KR100778383B1 - Apparatus for measurement of gas absorption characteristic of cryogenic pump absorption panel and method thereof - Google Patents

Abstract

An apparatus and a method for measuring gas absorption characteristic of a cryogenic pump absorption panel are provided to improve an exhaust method of a cryogenic pump by estimating exhaust capability of the cryogenic pump. An apparatus for measuring gas absorption characteristic of a cryogenic pump absorption panel includes an electronic gun(210), a sensor(240), and a calculating unit. The electronic gun is installed in a chamber and inputs an electronic beam to the absorption panel. The sensor is installed in the chamber and detects an ion flying time and the amount of ion output from the surface of the absorption panel. The calculating unit determines a sort of gas, absorbed in the absorption panel, and calculates the amount of the gas from the ion flying time and the amount of ion.

Description

Apparatus and method for measuring gas adsorption characteristics of cryopump adsorber {APPARATUS FOR MEASUREMENT OF GAS ABSORPTION CHARACTERISTIC OF CRYOGENIC PUMP ABSORPTION PANEL AND METHOD THEREOF}

1 is a schematic diagram of an apparatus for measuring gas adsorption characteristics of a cryopump adsorbent according to the present invention;

2 is a flowchart of a gas adsorption characteristic measurement method of a cryopump adsorber according to the present invention, and

3 is a graph showing the results measured by the present invention.

<Description of Symbols in Drawings>

100: gas adsorption characteristic measurement apparatus of cryo pump adsorbent

110: housing 110A: intake apparatus

110B: exhaust device 120: chamber

130: liquid nitrogen cooler 140: liquid helium cooler

150: absorbent 160: heat transfer member

170: thermometer 210: electron gun

220: metal mesh 230: micro channel plate

240: sensor 250: amplifier

260: signal detector 270: computer

The present invention relates to an apparatus and a method for measuring gas adsorption characteristics of a cryogenic pump or cryopump adsorbent, and more particularly, to measure the flight time of ions emitted by projecting an electron beam onto a low temperature surface of the adsorbent of a cryo pump. The present invention relates to an apparatus and a method for measuring gas adsorption and release characteristics of a cryo pump using a time of flight (TOF) method.

The cryo pump is a pump that physically adsorbs or condenses gas molecules to the surface of an object (adsorbent) cooled to cryogenic temperature, thereby creating a vacuum and evacuating it.

When gas molecules collide with the cryogenic adsorbent, the temperature of the gas molecules is lowered, and gas molecules cooled below the melting point condense on the adsorbent surface, and other gas molecules stay around the adsorbent in a slowed state. As a result, the gas molecules in the cryopump chamber gradually decrease, resulting in a lower pressure (good vacuum). The cryopump uses liquid nitrogen (melting point 63K) or liquid helium (melting point 4.2K) to cool the adsorbents such as metal surfaces, or coolers using compressed gas nitrogen or compressed gas helium. Use the method (about 15K for helium). These cryopumps are used as ultrahigh vacuum (10 ^-8 Pa or less) pumps.

In order to increase the pumping capacity of the cryo pump, the gas adsorbed on the low temperature surface of the adsorbent must stay long. The adsorption characteristic of the gas makes the exhaust pump and exhaust capacity of the cryo pump different. In particular, the measurement of adsorption and release characteristics of rare gases (Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), etc.)) on the adsorbent surface, which are the most active in the vacuum vessel and are difficult to exhaust, It is important to measure the pump performance.

However, since the cryopump is based on the fact that the gas is brought to a low temperature by heat exchange with the adsorbent and the movement speed decreases and is caught around the adsorbent, it is not easy to measure the amount of gas adsorbed around the adsorbent. not. In addition, due to the characteristics of the cryopump maintained in ultra-high vacuum, the amount of gas adsorbed around the adsorbent is small and it is not easy to measure it. In addition, since gas of various components is adsorbed or condensed around the adsorbent, it is difficult to distinguish and measure the adsorption characteristics of each gas component.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an apparatus and method for measuring the adsorption characteristics of the gas at the low temperature surface of the adsorbent of the cryopump. Moreover, an object of this invention is to be able to measure the adsorption characteristic according to the component of a gas.

