JP2008170175A - Method for estimating degree of vacuum - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for estimating a degree of vacuum, which can estimate the degree of vacuum in a vacuum vessel being highly vacuum or ultra-highly vacuum by using a simple technique needing no expensive nor large-sized apparatus. <P>SOLUTION: A process of bringing a cathode 3 disposed in the vacuum vessel 1 to emit electrons by using a cold cathode electric field emitting method and sequentially measuring electron emission current which is the quantity of current of the electrons emitted from the cathode 3 for at least a prescribed period of time, is carried out while the temperature of the cathode 3 is kept to be a predetermined temperature. The degree of vacuum in the vacuum vessel 1 is estimated based on time-series data of values of the electron emission current measured for the prescribed period of time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for estimating the degree of vacuum in a vacuum vessel that has been evacuated.

Conventionally, a hot cathode ionization vacuum gauge is generally used to estimate (measure) the degree of vacuum in a high-vacuum or ultra-high-vacuum vacuum vessel (see, for example, Patent Documents 1 and 2). This hot-cathode ionization vacuum gauge basically measures the ion current by ionizing the residual gas in the vacuum vessel by electrons emitted from the hot cathode, and determines the degree of vacuum in the vacuum vessel from the value of the ion current. Is to measure.
JP 7-77473 A JP 2000-241281 A

  However, the hot cathode ionization vacuum gauge is highly dependent on the type of residual gas in the vacuum vessel, and it is difficult to appropriately measure the degree of vacuum when the type of residual gas in the vacuum vessel is unknown. . In addition, the hot cathode is likely to be burned out and consumed, and it is troublesome to handle and maintain, and the running cost tends to be expensive. Furthermore, in the hot cathode ionization vacuum gauge, in order to measure the ultra-high vacuum degree, an expensive BA type vacuum gauge must be used, and the ultra-high vacuum degree can be easily measured. It was impossible.

  Some ionization vacuum gauges are of the cold cathode type, but this requires a means for generating a magnetic field, which tends to be large and has a disadvantage that the measurement accuracy of the degree of vacuum is relatively low. is there.

  The present invention has been made in view of such a background, and the degree of vacuum can be estimated by a simple method without requiring an expensive or large-sized apparatus, without requiring an expensive or large-sized apparatus. It aims to provide a method.

  The inventor of the present application provided a cathode for emitting electrons by a cold cathode field emission method in a vacuum vessel, and emitted electrons by the cold cathode field emission method while keeping the temperature of the cathode constant. At this time, the electron emission current, which is the amount of current of the emitted electrons (current flowing through the cathode according to the number of electrons emitted per unit time from the cathode), was sequentially measured over time. As a result, the inventors of the present application have found the following.

  That is, although a detailed description will be given later, this is because molecules or atoms of the residual gas in the vacuum vessel cause physical adsorption to the electron emission portion of the cathode and subsequent desorption (release of physical adsorption). Thus, the electron emission current causes instantaneous spike-like fluctuations. In this case, the value of the electron emission current fluctuates with a frequency depending on the number of molecules or atoms of the residual gas in the vacuum chamber (or the density of the residual gas in the vacuum chamber). In particular, when the cathode is made of a material having a relatively high work function value (for example, a material having a work function of 4.5 eV or more), the variation in the value of the electron emission current is a residual gas. Dependence on the kind of is low, and dependence on the degree of vacuum appears remarkably. Therefore, the form of fluctuation of the electron emission current value has a close correlation with the degree of vacuum in the vacuum vessel.

  Therefore, the vacuum degree estimation method of the present invention is a vacuum degree estimation method for estimating the degree of vacuum in a vacuum vessel that has been evacuated, and electrons are emitted from the cathode disposed in the vacuum vessel by a cold cathode field emission method. A process of sequentially measuring the electron emission current, which is the amount of electrons emitted from the cathode at this time, for at least a predetermined time period is performed while maintaining the cathode temperature at a predetermined temperature. And a step of estimating the degree of vacuum in the vacuum vessel based on time-series data of the measured electron emission current values for the predetermined time period (first invention) ).

