer for measuring a change in the ability of a substance to transfer power.

In some implementations, although not required, the sensing device 116 includes a second sensor 117, the second sensor 117 can be an oxygen sensor 117, the oxygen sensor 117 sensing oxygen in the range of 200-1000ppm within the new gas mixture 155.

One example of an oxygen sensor 117 suitable for this concentration range is an oxygen analyzer that utilizes a precision zirconia sensor to detect oxygen. The zirconia oxide sensor includes a unit cell made of a high purity, high density, stable zirconia ceramic. The zirconia sensor generates a voltage signal indicative of the oxygen concentration of the new gas mixture 155. In addition, the output of the zirconia oxide sensor is analyzed (e.g., converted and linearized) by a high speed microprocessor within the oxygen sensor 117 to provide a direct digital reading for use by the controller 130. A conventional zirconia cell comprises a zirconia ceramic tube coated on its inner and outer surfaces with porous platinum electrodes. When the zirconia oxide sensor is heated above a certain temperature (e.g., 600C or 1112 ° F), it becomes an oxygen ion conducting electrolyte. The electrode is oxygen molecule O₂The conversion to oxygen ions and the conversion of oxygen ions to oxygen molecules provides a catalytic surface. Oxygen molecules on the high concentration reference gas side of the cell acquire electrons and become ions, entering the electrolyte. At the same time, at the inner electrode, the oxygen ions lose electrons and are released from the surface as oxygen molecules. When the oxygen concentration is different on both sides of the zirconia sensor, oxygen ions migrate from the high concentration side to the low concentration side. This ion flow creates an electronic imbalance that results in a dc voltage on the electrodes. This voltage is a function of the sensor temperature and the ratio of the partial pressure (concentration) of oxygen on each side of the sensor. This voltage is then analyzed by a high speed microprocessor within the oxygen sensor 117 for direct readout by the controller 130.

The fluorine in the mixed gas 150 reacts with the hydroxide 145 because the chemical reaction between fluorine and hydroxide is a stoichiometrically simple chemical reaction that is easy to implement and control. Furthermore, the controlled stoichiometry of the chemical reaction is fixed. Furthermore, the chemical reaction between fluorine and hydroxide is a stable chemical reaction. The chemical reaction may be stable if the chemical reaction is irreversible and the components of the new gas mixture do not react with any other species within the new gas mixture to form fluorine. Next, a suitable chemical reaction between the fluorine of the mixed gas 150 and the hydroxide 145, which is stable and has a controlled stoichiometric ratio, is discussed.

In some implementations, the hydroxide 145 is in granular, solid, powder form. Further, the hydroxide 145 in a granular form may be tightly packed into the reaction vessel 135 (which may be a tube shape) so that particles in the powder of the hydroxide 145 do not move. The area or volume outside the powder of the hydroxide 145 and in the space inside the reaction vessel 135 is considered to be porosity, and by using the hydroxide 145 in a granular form, a large surface area can be ensured to allow a thorough chemical reaction between the hydroxide 145 and fluorine. In some implementations, and depending on the particular hydroxide, the hydroxide 145 and the reaction vessel 135 are maintained at room temperature and the reaction between the hydroxide 145 and the fluorine proceeds without the need for a catalyst.

The hydroxide 145 may fill the reaction chamber 140 within the reaction vessel 135. The shape of the reaction vessel 135 and thus the reaction chamber 140 is not limited to a specific form.

The hydroxide 145 includes a metal sigma, which may be an alkaline earth metal. In addition, hydroxide 145 is devoid of alkali metal and carbon. Thus, hydroxide 145 can be calcium hydroxide [ Ca (OH) ]₂]. (in this example,. sigma.is Ca). The calcium hydroxide is in granular and solid form and has sufficient porosity to provide sufficient surface area to allow chemical reaction with fluorine gas. The spaces between the calcium hydroxide particles are large enough to allow fluorine gas to flow into the calcium hydroxide, thereby performing a chemical reaction. For example, the calcium hydroxide may be in the form of particles packed in a column, and the packing level depends on the fluorine concentration level in the mixed gas 150 to be analyzed. The mixed gas 150 is passed or flowed through the hydroxide 145 to cause a chemical reaction between the fluorine and the calcium hydroxide.

Fluorine gas (F) is present in the mixed gas 150₂) In the case of (3), if the hydroxide is calcium fluoride Ca (OH)₂Then the following two chemical reactions take place:

2F₂+Ca(OH)₂＝CaF₂+OF₂+H₂O；

OF₂+Ca(OH)₂＝CaF₂+O₂+H₂O。

for the interaction with calcium hydroxide molecules [ Ca (OH)₂]145 every two fluorine (F) interacting₂) Molecule, two inorganic fluoride molecules (calcium fluoride or CaF) are exported₂) One oxygen molecule (O)₂) And two water molecules (H)₂O). The chemical reaction is a linear and stoichiometrically simple reaction. Thus, with regard to fluorine and water only, the chemical reaction is effected with one fluorine molecule F per input₂Chemical reaction to output a water molecule H₂And O. Another way of writing is for each mole of fluorine F fed into the chemical reaction₂One mole of H is output from the chemical reaction₂And O. Thus, if 2 moles of fluorine F are added₂When fed into a chemical reaction, 2 mol of water H are released after the chemical reaction₂And O. The water is detected by the water sensor 115. Thus, for example, because the controller 130 knows (by accessing data stored in memory) that the ratio of fluorine to water in the chemical reaction is 1:1, if the sensor 115 detects 0.6 moles of water, the controller 130 determines that 0.6 moles of fluorine are present in the gas mixture 107. In other implementations, the detection device 105 may assume that the conversion of fluorine is complete (and thus, that there is no residual molecular fluorine F in the gas after the chemical reaction)₂). For example, this assumption may be a valid assumption if a sufficiently long time has elapsed after the chemical reaction has begun.

In this example, if the sensing device 116 further includes an oxygen sensor 117, the measurement of oxygen concentration from the oxygen sensor 117 may be used in conjunction with the measurement of water from the water sensor 115. Thus, if 4 moles of fluorine F are fed in the chemical reaction₂Then 2 moles of oxygen O will be released after the chemical reaction₂. This oxygen is detected by the oxygen sensor 117. As an example, because the controller 130 knows that the ratio of fluorine to oxygen in the chemical reaction is 2:1, if the sensor 117 detects 0.3 moles of oxygen, the controller determines that 0.6 moles of fluorine are present in the gas mixture 107. The controller 130 may use data from both the oxygen sensor 117 and the water sensor 115 to estimate the concentration of fluorine present in the gas mixture 107 (due to the presence of oxygen, water, and fluorine)Weight or mass is known). For example, two sets of data can be used to more accurately determine fluorine. As will be appreciated by those skilled in the art, the controller may also use additional calibrations and corrections (e.g., to account for fluorine, oxygen, or water consumption or inefficient detection).

