WO2011037488A1

WO2011037488A1 - Plasma ion source

Info

Publication number: WO2011037488A1
Application number: PCT/RU2009/000486
Authority: WO
Inventors: Konstantin Viktorovich Vavilin; Elena Alexandrovna Kralkina; Vladimir Borisovich Pavlov; Seok Keun Koh; Cheol Su Lee
Original assignee: INANO Ltd
Current assignee: INANO Ltd
Priority date: 2009-09-22
Filing date: 2009-09-22
Publication date: 2011-03-31
Anticipated expiration: 2012-03-22

Abstract

A plasma ion source comprises a cathode chamber (1) including a gas-inlet branch pipe (2). A hollow anode (3) forms an anode chamber (4). An emission electrode (11) of an ion extraction system is arranged in an outlet of the anode chamber (4). Between the cathode and anode chambers there is an additional electrode (5) with orifices (9) formed therein. Protrusions are formed on the surface of the additional electrode (5). The anode chamber (4) comprises a grounded casing (7) to which the additional electrode (5) is electrically connected. A magnetic system comprises a magnetomotive force source made in the form of an electromagnetic coil (15) arranged coaxially with respect to the additional electrode (5). An induction vector of a magnetic field produced in the cathode and anode chambers has a predominantly axial direction. The magnetic induction decreases in the axial direction from the additional electrode (5) to the emission electrode (11) and from the additional electrode (9) to the end wall of the cathode chamber (1).

Description

PLASMA ION SOURCE

Field of the invention

The invention relates to a plasma technique, more particular, to plasma sources intended for the generation of intensive ion beams. The invention may be practiced in processing systems using ion beams for deposition of coatings, ion assistance, ion implantation, cleaning of surfaces, and modification of material surface properties.

Background of the invention

In recent years various types of plasma ion sources are known which include cold cathodes. For example, it is known from Japanese patent application JP 57011448 (IPC - HOI J 3/04, 27/08, published on 21.01.1982) a gas-discharge device comprising a hollow cathode. Such a device is employed as a part of ion sources. Electrons generated in a cathode cavity are extracted into an expansion chamber along magnetic field lines of a particular three- dimensional configuration. The magnetic field is produced in such a device with the use of a magnetic system comprising a number of electromagnetic coils mounted around the hollow cathode chamber. The design of such a device ensures minimized energy demands for generating a main discharge and, accordingly, for producing a wide-aperture ion beam.

Another alternative plasma ion source described in USA Patent N° 4782235 (IPC - HOI J 27/02, published on 01.11.1988) comprises a hollow cathode, an expansion anode chamber, and a magnetic system. The magnetic system includes a magnetic core forming a magnetic gap between two circular poles, through which gap ions are extracted into the expansion chamber. Such a structural design of the ion source ensures an increase in gas and energy efficiency and an enhancement of ion current extraction.

Plasma ion sources comprising cold hollow cathodes are extensively used in various ion- beam processes. Ion sources are developed which use both inert gases and chemically active gases. In such sources comprising an anode chamber separated from a cold cathode, a cold hollow cathode is used, a magnetic field for stabilizing a discharge being generated in the cavity of such a cathode. The value of ion current generated by such type ion sources ranges from 100 to 300mA depending on the diameter of a discharge chamber outlet. A discharge voltage between the hollow cathode walls and the anode chamber is chosen within a range of from 350 to 550V.

However, intensive wide-aperture ion beams generated by means of the above plasma ion sources provide for low homogeneity of the current density distribution across the beam. Inhomogeneity of ion current density inherent to such ion sources is due to nonuniform distribution of charged particles concentration in the anode chamber at an emission aperture thereof. The ion current nonuniformity value generally exceeds 10% of an average ion current density to substantially limit the application of such ion sources as a part of ion-beam processing equipment for processing different materials with the use of large section beams.