  In the first invention, as described above, the variation of the value of the electron emission current in the state where the temperature of the cathode is maintained at a constant temperature has a close correlation with the degree of vacuum in the vacuum vessel. Then, according to the time-series data of the measured value of the electron emission current obtained by measuring the value of the electron emission current for the predetermined time period, the electron emission current in a state where the cathode temperature is maintained at a constant temperature. The form of value fluctuation can be grasped. Therefore, the degree of vacuum in the vacuum vessel can be estimated based on the time series data of the value of the electron emission current. Further, even if the degree of vacuum is extremely high such as an ultra-high vacuum, if the predetermined time is appropriately set to a sufficiently long appropriate time, the high degree of vacuum is maintained within the time period. Since it is possible to capture the variation in the value of the corresponding electron emission current, it is possible to estimate the high degree of vacuum.

  As described above, according to the first aspect of the present invention, the electron emission from the cathode by the cold cathode field emission method is performed while keeping the temperature of the cathode arranged in the vacuum vessel at a predetermined temperature. By simply performing a very simple process of sequentially measuring the current for a predetermined time period, the vacuum vessel can be used without depending on the type of residual gas based on the time-series data of the measured electron emission current value. The degree of vacuum inside can be estimated. Even if the degree of vacuum is high vacuum or ultra-high vacuum, the degree of vacuum can be estimated. For this reason, the degree of vacuum in a high-vacuum or ultrahigh-vacuum vacuum vessel can be estimated by a simple method without requiring an expensive or large-sized apparatus. Further, since electrons are emitted from the cathode by the cold cathode field emission method, the life of the cathode can be increased as compared with the hot cathode, and the running cost can be reduced.

  In the first aspect of the invention, more specifically, the step of estimating the degree of vacuum includes, for example, per unit time based on time-series data of the value of the electron emission current for the measured predetermined time period. By providing a step of estimating the number of molecules or atoms of residual gas that has caused physical adsorption on the cathode, the degree of vacuum in the vacuum vessel can be estimated based on the estimated number (second). invention).

  That is, as described above, due to the physical adsorption of molecules or atoms of residual gas to the cathode and subsequent desorption, spike-like fluctuations of the electron emission current occur, and the spike-like portion is It is included in the time-series data of the value of the electron emission current for a predetermined time period. Although detailed description will be given later, the fluctuation amount of the electron emission current in the spike-like portion depends on the number of molecules or atoms of the residual gas that has caused physical adsorption on the cathode. Therefore, it is possible to estimate the number of molecules or atoms of the residual gas that has caused physical adsorption to the cathode per unit time based on the time-series data of the value of the electron emission current for the predetermined time period. Is possible. Further, the higher the degree of vacuum in the vacuum vessel, the smaller the total number of residual gas molecules or atoms present in the vacuum vessel, so that the residual gas molecules or atoms in the vacuum vessel cause physical adsorption to the cathode. The frequency (probability) is low.

  Therefore, the number of molecules or atoms of the residual gas that has physically adsorbed to the cathode per unit time decreases as the degree of vacuum in the vacuum vessel increases. For this reason, by estimating the number of molecules or atoms of residual gas that has caused physical adsorption to the cathode per unit time, the degree of vacuum in the vacuum vessel can be estimated appropriately based on the estimated number. Can do.

  In the present invention, it is preferable to use a material having a relatively high work function value (for example, a material having a work function of 4.5 eV or more) as the material of the cathode. And gold (Au), tungsten (W), rhenium (Re), nickel (Ni), osmium (Os), iridium (Ir), platinum (Pt), and the like.

  An embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a diagram showing a schematic configuration of an apparatus used in the residual gas discrimination method of the present embodiment, FIGS. 2 and 3 are graphs illustrating an electron emission current measured using the apparatus of FIG. (a), (b) is a figure for demonstrating the method of estimating the vacuum degree in a vacuum vessel.

