JP2003531465A - Independent plasma vacuum pump - Google Patents

Abstract

A housing surrounding at least one pump region located between a low pressure inlet and a high pressure outlet, and a magnetic flux channel for confining and guiding the plasma. And a permanent magnet arrangement providing at least one magnetic field region extending into the pump region; and coupling microwave power into the flux channel to accelerate electrons, ionize gas, and accelerate plasma ions. A member arranged to produce an electric field in the flux channel such that momentum transfer accelerates ions in the flux channel toward the outlet, and a neutral gas. A baffle near the outlet that prevents flow backflow while promoting flow of plasma ions and neutral atoms to the outlet. Separate plasma vacuum pump for evacuating the gas to the outlet from.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to industrial and other processes in which large quantities of gas must be vented at pressures as low as 1-10 milliTorr. Industrial processes within this category include various types of plasma processes such as, for example, plasma enhanced chemical vapor deposition of surfaces, plasma etching, as well as other types of surface modification processes.

[0002]

[Prior art]

For many of these processes utilizing plasma, 1 to 10 milliTor
It is generally considered by those skilled in the art that it is beneficial to create a processing plasma in a suitable gas mixture that is maintained at a pressure as low as r. Gas composition and purity (p
The urity) can be optimally controlled when the flow rate of the fresh gas into the processing chamber is high with respect to the processing speed. However, existing vacuum pump technology
In this pressure range it is possible to provide only a limited gas throughput.

For example, the pump speed of widely used turbomolecular pumps typically decreases rapidly with increasing pressure in the range of pressures above approximately 1 milliTorr. No effective cost robust system has been developed to date to achieve fast evacuation at pressures in the range of 1-10 milliTorr.

Furthermore, many gases required in industrial processes, such as VLSI systems, are toxic or dangerous and must be separated and controlled with great care. It would be beneficial if harmful or hazardous gases exiting the processing chamber could be converted to less harmful or non-hazardous forms via molecular dissociation of such gases. This treatment often involves the pyrolysis of harmful or hazardous gases.
zation) and has been studied for many years, especially in connection with toxic gases used in the military.

Conventional vacuum pump technology utilizes one of the following two fundamental mechanisms. (1) Ejecting the gas molecules through a valve or baffle structure that increases the momentum of the gas molecules in a preferred direction and prevents gas backflow, or (2) condensing the gas exhausted to a particular surface. The first mechanism is of a given type, which imparts momentum in a given direction to the gas, either from a stream of easily condensing pump oil or a stream of pump molecules such as mercury, or from a mechanical structure moving at high speed. It is usually implemented via a piston, blower, and high speed fan. The second mechanism is commonly used in systems where small to moderate throughput is required. Pressure range (1 to 100 milliTorr) at which industrial plasma treatment is performed
Therefore, the turbo molecular pump has a large flow rate of the processing gas (“the throughput (through
put) ") is used in almost all cases in the first stage of a combined pump system designed to exhaust.

[0006]

[Problems to be Solved by the Invention]

The turbo-molecular pump gives momentum in a predetermined direction to gas molecules through collision with a disk rotating at high speed. This mechanism is most effective at gas pressures that are low enough that the mean free path of the molecules is greater than the structural dimension of the pump. The limit that occurs with the maximum gas throughput that can be achieved using a turbo molecular pump is that sufficient throughput of the reaction gas is needed to prevent reaction products from accumulating and concentrating and harming the process. It is inconvenient in the plasma processing industry. Moreover, high speed turbomolecular pumps are necessarily complex and expensive devices with large angular momentum. Moreover, many plasma treatments produce solid and / or corrosive by-products that can potentially damage these pumps.

Pump performances of 3 to 5 times the currently available pump speeds have been demonstrated (using relatively small substrates) to enhance process reliability and etching and deposition performance. The current limit of pump speed in a properly designed system is determined both by the speed of the pump and the conductance of the chamber to the inlet of the pump. Currently, the performance of turbo molecular pumps is limited to 5500 liters per second, and the largest available turbo molecular pump is the cost of being a large pump and the expected reliability due to the size of the pump. Constrained due to the lack of. The cost of a turbo molecular pump of this size is $
It's over 80,000, which is $ 15.5 / (liter / sec),
$ 30,000 for a 3300 liter per second pump, or $ 10.6 /
It is considerably higher in cost per unit pump speed than (liter / sec).
Therefore, the cost per unit pump speed for the larger pump is 50% greater than for the smaller pump.

Even so, the 5500 liters / second (l / sec) pump is
Smaller than a pump that would be optimal for processing 200 mm wafers. Expansion to 300 mm wafers exacerbates the problem of providing adequate pump speed. The required pump speed is most closely sized (sca) in the area of the substrate.
le). Increased scale of processing equipment from 200 mm to 300 mm wafers (scal
ling) requires at least a 2.25-fold increase in pump speed. 3300liter / second to 5500liter / second
An increase to d is possible, but this is only a 1.67 fold increase. This leaves the 300 mm system with very poor pump choices.

The problems with handling gas in a 300 mm system are of utmost importance.
It is further complicated by the fact that it is the pump speed at the wafer (substrate). Providing pump speed to a location remote from the wafer means that gas atoms must be directed through a given transient structure to the inlet of the pump. In the transient region, the conductance, typically measured in liters / sec, decreases at a constant rate. A computer program can predict overall pump speed when gas atoms are in the laminar or molecular flow regime.
However, in many commercially interesting processes, the flow is characterized by transitional flow, and computer models are not very reliable in predictive performance. In many designs, the conductance between the wafer and the pump provides a 50% to 70% effective pump speed loss.

In addition, in considering effective handling of the gas stream, the gas species that must be removed from the system but that adhere to the walls of the processing chamber over time must be evaluated. Similar problems arise with rarely volatile species that can result from processing, such as, for example, multiple carbons that are decomposed by the electrons or photons of the plasma. It is easy for plasma electron or photon streams to affix debris of these molecules to the wall. Similarly, these materials are later separated from the wall, possibly as different species. Adhesion (
attachment), synthesis (synthesis), decomposition (decompo)
Similar processes, such as position) and evolution, occur on the substrate, but the substrate is made of a different material and the additional energy of ion bombardment is used, for example, to facilitate the etching process. Different in having flow. The substrate becomes a source of organic material and silicon by the etching process. When the voltage to the wafer is removed and the flow of new material is interrupted, volatile activating groups bond to the degraded brown film often found in plasma processing systems. In addition, the reactor tends to stabilize. The materials are cross-linked with each other and are very stable to heat absorption or plasma bombardment.

The quality of the processing results is significantly dependent on the presence or absence of weakly volatile materials, such as in the use of side wall passivation to provide straight walls in high aspect ratio channels. It This passivation results from the deposition of a material, which is sourced from photoresist or an injecting gas, is a free molecule in the plasma volume, is modified by electron bombardment, and is absorbed by the surface. , Can undergo multiple changes. This material is then redeposited on the surface of the wafer, especially on the newly etched surface of the feature being etched. The deposited material, which has interacted multiple times with the plasma, is particularly resistant to degradation by chemically activated molecules and ions that provide the flow for etching the wafer. Perhaps many process dynamics that allow the choice between organic and inorganic surfaces (plasma tend to spread molecular species across the surface of the plasma) are the walls in contact with the plasma. Affected by changes in thickness. Thus, if the residence time of these species in the processing chamber is probably less than a given adaptation time (the time for these species to reach a stable chemical position) and is sufficiently reduced, the etch chemistry in the chamber will be reduced. Can be controlled and optimized.