The closest analog of the invention to be patented is a plasma ion source disclosed in Russian Patent RU2167466C1 (IPC - H01J3/04, H01J 37/08, published on 20.05.2001). A known ion source comprises a cathode chamber including a gas-input unit, a hollow anode forming an anode chamber, and an electrostatic ion extraction system with an electrically insulated emission electrode provided in an outlet of the anode chamber. In the cathode chamber there is a discharge initiating electrode electrically connected to the hollow anode. Near the cathode chamber outlet there is an additional electrode which is electrically insulated from the hollow anode and the cathode chamber. An orifice provided in the additional electrode has a diameter which does not exceed 10% of a maximum internal cross-sectional size of the hollow anode.

The anode chamber is communicating with the cathode chamber via an outlet provided through an end wall of the cathode chamber and via an orifice formed in the additional electrode. The ion source comprises a magnetic system which generates a magnetic field with an induction vector of predominantly axial direction in the cathode and anode chambers. In addition, the magnetic field induction decreases from the walls of the cathode chamber and anode chamber towards their longitudinal axis of symmetry and towards the outlets of said chambers.

The utilization of a magnetic system with an induction vector of predominantly axial direction ensures a decrease of nonuniformity in the distribution of charged particles concentration and allows the losses of the generated ions on the walls of the chambers to be minimized. The given ion source ensures generation of wide-aperture ion beams of inert and chemically active gases with a sufficiently high homogeneous density of ion current. In case of utilizing the known ion source, inhomogeneous distribution of ion current density across the beam having a diameter of 40 mm did not exceed 5%. It should be pointed out, however, that the demanded uniformity of high-energy electrons distribution within the volume of the anode chamber of the known ion source was reached with the use of a specific electron reflector provided opposite the orifice in the additional electrode. At the same time high uniformity of the ion current density across the beam was reached during operation of the ion source at the extracted ion current intensity in a limited range of from 20 to 70mA. At the intensity of extracted ion current increased to 100- 120mA during operation of the plasma ion source the occurrence of the so-called "spoke" effect, that is, an axial region in the anode chamber having an essentially high current density in comparison with peripheral regions, had been observed. In this case, the deviation of the ion current density from an average level may reach up to 70%. Moreover, the employment of the electron reflector located in the anode chamber for leveling the ion current density and the application of a complicated magnetic system makes the design of the ion source substantially intricate.

Disclosure of the invention

The basic concept of the invention is the object aimed at increase in the uniformity of charged particles distribution in the anode chamber and, accordingly, in the uniformity of the current density distribution across the wide-aperture beam when the extraction extent of ion current is increased to a value greater than 100mA. Another object of the invention is to avoid utilization of a high-energy electron reflector in the device and to essentially simplify the design of the magnetic system.

The solution of the above problems ensures the achievement of a novel technical result including an increase in the value of extracted ion current of a wide-aperture beam at predetermined uniformity of current density across the beam. In addition, the invention is aimed at simplifying the design of the ion source by eliminating additional structural components, including the reflector and the magnetic system components located in the discharge volume of the ion source.

The cited technical results are ensured by utilizing a plasma ion source comprising a cathode chamber including a gas-input branch pipe and a discharge initiating electrode, a hollow anode forming an anode chamber, an ion extraction system with an emission electrode located in an outlet of the anode chamber, and a magnetic system for creating a magnetic field with an induction vector of predominantly axial direction in the cathode chamber and the anode chamber. The ion source is further provided with an additional electrode electrically insulated from the cathode chamber and located between the cathode and anode chambers. The additional electrode has at least one orifice. The cathode chamber is communicating with the anode chamber via a cathode chamber outlet provided through the end wall of the cathode chamber, the orifice in the additional electrode, and an inlet provided through the end wall of the anode chamber. According to the invention, the diameter d of the orifice in the additional electrode is chosen under the condition that 0,1 mm<d<l mm. The magnetic system comprises at least one magnetomotive force source arranged coaxially with respect to the additional electrode and intended for creating in the orifice of the additional electrode a magnetic field of axial direction with the induction value of from 2 to 15mT. The magnetic system is designed so that the magnetic field induction value B is axially decreased from the additional electrode towards the emission electrode and from the additional electrode towards the end wall of the cathode chamber opposite the outlet to the value of at least 0,6B.