In some implementations, the reaction between the hydroxide 145 and the fluorine in the mixed gas 150 occurs under one or more specifically designed conditions. For example, the reaction between the hydroxide 145 and the fluorine in the mixed gas 150 may occur in the presence of one or more catalysts, which are substances that change the rate of the chemical reaction but do not change their chemical properties at the end of the chemical reaction. As another example, the reaction between the hydroxide 145 and the fluorine in the mixed gas 150 may occur in a controlled environment, such as a temperature-controlled environment or a humidity-controlled environment.

Referring to fig. 2, the apparatus 100 may be implemented, for example, within an Ultraviolet (UV) or Deep Ultraviolet (DUV) light source 200 that generates a beam 211, which beam 211 is directed to a lithography apparatus 222 for patterning microelectronic features on a wafer. The light source 200 includes a control system 290 connected to various elements of the light source 200 to enable the generation of the light beam 211. Although the control system 290 is shown as a unitary block, it may be made up of multiple subcomponents, any one or more of which may be removed from the other subcomponents or local to the component within the light source 200. Further, the controller 130 may be considered part of the control system 290 or part of the apparatus 100.

In this implementation, the apparatus 100 is configured to calculate the fluorine concentration within one or more gas discharge cells 210 of an excimer gas discharge system 225 that produces a light beam 211 of the light source 200. Although only one gas discharge cell 210 is shown, the excimer gas discharge system 225 can include a plurality of gas discharge cells 210, wherein any one or more of the gas discharge cells 210 are in fluid communication with the detection apparatus 105 of the apparatus 100 and other elements (such as optical elements, metrology devices, and electromechanical elements), such as other elements not shown in fig. 2, for controlling aspects of the light beam 211. Furthermore, only the components of the light source 200 associated with the apparatus 100 are shown in fig. 2. For example, the light source 200 may include a beam preparation system placed at the output of the last gas discharge cell 210 to adjust one or more characteristics of the beam 211 directed to the lithographic device 222.

The gas discharge chamber 210 houses an energy source 230 and contains a gas mixture 207. The energy source 230 provides an energy source for the gas mixture 207; specifically, the energy source 230 provides sufficient energy to the gas mixture 2.07 to cause population inversion to achieve gain via stimulated emission within the chamber 210. In some examples, the energy source 230 is a discharge provided by a pair of electrodes placed within the gas discharge chamber 210. In other examples, the energy source 230 is an optical pumping source.

The gas mixture 207 includes a gain medium comprising a rare gas and a halogen such as fluorine. During operation of the DUV light source 200, fluorine in the gas mixture 207 (which provides a gain medium for light amplification) within the gas discharge chamber 210 is consumed, which over time reduces the amount of light amplification, thereby altering the characteristics of the light beam 211 generated by the light source 200. The lithographic device 222 seeks to maintain the fluorine concentration within the gas mixture 207 in the gas discharge chamber 210 within a certain tolerance range compared to the fluorine concentration set in the initial gas refill procedure. Thus, additional fluorine is added to the gas discharge chamber 210 at a regular rhythm and under the control of the gas maintenance system 120. The fluorine consumption varies from gas discharge cell to gas discharge cell, and therefore closed loop control is used to determine the amount of fluorine to be pushed or injected into the gas discharge cell 210 at each opportunity. The apparatus 100 is used to determine the concentration of fluorine remaining in the gas discharge chamber 210 and thus, in the overall scheme, to determine the amount of fluorine to be pushed or injected into the gas discharge chamber 210.

As described above, the gas mixture 207 includes a gain medium that includes a noble gas and fluorine. The gas mixture 207 may include other gases, such as a buffer gas. The gain medium is a laser active entity within the gas mixture 207 and may consist of a single atom, molecule or pseudo-molecule. Thus, by pumping the gas mixture 207 (and thus the gain medium) with an electrical discharge from the energy source 230, population inversion occurs in the gain medium via stimulated emission. As described above, the gain medium typically includes a rare gas and a halogen, and the buffer gas typically includes an inert gas. The noble gas includes, for example, argon, krypton, or xenon. Halogen includes, for example, fluorine. The inert gas includes, for example, helium or neon. Gases other than fluorine within the gas mixture 207 are inert gases (noble gases or noble gases), and therefore, it is assumed that the only chemical reaction that occurs between the mixed gas 150 and the hydroxide 145 is a reaction between the fluorine of the mixed gas 150 and the hydroxide 145.

Referring again to fig. 1, the gas maintenance system 120 is a gas management system for adjusting a characteristic, such as the relative concentration or pressure of a component within the

gas mixture

107 or 207.

Referring to fig. 3, in some implementations where the sensing device includes an oxygen sensor 117, the oxygen sensor 117 is used in conjunction with a water sensor 115 to determine or estimate the fluorine concentration in the gas mixture 107, the device is device 300 and the detection device 105 is a detection device 305 including a fluorine sensor 360, the fluorine sensor 360 being fluidly connected to the reaction chamber 140 and configured to determine when the fluorine concentration in the new gas mixture 155 falls below a lower limit. The fluorine sensor 360 may be a commercially available fluorine sensor that saturates above a fluorine concentration that is too low to be used to directly measure fluorine in the mixed gas 150. However, the fluorine sensor 360 has a minimum detection threshold and may be used to thereby detect when the fluorine concentration in the new gas mixture 155 is below a lower limit. For example, the fluorine sensor 360 may be saturated at a concentration of 10ppm, but it may have a minimum detection threshold of about 0.05ppm and may begin detecting fluorine in the new gas mixture 155 after the fluorine concentration in the new gas mixture 155 is below 0.1 ppm.

The controller 130 is configured as a controller 330 that receives an output from a fluorine sensor 360. The controller 330 includes a module that interacts with a flow control device 365 in the line that delivers the fresh gas mixture 155 to the oxygen sensor 117. The flow control device 365 may be a device such as a gate valve or other fluid control valve.

Only when the controller 330 determines from the output of the fluorine sensor 360 that the fluorine concentration in the new gas mixture 155 is below a lower limit value (e.g., 0.1ppm) does the controller 330 send a signal to the flow control device 365 to cause the new gas mixture 155 to flow to the oxygen sensor 117. Thus, if the fluorine concentration is below the lower limit, the oxygen sensor 117 is only exposed to the new gas mixture 155, thereby protecting the oxygen sensor 117 from unacceptable levels of fluorine. The lower limit value may be a value determined based on a damage threshold of the oxygen sensor 117. Therefore, when the fluorine concentration is higher than the lower limit value, damage may be caused to the oxygen sensor 117. The lower limit value may be a value determined based on an error threshold of the oxygen sensor 117. Therefore, when the fluorine concentration is higher than the lower limit value, the measurement error affects the accuracy of the oxygen sensor 117.

