Abstract:
A system and method of improving the performance and extending the lifetime of an ion source is disclosed. The ion source includes an ion source chamber, a suppression electrode and a ground electrode. In the processing mode, the ion source chamber may be biased to a first positive voltage, while the suppression electrode is biased to a negative voltage to attract positive ions from within the chamber through an aperture and toward the workpiece. In the cleaning mode, the ion beam is defocused so that it strikes the suppression electrode and the ground electrode. The voltages applied to the ion source chamber and the electrodes are pulsed to minimize the possibility of glitches during this cleaning mode.

Description:
FIELD 
     Present disclosure relates generally to methods of cleaning an extraction electrode assembly, particularly in an ion source, using pulsed biasing. 
     BACKGROUND 
     Ion implantation is a process by which dopants or impurities are introduced into a substrate via bombardment. In semiconductor manufacturing, the dopants are introduced to alter electrical, optical, or mechanical property. For example, dopants may be introduced into an intrinsic semiconductor substrate to alter the type and level of conductivity of the substrate. In manufacturing an integrated circuit (IC), a precise doping profile is often important for proper IC performance. To achieve a desired doping profile, one or more dopants may be implanted in the form of ions in various doses and various energy levels. 
     In some implementations, a plasma is created in an ion source chamber. This plasma contains positively charged dopant ions. An extraction electrode assembly may be disposed outside of and proximate the ion source chamber. This extraction electrode assembly may include at least a suppression electrode and a ground electrode. Each of the electrodes in the extraction electrode assembly may have an aperture, through which the positively charged dopant ions may pass. In addition, one or more of the electrodes may be negatively biased to attract the positively charged dopant ions through an extraction aperture in the ion source chamber and through the apertures in the extraction electrode assembly. These extracted dopant ions form an ion beam, which is then used to implant the substrate. 
     One cause of ion source failure is accumulation of materials on the inner wall of the ion source chamber, the suppression electrode and the ground electrode. In addition, the materials may accumulate on the apertures. If formed on the inner wall of the ion source chamber, the materials may reduce the rate by which ions are generated and reduce the beam current. 
     One way to prevent the effect of the material accumulation is to intermittently replace the ion source with a clean ion source. Alternatively, the ion source may have to be manually cleaned after powering down the entire ion source and after releasing the vacuum. However, these measures require the ion source or the entire ion implanter system to be powered down and to release the vacuum within the system. Moreover, the ion implanter system, after replacing or cleaning the ion source, must be powered and evacuated to reach operational condition. Accordingly, these maintenance processes may be very time consuming. In addition, the ion implanter system is not used during the maintenance processes. As such, frequent maintenance processes may decrease IC production time, while increasing its manufacturing cost and placing excessive financial burden on the manufacturers and, ultimately, the consumers. In view of the foregoing, it would be desirable to provide a new technique for improving the performance and extending the lifetime of an ion source to overcome the above-described inadequacies and shortcomings. 
     SUMMARY 
     A system and method of improving the performance and extending the lifetime of an ion source is disclosed. The ion source includes an ion source chamber, a suppression electrode and a ground electrode. In the processing mode, the ion source chamber may be biased to a first positive voltage, while the suppression electrode is biased to a negative voltage to attract positive ions from within the chamber through an aperture and toward the workpiece. In the cleaning mode, the ion beam is defocused so that it strikes the suppression electrode and the ground electrode. The voltages applied to the ion source chamber and the electrodes are pulsed to minimize the possibility of glitches during this cleaning mode. 
     In a first embodiment, an ion source is disclosed. The ion source comprises an ion source chamber for generation of a process plasma during a processing mode and a cleaning plasma during a cleaning mode, the ion source chamber having an extraction aperture; a suppression electrode having a suppression electrode aperture, the suppression electrode disposed proximate the extraction aperture, wherein an ion beam extracted from the extraction aperture during the cleaning mode is defocused so as to strike the suppression electrode; and a biasing system configured to periodically stop the ion beam from striking the suppression electrode during the cleaning mode and to ground the suppression electrode and the ion source chamber when the ion beam is periodically stopped. 
