JP3750767B2 - Ion pump - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In the present invention, gas molecules or atoms remaining in a vacuum are ionized by collision of electrons, and the generated ions are accelerated by the action of an electric field applied between two electrodes, the cathode and the anode, and collide with the cathode surface and captured. The present invention relates to a sputter ion pump configured to reduce the number of residual gas molecules or atoms, and an ion pump similar thereto.
[0002]
[Prior art]
Ion pumps that can be operated only by electrical control are widely used as vacuum pumps that are indispensable for creating ultra-high vacuum or clean vacuum free from oil contamination. However, conventionally, an ion pump that ionizes residual gas molecules or atoms in a vacuum and actively pumps the ions has not yet appeared, and currently available ion pumps do not perform sputtering action during ion bombardment. This is a sputter ion pump that uses a secondary phenomenon.
[0003]
This sputter ion pump is composed of a Penning cell named after the inventor. This cell consists of two parallel cathodes and a cylindrical anode placed between them, the axis of the anode being perpendicular to the parallel plane of the cathode. An electric field of several kilovolts is applied between the anode and the cathode, and the pumping action is sustained by a discharge in which a magnetic field of about kilogauss is applied in the direction of the anode axis. Electrons generated by the discharge are trapped in a potential valley formed by an electric field and a magnetic field in the cylinder, and efficiently ionize residual gas molecules while performing a spiral motion. Residual gas molecules are evacuated by accelerating the generated ions by the action of an electric field and striking them into the cathode. (1) Ion implantation action and fresh metal formed in and around the electrode by sputtered cathode material atoms during ion collision The active gas is adsorbed on the film (2) The chemical adsorption action, and further, the gas molecules are embedded in the solid by the effect of entrapment of neutral fragment molecules and atoms generated by sputtering. (3) Three actions of deposition action Has been exhausted by.
[0004]
[Problems to be solved by the invention]
However, in the conventional evacuation action, when the gas is evacuated by the ion implantation action of (1), the gas molecules previously embedded on the cathode appear again on the surface as the sputtering progresses and are re-emitted. The problem arises that it is only temporarily stable capture.
[0005]
In order to solve this problem, the main exhaust of the sputter ion pump is performed by (2) chemical adsorption. (2) In order to perform exhaust by chemisorption, as a cathode material, representative gas molecules remaining in vacuum, hydrogen, methane, water, nitrogen, carbon monoxide, oxygen, carbon dioxide, hydride, Titanium metal or the like that can be chemisorbed and fixed to the cathode in the form of a compound such as an oxide, nitride, or carbide is used.
[0006]
Further, chemically inert helium and argon gas is mainly exhausted by (3) deposition effect.
[0007]
However, the exhaust rate for the inert gas is about 1-2% of the exhaust rate of nitrogen or oxygen exhausted by (2) chemisorption, and this is the biggest drawback of the ion pump.
[0008]
In order to solve such a problem that the exhaust speed with respect to the inert gas is small, (3) a method of increasing the exhaust speed with respect to the inert gas by increasing the deposition effect has been attempted. As one of the methods, there is a method in which unevenness is formed on the cathode to improve ion sputtering efficiency and increase the deposition rate to prevent re-emission.
[0009]
In addition, as a second method, the cathode is formed in a honeycomb lattice shape, and a tripolar structure in which a new collector for depositing neutral sputtered atoms is added to the back side of the cathode, and ions having high energy are decelerated, There is a method for preventing re-emission by preventing high-speed ions from bombarding the collector.
[0010]
However, in the method as described above, the structure of the cathode is complicated and the depth in the direction of the magnetic field is increased, so that a stronger magnet is required, the entire apparatus is enlarged, and the life cycle of the apparatus is also increased. There is a problem of shortening and increasing the cost.
[0011]
The sputter ion pump can exert its effect in a state where the partial pressure of high mass atoms such as argon gas having a high sputter yield is high. The problem is that the speed is significantly reduced. In particular, in the case of light atoms or molecules such as helium and hydrogen, the sputtering yield is very small, and the atoms or molecules themselves are easily backscattered. In other words, it becomes a gas emission source for re-emissioning the gas exhausted in a low vacuum state.
[0012]
On the other hand, the exhaust by the ion implantation action (1) has caused the following problems.
[0013]
In general, the vacuum pump is often exposed to the atmosphere, and the active oxygen in the atmosphere at this time is preferentially chemically adsorbed on the cathode surface, so that the cathode surface is covered with a thick oxide layer. The thickness of this oxide layer depends on the exposure time, humidity and temperature, but may reach 100 angstroms or more.
[0014]
Since the oxide layer has a very high water adsorptivity and is quite porous, argon, hydrocarbons, etc. present in the atmosphere are simultaneously adsorbed on the cathode surface.
[0015]
For example, conventionally, in order to reduce the gas released from the ion pump, the entire vacuum apparatus including the pump is baked. When baking at about 200 ° C. to 450 ° C. for normal exhaust is performed, weakly bonded gas molecules physically adsorbed on the cathode surface are easily desorbed from the cathode. However, the oxide film formed on the cathode surface by chemical adsorption is not removed from the ion pump by baking at a low temperature of 450 ° C. or lower, and on the contrary, the surface is transformed into a dense and hard oxide film. The hydrocarbons taken into the oxide layer in the process of alteration remain on the cathode surface in the form of carbides.
[0016]
Further, since the depth at which ions accelerated at several kilovolts can penetrate the solid surface is at most several tens of angstroms, (1) exhaust by ion implantation at the start of the sputter ion pump is performed on this oxide layer. It will be. However, the gas solubility of the oxide layer is 1/100 to 1/1000 (see Iwanami Shoten “Physics of Ultra High Vacuum” on pages 98 to 100) compared to metals, etc. The amount of gas molecules that are exhausted by the gas, that is, the amount of gas that can be dissolved in the oxide layer is very small, and since the saturation value is reached immediately and gas re-emission occurs, the exhaust speed of the ion pump decreases immediately. Produce.