In recent years, the benefits that can be gained from using plasma as an effective element in vacuum pump technology have become increasingly understood. For example, plasma can exhaust a wide range of gases including hydrogen and helium with high efficiency as well. Plasma vacuum pumps can be highly resistant to solid or corrosive process by-products. As shown here, these advantages are caused by the general properties typical of plasma vacuum pumps, in which the three-dimensional flow of neutral gas being exhausted is magnetically compressed and properly baffled. It is transformed into a one-dimensional flow of magnetized plasma that can be guided through the structure. Neutral gas consists of atoms and molecules that are neutral, i.e. not ionized. Momentum is imparted to the plasma via various electromagnetic interactions and then to the neutral gas via collisions between charged particles and neutral gas molecules.

[0013] These potential advantages are of an important range in the application of plasma processing and in the generation of magnetic fields that are compatible with both the effective generation of plasma and the formation of the channels required for plasma flow. In practice it has not yet been fully realized for a number of technical reasons, including a simple and effective mechanism for driving a plasma flow at pressure. This last technical difficulty is exacerbated by the complex atomic and molecular processes that are important in the pressure range of interest and the nature of the plasma that shields it from low frequency external electric fields.

Another type of plasma vacuum pump is disclosed in International Application No. PCT / US99 / 12
827, filed June 29, 1999, name PLASMA VACUUM PUM
PING CELL, which is hereby incorporated by reference in its entirety, and in co-pending US provisional application no. 60 / 114,453, filed December 30, 1998, entitled PLASMA VACUM PUMP, the entire disclosure of which is hereby incorporated by reference. This pump is a high density plasma, such as a plasma using electron cyclotron resonance (ECR), inductively coupled plasma (ICP), or electrostatic shield radio frequency (ESRF) plasma, to exhaust gas out of the system. A plasma source utilizes an excited plasma within the processing system. This type of pump cell is designed and constructed according to the nature of the source plasma of the system and installed in the system. It cannot be used as a stand-alone vacuum pump.

[0015]

[Means for Solving the Problems]

According to the present invention, a stand-alone plasma vacuum pump for exhausting gas from a low pressure inlet to a high pressure outlet includes a magnetic field generated by a permanent magnet having a specific shape and an electron cyclotron so as to move ions from the inlet to the outlet. Combine with the effect of resonance.
The plasma vacuum pump provides a housing enclosing a pump region located between the inlet and the outlet, and at least one flux channel for confining and guiding a plasma between the inlet and the outlet. A plurality of permanent magnet arrangements that provide a magnetic field extending within the pump region of the plasma and heat the plasma electrons to ionize the gas and generate a force that propels the plasma ions in a direction from the inlet to the outlet. A microwave power source coupled to the magnetic flux channel. The pump is further configured to promote the flow of electrically neutral gas molecules and plasma towards the outlet while blocking the flow of neutral gas molecules from the outlet toward the inlet.

The plasma vacuum pump of the present invention exhausts a region in which electrons having a sufficient energy and density to ionize gas molecules that enter the region with high efficiency are exhausted from a region in which the electrons are concentrated. However, it is particularly well suited for decomposing effluent gases as it has to pass. The resulting molecular ions will typically dissociate into the constituent atomic species in less time than passing through this pump.

The pump of the present invention uses four separate and distinct plasma technologies in a novel arrangement. The first is an electron cyclotron heating technique that sufficiently ionizes the exhausted gas molecules. The second is a plasma confinement technique that confines the plasma resulting from electron cyclotron heating in the pump duct by creating at least one flux channel having an asymmetric magnetic mirror cross-sectional configuration. The third is a momentum-transfer-pumping technique that drives an electron cyclotron heated plasma along a flux channel. Fourth, it allows an outward free flow of plasma, but at a thermal temperature (therm)
a baffle technology that prevents the reverse flow of neutral gas molecules.

According to the first novel aspect of the invention, a longitudinally extending plasma region is created in a flux channel in a rectangular pump duct. Instead, four, eight, or more longitudinally extending plasma regions are created within each flux channel within the cylindrical enclosure, respectively. In this configuration, the plurality of channels are spaced from each other about an axis of the cylindrical enclosure, each channel extends along the axis, and each channel is configured to exhaust gas radially. To be done. This cylindrical arrangement provides a very large pump surface area to accommodate high gas loads. In addition, neutral gas molecules can enter the enclosure and move parallel to the axis of the enclosure within one or more spaces between the plasma regions. As the gas molecules pass through the electron cyclotron resonance region, the majority of the incident molecules will be ionized by the energetic electrons that accumulate in this region as a result of electron cyclotron heating. Once the molecules are ionized, they can escape from the plasma pump at the exit end of each flux channel, approximately across only a small predetermined solid angle.

Electron cyclotron heating provides the two essential functions of the present invention. Such that the inelastic collision of a gas molecule with an electron has the maximum probability of ionization of the molecule,
Energy around 100 eV provides a flexible and efficient means of heating electrons. In addition, electron cyclotron heating with the magnetic field arrangement of the present invention
An internal space charge electric field is generated which accelerates the ions along the magnetic field lines.

According to a second novel aspect of the present invention, each flux channel is defined by a highly effective magnetic field arrangement being created using permanent magnets. The magnetic field plays three important roles in the plasma pump mechanism. (1) Define electron cyclotron resonance (ECR) zones for effective electron heating and plasma generation. (2) Providing a diverging and diverging flux tube or channel in which the magnetic field lines or magnetic flux lines are diverging, ie the magnetic field strength is decreasing and also perpendicular to the magnetic field lines of the electrons. Kinetic energy related to orbital momentum in various directions is
It is converted into kinetic energy related to the momentum parallel to the lines of the magnetic field of the electron. (
3) From the ECR resonance region, through the momentum transfer pump duct and baffles,
Guide the plasma flow to the fore pump region. All three roles are accomplished with a minimal amount of permanent magnet material.

A flux tube is usually defined with a transverse surface, everywhere in a spatial region parallel to the magnetic field lines. A comprehensive description of flux tubes can be found, for example, in "The Structure of Magnet".
ic Fields ", AI Morozov and LS Solov.
'ev, Reviews of Plasma Physics, Vol. Two
, Pages 9-11, Ed. M. A. Leontovich, Consult
Ants Bureau, New York, 1966. In the rectangular embodiment of the invention, the magnetic field lines lie in a plurality of planes. In Cartesian coordinates, these planes can be chosen as planes with a constant coordinate z, and the magnetic field has only x and y components. The flux tube or channel is a length of magnetic structure extending in the z-direction. In the cylindrical embodiment, the magnetic field lines lie in a plane with a constant axial coordinate z.
The magnetic field has radial r and azimuthal components. The flux tube or channel is a length of magnetic structure extending along the axis z.

