CN116057795A

CN116057795A - Apparatus and method for fluorine measurement

Info

Publication number: CN116057795A
Application number: CN202180062081.6A
Authority: CN
Inventors: J·M·西莫内利; 陈思宇
Original assignee: Cymer LLC
Current assignee: Cymer LLC
Priority date: 2020-09-10
Filing date: 2021-08-11
Publication date: 2023-05-02
Also published as: TW202212785A; WO2022055654A1; JP2023541105A; KR20230045093A

Abstract

An apparatus and method for determining fluorine concentration in a mixed gas comprising: a detector that provides a measurement of fluorine concentration based on the amount of oxygen generated in the reaction involving fluorine, and wherein the amount of fluorine so measured is adjusted according to other factors. Other factors include the amount of oxygen remaining from the immediately previous measurement and the amount of time that has elapsed since the immediately previous measurement.

Description

Apparatus and method for fluorine measurement

Cross Reference to Related Applications

The present application claims priority from U.S. application Ser. No. 63/076,681, entitled "APPARATUS FOR AND METHOD OF FLUORINE MEASUREMENT," filed on even 10, 9/2020, the entire contents of which are incorporated herein by reference.

Technical Field

The disclosed subject matter relates to making indirect measurements of fluorine concentration in a gas mixture comprising fluorine.

Background

There are many applications where it is desirable to measure the concentration of fluorine in a mixed gas. As an example, a lithographic apparatus applies a desired pattern onto a substrate, such as a wafer of semiconductor material, typically onto a target portion of the substrate. A patterning device (alternatively referred to as a mask or reticle) may be used to generate circuit patterns formed on individual layers of the wafer. Transfer of the pattern is typically accomplished by imaging onto a layer of radiation-sensitive material (photoresist, or simply "resist") provided on the substrate. Typically, a single substrate will contain adjacent target portions that are continuously patterned.

The light source used to illuminate and project the pattern onto the substrate may be any of a variety of configurations. One configuration is an excimer laser. The name excimer laser derives from the fact that under appropriate electrical stimulation (energy providing) and high pressure (gas mixture) conditions, pseudo molecules called excimer molecules are generated, which exist only in an excited state and create amplified light in the ultraviolet range.

Excimer light sources typically use a combination of one or more noble gases (such as argon, krypton, or xenon) and an active species (such as fluorine or chlorine). Deep ultraviolet excimer lasers commonly used in lithography systems include krypton fluoride (krF) lasers with a wavelength of 248nm and argon fluoride (ArF) lasers with a wavelength of 193 nm. These gases are supplied to the laser discharge chamber. Fluorine is depleted during the laser discharge and must be replenished. The gas in the discharge chamber must be sampled from time to time and its F2 concentration measured to determine if replenishment is required.

One method of measuring the concentration of F2 includes reacting a sample gas including F2 with a metal oxide (such as activated alumina) in a scrubber, and then measuring the concentration of the reaction product O2 using a sensor to infer the concentration of F2 in the original sample gas. If the sensor has been idle for too long, the method may produce an indirect measurement of F2 concentration that is lower than the actual concentration of F2 unless countermeasures are taken. One countermeasure to prevent this measurement deficiency is to increase the size of the scrubber. However, this creates the problem that the O2 reading cannot converge or predictably develop to a final steady state value within the sampling time allowed for the scrubber volume.

The apparatus and methods disclosed herein appear in this context.

Disclosure of Invention

The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of such embodiments. This summary is not an extensive overview of all contemplated embodiments, and is intended to neither identify key or critical elements of all embodiments nor delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

According to one aspect of an embodiment, disclosed herein is a method of estimating an amount of F2 by: the amount of O2 generated by the F2 reaction in the reaction chamber that generates O2 (such as a scrubber) is measured and the amount of O2 generated is used to infer the actual F2 concentration in the gas sample. According to one aspect of the embodiment, an inert gas, such as nitrogen, is used to push residual O2 in the reaction chamber to the O2 sensor, where a residual O2 reading is taken. The gas to be sampled is then filled into the reaction chamber. In an example of a system used in conjunction with semiconductor lithography, the gas to be sampled may be a gas sample in one of the laser chambers, such as the master oscillator chamber. After the second F2 reaction is sufficiently completed, an inert gas is used to push the O2 in the reaction chamber to the O2 sensor, where another final O2 measurement is made to obtain a final indirect measurement of the F2 concentration. The final measurement is adjusted, for example, based in part on the residual O2 reading, to obtain a final and more accurate estimate of F2 concentration.

According to another aspect of the embodiment, the compensation method uses the total O2 measurement from the above sequence to obtain the F2 concentration in the gas sampled in the sensor. Specifically, the compensated fluorine concentration f ₂ (n) determining according to the following relationship：

Wherein k is ₃ 、k ₄ And k ₅ Is a constant coefficient determined from a curve fit of the test data,

O ₂ (n) is a measure of residual O2,

F ₂ (n) is the F2 concentration inferred from the second O2 measurement,

p (n) is the total pressure of the F2-containing gas filling the sensor from the chamber while F2 (n) is measured,

Δtidle is the amount of time in seconds since the last previous measurement, and Δtpush is the amount of time in seconds that uses N2 to push the residual O2 out of the reaction chamber.

