Abstract:
An ECR ion-beam source for use in an ion implanter has a sealed plasma chamber in which plasma is excited by microwave radiation of 2.45 GHz in combination with an external magnetic field generated by permanent magnets surrounding the plasma chamber. The magnets cause electron-cyclotron resonance for the electrons of the plasma thus creating conditions for efficient absorption of the microwave energy. The same magnets generate a magnetic field, which compresses the plasma toward the center for confining the plasma within the plasma chamber. The ion source also has an RF pumping unit that pumps into the plasma the RF energy. The RF pumping unit has a unique additional function of RF magnetron sputtering of solid targets converted into a gaseous working medium used for implantation in an ionized form. For obtaining elongated belt-type ion beams (having a width of 1 m or longer), the ion source may contain a microwave pumping system having several output windows arranged in series along the axis of the plasma chamber and on diametrically opposite sides thereof. The windows are continuously cleaned from the contaminants that might precipitate onto their surfaces. A standard-type sand blaster can be used for cleaning of the windows.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]    The present patent application is a continuation of U.S. patent application Ser. No. 09/476,529 filed Jan. 3, 2000, which is currently pending. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to ion-beam technology, in particular, to electron-cyclotron resonance type ion beam sources for use in ion implanters. Implanters of this kind find application for ion implantation in the manufacture of electronic devices such as LSI and VLSI semiconductor circuits.  
         BACKGROUND OF THE INVENTION  
         [0003]    An ion implanter is a device, which is used for material processing in industrial manufacture. Major application of them is concentrated on semiconductor device fabrication, especially on modifying electrical properties of semiconductor materials by ion implantation, and in particular for implantation of boron and phosphorus ions into silicon. An ion source constitutes an important part of the aforementioned implanter, and its operation determines the efficiency, reliability, and performance characteristics of the implanter. The ion-beam source used in the implanter ionizes neutral molecules and accelerates the obtained ions from hundreds of eV to the required energy level of several hundred KeV. The ions are then formed into a uniform beam of a given shape and extension.  
           [0004]    Until recently, however, the majority of ion-beam sources used in implanters for semiconductor industry were based on cumbersome, complicated, and expensive ion acceleration techniques. Examples of such technique are described, e.g., by V. V. Simonov, et al. in “ Oborudovanie lonnoi Implantatsii ” (Ion Implantation Equipment), Moscow, “Radio I Svyaz” Publishers, 1988, pp. 35-38.  
           [0005]    In 80&#39;s, ion-beam sources using large plasma volumes with simplified methods for the formation of ion beams, e.g., with the use of ion-plasma optics, came into use. Almost all of them consisted of two main functional units, i.e., a gas-discharge chamber for generating plasma used as an ion emitter and an ion-optical system for extracting ions from the plasma, accelerating the extracted ion, and forming a directional ion beam. The working medium used as a material for implantation was a gaseous substance supplied to the discharge chamber or a solid substance, e.g., a solid material sputterable into the plasma volume.  
           [0006]    Since requirements of operation conditions vary from one application to another in a very wide range, it is difficult to create a universal ion source that could satisfy all these conditions at the same time. The plasma-type ion sources have found wide application in ion implanters due to high reliability and operation performance. Depending on methods of plasma generation, these ion sources can be roughly classified as high-frequency and microwave ion sources, cold-cathode type ion sources, plasma sources with hot cathodes, Penning-discharge type ion sources with hot cathodes, quasi-magnetron sources, low-pressure ion sources with arc discharge, etc. Given below is a short description of the aforementioned ion sources which find practical application.  
           [0007]    High-frequency and microwave ion sources are based on the use of high-frequency or microwave energy for generating plasma. Of this group of ion sources, so called electron cyclotron resonance sources (hereinafter referred to as ECR sources) have found a very wide practical application. In these sources, a phenomenon of electron cyclotron resonance (ECR) is used for increasing effective concentration of electrons in plasma and thus makes it possible to generate plasma of high density. ECR is resonance of electrons in a magnetic field on a predetermined frequency, such as 2.45 GHz for the magnetic field of 0.0875 T intensity. ECR sources can be used as ion emitters with extraction of ions from both the end faces and sides of the gas-discharge chamber. Since the present invention pertains to implanters with ECR sources, they will be described later in more detail.  
           [0008]    Cold-cathode type ion sources are sources with cold cathodes, which generate plasma in a glow discharge due to emission of electrons into a working gas from the surfaces of cathodes, resulting in ionization of the working gas molecules. The ions formed in the working gas are accelerated toward the cathode and bombard the cathode surface causing the surface to emit secondary electrons. The plasma is formed as a result of multiple repetitions of the above process. Implanters with cold-cathode ion sources are used mainly for small and ultra-small doses of implantation. Their advantage is simplicity of construction and a relatively long service life. Disadvantages are low beam currents (not exceeding 100 μA), significant fluctuations in the beam, and the limitation of using only gaseous working media.  
           [0009]    Hot-cathode type ion sources generate an arc discharge, which is maintained by electrons emitted from the surface of a hot cathode and possessing energy exceeding the level of energy required for ionization of a gaseous working medium. Discharge occurs in a magnetic field, which is oriented parallel to the electron acceleration direction or perpendicular thereto. In the latter case the source is known as a magnetron type source. Although ion implanters utilizing such ion sources are advantageous in that they are simple in construction, are capable of generating high ion beam currents, and have a relatively stable discharge, they do not possess features required for controlling distribution of current in the resulting ion beam.  
