CN102928154A - Method for reducing error in polar altitude vacuum measurement of ESD (Electro Simulated Desorption) neutral particles - Google Patents

Abstract

The invention discloses a method for reducing error in polar altitude vacuum measurement of ESD (Electro Simulated Desorption) neutral particles, and belongs to the field of measurement. Devices adopted in the method include a vacuum valve, an ionization gauge, a vacuum chamber, a vacuum pump group and a quadrupole mass spectrograph, wherein the vacuum valve, the ionization gauge, the vacuum pump group and the quadrupole mass spectrograph are respectively connected with the vacuum chamber; the quadrupole mass spectrograph is capable of separating electron excitation desorption ions and gas-phase ions and an energy analyzer is installed between an ion source and a quadrupole rod; the vacuum valve is of a full metal structure; and the lower measurement limit of the ionization gauge is 10-10Pa magnitude. By utilizing the method, the problem that in the full-pressure measurement, the ionization gauge and the like can effectively separate ESD ions and gas phase ions but cannot discriminate ions generated from ESD neutral particles doped in the gas phase ions is solved; the error in polar altitude vacuum measurement is reduced; and the lower limit in accurate measurement is extended.

Description

A Very High Vacuum Measurement Method for Reducing the Error of Electron Excited Desorption Neutral Particles

technical field

The invention relates to an extremely high vacuum measurement method for reducing the error of electron stimulated desorption (ESD) neutral particles, especially the ultrahigh/extremely high vacuum system realized by adopting a quadrupole mass spectrometer with an energy analyzer structure The invention relates to a method for measuring vacuum degree, which belongs to the field of measurement.

Background technique

The ESD effect on the grid surface of the hot cathode ionization gauge will generate ESD ions and ESD neutral particles, and the ESD ions and gas phase ions have an energy difference. The document "Development of Extremely High Vacuum Technology, "Aerospace Measuring Technology" Volume 29, Issue 5, 2009, Page 71-76", introduces a variety of effective separation of ESD ions, reducing the limiting factors of extremely high vacuum measurement That is, the extremely high vacuum ionization gauge of ESD effect. The literature pointed out that in the measurement of extremely high vacuum, the ESD effect, soft X-ray effect, and cathode outgassing effect are considered to be the main limiting factors affecting the lower limit of the extremely high vacuum measurement of hot cathode ionization gauges. Usually, very high vacuum ionization gauges with different structures The energy difference between ESD ions and gas phase ions is used to separate the two ions, so as to extend the lower limit of measurement and improve the measurement accuracy.

The advantage of using this type of extremely high vacuum ionization gauge for measurement is that it can effectively avoid measurement errors caused by ESD ions. The disadvantage is that when the ultimate pressure of the vacuum system is less than 10 ^-8 Pa, the ions produced by ESD neutral particles have the same energy as the gas phase ions, and usually the ESD neutral particle component is much larger than the ESD ion component. Such extremely high vacuum Ionization gauges cannot distinguish between ions generated by ESD neutral particles and gas-phase ions, and cannot achieve accurate measurement in extremely high vacuum.

Contents of the invention

The purpose of the present invention is to provide a very high vacuum measurement method that reduces the error of electronically excited desorption neutral particles. The method solves the problem that the separation gauge in the full pressure measurement can effectively separate ESD ions and gas phase ions, but cannot distinguish gas phase ions. The problem of ions generated by neutral doped ESD particles; the error of extremely high vacuum measurement is reduced, and the lower limit of accurate measurement is extended.

The purpose of the present invention is achieved by the following technical solutions:

A very high vacuum measurement method for reducing the error of electron-excited desorption neutral particles, the device used in the method includes: a vacuum valve, an ionization gauge, a vacuum chamber, a vacuum pump group and a quadrupole mass spectrometer; wherein, the vacuum valve, the ionization gauge , a vacuum pump group, and a quadrupole mass spectrometer are respectively connected to the vacuum chamber;

The quadrupole mass spectrometer is a quadrupole mass spectrometer equipped with an energy analyzer between the ion source and the quadrupole rod, which can separate electron-excited desorption ions and gas-phase ions;

The vacuum valve is an all-metal structure;

The measurement lower limit of the ionization gauge is on the order of ^10-10 Pa;