     In a second embodiment, a method of cleaning an ion source is disclosed. The ion source comprises an ion source chamber having an extraction aperture, a ground electrode, and a suppression electrode disposed between the ion source chamber and the ground electrode. The method comprises flowing a cleaning gas into the ion source chamber; generating a plasma in the ion source chamber using the cleaning gas; defocusing an ion beam extracted from the ion source chamber, such that the ion beam strikes the suppression electrode; biasing the ion source chamber and the suppression electrode to a set of cleaning bias voltages so that the defocused ion beam removes material from the suppression electrode during a cleaning time interval; grounding the ion source chamber and the suppression electrode periodically during the cleaning time interval; and repeating the biasing and grounding a plurality of times during the cleaning time interval. 
     In a third embodiment, a method of operating an ion source is disclosed. The ion source comprises an ion source chamber having an extraction aperture, a ground electrode, and a suppression electrode disposed between the ion source chamber and the ground electrode. The method of operating the ion source comprises flowing a source gas into the ion source chamber during a processing mode; generating a process plasma in the ion source chamber using the source gas during the processing mode; applying a set of processing bias voltages to the ion source chamber and the suppression electrode during the processing mode; extracting an ion beam through the extraction aperture during the processing mode, the ion beam configured to implant a substrate; flowing a cleaning gas into the ion source chamber during a cleaning mode; generating a cleaning plasma in the ion source chamber using the cleaning gas during the cleaning mode; defocusing an ion beam extracted from the ion source chamber, such that the defocused ion beam strikes the suppression electrode during the cleaning mode; biasing the ion source chamber and the suppression electrode to a set of cleaning bias voltages so that the defocused ion beam removes material from the suppression electrode during the cleaning mode; grounding the ion source chamber and the suppression electrode periodically during the cleaning mode to remove charge build up; and repeating the biasing and grounding a plurality of times during the cleaning mode. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       For a better understanding of the present disclosure, reference is made to the accompanying drawings, which are incorporated herein by reference and in which: 
         FIG. 1  is an ion source according to a first embodiment; 
         FIG. 2  shows the ion source of  FIG. 1  operating in cleaning mode; 
         FIG. 3A-3B  show flowcharts illustrating operation of the ion source; 
         FIG. 4  shows an ion source according to a second embodiment; 
         FIG. 5  shows an ion source according to a third embodiment; and 
         FIG. 6  shows an ion source according to a fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Herein, a new method of cleaning an extraction electrode assembly using pulsed biasing is disclosed. For purposes of clarity and simplicity, the present disclosure may focus on the methods as used with an ion implanter having an indirectly heated cathode (IHC) as the ion generator. Those of ordinary skill in the art will recognize that the present disclosure, however, is not limited to a particular ion generator or a particular ion implantation system. The present disclosure may be equally applicable to other types of ion generators including, for example, Bernas source or RF plasma source, in other types of ion implantation systems including, for example, multiple wafer (e.g. batch), spot beam ion implantation system or plasma based ion implantation system, with or without the beam-line components. In addition, the present disclosure may be equally applicable to other plasma based substrate processing systems or other systems that use ions. 
     Referring to  FIG. 1 , there is shown simplified illustration of an exemplary ion source  100  according to one embodiment of the present disclosure. The ion source  100  may include an IHC, as illustrated in the figure, or other types of ion generators. The ion source  100  may include an ion source chamber  102 . On the front side of the ion source chamber  102 , an extraction aperture  104  may be disposed. A cathode  106  and a repeller electrode  108  (or anti-cathode) may be positioned in the opposite sides of the ion source chamber  102 . A filament  110  may be positioned outside the ion source chamber  102  and in close proximity to the cathode  106  to heat the cathode  106 . One or more source magnets (not shown) may also be provided to produce a magnetic field B (see arrow B) in the ion source chamber  102 . 
     Near the ion source chamber  102 , there may be one or more feed sources  118 . In the present disclosure, material provided from the feed source  118  may include source gasses and cleaning gasses. The source gasses may contain dopant species that may be introduced into the substrate in the form of ions during normal operating mode. The cleaning gas may comprise a gas that is used during a cleaning mode. 
     In the present disclosure, various species may be used as the source gas. Examples of the source gas may include atomic or molecular species containing, boron (B), gallium (Ga), germanium (Ge), phosphorus (P), arsenic (As), and others. Examples of cleaning gas may include argon (Ar). Those of ordinary skill in the art will recognize that the above species are not exhaustive, and other atomic or molecular species may also be used. 