           [0010]    In hot-cathode ion sources with the use of a Penning discharge phenomenon for increasing concentration of electrons in plasma, extraction of ions normally occurs through a round opening in an anti-cathode (axial extraction). Ion sources of such type are known as Nilson ion sources and are used in implanters of Veeco Co.(USA) and Balzers Co. (Liechtenstein). These ion sources make it possible to utilize both gaseous and solid working media. However, with standard ion extraction energy of 30 kV, currents extracted from the Nilson-type ion sources do not exceed several hundred microamperes. Thus the implanters containing such sources inherit their disadvantages.  
           [0011]    Quazi-magnetron ion sources, also known as Freeman ion sources, have a direct incandescence-type cathode arranged parallel to the axis of a cylindrical anode. In contrast to conventional magnetron sources, the sources of this type used for implantation have the incandescence filament offset toward the ion-emitting slit in the side surface of the cylindrical anode. Advantages of these sources, as compared to conventional hot-cathode sources, are relatively low intensity of the magnetic field (below 1 T) and weak dependence of the ion beam parameters to the parameters of discharge. The main disadvantage of quazi-magnetron ion sources is a short service life (no more than 20 hours), which is unacceptable for industrial use.  
           [0012]    Given below is a more detailed description of ECR ion sources, which are used in ion implanters and to which the device and method of the invention pertain.  
           [0013]    U.S. Pat. No. 5,625,195 issued to Andre Grouillet in 1997 discloses a high-energy implantation process using an ion implanter of the low-or medium-current type with an ECR ion source. In order to increase the implantation energy, this ion implanter incorporates a microwave generator with a traveling-wave tube generating an electromagnetic field with a frequency greater than or equal to 6 GHz. The initial ion source of the implanter is replaced by an electron cyclotron resonance multiply-charged ion source, including a waveguide-forming plasma cavity, whose characteristic dimension in the transverse plane of the cavity is of the same order of magnitude as the wavelength of the electromagnetic field. The microwave generator of this implanter and the plasma cavity of the multiple-charged ion source are electromagnetically coupled. A complex gaseous medium, compatible with the beam of ions desired, is admitted into the plasma cavity. The inlet flow rate of the gaseous medium is adjusted so as to maintain a residual vacuum in the plasma cavity, which is less than the pressure threshold compatible with production of multiply-charged ions. The focusing of the ion beam extracted from the plasma cavity is adjusted onto the focal point of the scanning magnet of the implanter. An ion optical system consists of three electrodes, which form an Einzel lens for adjusting the geometrical characteristics of the ion beam extracted from the cavity. This ion optics system interacts with the extraction electrode of the source, and one of the functions of this ion adjustment optics system is to focus the ion beam extracted from the cavity onto the object focal point of the scanning magnet, which allows the ion beam to pass entirely into the scanning element. More precisely, the flared extraction cone, matched to the general shape of the plasma in the plasma cavity, enables the plasma to be channeled and extracted in the form of a beam whose diameter corresponds substantially to the characteristics of the scanning magnet of the implanter. Thus an ion beam having a round cross section of a few centimeters in diameter is formed at the output of the implanter.  
           [0014]    Various internal modifications of the high-voltage terminal have allowed this implanter, with an initial implantation energy of 200 to 250 KeV, to be converted into a high-energy implantation machine (1 MeV for p 4+  ions or even 1.5 MeV for p 6+  ions). According to the inventors of the aforementioned implanter, it has thus been possible to implant with doses of 10 14  ions per cm 2 , and this being achieved within a time compatible with production requirements (a 10 14  dose obtained in two minutes for a wafer 100 mm in diameter). Finally, these operating conditions, which do not require the use of a hot filament, or moving parts, or of low pressure in the plasma chamber, considerably increase the lifetime of the source compared to that of hot-filament sources.  
           [0015]    However, in spite of all advantages, the ion source used in the implanter of U.S. Pat. No. 5,625,195 possesses a number of disadvantages. In particular, the ion beam generated by this source, which has a round cross section of a few centimeters at the source output, has an energy of about 20-25 KeV. For further acceleration of ions to the level of energy required for implantation, the implanter that utilizes this source requires the use of an expensive and complicated ion-accelerating system, and without this system the implanter cannot develop beam energies sufficient for effective implantation. Furthermore, the ion source of U.S. Pat. No. 5,625,195 does not ensure uniformity of the ion beam current over the entire cross section of the beam extracted directly from the ECR plasma source. Another disadvantage of the known ion source is that it does not allow for adjustment of ion beam current distribution at the input to the magnetic separator and beam accelerator.  
           [0016]    The applicants of the present patent application made an attempt to solve the problems of the prior art by developing an improved ion source for use in conjunction with an ion implanter, which is described in pending U.S. patent application Ser. No. 09/476,529 filed on Jan. 3, 2000. This patent application describes an ion source for implanting charged ions, e.g., of B ++ , P ++ , or the like, accelerated to the energy of a few hundred KeV. This ion source is characterized by radial direction of plasma extraction. The device is provided with a confinement space formed within a sealed vacuum chamber inside the housing of the implanter. The ions are extracted by means of a trans-axial electrostatic ion lens having a profile conforming to the boundaries of the plasma. The ion beam is then expanded by a second lens, which emits a substantially parallel ion beam of a rectangular cross-section onto the surface of the object being treated, which is moved across the ion beam. The profile of the plasma boundaries in the confinement space is determined by currents in a plurality of magnetic coils arranged in a number of horizontal layers around the plasma confinement space. If necessary, the profile of the plasma could be adjusted by measuring the ion beam current density distribution with sensors, such as Faraday cylinders, and then adjusting the currents in the aforementioned coils via a feedback mechanism.  