[0017]
In the case of (1) ion implantation, since a portion of the oxide film is destroyed by ion bombardment at the same time as ion implantation, radical fragment molecules having extremely high chemisorbability including ions are present at a solid angle of 180 °. There is a problem that it scatters in the cell, contaminates the surrounding area and causes vacuum deterioration. These fragment molecules are ionized again in the cell and accelerate, resputtering the cathode and reoxidizing the cathode surface with the simultaneously generated neutral radical species.
[0018]
Along with the simultaneous progress of the oxide layer destruction and re-oxidation due to the above-mentioned sputtering, the cathode oxide film in the center of the cell gradually becomes thinner, and the cathode metal atoms themselves are sputtered.
[0019]
Only after this state is reached, the sputter ion pump begins to exhaust by the chemical adsorption action shown in (2).
[0020]
For this reason, various problems as described below occur.
[0021]
First, since a large amount of harmful gas is discharged into the vacuum chamber at the start of sputtering, the vacuum device is contaminated.
[0022]
Secondly, since the oxide surface remains on the cathode surface other than the central part of the cell, (2) no exhaustion by chemisorption occurs, and even if an inert gas is ion-implanted, it is an oxide layer. The amount of dissolution is orders of magnitude smaller.
[0023]
Third, only metal atoms sputtered from the center of the cell can contribute to (2) exhaust by chemisorption, but in a state where the number of pollutant gas molecules has decreased after the destruction of oxide at the center, Since the vacuum is improved, the number of cathode metal atoms to be sputtered is reduced, and the exhaust speed for residual gas molecules in the vacuum apparatus is lowered.
[0024]
Fourthly, since only pure metal is sputtered only at the center of the cell, the metal consumption of this portion increases, and as erosion progresses, holes are opened. Therefore, the thickness of the cathode material is increased by 1 mm or more. There must be. When the plate thickness of the cathode material is increased to 1 mm or more, the utilization efficiency of the cathode material becomes very bad and a problem arises that it becomes a gas source.
[0025]
Fifth, an inert gas such as argon or helium is exhausted by (3) deposition effect when it is taken in between the fragment molecules due to the simultaneous progress of this oxide destruction and re-adsorption oxidation. In the state where the oxide breakdown due to (3) is finished, (3) the exhaust speed for the inert gas due to the deposition effect becomes extremely small.
[0026]
Sixth, (3) an inert gas such as argon or helium exhausted by the deposition effect is sandwiched between sputtered neutral fragment molecules inside the cell where ions do not fly, such as the edge of the cathode and the surface of the anode. Captured. Metals that are prone to spatter, and the three-pole structure of an uneven cathode and a honeycomb lattice cathode that are easily sputtered are only captured in a state where an inert gas is sandwiched between molecules. For this reason, the structure such as the uneven cathode has a weak trapping force for the inert gas, and even when the temperature rises slightly, the trapping molecules leave the solid surface, and the inert gas is likely to be re-released.
[0027]
Seventh, the only exhaust action left in the inert gas when the pressure is reduced is (1) exhaust by ion implantation, but most of the cathode surface has an oxide layer with an order of magnitude lower gas solubility. The exposed metal surface with high gas solubility is only at the center of the cell, and this part is the place where gas re-emission is most likely to occur due to ion bombardment. When the vacuum region is reached, the exhaust speed for the inert gas becomes zero.
[0028]
As described above, the conventional sputter ion pump has a defect that the exhaust speed is lowered as the vacuum is improved, and the exhaust speed with respect to the inert gas is lowered and is almost lost in the ultra-high vacuum.
[0029]
This is because (2) chemisorption of atoms sputtered by ion bombardment, rather than (1) exhausting the ionized ion atoms or molecules present in the ion pump directly into the cathode metal by ion implantation. (3) It is thought that this is because it relies on the exhaust action due to the secondary phenomenon of the deposition action.
[0030]
In addition, (1) the biggest factor that makes it impossible to exhaust the cathode to the metal by the ion implantation action is considered to be that the cathode material surface of the ion pump is covered with an oxide film.
[0031]
Therefore, in view of the above problems, the present invention prevents the generation of contaminating sputtered debris molecules at the start of the pump, and (2) chemical adsorption action and (3) deposition by chemical bonding between residual gas molecules or atoms and sputtered atoms. The function to suppress the trapping of inert gas by the action and to inject ionic atoms and ionic molecules directly into the cathode for dissolution and diffusion by providing means for removing oxide on the cathode surface and reducing the surface impurity concentration. An ion pump that improves the pumping speed for inert gas, reduces the pumping speed difference due to the difference between the active gas and the inert gas species, and improves the decrease in pumping speed in low pressure ultra-high vacuum The purpose is to provide.
[0032]
[Means for Solving the Problems]
In the invention described in claim 1 of the present application, gas molecules or atoms remaining in a vacuum are ionized by electron collision, and the generated ions are accelerated by the action of an electric field applied between two electrodes, an anode and a cathode. In the ion pump that reduces the number of gas molecules or atoms remaining in the vacuum by being collided with and captured by the cathode surface, regardless of the presence or absence of an acceleration electric field by application, There is provided means for energizing a part or all of the material forming the cathode and increasing the temperature of the cathode to 500 ° C. or more by self-heating of the cathode itself. It is an ion pump of composition.