According to one aspect of the embodiments, an apparatus is disclosed, the apparatus comprising: a vessel defining a reaction chamber adapted for placement in selective fluid communication with a mixed gas source comprising fluorine to be sampled, the vessel comprising a metal oxide arranged to react with fluorine in the mixed gas to form a product gas comprising oxygen, the vessel further adapted for placement in selective fluid communication with an inert gas source; and an oxygen sensor configured to be placed in selective fluid communication with the vessel to receive the product gas and to sense an amount of oxygen in the product gas. The container may also be adapted for placement in selective fluid communication with a vacuum source. The metal oxide may include aluminum oxide. The mixed gas source to be sampled, which includes fluorine, may include a laser discharge chamber. The inert gas source may include a nitrogen source.

According to another aspect of the embodiments, an apparatus is disclosed, the apparatus comprising: a laser discharge chamber; a vessel defining a reaction chamber adapted to be placed in selective fluid communication with the laser discharge chamber to receive a sample of a mixed gas comprising fluorine to be sampled, the vessel comprising a metal oxide arranged to react with fluorine in the mixed gas to form a product gas comprising oxygen; an inert gas source in selective fluid communication with the vessel; and an oxygen sensor configured to be placed in selective fluid communication with the vessel to receive the product gas and to sense an amount of oxygen within the product gas. The container may also be adapted for placement in selective fluid communication with a vacuum source. The metal oxide may include aluminum oxide. The mixed gas source to be sampled, which includes fluorine, may include a laser discharge chamber. The inert gas source may include a nitrogen source.

According to another aspect of the embodiment, the apparatus may further include: a gas maintenance system comprising a gas supply system in fluid connection with the laser discharge chamber; a control system coupled to the gas maintenance system and the detection device and configured to: receiving an output of the oxygen sensor and estimating a concentration of fluorine in the mixed gas received from the gas discharge chamber; determining whether the concentration of fluorine in the gas mixture from the gas supply system of the gas maintenance system should be changed based on the estimated concentration of fluorine in the mixed gas; and sending a signal to the gas maintenance system to change the relative concentration of fluorine in the gas mixture supplied to the laser discharge chamber from the gas supply system of the gas maintenance system during a gas renewal of the laser discharge chamber.

According to another aspect of the embodiments, a method is disclosed, the method comprising: pushing residual gas in the reaction chamber to the sensor using a first portion of the inert gas; sensing a first oxygen concentration within the residual gas using a sensor; supplying at least a portion of a mixed gas from the laser discharge chamber to the reaction chamber, wherein the mixed gas comprises fluorine; reacting fluorine in the mixed gas portion with the metal oxide in the reaction chamber to form a product gas comprising oxygen; pushing the product gas in the reaction chamber to the sensor using a second portion of the inert gas; sensing a second oxygen concentration within the product gas; inferring an estimated fluorine concentration in the portion of the mixed gas from the laser discharge chamber based on the sensed second oxygen concentration; and determining a compensated fluorine concentration in the portion of the mixed gas from the laser discharge chamber based at least in part on the first oxygen concentration and the estimated fluorine concentration. The method may further comprise: the reaction chamber is evacuated between sensing a first oxygen concentration in the residual gas using the sensor and supplying at least a portion of a mixed gas from the laser discharge chamber to the reaction chamber, wherein the mixed gas comprises fluorine. The method may further comprise: determining an amount Δtidle, the amount Δtidle indicating an amount of time that has elapsed from an immediate previous determination of the fluorine concentration to a current measurement start, and determining an amount Δtpush, the amount Δtpush indicating an amount of time that a first portion of the inert gas has been pushing the generated gas mixture to the sensor, and determining the compensated fluorine concentration in the portion of the mixed gas from the laser discharge chamber may also be based at least in part on Δtidle and Δtpush. The residual gas may be from an immediate previous measurement. The metal oxide may include aluminum oxide. The inert gas may include nitrogen. The method may further comprise: based on the estimated fluorine concentration, an amount of additional fluorine-containing gas supplied to the mixed gas in the laser discharge chamber is determined, and the above amount of additional fluorine-containing gas is supplied to the mixed gas in the laser discharge chamber.

According to another aspect of the embodiments, a method is disclosed, the method comprising: pushing residual gas in the reaction chamber to the sensor using a first portion of the inert gas; sensing a first oxygen concentration within the residual gas using a sensor; supplying at least a portion of a mixed gas from the laser discharge chamber to the reaction chamber, wherein the mixed gas comprises fluorine; reacting fluorine in the mixed gas portion with the metal oxide in the reaction chamber to form a product gas comprising oxygen; using a second portion of the inert gas to push the product gas in the reaction chamber to the sensor; sensing a second oxygen concentration in the product gas; inferring an estimated fluorine concentration in the portion of the mixed gas from the laser discharge chamber based on the sensed second oxygen concentration; determining a compensated fluorine concentration in the portion of the mixed gas from the laser discharge chamber based at least in part on the first oxygen concentration and the estimated fluorine concentration; determining an additional fluorine-containing gas amount of the mixed gas supplied into the laser discharge chamber based on the estimated fluorine concentration; and supplying the amount of additional fluorine-containing gas to the mixed gas in the laser discharge chamber.

Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to the specific embodiments described herein. These examples are presented herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the relevant art based on the teachings contained herein.

Drawings

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate by way of example, and not limitation, methods and systems of embodiments of the present invention. The accompanying drawings, which are included to provide a further understanding of the principles of the methods and systems presented herein, and are incorporated in and constitute a part of the specification. In the drawings, like reference numbers indicate identical or functionally similar elements.

FIG. 1 is a partially schematic block diagram, not to scale, of the general broad concept of a lithographic system in accordance with one aspect of the disclosed subject matter.

Fig. 2 is a partially schematic block diagram, not to scale, of an apparatus including a detection apparatus configured to measure fluorine concentration in a gas mixture within a chamber in accordance with an aspect of the disclosed subject matter.

FIG. 3 is a flow chart of a process performed by a detection apparatus for measuring fluorine concentration in a gas mixture of a chamber in accordance with one aspect of the disclosed subject matter.

Fig. 4 is a flow chart of a process performed by a detection apparatus for measuring fluorine concentration in a gas mixture of a chamber in accordance with another aspect of the disclosed subject matter.

Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to the specific embodiments described herein. These examples are presented herein for illustrative purposes only. Other embodiments will be apparent to those skilled in the relevant art based on the teachings contained herein.

Detailed Description

This specification discloses one or more embodiments that incorporate the features of the invention. The disclosed embodiments merely exemplify the invention. The scope of the invention is not limited to the embodiment(s) disclosed. The invention is defined by the appended claims.

References in the specification to "one embodiment," "an example embodiment," etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

Before describing particular embodiments in more detail, it is beneficial to provide an example environment in which embodiments of the present invention may be implemented. Referring to FIG. 1, a lithographic system 10 includes an illumination system 100. As described more fully below, the illumination system 100 includes a light source that generates and directs a pulsed light beam 20 to a lithographic exposure apparatus or scanner 30, which lithographic exposure apparatus or scanner 30 patterns microelectronic features on a wafer 40. The wafer 40 is placed on a wafer stage 50, the wafer stage 50 being configured to hold the wafer 40 and being connected to a positioner configured to accurately position the wafer 40 in accordance with certain parameters.

The lithography system 10 uses a light beam 20, the light beam 20 having a wavelength in the Deep Ultraviolet (DUV) range, for example, of 248 nanometers (nm) or 193 nm. The smallest dimension of the microelectronic features that can be patterned on wafer 40 is related to the wavelength of beam 20, with lower wavelengths allowing for smaller smallest feature sizes. When the wavelength of the light beam 20 is 248nm or 193nm, the minimum size of the microelectronic features may be, for example, 50nm or less. The bandwidth of the light beam 20 may be the actual instantaneous bandwidth of its spectrum (or emission spectrum) containing information about how the light energy of the light beam 20 is distributed over different wavelengths. The scanner 30 includes an optical arrangement having, for example, one or more beam focusing lenses, a mask and an objective lens arrangement. The mask may be moved in one or more directions, such as along the optical axis of the beam 20 or in a plane perpendicular to the optical axis. The objective arrangement includes a projection lens and enables transfer of an image from the mask to the photoresist on the wafer 40. Illumination system 100 adjusts the angular range over which beam 20 impinges on the mask. Illumination system 100 also homogenizes (homogenizes) the intensity distribution of beam 20 across the mask.

Scanner 30 may include features such as a photolithography controller 60, an air conditioner, a power supply for various electrical components, and the like. The lithography controller 60 controls how the layers are printed on the wafer 40. The photolithography controller 60 includes a memory that stores information such as a process recipe. The process or recipe determines the length of exposure on wafer 40 based on, for example, the mask used and other factors that affect exposure. During lithography, multiple pulses of beam 20 irradiate the same area of wafer 40 to form an irradiation dose.

For some embodiments, the lithography system 10 also preferably includes a control system 70. Typically, the control system 70 includes one or more of digital electronic circuitry, computer hardware, firmware, and software. The control system 70 also includes memory that may be read only memory and/or 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 disk; CD-ROM discs.

The control system 70 may also include one or more input devices (such as a keyboard, touch screen, microphone, mouse, handheld input device, etc.) and one or more output devices (such as a speaker or monitor). The control system 70 may also include one or more programmable processors and one or more computer program products tangibly embodied in a machine-readable storage device for execution by the one or more programmable processors. One or more programmable processors may each execute a program of instructions to perform desired functions by operating on input data and generating appropriate outputs. Typically, a processor receives instructions and data from a memory. Any of the foregoing may be supplemented by, or incorporated in, specially-designed ASICs (application-specific integrated circuits). The control system 70 may be centralized or distributed, partially or entirely, throughout the lithography system 10.