           [0017]    The ion-beam source of U.S. patent application Ser. No. 09/476,529 will now be described in more detail with reference to the most essential parts and their operation. FIG. 1 is a longitudinal sectional view of the aforementioned ion beam.  
           [0018]    The ion source, which as a whole is designated by reference numeral  20 , is an ECR plasma source. ECR plasma source  20  has a housing  22  which is composed of two concentric cylindrical bodies, i.e., an outer cylindrical body  24 , which is made of a non-magnetic material such as a stainless steel and is grounded at G 1 , and an inner cylindrical body  26 , which functions as an anode, which also is made of a non-magnetic material such as a stainless steel. A positive potential, e.g., 80 kV, is applied to the inner body or anode  26  from a DC power source  28  via a conductor  30  and a high-voltage high-vacuum feedthrough  31 . Such feedthroughs are standard devices, produced e.g., by Ceramsel Co., N.Y. and are intended to supply electric current to internal units of high-vacuum systems without violation of vacuum conditions. Outer cylindrical body  24  and anode  26  are interconnected by means of insulating spacers  32  and  34  to form an integral unit.  
           [0019]    A cylindrical space  36 , sufficient for placing magnetic coils described below, is formed between outer cylindrical body  24  and anode  26 . Housing  22  is closed from both ends by covers  38  and  40  via sealing devices  42  and  44  so that the interior of housing  22  is sealed.  
           [0020]    A plasma-confining magnetic system of ECR ion source  20  is defined by a plurality, e.g., four or six, of diametrically opposite paired magnets. Only two rows of such geometrically opposite magnets of these pairs, i.e.,  46   a ,  46   b , . . .  46   n  on one side and  48   a ,  48   b , . . .  48   n  on the opposite side are shown in FIG. 1. An inner cavity  50  of anode  26  functions as a plasma-confining cavity. The plasma generated in this plasma-confining cavity is shown in FIG. 1 as a shaded area designated by reference numeral  52 .  
           [0021]    Magnets  46   a ,  46   b , . . .  46   n  and  48   a ,  48   b , . . .  48   n  are designed for confining plasma  52  in the inward radial direction in plasma-confining cavity  50 , thus compacting it away from the inner walls of cylindrical anode  26 . In order to confine the plasma in cavity  50  from end faces of this cavity, plasma source  20  is equipped with annular magnetic coils  54  and  56  arranged on opposite ends of housing  22 .  
           [0022]    Inner cavity  50  is connected to a source of vacuum (not shown) via an evacuation port (not shown) formed in lower cover  40 .  
           [0023]    As has been mentioned earlier, cylindrical space  36  is formed between outer cylindrical body  24  and anode  26 . This space is necessary to install several pairs of magnetic coil arrays. Two such arrays  47  and  49  are shown in FIG. 1.  
           [0024]    A trans-axial lens unit  58  (FIG. 1) is formed in the wall of anode  26  and projects radially outwardly from housing  22  of the ion source. Trans-axial lens unit  58  extends in the longitudinal direction of housing  22  almost along the entire length of the housing. Trans-axial lens  58  consists of three hollow electrodes  60 ,  62 , and  64  located one inside the other with spaces  66  and  68 , respectively, between the adjacent electrodes. In other words, space  66  is formed between the inner wall of electrode  60  and the outer wall of electrode  62 , whereas space  68  is formed between the inner wall of electrode  62  and the outer wall of electrode  64 .  
           [0025]    Hollow electrode  60 , which is the outermost electrode of the package, is supported by cylindrical anode  26  and is in electric contact therewith. As has been mentioned above, a potential of 80 kV is applied to cylindrical anode  30  from power source  32 . Therefore the same potential will be applied to hollow electrode  60 . A distal end of trans-axial lens  58  is open into plasma-confining cavity  50  in the form of a narrow ion-extracting slit of the same geometry as slit  68  shown in FIG. 4 of our previous patent application No. 09/476,529. This slit has a special profile described in the aforementioned patent application.  
           [0026]    Innermost hollow electrode  64  has the same configuration as outermost electrode  60 . Hollow electrode  64  is grounded. Electrode  64  has an ion extraction slit on its distal end and an ion outlet opening  70  on the outer or proximal end. The construction of the electrodes  60 ,  62 ,  64  and their slits are the same as in our previous patent application.  
           [0027]    Located between outermost electrode  60  and innermost electrode  64 , is intermediate hollow electrode  62 . A negative potential, e.g., −3 to −5 kV, is applied to intermediate electrode  62  from a negative terminal of an electric power source (not shown). Intermediate electrode  62  is electrically insulated from innermost electrode  64  and outermost electrode  60 .  
           [0028]    Reference numeral  72  designates a second ion optical lens, which may be installed inside a hollow ion-beam guide  74  which extends further in the direction of propagation of the ion beam extracted from the plasma source  20 . Similar to trans-axial ion lens  58 , lens  72  is formed by hollow electrodes; in this case by two hollow electrodes  76  and  78  located one inside the other with a space  80  between them. This ion beam lens has a convex profile on the side facing trans-axial lens  58 . Electrodes  76  and  78  have slits (not shown), which are aligned with each other and with the slits of trans-axial lens  58 .  