[0033]
Thus, the ion pump of the present invention, regardless of the presence or absence of an acceleration electric field by application, By energizing a part or all of the material forming the cathode and raising the temperature of the cathode to 500 ° C. or more by self-heating of the cathode itself, hydrogen or carbon atoms dissolved in the cathode material itself are removed. The cathode surface oxide can be decomposed by heat and reacted with the cathode surface oxide to promote decomposition or reduction, thereby removing the cathode surface oxide. In addition, if the present invention is used, even if the pump is operated after being exposed to the atmosphere, the oxide on the cathode surface can be removed in advance by energization to expose the metal surface of the cathode. Thereafter, by applying an acceleration voltage, the remaining gas molecules or atoms can be ionized, and the ions can be directly implanted into the metal surface. For this reason, unlike the conventional case, generation of sputtered fragment molecules due to oxide breakdown during ion implantation can be prevented, and vacuum deterioration and peripheral contamination can be prevented. Furthermore, the removal of surface oxides can be extended not only to the center of the cathode as in the prior art, but also to the region in front of the cathode. Can be injected and diffused, can greatly increase the exhaust speed .
[0037]
In this case, the decomposition reaction or reduction reaction is a quiet reaction between an oxide of hydrogen or carbon dissolved in the cathode material itself and an oxide, so that water or carbon monoxide is generated even if the reaction is accelerated. However, it is possible to eliminate the generation of fragment molecules due to radical sputtering as in the prior art and to prevent contamination around the cell.
[0038]
Moreover, since the thermal diffusion inside the metal of hydrogen or carbon atoms and ion-implanted gas atoms becomes active by raising the temperature of the cathode to 500 ° C. or higher, the amount of inert gas that can be exhausted by ion implantation is increased. Compared with the conventional method, the size can be increased by orders of magnitude.
[0041]
No. of this application 2 The invention recited in the claims is directed to the claims. 1 In the described invention, The means for raising the temperature is: Connected to the open ends of a connection cathode formed by connecting multiple cathodes in series Power supply It is an ion pump of the structure which is a means using the simultaneous heat_generation | fever by electricity supply from.
[0042]
As described above, when a plurality of cathodes are used, since the cathodes can be heated by energization heating from the open ends of the connection cathodes by using the connection cathodes in which the cathodes are connected in series, there are many cathodes. Even in this case, it is possible to energize all at once by adding one or two vacuum terminals with the same current standard for energization to the pump wall, and achieve the purpose of raising the cathode temperature using a simple structure. Can do.
[0043]
No. of this application 3 The invention described in claim 1 is the invention described in claim 1. Or 2 In the described invention, the cathode is an ion pump having a planar shape approximating a substantially cross section of the anode and formed in a plate shape having a thickness of 0.1 mm or less.
[0044]
Thus, when the cathode is formed in a thin plate shape having a thickness of 0.1 mm or less, the resistance can be increased, so that it is easy to heat to a high temperature of 500 ° C. or more with a small current.
[0045]
No. of this application 4 The invention described in the claims is the first to the first aspects. 3 In any one of the inventions, the cathode has a hydrogen gas solubility at room temperature of 1.0 cm. ² (STP) cm ^-1 atm ^-1 ] And the sputtering yield by argon ions of 5 KeV is 2.0 or less Simple metal And the ion pump of the structure currently formed using the alloy containing those metals.
[0046]
Thus, hydrogen gas solubility is high Simple metal When the cathode is formed using an alloy containing these metals, the amount of hydrogen dissolved in the metal is large in each metal. By diffusion, the surface oxide can be reduced, and the oxide can be released into the vacuum as water molecules, and the subsequent ion implantation action can be improved.
[0047]
In addition, since the metal having a high hydrogen solubility tends to have a high solubility for dissolving argon or helium gas, a large amount of exhaust gas can be absorbed.
[0048]
Furthermore, since the metal having a high hydrogen solubility tends to have a low sputtering yield, the rate of erosion of only the central portion of the cathode is reduced, and the cathode thickness can be reduced. As described in the fifth aspect, the cathode can be formed into a thin plate having a thickness of 0.1 mm or less. Moreover, the ratio of the inert gas trapped with a weak trapping force can be reduced by the deposition effect by the sputtered atoms.
[0051]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific examples of the present invention will be described in detail with reference to the drawings.
[0052]
FIG. 1 shows a schematic configuration diagram of an ion pump according to a specific example of the present invention.
[0053]
As shown in FIG. 1, in this example, the ion pump 21 is formed by arranging three penning cells. The anode 22 of the ion pump 21 is a triple anode in which the circumferences of the three anodes 22 of the metallic cylinders A 1, A 2, A 3 are integrated with each other, and are arranged outside the vacuum through the vacuum terminal 23. It is connected to the positive side of the high-voltage power supply E1.
[0054]
Further, the cathode 24 of the ion pump 21 has high hydrogen solubility, and is a high melting point metal disk, and one set of two disks per cell consists of three sets K1, K1 ', K2, K2', K3, K3 'is arranged in parallel to the positions on both sides corresponding to the cylinders A1, A2, A3 of each anode 22. That is, since there are three sets of two disks, a total of six disk-shaped cathodes are arranged with K1, K2, K3 on one side with the anode 22 in between, and K1 ', K2 'and K3' are arranged. These continuously arranged cathodes are connected in series by a long cathode connection line 25 to form one connection cathode 26.
[0055]
In addition, the triple Penning cell of this example is installed in the magnetic field B formed in the up-down direction.
[0056]
Further, in this example, the case of three stations has been described. However, when a single cell is used, two disks are connected as cathodes, and in the case of a plurality of n cells, 2n disks are connected by a cathode connection line. A cathode will be formed.
[0057]
In addition, a metal plate having the same width as the cylindrical diameter of the anode may be bent in a U shape so as to sandwich the anode in parallel, and used instead of the connection cathode as described above.