The combination of the above essential features of the invention ensures the achievement of a novel technical result provided by an increase in the uniformity of ion current density distribution across an intensive ion beam with the current value greater than 100mA. The given effect is reached without application of additional structural components in comparison with the chosen prototype due to providing adequate conditions for uniform distribution of charged particles concentration within the volume of the anode chamber near an emission aperture thereof.

During functioning of the plasma ion source, ions emitted from the cathode surface are accelerated in a cathode layer to intersect the cathode chamber cavity and get into the cathode layer region adjoining the opposite wall of the chamber. Oscillation of electrons continues until said electrons reach an outlet formed in the end wall of the cathode chamber. The given outlet is communicating with one or more orifices formed in the additional electrode which is electrically insulated from the cathode chamber.

The superimposing of the magnetic field in the cathode and anode chambers hinders radial motion of electrons, primarily in the vicinity of the cathode chamber outlet and the anode chamber inlet, wherein the magnetic field induction reaches a maximum value. An increase in the magnetic induction of the magnetic field near the cathode chamber outlet provides optimum conditions for oscillation of electrons in the volume of the cathode chamber. This results in lengthening of an electron free motion path within the cathode chamber and in enhancing the degree of probability of particles non-elastic collision. In this case ionization of a working gas is probable. On the whole, generation of a magnetic field of a particular configuration and predetermined field induction (from 2 to 15mT) near the orifices in the additional electrode ensures a prolonged lifetime of electrons and an increased probability of ionizing the working gas atoms.

Of essential importance is the lateral size of the orifice (or a number of orifices) in the additional electrode which is under a floating potential during operation of the ion source. When choosing the diameter of orifices in the additional electrode according to the established condition (0.1mm<d<lmm), the probability of influence of a discharge voltage between the cathode and anode chambers on energy distribution of extracted ions is eliminated. In this case the energy and current density of ions extracted from the anode chamber are adjusted by changing the potentials on electrodes of an ion-optical system for ion extraction.

A minimum size of orifices in the additional electrode (0.1mm<d) .is chosen on the condition that it exceeds Debye length, i.e., the condition providing plasma state of a working substance. So, the selection of a predetermined size of orifices in the additional electrode allows the working gas near the orifices in the additional electrode to be maintained in a plasma state at operating modes characteristic of gas-discharge ion sources. The given conditions ensure penetration of an electric field through the orifices from the anode chamber into the cathode chamber which is necessary for extraction of electrons from the cathode chamber into the anode chamber.

A maximum size of orifices in the additional electrode (d<lmm) is limited by a size of the region in the vicinity of the cathode wherein the potential fall takes place, said size being characteristic of the given type of devices. So, keeping to the condition (0.1mm<d<lmm) allows the influence of the cathode potential on the space potential of the anode chamber in the plasma ion source to be eliminated.

The compliance with the above conditions provides on the whole the possibility of uniform potential distribution in the volume of the anode chamber and the charged particles concentration near the emission orifice. Such a possibility determines the demanded extent of uniformity in distribution of the current density across the ion beam to be extracted.

A number of orifices of diameter d can be formed in the additional electrode. In this case the orifices should be spaced from each other by a distance of at least 2d between the centers of adjacent orifices. The total cross-sectional area S_∑ of the orifices in the additional electrode is chosen in compliance with the condition that 0.03mm 2 <S_∑<3mm 2.

In the preferable variant of embodiment of the ion source, five orifices are formed in the additional electrode, one of said orifices extending in axially aligned relation with respect to a longitudinal axis of symmetry of the additional electrode while the remaining four orifices being equally spaced apart from each other along the circumference of said one orifice.

