Abstract:
Incorporating the use of a permanent magnet within a GCIB apparatus to separate undesirable monomer ions from a gas cluster ion beam to facilitate improved processing of workpieces. In an alternate embodiment, the effect of the permanent magnet may be controlled by the use of an electrical coil. The above system eliminates problems related to power consumption and heat generation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority of the U.S. Provisional Application Ser. No. 60/169,345 filed Dec. 6, 1999 entitled GAS CLUSTER ION BEAM LOW MASS ION FILTER. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates generally to gas cluster ion beam (GCIB) processing equipment, and, more particularly to incorporating means within GCIB processing equipment for eliminating monomer ions from the ion cluster beam without the production of unwanted heat.  
           [0003]    The use of gas cluster ion beams for etching, cleaning, and smoothing of material surfaces is known in the art(see for example Deguchi et al., U.S. Pat. No. 5,814,194). For purposes of better understanding the present invention, gas clusters are nano-sized aggregates of materials that are gaseous under conditions of standard temperature and pressure. Such clusters typically consist of aggregates of˜several tens to˜several thousand atoms or molecules loosely bound to form the cluster. Such clusters can be ionized by electron bombardment or other means, permitting them to be formed into directed beams of known and controllable energy. The larger sized clusters are the most useful because of their ability to carry substantial energy per cluster ion, while having modest energy per atom or molecule. The clusters disintegrate on impact, with each individual atom or molecule carrying only a small fraction of the total cluster energy. Consequently the impact effects of large clusters are substantial, but are limited to a very shallow surface region. This makes ion clusters effective for a variety of surface modification processes, without the tendency to produce deeper subsurface damage characteristic of monomer ion beam processing.  
           [0004]    Means for creation of and acceleration of such GCIB are described in the reference previously cited. Presently available ion cluster sources produce clusters ions having a wide distribution of sizes, N (where N=the number atoms or molecules in each cluster).  
           [0005]    Because monomer ions as well as cluster ions are produced by presently available cluster ion beam sources, those monomer ions are accelerated and transported to the workpiece being processed along with the cluster ions. Upon acceleration in an electric field, monomers, having low mass, obtain high velocities that allow the light monomers to penetrate the surface of the workpiece and produce deep damage which is likely to be detrimental to the intended process. Such sub-surface ion damage is well-established and well-known from the more traditional monomer ion beam processing art and can produce a wide variety of deep damage and implantation.  
           [0006]    It is also known in the ion cluster beam art that many GCIB processes benefit from incorporating means within GCIB processing equipment for eliminating monomer ions from the ion cluster beams. Electrostatic and electromagnetic mass analyzers have been employed to remove light ions from the beam of heavier clusters (see Knauer, U.S. Pat. No. 4,737,637 and Aoyanagi et al. in Japanese laid open application JP 03-245523A1 corresponding to Japanese application JP 2-43090, cited as prior art in Aoyagi et al., U.S. Pat. No. 5,185,287). Electrostatic and electromagnetic mass analyzers have also been employed to select ion clusters having a narrow range of ion masses from a beam containing a wider distribution of masses (see Knauer, U.S. Pat. No. 4,737,637 and Aoki, Japanese laid open application JP 62-112777A1).  
           [0007]    In the past, electromagnetic beam filters have been used to separate ion masses. However, electromagnets are costly and, while in use, continually consume electrical power. Furthermore, the electrical power is converted to heat. Since the magnetic beam filter must be deployed in a vacuum chamber, namely the ionization/acceleration chamber, convection cooling of the beam filter is not practical. Generally, conductive paths to water or other fluid cooling systems must be provided and heat exchangers are required to remove heat from the cooling fluid and transfer it to the environment. Such cooling apparatus adds additional cost and introduces maintenance problems. The use of an electromagnetic beam filter is undesirable for these and other reasons.  
           [0008]    It is therefore an object of this invention to reduce the heat produced in GCIB processing equipment and to eliminate the need for water or other cooling of a beam filter device.  