The detection apparatus 305 further comprises a measurement vessel 370 in fluid connection with the reaction chamber 140 of the reaction vessel 135. The measurement vessel 370 defines a measurement cavity 375, the measurement cavity 375 configured to receive the new gas mixture 155. Further, the water sensor 115 and the oxygen sensor 117 are accommodated within the measurement cavity 375. The measurement vessel 370 is any vessel that contains the new gas mixture 155 to enable the water sensor 115 to sense the water concentration in the new gas mixture 155 and to enable the oxygen sensor 115 to sense the oxygen concentration in the new gas mixture 155. The interior of the measurement vessel 370 defining the measurement cavity 7375 should be made of a non-reactive material so as not to alter the composition of the new gas mixture 155. For example, the interior of the measurement container 370 may be made of a non-reactive metal.

Referring to fig. 4, in some implementations, the apparatus 100 is designed as an apparatus 400 and the detection apparatus 105 is designed as a detection apparatus 405, the detection apparatus 405 including a buffer vessel 470, the buffer vessel 470 separating the flow rate of the exhaust gas from the chamber 110 from the flow rate required by the reaction vessel 135. In this way, buffer vessel 470 is capable of fluorine measurements via detection device 405 without affecting the steady state operation of the gas exchange performed by gas maintenance system 120.

In one example, the fluorine concentration within the chamber 110 is about 1000ppm, the volume of the chamber 110 is 36 liters (L), and the pressure within the chamber 110 is 200 kPa 400 kilopascals (kPa). The interior cavity of the buffer vessel 470 has a volume of about 0.1L and a pressure of 200 and 400 kPa. The measurement chamber 175 has a volume of 0.1L, a pressure of about 200 and 400kPa, a water concentration of 1000ppm and an oxygen concentration of about 500 ppm. After the water sensor 115 takes a measurement of the water concentration (and optionally the oxygen sensor 117 takes a measurement of the oxygen concentration) and outputs the data to the controller 130, the measurement chamber 175 may be evacuated in a controlled manner.

As described above with reference to fig. 1, the apparatus 100 is configured to measure or estimate the fluorine concentration in the gas mixture 107 in the chamber 110. In some implementations, as shown in fig. 5, the apparatus 100 is designed as an apparatus 500 and the detection apparatus 105 is designed as a detection apparatus 505, the detection apparatus 505 being configured to measure or estimate the fluorine concentration in the gas mixture 507_1, 507_2,. In the detection device 505, there are separate or dedicated sensing devices 516_1, 516_2,.., 516_ i associated with the respective chambers 510_1, 510_2,.., 510_ i. In this manner, each sensing device 516_1, 516_2, ·, 516_ i may be used to measure the fluorine concentration in the respective chamber 510_1, 510_2, ·, 510_ i.

The detection device 505 is connected to a gas maintenance system 520, the gas maintenance system 520 comprising a gas supply system in fluid connection with each chamber 510_1, 510_2,.. 510_ i via a respective conduit system 527_1, 527_3,.. 527_ i, which is part of the main conduit system 527. The gas maintenance system 520 includes one or more gas supplies and a control unit for controlling which gases from the supplies are transferred into and out of the respective chambers 510_1, 510_ 2. The detection device 505 comprises a respective reaction vessel 535_1, 535_2,.. 535_ i which receives the mixed gas 550_1, 550_2,... 550_ i (which comprises fluorine) from the respective chamber 510_1, 510_2,... 510_ i via a respective conduit 537_1, 537_2,... 537_ i. The new gas mixture 555_1, 555_2, the.

The detection device 505 further comprises a controller 530, the controller 530 being connected to the gas maintenance system 520 and to each of the sensing devices 516_1, 516_ 2. As with the controller 530, the controller 530 receives the output from the sensing devices 516_1, 516_2,. 516_ i and calculates or estimates how much fluorine is present before the chemical reaction in the reaction vessels 535_1, 535_2,... 535_ i begins to estimate the fluorine content in the respective gas mixtures 507_1, 507_2,. 507_ i.

In other implementations, a single sensing device 516 may be used to measure fluorine in all chambers 510_1, 510_2,.. 510_ i, so long as the detection device 505 includes a suitable piping system between the chambers 510_1, 510_2,.. 510_ i and the detection device 505 to prevent cross-talk between measurements performed by the sensing device 516 on each of the chambers 510_1, 510_2,.. 510__ i. Furthermore, if gas exchange is performed only for one chamber 510 at a time, a single sensing device 516 design may work, so the controller 530 may measure fluorine in a single chamber 510 at any time.

Referring to fig. 6, this figure shows an exemplary DUV light source 600 that incorporates a detection device 605, such as detection device 105, and a controller 630, such as controller 130 of fig. 1, 3, 4, or 5. DUV light source 600 includes an excimer gas discharge system 625, which is a dual-stage pulsed output design. The gas discharge system 625 has two stages: a first stage 601, which is a master controlled oscillator (MO) that outputs a pulse amplified light beam 606, and a second stage 602, which is a Power Amplifier (PA), receives the light beam 606 from the first stage 601. The first stage 601 includes an MO gas discharge cell 610_1 and the second stage 602 includes a PA gas discharge cell 610_2, the MO gas discharge cell 610_1 including two elongated electrodes 630_1 as its energy source. The electrode 630_1 provides a source of energy for the gas mixture 607_1 in the chamber 610_ 1. The PA gas discharge chamber 610_2 includes two elongated electrodes 630_2 as its energy source, which provide the energy source for the gas mixture 607_2 within the chamber 610_ 2.

The MO 601 provides a light beam 606 (which may be referred to as a seed light beam) to the PA 602. The MO gas discharge cell 610_1 contains a gas mixture 607_1, the gas mixture 607_1 comprising a gain medium in which amplification occurs, and the MO 601 further comprises an optical feedback mechanism such as an optical resonator formed between a spectral feature selection system 680 on one side of the MO gas discharge cell 610_1 and an output coupler 681 on a second side of the MO gas discharge cell 610_ 1.

The PA gas discharge cell 610_2 contains a gas mixture 607_2, which gas mixture 607_2 comprises a gain medium 607_2 in which amplification occurs when fed with a seed beam 606 from the MO 601. If the PA602 is designed as a regenerative ring resonator, it will be described as a Power Ring Amplifier (PRA), in which case sufficient optical feedback can be provided from the ring design. The PA602 includes a beam return 682 that returns the beam (e.g., via reflection) into the PA gas discharge cell 610_2 to form a circular and closed-loop path in which the input of the ring amplifier intersects the output of the ring amplifier at the beam coupling 683.