     Preferably, the source gas and/or the cleaning gas is provided into the ion source chamber  102  in gaseous or vapor form. If the source gas and/or the cleaning gas is in non-gaseous or non-vapor form, a vaporizer (not shown) may be provided near the feed source  118  to convert the material into gaseous or vapor form. To control the amount and the rate by which the source and/or the additional material is provided into the ion source chamber  102 , a flowrate controller  134  may be provided. 
     Proximate to the ion source chamber  102 , near the extraction aperture  104 , an extraction electrode assembly  114  may be disposed. In the present embodiment, the extraction electrode assembly  114  may comprise a suppression electrode  114   a  and a ground electrode  114   b . Each of the suppression electrode  114   a  and the ground electrode  114   b  may have an aperture that is in communication with the extraction aperture  104  of the ion source chamber  102 . In the suppression electrode  114   a , there may be a suppression electrode aperture  114   a - 1 , whereas a ground electrode aperture  114   b - 1  may be disposed and defined in the ground electrode  114   b . Hereinafter, the suppression electrode aperture  114   a - 1  and the ground electrode aperture  114   b - 1  may be collectively referred to as an extraction electrode aperture, which is in communication with the extraction aperture  104  of the ion source chamber  102 . 
     In order to power the ion source chamber  102 , the cathode  106 , the filament  110 , the repeller electrode  108 , the suppression electrode  114   a , and/or the ground electrode  114   b , one or more power supplies may be provided. For the purpose of clarity and simplicity, only three power supplies are shown. Those of skill in the art will recognize that there may be multiple power supplies, each of which may be electrically coupled to different components of the ion source  100 . Or, there may be multiple power supplies where one of the power supplies may be electrically coupled to multiple components. In yet another embodiment, a single power supply, having a plurality of outputs may be used to power all of the components in the system  100 . In the present disclosure, the power supplies  153 ,  154 ,  155  may provide continuous or pulsed, alternating current (AC) or direct current (DC). The power supplies  153 ,  154 ,  155  may also provide positive or negative bias voltage. 
     The ground electrode  114   b  may be biased by a ground electrode power supply  155 . In some embodiments, the ground electrode  114   b  is grounded, thereby obviating the need for the ground electrode power supply  155 . The suppression electrode  114   a  may be powered by a suppression power supply  153 . An extraction power supply  154  is used to bias the walls of the ion source chamber  102 . In some embodiments, the suppression power supply  153  and/or the extraction power supply  154  may be referenced to the ground electrode  114   b.    
     As noted above, one cause of the ion source  100  failure may be excessive accumulation of materials during its extended use. For example, materials may accumulate on the walls of, among others, the ion source chamber  102 , the suppression electrode  114   a , and the ground electrode  114   b . To prevent excessive accumulation, the ion source  100  of the present embodiment may operate in two modes: processing mode and cleaning mode. During the processing mode, the ion source  100  may generate dopant ions, which are implanted in a substrate disposed downstream of the ion beam  10 . During the cleaning mode, the ion source  100  may be in situ cleaned. In the present disclosure, the ion source  100  may operate in the processing mode and cleaning mode. 
     During the processing mode, the source gas containing dopant species may be introduced into the ion source chamber  102  from the feed source  118 . Meanwhile, the filament  110  may be powered to emit electrons toward the cathode  106  via thermionic emission. The cathode  106 , in turn, may emit electrons in the ion source chamber  102  to generate a plasma  120  containing, among others, dopant ions. 
     The ground electrode  114   b  may be biased by the ground electrode power supply  155  so as to extract the ions  10  from the ion source chamber  102 . In some embodiments, the ground electrode  114   b  may be grounded and is not in communication with a power supply. Such ions  10  may be directed toward the substrate. In one embodiment, the suppression power supply  153  may provide +/−bias voltage and continuous/pulsed, AC/DC to the suppression electrode  114   a . In one particular embodiment, the suppression power supply  153  may supply about −2 kV to −30 kV at about 100 mA to the suppression electrode  114   a . The extraction power supply  154  may supply between about 10 kV and 70 kV to the walls of the ion source chamber  102 . The extraction power supply  154  may be able to supply between 25 mA and up to about 200 mA of current. 