  Referring to FIG. 1, reference numeral 1 denotes a vacuum container that is evacuated. Inside the vacuum vessel 1, a heating filament 2, a cathode 3, an extraction electrode (anode) 4 and a Faraday cup 5 are accommodated. The material of the vacuum vessel 1 is, for example, quartz glass, oxygen-free copper, or stainless steel.

  Both ends of the heating filament 2 are conductively held by metal (conductive) holding members 6a and 6b attached to one end (lower end in the figure) of the vacuum vessel 1, respectively. In the present embodiment, the heating filament 2 is made of tungsten (W). The holding members 6a and 6b are connected to a positive electrode and a negative electrode of a heating DC power source 7 provided outside the vacuum vessel 1, respectively. As a result, the heating filament 2 can be energized from the heating DC power source 7, and the filament 2 generates heat by the energization.

  In this case, the heating DC power source 7 is a power source capable of variably setting a current value to be supplied to the heating filament 2, and the current value can be changed in a range of 0 to 2A, for example. Thereby, the heat generation temperature of the filament 2 can be adjusted. In addition, the range of the output voltage of the direct current power supply 7 for a heating is 0-5V, for example.

  The cathode 3 is fixed to the heating filament 2 and is electrically connected to the filament 2. In the present embodiment, the cathode 3 is made of a carbon-based material, and the tip portion (electron emission portion) is constituted by a carbon nano tube (CNT) or the like. The cathode 3 is bonded to the heating filament 2 via a carbon paste or the like. In this case, since the heat of the heating filament 2 is transmitted to the cathode 3, the temperature of the cathode 3 can be changed by adjusting the current value supplied to the filament 2 from the heating DC power supply 7. .

  The cathode 3 is connected to the negative electrode of the DC high-voltage power supply 8 through one of the holding members 6a and 6b, for example, the holding member 6b. The DC high-voltage power supply 8 is provided outside the vacuum vessel 1 and its positive electrode is grounded. Accordingly, a negative high voltage is applied to the cathode 3 from the DC high-voltage power supply 8 with respect to the ground portion. The magnitude of the output voltage (applied voltage of the cathode 3 to the ground portion) of the DC high-voltage power supply 8 is set to a constant value of about 5 kV, for example.

  The Faraday cup 5 captures electrons emitted from the cathode 3 and is fixed to the other end (upper end in the drawing) of the vacuum vessel 1 so as to face the cathode 3. The Faraday cup 5 is connected to the grounding part via an ammeter 9 provided outside the vacuum vessel 1. As a result, a current corresponding to the number of electrons captured by the Faraday cup 9 flows through the ammeter 9. In this case, an ammeter 9 that can detect a pico-order current (picoammeter) is used. The detection output of the ammeter 9 is input to a data processor 10 provided outside the vacuum vessel 1. The data processor 10 records time-series data of the measured current value indicated by the detection output of the ammeter 9 and analyzes and displays the time-series data.

  The extraction electrode 4 is made of a conductive plate member and is disposed between the cathode 3 and the Faraday cup 5. The extraction electrode 4 is held in the vacuum vessel 1 through a holder (not shown). The lead electrode 4 has a through hole 4 a on the axis of the cathode 3. The through hole 4 a allows electrons emitted from the cathode 3 to pass toward the Faraday cup 5.

  The extraction electrode 4 is connected to a negative electrode of a DC high-voltage power supply 11 provided outside the vacuum vessel 1. The DC high-voltage power supply 11 has its positive electrode grounded to the grounding part. As a result, a negative high voltage is applied to the extraction electrode 4 from the DC high-voltage power supply 11 with respect to the ground portion. In this case, the output voltage of the DC high-voltage power supply 11 (the voltage applied to the extraction electrode 4 with respect to the ground portion) is smaller than the output voltage of the DC high-voltage power supply 8 on the cathode 3 side, for example, a constant value of about 2 kV. It is said that. Therefore, in this embodiment, a constant high voltage of about 3 kV is applied between the extraction electrode 4 and the cathode 3 by the cooperation of the DC high-voltage power supplies 8 and 11. A constant high voltage may be applied between the extraction electrode 4 and the cathode 3 from a single DC high-voltage power supply.