           [0009]    It is a further object of this invention to separate undesired monomer ions from the GCIB.  
           [0010]    It is still a further object of this invention to reduce the cost, weight, and maintenance complexity of a GCIB processing system  
         SUMMARY OF THE INVENTION  
         [0011]    The objects set forth above as well as further and other objects and advantages of the present invention are achieved by the embodiments of the invention described hereinbelow.  
           [0012]    The present invention is capable of reducing the heat produced in GCIB processing equipment, thus eliminating the need for water or other cooling of a beam filter device utilized therein. The invention utilizes a permanent magnet beam filter or a hybrid permanent electromagnetic beam filter to separate undesired monomer ions from the GCIB. Consequently the present invention substantially reduces the cost, weight, and maintenance complexity of a GCIB processing system over GCIB systems which incorporate a conventional electromagnetic beam filter system therein.  
       
    
    
       [0013]    For a better understanding of the present invention, together with other and further objects thereof, reference is made to the accompanying drawings and detailed description.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a graph showing a typical ion cluster size distribution for a GICB source;  
         [0015]    [0015]FIG. 2 is a schematic that shows the basic elements of a prior art GCIB processing system;  
         [0016]    [0016]FIG. 3 is a schematic that shows a GCIB processing system of this invention, with dipole magnet following beam formation and acceleration for separating undesired ions from the GCIB;  
         [0017]    [0017]FIG. 4 is a schematic of a permanent dipole magnet for separation of undesired ions from a GCIB with the present invention;  
         [0018]    [0018]FIG. 5 is a schematic geometric diagram to explain deflection in the magnetic beam filter of this invention;  
         [0019]    [0019]FIG. 6 shows details of the GCIB and mass analysis plate of this invention under nominal beam conditions;  
         [0020]    [0020]FIG. 7 shows details of the GCIB and the mass analysis plate of this invention under worst case beam alignment conditions;  
         [0021]    [0021]FIG. 8 is a schematic geometric diagram showing GCIB beamlet separation in an example case of this invention;  
         [0022]    [0022]FIG. 9 is a schematic of a hybrid permanent/electro-magnetic GCIB beam filter for use with the present invention;  
         [0023]    [0023]FIG. 10 is a schematic diagram of controls for the hybrid permanent/electromagnetic GCIB beam filter of this invention; and  
         [0024]    [0024]FIG. 11 is a schematic of the GCIB processing system of this invention employing the hybrid beam filter invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    In order to understand better the present invention, the following information is directed toward typical ion cluster size distribution. FIG. 1 shows the typical ion cluster size distribution produced by a typical GICB source. The cluster formation process has been shown by N. Kofuji, et al., in “Development of gas cluster source and its characteristics”,  Proc.  14 th Symp. on Ion Sources and Ion-Assisted Technology,  Tokyo (1991), p. 15, to produce few small size clusters (values of N from 2 to about 10), but monomer ions (N−1) are produced in abundance as are larger clusters ( N&gt;a few tens, up to a few thousands.) It is known (Yamada, U.S. Pat. No. 5,459,326) that such atoms in a cluster are not individually energetic enough (on the order of a few electron volts) to significantly penetrate a surface to cause the residual surface damage typically associated with the other types of ion beam processing in which individual monomer atoms may have energies on the order of thousands of electron volts. Nevertheless, the clusters themselves can be made sufficiently energetic (some thousands of electron volts), to effectively etch, smooth or clean surfaces (see Yamada and Matsuo, in “Cluster ion beam processing”,  Matl. Science in Semiconductor Processing I , (1998), pp 27-41).  