           [0029]    Thus, trans-axial lens  60  and ion beam lens  72  in combination form a telescopic ion beam system which may form an ion beam of a rectangular cross-section or a strip-like substantially parallel ion beam, i.e., an ion beam with very small angles of divergence in mutually perpendicular planes, i.e., in the plane of FIG. 1 and in the plane perpendicular thereto.  
           [0030]    In FIG. 1, reference numeral  82  designates a waveguide for transmitting microwave energy with the frequency, e.g., of 2.45 GHz, required for creating so-called electron-cyclotron resonance (ECR) conditions described in our previous patent application. Waveguide  82  comprises a hollow metallic tube  84  of a rectangular cross-section made of a highly conductive material, e.g., silver-coated copper. Tube  84  is connected to cylindrical anode  26  and is electrically isolated therefrom by means of a sealing device  86 . An outlet opening  88  of tube  84  into plasma-confining cavity  50  is closed by a heat-resistant window  90  transparent to microwave energy. An example of such a material is quartz. The interior of outer cylindrical body  24 , i.e., plasma-confining cavity  50 , as well as space  36 , and the entire inner cavity  50  of ion-beam source  20  are sealed from the environment surrounding ion-beam source  20 .  
           [0031]    A working medium, e.g., a boron-containing gas such as BCl 3 , BF 3 , or a phosphorus-containing gas such as PH 3 , etc., is supplied into interior cylindrical anode  26  via a tube  92  which passes into this interior through a standard high-vacuum, high-voltage resistant feedthrough device  94 . Such a feedthrough device is produced, e.g., by Insulator Seal Incorporated, Hayward, Calif., USA.  
           [0032]    In order to enhance the energy of plasma, ion-beam source  20  is equipped with at least one antenna for supplying a radio-frequency (RF) power into the plasma  52 . In the embodiment, illustrated in FIG. 1, this device has two such antennas  96  and  98 , which can be inserted into plasma-confining cavity  50 , e.g., through magnets  54  and  56 , although the antennas can be inserted through any other locations. It is understood that antennas  96  and  98  should be inserted into cavity  50  without violation of vacuum conditions, i.e., through appropriate high-vacuum, high-voltage resistant feedthrough devices  100  and  102  of the same type as those mentioned above. Terminals  104  and  106  located on outer ends of antennas  96  and  98  are connected to appropriate microwave sources (not shown), e.g., of 13.72 MHz frequency.  
           [0033]    Operation of ion source  20  will be further described with reference to aforementioned FIGS. 1. Plasma-confining cavity  50  of ion source  20  is evacuated via the evacuation port by means of a vacuum pump (not shown). Microwave energy of 2.45 GHz is pumped into cavity  50  inside hollow anode  26  (a MW generator is not shown). When vacuum reaches a predetermined level, e.g., of 0.5 mTorr, a working medium, e.g., a boron-containing gas, is supplied via gas supply tube  92  into cavity  50 . The plasma-confining magnetic system formed by the magnet arrays  46 ,  48 , etc., generates plasma magnetizing and confining magnetic fields inside cavity  50 .  
           [0034]    In some areas of cavity  50 , magnet arrays  46 ,  48 , etc. generate magnetic fields within a strength of 0.0875 Tesla, which is a resonance field for 2.45 GHz frequency oscillation of electrons. As a result, these electrons begin to intensively consume the microwave energy. This phenomenon, which is known as an electron cyclotron resonance (ECR), enhances plasma and allows the development of plasma charge densities of up to 10 13  e/cm 3 . In other words, a very dense plasma  52  is developed in the cavity  50 . Plasma  52  is further intensified by radio frequency supplied into cavity  50  via antennas  96  and  98 .  
           [0035]    For effective extraction of plasma  52  from plasma-confining cavity  50 , it is necessary that the outer plasma boundary conform to the profile of the trans-axial lens  60  on its distal end, where plasma-extracting slits are formed. This is achieved by means of the aforementioned arrays  47  and  49  of magnetic coils. Since the coils of these arrays have their own individual power sources (not shown), the magnetic fields developed by these coils can be individually adjusted to ensure fine conformity of the plasma boundary to the lens profile. After such conformity is achieved, positive boron ions are extracted from plasma  52  via the plasma emitting slits of trans-axial lens  60 . Due to the fact that the boron ions are double-charged (B ++ ) and that above-described potential difference between three outermost hollow electrodes  60  and innermost hollow electrode  64  of trans-axial lens  60  is about 85 kV, boron ions may develop in the interelectrode magnetic fields energies of about 170 KeV. An ion beam IB formed on the output of trans-axial lens unit  58  is diverged (FIG. 1), and when it passes through ion lens  72 , its angle of divergence is reduced, so that an almost parallel ion beam of a rectangular cross section exits ion-beam guide  74  and enters a working vacuum chamber (not shown).  