  In the apparatus configured as described above, when a voltage is applied to the cathode 3 and the extraction electrode 4 from the DC high voltage power supplies 8 and 11, respectively, and a high voltage is applied between the cathode 3 and the extraction electrode 4, a cold cathode electric field is generated. Electrons are emitted from the tip of the cathode 3 by the emission method. A part of the emitted electrons passes through the through hole 4 a of the extraction electrode 4 and is captured by the Faraday cup 5. At this time, a current flows through the ammeter 9 between the Faraday cup 5 and the ground portion, and the current is detected by the ammeter 9. Further, the detection output of the ammeter 9 is input to the data processor 10. Note that the current detected by the ammeter 9 is substantially proportional to the number of electrons emitted from the cathode 3 per unit time. Therefore, the current detected by the ammeter 9 corresponds to the electron emission current in the present invention. Therefore, the current detected by the ammeter 9 is hereinafter referred to as an electron emission current.

  Further, the temperature of the cathode 3 can be changed to various values by adjusting the value of the current supplied to the filament 2 from the heating DC power supply 7.

  Instead of detecting the electron emission current using the Faraday cup 5 as described above, for example, a current flowing from the DC high voltage power supply 8 to the cathode 3 may be detected as an electron emission current. Further, in this embodiment, the value of the current supplied to the heating filament 2 can be changed, and consequently the temperature of the cathode 3 can be changed. However, the temperature of the cathode 3 is maintained at one predetermined temperature. As described above, a constant current may be applied to the heating filament 2.

  Next, a method for estimating the degree of vacuum in the vacuum vessel 1 using the apparatus described above will be described.

First, the principle of the method for estimating the degree of vacuum will be described. While maintaining the temperature of the cathode 3 at a certain temperature, electrons are emitted from the cathode 3 by the cold cathode field emission method as described above. At this time, the electron emission current (electrons emitted from the cathode 3 per unit time) is emitted. When the current corresponding to the number is sequentially measured over time, measurement data such as that shown in the graph of FIG. 2 or FIG. 3 is obtained. 2 and 3, the temperature of the cathode 3 is 300K and 1203K, respectively. The degree of vacuum in the vacuum container 1 is 5 × 10 ⁻⁶ Torr (= 6.7 × 10 ⁻⁴ Pa). The sampling time for measuring the electron emission current is set to 10 ms or less. Moreover, the measurement data of the electron emission current in FIGS. 2 and 3 are measurement data in a period of 400 seconds.

  As shown in FIGS. 2 and 3, the electron emission current causes spike-like fluctuations (fluctuations). This is because the physical adsorption of the atoms or molecules of the residual gas in the vacuum vessel 1 and subsequent detachment instantaneously occur with respect to the electron emission portion of the cathode 3 (carbon nano tube in this embodiment). This is probably because the work function of the electron emission portion of the cathode 3 changes in a spike shape. In the example of FIGS. 2 and 3, noise components other than spike-like fluctuations in the electron emission current caused by physical adsorption of residual gas atoms or molecules on the cathode 3 are also included.

  The phenomenon in which the electron emission current fluctuates due to the physical adsorption of the residual gas on the cathode 3 as described above will be further described. In the present embodiment, since the material of the cathode 3 is a carbon-based material, the electron emission portion in a state where no physical adsorption of residual gas occurs in the electron emission portion (hereinafter referred to as a gas non-adsorption state). The work function is relatively high. The value of the work function is about 4.5 eV. When the electron emission portion of the cathode 3 is made of a material having a relatively high work function in a gas non-adsorbed state as described above, the residual gas is transferred to the cathode 3 regardless of the type of the residual gas. Due to the physical adsorption, the work function of the electron emission portion of the cathode 3 is smaller than that in the gas non-adsorption state. As a result, electrons tend to be emitted from the cathode 3 and the electron emission current tends to increase. is there.