In order to provide the demanded thermal conditions for the plasma ion source, the cathode chamber of the preferred variant of embodiment may be furnished with a forced cooling system. Different variants of a magnetomotive force source for the magnetic system may be used, including a variant which comprises permanent magnet assemblies or a circular electromagnetic coil.

The additional electrode is predominantly equipped with a projection directed towards the cathode chamber cavity. In this case the orifice is formed in the projection of the additional electrode. The projection of the additional electrode can be formed as a truncated cone. The given shape of the additional electrode serves to enable conditions for ignition and maintaining of electrical discharge between the cathode and anode chambers owing to the usage of electric field concentrators such as electrode projections.

In the preferred variant of embodiment of the ion source, the anode chamber can be equipped with a grounded casing which is electrically connected to the additional electrode.

Brief description of drawings

The invention is explained by a particular example of embodiment of a plasma ion source to be employed as a part of an ion-beam processing installation.

The design of the ion source is illustrated in the accompanying drawings, wherein:

Fig. 1 is a schematic view of a longitudinal section of a plasma ion source.

Fig. 2 is a schematic view of a transverse section of an anode chamber of a plasma ion source illustrated in Fig. 1 (section A-A).

Fig. 3 is an electric supply circuit of a plasma ion source.

Fig. 4 is a curve of changes in the values of magnetic field induction represented in relative units B_z/B_max along a longitudinal axis of symmetry Z of cathode and anode chambers.

Preferable example of embodiment of the invention

The plasma ion source illustrated in Figs 1 and 2 comprises a cathode chamber 1 including a gas-inlet branch pipe 2 which also serves as a discharge initiating electrode, and a hollow anode 3 forming an anode chamber 4. An additional electrode 5 arranged between the cathode chamber 1 and the anode chamber 4 is electrically insulated from the cathode chamber 1 by means of a circular insulator 6 and electrically connected to a grounded casing 7 of the anode chamber 4. The hollow anode 3 is electrically insulated from the casing 7 by means of three insulators 8 arranged in equally spaced apart relation along the circumference between the hollow anode 3 and the casing 7 (see Fig. 2).

Five orifices 9 of a diameter d=0.5mm are provided in the additional electrode 5, said diameter complying with the condition: 0.1mm<d<lmm. One of the orifices 9 is axially aligned with an outlet of the cathode chamber 1 and an inlet of the anode chamber 4 while four other orifices are uniformly distributed along the circumference around the axial orifice (see Fig 2). The orifices 9 are equally spaced apart from each other by a distance / = 5mm. In the given case the condition / > 2d is complied with. The total cross-sectional area S_∑ of the transverse orifices 9 in the additional electrode 5 is 2.4mm² under the condition: 0.03mm² < S∑ < 3mm². The orifices 9 are made in the projections formed on the surface of the additional electrode 5. The projections are directed towards the cavity of the cathode chamber

I and shaped as truncated cones in the regions near the orifices 9.

The cathode chamber 1 and the hollow anode 3 are made in the form of hollow steel cylinders with an internal diameter of 50mm. The cathode chamber 1 is intended to be force cooled. For this purpose, the cathode chamber is fitted with pipes 10 forming an outer wall of the cathode chamber 1 and intended for circulation of a cooling liquid therein. The pipes 10 are made of a fire-resistant stainless steel and electrically insulated from other components of the ion source.

The anode and cathode chambers are communicating to each other via an outlet formed in an end wall of the cathode chamber 1, the orifices 9 formed in the additional electrode 5, and an emission inlet formed in an end wall of the anode chamber 4. An electrostatic ion extraction system is arranged at an emission outlet of the anode chamber 4. An emission electrode 11 is located directly in the outlet of the anode chamber 4. An accelerating electrode 12 and a grounded output decelerating electrode 13 are located rearward of the emission electrode 11. The electrodes of the electrostatic system are insulated from each other by means of insulators 14.