           [0036]    In spite of the advantages inherent in the ion-beam source of U.S. patent application Ser. No. 09/476,529 filed on Jan. 3, 2000, it still possesses some drawbacks. In particular, the aforementioned ion-beam sources can produce ions only from gaseous working materials. In other words, material to be implanted is supplied to the plasma chamber only in a gaseous phase. Furthermore, when the aforementioned source generates a belt-like ion beam of a rectangular cross section, which is to be delivered to the treated object through the output of the implanter, the longer dimension of the aforementioned rectangular cross section, which hereinafter will be referred to as a width of the ion beam, is limited substantially to the length of the microwave pumping waveguide. For microwave energy pumping, e.g., of 2.45 GHz, such a waveguide cannot have an ion beam width exceeding 15-20 cm, even with waveguide output cross-section modified for obtaining the maximum dimension. This, in turn, limits efficiency of the source.  
           [0037]    As mentioned above, the interior of vacuum chamber  50  of ion source  20 , which normally operates under conditions of deep vacuum at about 10 −8  Torr or lower is sealed from the microwave pumping system by quartz or ceramic windows  90  transparent to microwave energy. During operation of ion source  20 , these windows are contaminated by plasma particles from the side of plasma chamber  50 . Contamination of the windows may reach such a level that further use of the source becomes impossible because of non-transparency of windows  90 , which in this case do not pass microwave energy to cavity  50 . This violates plasma-sustaining conditions. Therefore, when the windows are contaminated, the entire system has to be stopped, the source has to be disassembled and the windows have to be cleaned or replaced. This disadvantage is reflected in increased costs of production and maintenance.  
           [0038]    Another specific disadvantage inherent in the ECR ion source described in the aforementioned U.S. patent application Ser. No. 09/476,529 consists in that radial extraction of ions is carried out with the use of a trans-axial three-electrode ion lens. Although the aforementioned trans-axial three-electrode ion lens is advantageous in that it provides an extremely high uniformity of distribution of ions in the narrow beam produced by this lens, the drawback of this lens is the use of three electrodes. This is because these electrodes work under conditions of significant potential difference with respect to each other. Such a mode results in high current losses which lead to decrease in the efficiency of the ion source as a whole.  
         OBJECTS OF THE INVENTION  
         [0039]    It is an object of the invention to provide an ion-beam source for use in an ion implanter which is suitable for operation with gaseous as well as with solid materials for generation of ions. Another object is to provide an ion-beam source of the aforementioned type having an increased width of the ion beam, which may exceed 20 cm. Still another object is to provide an ion-beam source for use in an ion implanter with a mechanism for periodic or continuous cleaning of waveguide output windows. Further object is to provide an ion-beam source for an ion implanter, which is simple in construction because it is free of a trans-axial three-electrode lens, reliable and efficient in operation, and inexpensive to manufacture. Still another object is to provide a method for generation of ions from gaseous and solid materials in efficient way and in the form of wide ion beams. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0040]    [0040]FIG. 1 is a longitudinal sectional view of a known an ion-beam source for use in an ion implanter.  
         [0041]    [0041]FIG. 2 is a longitudinal section of an ion-beam source of the present invention.  
         [0042]    [0042]FIG. 3 is a cross-sectional view along the line III-III of FIG. 2.  
         [0043]    [0043]FIG. 4 is a schematic view of a window cleaning mechanism.  
         [0044]    [0044]FIG. 5 is a three-dimensional external general view of the ion-beam source of the invention.  
         [0045]    [0045]FIG. 6 is an end view of the ion-beam source of FIG. 5 in the direction of arrow C.  
       SUMMARY OF THE INVENTION  
       [0046]    An ECR ion-beam source of the invention for use in an ion implanter has a sealed plasma chamber in which plasma is excited by microwave radiation of 2.45 GHz in combination with an external magnetic field generated by permanent magnets surrounding the plasma chamber. The magnets cause electron-cyclotron resonance of electrons in the plasma thus creating conditions for efficient absorption of the microwave energy. The same magnets generate a magnetic field, which compresses the plasma toward the center for confining the plasma within the plasma chamber. The ion source also has an RF pumping unit that pumps RF energy into the plasma. The RF pumping unit has a unique additional function of RF magnetron sputtering of solid targets converted into a gaseous working medium used for implantation in an ionized form. For obtaining elongated belt-type ion beams (having a width of 1 m or longer), the ion source may contain a microwave pumping system having several output windows arranged in series along the axis of the plasma chamber and on diametrically opposite sides thereof. These windows seal the plasma chamber, which is under conditions of deep vacuum, from the surrounding environment but are transparent for microwave radiation. As the windows are subject to contamination, especially in the case of using magnetron solid target sputtering, the ion source is provided with a special mechanism for restoration of transparency of windows.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0047]    The ion-beam source of the invention, which is shown in a longitudinal sectional view in FIG. 2, is in some part similar to ion-beam source  20  of my previous patent application shown in FIG. 1.  
         [0048]    Since ion-beam source  20  of the previous patent application has been described in detail, some parts and units of the present ion source of FIG. 2 identical to those shown in FIG. 1 will be omitted from the description. Furthermore, parts of the ion source of the invention similar to those of the previous patent application will be designated where appropriate by the same reference numerals but with an addition of 100.  
         [0049]    The ion source of the invention, which as a whole is designated by reference numeral  120 , is an ECR plasma source. ECR plasma source  120  has a housing  122 , which is made of a non-magnetic material such as a stainless steel and is connected to a positive terminal  128   a  of a DC power source  128 . The negative terminal  128   b  of the DC power source  128  is grounded at G 2 . The positive terminal  128   a  applies to the housing or anode  122  a positive potential, e.g., 80 kV. Housing or anode  122  has an elongated tubular shape and is closed from both ends by covers  138  and  140  via sealing devices  142  and  144  so that the interior of housing  136  is sealed.  