  The work function of the electron emission portion of the cathode 3 increases as the number of molecules or atoms causing physical adsorption of molecules or atoms of the residual gas to the cathode 3 (hereinafter simply referred to as the number of adsorption of the residual gas) increases. Decrease amount (decrease amount from the value of work function in the gas non-adsorbed state) becomes large. For this reason, as the number of residual gases adsorbed on the cathode 3 increases, the amount of increase in the electron emission current (the amount of increase from the value of the electron emission current in the gas unadsorbed state) increases. Thus, the phenomenon in which the electron emission current changes due to physical adsorption of the residual gas to the cathode 3 is quantitatively expressed by the following equation (1).

I (n) = i0 + η · n (1)

Here, I (n) is the value of the electron emission current when the number of residual gases adsorbed to the electron emission portion of the cathode 3 is n, i0 is the value of the electron emission current in the gas unadsorbed state, and η is the electron. This is the amount of increase in the electron emission current per the number of residual gas adsorbed on the emission part.

  Therefore, in principle, the fluctuation of the electron emission current is considered to occur as shown in FIGS. 4 (a) and 4 (b), for example. 4 (a) and 4 (b) show that the noise component is not mixed in the electron emission current, the value i0 of the electron emission current in the gas non-adsorbed state is accurately maintained at a constant value, and the temperature of the cathode 3 is accurate. 3 conceptually shows fluctuations in the electron emission current (fluctuations caused by physical adsorption of residual gas on the cathode 3) under ideal conditions such as being held at a constant value. 4A shows the fluctuation of the electron emission current when the vacuum degree of the vacuum vessel 1 is relatively high, and FIG. 4B shows the electrons when the vacuum degree of the vacuum vessel 1 is relatively low. The fluctuation of the emission current is shown. 4A and 4B, the height of the spike-like portion (the amount of change in the electron emission current of the spike-like portion) corresponds to the number of residual gas adsorbed. That is, the spike-like portions having the peak values of the electron emission currents I1, I2, I3, and I4 have 1, 2, 3, and 4 instantaneous adsorption numbers of the residual gas to the cathode 3, respectively. It corresponds to the case of.

  As shown in FIGS. 4A and 4B, the higher the degree of vacuum of the vacuum vessel 1 (the lower the total number or density of molecules or atoms of the residual gas in the vacuum vessel 1, or the vacuum vessel The smaller the total pressure in 1), the lower the frequency at which the electron emission current instantaneously spikes due to the physical adsorption of the residual gas on the cathode 3, or the instantaneous The probability that the number of adsorbed residual gases is reduced increases. This is because, as the degree of vacuum is higher, the number of molecules or atoms of the residual gas in the vacuum vessel 1 is smaller, so the probability that the cathode 3 and the molecules or atoms of the residual gas are in contact with each other is lower.

  Supplementally, as the temperature of the cathode 3 is higher, the physical adsorption of the residual gas on the cathode 3 is less likely to occur. For this reason, the frequency at which the residual gas is physically adsorbed on the cathode 3 and the frequency at which the spike-like fluctuation of the electron emission current occurs is the same as the temperature of the cathode 3 even when the vacuum degree of the vacuum vessel 1 is the same. The higher it is, the lower it is. In other words, as the temperature of the cathode 3 is higher, the spike-like fluctuation of the electron emission current is less likely to occur, and the electron emission current is stabilized. This tendency is also shown in FIG. 2 and FIG.