[0058]
Both ends of the connection cathode 26 are connected to a heating power source E2 outside the vacuum through vacuum terminals 27 and 28 to form an electric loop. Independent of the application of the high-voltage power supply E1, the cathode 24 can be energized and heated arbitrarily by opening and closing the switch S2. One vacuum terminal 28 coupled to both ends of the connection cathode 26 is connected to the negative side of the high-voltage power supply E1. Therefore, an electric field can be freely applied between the anode 22 and the cathode 24 by opening and closing the ion acceleration field switch S1.
[0059]
Further, when the ion pump 21 is exposed to atmospheric pressure and evacuation is started from the atmospheric pressure, an oxide film 241 is formed on the surface of each cathode 24 in the ion pump 21.
[0060]
Since the connection cathode 26 formed of six disks as in this example is a loop circuit provided with a heating power source E2, regardless of whether or not the high voltage power source E1 is applied, that is, whether the switch S1 is opened or closed, By adjusting the voltage of the heating power source E2, the disks K1, K1 ′, K2, K2 ′, K3, K3 ′ of the connection cathode 26 can be heated to 500 ° C. or higher. In particular, when the connection cathode 26 is heated to a high temperature of about 800 ° C., the thermal diffusion of hydrogen atoms dissolved in each cathode 24 becomes very active, so that hydrogen easily diffuses to the cathode surface. On the solid surface, the oxide is reduced in the form of the chemical reaction described below.
[0061]
MO (oxide film) + 2H (diffusion hydrogen atom) → H ₂ O (water) + M (metal)
Thus, since the oxide film (MO) is reduced by the diffusion of hydrogen dissolved in the cathode, the metal (M) surface of the cathode 24 is exposed in vacuum.
[0062]
After that, when the switch S1 is closed and an accelerating electric field is formed between the anode 22 and the cathode 24, discharge occurs in each cell between the two electrodes 22, 24, and is generated in the cylinders A1, A2, A3 of the anode 22. The cations are accelerated toward the cathode 24 and injected into the metal surface of the cathode 24 to be captured.
[0063]
When the surface concentration increases due to gas molecules and gas atoms trapped on the surface of the cathode 24, when a current is again supplied from the heating power source E2 to each cathode 24, the temperature of the cathode 24 is raised to about 500 ° C to 600 ° C. Further, the thermal diffusion of trapped gas molecules or gas atoms into the cathode 24 is promoted, so that the impurity concentration on the surface of the cathode 24 can be lowered. In this case, some of the gas molecules or gas atoms trapped by the cathode 24 are re-emitted, but by operating the ion pump 21 with the switch S1 of the high-voltage power supply E1 kept closed, The exhaust can be immediately performed simultaneously with the re-release, and the exhaust speed can be improved.
[0064]
For example, if the cathode 24 is kept at a high temperature of 800 ° C. or higher, this temperature is sufficient to allow the inert gas on the surface that has reached saturation by ion implantation to be re-emitted into the vacuum. The pump 21 can be regenerated and consumption of the cathode material can be suppressed.
[0065]
The material of the cathode 24 has a hydrogen gas solubility at room temperature of 1.0 [cm. ² (STP) cm ^-1 atm ^-1 ]More than Simple metal In addition, when an alloy containing these metals is used, these metals are refractory metals that can be heated to 1000 ° C. or higher, so that a large amount of diffused hydrogen is generated and the surface oxide 241 is formed in a short time. By reducing, the metal surface of the cathode 24 can be exposed in vacuum, and the exhaust speed can be improved.
[0068]
In this example, an example of a Penning cell type ion pump conventionally used for a sputter ion pump has been shown. However, the present invention is not limited to the Penning cell type and can be used for an orbitron type ion pump that does not use a magnetic field. is there.
[0069]
Next, the result of an experiment in which the exhaust of the vacuum apparatus was actually measured in the vacuum apparatus 1 shown in FIG. 2 equipped with the ion pump of the sputter ion pump type described in FIG. 1 will be described based on the drawings.
[0070]
FIG. 2 is a schematic configuration diagram of the vacuum apparatus 1 on which the ion pump 2 is mounted, and FIG. 3 is a perspective view illustrating a schematic configuration of the single-cell ion pump 2 mounted on the vacuum apparatus 1 used in this experiment. is there.
[0071]
As shown in FIG. 2, in the vacuum apparatus 1, a tantalum metal single cell type ion pump 2 described later is installed in a vacuum chamber 3. In addition to the ion pump 2, a non-evaporable getter pump (NEG pump) 4 having a displacement of 100 liters / second, a BA gauge 5, and a quadrupole residual gas analyzer 6 are attached to the chamber 3.
[0072]
The chamber 3 is provided with a turbo molecular pump 7 and a rotary pump 8 which are roughing systems via a metal cut valve 9. When the valve 9 is closed, the total volume of the vacuum vessel 1 including the gauge 5 and the residual gas analyzer 6 is 2 liters.
[0073]
Further, a minute leak valve 10 is attached to the chamber 3, and pure argon gas or pure helium gas can be introduced into the vacuum chamber 3 from the gas cylinder 11 through the leak valve 10.
[0074]
2, 12 and 12 are permanent magnets for the ion pump 2 placed outside the vacuum apparatus, and the magnetic flux density at the center between the two magnetic poles of the permanent magnets 12 and 12 is 2.3 kilogauss.
[0075]
As shown in FIG. 3, the ion pump 2 of this example is a single cell type ion pump constituted by one cylinder A 1 of the anode 22 and a set of disks K 1 and K 1 ′ of the cathode 24. 3 represents the oxide 241 on the surface of the cathode 24.