In the ECR resonance zone, a high density plasma with a density of 10 ¹² to 10 ¹³ ions / cm ³ is generated by whistler waves launched from a high magnetic field region close to the microwave antenna. R. A. Dandl and G.D. E. Guest
("On the Low-Pressure Mode Transitio
n in Electron Cyclotron Heated Plasma
as ", J. Vac. Sci. Technol. A9 (6), Nov / Dec.
1991, pp. 3119-3125), the density produced is approximately proportional to the microwave power coupled into the plasma region.

The plasma includes a primary electron and a second electron. The main resonance heating electron may have an energy close to 100 eV. Given the proper electron cyclotron heating power, these electrons have a strong ionization effect and can ionize large flow rates of gas molecules, thus achieving fast pump speeds. The temperature of the second electrons resulting from the ionization due to the collision of the incident gas molecules is in the range of 3 to 10 eV, depending on the heating power and operating pressure.

According to another novel aspect of the present invention, plasma ions are collectively accelerated by an internal space charge electric field in the region of diverging magnetic field lines downstream of the ECR zone.

In accordance with yet another novel aspect of the present invention, neutral gas atoms rapidly gain momentum in a given direction due to resonant charge conversion collisions with plasma ions and other collisions. The directed neutral gas flow in the flux channel is significantly increased. Thus, the parallel momentum is continuously transferred to the neutral molecule, while the newly charge-exchanged ions quickly gain energy in a given direction from the collective electric field. Plasma ions can almost recombine with plasma electrons at the exit of the magnetic flux channel, at which exit the neutral molecular backflow is impeded. Since the plasma can easily flow along the converging magnetic field lines, it can be guided through a well-defined outlet orifice, i.e. the geometry of the pump duct is designed to match the magnetic field lines. obtain. Using criteria well known in the art (eg, Scientific Foundations of Vacuum T
echnique, 2nd edition, Saul Dushman, Ed. J. M. La
fferty, John Wiley and Sons, New York,
(1962 Chapter 2), the dimension of the outlet orifice may be selected to limit the flow of gas from the outlet side of the high pressure orifice to the low pressure inlet side. Thus, the flow velocity of the gas flowing back through the orifice is
It may be less than the forward flow velocity of the plasma and the gas that is entrained in the flow.

[0026]

DETAILED DESCRIPTION OF THE INVENTION

The construction and performance of the pump duct is described in detail below. Figure 1 shows a spiral orbit of an electron moving in a static magnetic field, which is
The magnetic lines of force extend substantially in the direction of arrow M. Well known in the art,
For example, Plasmas and Controlled Fusion, Da
vid J. Rose and Melville Clark, Jr. Author, J
own Wiley and Sons, New York (1961) Cha
As shown fully in pter 10, the spiral orbit shown in FIG.
It can be considered that it results from the superposition of the lateral rotational movement around the magnetic field lines (“gyro”) and the linear movement along the magnetic field lines. The angular frequency of the gyro motion (“electronic gyro frequency”) Ω _e is proportional to the magnitude of the magnetic field strength B.

[Equation 1] Here, e and m are the charge and mass of the electron, respectively. For example, 875 Gau
At a magnetic field of ss, the electronic gyro frequency f _e is equal to 2.45 GHz, the frequency of microwaves used in many commercial applications.

Microwave power of a specific frequency f _μ is incident on a spatial region in which the electronic gyro frequency is equal to the frequency of this microwave power,
If the value of the magnetic field strength is fixed, the electron will be continuously accelerated in the direction across the magnetic field as long as it stays in this "resonance region". The resonance value of the magnetic field strength is given by the following equation.

[Equation 2] As is known in the art, this resonant acceleration can easily increase the kinetic energy of an electron by more than 100 eV before it leaves the resonance region. Thus, such resonantly heated electrons may have optimal energy to ionize gas molecules with which they may collide.

If the magnetic field strength is spatially and gradually varying, the electron motion can be further characterized by the magnetic moments associated with the (transverse) gyro motion. The gyroscopic electrons make up a micro loop current, which is j _e = ef _e . Furthermore, if the velocity of the electrons across the magnetic field has a magnitude v _⊥ , the radius of the gyro motion is given by ρ _e = v _⊥ / Ω _e . The magnetic moment associated with the microelectron loop current is the product of the current and the area of the loop.

[Equation 3] Where W _⊥ is the kinetic energy of the electrons associated with the motion across the magnetic field. In a spatially varying magnetic field, the electron will experience a force along the magnetic field given by −μ _e ∇B. Here, ∇B is the gradient of the magnitude of the magnetic field strength. Since this force is parallel and opposite to the gradient, it will accelerate the electrons along the field lines towards areas of relatively small magnetic field strength.

FIG. 2 is a simplified diagram showing the magnetic field that cooperates with the electron cyclotron resonance power source 2 to form the plasma region that produces the pumping action of the present invention. The magnetic field is shown by two lines L, which are in a plurality of flux planes extending perpendicular to the plane of FIG. Each magnetic flux plane is shown in FIG.
Has a generatrix in a direction perpendicular to the plane. The magnetic flux pattern of the magnetic field has a mirror-symmetrical form with respect to a plane extending perpendicular to the plane of FIG. 2 and extending horizontally in the direction of arrow M in the plane of FIG. The arrow M here indicates the direction in which the plasma will be exhausted and also indicates the approximate direction of the magnetic field. The magnetic field shown forms one flux channel, which consists of four parts,
Each part is at least approximately defined by a respective set of ideal boundary planes a, b, c, d. It should be noted that the flux channels may have some size perpendicular to the plane of FIG.

The flux channel has a substantially constant magnetic flux density along each line perpendicular to the plane of FIG. 2, while the magnetic flux density is indicated by the arrow M, as shown in the form of the line L. Is changing in the direction of. In particular, at each point along the direction of the arrow M, the larger the space between the lines L, the smaller the magnetic flux density, ie the smaller the magnetic field strength. Therefore, while the magnetic flux density gradually decreases from the plane a to the plane c, it increases from the plane c to the plane d and decreases again from the plane d to the plane e. There is.

The line L is intended to represent qualitative properties and directions of change, rather than quantitative changes in magnetic flux density. However, as shown,
It is desirable that the magnetic flux density on the plane d is smaller than the magnetic flux density on the plane a. The microwave power source 2 introduces high frequency microwave energy into the flux channel and produces high energy electrons in the electron cyclotron resonance zone (ECR) between the planes a and b. It is arranged to ionize gas molecules, and within this zone, the electrons gyro at the resonance frequency, receive a force along the weakening magnetic field, and move along the magnetic field, as described above. Generate an internal space charge electric field that accelerates the ions. The part of the flux channel between the planes a and b will preferably constitute the position of the inlet end of the flux channel. However, the exhausted gas can also be introduced into the part of the flux channel between the planes b and c.

The internal space charge electric field is said to cause the electrons to undergo a force of −μ _e ∇ B along the magnetic field between the planes a and c where the magnetic flux density is decreasing, and thus be separated from the ions. Caused by facts. As a result, the electrons "drag" the ions along the flux channel by an electrical force. This is known in the art.

Therefore, the plasma ions are collectively accelerated by the internal space charge electric field and drift with the electrons confined to the flow parallel to the magnetic field. Drift energies of plasmas of tens of electrovolts are expected from this acceleration mechanism.