  From the above, if the number of residual gas adsorbed per unit time on the cathode 3 is estimated with the temperature of the cathode 3 kept constant, the number is approximately proportional to the total pressure of the vacuum vessel 1, The higher the degree of vacuum of the vacuum vessel 1, the smaller. Therefore, the number of residual gas adsorbed per unit time can be used as an index for estimating the degree of vacuum. In this case, a spike-like portion due to physical adsorption of residual gas on the cathode 3 is extracted from the measurement data (time-series data) of the electron emission current in a certain period of time (for example, a period of 60 seconds), Based on the amount of change in the electron emission current in each spike-like portion, it is possible to estimate the number of adsorbed residual gases corresponding to the spike-like portion. Furthermore, if the sum of the number of adsorbed residual gases corresponding to each spike-like portion in the predetermined time period is obtained, the number of adsorbed residual gases per unit time can be estimated. This is the basic principle of the method for estimating the degree of vacuum in the vacuum vessel 1 in this embodiment.

Based on the principle described above, the process of estimating the degree of vacuum in the vacuum container 1 in this embodiment will be described below. This process is executed in the following procedure.
(Procedure 1) First, a constant current is applied to the heating filament 2 from the heating DC power source 7 to control the temperature of the cathode 3 to a certain constant temperature. In this case, the temperature (target temperature) of the cathode 3 to be controlled is determined in advance, for example, 1000K. Here, in this embodiment, data representing the relationship between the value of the current passed through the filament 2 and the temperature of the cathode 3 (temperature in a steady state) (hereinafter referred to as current / temperature data) is a colorimetric thermometer in advance. And measured using a radiation thermometer. Then, a current value corresponding to the target temperature of the cathode 3 is determined based on the current / temperature data. Furthermore, the current having the determined current value is continuously supplied from the heating DC power source 7 to the heating filament 2. Thereby, the temperature of the cathode 3 is held at a predetermined target temperature.
(Procedure 2) Next, the DC high voltage power supplies 8 and 11 are operated in a state where the temperature of the cathode 3 is maintained at the target temperature as described above, so that a constant high voltage is provided between the cathode 3 and the extraction electrode 4. A voltage (about 3 kV in this embodiment) is applied, and electrons are emitted from the cathode 3. While the electrons are continuously emitted, the detection output of the ammeter 9, that is, the measured value of the electron emission current, is sequentially transmitted to the data processing unit 10 for a predetermined time (for example, 60 seconds). Capture and record. In this case, the predetermined time is basically set to such a length that the physical adsorption of the residual gas to the cathode 3 can occur a plurality of times within the time period. Good. Further, the period of the predetermined time may not include the period immediately after the start of electron emission from the cathode 3.
(Procedure 3) Next, from the entire time-series data of the measured values of the electron emission current obtained in the procedure 2 or a part of the time-series data for a predetermined time, the cathode A spike-like portion generated due to physical adsorption of residual gas to 3 is extracted. In this case, for example, in the waveform of the electron emission current represented by the time-series data of the measured value of the electron emission current, a portion where the differential value is equal to or greater than a predetermined value and the amount of change in the electron emission current is equal to or greater than the predetermined value, What is necessary is just to extract as a spike-like part resulting from the physical adsorption | suction of residual gas. Then, the amount of change in the current in each extracted spike-like part (difference between the peak value of the spike-like part and the value of the electron emission current i0 in the gas non-adsorbed state) is obtained, and each spike-like part is obtained. From the amount of change in the current of the portion, the number of residual gas adsorbed corresponding to the spike-like portion is obtained. In this case, the value i0 of the electron emission current in the gas non-adsorbed state can be obtained, for example, by subjecting the time series data of the measured value of the electron emission current to a low pass characteristic filtering process. Further, the amount of change in the electron emission current per one of the number of residual gas adsorbed (that is, η in the above formula (1)) may be identified based on experiments in advance.
(Procedure 4) Next, by adding together the number of adsorption of the residual gas corresponding to each spike-like portion obtained as described above, the total number of adsorption of the residual gas (total number of adsorption) in a predetermined time period is obtained. Then, by dividing the obtained total adsorption number by the time of the period, the adsorption number of the residual gas per unit time on the cathode 3 is obtained. For example, in the case where a spike-like portion is extracted as shown in FIG. 4A, when the period for obtaining the total number of adsorption is a period of 0 to 60 seconds, the total number of adsorption is three. Further, when spike-like portions are extracted as shown in FIG. 4B, the total number of adsorptions in the period of 0 to 60 seconds is 26. Therefore, the number of adsorptions per unit time is 3/60 in the example of FIG. 4A, and 26/60 in the example of FIG. 4B. The unit time does not need to be 1 second, and for example, 60 seconds may be the unit time. In this case, the number of adsorptions per unit time is 3 in the example of FIG. 4A and 26 in the example of FIG. 4B.