The plasma ion source is further equipped with a magnetic system for producing in the anode and cathode chambers of a magnetic field with a magnetic induction vector of predominantly axial direction. A circular electromagnetic coil 15 used as a magnetomotive force source for the magnetic system is arranged coaxially with respect to the additional electrode 5. The electromagnetic coil 15 generates a magnetic field with an induction value B=8mT in the orifices 9 of the additional electrode 5.

The electromagnetic coil 15 is formed so as to enable a decrease in the induction value of the magnetic field B axially from the additional electrode 5 towards the emission electrode

I I and from the additional electrode 5 towards the end wall of the cathode chamber 1, said end wall being arranged opposite the outlet of this chamber. The magnetic field induction value decreases in said directions from B_max=B=8mT to 0.4B=3.2mT. In other alternative variants of embodiment of the invention, permanent magnet assemblies may be used as a magnetomotive force source, said permanent magnet assemblies creating a magnetic field having the above parameters in the cavities of the cathode and anode chambers. In different variants of embodiment of the invention, the magnetic field induction value near the orifices in the additional electrode may vary in the range of from 2 to 15mT.

Components of the plasma ion source are attached to a mounting flange 16. The casing of the cathode chamber 1 is electrically insulated from the mounting flange 16 by means of four rod-like insulators 17 located in a circumferential direction of the flange 16 (see. Figs 1 and 2). The gas-inlet branch pipe 2 functioning as a discharge initiating electrode is electrically insulated from the cathode chamber 1 and the mounting flange 16 by means of insulators 18 and 19, respectively.

The mounting flange 16 intended for attaching the plasma ion source in a vacuum chamber provides for vacuum tightness of joints between the vacuum chamber and the ion source. The flange 16 is fitted with air tight electrically insulated connectors 20 of power points 21 of a power supply system for the ion source and air tight electrically insulated connectors 22 for the pipes 10 with a cooling liquid circulating therein.

The power supply system for the ion source consists of a discharge voltage source 23 (DVS), an accelerating voltage source 24 (AVS), an electrostatic ion extraction system, and a constant-current source 25 (CCS) for supplying current to the electromagnetic coil 15. A connection diagram for connecting the power supply system to the ion source components is illustrated in Fig. 3.

The walls of the cathode chamber 1 are connected to a negative pole of the discharge voltage source 23 whose positive pole is connected to the gas-inlet branch pipe 2. The cathode chamber 1 and the anode chamber 4 are electrically insulated from each other by means of an insulator 6 (see Fig. 1). The hollow anode 3 is electrically insulated from the walls of the anode chamber casing by means of three insulators 8 (see Fig 2) and connected to the positive pole of the discharge voltage source 23 and to a positive pole of the accelerating voltage source 24. The additional electrode 5 electrically insulated from the cathode chamber is electrically connected to the grounded casing 7 of the anode chamber 4. The emission electrode 11 of the electrostatic ion extraction system is electrically insulated by the insulators 14 from other electrodes of the electrostatic ion extraction system and is under a plasma floating potential. The accelerating electrode 12 is connected to a negative pole of the accelerating voltage source 24 whose positive pole is connected to the hollow anode 3. The decelerating electrode 13 of the electrostatic ion extraction system is grounded. Leads of the electromagnetic coil 15 are connected to terminals of the constant-current source 25. Functioning of the plasma ion source whose design and electric supply diagram are illustrated in Figs 1 to 3 is effectuated as follows.

The ion source is attached to the mounting flange 16 in the cavity of the vacuum chamber. Power is supplied to the electrodes and the magnetic system of the ion source through power points 21 positioned within vacuum air tight connectors 20 of the mounting flange 16. A forced cooling system for the walls of the cathode chamber 1 is connected to the pipes 10 through which pipes a cooling liquid is circulating. The pipes 10 are hermetically positioned in the mounting flange 16 by means of electrically insulated connectors 22.