In the magnetic flux channel, downstream of the ECR resonance zone, electrons that are directly heated in the ECR zone and above the thermal temperature (supra-thermal) are transferred to the plane of the magnetic field when they are transferred to the plane c. Some of the vertical energy is converted to energy parallel to the magnetic field lines. Vertical energy refers to the kinetic energy that is related to the velocity of electrons perpendicular to the lines of the magnetic field. That is,

[Equation 4] Parallel energy refers to kinetic energy that is related to the speed of electrons in a direction parallel to the lines of the magnetic field. That is,

[Equation 5] The electrons and ions continue to move through the part of the magnetic field between the planes c and d and enter the part of the exit between the planes d and e.

The magnetic flux density in the magnetic flux channel has a positive slope between the planes c and d, but the electrons and ions are sufficiently parallel to move through the plane d. It has great kinetic energy. This movement is allowed by the fact that the magnitude of the gradient between the planes c and d is smaller than the magnitude of the gradient between the ECR and the plane c.

The electrons and ions then enter the part between the planes d and e, which part constitutes the exit end of the flux channel, where the electrons and ions are
It will recombine to neutral gas and will be affected by the fore pump. Electrons downstream of the plane e see an increasing magnetic field between the planes d and e in the flux channel, which prevents the electrons from moving back into the flux channel. The movement of gas in this direction is further hindered by the effective narrowing of the channel in said plane d, which also reduces the cross-sectional area of the channel seen from the outlet end of the channel. , Has been reduced. In addition, neutral molecules are moved along the channel by collision with positive ions moving downstream of the flux channel.

FIG. 3 is a diagram showing changes in magnetic flux density along the axis of symmetry of the magnetic field shown in FIG. The magnitude of the magnetic field strength B is plotted against the distance along the axis of symmetry for an exemplary pump intended to be used with 2.45 GHz microwave power from the source 2. . The microwave window will be located at the position of the peak B _max of the magnetic field strength, ie the position of said plane a. Also, the magnetic field strength may be approximately 1100 Gauss in this example. Immediately thereafter, in the resonance zone ECR between the planes a and b, a resonance plane with a specific magnetic field strength B = B _res is arranged, for example 875 Gauss. Following to the left, the magnetic field lines continue to diverge and the magnetic field strength decreases. Lines of magnetic field, when they are spread widest range the plane c, magnetic field B has reached the minimum value B _{mi n.} In the regions on both sides of B _min , the magnetic field strength is smaller than B _max ,
It is similar to the magnetic mirror used for plasma confinement and will be referred to as the "mirror region". The magnetic field lines then converge to reach another maximum B _max2 (such as B _max2 <B _res , as will be shown later). The magnetic field strength peak B _max2 near the exit end is somewhat smaller than B _res .

FIG. 4 shows an embodiment of a rectangle of the permanent magnet arrangement of the invention, which produces the magnetic field represented in FIGS. 2 and 3. This embodiment comprises one magnetic flux channel forming one pump region and is essentially formed by a permanent magnet arrangement consisting of two identical half members. Each half member has four permanent magnets 1.
2, 14, 16, 18 and a steel pole piece 20 connected between these magnets so as to provide a return path of magnetic flux between these magnets. Each steel pole piece may be made of 1010 steel, for example. The permanent magnet arrangement extends over the entire width of the pump area, which area is perpendicular to the plane of FIG. The direction of magnetization of the magnet is indicated by the thick black arrow shown in the magnet. All of these directions can be reversed.

As shown, the magnets 12 and 14 are longer than the magnets 16 and 18, respectively. This helps to generate the magnetic field pattern described above. Behalf,
Alternatively, or in addition, the magnets 12 and 14 may be made of stronger magnets than the magnets 16 and 18, respectively. In the pump region of the present invention, the source 2 (FIG. 2) would be located behind the magnet 12 and the outlet end would be located at the magnet 18.

FIG. 5 is a bottom perspective view of a simple rectangular embodiment of the stand-alone plasma vacuum pump of the present invention. 6 is a side elevational view of this embodiment and FIG. 7 is a side elevational view of FIG.
It is the figure seen from the direction of arrow 22 of. This embodiment comprises the permanent magnet arrangement shown in FIG. 4, in which the microwave power source maximizes the forward transfer of power by a microwave coupler 26 and a slotted microwave guide. Wave tube antenna 2
7, coupled to the plasma, the antenna comprises means for transmitting and coupling microwave power. The design of such systems is known in the art. The exemplary antenna shown is composed of a slotted waveguide, the geometric arrangement of slots 25 being designed to emit the desired polarization and radiation pattern in the resonance region. . The slot is formed on the surface of the waveguide antenna 27 in a narrow area. Therefore, the state when viewed through the window 24 is shown by a dotted line. The antenna has a microwave window 24,
It can be separated from the vacuum region. This window 24 can be a quarter-wave thick quartz or alumina plate with a vacuum seal. The microwave windows utilized in the other illustrated embodiments may have similar conventional configurations.

The pump is formed by two side walls 30 (not shown in FIG. 5, only one of the side walls is shown in FIG. 6) surrounding the pump area and the pole piece 20. It is composed of a rectangular enclosure. The source 2 is
Fundamental wave mode waveguide antenna with slot (fundamental mod)
It may consist of a microwave antenna, such as an e slotted waveguide antenna). A vacuum seal is formed by the microwave window 24 between the source 2 and the pump area. The exhausted gas passes through the inlet opening 34 in the side 30 on each side of the enclosure in the direction indicated by the arrow 32,
Enter the enclosure. The outlet end of the enclosure is on the right hand side in FIG. 6 and is closed by an end wall 36 or outlet plate (not shown in FIGS. 5 and 7) defining the outlet of the pump. The outlet of the pump is at the outlet end of the plasma vacuum pump, a suitable connector (
Coupler) or conduit.

The slotted waveguide 27 is provided with Tef to reduce the size of the components.
It may be loaded with a dielectric material such as lon®. Furthermore, FIG.
The backside of the window 24 may be cooled via a forced cooling nitrogen stream, as indicated by the dashed line at.

As shown in FIG. 6, the pump further comprises a baffle structure 38 (not shown in FIGS. 5 and 7) made up of an array of plates,
The relative separation of these plates and their length along the magnetic field are chosen to give the optimum differential conductance. The plasma flows along the magnetic field lines without colliding with the baffle plate, whereas the conductance of the gas flowing from the high pressure outlet end to the low pressure inlet end is, for example, as described in the chapter cited above.
It is reduced to the appropriate value using standard vacuum techniques as described by Dushman in er 2. The plates of the baffle structure 38 extend across the width of the pump.

The embodiments shown in FIGS. 5, 6 and 7 can be operated as follows. The microwave power is radiated from the antenna of the source 2 into the pump and absorbed by plasma electrons in a narrow region located on the ECR resonance plane. In this region, the main electrons gain kinetic energy perpendicular to the magnetic field and are heated to energy around 100 eV.
With this energy, the main electrons efficiently ionize the gas entering the pump through the inlet opening 34. In addition, the main electrons, due to the effect of their magnetic moment, tend to be accelerated parallel to the magnetic field and away from the plasma ions, thus creating a space charge electric field. The electric field created by this space charge imbalance accelerates the plasma so that the ions and plasma move along the magnetic field through the pump toward the exit at a common "dipolar" velocity. The mechanism of this acceleration is explained in detail below.