[0076]
This ion pump 2 uses a cylinder A1 obtained by rolling a tantalum metal plate having a thickness of 0.1 mm as the anode 22, and the cylinder has a diameter of 7 mm and a height of 5 mm. Further, as the cathode 24, tantalum metal plate disks K1, K1 ′ having a thickness of 0.1 mm are used, and the diameter of the disk is 8 mm. Further, the cathode connection line 25 for connecting the disks K1, K1 ′ is also made of a tantalum metal plate having a width of 2 mm.
[0077]
The cylinder A1 of the anode 22 is connected through the vacuum terminal 23 to the plus side of the 5 KV high-voltage power supply E1 via the switch S1. The two disks K1, K1 ′ of the cathode 24 are connected by a cathode connection line (plate) 25, and the other end is connected to the heating power source E2 through the vacuum terminals 27, 28 via the switch S2.
[0078]
Either the negative side of E1 or E2 is connected to the ground potential, that is, the vacuum apparatus 1.
[0079]
Next, an experimental method and experimental results using the vacuum apparatus 1 will be described with reference to the drawings.
[0080]
FIG. 4 shows the pressure drop due to the exhaust of the ion pump of this example with respect to argon, and shows the relationship between the argon gas pressure (Pa) and time (minutes). FIG. 5 shows the cathode rise of the argon once exhausted. It is a figure which shows the re-emission accompanying temperature and shows the relationship between argon gas pressure (Pa) and the temperature of a cathode (° C.).
[0081]
First, when exhausting from the atmospheric pressure, the cut valve 9 of the vacuum apparatus 1 shown in FIG. ^-6 Exhaust to Pa. Thereafter, the chamber 3, the ion pump 2, the NEG pump 4, the gauge 5, the residual gas analyzer 6, and the valves 9 and 10 are baked and exhausted at 250 ° C., and the NEG pump 4 is activated. When cooled and left at room temperature, chamber 3 is 10 ^-9 It reaches the ultra high vacuum state of Pa level. When the valve 9 is closed in this state, the vacuum state is somewhat deteriorated. ^-8 The value is almost constant at Pa level. The main components of the residual gas at this time are hydrogen, methane, carbon monoxide, and argon.
[0082]
Next, this 10 ^-8 About 2 × 10 pure argon gas from the ultra-vacuum state on the Pa level through the leak valve 10 ^-Four Introduced up to a pressure of Pa. At this time, since the NEG pump 4 does not exhaust argon at all, 99.9% of the residual gas becomes argon gas. Further, even if the vacuum chamber 3 is left in this state, the pressure hardly changes.
[0083]
In this state, when the switch S1 of the circuit of the ion pump 2 shown in FIG. 3 is closed and a 5 KV electric field is applied between the cylinder A1 of the anode 22 and the disks K1 and K1 ′ of the cathode 24, a discharge is generated between the two electrodes. The electrons generated by the discharge are trapped in the valley of the potential formed by the electric and magnetic fields in the cylinder. The trapped electrons efficiently ionize argon atoms while performing a spiral motion.
[0084]
Immediately after the exhaust is started, the oxide film formed on the surfaces of the disks K1 and K1 ′ of the cathode 24 is destroyed by the sputtering of argon ions. At this time, a large amount of polluted gas is released, and the pressure is 1 × 10 once. ^-3 It rises rapidly to Pa. Thereafter, the pollutant gas gradually begins to drop due to the pump action. 10 ^-3 When observing the partial pressure at the time of a rapid pressure rise in the Pa range, carbon monoxide, water, methane, various hydrocarbons, oxygen, etc. are observed, whereas the argon partial pressure decreases rapidly. Yes. After that, the overall pressure gradually decreased and 1 × 10 ^-6 It will not drop below that at Pa. The residual gas component under this pressure contains methane and argon at almost the same rate. 1 × 10 ^-6 The time required to reach Pa is about 30 minutes, and the change in the argon gas pressure (Pa) during this period is shown by a curve O in FIG.
[0085]
The active pollutant gas released immediately after the start of exhaust is exhausted by the NEG pump 4 in addition to the ion pump of this example. However, since the NEG pump 4 does not exhaust any argon, the curve O in FIG. An exhaust velocity curve for argon gas in a state where the oxide films of 22 disks K1 and K1 ′ are not removed is shown.
[0086]
In this case, the partial pressures of methane, water, carbon monoxide, etc. released immediately after the start of exhausting also decrease at the same rate as the argon partial pressure. Therefore, the exhaust operation from the state where the oxide film 241 is not removed is performed by conventional sputtering. It can be seen that it works the same as the ion pump. That is, it can be confirmed that the argon ions are exhausted by the deposition effect due to the action of this pollutant gas while stripping the surface oxides 241 of the disks K1, K1 ′ of the cathode 24 made of tantalum metal.
[0087]
1 × 10 with stable argon partial pressure ^-6 When the switch S1 is opened at Pa, the pump is stopped and left for several hours, the pressure of the system is about 1.5 × 10 ^-6 Slightly increases to Pa.
[0088]
From this state, only the switch S2 is closed (at this time, the high-voltage power switch S1 is opened), and a current is passed through the disks K1, K1 'of the cathode 24 to gradually raise the cathode temperature and re-emit from the cathode. Measure the pressure increase of the argon gas.
[0089]
The measurement result in this case is as shown by curve X in FIG. The cathode temperature is measured by attaching a thermocouple thermometer on the back side of the cathode. When the cathode temperature reaches 600 ° C., argon is 100% re-released and the argon partial pressure rises to the same pressure as before evacuation. This is because the argon atoms trapped by the anode 22 with a trapping force weaker than the deposition effect as well as the argon atoms exhausted on the surface layers of the disks K1 and K1 ′ of the cathode 24 are all radiated by the radiant heat of the cathode 24. This is thought to be due to release. At the same time, a large amount of water, carbon monoxide, carbon dioxide, methane, and the like are released, and these gases are also released. Therefore, the pressure of the entire vacuum apparatus 1 is 10 when argon is introduced. ^-Four 10 orders of magnitude higher than Pa ^-3 It rises to Pa level.