The method steps are as follows:

(1) Keep the vacuum valve closed, turn on the vacuum pump unit, and pump air into the vacuum chamber;

(2) When the vacuum degree of the vacuum chamber drops to the order of 10 ^-6 Pa, the whole device is baked and degassed. Rise to the respective maximum baking temperature and keep for 60-80 hours, wherein the maximum baking temperature of the vacuum valve, ionization gauge and quadrupole mass spectrometer is 150°C, and the maximum baking temperature of the vacuum chamber is 350°C; After the uniform rate of 30°C/h is gradually reduced to 150°C, the ionization gauge and quadrupole mass spectrometer are degassed for 3 to 5 minutes, and the vacuum valve, ionization gauge, vacuum chamber and quadrupole mass spectrometer are simultaneously degassed at a uniform rate of 30°C/h. to room temperature, then continue to pump air, measure the vacuum degree in the vacuum chamber with an ionization gauge, until the ultimate vacuum degree in the vacuum chamber reaches the order of magnitude of ^10-9 Pa, then turn off the vacuum pump group;

(3) Turn on the quadrupole mass spectrometer and stabilize for more than 1 to 3 hours;

(4) Set the reflector voltage in the energy analyzer of the quadrupole mass spectrometer to the corresponding voltage of the gas phase ions, so that only the gas phase ions and the ions generated by the electron-excited desorbed neutral particles can pass through, and record the ion currents corresponding to the peaks of different mass spectra value, and determine the gas composition in the vacuum chamber;

(5) Set the reflex electrode voltage in the energy analyzer of the quadrupole mass spectrometer to the voltage corresponding to the electron excitation desorption ion, so that only the electron excitation desorption ion can pass through, and record the electron excitation desorption ion flow corresponding to different mass number spectrum peaks value; and refer to the gas composition in the vacuum chamber determined in step (4) to determine the gas composition that may cause electron excitation to desorb ions and neutral particles;

(6) According to the gas composition determined in step (5) that may lead to the generation of electron-excited desorption ions and neutral particles, refer to the manual of the quadrupole mass spectrometer to provide the relative abundance coefficient of each fragment peak of the gas composition spectrum peak, and calculate the gas in the vacuum chamber The contribution of the components to the ion current value of each fragment peak;

(7) Subtract the calculation result of step (6) from the ion current value of the mass fragment peak corresponding to step (6) in step (4) to obtain the ion current value generated by the actual electronic excitation of desorbed neutral particles;

(8) Subtract the ion current value generated by the actual electronic excitation and desorption of neutral particles from the sum of the ion current values of each sub-pressure of the quadrupole mass spectrometer in step (4) to obtain an accurate and extremely high vacuum measurement result.

principle:

The method of the present invention utilizes the energy difference between ESD ions and gas-phase ions to realize the separation of the two. When the reflex electrode voltage in the energy analyzer is set to the corresponding voltage of the ESD ions, only the ESD ions can pass through; when the energy analyzer When the middle repeller voltage is set to the corresponding voltage of gas phase ions, only gas phase ions and ions produced by ESD neutral particles can pass through.

Beneficial effect

(1) The present invention measures the ion flow that ESD neutral particle produces by utilizing the quadrupole mass spectrometer quadrupole mass spectrometer that has energy analyzer structure, solves that separation gauge etc. can effectively separate ESD ion and gas phase ion in the full pressure measurement, but The problem of ion generation from doped ESD neutrals in gas phase ions cannot be distinguished.

(2) The method of the present invention reduces the error of extremely high vacuum measurement and extends the lower limit of accurate measurement.

Description of drawings

Fig. 1 is the device structure schematic diagram that method of the present invention adopts;

Among them, 1-vacuum valve, 2-ionization gauge, 3-vacuum chamber, 4-vacuum pump group, 5-quadrupole mass spectrometer.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments, but is not limited thereto.