Referring to fig. 2, the illumination system 100 comprises a detection device 105 configured to measure or estimate the concentration of fluorine (F2) in the gas mixture 107 within the laser discharge chamber 110. The concentration of fluorine molecules F2 in the laser discharge chamber 110 may be in a range that is too high to directly detect fluorine. For example, the fluorine concentration in the laser discharge chamber 110 may be greater than about 500 parts per million (ppm), and may be about 1000ppm or up to about 2000ppm. However, commercial fluorine sensors typically saturate at 10ppm, so it is impractical to use such commercial fluorine sensors to directly measure the fluorine concentration in laser discharge chamber 110. Instead, the detection device 105 relies on a chemical reaction that generates O2, wherein the amount of O2 generated is related to the amount of fluorine that participates in the reaction in a known manner. The amount of O2 may then be measured using a commercially available O2 sensor 115. The detection device 105 may thus calculate the basis of how much fluorine is present before the chemical reaction starts based on the amount of O2 present after the chemical reaction (provided by the O2 sensor 115) and based on information about the chemical reaction. The terms "amount" and "concentration" are used interchangeably herein and elsewhere as the context allows, it being understood that one may be calculated directly from the other.

To make this estimate accurate, the operation of the detection device 105 is based on the following assumptions: the chemical reaction that consumes fluorine and releases O2 is a linear reaction in which there is a direct known correlation between the concentration of fluorine before the chemical reaction starts and the concentration of O2 at the end of the chemical reaction. In some cases, the operation is based on the following assumptions: the fluorine is completely consumed and thus there is no residual molecular fluorine F2 in the gas after the chemical reaction.

The lithography system 10 (fig. 1) includes a gas maintenance system 120, the gas maintenance system 120 including at least a gas supply system fluidly connected to the laser discharge chamber 110 via a conduit system 127. The gas maintenance system 120 includes one or more gas supply sources and a control unit (which also includes a valve system) for controlling which of the gases from the supply sources are conveyed into or out of the laser discharge chamber 110 via a conduit system 127.

The detection device 105 interfaces with the controller 130, and the controller 130 receives the output from the O2 sensor 115 and calculates how much fluorine is present before the chemical reaction begins to estimate the amount of fluorine in the gas mixture 107. The controller 130 may be part of the control system 70 (FIG. 1), a stand alone controller or some other control system in the lithography system 10, or distributed among some or all of these. The controller 130 uses this information to determine if the fluorine concentration in the gas mixture 107 needs to be adjusted. The controller 130 thus determines how to adjust the relative amounts of gas in the supply of the gas maintenance system 120 to be transferred into or out of the laser discharge chamber 110 based on the determination. The controller 130 sends a signal to the gas maintenance system 120 to adjust the relative concentration of fluorine in the gas mixture 107 during a gas renewal of the laser discharge chamber 110.

The detection apparatus 105 includes a reaction vessel 135 defining a reaction chamber 140, the reaction chamber 140 containing a metal oxide 145, such as alumina. Reaction chamber 140 may also be referred to as a scrubber. The reaction chamber 140 is fluidly connected to the laser discharge chamber 110 via a conduit 137 to receive a mixed gas 150 comprising fluorine from the laser discharge chamber 110. A fluid control device 138, such as a valve, may be placed in conduit 137 to regulate the time that the mixed gas 150 is supplied to the reaction chamber 140, and to control the flow rate of the mixed gas 150 into the reaction vessel 135 under the control of the controller 130. In this way, the reaction chamber 140 allows a chemical reaction between fluorine in the received mixed gas 150 and the metal oxide 145 to occur that can 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 fluorine and the metal oxide 145 of the received mixed gas 150. For example, the interior of the reaction vessel 135 may be made of a non-reactive metal such as stainless steel or monel.

The O2 sensor 115 is fluidly connected to receive the fresh gas mixture 155, i.e. in fluid communication with the fresh gas mixture 155, and is arranged to sense the amount of O2 within the fresh gas mixture 155. The O2 sensor 115 may be a commercially available O2 sensor capable of detecting O2 concentration within a concentration range expected due to a chemical reaction in the reaction chamber 140. For example, in some embodiments, the O2 sensor 115 senses O2 in the fresh gas mixture 155 in the range of 200-1000 ppm.

One example of an O2 sensor suitable for this concentration range is an O2 analyzer that utilizes a precision zirconia sensor for detecting O2. The zirconia sensor includes a unit made of a high purity, high density, stable zirconia ceramic. The zirconia sensor produces a voltage signal indicative of the O2 concentration of the new gas mixture 155. In addition, the output of the zirconia sensor is analyzed (e.g., converted and linearized) by a high-speed microprocessor within the O2 sensor 115 to provide a direct digital readout used by the controller 130. Conventional zirconia cells include zirconia ceramic tubes plated with porous platinum electrodes on the inner and outer surfaces thereof. When the sensor is heated above a certain temperature (e.g., 600 ℃ or 1112°f), it becomes an O2 ion conducting electrolyte. The electrode provides a catalytic surface for O2 molecules, O2 to oxygen ions, and oxygen ion to O2 molecule changes. The O2 molecules on the high concentration reference gas side of the cell acquire electrons to become ions that enter the electrolyte.

At the same time, at the internal electrode, oxygen ions lose electrons and are released from the surface as O2 molecules. When the O2 concentration on each side of the sensor is different, oxygen ions migrate from the high concentration side to the low concentration side. This ion flow creates an electrical imbalance, resulting in a DC voltage across the electrodes. This voltage is a function of the ratio of the sensor temperature and the partial pressure (concentration) of O2 on each side of the sensor. This voltage is then analyzed by a high-speed microprocessor within the O2 sensor 115 for direct readout by the controller 130.