In order to achieve this object, the present invention provides a gas adsorption characteristic measuring apparatus for cryopump adsorption material for cryopump including cryopump comprising a chamber, a cooler installed in the chamber, and an adsorbent contacted and cooled. An electron gun installed in the chamber to project the electron beam to the adsorbent in the configuration, a sensor installed in the chamber to detect the flight time and amount of ions released from the adsorbent surface, and the adsorbed material from the flight time and ion amount detected by the sensor Provided is a gas adsorption characteristic measurement apparatus for a cryopump adsorbent, comprising calculation means for calculating the kind and adsorption amount of the gas.

Such devices include microchannel plates installed between the adsorbent and the sensor to amplify the amount of ions released from the adsorbent surface, and copper and gold installed between the adsorbent and the microchannel plate to form a uniform electric field within the chamber of the cryopump. Or it may further include a mesh made of aluminum.

The present invention also provides a method for measuring gas adsorption characteristics of a cryopump adsorbent for a cryopump including a chamber, a cooler installed in the chamber, and an adsorbent contacted and cooled by the chiller, wherein the cooler is operated to adjust the temperature of the adsorbent to a predetermined temperature. Maintaining the following, injecting gas into the chamber and adsorbing the gas to the adsorbent, projecting an electron beam of the electron gun to the adsorbent surface, detecting the flight time and amount of ions released from the adsorbent surface, and detecting Comprising a step of calculating the type and amount of adsorption of gas adsorbed on the adsorbent by the flight time measurement method from the flight time and the amount of ions provides a method for measuring the gas adsorption characteristics of the cryopump adsorbent.

The method may further comprise amplifying ions released from the adsorbent surface using the micro channel plate.

The method may further comprise lowering the pressure in the chamber to a predetermined pressure value, preferably 10 ⁻⁸ Pa or less, using a pump attached to the exhaust of the chamber prior to operation of the cooler.

The present invention is particularly useful in the case of rare gases that are most active and difficult to evacuate in vacuum vessels.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention;

1 is a schematic diagram of an apparatus 100 for measuring gas adsorption characteristics of a cryopump adsorbent according to the present invention. The measuring device 100 is a configuration in which a component for measurement is coupled to a cryopump according to the prior art, and the configuration of the cryopump that can be applied is not limited to the configuration disclosed in the configuration of the present embodiment.

The measuring device 100 includes a housing 110 to which an intake device 110A and an exhaust device 110B are connected, a chamber 120 defined by the housing, a cooler 130 using liquid nitrogen, and a cooler 140 using liquid helium. ), An electron gun 210 to a cryopump including a heat absorbing member 160 and a thermometer 170 for heat transfer between the liquid helium cooler 140 and the absorbent 150 to which the low-temperature gas is condensed or adsorbed. ), A metal mesh 220, a micro channel plate (MCP) 230, a sensor 240, a signal amplifier 250, a signal detector 260, and a computer 270 for analysis.

The housing 110 defines a chamber 120 for ultra-vacuum therein, the intake apparatus 110A for inhaling gas from the outside at a relatively high pressure, and the pressure in the chamber prior to the operation of the cryopump. Exhaust apparatus 110B for regeneration of the cryopump is installed after the value is lowered or after operation of the cryopump.

The housing 110 should ensure the tightness of the chamber 120 and be able to reduce heat transfer from the outside. The housing 110 is preferably made of stainless steel with a small amount of gas escape from the housing itself.

The intake apparatus 110A is connected to the gas inlet. In the present invention for measuring the adsorption characteristics of the cryopump, it is preferable that rare gas which is difficult to adsorb is injected into the adsorption material 150, and in this embodiment, krypton (Kr) is injected.

The exhaust device 110B is connected to a pump to pre-press the pressure inside the chamber 120 to 10 ⁻⁸ Pa or less before the cryo pump operates in ultra low vacuum (10 ⁻⁸ Pa or less). Before the gas is adsorbed on the surface of the adsorbent 150, the vacuum degree of the chamber 120 should be 10 ⁻⁸ Pa or less to minimize the influence of impurities or residual gas in the chamber 120. As the pump connected to the exhaust device 110B, a rotary pump, a turbo molecular pump, or a combination thereof may be used. In this embodiment, a rotary pump and a turbo molecular pump are used in combination. Rotary pumps use a dry pump with low oil backflow. On the other hand, when the cryopump is operated for a long time, many gases are condensed or adsorbed around the adsorbent, thereby degrading the cryopump performance. In this case, the cryopump should remove gas condensed or adsorbed around the adsorbent through regeneration, and the exhaust device 110B is used to exhaust the removed gas.