A simplified perspective view of a cylindrical plasma vacuum pump of the cylindrical embodiment of the present invention is shown in FIG. The pump is constituted by a cylindrical enclosure 50 which encloses four pump areas. The upper end of the enclosure 50 is closed by an inlet plate 52 having four openings 54 defining the inlet of the pump. The lower end of the enclosure 50 is closed by an outlet plate 56 having a central outlet opening 58 defining the outlet of the pump.

A central partition structure 60 extends along the axis of the enclosure 50 between the plate 52 and the outlet opening 58. The structure 60 separates the plasma and gas flow into four axially extending pump ducts or channels to provide a surface on which plasma ions can recombine with the plasma ions to form a neutral gas. . The structure 60 then divides the central conduit into four quadrants to prevent plasma and gas from flowing from one of the four pump regions to the adjacent pump region.

A plurality of microwave antennas 70 are used to form and superheat the plasma in each of the four pump ducts. In accordance with one embodiment of the present invention, each antenna 70
Is a standard 4-port, side-wall combiner with tunable impedance matching front end section.
It is formed by improving the hybrid coupler).
This conventional type of antenna is manufactured by Raphael A.A. U.S. Patent No. 5,133,826, 5,203,960 and 5,370
, 765, which has been successfully used in the plasma source. Modifications to adapt microwave couplers and antennas to particular embodiments are known to those skilled in the microwave system art.

Each microwave antenna 70 separates, for example, 2.45 GHz microwave power into each pump region within the enclosure 50, by four quartz microwave windows 7 that are separated.
Radiate through each of the two. This microwave power may be provided by one or more purchasable sources connected to the antenna 70. The number of sources and the means such as distributing power from each source can be determined by the total power required and the availability of suitable sources. In general, pump speeds will be proportional to microwave power, so faster speed pumps will require multiple microwave power sources. An example of a 2.45 GHz microwave source that can be purchased is the ASTEX 1500 (maximum power 1500 W@2.45 GHz). Other sources include ASTEX S1000i (1kW) and ASTEX S700
There is i (700W).

The pump is mounted on the cylindrical wall of the enclosure 50 and has four axially extending outer magnet devices and four axially extending radially outwardly spaced apart magnet devices. And two inner magnet devices. These magnet arrangements generate four magnetic fields, each magnetic field being similar to that shown in FIGS. As shown in FIGS. 9-11 in addition to FIG. 8, each outer magnet arrangement includes two axially extending permanent magnets 130 and a plurality of magnets 130 to provide a suitable flux path.
And a steel pole piece 132 extending in the axial direction. Each inner magnet assembly consists of two axially extending permanent magnets 134 and an axially extending steel pole piece 136 connecting between the magnets 134 to provide a suitable flux path. ing. Each steel pole piece 132, 1
36 may be made of 1010 steel, for example.

FIG. 9 shows the directions and directions of magnetization of the magnets 130 and 134 and their relationship to the poles 132 and 136. The direction of magnetization is indicated by the thick arrow shown in the magnet. A suitable magnetic circuit is formed by arranging the pole pieces 132 and 136 and the magnets 130 and 134 in a predetermined orientation, as shown particularly in FIG.

The magnetic flux in the air gap between adjacent pairs of inner and outer magnets forms a particular form of magnetic flux channel that functions as a plasma pump channel 138. Thus, in the illustrated cylindrical embodiment, four such pump channels 138 are formed. The relatively contracted portion of the exit end of the flux channel passes through a properly designed orifice that forms a baffle that prevents ions from flowing back into the flux channel, as described above. is doing. In the cylindrical embodiment, the set of baffles represented by slats is shown in dashed lines for one quadrant in FIGS. 10 and 11.

Electron cyclotron resonance plane 140 (FIG. 11) in which the strength and dimensions of the magnets 130 and 134 correspond to the ECRs of FIGS. 2 and 6 within the region located near each microwave antenna 70. Have been selected to form. For example, for 2.45 GHz microwave power, this plane has a magnetic field strength of 875
It is a surface that is Gauss. Each microwave antenna 70 has a magnetic field strength B _max1 typically 1.2 to 1.5 times greater than this resonance value, ie 1100 to 1
It is placed in an area that is 300 Gauss. For this reason, this type of electron cyclotron heating is commonly referred to as "high-field launching".
unch) ". The characteristics of high field launching electron cyclotron heating are described in detail below.

FIG. 10 shows details of an exemplary embodiment of the construction of the pump of the present invention.
This figure shows that each antenna 70 may have a waveguide that is tapered to accommodate the combined coupler to the pump geometry.

An example of magnetic flux planes generated by the magnetic structure is shown in FIG. Figure 11
The lines shown in Figure 2 represent the magnetic field lines, and the direction of the local magnetic field is indicated by arrows throughout. Dotted line shown in the figure, the magnetic field strength, constant value _{B r es,} as _well, indicates the position of the surface taking B _min, the _{B max2.} These are the resonance magnetic field strengths (875 G for microwave power of 2.45 GHz, respectively).
aus) and the minimum and maximum magnetic field strengths along the centerline of the illustrated flux channel. Two local flux channels (each corresponding to flux channel 138 of FIG. 9) are formed near the vertical and horizontal boundaries (vertical and horizontal axes) of FIG. 11, respectively. Each half of the flux channel is shown in FIG. 11, the vertical and horizontal axes of which also show the mid-plane of these two flux channels. Along each mid-plane, the pattern of magnetic flux density has the morphology shown in FIG. It should be noted that these flux channels extend axially over the entire length of the pump and the magnetic field lines extend radially between the outer magnet arrangement and the inner magnet arrangement.

As is particularly shown in FIG. 10, microwave power is applied to the four antennas 7
0 through the microwave window 72 into each plasma pump duct of the pump. The magnetic field lines are oriented radially inward or outward, depending on the direction of magnetization of the particular set of magnets forming the duct, as shown in FIG. The pump mechanism described above depends only on the orientation of the gradient of the magnetic field strength, not on the orientation of the magnetic field.

The pump inlet of the cylindrical stand-alone plasma vacuum pump shown in FIGS. 8-11 can be sized as desired, and the pump can be provided with additional plasma channels. The pump uses no mechanical parts or pump oil, does not contaminate the vacuum system, and can be mounted directly on the processing system. The only pump "fluid" used in plasma pumps is the gas from the system being evacuated.

According to a further feature of the embodiment shown in FIGS. 8-11, each inner magnet arrangement is surrounded by a wall 160 of non-magnetic material, preferably aluminum, as shown in FIG. This wall extends the entire length or height of the enclosure 50 between the plates 52 and 56. Said wall 160 defines a part of the outlet end of the pump duct, in particular a part which is deflated, so as to separate the gas flow regions of the pump duct from one another. At these outlets, the magnetic field lines of the flux channels abut the relevant surface of the wall 160.

In the pump of the present invention, exhausted gas can enter each duct in a direction perpendicular to the exhausted direction. In the embodiment of FIGS. 3-7, the gas is parallel to the flux plane, ie
Flow parallel to the width of each channel, and in Figures 8 to 11, the inlet flow is perpendicular to the flux plane.