Example 1

A very high vacuum measurement method for reducing the error of electron-excited desorption neutral particles, the device used in the method includes: a vacuum valve 1, an ionization gauge 2, a vacuum chamber 3, a vacuum pump group 4 and a quadrupole mass spectrometer 5; wherein, Vacuum valve 1, ionization gauge 2, vacuum pump group 4, and quadrupole mass spectrometer 5 are respectively connected with vacuum chamber 3, as shown in Figure 1;

The quadrupole mass spectrometer 5 is a quadrupole mass spectrometer 5 that is equipped with an energy analyzer between the ion source and the quadrupole rod to separate electron-excited desorption ions and gas-phase ions;

The vacuum valve 1 is an all-metal structure;

The measurement lower limit of the ionization gauge 2 is on the order of ^10-10 Pa;

The method steps are as follows:

(1) Keep the vacuum valve 1 closed, turn on the vacuum pump group 4, and pump air to the vacuum chamber 3;

(2) When the vacuum degree of the vacuum chamber 3 drops to the order of 10 ^-6 Pa, the whole device is baked and degassed. The uniform rate of /h rises to the respective maximum baking temperature respectively, and keeps for 72 hours, wherein, the maximum baking temperature of vacuum valve 1, ionization gauge 2 and quadrupole mass spectrometer 5 is 150°C, and the maximum baking temperature of vacuum chamber 3 is 350°C; after the vacuum chamber 3 gradually drops to 150°C at a uniform rate of 30°C/h, the ionization gauge 2 and the quadrupole mass spectrometer 5 are degassed for 3 minutes by using the degassing function of the control unit of the two, the vacuum valve 1, ionization Gauge 2, vacuum chamber 3 and quadrupole mass spectrometer 5 are simultaneously lowered to room temperature at a uniform rate of 30°C/h, and then continuously pumped for 48 hours, and the vacuum degree in vacuum chamber 3 is measured with ionization gauge 2 until the vacuum in vacuum chamber 3 When the ultimate vacuum reaches 8.26×10 ^-9 Pa, the vacuum pump group 4 is turned off, and the corresponding quadrupole mass spectrometer 5 gas phase ion current is 9.32×10 ^-12 A;

(3) Turn on the quadrupole mass spectrometer 5 and stabilize for 1 hour;

(4) Set the reflector voltage of quadrupole mass spectrometer 5 energy analyzer as the corresponding voltage of gas phase ions, that is, V _D =105V, perform analog spectrum scanning in the mass range of (1-50) amu, and record the corresponding gas phase ion current value ,As shown in Table 1:

Table 1

gas phase ions H ⁺ H ₂ ⁺ C ⁺ O ⁺ OH ⁺ H ₂ O ⁺ CO ⁺ O ₂ ⁺ Ion current value Ion current value (×10 ^-11 A) 1.97 83.02 0.56 2.53 0.66 1.40 2.63 0.47

(5) Set the reflector voltage of quadrupole mass spectrometer 5 energy analyzer as the corresponding voltage of ESD ions, that is, V _D =60V, perform analog spectrum scanning in the mass range of (1-50) amu, and record the corresponding ESD ion current value ,As shown in table 2:

Table 2

ESD ion H ⁺ H ₂ ⁺ O ⁺ Ion current value (×10 ^-11 A) 0.09 0.05 0.28

(6) According to the measurement results of steps (4) and (5), it is determined that the main gas components in the vacuum chamber 3 are H ₂ , O ₂ , H ₂ O, and CO;

(7) Determine the gas composition according to step (6). Refer to the quadrupole mass spectrometer 5 manual to provide the relative abundance coefficient of each fragment peak of the gas composition spectrum peak. For example, the relative coefficients of _H2 corresponding to each spectrum peak are H: 0.008, H2: 1.00 . The contribution of different gas molecules to the ion current value of corresponding ions can be calculated;

(8) Subtract the contribution of gas molecules in step (7) from the gas-phase ion current value containing the ESD neutral particle component to obtain the ion current value corresponding to the ESD neutral particle, as shown in Table 3:

table 3

ESD neutral particles h C o Oh Ion current value Ion current value (×10 ^-11 A) 1.17 0.42 2.28 0.26

(9) Subtract the ESD neutral ion current value from the ESD neutral ion current value in step (8) from the sum of the 5 sub-pressure ion current values of the quadrupole mass spectrometer in step (5), and obtain the extremely high vacuum measured ion current I=8.91×10 ^-12 A .

The present invention includes but is not limited to the above embodiments, and any equivalent replacement or partial improvement under the principle of the spirit of the present invention will be considered within the protection scope of the present invention.