[0090]
Next, experimental results using the means for removing oxide and reducing the surface impurity concentration of this example will be described.
[0091]
First, after the cut valve 9 of the vacuum apparatus 1 shown in FIG. 2 is opened, a current is passed between the vacuum terminals 27 and 28 of the ion pump 2 and the disks K1 and K1 ′ of the cathode 24 to set the temperature of the cathode 24 to 800 ° C. Raise to above and hold for about 1 minute. At this time, a large amount of hydrogen, water, and carbon monoxide are released, but the release of these gases is almost completed in about 10 seconds.
[0092]
At this time, the generated water and carbon monoxide are considered to be discharged by the reaction represented by the following reaction formula.
[0093]
MO (oxide film) + 2H (thermal diffusion hydrogen atom) → H ₂ O (water) + M (metal)
MO (oxide film) + C (thermal diffusion carbon atom) → CO (carbon monoxide) + M (metal) That is, the surface oxide 241 of the cathode 24 is formed by thermal diffusion of hydrogen atoms or carbon atoms dissolved in the cathode. It is considered that they are reduced by reacting with each of the above atoms and discharged as water or carbon monoxide.
[0094]
Thereafter, the switch S2 is opened, the temperature of the disks K1, K1 'of the cathode 24 is returned to room temperature, the valve 9 is closed, and pure argon gas is again supplied from the leak valve 10 to about 2 × 10 at the same pressure. ^-Four When the pressure is introduced to Pa, the switch S1 is closed and the ion pump 2 is operated again, the partial pressure of the argon gas is an exhaust curve as shown by the curve M in FIG. The pressure of the argon gas at this time is 10 at a time in about 3 minutes. ^-8 It descends linearly to Pa level.
[0095]
Here, when the case shown by the curve O in FIG. 4 without using the oxide removing means is compared with the case shown by the curve M in FIG. 4 using the oxide removing means, the exhaust action for the argon gas is almost saturated. It can be confirmed that when the oxide removing means is used, the time required for this is about 1/10 of the time required when the oxide removing means is not used. ^-8 It shows that the exhaust speed up to Pa level is constant.
[0096]
The pumping speed for argon gas calculated from the curve M shown in FIG. 4 is about 0.1 liter / second. This pumping speed value is about 10 times the pumping speed for argon of a conventional 1-inch cell single cell pump. For this reason, the pumping speed of the ion pump that is simply calculated from the comparison of the size of the ion pump cell of the ultra-small cell size of 7 mm × 5 mm used in this example and the size of a general ion pump cell is the conventional ion pump. It can be confirmed that it is about 50 to 60 times higher than the exhaust speed.
[0097]
After that, when the switch S1 is turned off and the pump is stopped and left to stand, the pressure is 3 × 10 ^-7 Up to Pa, it increases by about one digit. Thus, the large pressure rise is considered to mean that the oxide film was removed and that the argon atoms on the surface became free.
[0098]
Thus, after the pump is stopped, the pressure increases, but the value of the pressure that reaches a certain level and becomes stable is one digit lower.
[0099]
Next, when the argon gas pressure re-emitted from the cathode is graphed while increasing the cathode temperature by supplying current again to the disks K1, K1 ′ of the cathode 24 from this state, a curve Y shown in FIG. An argon gas re-release curve is obtained.
[0100]
As shown in FIG. 5, when the partial pressure of the argon gas released at the same temperature of 600 ° C. is compared between the curve X and the curve Y, the curve Y using the oxide removing means and the curve not using the oxide removing means With X, the curve Y using the oxide removing means has a smaller re-release of argon gas by about one digit than the curve X without using the oxide removing means, and even if the temperature is raised to 800 ° C., the argon gas It can be confirmed that the re-release of does not reach the saturation value. This is presumably because argon atoms are diffused inside the tantalum metal.
[0101]
That is, it can be concluded that the ion pump 2 using the oxide removing means of the present example is evacuated based on a completely different principle from the conventional sputter ion pump.
[0102]
In this example, as shown in FIG. 4 and FIG. 5, the exhaust characteristic for argon gas and the re-release characteristic due to cathode temperature rise were confirmed. It has been confirmed that each characteristic is similar to the characteristic, and the correctness of the principle of exhaust in the present invention can be confirmed.
[0103]
Next, the results of using a means for reducing the surface impurity concentration by thermal diffusion of argon atoms trapped on the surface of the cathode 24 into the cathode will be described below.
[0104]
As described above, when the electrodes K 1 and K 1 ′ of the cathode 24 are energized and heated to remove the oxide film 241 and then the argon gas is exhausted, the pressure of the argon gas in the chamber 3 is 2 in a few minutes. × 10 ^-Four Pa to 10 ^-8 Descent to Pa level at once. However, the pressure is about 6 × 10 ^-8 After reaching Pa, it does not go any further.
[0105]
With the pressure reaching this constant value, the switch S2 of the ion pump 2 is closed, the switch S2 is closed, the cathode temperature is increased to 600 ° C. and held for several seconds, and then the switch S2 is turned on. Open again. That is, when intermittent heating is performed on the disks K1, K1 'of the cathode 24, a part of the exhausted argon gas is released at the moment when the intermittent heating is performed. ^-Five It rises to Pa level. Thereafter, the argon gas pressure was 10 ^-8 Pa-10 ^-9 It drops rapidly to Pa level.
[0106]
Further, when the pump 2 is stopped after the intermittent temperature raising process at 600 ° C. during the ion pump operation and the disks K 1 and K 1 ′ of the cathode 24 are raised again to 800 ° C., the pressure for re-releasing the argon gas becomes It was confirmed that the re-release pressure was lower than the pressure before the intermittent temperature increase.