The multi-channel plasma arrangement provides a large plasma surface that ionizes the gas molecules that enter the plasma pump. Therefore, this pump can exhaust large gas loads. The four-channel pump is designed to have a total plasma surface area of greater than 1000 cm ² so that the gas passing through the inlet openings 54 can enter the four pump ducts, 10 Torr · liter.
Gas loads of / sec or more can be exhausted. The gas entering the pump through the inlet opening 54 is first ionized by the first electrons heated by the microwaves launched from the antenna in the high magnetic field region. The plasma parameters that can be obtained in this way are in the following ranges: n _i = 10 ¹² to 10 ¹³ cm ⁻³ , T _e = 3 to 10 eV, degree of ionization = 1 to 10%
, Where n _i is the plasma density and T _e is the temperature of the second electron.

Plasma is introduced into the flux channels 138, which are
While backflowing the gas to the exit end of each flux channel, gas backflow is prevented by the orifices defining the flux channels. The plasma throughput resulting from the free flow of plasma along the magnetic field is about 10 to 30 Torr.
liter / sec.

The present invention utilizes collective plasma acceleration so that the plasma throughput is further increased by a factor of 3 to 5. Plasma acceleration results from microwave heating dynamics and magnetic field design. Additional component (har
No dware component) is required.

Finally, the arrangement of the magnetic field downstream of said plane d in FIG. 2 further increases the compression ratio such that the outlet pressure measured at the outlet face of the pump operates in the range 10 ⁻² to 1 Torr. Is designed to The inlet pressure operating at the inlet opening 54 is
It is in the range of 10 ⁻⁵ to 10 ⁻² Torr.

Details of the theory of operation of a stand-alone plasma vacuum pump are given below. In particular, the items required for the plasma vacuum pump, the design and calculation of the magnetic field, 2.45GH
The formation and heating of an over-dense plasma using high field launching Whistler wave heating at the microwave frequency of z, the collective plasma acceleration mechanism utilized in the present invention, and the momentum transfer pump mechanism are ,It is shown.

Required Items for Plasma Vacuum Pump Plasma Surface Area For a desired gas throughput (“load”) Q ₀ , the plasma pump is of sufficient size to maintain the desired operating pressure P. You have to give speed S ₀ . The required pump speed is given by:

[Equation 6] Pump speed is the volumetric flow rate in units of volume per unit of time, ie, liters per second. The working pressure is assumed to be the working pressure of the pump duct, and the pump speed is the volumetric flow rate through the sum of the "outer" magnetic field surfaces, which are later referred to as the vacuum-plasma interface.

For plasma vacuum pumps, gas molecules must be ionized before being pumped or removed out of the system. Since gas molecules enter the plasma at a given characteristic speed v ₀ , the surface area of the plasma must be large enough so that the gas can enter the plasma at a rate corresponding to the desired pump speed. The required plasma surface area A is given below.

[Equation 7] Where S ₀ is the desired pump speed, A is the total surface area of all surfaces of the vacuum-plasma interface, and v ₀ is the integral of these surfaces, perpendicular to these surfaces. The speed of gas. In the embodiment of FIGS. 8-11, the vacuum-plasma interface has all channels 138 such that the gas enters four flux channels.
Would include both aspects of. The factor 1/4 in equation (2) results from the three-dimensional effect. The first half is explained by the fact that half of the molecules flow in the direction of the pump and the second half is the azimuth cosine of the velocity vector.
al cosine) integration. If the plasma surface is too small,
The gas molecules cannot enter the plasma at a rate sufficient to provide the desired pump speed. This situation is similar to gas flow, which is limited to small conductances.

[0066]     Ion throughput   The ion throughput is given by the following ion flow equation.

[Equation 8] Where Q _ion is the total ion throughput through all pump ducts, n _i is the ion density, v _i is the ion velocity, and A _p is the total plasma flow. It is the total cross-sectional area of the channel. Here, the factor 1/4 is a three-dimensional effect similar to the case of the neutral gas flow. Ion density and ion speed are
Since both are limited to a narrow parameter range, the cross sectional area must be large enough to produce large ion throughputs. For typical plasma densities n _i = 5 × 10 ¹² cm ⁻³ and Te = 5 eV (ion velocity v _i is approximately 3 × 10 ⁵ cm / sec for Ar), such an ion throughput, ie approximately 10 Torr · liter / sec or almost 3 × 10 ²⁰ particles
The cross-sectional area required to achieve a Q _{ion of} le / sec is quite large as follows.

[Equation 9]

Pressure Difference The balance between gas throughput and load of the pump will determine the pressure difference between the inlet and outlet of the pump.

[Equation 10] Here, Q _pump is the throughput generated by the pump, C is the conductance of the pump, P _in is the pressure at the inlet, and P _out is the pressure at the outlet. The compression ratio of the pump is defined by P _out / P _in . The pressure difference and the compression ratio can be expressed by the following equation.

[Equation 11] as well as

[Equation 12] From equation (7), it is clear that Q _pump must be greater than Q ₀ to yield a compression ratio greater than 1. In the present invention, several augmentation devices (en
Hencement) is used to increase the throughput of the pump. When indicated by a symbol,

[Equation 13] Where β is the growth factor. β ≧ 100 is possible by implementing an augmentation mechanism, as will be shown in detail below.

Arrangement of Magnetic Fields The magnetic fields shown as practicing the invention are two-dimensional SUPERFISH-PAN.
DIRA code and three-dimensional ANSYS / Multiphysics code v5.
Designed using 4. Designs have been made for rectangular plasma pumps and cylindrical plasma pumps with 4, 6, and 8 plasma channels. A four channel arrangement is shown in FIGS. FIG. 11 shows only one half of each of the two mirror sections. The other half mirrors this arrangement including the direction of magnetization with respect to the straight edges (ie, the x and y axes).
ry reflection). Such mirroring is repeated until the complete array is completed. The magnetic field is oriented along these lines of symmetry. That is, a parallel boundary condition of magnetic flux is imposed.

At each quadrant of the four-channel pump, the pole piece 136 and a supplementary set of rectangular magnets 134 are arranged in a central region to optimize the local mirror field as follows: Used nearby.

The flux channel 138 extends from the local maximum magnetic field B _max2 towards the cylindrical axis of the enclosure 50 so as to guide the plasma flowing in the pump duct in a one-dimensional manner.

Most of the radially and inwardly directed magnetic flux is connected to the magnet 134 and then returns to the outer magnet 130. This further improves the magnetic field strength in the mirror area. The mirror region is usually the region extending radially between two maxima in the magnetic field, ie between the two maxima B _max1 and B _max2 of the magnetic field B in FIGS. 3 and 11.

ECR resonance (for microwave frequency of 2.45 GHz, B _res = 875
The Gauss) surface 140 is located a few inches inward from the outer magnet 130, allowing the outer magnet 130 to be located outside the vacuum vessel.

In order for the arranged waveguide antenna to perform “high field launching” heating,
The magnetic field strength B _max1 in the gap between each pair of the outer magnets 130 is sufficiently larger than the resonance magnetic field and B _max1 / so that Whistler waves can be emitted from the high magnetic field side.
B _res = 1.2. The magnetic field strength B _max1 is at the peak of the curve on the right side of B _res in FIG.