         [0026]    [0026]FIG. 2 shows a typical configuration for a GCIB processor  100  of a form known in prior art, and which may be described as follows. A vacuum vessel  102  is divided into three communicating chambers, a source chamber  104 , a ionization/acceleration chamber  106 , and a processing chamber  108 . The three chambers are evacuated to suitable operating pressures by vacuum pumping systems  146   a,    146   b,  and  146   c,  respectively. A condensable source gas  112  (for example argon) is admitted under pressure through gas feed tube  114  to stagnation chamber  116  and is ejected into the substantially lower pressure vacuum through a properly shaped nozzle  110 . A supersonic gas jet  118  results. Cooling, which results from the expansion in the jet, causes a portion of the gas jet  118  to condense into clusters, each consisting of from several to several thousand weakly bound atoms or molecules. A gas skimmer aperture  120  separates the gas products that have not been formed into a cluster jet from the cluster jet so as to minimize pressure in the downstream regions where such higher pressures would be detrimental (e.g., ionizer  122 , high voltage electrodes  126 , and process chamber  108 ). Suitable condensable source gases  112  include, but are not necessarily limited to argon, nitrogen and other inert gases.  
         [0027]    After the supersonic gas jet  118  containing gas clusters has been formed, the clusters are ionized in an ionizer  122 . The ionizer  122  is typically an electron impact ionizer that produces thermoelectrons from one or more incandescent filaments  124  and accelerates and directs the electrons causing them to collide with the gas clusters in the gas jet  118 , where the jet passes through the ionizer  122 . The electron impact ejects electrons from the clusters, causing a portion the clusters to become positively ionized. A set of suitably biased high voltage electrodes  126  extracts the cluster ions from the ionizer, forming a beam, then accelerates them to a desired energy (typically from 1 keV to several tens of keV) and focuses them to form a GCIB  128 . Filament power supply  136  provides voltage V F  to heat the ionizer filament  124 . Anode power supply  134  provides voltage V A  to accelerate thermoelectrons emitted from filament  124  to cause them to bombard the cluster containing gas jet  118  to produce ions. Extraction power supply  138  provides voltage V E  to bias a high voltage electrode to extract ions from the ionizing region of ionizer  122  and to form a GCIB  128 . Accelerator power supply  140  provides voltage V ACC  to bias a high voltage electrode with respect to the ionizer  122  so as to result in a total GCIB acceleration energy equal to V ACC . One or more lens power supplies ( 142  and  144  shown for example) may be provided to bias high voltage electrodes with potentials (V L1  and VL 2  for example) to focus the GCIB  128 .  
         [0028]    A workpiece  152 , which may be a semiconductor wafer or other workpiece to be processed by GCIB processing, is held on a workpiece holder  150 , disposed in the path of the GCIB  128 . Since most applications contemplate the processing of large workpieces with spatially uniform results, a scanning system is desirable to uniformly scan the GCIB  128  across large areas to produce spatially homogeneous results. Two pairs of orthogonally oriented electrostatic scan plates  130  and  132  can be utilized to produce a raster or other scanning pattern across the desired processing area. When beam scanning is performed, the GCIB  128  is converted into a conical scanned GCIB  148 , which scans the entire surface of workpiece  152 .  
         [0029]    The present invention relies upon the understanding that GICB sources, including the one described in FIG. 1, produce a broad distribution of ion cluster sizes with limited cluster ion currents available. Therefore it is not practical to perform GICB processing by selecting a single cluster size or a narrow range of cluster sizes—the available fluence of such a beam is too low for productive processing. It is preferred to eliminate only the monomer ions and other lowest mass ions from the beam and use all remaining heavier ions for processing. It has been determined by the present invention that it is sufficient to provide filtering to eliminate monomer ions while depending on cluster size distribution characteristics shown in FIG. 1 to limit the small clusters (N=2 to ˜10) in the beam. Clusters of size N&gt;10 are adequately large to provide acceptable results in most processes. Since the typical cluster distribution contains clusters of up to N=several thousand and there are few clusters of mass less than 100, it is not significantly detrimental if clusters up to size 100 are removed from the beam in the process of eliminating the monomer ions.  