Claims (5)

1. extra-high vacuum measuring method that reduces Electron Excitation desorption neutral particle error, it is characterized in that: described method step is as follows:

(1) opens vacuum pump group (4), vacuum chamber (3) is bled;

(2) be down to 10 when the vacuum tightness of vacuum chamber (3) ^-6During the Pa magnitude, whole device is carried out bakeout degassing, vacuum valve (1), ionization gauge (2), vacuum chamber (3) and quadrupole mass spectrometer (5) rise to respectively separately the highest baking temperature with 30 ℃/h uniform speed respectively, kept 60～80 hours, wherein, the highest baking temperature of vacuum valve (1), ionization gauge (2) and quadrupole mass spectrometer (5) is 150 ℃, and the highest baking temperature of vacuum chamber (3) is 350 ℃; After vacuum chamber (3) is down to 150 ℃ gradually with 30 ℃/h uniform speed, to ionization gauge (2) and quadrupole mass spectrometer (5) degasification 3～5 minutes, vacuum valve (1), ionization gauge (2), vacuum chamber (3) and quadrupole mass spectrometer (5) are down to room temperature with 30 ℃/h uniform speed simultaneously, then continuous air extraction, measure the interior vacuum tightness of vacuum chamber (3) with ionization gauge (2), until the final vacuum in the vacuum chamber (3) reaches 10 ^-9The Pa order of magnitude is closed vacuum pump group (4);

(3) open quadrupole mass spectrometer (5), stablize more than 1～3 hour;

(4) reflector voltage is the gaseous ion corresponding voltage in the energy analyzer of setting quadrupole mass spectrometer (5), so that the ion that only has gaseous ion and Electron Excitation desorption neutral particle to produce can pass through, ion flow valuve corresponding to record different quality number spectrum peak, and the gas componant in definite vacuum chamber (3);

(5) reflector voltage is Electron Excitation desorption ion corresponding voltage in the energy analyzer of setting quadrupole mass spectrometer (5), so that only have Electron Excitation desorption ion to pass through, and Electron Excitation desorption ion flow valuve corresponding to record different quality number spectrum peak; And vacuum chamber (3) composition of gases within of determining in the refer step (4) determines wherein may cause the gas componant of Electron Excitation desorption ion and neutral particle generation;

(6) gas componant that may cause Electron Excitation desorption ion and neutral particle to produce of determining according to step (5), provide gas componant spectrum peak each fragment peak relative abundance coefficient with reference to quadrupole mass spectrometer (5) handbook, calculate vacuum chamber (3) composition of gases within to the contribution amount of each fragment peak ion flow valuve;

(7) utilize the ion flow valuve of mass number fragment peak corresponding with step (6) in the step (4) to deduct the result of calculation of step (6), obtain the ion flow valuve that actual Electron Excitation desorption neutral particle produces;

(8) each partial pressure ion flow valuve sum of quadrupole mass spectrometer (5) deducts the ion flow valuve that actual Electron Excitation desorption neutral particle produces in the step (7) in the step (4), obtains accurate extra-high vacuum measurement result.

2. a kind of extra-high vacuum measuring method that reduces Electron Excitation desorption neutral particle error according to claim 1 is characterized in that: the device that described method adopts comprises: vacuum valve (1), ionization gauge (2), vacuum chamber (3), vacuum pump group (4) and quadrupole mass spectrometer (5); Wherein, vacuum valve (1), ionization gauge (2), vacuum pump group (4), quadrupole mass spectrometer (5) link to each other with vacuum chamber (3) respectively.

3. a kind of extra-high vacuum measuring method that reduces Electron Excitation desorption neutral particle error according to claim 1 is characterized in that: described quadrupole mass spectrometer (5) is for being equipped with the separable Electron Excitation desorption ion of energy analyzer and the quadrupole mass spectrometer (5) of gaseous ion between ion gun and the quadrupole rod.

4. a kind of extra-high vacuum measuring method that reduces Electron Excitation desorption neutral particle error according to claim 1, it is characterized in that: described vacuum valve (1) is all-metal construction.

5. a kind of extra-high vacuum measuring method that reduces Electron Excitation desorption neutral particle error according to claim 1, it is characterized in that: the measurement lower limit of described ionization gauge (2) is 10 ^-10The Pa magnitude.

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