The MO 601 is capable of fine tuning spectral parameters, such as center wavelength and bandwidth, at relatively low output pulse energies (compared to the output of the PA 602). The PA receives the seed beam 606 from the MO 601 and amplifies the output to obtain the power required for the output beam 211 to be used in an output device, such as the lithographic device 222. The seed beam 606 is amplified by repeated passes through the PA602, and the spectral characteristics of the seed beam 606 are determined by the configuration of the MO 601.

The gas mixtures 607_1, 607_2 used in the respective gas discharge cells 610_1, 610_2 may be a combination of suitable gases for producing amplified light beams (such as the seed beam 606 and the output beam 211) around the desired wavelength and bandwidth. For example, the gas mixtures 607_1, 607_2 may include argon fluoride (ArF) that emits light having a wavelength of about 193 nanometers (nm) or krypton fluoride (KrF) that emits light having a wavelength of about 248 nm.

The detection apparatus 605 includes a gas maintenance system 620, the gas maintenance system 620 being a gas management system of an excimer gas discharge system 625, in particular of the gas discharge cells 610_1 and 610_ 2. The gas maintenance system 620 includes one or

more gas sources

651A, 651B, 651C, etc. (such as sealed gas cylinders or canisters) and a valve system 652. One or

more gas sources

651A, 651B, 651C, etc. are connected to the MO gas discharge cell 610_1 and PA gas discharge cell 610_2 through a set of valves within a valve system 652. In this manner, gas can be injected into the respective gas discharge cell 610_1 or 610_2 with a particular relative amount of the components within the gas mixture. Although not shown, the gas maintenance system 620 may also include one or more other components, such as flow restrictors, vent gas valves, pressure sensors, meters, and test ports.

Each of the gas discharge cells 610_1 and 610_2 contains a gas mixture (gas mixtures 607_1, 607_ 2). As an example, the gas mixtures 607_1, 607_2 contain halogens (such as fluorine) and other gases (such as argon, neon) and possibly other gases with different partial pressures, which add up to the total pressure. For example, if the gain medium used in the gas discharge cells 610_1, 610_2 is argon fluoride (ArF), the gas source 651A comprises a gas mixture comprising halogen fluorine, the noble gas argon, and one or more other noble gases, such as a buffer gas (which may be an inert gas, such as neon). This mixture within the gas source 651A may be referred to as a ternary mixture because it contains three gases. In this example, another gas source 651B may contain a gas mixture including argon and one or more other gases, but no fluorine. This mixture in the gas source 651B may be referred to as double mixing because it contains two gases.

The gas maintenance system 620 can include a valve controller 653 configured to send one or more signals to the valve system 652 to cause the valve system 652 to transmit gas from a

particular gas source

651A, 651B, 651C, etc. into the gas discharge chambers 610_1, 610_2 as the gas is refreshed. The gas renewal may be a refilling of the gas mixture 607 within the gas discharge chamber, wherein the existing mixed gas within the gas discharge chamber is replaced by at least a mixture of gain medium and buffer gas and fluorine. The gas renewal may be an injection scheme in which a mixture of gain medium and buffer gas and fluorine is added to the existing mixed gas in the gas discharge chamber.

Alternatively or additionally, the valve controller 653 may send one or more signals to the valve system 652 to cause the valve system 652 to bleed gas from the discharge cells 610_1, 610_2 as necessary, and may discharge such bled gas to a gas dump indicated at 689. In some implementations, it is possible to feed the vented gases to the detection device 605 instead, as shown in fig. 7.

During operation of the DUV light source 600, fluorine from the argon (or krypton) fluoride molecules (which provide a gain medium for light amplification) within the gas discharge cells 610_1, 610_2 is consumed, which over time reduces the amount of light amplification and thus reduces the energy of the beam 211 used by the lithographic device 222 for wafer processing. In addition, during operation of DUV light source 600, contaminants may enter gas discharge cells 610_1, 610_ 2. Therefore, it is necessary to inject gas from one or more of the

gas sources

651A, 651B, 651C, etc. into the gas discharge chambers 610_1, 610_2 in order to flush contaminants out or replenish lost fluorine.

Multiple gas sources

651A, 651B, 651C, etc. are required because the fluorine in the gas source 651A is at a specific partial pressure, which is typically higher than the partial pressure required for laser operation. To add fluorine to the gas cell 610_1 or 610_2 at the desired lower partial pressure, the gas in the gas source 651A can be diluted and a halogen-free gas in the gas source 651B can be used for this purpose.

Although not shown, the valves of the valve system 652 may include a plurality of valves assigned to each of the gas discharge cells 610_1 and 610_ 2. For example, an injection valve that allows gas to enter and exit each gas discharge chamber 610_1, 610_2 at a first flow rate may be used. As another example, a chamber fill valve may be used that allows gas to enter and exit each gas discharge chamber 610_1, 610_2 at a second flow rate that is different (e.g., faster) than the first flow rate.

When a refilling scheme is performed for the gas discharge cell 610_1 or 610_2, all of the gas in the gas discharge cell 610_1 or 610_2 is replaced by, for example, evacuating the gas discharge cell 610_1 or 610_2 (by exhausting the gas mixture to the gas dump 689) and then refilling the gas discharge cell 610_1 or 610_2 with fresh gas mixture. Refilling is performed with a target to obtain a specific pressure and fluorine concentration in the gas discharge chamber 610_1 or 610_ 2. When the injection scheme is performed for the gas discharge cell 610_1 or 610_2, the gas discharge cell is not evacuated or evacuated only a small amount before the gas mixture is injected into the gas discharge cell. In both gas regenerations, the sensing device 605 (which is similar in design to the sensing device 105) may receive some of the exhaust gas mixture as the mixed gas 150 for analysis within the sensing device 605 to determine the concentration of fluorine within the gas discharge chamber 610_1 or 610_2 to determine how to perform the gas regeneration.

The valve controller 653 interfaces with the detection device 605 (and specifically with the controller 130 in the detection device 605). In addition, the valve controller 653 may interface with other control modules and subcomponents that are part of the control system 690, which will be discussed below.

Referring to fig. 7, a control system 790 (which may be control system 290 or 690) is shown in a block diagram as part of a DUV light source, such as

light source

200 or 600. Details regarding the control system 790 are provided that relate to aspects of the detection device 105/605 and methods related to gas control and fluorine concentration estimation as described herein. In addition, the control system 790 may include other features not shown in fig. 7. Typically, the control system 790 includes one or more of digital electronic circuitry, computer hardware, firmware, and software.