In the region of the magnetic field strength that is directed radially towards the pump duct and is decreasing radially and inwardly between the position of B _{max1 and} the position of B _min , the resonance plane (ECR) is It is formed at a position of B _res = 875 Gauss. The magnitude of the magnetic field gradient has been optimized for improved electronic heating.

The flux channels converge along the flow from B _min to B _max2 to direct the plasma to the outlet of the pump duct and into the quadrant formed by the structure 60. The gas is then exhausted to the outlet 58 along these quadrants by a pump (not shown) connected to the outlet 58. However, the maximum value B _max2 of the magnetic field is smaller than the resonance magnetic field strength. The local minimum B _min of the magnetic field in the mirror region is sufficiently smaller than the resonant magnetic field strength to enable effective plasma acceleration.

Formation and Heating of Overcrowded Plasma For example, B. H. Quon, R.A. A. By Dandl "Preferrentia"
l electron-cyclotron heating of hot
electrons and formation of overdense
plasma ", Physics of Fluids B1 (10), 19
October 1989, and G. E. Guest, M .; E. Fetzer, R.F. A.
Dandl, "Whistler-wave electron cyclot"
ron heating in uniform and nonuniform
m magnetic fields ", Physics of Fluids
As described in B2 (6), June 1990, experiments in electron cyclotron heating plasma technology show that whistler waves produce strong magnetic field strengths, B> Bre.
It proves that when launching from the position of s, where B _res = 2πf _μ / (m / e) toward the resonance region, strong wave absorption occurs and a dense plasma is generated. Where f _μ is the applied microwave frequency and e and m are the charge and mass of the electron, respectively. The Whistler wave propagates in the plasma in the following states.

[Equation 14] In this representation, k is the magnitude of the wave vector, E is the strength of the microwave electric field having a component E _⊥ perpendicular to the static magnetic field, z is the distance along the line of the magnetic field, and k
= 2π / λ is the magnitude of the wave propagation vector whose wavelength and (angular) frequency are λ and ω, respectively.

The Whistler wave has the right-handed circular polarization mode (ri
ght-hand circularly-polarized mode).

[Equation 15] Here, n ² = (kc / ω) ² is the square of the refractive index, α = (ω _pe / ω), Ω = e
B / m, θ is the angle between the wave vector k and the magnetic field B, c is the speed of light, e is the electron charge, m is the electron mass, ω _pe is the electron plasma frequency, and ω is The angular frequency of the wave. For small θ, the power absorbed by the plasma is expected based on the theory presented below.

[Equation 16] Here, P _abs is the power absorbed, P ₀ is the power of the incident wave, k _i is the imaginary part of the wave number, ω _ce = eB / m is the cyclotron frequency, v _e = (2T _e / m ) ^1/2 is the electron thermal speed (thermal speed).

From a waveguide horn with a quarter-wave window or a matched antenna, the Whistler wave with microwave power launched at ω _ce /ω=1.2 to 1.3 , Will predominantly propagate along the magnetic field lines with an intensity decay (eg, an increase in ki) due to absorption of the plasma and a corresponding decrease in wavelength (eg, an increase in k). Wave absorption occurs when the next Doppler shift resonance condition is established.

[Equation 17] | V _‖ | ≦ 2v _e electrons as can resonate with waves. For T _e or approximately 6 eV, the resonance zone is the magnetic field strength in the range of 810 ≦ B ≦ 940 G, or

[Equation 18] It extends to. _Note that on the high field side, v _∥ is negative, that is, the heated electrons move towards the antenna. These heated electrons are reflected by the relatively strong magnetic field on the front face of the antenna.

Typical plasma densities produced by whistler waves launched from high field regions are 1 to 3 × 1 without antenna tuning.
It is in the range of 0 ¹² cm ⁻³ . Specific coupling networks and low impedance antennas will be provided to achieve even higher plasma densities. A standard Fourport sidewall composite coupler with a low impedance horn and a quarter wave quartz window would be provided to achieve higher plasma intensities. A waveguide filled with alumina will be used to reduce the dimensions of the network when needed. Such coupling networks and antennas can be obtained in a manner known in the art by improving the available components.

Plasma Acceleration Technology Electron cyclotron heating electrons gain kinetic energy of motion perpendicular to the lines of the magnetic field.

[Formula 19] For example, David J. Rose, Melville Clark, Jr.
Plasmas and Controlled Fusion, The M. et al.
I. T Press and John Wiley & Sons (1961),
The motion of the electron in the space beyond the resonant interaction zone can be described by terms of the total energy ε and the magnetic field moment μ, as described particularly in Chapter 10.

[Equation 20] Where ψ is the possible electrostatic potential,

[Equation 21] Outside the resonant interaction region, ε and μ are kept constant by the law of conservation of energy and magnetic moment when the magnetic field does not change sharply in space.

The electron is subjected to a force F _∥ which is parallel to the magnetic field.

[Equation 22] Thus, in the absence of an electrostatic field, the electron's "parallel" kinetic energy is given at all points beyond the plane of resonance as:

[Equation 23]

For a radially extending magnetic flux channel as shown in FIG. 11, a coordinate system may be defined such that the s direction is along the centerline of the magnetic flux channel. "S"
Is the distance or position along the centerline of the flux channel from a reference point that can be arbitrarily determined. “B (s)” is the magnetic field strength at this position, that is, the magnetic field strength on this surface perpendicular to the magnetic flux lines and having a constant magnetic field strength. “S _res ” is the position of the plane perpendicular to the magnetic flux lines where the magnetic field strength is constant and equal to the resonance value.

Equation (19) shows that the electrons are accelerated radially and inward, parallel to the spatially decreasing magnetic field, parallel to and opposite the gradient. The heated electrons will be accelerated, but the ions will not be accelerated, so charge separation will occur and an electrostatic potential ψ will be generated. This potential is
Until the electron and ion species both have the same "ambipolar" parallel drift velocity, they impede electron travel and accelerate the ion.

[0084]   About electronic,

[Equation 24] This is because W _⊥ = μB = W _{⊥, res} B / B _res . For monovalent ions of charge e,

[Equation 25] Here, the subscript e indicates an electron.

[0085]   Adding equation (21) for ions and equation (20) for electrons,

[Equation 26] Here, the subscript i indicates an ion. In equilibrium, v _||, i = v _||, e = _{v a} So, "bipolar" speed,

[Equation 27] That is,

[Equation 28] Here, M is the mass of the ion.

It is important to ensure that as the plasma approaches the local high field region near the duct exit, it is not reflected by the magnetic field and significantly impedes its progress. The state of plasma that flows through the maximum value B _{max of the} magnetic field can be expressed by the following equation.

[Equation 29] Here, the kinetic energy of the ions is given by equation (25). Therefore, the maximum of the magnetic field should be below the resonant magnetic field.

Momentum Transfer Pump Mechanism The moving plasma ions are not only subject to internal and magnetic field forces,
It also has the stochastic effect of diffusing the plasma ions or impeding their movement. Momentum transfer collisions can cause these effects in the presence of an electric field. In this case, the throughput associated with the plasma is improved by including a term proportional to the ion mobility μ.