[0107]
This is considered to indicate that the argon concentration in the surface layer is reduced due to thermal diffusion of some of the argon atoms that have been injected and trapped on the surface during the intermittent temperature rise. .
[0108]
In this way, the exhaust characteristics of an ion pump that has just been baked (up to 450 ° C.) and, as in this example, the temperature of the ion pump cathode is once raised to 800 ° C. to remove surface oxides and surface impurities. Comparing the exhaust characteristics after concentration reduction, the ultimate vacuum during pump operation after raising the temperature of the cathode of the ion pump to 800 ° C. to remove the oxide and lowering the surface impurity concentration The pressure value can be lowered by about two orders of magnitude compared to the ultimate vacuum during pump operation when not performed.
[0109]
In addition, it was confirmed that the gas re-release due to the temperature rise after stopping the pump was an order of magnitude lower. In this example, it was confirmed that the re-release of the gas was suppressed to prevent the exhaust speed of the ion pump from being lowered. it can.
[0110]
These effects are not the result of raising the temperature of the cathode in order to perform the simple degassing action that has been conventionally performed, but by performing a heat treatment of the cathode at a temperature of 500 ° C. or higher, preferably about 800 ° C. This is presumably because hydrogen or oxygen atoms dissolved inside thermally diffused to reduce the oxide on the cathode surface and disappear the oxide on the cathode surface.
[0111]
Conventionally, the vacuum apparatus 1 is used for 2 × 10. ^-Four When argon and helium gas evacuation from the Pa stage is repeated 10 times, it is confirmed that both the pump exhaust speed and the ultimate vacuum decrease, and a large amount of argon atoms are occluded on the cathode surface. it is conceivable that.
[0112]
In the ion pump of this example, this dissolved argon can be discharged by energizing and heating the cathode, so that the same performance can be recovered repeatedly.
[0113]
Further, in the ion pump 2 of this example, if the cathode is intermittently heated to about 600 ° C. during the pump operation, the argon atoms that have been exhausted and trapped in the surface layer are thermally diffused inside the cathode. Thus, the exhaust capacity can be recovered.
[0114]
As described above, the present invention includes means for removing oxide on the cathode surface and lowering the surface impurity concentration, so that the temperature of the cathode is raised to 500 ° C. or higher to thermally diffuse hydrogen or carbon atoms dissolved in the cathode itself. The oxide on the cathode surface reacts with hydrogen or carbon atoms to remove the cathode oxide. Since only water and carbon monoxide are generated at this time, it is possible to prevent contamination around the pump cell due to sputtered debris molecules as in the prior art.
[0115]
Further, when the temperature of the cathode is raised to 500 ° C. or higher, the temperature at which the gas molecules that are ion-implanted easily cause thermal diffusion inside the metal in a state where the thermal diffusion such as hydrogen atoms and the oxide are removed and the ions are easily implanted. Therefore, the amount of inert gas that can be evacuated by ion implantation can be increased by orders of magnitude compared to the conventional case, and the problem that the evacuation speed is reduced while the vacuum is increased in the conventional case can be solved.
[0116]
As the cathode of the ion pump of this example, the structural dimensions were exactly the same, and when the experiment was performed by changing the material to niobium, zirconium, or hafnium, the same result as that of tantalum was obtained. In addition, it has been confirmed that titanium that has been used in the past has both an ultimate pressure and an exhaust speed that are a few times worse than those of the four metals. This can be considered to be because the oxide is stable and the decomposition reaction or the reduction reaction hardly occurs. Further, the performance of the present invention could not be exhibited at all with gold or silver that does not form an oxide film, or with tungsten or molybdenum that has a high melting point but low hydrogen solubility.
[0117]
【The invention's effect】
As described above, according to the present invention, gas molecules or atoms remaining in a vacuum are ionized by electron collision, and the generated ions are accelerated by the action of an electric field applied between two electrodes, an anode and a cathode. In the ion pump that reduces the number of gas molecules or atoms remaining in the vacuum by colliding with the cathode surface and being captured, regardless of the presence or absence of an accelerating electric field by application, By energizing a part or all of the material forming the cathode and raising the temperature of the cathode to 500 ° C. or more by self-heating of the cathode itself, hydrogen or carbon atoms dissolved in the cathode material itself are The pump is capable of thermally diffusing and reacting with the cathode surface oxide to decompose or reduce the cathode surface oxide and remove the cathode surface oxide. Even if the pump of the present invention is operated after the pump is once exposed to the atmosphere, the oxide on the cathode surface can be removed by energization in advance to expose the metal surface of the cathode, so that acceleration is performed thereafter. By applying a voltage, residual gas molecules or atoms can be ionized, and the ions can be directly implanted into the metal surface. For this reason, unlike the conventional case, it is possible to prevent the generation of sputtered debris molecules due to oxide breakdown during ion implantation, and it is possible to prevent the deterioration of the vacuum and the surrounding contamination. Furthermore, the removal of surface oxides can be extended not only to the center of the cathode as in the prior art, but also to the region in front of the cathode. Can be injected and diffused, and has the effect of dramatically increasing the exhaust speed .
[0126]
No. of this application 2 The invention recited in the claims is directed to the claims. 1 In the described invention, The means for raising the temperature is: Connected to the open ends of a connection cathode formed by connecting multiple cathodes in series Power supply It is an ion pump of the structure which is a means using the simultaneous heat_generation | fever by electricity supply from.
[0127]
As described above, when a plurality of cathodes are used, since the cathodes can be heated by energization heating from the open ends of the connection cathodes by using the connection cathodes in which the cathodes are connected in series, there are many cathodes. Even in this case, it is possible to energize all at once by adding one or two vacuum terminals with the same current standard for energization to the pump wall, and achieve the purpose of raising the cathode temperature using a simple structure. Can do.