The O2 sensor 115 may be within a measurement cavity 175 of the measurement vessel 170. Measurement chamber 175 is in fluid communication with reaction chamber 140 via conduit 177. According to one embodiment, one or more fluid control devices 178 (such as valves) may be placed in the conduit 177 to regulate the timing of the introduction of the fresh gas mixture 155 to the measurement cavity 175, and to control the flow rate of the fresh gas mixture 155 into the measurement vessel 170, under the control of the control unit 130.

Because the chemical reaction between fluorine and metal oxide is stoichiometrically simple and easy to implement and control, metal oxide 145 is selected to react with fluorine in mixed gas 150. Furthermore, the controlled stoichiometry of the chemical reaction is fixed. Additionally, the chemical reaction between fluorine and metal oxide is a stable chemical reaction. The chemical reaction may be stable if it does not proceed simultaneously in the opposite direction and the components of the new gas mixture do not react with any other species in the new gas mixture to form fluorine. One suitable chemical reaction between fluorine and metal oxide 145 of mixed gas 150 is discussed below, which is stable and has a controlled stoichiometric ratio.

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

The metal oxide 145 may include a metal such as aluminum. In addition, the metal oxide 145 preferably does not contain alkali metals, alkaline earth metals, hydrogen, and carbon. Thus, the metal oxide 145 may be alumina (which is alumina or Al2O 3). Alumina is in powder and solid form with sufficient pores to provide sufficient surface area to promote chemical reactions with fluorine in the gas. The spaces between the powder particles are large enough to allow fluorine-containing gas to flow into the alumina, thereby enabling chemical reactions. For example, the alumina may be in the form of a powder or granules packed in a column and having a total pore volume of at least 0.35 cc/g. The mixed gas 150 flows through (e.g., flows over) the metal oxide 145 or across the metal oxide 145 to effect a chemical reaction between fluorine and aluminum oxide.

In the presence of fluorine in the mixed gas 150, the following chemical reaction occurs:

6F2+2Al2O3＝4AlF3+3O2。

thus, for every six fluorine molecules to react with two metal oxide (Al 2O 3) molecules, four inorganic fluoride compound (aluminum fluoride or AlF 3) molecules and three O2 molecules (O2) are output. The chemical reaction is a linear and stoichiometrically simple reaction. Thus, in order to concentrate only on fluorine and O2, one O2 molecule is output from the chemical reaction for every two fluorine molecules F2 input to the chemical reaction. Thus, if the concentration of fluorine F2 input into the chemical reaction is 1000ppm, O2 having a concentration of 500ppm is released after the chemical reaction and detected by the O2 sensor 115. Thus, for example, because it is assumed that the ratio of fluorine consumed to O2 generated in the chemical reaction is 2 when interpreting the measurement result in the detection device 105: 1, if the O2 sensor 115 detects 600ppm O2, this means that 1200ppm fluorine is present in the gas mixture 107. In other implementations, the detection device 105 may operate based on the following assumptions: the fluorine in the sample is completely converted (and thus, there is no residual fluorine molecule F2 in the gas after the chemical reaction). For example, if sufficient time has elapsed after the chemical reaction has started, this assumption may be a valid assumption.

In some implementations, the reaction between the metal oxide 145 and fluorine in the mixed gas 150 occurs under one or more specifically designed conditions. For example, the reaction between the metal oxide 145 and fluorine in the mixed gas 150 may occur in the presence of one or more catalysts, which are substances that alter the rate of the chemical reaction but are chemically unchanged at the end of the chemical reaction. As another example, the reaction between the metal oxide 145 and fluorine in the mixed gas 150 may occur in a controlled environment such as a temperature controlled environment or a humidity controlled environment.

The gas mixture 107 includes a gain medium including a rare gas and a halogen such as fluorine. During operation, fluorine in the gas mixture 107 (which provides the gain medium for optical amplification) is depleted over time. This reduces the amount of light amplification and thus changes the characteristics of the light beam 20 (fig. 1) produced by the illumination system 100. See U.S. patent No. 5,978,406, entitled "Fluorine Control System for Excimer Laers," published on month 11 and 2 of 1999, the description of which is incorporated herein by reference in its entirety. The gas maintenance system 120 seeks to maintain the fluorine concentration in the gas mixture 107 in the laser discharge chamber 110 within a tolerance of a target value, as compared to the fluorine concentration set during initial gas refill. Fluorine will react with the walls and other laser components, resulting in fluorine being depleted relatively regularly. The depletion rate is related to many factors, but for a given laser at a particular time during its lifetime, the depletion rate is primarily related to the pulse rate and loading factors while the laser is operating. Thus, additional fluorine is regularly added to the laser discharge chamber 110 under the control of the gas maintenance system 120. The amount of fluorine consumed varies from gas cell to gas cell, so closed loop control is used to determine the amount of fluorine that is pushed or injected into the laser discharge cell 110 at each occasion. Thus, fluorine is injected into the laser chamber when the laser is operating and generating pulses. The detection device 105 is used to determine the concentration of fluorine in the gas mixture in the laser discharge chamber 110 and thus in the overall scheme to determine the amount of fluorine pushed into or injected into the laser discharge chamber 110.