In the chamber 120, coolers 130 and 140 using liquid nitrogen and liquid helium are installed. In this embodiment, the liquid nitrogen cooler 130 is used to lower the temperature of the adsorbent 150 to about 77K prior to the operation of the liquid helium cooler 140. When the temperature of the adsorbent 150 is maintained at about 77K by the liquid nitrogen cooler 130, the liquid helium cooler 140 operates to lower and maintain the temperature of the adsorbent 150 below about 17K.

The adsorbent 150 is used to condense or adsorb gas at very low temperatures. Adsorbent 150 is often a metal used in some cases adsorbent charcoal is bonded. In this embodiment, the adsorbent 150 is made of copper (Cu).

The liquid helium cooler 140 and the adsorbent 150 are connected by the heat transfer member 160. As the heat transfer member 160, a material having good thermal conductivity at cryogenic temperatures should be used, and in this embodiment, sapphire is used.

Then, a thermometer 170 for monitoring the temperature change of the adsorbent 150 during the operation of the measuring device 100 is installed.

The above configuration is an example of the configuration of the cryopump according to the prior art. It will be appreciated that the present invention is not limited to the above configuration.

In this configuration, the electron gun 210 for projecting the electron beam on the surface of the absorbent material 150 is further provided. Among the gas molecules adsorbed around the adsorbent 150, molecules that collide with electrons emitted from the electron gun 210 are ionized and are released from the adsorbent 150.

The ions emitted from the adsorbent 150 pass through the metal mesh 220 and the MCP 230 to the sensor 240 by the electric field generated by the MCP 230 and the sensor 240.

The metal mesh 220 forms a uniform electric field inside the chamber 120 and is used to pass ions at the same time. The metal mesh 220 may be made of copper (Cu), gold (Ag), aluminum (Al), and the like, and gold is used in the present embodiment.

The MCP 230 is used to amplify the ions released from the adsorbent 150.

Ions passing through the metal mesh 220 and the MCP 230 are detected by the sensor 240. The signal detected by the sensor 240 is transmitted to the amplifier 250 located outside the housing 110 and amplified, based on the time when the gas is ionized by the amplified signal and electrons from the electron gun 210. The time at which ions are detected, ie the flight time of ions, is counted by signal detector 260 by 240. The counted signal is sent to the computer 270.

Since the square of the flight speed of ions is proportional to the number of charges (e) of the ions and inversely proportional to the mass (or molecular weight (M)) of the ions, the flight time of the ions is proportional to (M / e) ^1/2 . Computer 270 can measure the molecular weight of ions from the flight time of ions and identify ions therefrom, and thereby calculate the components and amounts of gas adsorbed on adsorbent 150 surface.

Hereinafter, a method of measuring the adsorption characteristics of the cryopump adsorption material 150 using the apparatus 100 configured as described above will be described in detail with reference to the flowchart of FIG. 2.

First, the chamber 120 is inspected for leakage by a helium leak detector or the like, and a pressure in the chamber 120 is set by using a high vacuum pump such as a pump combining a turbo pump and a rotary pump connected to the exhaust device 110B. Pressure, preferably reduced to 10 ^-8 Pa or less (step S10). This is to minimize the influence by removing impurities or residual gas in the chamber 120 before the gas to be measured is introduced.

After injecting liquid nitrogen into the liquid nitrogen cooler 130 to maintain the adsorbent 150 temperature at about 77K (step S20), the liquid helium is injected into the liquid helium cooler 140 to lower the adsorbent 150 temperature to 17K or less. Keep (step S30). In this process the temperature is monitored by thermometer 170. By cooling to an intermediate temperature using the liquid nitrogen cooler 130 prior to cooling using the liquid helium cooler 140, it becomes possible to reduce the load on the liquid helium cooler 140 and make the liquid helium cooler 140 small. . However, it will be appreciated that the present invention is not limited to this two stage cooling.

Thereafter, the krypton gas is introduced through the intake apparatus 110A to adsorb the krypton gas to the adsorbent 150 (step S40). After the krypton gas is adsorbed to the adsorbent 150, the electron beam of the electron gun 210 is projected onto the surface of the adsorbent 150 (S50). At this time, the gas molecules collided with the electrons projected by the electron gun 210 may lose electrons and be ionized. Ions will be released from the adsorbent 150 by the electric field formed inside the chamber 120 and proceed to the sensor 240.