         [0050]    As shown in FIG. 3, which is a sectional view of FIG. 2 along line III-III, a plasma-confining magnetic system of the ECR ion source  120  is defined by a plurality of circumferentially arranged pairs of magnets  146   a - 146   b ,  146   c - 146   d ,  146   e - 146   f , and  146   g - 146   h  (FIG. 3). Two adjacent poles of each pair of magnets have different polarity. For example, the pole of the magnet  146   a  nearest to the anode  122  is negative, and the pole of the magnet  146   b  nearest to the anode  122  is positive, etc. As shown in FIG. 2, the magnets  146   a  . . .  146   h  extend along the entire length of the anode or housing  122 . Although four pairs of such magnets are shown in FIG. 3, it is understood that the number magnet pairs may be different.  
         [0051]    An inner cavity  136  of anode  122  functions as a plasma-confining cavity. The plasma generated in this plasma-confining cavity is shown in FIG. 2 as a shaded area designated by reference numeral  152 .  
         [0052]    Magnets  146   a - 146   h  designed for confining plasma  152  in the inward radial direction in plasma-confining cavity  136  for compacting it away from the inner walls of cylindrical anode  122 . In order to confine the plasma in cavity  136  from end faces of this cavity, plasma source  120  is equipped with permanent magnets  154  and  156  arranged on opposite ends of housing  122 . The permanent magnets  154  and  156  are insolated from the covers  138  and  140  by respective ceramic caps  155  and  157 .  
         [0053]    Inner cavity  136  connected to a source of vacuum (not shown) via an evacuation port  137  shown in FIG. 3.  
         [0054]    Extraction of ions from the plasma  152  contained in the plasma-confining cavity  136  is carried out with the use of a two-electrode lateral ion-extraction lens  158  which is formed in the wall of anode  122  and projects radially outwardly from housing or anode  122  of ion source  120 . The lens  152  extends in the longitudinal direction of housing  122  along almost the entire length of the housing. As shown in FIG. 3, which is a cross-sectional view along the line III-III of FIG. 2, two-electrode lateral ion-extraction lens  158  consists of two hollow electrodes  160  and  162 . The outer electrode  160  is formed as a tapering recess of the housing  122  directed inwardly and having a large angle of taper (an obtuse angle), and the inner electrode  162  is formed as a tubular tapering body with a small taper angle and with the tip of the electrode  162  inserted into the recess formed by the electrode  160 . As has been mentioned above, the anode  122  and, hence, the outer electrode  160  are maintained under the high-voltage potential, while inner electrode  162  is maintained under the ground potential. The outer end of the inner electrode  162  extends in the radial outward direction from the ion source  122  in the form of a tunnel having a rectangular cross-section and is intended for delivery of the ion beam to the destination.  
         [0055]    Reference numeral  164  in FIG. 3 designates a ceramic isolation unit use for attaching the inner electrode  162  to the outer surface of the housing  122  via a flanged part  166  of the housing. Thy connection is sealed by a seal ring  168 .  
         [0056]    A inner end of the inner electrode  162  has a longitudinal slit  170 , which faces the longitudinal slit  172  formed in the innermost area of the outer electrode  160 . Thus, the two-electrode lens connects the plasma-confined space  136  with the ion-beam guide  174  formed by the extension of the inner electrode  160 . It is understood that the narrow ion-extracting slits  170  and  172  (FIGS. 2 and 3 extends in the axial direction of the housing or anode  122  along the entire plasma column  152  generated inside the plasma-confining cavity  136 . In a real construction, the extracted ion beam  176  may have a width of  1  m or greater, which could not be attained in a high-energy type ion-beam source of any known construction.  
         [0057]    For obtaining the aforementioned elongated belt-type ion beams (having a width 1 m or longer), ion source  120  may contain a microwave-energy (ME) pumping system (FIGS. 2) having several output windows arranged in series along the axis of the plasma chamber and on diametrically opposite sides thereof. The ME pumping system is intended for transmitting to plasma cavity  136  microwave energy with the frequency, e.g., of 2.45 GHz, required for creating so-called electron-cyclotron resonance (ECR) conditions described in our previous patent application. The ME waveguide system comprises several (four in FIG. 2) ME pumping units  182   a ,  182   b ,  182   c , and  182   d.    
         [0058]    Since all these units are identical, only one of them, e.g., the ME pumping unit  182   b , is described. The unit comprises a hollow metallic waveguide  184  of a rectangular cross section made of a highly conductive material, e.g., silver-coated copper. The waveguide  184  is electrically and mechanically connected to cylindrical anode  122  (FIG. 3).  
         [0059]    ME pumping units  182   a ,  182   b ,  182   c , and  182   d  are arranged on opposite sides of plasma-confining cavity  136  in an alternating order and, as shown in FIG. 2, are shifted in a cavity axial direction for a pitch P equal to a distance between two maximums of amplitudes in the alternating magnetic field of a cylindrical resonator for the case of low-order modes with a toroidal magnetic field. In other words, each ME pumping unit in principle generates conditions of a single pumping unit of the previous patent application, but in order to provide uniformity of plasma over the width of the plasma beam  176 , the alternating ME units located on the opposite sides of cavity  136  have to be shifted with respect to each other in a manner described above.  