The control system 790 includes a memory 700, which may be a read-only memory and/or a random access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and a CD-ROM disk. The control system 790 may also include one or more input devices 705 (such as a keyboard, touch screen, microphone, mouse, handheld input device, etc.) and one or more output devices 710 (such as a speaker or monitor).

The control system 790 includes one or more programmable processors 715, and one or more computer program products 720, the computer program products 720 being tangibly embodied in a machine-readable storage device for execution by the programmable processors (such as the processors 715). The one or more programmable processors 715 can each execute a program of instructions to perform a desired function by operating on input data and generating appropriate output. Generally, processor 715 receives instructions and data from memory 700. Any of the above may be supplemented by, or incorporated in, specially-designed ASICs (application-specific integrated circuits).

The control system 790 may include, among other components or modules, the

controllers

130, 330, 530 (represented in fig. 7 as block 730) of the detection device 105 and a gas maintenance module 731 that interfaces with a valve controller 653 of the gas maintenance system 620. Each of these modules may be a set of computer program products that are executed by one or more processors, such as processor 715. Further, either of the controllers/

modules

730, 731 can access data stored in the memory 700.

The connections between the controllers/features/modules within control system 790 and other components of apparatus 100 (which may be DUV light source 600) may be wired or wireless.

Although only a few modules are shown in fig. 7, the control system 790 may include other modules. Further, while the control system 790 is shown as a box, where all of the components appear to be co-located, the control system 790 may be comprised of components that are physically remote from each other, either spatially or temporally. For example, the controller 730 may be physically co-located with the sensing device 116 or the gas maintenance system 120. As another example, gas maintenance module 731 may be physically co-located with valve controller 653 of gas maintenance system 620 and may be separate from other components of control system 790.

In addition, the control system 790 may include a lithography/module 732 that receives instructions from a lithography controller of the lithography apparatus 222, for example, instructions to measure or estimate the fluorine concentration within the gas mixture 107 of the chamber 110.

Referring to fig. 8, in some implementations, the apparatus 100 is designed as an apparatus 800 and the detection apparatus 105 is designed as a detection apparatus 805 that operates in parallel with a fluorine scrubber 804 in fluid communication with a gas maintenance system 820. The fluorine scrubber 804 is used in conjunction with a gas maintenance system 820 to properly exhaust the gas mixture 807 from the chamber 110 by chemically reacting fluorine within the gas mixture 807 to form chemicals that may be safely disposed of (e.g., via the exhaust gas).

A portion of the mixed gas 150 exiting the gas maintenance system 820 is directed to a surge vessel 870 and then to another fluorine scrubber 835 comprising hydroxide 845. The fluorine in the mixed gas 150 chemically reacts with the hydroxide 845 in the fluorine scrubber 835 (in the manner described above) and is converted to a new gas mixture 155 comprising oxygen. The new gas mixture 155 is directed to the sensing device 116 where it is sensed. The controller 130 estimates the oxygen concentration and the fluorine concentration within the mixed gas 150 and the gas mixture 107 and determines how to adjust the gas maintenance system 820 to perform the gas update. In this example, the gas maintenance system 820 includes a valve system 852, the valve system 852 fluidly connected to a ternary mixing source 851A and a binary mixing source 851B. Various control valves 891 are placed along the line to control the flow rate and control the amount of gas directed through the line.

Referring to fig. 9, a routine 900 is performed by the apparatus 100 for detecting a fluorine concentration in the gas mixture 107 of the chamber 110. The apparatus of fig. 1 is referenced, but the process 900 is also applicable to the apparatus described with reference to fig. 2-8. The detection device 105 receives a portion of the mixed gas 150 containing fluorine from the gas discharge chamber 110 (905). The fluorine in the mixed gas 150 chemically reacts with the hydroxide 145 to form a new gas mixture 155, which includes water (910). For example, the water concentration in the new gas mixture 155 is sensed with the water sensor 115 (915). And, the fluorine concentration in the mixed gas 150 is estimated based on the sensed water concentration (920). For example, the controller 130 may estimate the fluorine concentration in the mixed gas 150 based on the output from the water sensor 115.

Detection device 105 may receive mixed gas 150(905) by exhausting gas mixture 107 (released under pressure) from chamber 110. For example, the gas maintenance system 120 may include a set of valves that enable the gas mixture 107 to be exhausted from the chamber 110 and then directed to the detection device 105 as the mixed gas 150. The pressure in the chamber 110 may be used to pressurize the reaction vessel 135 or the buffer vessel 470, for example, by using a series of valves and vacuum pumps to create a negative pressure, push the gas mixture 107 out of the chamber 110 and to the detection device 105. The amount of mixed gas 150 required in the reaction vessel 135 may be determined based on the need for the water sensor 115 to obtain accurate and stable readings. One limiting factor in the amount of mixed gas 150 is the fluorine conversion capability of the hydroxide 145 in the reaction chamber 7140. For example, it is desirable to obtain accurate readings from the water sensor 115, but it is also desirable to minimize the total gas flow so that the hydroxide 145 can have the longest useful life.

The mixed gas 150 received 905 by the detection device 105 may be the mixed gas 150 exhausted from the chamber 110 to the fluorine scrubber, and thus the mixed gas 150 may be considered an exhaust gas. This implementation is illustrated in fig. 8, where fluorine in the mixed gas 150 chemically reacts with hydroxide 845 in the fluorine scrubber 835 and is converted to a new gas mixture 155 comprising oxygen.

The routine 900 may be performed in anticipation of a gas update, such as a gas refill or gas injection. For example, the first gas update may be performed by adding a first gas mixture from the gas maintenance system 120 to the chamber 110, and the routine 900 may be performed after a period of use of the chamber 110. After performing routine 900, a second gas refresh may be performed by adding the adjusted second gas mixture from the gas maintenance system 120 to the chamber 110. The adjusted second gas mixture has a fluorine concentration (or amount of fluorine) that may be based on the measurements made by the routine 900.

Fluorine can chemically react with hydroxide 145 by forming inorganic fluoride plus water and oxygen (910). The inorganic fluoride (present in the new gas mixture 155) does not interact with the water sensor 115.

After the fluorine chemically reacts with the hydroxide 145 to form a new gas mixture 155(910), the new gas mixture 155 may be transferred from the reaction vessel 135 to the measurement vessel 170 to enable the water concentration within the new gas mixture 155 to be sensed (915). The concentration of water in the new gas mixture 155 may thus be sensed by exposing the sensor 115 within the measurement vessel 170 to the new gas mixture 155 (915). The water concentration in the new gas mixture 155 is sensed 915 without having to dilute the mixed gas 150 with another material.