As mentioned above, if the sensor has been idle for too long, i.e. on the order of minutes or hours, the resulting indirect measurement of the F2 concentration tends to be lower than the actual concentration of F2. Increasing the size of the reaction chamber counteracts this trend to some extent, but introduces the following problems: the O2 readings cannot converge or predictably develop to a final steady state value within the sampling time allowed for the reaction chamber volume.

In accordance with one aspect of the embodiments, to avoid these problems, the measurement includes pushing residual O2 in the reaction chamber 140 to the O2 sensor 115 using an inert gas, such as nitrogen, and taking a residual O2 reading at the O2 sensor 115. Then, the gas to be sampled is filled into the reaction chamber 140. In an example of a system used in conjunction with semiconductor lithography, the gas to be sampled is a gas sample in one of the laser discharge cells, such as the master oscillator cell. After the second F2 reaction is sufficiently near completion, an inert gas is used to push the resulting O2 in the reaction chamber to the O2 sensor 115, and a second O2 measurement is made at the O2 sensor 115 to obtain a basis for a final adjusted measurement of F2 concentration.

To perform this process, the detection device 105 is selectively connected to an inert gas source 200, the inert gas source 200 being arranged to supply an inert gas 220, such as nitrogen, to the reaction chamber 140 via a conduit 210. A fluid control device 230, such as a valve, may be placed in conduit 210 to adjust the timing of the flow of inert gas 220 to reaction chamber 140 under the control of control unit 130. As also shown in fig. 2, according to some embodiments, there is a conduit 410 with a valve 430, the valve 430 selectively placing the reaction chamber 140 in fluid communication with a vacuum source 400 (such as a pump or container near vacuum pressure) to evacuate the reaction chamber 140 as part of the process described below in connection with fig. 4.

Fig. 3 is a flow chart further explaining the process just described. In step S10, the inert gas source 200 supplies inert gas to the reaction chamber 140 to push any gas in the reaction chamber 140 to the O2 sensor 115. In step S20, the O2 sensor 115 measures the O2 concentration in the gas that has been pushed toward it. According to one embodiment, these readings are collected and integrated to obtain an O2 measurement. Since this measurement is a residual amount of O2 in the reaction chamber 140, it is referred to herein as a residual O2 measurement.

In step S30, the reaction chamber 140 is filled to a fixed pressure with a chamber gas that remains known to be sufficient for the reaction in the reaction chamber 140 to proceed to substantially complete for a period of time.

In step S40, the inert gas source 200 supplies a second portion of the inert gas to the reaction chamber 140 to push the gas in the reaction chamber 140 to the O2 sensor 115. In step S50, the O2 sensor 115 measures the O2 concentration in the gas that has been pushed toward it. According to one embodiment, the readingIs collected and integrated to obtain a second O2 measurement. Because this second measurement is the amount of O2 generated in reaction chamber 140 for measuring F2 (n), it is referred to herein as the final O2 measurement. In step S60, F is inferred from the final O2 measurement ₂ (n). In step S70, the determined F2 concentration F is adjusted based at least in part on the residual O2 measurement ₂ (n). In some embodiments, the process proceeds to step S80, in which the amount of additional fluorine-containing gas supplied to the mixed gas in the laser discharge chamber is determined based on the estimated fluorine concentration, and then proceeds to step S90, in which the above amount of additional fluorine-containing gas is supplied to the mixed gas in the laser discharge chamber.

As shown in fig. 4, according to some embodiments, the process may include a step S100 in which the reaction chamber 140 is evacuated by placing the reaction chamber 140 in fluid communication with a vacuum source 400 between steps S20 and S30.

According to another aspect of the embodiment, the compensation method uses the total O2 measurement from the above sequence to obtain the F2 concentration in the gas sampled in the sensor. The term "total O2 measurement" as used herein refers to the O2 measurement not only for the determination of uncompensated F2 (i.e., F2 (n)), but also to a preliminary measurement of residual O2, which preliminary measurement of residual O2 is used as a basis for compensation of the F2 measurement. Specifically, the corrected or compensated fluorine concentration f ₂ (n) is determined according to the following relationship:

O ₂ (n) is the result of the residual (first) O2 measurement,

F ₂ (n) is the uncompensated F2 concentration inferred from the final (second) O2 measurement,

p (n) is F ₂ (n) during the measurement, the total pressure of the chamber gas filling the sensor, Δtidle, is the value of the total pressure of the chamber gas from the most recent (i.e., immediately previous measurement) And the amount of time in seconds since the current measurement began, and

Δtpush is the amount of time in seconds that residual O2 is pushed out of the reaction chamber using an inert gas (e.g., N2) to obtain a residual O2 measurement at the beginning of the current measurement.

Thus, with the above apparatus and the above method, an improved F2 concentration measurement can be obtained, irrespective of the amount of time that has elapsed between measurements.

It should be appreciated that the detailed description section, and not the summary and abstract sections, is intended to be used to interpret the claims. The summary and abstract sections may set forth one or more, but not all exemplary embodiments of the invention as contemplated by the inventors, and are therefore not intended to limit the invention and the appended claims in any way.

The invention has been described above with the aid of functional building blocks illustrating the implementation of specific functions and relationships thereof. For ease of description, the boundaries of these functional building blocks are arbitrarily defined herein. Alternate boundaries may be defined so long as the specified functions and relationships thereof are appropriately performed.