         [0060]    The inner surface of the waveguide  184  has a shape tapering in the radial inward direction, i.e., toward the anode  122  and is open into the plasma-confining cavity in the form of ME pumping windows. As shown in FIG. 3, the waveguide  184  (as well as the three other waveguides) has a ME pumping windows  186  formed by a metal rod  188  with a through longitudinal slit  190 . The rod  188  is stationary with respect to the ion source  122  and is inserted with a sliding fit into a protective rotating tube  192  made of a material transparent to a microwave energy, e.g., of quartz or ceramic. The rotation mechanism for tube  192  will be described later. It is understood that all four ME pumping units  182   a ,  182   b ,  182   c , and  182   d  are identical. The tubes  192  and  193  (FIG. 2) extends through the entire axial length of the ion-beam source  122  and even further beyond the boundary of the housing  122  for connection to the tube rotation mechanism shown in FIG. 4. The tubes  192  and  193  are intended for sealing the plasma-confining space  136 , which is under high vacuum of about 10 −8  Torr, from the outer space, as well as for passing the microwave energy from the ME pumping units  182   a ,  182   b ,  182   c , and  182   d  to the plasma-confining space  136 .  
         [0061]    The ion source  120  of the present invention is also provided with an RF pumping system for pumping 13.7 MHz RF energy into plasma-confining cavity  136 . In the embodiment of the ion source  120  shown in FIG. 2, this pumping system is presented in the form of two RF pumping units  195  and  197  installed in covers  138  and  140  of the housing of ion source  120 . Each of these units fulfills two functions, i.e., it enhances the energy of plasma  152  and at the same time serves as a source of a solid sputterable material turned by magnetron sputtering into a gaseous form and used for the formation of an ion beam and hence for the implantation.  
         [0062]    Since both RF pumping units are identical, only one of them, e.g., unit  195 , will be described in detail. Unit  195  consists essentially of two parts, i.e., an RF antenna-feeder  196 , which receives an RF energy from an RF source and matching unit (not shown), e.g., of 13.72 MHz frequency, for transmission into plasma  152 , and a magnetron sputtering target  199 . The second magnetron target is designated by reference numeral  201  (FIGS. 2 and 3). The aforementioned permanent magnets  154  and  156  serve as sources of a magnetic field for the magnetron-sputtering effect of the targets  199  and  201 , respectively. The targets may comprise any material which has to be implanted into the object of implantation and which cannot be delivered in a gaseous form. Such materials can be represented, e.g., by boron-containing materials which can be sputtered due to interaction with plasma  152  and delivered in the form of ions into the ion beam  176  generated by ion source  120 .  
         [0063]    As tubes  192  and  193  are subject to contamination, especially in the case of using magnetron solid target sputtering, the ion source  120  is provided with a special mechanism for restoration of transparency of windows. This mechanism, which is shown in FIG. 4 for tube  192  and is identical to the mechanism for cleaning the tube  193 , is designated as a whole by reference numeral  210 . The mechanism  210  consists of a elongated nut  212  which is pressed onto the outer surface of the ceramic or quartz tube  192  or connected to the tube  192  an via adhesive layer  214 . The outer thread  216  of the nut  212  engages the inner thread  213  formed in the opening of a gear wheel  218 , which is in mesh with another gear  220 . The gear  220  is rotated by a reversing motor  222 , so that rotation of the motor  222  causes, via the gear  220 , gear  218 , and the threaded connection between the nut  212  and the inner thread  213  in the opening of the gear  218 , rotation and axial reciprocation of the tube  192 .  
         [0064]    For cleaning the contaminated surfaces of the tube  192 , the cleaning mechanism  210  is equipped with a sand-blast apparatus  228 , the nozzle  230  of which is positioned near the exit of the tube  192  from ion source  120 . It is understood that the nozzle is located in a confined space shown by a casing  141 , which protects the outer surfaces of the ion source from contamination with the products of sand-blasting and contaminants removed from the rods.  
         [0065]    For convenience of explanation and designation of multiple parts and units of the ion source of the invention, the ion source  120  is shown in FIGS. 2 and 3 in an exaggerated form without proper proportions between the parts and units. FIGS. 5 and 6 show the ion source of the invention  120  in a form close to real construction. In particular, FIG. 5 is a three-dimensional external general view of the ion-beam source  120 , and FIG. 6 is an end view of the ion-beam source of FIG. 5 in the direction of arrow C of FIG. 5. The main externally seen parts of the ion source  120  shown in FIGS. 5 and 6 are designated by the same positions as in FIGS. 2 and 3. In FIG. 5, reference numerals  146   a - 146   b ,  146   c - 146   d ,  146   e - 146   f , and  146   g - 146   h  designate pairs of permanent magnets shown in FIG. 3. Reference numerals  234   a ,  234   b , . . .  234   n  designate magnetron-type ME generators. FIG. 6 shows a matching device  232  with matching elements  232   a ,  232   b , and  232   c  intended for matching the respective magnetron ME generators with the plasma-plasma confining space  236 .  
         [0066]    The ion-beam source  120  of the present invention operates as follows:  
         [0067]    Plasma-confining space  136  of ion source  120  is evacuated via the evacuation port  137  by means of a vacuum pump (not shown). Microwave energy of 2.45 GHz is pumped into space  136  inside hollow anode  122  (a ME generators  234   a ,  236   b  . . . are shown in FIGS. 5 and 6). When vacuum reaches a predetermined level, e.g., of 0.5 mTorr, a carrier gas, such as argon, is supplied via the gas supply tube (not shown) into the space  136 . The plasma-confining magnetic system formed by magnet arrays  146   a - 146   h  and the magnets  154 ,  156  generates plasma magnetizing and confining magnetic fields inside the space  136 .  