Ions emitted from the adsorbent 150 pass through the metal mesh 220 and are amplified by the MCP 230 (step S60).

The amplified ions are detected by the sensor 240 and converted into an electrical signal (step S70), and the electrical signals are amplified by the amplifier 250 until the ions are released from the adsorbent 150 and arrive at the sensor 240. It is counted in the signal detector 260 together with the time (flight time) of (step S80). The computer 270 determines the type of ions detected from the flight time and calculates the adsorption characteristics of the gas attached to the adsorbent 150 from the signal intensity for each ion (step S90).

3 is an intensity showing the flight time and ion detection intensity measured by the present invention. The horizontal axis represents the flight time in microseconds, the vertical axis represents the measured intensity and the (M / e) value is displayed for each peak. Krypton ions having an atomic weight (M) of 83.80 are detected in about 20 microseconds (Kr ²⁺ , M / e-42) and about 30 microseconds (Kr ⁺ , M / e-84). On the other hand, other ions detected (H ⁺ (M / e ~ 1), H ₂ ⁺ (M / e ~ 2), H ₂ O ⁺ (M / e ~ 18), H ₃ O ⁺ (M / e ~ 19 ), CO ⁺ (M / e ~ 28)) is estimated to be due to the effect of water (H ₂ O) or carbon dioxide (CO ₂ ), which condensed on the surface of the adsorbent 150 and not completely removed in advance. The krypton gas adsorption characteristics of the adsorbent 150 may be measured by calculating the amount of krypton gas adsorbed on the adsorbent 150 from the detected strength of the krypton ion. Although the present embodiment has described the case where only krypton gas is introduced, even when the gas mixture is introduced, it is possible to separately measure each component of the gas mixture by the flight time measurement method.

The present invention provides an apparatus and method capable of measuring the adsorption characteristics of gases at low temperature surfaces of adsorbents of cryopumps. It is possible to measure adsorption characteristics in various environments by changing various kinds of conditions such as the type of gas, the temperature of the adsorbent, the constituent material of the adsorbent, the intake amount of the cryopump or the intake time. The present invention can help to improve the cryo pump's exhaust technology by predicting the cryo pump's exhaust capacity from the measured adsorption characteristics.

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it will be readily apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the invention, and all such changes and modifications are It is obvious that it belongs to the scope of the appended claims.

Claims (9)

An apparatus for measuring gas adsorption characteristics of a cryopump adsorbent for a cryopump comprising a chamber defined by a housing, a cooler installed in the chamber, and an adsorbent contacted and cooled by the chiller, the apparatus comprising: An electron gun installed in the chamber to project an electron beam onto the adsorbent; A sensor installed in the chamber to detect a flight time and an amount of ions of ions released from the surface of the adsorbent; And And calculating means for calculating the type and amount of adsorption of the gas adsorbed on the adsorbent from the flight time and the amount of ions detected by the sensor. The apparatus of claim 1, further comprising a micro channel plate provided between the adsorbent and the sensor to amplify the amount of ions released from the surface of the adsorbent. 3. The apparatus of claim 2, further comprising a metal mesh provided between the adsorbent and the microchannel plate to form a uniform electric field in the chamber of the cryopump. The gas adsorption characteristic device of a cryopump adsorber according to claim 3, wherein the metal mesh comprises gold. A method of measuring gas adsorption characteristics of a cryopump adsorbent for a cryopump comprising a chamber defined by a housing, a cooler installed within the chamber, and an adsorbent contacted and cooled by the chiller, the method comprising: Operating the cooler to maintain the temperature of the adsorbent below a predetermined temperature; Injecting gas into the chamber and adsorbing gas to the adsorbent; Projecting an electron beam of an electron gun onto a surface of the adsorbent; Detecting the flight time and the amount of ions released from the surface of the adsorbent; And And calculating the type and amount of adsorption of the gas adsorbed on the adsorbent by the flight time measurement method from the flight time and the amount of ions of the detected ions. 6. The method of claim 5, further comprising amplifying the ions released from the surface of the adsorbent using a micro channel plate. 6. The cryopump adsorbent of claim 5, further comprising lowering the pressure in the chamber to 10 ^-8 Pa or less using a pump attached to the exhaust of the chamber prior to operation of the cooler. Method for measuring gas adsorption characteristics of delete The gas adsorption characteristic measurement method of a cryopump adsorbent according to claim 5, wherein the gas adsorbed on the adsorbent is a rare gas.

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