     In the processing mode, the ions may be extracted from the ion source chamber  102  as a focused ion beam  10 . It will be understood that the voltage and current noted above are given by way of example only and are not limiting as to the scope of present disclosure. Also, it will be understood that the voltage and current provided by the power supplies  153 ,  154 ,  155  may be constant or varied. 
     Referring to  FIG. 2 , there is shown the ion source  100  operating under the cleaning mode, according to one embodiment of the present disclosure. It should be appreciated that most of the components illustrated in  FIG. 1  are incorporated into  FIG. 2 . As such, most of the components in  FIG. 2  should be understood in relation to the components in  FIG. 1 . 
     During the cleaning mode, ion source  100  may be in situ cleaned. In the present embodiment, the cleaning gas may be introduced into the ion source chamber  102 . As described above, various species may be introduced as the cleaning gas. 
     As is done in the processing mode, a cleaning plasma  220  is created in the ion source chamber  102 . Unlike the plasma  120  created in processing mode, however, this cleaning plasma  220  may not contain dopants. Rather, the cleaning gas may be selected based on its effectiveness to sputter onto the extraction electrode assembly  114  and remove material therefrom. 
     In addition, in cleaning mode, the ion beam  210  is defocused. This defocusing may be accomplished in a number of ways. In one embodiment, the distance between the extraction electrode assembly  114  and the extraction aperture  104  is varied. In one embodiment, the distance between these components is increased. In another embodiment, defocusing is accomplished by modifying the bias voltages applied to the walls of the ion source chamber  102 , the suppression electrode  114   a  and/or the ground electrode  114   b . For example, in one example, the walls of the ion source chamber  102  are biased at about 5 kV, the suppression electrode  114   a  is biased at −7 kV and the ground electrode  114   b  is grounded. In other embodiments, defocusing is accomplished by a combination of these techniques, whereby the distance between the extraction aperture  104  and the extraction electrode assembly  114  is modified, and the bias voltages applied to at least one of the walls of the ion source chamber  102 , the suppression electrode  114   a  and the ground electrode  114   b  is also modified. 
     As illustrated in  FIG. 2 , the defocusing of the ion beam  210  causes ions to strike the extraction electrode assembly  114 , and particularly the suppression electrode  114   a  and the ground electrode  114   b . Energetic ions striking these surfaces may serve to remove material that has built up on the extraction electrode assembly  114  during the processing mode. 
     However, in some cases, the sustained striking of the extraction electrode assembly  114  by the energetic ions may result in arcs between two adjacent components. For example, arcs may be created between the wall of the ion source chamber  102  and the suppression electrode  114   a , as these components are biased at different voltages. Likewise, arcs may be created between the suppression electrode  114   a  and the ground electrode  114   b.    
     Thus, according to one embodiment, the bias voltages being applied to each of the walls of the ion source chamber  102 , the suppression electrode  114   a  and the ground electrode  114   b  are all disabled and each of these components is connected directly to ground. This direct connection to ground serves to eliminate any electrostatic energy that has accumulated on the surfaces of these components and to allow any arcs that may have been created to dissipate. After the components have been grounded for a sufficient amount of time, the respective bias voltages are restored to each component. 
     For example, the cleaning mode may begin by optionally moving the extraction electrode assembly  114  and modifying the bias voltages applied to the walls of the ion source chamber  102 , the suppression electrode  114   a  and/or the ground electrode  114   b . After a first time duration, the walls of the ion source chamber  102 , the suppression electrode  114   a  and the ground electrode  114   b  are all grounded. This removes any charge that may build up on the surfaces of these components. After a second time duration, the bias voltages are restored to each of these components. This sequence may be repeated for the entirety of the cleaning mode. The pulsed bias voltage duty cycle, defined as the duration of time where the bias voltages are being applied divided by the total elapsed time, may vary. In some embodiments, the duty cycle may be between 1-80%. In some embodiments, the duty cycle may be less than 50%. In some other embodiments, the duty cycle may be 10-25%. 
     Thus, an ion source may be operated as shown in  FIG. 3A . First, the ion source is operated in processing mode (see Box  310 ) for a first operating time period. In some embodiments, this first operating time period may be between 20-50 hours, or more particularly between 40-50 hours. During this time, the walls of the ion source chamber  102 , the suppression electrode  114   a  and the ground electrode  114   b  are respectively biased to a set of processing bias voltages. A source gas is used to generate the plasma  120  used for the ion beam. 