Further, waiting to sense the water concentration (915) in the new gas mixture 155 is not appropriate until or only after a predetermined period of time has elapsed after the chemical reaction (910) has begun. This will ensure that sufficient fluorine in the mixed gas 150 has been converted to water and inorganic fluoride before exposing the water sensor 115 to the new gas mixture 155. This may take several seconds or minutes depending on the relative amount of fluorine in the mixed gas 150 and the total volume of hydroxide 145 that completely converts the fluorine to water.

In some implementations, the chemical reaction (910) can be performed by flowing the mixed gas 150 through the hydroxide 145 at a low rate (e.g., about 0.1slpm or less) or at a specific flow rate to form a new gas mixture 155. In this case, water may be sensed (915) in a continuous manner. The concentration of fluorine may be estimated (920) from an integration of the sensed water measurement (915) over a period of time or when the sensed water measurement (915) reaches a steady state.

The fluorine in the new gas mixture 155 is estimated based on the sensed water concentration (915) and also based on knowledge of the chemical reaction that converts the fluorine in the mixed gas 150 to water (920).

After the process 900 is complete (i.e., after the fluorine concentration within the mixed gas 150 has been estimated at 920), the new gas mixture 155 is then exhausted (removed) from the measurement vessel 170 to allow the process 900 to be performed on a new batch of mixed gas 150.

Referring to fig. 10, once the fluorine concentration is estimated (920) and upon completion of the procedure 900, the procedure 1000 is performed by the apparatus 100. The gas maintenance system 120 receives an output from the controller 130 of the detection device 105 and adjusts the relative concentration of fluorine in the gas mixture of a set of gas supplies, such as

gas sources

651A, 651B, 651C, etc., based on the estimated concentration of fluorine (1005). Gas maintenance system 120 performs gas rejuvenation by adding the adjusted gas mixture to chamber 110 via conduit system 127(1010) until the pressure within chamber 110 reaches a desired level. Gas renewal may be accomplished and tracked by monitoring the timing of valves within the gas maintenance system 120.

For example, referring to fig. 2, the gas refresh (1010) may include filling the gas discharge cell 210 with a mixture of a gain medium and a buffer gas and fluorine, wherein the gain medium includes a rare gas and fluorine and the buffer gas includes an inert gas. The execution of the gas update (1010) may be delayed relative to the time the fluorine concentration estimation (900) is performed. In some implementations, if the controller 130 determines that the fluorine concentration in the gas mixture 107 has dropped below an acceptable level, the adjusting (1005) and gas updating (1010) may be performed immediately after the estimating (900). In some implementations, the adjustment of the fluorine (1005) may be delayed until it is determined that the fluorine concentration in the gas mixture 107 has dropped below an acceptable level. For example, if the controller 130 determines that the fluorine concentration in the gas mixture 107 is still high, but the apparatus 100 must perform a gas refresh for other reasons, the gas refresh may be performed without targeting an increase in the fluorine level in the gas mixture 107.

Referring to fig. 11, in some implementations, the detection device 305 performs a procedure 1100 instead of the procedure 900 to estimate the fluorine concentration in the mixed gas 150. The process 1100 is similar to the process 900 and includes the steps of receiving 905 a portion of the mixed gas 150 including fluorine from the gas discharge chamber 110; and chemically reacting the fluorine in the mixed gas 150 with the hydroxide 145 to form a new gas mixture 155(910) comprising water and oxygen. Routine 1100 determines whether the fluorine concentration in the new gas mixture 155 has dropped below a lower limit (1112). For example, a fluorine sensor 360 fluidly connected to the reaction chamber 140 may make this determination (1112), and only when the fluorine concentration in the new gas mixture 155 falls below the lower limit value (1112), the controller 330 may proceed to instruct the sensing arrangement 116 to sense the water concentration (via sensor 115) and the oxygen concentration (via sensor 117) in the new gas mixture 155 (915). As previously described, the fluorine concentration in the mixed gas 150 is estimated based on the sensed oxygen concentration (920).

In some implementations, the lower limit value is a value determined based on a damage threshold of the sensor 115. In other implementations, the lower limit value is a value determined based on an error threshold of the sensor 115. For example, the lower limit may be 0.1 ppm.

Other aspects of the invention are set forth in the following numbered clauses.

1. A method, comprising:

receiving at least a portion of a mixed gas from a gas discharge chamber, wherein the mixed gas comprises fluorine;

reacting the fluorine in the portion of the mixed gas with a hydroxide to form a new gas mixture comprising oxygen and water;

sensing a water concentration within the new gas mixture; and

estimating a fluorine concentration within a portion of the mixed gas based on the sensed water concentration.

2. The method of clause 1, wherein the hydroxide comprises an alkaline earth metal hydroxide.

3. The method of clause 1, wherein the hydroxide is free of alkali metal and carbon.

4. The method of clause 1, wherein the mixed gas is an excimer laser gas comprising at least a mixture of a gain medium and a buffer gas.

5. The method of clause 1, further comprising:

adjusting the relative concentration of fluorine in a gas mixture from a set of gas supplies based on the estimated concentration of fluorine in the portion of the mixed gas; and

performing gas renewal by adding the adjusted gas mixture from the gas supply source to the gas discharge chamber.

6. The method of clause 5, wherein performing the gas renewal comprises filling the gas discharge chamber with a mixture of gain medium and buffer gas and fluorine.

7. The method of clause 6, wherein filling the gas discharge cell with the mixture of the gain medium and the buffer gas comprises filling the gas discharge cell with a gain medium comprising a rare gas and a halogen and a buffer gas comprising an inert gas.

8. The method of clause 7, wherein the noble gas comprises argon, krypton, or xenon; the halogen comprises fluorine; and the inert gas comprises helium or neon.

9. The method of clause 6, wherein filling the gas discharge chamber with the mixture of the gain medium and the buffer gas and fluorine comprises:

adding the mixture of the gain medium and the buffer gas and fluorine to an existing mixed gas in the gas discharge chamber; or

Replacing an existing mixed gas in the gas discharge chamber with at least the mixture of the gain medium and the buffer gas and fluorine.

10. The method of clause 5, wherein performing the gas renewal comprises performing one or more of a gas refill protocol or a gas injection protocol.

11. The method of clause 1, wherein receiving at least a portion of the mixed gas from the gas discharge chamber comprises: receiving a portion of the mixed gas prior to performing a gas refresh on the gas discharge chamber, wherein the gas refresh comprises adding a gas mixture from a set of gas supplies to the gas discharge chamber, wherein the gas mixture includes at least some fluorine.

12. The method of clause 11, wherein performing the gas renewal comprises performing one or more of a gas refill protocol or a gas injection protocol.

13. The method of clause 1, wherein receiving at least a portion of the mixed gas from the gas discharge chamber comprises: discharging the mixed gas from the gas discharge chamber and guiding the discharged mixed gas to a reaction vessel containing the hydroxide.