The working plasma-forming gas such as argon is fed into the cathode chamber 1 through the gas-inlet branch pipe 2. Upon switching of the constant-current source 25 electric current flows through the electromagnetic coil 15 to create in the cathode chamber 1 and the anode chamber 4 a magnetic field of a specific configuration with a magnetic induction vector of predominantly axial direction. According to a chart of changing the induction of magnetic field in relative units B_z/B_max along the longitudinal axis of symmetry Z of the cathode and anode chambers (see Fig. 4) an axial induction component of the magnetic field B_z smoothly increases from 0.4B_max=3.2mT at the end wall of the cathode chamber 1 (Z^cm) to the maximum value of Bmax^SmT near the orifices 9 in the additional electrode 5 (Z=7cm), followed by smooth decrease to the value of 0.4 B_max=3.2mT near the emission outlet of the cathode chamber 4 (Z=T2cm). In the represented dependence chart of B_z/B_max(Z) an axial distance Z is measured from the surface of the mounting flange 16 laterally of the vacuum chamber towards the emission electrode 11 of the electrostatic ion extraction system.

The electric discharge is initiated by supplying voltage from the discharge voltage source 23 to the walls of the cathode chamber 1 and to the gas-inlet branch pipe 2 insulated from the cathode chamber 1. A positive pole voltage is applied to the branch pipe 2 and a negative pole voltage is applied to the walls of the cathode chamber 1 from the respective poles of the discharge voltage source 23. At the same time the discharge voltage is applied between the walls of the cathode chamber 1 and the hollow anode 3 by connecting the hollow anode 3 to the positive pole of the discharge voltage source 23.

The discharge initiating voltage applied to the branch pipe 2 can be adjusted until a value is set at which value an electric breakdown occurs in the discharge gap and a discharge is ignited in the cathode chamber 1. The main discharge is ignited between the cathode and anode chambers by the effect of an applied potential difference of 350V owing to the extraction of electrons from the cathode chamber 1 into the anode chamber 4 via the orifices 9 in the additional electrode 5. 09 000486

10

The ignition of the main discharge between the cathode and anode chambers is accompanied by passage of discharge current in the electric circuit followed by reducing the discharge voltage to 300V. The applied discharge voltage can be adjusted through the use of a controlled resistor inserted into the electric power circuit (not shown in Fig. 3). Upon ignition of the main discharge, the additional electrode 9, which is electrically insulated from the walls of the cathode chamber 1 and connected to the grounded casing 7 of the anode chamber, is under the floating potential of the plasma filling the cavity of the anode chamber 4.

The magnetic field of specific configuration generated in compliance the dependence B_z/B_max(Z) shown in Fig. 4 and having magnetic induction B_z/B_max=8mT ensures electron oscillation in the cathode chamber 1 accompanied by effective working gas ionization. Electrons in the cathode chamber are directed into the anode chamber 4 via the orifices 9 in the additional electrode 5 by the action of the potential difference applied between the cathode and anode chambers with minimum losses on the walls of the chambers. The magnetic field of specific configuration generated in the anode chamber 4 ensures adequate conditions for uniform distribution of charged particles concentration at the emission outlet. As a consequence, the extracted ion beam is highly homogeneous with regard to the ion current density across the beam.

Ions are extracted from the anode chamber 4 upon supplying of voltage to the accelerating electrode 12 of the electrostatic ion extraction system from the accelerating voltage source 24. The ion beam is extracted and formed in the example of embodiment of the invention under investigation using a three-electrode electrostatic ion extraction system, based on an accelerating-decelerating principle. A predetermined space distribution of electrostatic potential is ensured between a gas discharge plasma produced in the anode chamber 4 and having a potential set by the potential of the hollow anode 3, the emission electrode 11 being under the floating plasma potential, the accelerating electrode 12 to which the negative pole voltage is supplied from the accelerating voltage source 24, and the grounded decelerating electrode 13. Ions are extracted from the anode chamber 4 under the influence of the electrostatic field and the ion beam is formed, said ion beam having a desired ion current density and a predetermined section.