     After this first operating time period, cleaning mode (see Box  320 ) is entered for a second operating time period. This second operating time period is much shorter than the first operating time period, for example less than 1 hour. In some embodiments, the second operating time period may be less than 30 minutes, such as about 20 minutes. As described above, cleaning mode involves several modifications to the operating parameters used in processing mode. For example, the source gas used to create the plasma is replaced with a cleaning gas. In addition, the ion beam is defocused, either by a change in spacing between the extraction aperture  104  and the extraction electrode assembly  114 , a change in bias voltages of the various components, or a combination of these two actions. 
     This cycle of processing mode and cleaning mode can be repeated indefinitely, or until the ion source is taken off-line for preventative maintenance. 
       FIG. 3B  shows the operation of the ion source during the cleaning mode. First, as shown in Box  321 , a defocused ion beam is generated to clean the extraction electrode assembly  114 . The walls of the ion source chamber  102 , the suppression electrode  114   a  and the ground electrode  114   b  are respectively biased to a set of cleaning voltages. During this first cleaning time period, the defocused ion beam serves to remove built up material from the extraction electrode assembly  114 . After the first cleaning time period, the walls of the ion source chamber  102 , the suppression electrode  114   a  and the ground electrode  114   b  are all directly connected to ground for a second cleaning time period, as shown in Box  322 . This step serves to removal any charge that has built up on these components. This sequence of cleaning steps  321 ,  322  is repeated while the ion source is in cleaning mode. In one embodiment, this sequence of cleaning steps is executed at a frequency of about 1 kHz, although other frequencies are within the scope of the disclosure. As described above, the duty cycle (i.e. first cleaning time period divided by the sum of the first cleaning period and the second cleaning period) may be less than 50% in some embodiments. In some embodiments, this duty cycle may be between 10-25%. In other embodiments, the duty cycle may be between 1-80%. 
     Various embodiments may be employed to create the ion source described herein.  FIG. 4  shows a first embodiment of an ion source  400 . In this embodiment, each of the walls of the ion source chamber  102 , the suppression electrode  114   a  and the ground electrode  114   b  are in communication with a respective switching device  410   a - c . One terminal of each respective switching device  410   a - c  is in communication with the associated power supply  153 ,  154 ,  155 . Another terminal of each switching device  410   a - c  is directly connected to ground. Thus, when the switching devices  410   a - c  are in a first position, the components are each biased to a respective bias voltage, as determined by the respective power supply. When the switching devices  410   a - c  are in a second position, each of these components is grounded. 
     Each of the power supplies  153 ,  154 ,  155  may be a variable or programmable power supply, capable of switching between 2 or more different output voltages. In one embodiment, the power supplies  153 ,  154 ,  155  are each in communication with a controller  420 . The controller  420  includes a processing unit and a memory device. The memory device contains instructions that allow the controller  420  to perform the steps and functions described herein. 
     For example, this controller provides an output to each of the power supplies  153 ,  154 ,  155 , instructing them to switching between processing mode and cleaning mode. Thus, the power supplies  153 ,  154 ,  155  may be instructed to switch between a set of processing bias voltages and a set of cleaning bias voltages. In addition, the controller  420  may be in communication with the switching devices  410   a - c . The controller  420  provides an output to the switching devices  410   a - c  instructing them to switch between the terminal connected to the associated power supply and the terminal connected to ground. 
     The controller  420  may also be in communication with the flow rate controllers, so as to select the gas that is supplied to the ion source chamber  102 . For example, the controller  420  may select the source gas during processing mode and the cleaning gas during the cleaning mode. In one embodiment, the controller  420  may also be in communication with an actuator (not shown), which is used to move the position of the extraction electrode assembly  114  relative to the ion source chamber  102 . Thus, the controller  420  may be used to implement the steps illustrated in flowcharts shown in  FIGS. 3A and 3B . 