         [0030]    The present invention further relies upon the understanding that a magnet can be used to provide a magnetic field appropriate for separating monomer ions from a GCIB having a distribution of ion cluster sizes similar to that shown in FIG. 1. FIG. 3 shows GCIB apparatus having such a magnetic beam filter  250  placed in a location after beam formation by high voltage electrodes  126  and before and before beam scanning at electrostatic scan plates  130  and  132 . The GCIB  128  containing unwanted monomer ions passes through a magnetic B field between pole faces of permanent magnet assembly  250 , where the lighter monomer ions are deflected away from the initial trajectory of GCIB  128 . The light monomer ions follow deflected trajectory  264 , while the heavy cluster ions are negligibly perturbed and follow trajectory  262 , which is substantially the same as the initial trajectory of GCIB  128 . The unwanted monomer ions following deflected trajectory  264  strike mass analysis plate  210 , which has an aperture to permit passage of the heavy cluster ions following trajectory  262 . In order to ensure that the beam trajectories in the magnetic beam filter are predictable, it is important that the entire radial extents of the portions of the GCIB following trajectories  128 ,  262 , and  264  be substantially within the uniform magnetic field region of the magnetic beam filter  250 . In some cases it may be desirable to limit the diameter or size of the incoming GCIB  128  in order to assure this condition. In such case, an upstream beam defining aperture  209  may be included to collimate the GCIB  128  prior to entry into the magnetic beam filter  250 .  
         [0031]    Because effective GCIB processing can be accomplished at energies of 30 keV and lower, and because the monomer ions are typically of relatively low mass, for example AMU 40 for argon, powerful magnetic B fields are not required to effectively separate the monomer ions from the GCIB. Furthermore, since it is acceptable with the present invention to remove other higher mass (N&lt;100) clusters from the GCIB, it is practical to use a fixed magnetic B field. A permanent magnet can be used effectively within the GCIB apparatus of the present invention. FIG. 4 shows detail of a permanent magnet beam filter  250 .  
         [0032]    More specifically, as shown in FIG. 4, permanent magnet beam filter  250  comprises permanent magnet  252  having north (N) and south (S) poles. Iron pole pieces  254  and  256  are attached to permanent magnet  252  forming a magnetic circuit having a two pole faces  266  and  268  separated by a gap, having within it a magnetic B-field  258  signified by an arrow and the symbol B. Pole face  266  is the north pole face and pole face  268  is the south pole face. The permanent magnet beam filter  250  is disposed such that the GCIB  128  trajectory  260  passes centrally through the gap between pole faces  266  and  268 . Light monomer ions are deflected along trajectory  264  and the heavy cluster ions continue substantially unperturbed along trajectory  262  which differs negligibly from trajectory  260 . The permanent magnet beam filter  250  does not produce heat.  
         [0033]    [0033]FIG. 5 shows a diagram to explain the deflection that occurs in such a filter. Referring to FIG. 5, south pole face  268  is seen from the direction of north pole face  266  (not shown). A GCIB enters from the left on initial trajectory  260 . The GCIB has an ion size distribution similar to that shown in FIG. 1 and includes positive ion clusters as well as positive monomer ions and is assumed to have been formed and accelerated in the GCIB apparatus of this invention, a type of which is shown in FIG. 3. A magnetic flux (B-field) exists in the gap between the two pole faces and is symbolized by B and the circled cross, which means that the direction of the B-field is into the plane of the paper (from the north pole face to the south pole face). The width of the pole face  268  in the direction of the trajectory  260  is signified by the lower case letter “l”. In the magnetic field, which is assumed to be uniform within the gap and zero outside the gap, the positive monomer ions travel in a circular path of radius “R” and exit the magnetic gap along deflected trajectory  264 . Heavy cluster ions are not substantially perturbed and exit the magnetic gap along trajectory  262  which is substantially the same as trajectory  260 .  
         [0034]    Cluster ions having small sizes of N=2, 3, . . . if present, follow trajectories between monomer ion trajectory  264  and heavy cluster trajectory  262 . After exiting the magnetic gap and drifting an additional distance “L”, the trajectories  264  and  262  are separated by distance “d” referred to as the “deflection” of the monomer ion beam.  