Since the cathode chamber 1 is the most thermally-stressed component of the ion source, the temperature conditions are maintained in the cathode chamber by means of a forced cooling system. Walls of the cathode chamber 1 are cooled by forced circulation of a cooling liquid through the pipes 10 embracing the chamber casing (see Fig. 1). The value of the extracted ion beam current is stabilized during 5min. On variation of the discharge voltage in the range of from 300 to 600V, the discharge current between said chambers correspondingly varies in the range of from 100 to 1,500mA. The value of the extracted ion current reaches 150mA.

Along with predetermined parameters of a magnetic field, choosing of diameter d of the orifices 9 in the additional electrode 5 is of prime importance to provide for a desired uniformity in the current density across section of a wide-aperture ion beam, said choosing being based on the condition: 0.1mm< d <lmm. The given condition, on the one hand, designates the possibility of free extraction of electrons from the cathode chamber 1 into the anode chamber 4 via the orifices 9 with d > 0.1mm. The selection of sizes of the orifices 9 greater than a Debye length, which is not greater than 0.1mm for the type of device under investigation, characterizes the condition under which the working gas in the orifice is in a plasma state. In this case, on passage of electron current tlirough the orifice 9, the probability of occurrence of an electron space charge, which may affect the potential distribution in the anode chamber 4, is avoided.

On the other hand, limitation of the size of orifices 9 to a value under the condition d<lmm eliminates the influence of the cathode potential on the space potential in the anode chamber 4 and, as a consequence, on distribution of the charged particles concentration in the cavity of the anode chamber 4.

In case a number of orifices are formed in the additional electrode, the total cross- sectional area S_∑ of the orifices 9 in the additional electrode is chosen in compliance with the condition: 0.03mm² < S_∑ < 3mm². When said condition is satisfied, the uniformity of extracted ion current density across the beam is improved and the influence of discharge voltage on the energy of ions extracted from the anode chamber is eliminated.

In the example of embodiment of the invention under investigation, each of the five orifices 9 in the additional electrode 5 has a diameter of 0.5mm (S∑ =2.4mm²) at a spacing between adjacent orifices / =5 mm (/ > 2d).

Variations of the discharge voltage in the range of from 300 to 600V caused corresponding variations in the density of ion current generated by the plasma ion source in the range of from 0.2 to 6mA/cm². Nonuniformity of ion current density across the beam having a diameter of 50mm did not exceed 5%. Measurements were talcen using a target spaced from the decelerating electrode 13 of the electrostatic ion extraction system by a distance of 200mm. The maximum value of extracted ion current made 150mA at the demanded uniformity of the ion current across the beam section. The measured ion current value was in compliance with the diameter D_e=50mm of the emission outlet of the anode chamber.

The results of the conducted researches showed that the uniformity of the extracted ion current density across the beam decreased when the magnetic field in the cathode and anode chambers deviated from a specific configuration and the magnetic field induction in the orifices of the additional electrode deviated from the predetermined range of values. The similar effect was stated at an increased or decreased diameter d of the orifices 9 in the additional electrode 5 in comparison with the set range of values d: 0.1mm < d < 1mm. The indicated effects came out at the extracted ion current values exceeding 100mA.

In the above preferential example of embodiment of the invention, the circular electromagnetic coil is used as a magnetomotive force source, however the given version of embodiment of the invention does not deny the employment of other types of magnetomotive force sources. For example, the magnetic system may comprise permanent magnet assemblies instead of the electromagnetic coil, said permanent magnet assemblies ensuring predetermined distribution of the magnetic field in the anode and cathode chambers with a demanded field induction in the orifices of the additional electrode.