The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments without undue experimentation, without departing from the generic concept of the present invention. Accordingly, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.

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

1. an apparatus, comprising:

a vessel defining a reaction chamber adapted for placement in selective fluid communication with a mixed gas source comprising fluorine to be sampled, the vessel comprising a metal oxide arranged to react with fluorine in the mixed gas to form a product gas comprising oxygen, the vessel further adapted for placement in selective fluid communication with an inert gas source; and

An oxygen sensor configured to be placed in selective fluid communication with the vessel to receive the product gas and to sense an amount of oxygen in the product gas.

2. The apparatus of clause 1, wherein the container is further adapted for placement in selective fluid communication with a vacuum source.

3. The apparatus of clause 1, wherein the metal oxide comprises aluminum oxide.

4. The apparatus of clause 1, wherein the mixed gas source comprising fluorine to be sampled comprises a laser discharge chamber.

5. The apparatus of clause 1, wherein the inert gas source comprises a nitrogen source.

6. An apparatus, comprising:

a laser discharge chamber;

a vessel defining a reaction chamber adapted to be placed in selective fluid communication with the laser discharge chamber to receive a sample of a mixed gas comprising fluorine to be sampled, the vessel comprising a metal oxide arranged to react with fluorine in the mixed gas to form a product gas comprising oxygen;

an inert gas source in selective fluid communication with the vessel; and

an oxygen sensor configured to be placed in selective fluid communication with the vessel to receive the product gas and to sense an amount of oxygen within the product gas.

7. The apparatus of clause 6, wherein the container is further adapted for placement in selective fluid communication with a vacuum source.

8. The apparatus of clause 6, wherein the metal oxide comprises aluminum oxide.

9. The apparatus of clause 6, wherein the mixed gas source comprising fluorine to be sampled comprises a laser discharge chamber.

10. The apparatus of clause 6, wherein the inert gas source comprises a nitrogen source.

11. The apparatus of clause 6, further comprising:

a gas maintenance system comprising a gas supply system in fluid connection with the laser discharge chamber,

a control system connected to the gas maintenance system and the detection device and configured to: receiving an output of the oxygen sensor and estimating a fluorine concentration in the mixed gas received from the gas discharge chamber; determining whether the fluorine concentration in the gas mixture from the gas supply system of the gas maintenance system should be changed based on the estimated fluorine concentration in the mixed gas; and sending a signal to the gas maintenance system to change the relative concentration of fluorine in the gas mixture supplied to the laser discharge chamber from the gas supply system of the gas maintenance system during a gas renewal of the laser discharge chamber.

12. A method, comprising:

pushing residual gas in the reaction chamber to the sensor using a first portion of the inert gas;

sensing a first oxygen concentration within the residual gas using a sensor;

supplying at least a portion of a mixed gas from the laser discharge chamber to the reaction chamber, wherein the mixed gas comprises fluorine;

reacting fluorine in the mixed gas portion with the metal oxide in the reaction chamber to form a product gas comprising oxygen;

pushing the product gas in the reaction chamber to the sensor using a second portion of the inert gas;

sensing a second oxygen concentration within the product gas;

inferring an estimated fluorine concentration in the portion of the mixed gas from the laser discharge chamber based on the sensed second oxygen concentration; and

the compensated fluorine concentration in the portion of the mixed gas from the laser discharge chamber is determined based at least in part on the first oxygen concentration and the estimated fluorine concentration.

13. The method of clause 12, further comprising: the reaction chamber is evacuated between sensing a first oxygen concentration within the residual gas using the sensor and supplying at least a portion of a mixed gas from the laser discharge chamber to the reaction chamber, wherein the mixed gas comprises fluorine.

14. The method of clause 12, further comprising determining an amount Δtidle and an amount Δtpush, the amount Δtidle indicating an amount of time that has elapsed from an immediate previous determination of the fluorine concentration to a current measurement start, and the amount Δtpush indicating an amount of time that the first portion of inert gas has pushed the generated gas mixture to the sensor; and determining the compensated fluorine concentration in the portion of the mixed gas from the laser discharge chamber may also be based at least in part on Δtidle and Δtpush.

15. The method of clause 12, wherein the compensated fluorine measurement f2 (n) is determined according to the following equation:

wherein k is ₃ 、k ₄ And k ₅ Is a constant coefficient determined from the test data,

O ₂ (n) is the result of sensing a first O2 concentration within the residual gas using a sensor,

F ₂ (n) is the measured estimated fluorine concentration,

p (n) is the total pressure charged to the sensor when obtaining an estimate of F2 in the resulting gas mixture,

Δtidle is the amount of time in seconds since the last previous measurement and the current measurement, and

Δtpush is the amount of time in seconds that residual O2 is pushed out of the reaction chamber using an inert gas to obtain a measurement of residual O2 at the beginning of the current measurement.

16. The method of clause 12, wherein the residual gas is from an immediately previous measurement.

17. The method of clause 12, wherein the metal oxide comprises aluminum oxide.

18. The method of clause 12, wherein the inert gas comprises nitrogen.

19. The method of clause 12, further comprising determining the amount of additional fluorine-containing gas supplied to the mixed gas in the laser discharge chamber based on the estimated fluorine concentration.