             R   =           2   ·   m   ·   V     e       B             Eqn   .              1                               
 
         [0035]    Equation 1 is the well-known equation of motion of a charged particle, having a single electrical charge, in a magnetic field where:  
         [0036]    R is the radius of the circular orbit of the charged particle  
         [0037]    B is the magnetic B-field strength  
         [0038]    m is the mass of the charged particle  
         [0039]    V is the energy in electron volts of the charged particle, which for a singly charged ion, equals the total potential, V ACC , through which it has been accelerated.  
         [0040]    e is the magnitude of the charge of a single electron (charge quantum)  
         [0041]    Equation 2 is obtained from the geometry of FIG. 5.  
                 1   R     =     sin                 θ       ,           Eqn   .              2                               
 
         [0042]    where  1  is the width of pole face  268   
         [0043]    Equation 3 is obtained by solving Eqn. 2 for the deflection angle, θ and substituting Eqn. 1 for R.  
             θ   =     a                   sin   [       1   ·   B           2   ·   m   ·   V     e         ]               Eqn   .              3                               
 
         [0044]    Equation 4 is obtained from the geometry of FIG. 5. 
           d=L· tan θ+ R− {square root}{square root over (( R   2   −l   2 ))}  Eqn. 4 
         [0045]    The total deflection d is the sum of the deflection occurring in the magnet gap and the additional drift after exiting the magnet gap.  
         [0046]    Equation 5 results from substituting the expression for θ from Eqn. 3 into Eqn. 4 and simplifying.  
             d   =         B   ·   L   ·   1             2   ·   V   ·   m     -       B   2     ·   e   ·     l   2         e         +         (       2   ·   V   ·   m     B     )       B     -             2   ·   V   ·   m     -       B   2     ·   e   ·     l   2         e       B               Eqn   .              5                               
 
         [0047]    Eqn. 5 gives the total deflection “d” given the magnet and drift geometry and the magnetic B-field strength, neglecting magnetic field fringing effects. By using Eqn. 5 and solving by indirect means it is possible to determine the required value of B, magnetic B-field strength required to produce a desired deflection d in a given geometry and for a specific particle and energy.  
         [0048]    The actual separation of the deflected monomer beam from the desired heavy cluster beam occurs at the mass analysis plate  210 . FIG. 6 shows an example mass analysis plate  210  for illustration. Mass analysis plate  210  has a slit-like aperture  270  through which the desired heavy cluster beam trajectory may pass. Because there may be aberrations in the beam forming optics of a GCIB forming system, it is generally the case that in a GCIB containing monomer ions, the beam diameter of the beam of desired heavy cluster ions may be different from the diameter of the beam of co-traveling monomer ions. This is illustrated in FIG. 6 by the fact that the beam spot size  274  of the monomer ion beam where it strikes the plate  210  is different from the spot size  272  of the heavy cluster ion beam where it passes through the plane of the plate  210 . The respective beam spot sizes may be measured or determined by mathematical modeling by those skilled in the arts. The addition of upstream beam defining apertures may be employed to control the maximum size of the beam spot sizes.  
         [0049]    If the heavy cluster ion beam spot radius is R H  and the monomer ion spot radius is R M , and the maximum misalignment (circular error) of the center of the analysis aperture  270  with respect to the beam is E then the aperture slit width must be greater than the beam diameter. Additionally, for tolerance reasons, it may desirable to allow an additional amount δ, to the slit width. In such case, the slit width will be: 
           A= 2  R   H +2ε+δ  Eqn. 6 
         [0050]    and the necessary separation between the centers of the monomer and heavy beam spots to assure complete separation under worst case alignment conditions is: 
           d=R   H +2ε+δ/2+ R   M   Eqn. 7 
         [0051]    [0051]FIGS. 6 and 7 shows the geometry for beam separation with slit width A and beam deflection d designed according to Equations  6  and  7  in the case (FIG. 6) where there is no misalignment of the beam to the aperture, and in the case (FIG. 7) where there is worst case misalignment.  