Moreover, the invention can be carried out with the use of a single axial orifice provided in the additional electrode. The additional electrode can be free from projections faced towards the cavity of the cathode chamber. In addition, variants of embodiment of the ion source are possible, wherein the additional electrode is electrically insulated not only from the cathode chamber, but also from the anode chamber casing. Along with inert gases, chemically active gases such as oxygen may be used as a working gas. Industrial applicability

The carried out experimental researches prove that the application of the above variants of embodiment of the invention also ensures the achievement of the technical result including an increase in the wide-aperture ion beam current value greater than 100mA at a demanded uniformity of current density across the extracted beam. The possibility of achieving a novel technical result allows the plasma ion source to be utilized as a part of ion-beam technological installations using intensive wide-aperture ion beams. Homogeneous large diameter ion beams generated with the use of the plasma ion source may be employed in various processes, including those used for processing of semiconductor materials.

Claims

1. A plasma ion source, comprising a cathode chamber (1) equipped with a gas-inlet branch pipe (2) and a discharge initiating electrode, a hollow anode (3) forming an anode chamber (4), an ion extraction system with an emission electrode (11) located in an anode chamber (4) outlet, a magnetic system for producing a magnetic field with an induction vector of predominantly axial direction in the cathode and anode chambers (1, 4), and an additional electrode (5) electrically insulated from the cathode chamber (1) and located between the cathode and anode chambers (1, 4), wherein at least one orifice (9) is formed in the additional electrode (5), the cathode and anode chambers (1, 4) are communicating with each other via a cathode chamber outlet formed in an end wall of the cathode chamber (1), the orifice (9) formed in the additional electrode (5), and an anode chamber inlet formed in an end wall of the anode chamber (4), is characterized in that a diameter d of the orifice (9) formed in the additional electrode (5) is chosen under the condition: 0.1mm < d < 1mm, the magnetic system comprises at least one magnetomotive force source arranged coaxially with respect to the additional electrode (5) and intended for producing a magnetic field in the orifice (9) of the additional electrode (5), said magnetic field being axially directed and having an induction value of from 2 to 15mT, said magnetic system being formed in such a way that the induction B of the magnetic field axially decreases from the additional electrode (5) to the emission electrode (11) and from the additional electrode (5) to the cathode chamber end wall opposite the outlet to the value not greater than 0.6B.

2. The plasma ion source of the claim 1 is characterized in that at least two orifices (9) of the diameter d are formed in the additional electrode (5), said orifices being arranged at a distance of at least 2d between the centers of the adjacent orifices, and the total cross- sectional area S_∑ of the orifices (9) in the additional electrode (5) being chosen under the condition: 0.03mm² < S_∑< 3mm².

3. The plasma ion source of the claim 2 is characterized in that five orifices (9) are formed in the additional electrode (9), one of said orifices being axially aligned with an axis of symmetry of the cathode and anode chambers (1, 4) and four other orifices being uniformly distributed along the circumference around said one orifice.

4. The plasma ion source of the claim 1 is characterized in that the cathode chamber (1) is provided with a forced cooling system.

5. The plasma ion source of the claim 1 is characterized in that the magnetomotive force source is made in the form of permanent magnet assemblies.

6. The plasma ion source of the claim 1 is characterized in that the magnetomotive force source is made in the form of a circular electromagnetic coil (15).

7. The plasma ion source of the claim 1 is characterized in that the additional electrode (9) comprises at least one protrusion directed towards the cathode chamber cavity, the orifice (9) being formed in the protrusion of the additional electrode (5).

8. The plasma ion source of the claim 7 is characterized in that the protrusion of the additional electrode (5) is made in the form of a truncated cone.

9. The plasma ion source of the claim 1 is characterized in that the anode chamber (4) comprises a grounded casing (7) electrically connected to the additional electrode (5).