14. The method of clause 13, further comprising transferring the new gas mixture from the reaction vessel to a measurement vessel, wherein sensing the water concentration within the new gas mixture comprises: sensing the water concentration in the new gas mixture in the measurement vessel.

15. The method of clause 13, wherein sensing the water concentration within the new gas mixture comprises exposing a sensor within the measurement container to the new gas mixture.

16. The method of clause 1, further comprising venting the new gas mixture from the measurement vessel after the fluorine concentration within the portion of the mixed gas has been estimated.

17. The method of clause 1, wherein sensing the water concentration within the new gas mixture comprises: sensing the water concentration within the new gas mixture without diluting a portion of the mixed gas with another material.

18. The method of clause 1, wherein reacting a portion of the mixed gas with the hydroxide to form the new gas mixture comprising water comprises: inorganic fluoride and water are formed.

19. The method of clause 18, wherein the hydroxide comprises calcium hydroxide and the inorganic fluoride comprises calcium fluoride.

20. The method of clause 1, wherein sensing the water concentration within the new gas mixture comprises sensing the water concentration within the new gas mixture only after a predetermined period of time has elapsed after the reaction started.

21. The method of clause 1, wherein the portion of the mixed gas is an effluent gas and reacting the portion of the mixed gas with the hydroxide to form the new gas mixture comprising water comprises removing fluorine from the effluent gas.

22. The method of clause 1, wherein estimating the fluorine concentration within the portion of the mixed gas based on the sensed water concentration comprises: estimating based only on the sensed water concentration and a chemical reaction between fluorine and the hydroxide in the portion of the mixed gas.

23. The method of clause 1, wherein the fluorine concentration in the portion of the mixed gas is about 500-2000 ppm.

24. The method of clause 1, wherein the reaction of the fluorine in the portion of the mixed gas to form the new gas mixture comprising water with the hydroxide is stable.

25. The method of clause 1, wherein reacting the fluorine in the portion of the mixed gas with the hydroxide to form the new gas mixture comprising water comprises performing a linear reaction and providing a direct correlation between the fluorine concentration in the portion of the mixed gas and the water concentration in the new gas mixture.

26. The method of clause 1, further comprising sensing an oxygen concentration within the new gas mixture, wherein estimating the fluorine concentration within the portion of the mixed gas is also based on the sensed oxygen concentration.

27. A method, comprising:

performing a first gas refresh by adding a first gas mixture from a set of gas supplies to the gas discharge chamber;

removing at least a portion of the mixed gas from the gas discharge chamber after the first gas is refreshed, wherein the mixed gas comprises fluorine;

reacting the removed portion of the fluorine of the mixed gas with a reactant to form a new gas mixture comprising oxygen and water;

sensing a water concentration within the new gas mixture;

estimating a fluorine concentration within the removed portion of the mixed gas based on the sensed water concentration;

adjusting a relative concentration of fluorine in a second gas mixture from the set of gas supplies based on the estimated concentration of fluorine in the removed portion of the mixed gas; and

performing a second gas refresh by adding the adjusted second gas mixture from the gas supply to the gas discharge chamber.

28. The method of clause 27, wherein the reactant comprises a hydroxide.

29. The method of clause 27, wherein the mixed gas in the gas discharge chamber comprises an excimer laser gas comprising at least a mixture of a gain medium and a buffer gas.

30. The method of clause 27, wherein estimating the fluorine concentration within the removed portion of the mixed gas based on the sensed concentration of water comprises estimating the fluorine concentration within the removed portion of the mixed gas without measuring the fluorine concentration within the removed portion of the mixed gas.

31. An apparatus, comprising:

a detection device in fluid connection with each gas discharge cell of an excimer gas discharge system, wherein each detection device comprises:

a vessel defining a reaction chamber containing a hydroxide and fluidly connected to the gas discharge chamber for receiving a mixed gas comprising fluorine from the gas discharge chamber in the reaction chamber, the vessel causing a reaction between the fluorine and the hydroxide of the received mixed gas to form a new gas mixture comprising oxygen and water; and

a water sensor configured to be in fluid connection with the new gas mixture and to sense an amount of water within the new gas mixture when in fluid connection with the new gas mixture; and

a control system connected to the detection device, the control system configured to: receiving the output from the water sensor and estimating a fluorine concentration in the mixed gas received from the gas discharge chamber;

determining whether a fluorine concentration in a gas mixture from a gas supply system of a gas maintenance system should be adjusted based on the estimated fluorine concentration in the mixed gas; and

sending a signal to the gas maintenance system instructing the gas maintenance system to adjust the relative concentration of fluorine in a gas mixture supplied to the gas discharge chamber from the gas supply system of the gas maintenance system during gas renewal performed to the gas discharge chamber.

32. The apparatus of clause 31, wherein each gas discharge cell of the excimer gas discharge system contains an energy source and contains a gas mixture comprising an excimer laser gas comprising a gain medium and fluorine.

33. The apparatus of clause 31, wherein:

the detection apparatus further comprises a measurement vessel fluidly connected to the reaction chamber of the reaction vessel and defining a measurement chamber configured to receive the new gas mixture; and

the water sensor is configured to sense an amount of water within the new gas mixture in the measurement cavity.

34. The apparatus of clause 31, wherein the fluorine concentration in the portion of the mixed gas removed is about 500-2000 ppm.

35. The apparatus of clause 31, wherein the excimer gas discharge system comprises a plurality of gas discharge chambers and the detection apparatus is fluidly connected to each of the plurality of gas discharge chambers, wherein the detection apparatus comprises a plurality of containers, each container defining a reaction chamber containing the hydroxide, and each container being fluidly connected to one of the gas discharge chambers, and the detection apparatus comprises a plurality of water sensors, each water sensor being associated with one container.

36. The apparatus of clause 31, wherein the excimer gas discharge system comprises a plurality of gas discharge chambers and the detection apparatus is fluidly connected to each of the plurality of gas discharge chambers, wherein the detection apparatus comprises a plurality of containers, each container defining a reaction chamber containing the hydroxide, and each container being fluidly connected to one of the gas discharge chambers, and the detection apparatus comprises a single water sensor associated with all of the containers.

Other implementations are within the scope of the following claims.

Claims

1. A method, comprising:

sensing a water concentration within the new gas mixture; and

2. The method of claim 1, wherein the hydroxide comprises an alkaline earth metal hydroxide.

3. The method of claim 1, wherein the hydroxide is free of alkali metal and carbon.

4. The method of claim 1, wherein the mixed gas is an excimer laser gas comprising at least a mixture of a gain medium and a buffer gas.