[0128]
No. of this application 3 The invention described in claim 1 is the invention described in claim 1. Or 2 In the described invention, the cathode is an ion pump having a planar shape approximating a substantially cross section of the anode and formed in a plate shape having a thickness of 0.1 mm or less.
[0129]
Thus, when the cathode is formed in a thin plate shape having a thickness of 0.1 mm or less, the resistance can be increased, so that it is easy to heat to a high temperature of 500 ° C. or more with a small current.
[0130]
No. of this application 4 The invention described in the claims is the first to the first aspects. 3 In any one of the inventions, the cathode has a hydrogen gas solubility at room temperature of 1.0 cm. ² (STP) cm ^-1 atm ^-1 ] And the sputtering yield by argon ions of 5 KeV is 2.0 or less Simple metal And the ion pump of the structure currently formed using the alloy containing those metals.
[0131]
Thus, hydrogen gas solubility is high Simple metal When the cathode is formed using an alloy containing these metals, the amount of hydrogen dissolved in the metal is large in each metal. By diffusion, the surface oxide can be reduced, and the oxide can be released into the vacuum as water molecules, and the subsequent ion implantation action can be improved.
[0132]
In addition, since the metal having a high hydrogen solubility tends to have a high solubility for dissolving argon or helium gas, a large amount of exhaust gas can be absorbed.
[0133]
Furthermore, since the metal having a high hydrogen solubility tends to have a low sputtering yield, the rate of erosion of only the central portion of the cathode is reduced, and the cathode thickness can be reduced. As described in the fifth aspect, the cathode can be formed into a thin plate having a thickness of 0.1 mm or less. Further, the deposition effect by the sputtered atoms can reduce the ratio of the inert gas trapped with a weak trapping force, and the inert gas re-emission generated by the cathode temperature rise can be reduced.
[0136]
As described above, according to the ion pump of the present invention, it is possible to suppress the initial gas release and discharge at the time of 1: starting the ion pump. 2: The portion where ions can be implanted can dramatically increase the gas storage capacity per unit area of the entire surface of the cathode metal where the oxide film is reduced, and the difference in pumping speed due to the gas species can be reduced. 3: Since ions are directly implanted into a metal having a very high gas solubility, it diffuses quickly into the metal and is less likely to be re-emitted. 4: Since the exhaust method does not depend on the deposition effect by the sputtered atoms, the re-emission can be reduced even when the vacuum is improved and the pressure is low, and the exhaust capability is not lowered. 5: Since the degree of consumption of the cathode metal by sputtering is small, it is not necessary to replace the cathode. 6: The cathode does not need to be uneven or have a tripolar structure. 7: It has the advantage that the previously exhausted gas can be self-diffused into the cathode solid at the time of temperature increase during reduction.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an ion pump using a triple cell type according to a specific example of the present invention.
FIG. 2 is a schematic configuration diagram of a vacuum device for performance testing according to a specific example of the present invention.
FIG. 3 is a perspective view showing a schematic configuration of an ion pump using a single cell type according to a specific example of the present invention.
FIG. 4 is a diagram showing a result of a test performed using the apparatus shown in FIG. 2 according to an example of the present invention, and showing a relationship between time (minutes) and pressure drop due to argon gas pressure (Pa) exhaust. is there.
FIG. 5 is a result of a test conducted using the apparatus shown in FIG. 2 according to a specific example of the present invention, and shows a relationship between re-emission of argon gas pressure (Pa) with respect to a rise in cathode temperature (° C.). It is.
[Explanation of symbols]
1 Vacuum equipment
2 Ion pump
3 Vacuum chamber
4 NEG pump
5 BA gauge
6 Quadrupole residual gas analyzer
7 Turbo molecular pump
8 Rotary pump
9 Cut valve
10 Leak valve
11 Gas cylinder
12 Permanent magnet for ion pump
21 Ion pump
22 Anode
23 Vacuum terminal
24 Cathode
25 Cathode connection line
26 Connecting cathode
27 Vacuum terminal
28 Vacuum terminal
A1 Anode cylinder
A2 Anode cylinder
A3 Anode cylinder
K1 Disc of cathode
K1 'cathode disc
K2 cathode disc
K2 'cathode disc
K3 cathode disc
K3 'cathode disc
S1 switch
S2 switch
E1 High voltage power supply
E2 Heating power source

Claims (4)

The gas molecules or atoms remaining in the vacuum are ionized by the collision of electrons, and the generated ions are accelerated by the action of the electric field applied between the two electrodes of the anode and the cathode and collide with the cathode surface and captured. In an ion pump that reduces the number of gas molecules or atoms remaining in the vacuum by
Regardless of the presence or absence of an accelerating electric field due to application, a means is provided for energizing a part or all of the material forming the cathode and raising the temperature of the cathode to 500 ° C. or more by self-heating of the cathode itself. A featured ion pump. 2. The ion according to claim 1, wherein the means for raising the temperature is a means using simultaneous heat generation by energization from a power source connected to open ends of a connection cathode formed by connecting a plurality of cathodes in series. pump. 3. The ion pump according to claim 1 , wherein the cathode has a planar shape that approximates a substantially transverse section of the anode and is formed in a plate shape having a thickness of 0.1 mm or less . The cathode has a hydrogen gas solubility at room temperature of 1.0 [cm ² (STP) cm ⁻¹ atm ⁻¹ ] or more, and a single metal having a sputtering yield of 5 KeV argon ions or less and 2.0 or less thereof The ion pump according to any one of claims 1 to 3, wherein the ion pump is formed using an alloy containing .

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