         [0068]    In some areas of  136 , magnet arrays  146   a - 146   h  generate magnetic fields with a strength of 0.0875 Tesla, which is a resonance field for 2.45 GHz frequency oscillation of electrons. As a result, these electrons begin to intensively consume the microwave energy. This phenomenon, which is known as an electron cyclotron resonance (ECR), enhances plasma and allows for the developing of plasma charge densities of up to 10 13  e/cm 3 . In other words, a very dense plasma  152  is developed in the plasma-confining space  136 . The aforementioned 2.45 GHz microwave energy is generated by magnetron sources  134   a - 134   n  (FIGS. 5 and 6) and is supplied to the space  136  via ME waveguide system of several (four in FIG. 2) ME pumping units  182   a ,  182   b ,  182   c , and  182   d  and via the windows (such as the window  186  shown in FIG. 3). Plasma  152  is further intensified by radio frequency supplied into the space  136  via antennas-feeders  196  and  198 .  
         [0069]    For effective extraction of plasma  152  from plasma-confining space  136 , it is necessary that the outer plasma boundary conform to the profile of the two-electrode lens  158  in the area of plasma-extracting slits  170  and  172 . This is achieved by individual adjustments of the magnetron ME pumping generators  234   a - 234   n . The RF pumping source is energized for supplying the RF energy via antennas-feeders  196  and  198  to plasma  152  and for feeding the RF energy to magnetron targets  199  and  201 . When pressure of argon in the space  136  reaches a predetermined level, and RF power is supplied to the magnetron targets  199  and  201 , a process of RF magnetron sputtering is initiated. This process is known and is described in detail, e.g., in book “Glow Discharge Processes” by Brian Chaspman, John Willey &amp; Sons Publishers, N.Y., 1980. Since this process is beyond the scope of this invention, its detailed description is omitted. It should be noted, however, that in the system of the invention, a part of RF energy supplied to magnetron targets  199  and  201  enters the plasma  152  and increases plasma density. Furthermore, the plasma  152  is maintained under a potential close to the potential of anode  122 , e.g., about 80 kV. The effect of magnetron sputtering is possible when the potential on magnetron targets  199  and  201  is close to that of the plasma. This condition can be achieved, e.g., by applying the anode potential also to the magnetron targets  199  and  201 . For sputtering under these conditions, it is required that the constant potential of antennas-feeders  199  and  201  be of a floating nature, i.e., could accept the constant component of the target potential. This is achieved by isolating the RF power supply source to withstand 80 KV and by connecting it to the power supply circuit via a special 80 KV high-voltage dividing transformer (not shown).  
         [0070]    The material of the magnetron targets  199  and  201  is sputtered, and the sputtered molecules enter the plasma-confining space  136 , where they are uniformly distributed over the plasma  152 . In the plasma  152 , the molecules of the target material are ionized due to collisions with electrons and ions of the carrier gas. These ions are extracted from ion-beam source  120  via ion extracting slit  170  and  172  (FIGS. 2 and 3).  
         [0071]    The process of RF magnetron sputtering was chosen for the ion-beam source of the present invention since this process allows sputtering of conductive as well as non-conductive materials and easily transfers these materials into a gaseous plasma state.  
         [0072]    During operation of ion source  120 , the products of sputtering contaminate the quartz or ceramic tubes  192  and  193  of the windows for ME pumping. Therefore the tubes  192  and  193  are constantly cleaned by the cleaning mechanism shown in FIG. 4. More specifically, the gear  220  is rotated by a reversing motor  222 , so that rotation of the motor  222  causes, via the gear  220 , gear  218 , and the threaded connection between the nut  212  and the inner thread  213  in the opening of the gear  218 , rotation and axial reciprocation of the tube  192 . During rotation and axial movement each tube passes by the nozzle  230  (FIG. 4) of a sand blast apparatus.  
         [0073]    Although the invention has been described with reference to specific embodiments and drawings, it is understood that these embodiments are shown only as examples and that many changes and modifications are possible within the scope of the attached patent claims. For example, the antennas-feeders are shown passing through the covers. However, they can be inserted through any other locations, provided they are inserted into space  136  without violation of vacuum conditions, i.e., through appropriate high-vacuum, high-voltage resistant feedthrough devices. Although two rows of windows and ME pumping units arranged in diametrically opposite directions have been shown and described in connection with the invention, it is understood that three or more axial rows of ME pumping windows with three or more windows closed by three or more quartz rods uniformly angularly spaced can be used. The invention has been described in reference to magnetron sputtering of the target material in combination with RF pumping. However, the functions of magnetron sputtering and RF pumping can be separated. Moreover, these two processes can be performed simultaneously on different RF frequencies with the use of individual RF pumping sources, e.g., of 13.7 MHz on one of them and 80 MHz on the other or vice verse. The rod cleaning mechanism and the sand blast system can be installed above the cover  138  on the opposite side of the ion-beam source housing. The ion source of the invention can be used as the ion source of the previous patent application, i.e., with the extraction of ions directly from the gaseous working medium, i.e., without the supply of solid sputterable materials. Cleaning of the rods can be carried out by means other than sand blasting, e.g., by chemical treatment.