20. A method, comprising:

sensing, using a sensor, a first oxygen concentration within the residual gas;

using a second portion of the inert gas to push the product gas in the reaction chamber to the sensor;

sensing a second oxygen concentration within the product gas;

inferring an estimated fluorine concentration in the portion of the mixed gas from the laser discharge chamber based on the sensed second oxygen concentration;

Determining a compensated fluorine concentration in the portion of the mixed gas from the laser discharge chamber based at least in part on the first oxygen concentration and the estimated fluorine concentration;

determining an amount of additional fluorine-containing gas of the mixed gas supplied into the laser discharge chamber based on the estimated fluorine concentration; and

the above amount of additional fluorine-containing gas is supplied to the mixed gas in the laser discharge chamber.

Claims

1. An apparatus, comprising:

a vessel defining a reaction chamber adapted for placement in selective fluid communication with a source of a mixed gas to be sampled comprising fluorine, the vessel comprising a metal oxide arranged to react with the fluorine in the mixed gas to form a product gas comprising oxygen, the vessel further adapted for placement in selective fluid communication with a source of an inert gas; and

2. The apparatus of claim 1, wherein the container is further adapted for placement in selective fluid communication with a vacuum source.

3. The apparatus of claim 1, wherein the metal oxide comprises aluminum oxide.

4. The apparatus of claim 1, wherein the mixed gas source comprising fluorine to be sampled comprises a laser discharge chamber.

5. The apparatus of claim 1, wherein the inert gas source comprises a nitrogen source.

6. An apparatus, comprising:

a laser discharge chamber;

a container defining a reaction chamber adapted to be placed in selective fluid communication with the laser discharge chamber to receive a sample of a mixed gas comprising fluorine to be sampled, the container comprising a metal oxide arranged to react with the fluorine in the mixed gas to form a product gas comprising oxygen;

an inert gas source in selective fluid communication with the vessel; and

7. The apparatus of claim 6, wherein the container is further adapted for placement in selective fluid communication with a vacuum source.

8. The apparatus of claim 6, wherein the metal oxide comprises aluminum oxide.

9. The apparatus of claim 6, wherein the mixed gas source comprising fluorine to be sampled comprises a laser discharge chamber.

10. The apparatus of claim 6, wherein the inert gas source comprises a nitrogen source.

11. The apparatus of claim 6, further comprising:

a control system connected to the gas maintenance system and the detection device and configured to: receiving an output of the oxygen 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 the gas supply system of the gas maintenance system should be changed based on the estimated fluorine concentration in the mixed gas; and sending a signal to the gas maintenance system to change the relative concentration of fluorine in the gas mixture supplied to the laser discharge chamber from the gas supply system of the gas maintenance system during a gas renewal of the laser discharge chamber.

12. A method, comprising:

Sensing a first oxygen concentration within the residual gas using the sensor;

supplying at least a portion of a mixed gas from a laser discharge chamber to the reaction chamber, wherein the mixed gas comprises fluorine;

reacting the fluorine in the mixed gas portion with a metal oxide in the reaction chamber to form a product gas comprising oxygen;

sensing a second oxygen concentration within the product gas;

a compensated fluorine concentration in the portion of the mixed gas from the laser discharge chamber is determined based at least in part on the first oxygen concentration and the estimated fluorine concentration.

13. The method of claim 12, further comprising: the reaction chamber is evacuated between sensing a first oxygen concentration within the residual gas using the sensor and supplying at least a portion of a mixed gas from a laser discharge chamber to the reaction chamber, wherein the mixed gas comprises fluorine.

14. The method of claim 12, further comprising: determining an amount Δtidle and an amount Δtpush, the amount Δtidle indicating an amount of time that has elapsed from an immediate previous determination of fluorine concentration to a current measurement start, and the amount Δtpush indicating an amount of time that the first portion of the inert gas has pushed the generated gas mixture to the sensor; and determining a compensated fluorine concentration in the portion of the mixed gas from the laser discharge chamber is also based at least in part on the Δtidle and the Δtpush.

15. The method of claim 12, wherein the compensated fluorine measurement f2 (n) is determined according to the following equation:

O ₂ (n) is the result of sensing a first O2 concentration in the residual gas using the sensor, F ₂ (n) is the measured estimated fluorine concentration,

p (n) is the total pressure filling the sensor when obtaining an estimate of F2 in the gas mixture produced,

Δtpush is the amount of time in seconds that the inert gas is used to push residual O2 out of the reaction chamber to obtain a residual O2 measurement at the beginning of the current measurement.

16. The method of claim 12, wherein the residual gas is from an immediately previous measurement.

17. The method of claim 12, wherein the metal oxide comprises aluminum oxide.

18. The method of claim 12, wherein the inert gas comprises nitrogen.

19. The method of claim 12, further comprising determining an amount of additional fluorine-containing gas supplied to the mixed gas in the laser discharge chamber based on the estimated fluorine concentration.

20. A method, comprising:

sensing a first oxygen concentration within the residual gas using the sensor;

sensing a second oxygen concentration within the product gas;

the amount of additional fluorine-containing gas is supplied to the mixed gas in the laser discharge chamber.