Supplementally, the longer the period of time for obtaining the total number of adsorbed residual gases (total number of adsorbed), the higher the degree of vacuum, including ultra-high vacuum, can be estimated.
(Procedure 5) Next, the degree of vacuum is estimated based on the number of residual gases adsorbed per unit time to the cathode 3 obtained as described above. That is, the total pressure in the vacuum chamber 1 is estimated by multiplying the obtained number of adsorbed residual gases by a proportional constant determined experimentally in advance. The proportionality constant is a value experimentally determined using a known vacuum gauge or the like corresponding to the state in which the temperature of the cathode 3 is maintained at the target temperature. Thereby, the degree of vacuum in the vacuum vessel 1 is estimated.

  The above is the detail of the estimation process of the vacuum degree in this embodiment.

  With such a process, the degree of vacuum in the vacuum vessel 1 (high vacuum or ultra-high vacuum) can be used while using an inexpensive and simple device without requiring an expensive device, a large device, or a complicated device. The degree of vacuum) can be estimated by a simple method. Further, the degree of vacuum of high vacuum or ultra high vacuum can be appropriately estimated without depending on the type of residual gas in the vacuum vessel 1.

  In the present embodiment, when the degree of vacuum of the vacuum vessel 1 is estimated, the measurement data of the electron emission current in a state where the temperature of the cathode 3 is held at one target temperature is used. Electron emission current measurement data obtained corresponding to each type of target temperature may be used. In this case, for example, the degree of vacuum is estimated by the procedures 3 to 5 from the measurement data respectively obtained by the same process as the procedure 2 in the state where the temperature of the cathode 3 is held at each target temperature. The average value of the degree of vacuum may be estimated as the actual degree of vacuum of the vacuum container 1.

  In the present embodiment, a carbon-based material is used as the material of the cathode 3, but other than this, gold (Au), tungsten (W), rhenium (Re), nickel (Ni), osmium (Os) The cathode 3 may be made of a material such as iridium (Ir) or platinum (Pt).

The figure which shows schematic structure of the apparatus used for the residual gas discrimination | determination method of one Embodiment of this invention. The graph which illustrates the electron emission current measured using the apparatus of FIG. The graph which illustrates the electron emission current measured using the apparatus of FIG. 4A and 4B are views for explaining a method for estimating the degree of vacuum in the vacuum vessel.

Explanation of symbols

  1 ... vacuum container, 3 ... cathode.

Claims (2)

A vacuum level estimation method for estimating a vacuum level in a vacuumed vacuum container,
A process in which electrons are emitted from a cathode disposed in the vacuum vessel by a cold cathode field emission method, and an electron emission current, which is an amount of electrons emitted from the cathode at this time, is sequentially measured for at least a predetermined time period. In a state in which the temperature of the cathode is held at a predetermined temperature, and the time series data of the electron emission current values for the measured predetermined time period. And a step of estimating a degree of vacuum.   2. The method for estimating the degree of vacuum according to claim 1, wherein the step of estimating the degree of vacuum is performed on the cathode per unit time based on time-series data of the measured electron emission current values for a predetermined time period. And a step of estimating the number of molecules or atoms of the residual gas that has undergone physical adsorption, and the degree of vacuum in the vacuum vessel is estimated based on the estimated number.

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