5. The method of claim 1, further comprising:

adjusting a relative concentration of fluorine in a gas mixture from a set of gas supplies based on the estimated fluorine concentration in a portion of the mixed gas; and

6. The method of claim 5, wherein performing the gas update comprises: the gas discharge chamber is filled with a mixture of gain medium and buffer gas and fluorine.

7. The method of claim 6, wherein filling the gas discharge cell with the mixture of the gain medium and the buffer gas comprises: the gas discharge chamber is filled with a gain medium containing a rare gas and a halogen, and a buffer gas containing an inert gas.

8. The method of claim 7, wherein the noble gas comprises argon, krypton, or xenon; the halogen comprises fluorine; and the inert gas comprises helium or neon.

9. The method of claim 6, wherein filling the gas discharge chamber with the mixture of the gain medium and the buffer gas and fluorine comprises:

10. The method of claim 5, wherein performing the gas update comprises performing one or more of: a gas refill scheme or a gas injection scheme.

11. The method of claim 1, wherein receiving at least a portion of the mixed gas from the gas discharge chamber comprises: receiving a portion of the mixed gas prior to performing a gas refresh on the gas discharge chamber, wherein the gas refresh comprises: adding a gas mixture from a set of gas supplies to the gas discharge chamber, wherein the gas mixture comprises at least some fluorine.

12. The method of claim 11, wherein performing the gas update comprises: performing one or more of the following: a gas refill scheme or a gas injection scheme.

13. The method of claim 1, wherein receiving at least the portion of the mixed gas from the gas discharge chamber comprises: discharging the mixed gas from the gas discharge chamber and guiding the discharged mixed gas to a reaction vessel containing the hydroxide.

14. The method of claim 13, further comprising transferring the new gas mixture from the reaction vessel to a measurement vessel, wherein sensing the water concentration within the new gas mixture comprises: sensing the water concentration within the new gas mixture within the measurement vessel.

15. The method of claim 13, wherein sensing the water concentration within the new gas mixture comprises: exposing a sensor within the measurement vessel to the new gas mixture.

16. The method of claim 1, further comprising venting the new gas mixture from the measurement vessel after the fluorine concentration within the portion of the mixed gas is estimated.

17. The method of claim 1, wherein sensing the water concentration within the new gas mixture comprises: sensing the water concentration within the new gas mixture without diluting a portion of the mixed gas with another material.

18. The method of claim 1, wherein reacting a portion of the mixed gas with the hydroxide to form the new gas mixture comprising water comprises: inorganic fluoride and water are formed.

19. The method of claim 18, wherein the hydroxide comprises calcium hydroxide and the inorganic fluoride comprises calcium fluoride.

20. The method of claim 1, wherein sensing the water concentration within the new gas mixture comprises: sensing the water concentration in the new gas mixture only after a predetermined period of time has elapsed after the reaction has begun.

21. The method of claim 1, wherein the portion of the mixed gas is an exhaust gas and reacting the portion of the mixed gas with the hydroxide to form the new gas mixture comprising water comprises: removing fluorine from the exhaust gas.

22. The method of claim 1, wherein estimating the fluorine concentration within a portion of the mixed gas based on the sensed water concentration comprises: estimating based only on the sensed water concentration and a chemical reaction between fluorine and the hydroxide in the portion of the mixed gas.

23. The method as claimed in claim 1, wherein the fluorine concentration in the portion of the mixed gas is about 500-2000 ppm.

24. The method of claim 1, wherein the reaction of the fluorine in the portion of the mixed gas to form the new gas mixture comprising water with the hydroxide is stable.

25. The method of claim 1, wherein reacting the fluorine in the portion of the mixed gas with the hydroxide to form the new gas mixture comprising water comprises: performing a reaction that is linear and provides a direct correlation between the fluorine concentration in the portion of the mixed gas and the water concentration in the new gas mixture.

26. The method of claim 1, further comprising sensing an oxygen concentration within the new gas mixture, wherein estimating the fluorine concentration within the portion of the mixed gas is also based on the sensed oxygen concentration.

27. A method, comprising:

removing at least a portion of a mixed gas from the gas discharge chamber after the first gas is refreshed, wherein the mixed gas comprises fluorine;

sensing a water concentration within the new gas mixture;

performing a second gas refresh by adding the adjusted second gas mixture from the gas supply source to the gas discharge chamber.

28. The method of claim 27, wherein the reactant comprises a hydroxide.

29. The method of claim 27, wherein the mixed gas in the gas discharge chamber comprises an excimer laser gas comprising at least a mixture of a gain medium and a buffer gas.

30. The method of claim 27, wherein estimating the fluorine concentration within the removed portion of the mixed gas based on the sensed water concentration comprises: estimating the fluorine concentration within the removed portion of the mixed gas without measuring the fluorine concentration within the removed portion of the mixed gas.

31. An apparatus, comprising:

a detection device in fluid connection with each gas discharge cell of the excimer gas discharge system, wherein each detection device comprises:

a vessel defining a reaction chamber containing a hydroxide and fluidly connected to the gas discharge chamber for receiving a mixed gas comprising fluorine from the gas discharge chamber in the reaction chamber, the vessel causing a reaction between the fluorine of the received mixed gas and the hydroxide to form a new gas mixture comprising oxygen and water; and

a control system coupled to the detection device, the control system configured to:

receiving an output from the water sensor and estimating a fluorine concentration in the mixed gas received from the gas discharge chamber;

sending a signal to the gas maintenance system during a gas refresh performed on the gas discharge cell, the signal instructing the gas maintenance system to adjust a relative concentration of fluorine in a gas mixture supplied to the gas discharge cell from the gas supply system of the gas maintenance system.

32. The apparatus of claim 31, wherein each gas discharge cell of the excimer gas discharge system houses an energy source and contains a gas mixture comprising an excimer laser gas comprising a gain medium and fluorine.

33. The apparatus of claim 31, wherein:

34. The apparatus as claimed in claim 31, wherein the fluorine concentration in the removed portion of the mixed gas is about 500-2000 ppm.

35. The apparatus of claim 31, wherein the excimer gas discharge system comprises a plurality of gas discharge chambers and the detection apparatus is in fluid connection with each of the plurality of gas discharge chambers, wherein the detection apparatus comprises a plurality of containers, each container defining a reaction chamber containing the hydroxide and each container being in fluid connection with one of the gas discharge chambers, and the detection apparatus comprises a plurality of water sensors, each water sensor being associated with one container.

36. The apparatus of claim 31, wherein the excimer gas discharge system comprises a plurality of gas discharge chambers and the detection apparatus is in fluid connection with each of the plurality of gas discharge chambers, wherein the detection apparatus comprises a plurality of containers, each container defining a reaction chamber containing the hydroxide and each container being in fluid connection with one of the gas discharge chambers, and the detection apparatus comprises a single water sensor associated with all of the containers.