         [0052]    As an example case, consider the GCIB processor of apparatus  200  shown in FIG. 3, wherein the permanent magnet beam filter  250  has a pole face width,  1 =2″ and the drift distance L from the magnet  250  to the mass analysis plate  210  is 8″. The monomer spot size  274  is 0.7″ and the heavy cluster ion beam spot size  272  is 0.3″. Alignment error, ε is 0.05″ and we choose δ to be 0.1″. We have:  
         [0053]    l=2″ 
         [0054]    L=8″ 
         [0055]    R M =0.35″ 
         [0056]    R H =0.15″ 
         [0057]    from Eqn. 6: A=0.5″ 
         [0058]    from Eqn. 7: d=0.65″ 
         [0059]    the beam is a 30 keV argon GCIB having zero alignment error from Eqn. 5:, solving implicitly, given d  
         [0060]    B≈0.2237 tesla=2237 gauss  
         [0061]    and the trajectories of the monomer and heavy cluster ion beamlets are as shown in FIG. 8.  
         [0062]    The monomer beamlet is deflected by approximately 4.13° from the heavy cluster ion beamlet. All of the heavy cluster beamlet, following trajectory  262  passes through the slit  270  in the mass analysis plate  210 , while all of the monomer ion beamlet, following trajectory  264  strikes the mass analysis plate  210 .  
         [0063]    A problem, however, may still, under certain circumstances, exist with the use of a permanent magnet beam filter for separation of monomer ions from a GCIB. Occasionally, for beam diagnostic purposes, it may be desirable to transmit the entire beam including any monomer ions present (for example to determine the ratio of monomer ions to cluster ions for the source, as may be required to tune the source to minimize the production of monomer ions). In such case, it is desirable to remove the beam filter effect, but because of the permanent magnet nature of the filter this will only be straightforwardly achieved by removal of the entire beam filter from the system, which is not a practical method from a point of maintenance effort and equipment availability.  
         [0064]    A further embodiment of this invention is directed to the above problem. In this embodiment of this invention a novel combination of permanent magnet and electromagnet is incorporated within the GCIB apparatus  200  shown in FIG. 3. FIG. 9 shows a hybrid permanent/electromagnetic beam filter  300 , made by adding an exciting coil to the permanent magnet beam filter  250  described in FIG. 4. Specifically, permanent/electromagnetic beam filter  300  comprises a permanent magnet  252  having north (N) and south (S) poles. Iron pole pieces  254  and  256  are attached to permanent magnet  252  forming a magnetic circuit having a two pole faces  266  and  268  separated by a gap, having within it a magnetic B-field  258  signified by an arrow and the symbol B. Pole face  266  is the north pole face and pole face  268  is the south pole face. The permanent/electromagnetic beam filter  300  is disposed such that the GCIB  128  trajectory  260  passes centrally through the gap between pole faces  266  and  268 . Light monomer ions are deflected along trajectory  264  and the heavy cluster ions continue substantially unperturbed along trajectory  262  which differs negligibly from trajectory  260 . Permanent magnet  252  is chosen to have a magnetic strength at least great enough to produce a B-field  258  in the gap that is large enough to provide a desired minimum deflection of light monomer ions trajectory  264  from the heavy cluster ions trajectory  262  sufficient to separate the monomer ions from the transmitted beam of heavy cluster ions under conditions of maximum beam energy and for the heaviest monomer ions that will be used (for example argon, AMU  40 ), and under conditions of worst case beam alignment. Permanent/electromagnetic beam filter  300  also has an electrical excitation coil  302 , which can be energized by power supply/controller  308  to provide an electromagnetic B-field to oppose and counteract the permanent magnet produced B-field in the gap, thus rendering the gap B-field  258  substantially equal to zero, during the time while the coil  302  is thus suitably energized. The characteristics of the coil and power source are chosen to provide sufficient ampere-turns to produce a B-field  258  in the gap which is at least greater than that provided by the permanent magnet  252 . The method of calculating the proper number of ampere-turns to produce a desired B-field is well known and may be found in various references including M.S. Livingston, et al.,  Particle Accelerators , p. 242, eqn. (8-5), McGraw-Hill, New York (1962). When the coil  302  is not energized, the permanent magnet  252  provides the predetermined B-field  258  in the gap, and when the coil  302  is suitably energized, the B-field  258  in the gap is zero. When the coil  302  is not energized, the permanent/electromagnetic beam filter  300  does not produce heat.  