[Equation 30] Here, E is an electric field. _Let v _d = Eμ, where v _d is the drift velocity of the ions and the throughput of the ions can be expressed as:

[Equation 31] If (1 + v _d / v _i ) is replaced by β _μ ,

[Equation 32] Here, when E is large at a high pressure, the value of β _μ can be a large value.

The throughput of the pump is actually higher when the drift velocity of the neutral species is included. In fact, most of the neutral molecules in the system under consideration are also drifting at about the same drift velocity due to ion-neutral momentum transfer collisions. Therefore, the total pump throughput is

[Expression 33] Where n ₀ is the number density of the neutral gas and β _t is the enhancement factor for ions and neutral flow. Experimental tests in one plasma duct have demonstrated a strong boosting effect using the momentum transfer pump technique of the present invention.

The method and apparatus of the present invention can also be used to decompose exhaust gas by operating the pump as described above and supplying exhaust gas to the inlet of the pump. The stand-alone plasma vacuum pump of the present invention is capable of pumping any composition in gaseous form as long as the ionization of the gas produces a plasma of predominantly electron and cations.

[0090]

【The invention's effect】

While the above description illustrates specific embodiments of the present invention, it will be appreciated that many modifications may be made without departing from the essence of the invention. The claims are intended to cover such modifications as would fall within the true scope and nature of the invention.

The embodiments disclosed in this application are therefore considered in all respects by way of example and not by way of limitation, and the scope of the invention is indicated by the claims rather than the detailed description. Accordingly, it is intended that all modifications that come within the scope and spirit of the claims are to be embraced therein.

[Brief description of drawings]

[Figure 1]   FIG. 1 is a diagram showing the movement of electrons above the thermal temperature in a magnetic field.

FIG. 2 is a simplified diagram showing the magnetic field generated in the plasma region of the present invention.

3 is a diagram showing changes in magnetic flux density along the center line of the magnetic field shown in FIG.

FIG. 4 is a simplified side view showing one arrangement of the invention forming the rectangular embodiment of the magnetic field shown in FIGS. 2 and 3.

FIG. 5 is a bottom perspective view of a convenient rectangular embodiment of the stand-alone plasma vacuum pump of the present invention.

[Figure 6]   6 is a side sectional view of the embodiment of FIG.

[Figure 7]   FIG. 7 is a diagram viewed from the direction of arrow 22 in FIG.

FIG. 8 is a cutaway perspective view of a cylindrical embodiment of the stand-alone plasma vacuum pump of the present invention.

9 is a simplified plan view showing the underlying magnetic field arrangement of the components of the pump of FIG.

10 is a bottom view of the interior of the pump of FIG. 8 with the bottom panel removed.

11 is a detailed plan view showing a portion of the magnetic field associated with the permanent magnet arrangement of the pump of FIG.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01L 21/31 H05H 1/14 H05H 1/14 H01L 21/302 101G (81) Designated country EP (AT, BE , CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE, TR), OA (BF, BJ, CF, CG, CI, CM) , GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZW), EA ( AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY BZ, CA, CH, CN, CO, CR, CU, CZ, DE, DK, DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN , IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW F terms (reference ) 5C038 AA01 AA04 AA14 5F004 AA16 BB32 BC02 5F045 AA03 AA06 AA08 AE15 AE17 BB20 EG03 EG07

Claims (16)

[Claims] 1. A housing enclosing at least one pump region located between a low pressure inlet end and a high pressure outlet end; and said housing between said inlet end and said outlet end. At least one extending within the pump region
Two magnetic field regions which provide a magnetic flux channel for confining and guiding the plasma, the magnetic flux channel being such that the magnetic field has a negative intensity gradient from the inlet end towards the outlet end. A permanent magnet device having a first portion, and exciting the electrons in the first portion of the magnetic flux channel to a resonance state so as to generate a plasma by ionizing a gas in the magnetic flux channel. And a microwave source that imparts microwave energy in the flux channel such that the interaction between the electrons and the magnetic field creates a force that drives electrons and ions in the plasma to the exit end. An independent plasma vacuum pump for exhausting gas from the inlet end to the outlet end. 2. The magnetic flux channel has a second portion disposed between the first portion and the outlet end, in which the magnetic field is directed to the inlet end. The plasma vacuum pump of claim 1 having a positive intensity gradient from the outlet end toward the outlet end. 3. The plasma vacuum pump of claim 2, wherein the negative intensity gradient has a larger absolute value than the positive intensity gradient. 4. The magnetic flux channel has a third portion located between the second portion and the outlet end, in which the magnetic field extends from the inlet end. The plasma vacuum pump of claim 2, having a negative intensity gradient toward the outlet end. 5. The third portion has a baffle for impeding the flow of ions from the outlet end to the inlet end, and the pump region is cylindrical with a long axis, The plasma vacuum pump of claim 4, wherein the flux channel extends from the inlet end to the outlet end in a direction transverse to the major axis. 6. The first portion and the third portion within the channel being evacuated to minimize the flow of electrically neutral gas molecules from the outlet end toward the inlet end. 6. The pump of claim 5, further comprising a member disposed between the baffle and having a plurality of narrow slots associated with the baffle. 7. The plasma vacuum pump according to claim 2, wherein the microwave source is a microwave antenna connected to the magnetic flux channel. 8. The plasma pump of claim 7, wherein the antenna is a Four Port Sidewall Combiner with impedance tuning transitions. 9. The antenna comprises a waveguide having a narrow aperture formed therein and comprising a waveguide window, the window cooling the window and the waveguide and the waveguide window. The plasma pump according to claim 7, wherein the plasma pump is pressurized with forced cooling nitrogen gas so as to suppress discharge. 10. The plasma pump of claim 9, wherein the waveguide window is formed of a quarter-wave thick plate of quartz and alumina having a vacuum seal. 11. The plasma pump of claim 9, wherein the antenna further comprises a wall with an alumina liner in a region extending from the waveguide window beyond a resonance zone in the flux channel. . 12. A plurality of pump regions, said permanent magnet arrangement providing a plurality of said flux channels respectively disposed within each pump region, wherein mass flow from one of said pump regions to the other is provided. The partition wall member for preventing the above is further provided.
1 pump. 13. A means arranged to couple microwave power and the permanent magnet arrangement are such that the magnetic flux is such that a collective plasma acceleration towards the outlet end of the pump region is produced. The pump of claim 1 arranged to optimize acceleration of electrons along the channel. 14. The permanent magnet device generates a magnetic field having an electron cyclotron resonance surface having a constant magnetic field strength B _res in the magnetic flux channel, the magnetic flux channel having a magnetic field strength close to that of the microwave source. At position 1
． 2 comprises a region that exceeds the larger factor amount corresponding B _res, magnetic field strength of the magnetic flux within the channel, between the resonance surface and said outlet end, has a substantially smaller minimum value from the B _res The pump according to claim 1, wherein the magnetic field strength has a maximum value smaller than B _res at a surface close to the outlet end. 15. A method of decomposing effluent gas, comprising activating the pump of claim 1 and supplying effluent gas to an inlet end of the pump. 16. A pump according to claim 1, wherein the inlet end of the pump is connected to a low pressure region, and the pump is operated to exhaust gas from the low pressure region. Exhausting gas from low pressure areas.