         [0065]    To facilitate adjustment of the gap B-field  258  to zero value, a magnetic field sensor  304  may be disposed in the gap to measure the gap B-field  258 . Such a sensor may be a small Hall-effect sensing device and is so disposed as to sense the B-field  258  without interfering with the transmission of the GCIB through the magnet gap.  
         [0066]    During the time the coil  302  is energized to disable the beam filter, resistive heating heats coil  302 . The coil  302  may be encapsulated and may be in thermal contact with the magnet pole piece  256  and heat produced by the coil may be conducted into the encapsulation and pole piece to allow short periods of operation without excessive temperature rise due to the combined heat capacity of coil, encapsulation, and pole pieces. As a safety measure, temperature sensor  306 , which may be a bi-metallic thermostat, a thermistor, a thermocouple, or the like, may be attached to the coil  302  and connected by cable  312  to power supply/controller  308 . Signals from temperature sensor  306  are used by power supply/controller  308  to shut down the coils  302 , in the event that an excessive temperature rise is detected in coil  302 .  
         [0067]    [0067]FIG. 10 shows details of the controls for the hybrid permanent/electromagnetic beam filter. Cable  312  connects power supply/controller  308  to coil  302 , magnetic field sensor  304 , and temperature sensor  306 . Operation is as follows: a system control device  310  which may be a small computer or microcomputer provides a magnetic B-field set-point signal  326  corresponding to zero magnetic B-field and power supply enabling signal  324  to power supply/controller  308 . Signals  324  and  326  are connected through cable  314 . When power supply enabling signal  324  does not enable power supply/controller  308 , switch device  320  disconnects coil  302  from power amplifier  318 , de-energizing coil  302 .  
         [0068]    When power supply enabling signal  324  enables power supply/controller  308 , switch device  320  connects coil  302  to the output of power amplifier  318 , energizing coil  302 . Set-point signal  326  is compared to the signal from magnetic field sensor  304  at error amplifier  316 , producing an error signal which drives power amplifier  318  to deliver current through switch device  320  to coil  302 . Current in the coil  302  increases until feedback from magnetic field sensor  304  compares with the zero field set-point signal  326 , and regulates the B-field in the magnet gap to zero. System control device  310  limits the duty cycle of enabling power supply/controller  308  to a predetermined value that does not produce excessive heating of coil  302 .  
         [0069]    Temperature sensor  306  monitors coil temperature as a protective measure against system control device failure. If temperature sensor detects a coil over-temperature condition, it overrides control inputs to switch device  320 , shutting down power to coil  302 . If temperature sensor  306  is a low level analog device such as a thermistor or thermocouple, amplifier  322  may be employed to create a control level signal for switch device  320  from the low level sensor signal.  
         [0070]    [0070]FIG. 11 shows the GCIB processing system or apparatus  400  of this invention with the hybrid permanent/electromagnetic beam filter invention. During normal beam operation of the GCIB processing device, system control device  310  does not enable the coil  302  and the hybrid permanent/electromagnetic beam filter  300  filters low mass monomer ions from the beam by virtue of it&#39;s permanent magnetic B-field. During periods of beam diagnostic tests, the system control device  310 , enables the power supply control device  308  and sets current in the electromagnet coil  302  to zero the field in the magnet gap, disabling the beam filter and permitting the entire GCIB including monomer ions, if present, to be transmitted through the system. During normal beam processing, no heat is generated in the beam filter. During diagnostic testing, heat is generated in the beam filter but is limited to a safe duty cycle.  
         [0071]    Although the invention has been described with respect to various embodiments, it should be realized this invention is also capable of a wide variety of further and other embodiments within the spirit and scope of the appended claims.