     In a further embodiment, the controller  420  may be in communication with one or more glitch detectors (not shown). These glitch detectors may monitor the bias voltage at each component, or may monitor the current being provided by each respective power supply  153 ,  154 ,  155 . The glitch detectors may be discrete components, or may be integrated into the respective power supplies. If the bias voltage drops below a certain threshold (or the current increases above a certain threshold), a glitch detector may determine that a glitch has occurred. This information is input to the controller  420 . The controller  420  may then instruct the switching devices  410   a - c  to switch so as to ground the walls of the ion source chamber  102 , the suppression electrode  114   a  and the ground electrode  114   b . By doing this, the glitch may be eliminated more quickly, thereby preventing shutdown of the affected power supply. In some embodiments, the glitch detection and remediation technique is only performed in processing mode. 
     In a different embodiment, cleaning mode is performed by only moving the extraction electrode assembly  114  relative to the ion source chamber  102 . In this embodiment, the power supplies  153 ,  154 ,  155  may not be programmable, and simply output a constant voltage during both modes. In this embodiment, the extraction electrode assembly  114  is moved relative to the ion source chamber  102  during the cleaning mode. As described above, the controller  420  interacts with the switching devices  410   a - c  to pulse the bias voltages to the components during the cleaning mode. 
     In another embodiment, the programmable power supplies  153 ,  154 ,  155  are replaced by separate processing power supplies and cleaning power supplies, as illustrated in the ion source  500  of  FIG. 5 . For example, switching device  510   a  may have three terminals, one in communication with an extraction processing power supply  554   a , a second in communication with an extraction cleaning power supply  554   b  and a third in communication with ground. Any of these three terminals can be selected so as to be in communication with the walls of the ion source chamber  102 . 
     Similarly, switching device  510   b  may have three terminals, one in communication with a suppression processing power supply  553   a , a second in communication with a suppression cleaning power supply  553   b  and a third in communication with ground. Any of these three terminals can be selected so as to be in communication with the suppression electrode  114   a.    
     Switching device  510   c  may have three terminals, one in communication with a ground electrode processing power supply  555   a , a second in communication with a ground electrode cleaning power supply  555   b  and a third in communication with ground. Any of these three terminals can be selected so as to be in communication with the ground electrode  114   b . As described above, in some embodiments, the ground electrode  114   b  may be permanently connected to ground, thereby eliminating the needs for the switching device  510   c , the ground electrode processing power supply  555   a  and the ground electrode cleaning power supply  555   b.    
     In this embodiment, the controller  520  is in communication with the switching devices  510   a - c  and instructs these switching devices to select one of the three terminals, based on the operating mode of the ion source  500 . In the first position, the switching devices  510   a - c  connect the components to a respective processing power supply  553   a ,  554   a ,  555   a . In a second position, the switching devices  510   a - c  connect the components to a respective cleaning power supply  553   b ,  554   b ,  555   b . In the third position, the switching devices  510   a - c  connect each of the components to ground. In addition, as described earlier, glitch detectors (not shown) may be utilized to detect glitches that occur during processing mode. In the event of a glitch, the controller  520  may instruct the switching devices  510   a - c  to switch to the third position, thereby grounding the components to remove the glitch. 
     As described above, the controller  520  may also be in communication with flow rate controllers, so as to select the gas that is fed into the ion source chamber  102 . In addition, the controller  520  may be in communication with an actuator which moves the extraction electrode assembly  114  relative to the ion source chamber  102 . 
       FIG. 6  shows another embodiment of an ion source  600 . In this embodiment, the ground electrode  114   b  is tied to ground. In addition, the switching devices  610   a - b  are disposed within a modulator  660 . This modulator is in communication with the controller  620 , such that, based on an output from the controller  620 , the switching devices  610   a - b  in the modulator  660 , will either both select the respective power supply  653 ,  654 , in a first position, or the ground connection in a second position. 
     As described earlier, the controller  620  may also be in communication with flow rate controllers to select the gas which enters the ion source chamber  102 . Additionally, the controller  620  may also be in communication with an actuator (not shown), used to move the extraction electrode assembly  114  relative to the ion source chamber  102 . 
     Optionally, glitch detectors may be employed to detect the presence of a glitch during processing mode. As described above, this can be achieved by either monitoring the current or voltage output from each respective power supply  653 ,  654 . The glitch detectors may be integrated into the respective power supplies  653 ,  654 , or may be separate devices. The controller  620  may receive inputs from these glitch detectors, and instruct the modulator  660  to switch the switching devices  610   a - b  to the second position (i.e. the ground connection) if a glitch is detected. The switching devices  610   a - b  in the modulator  660  revert to the first position when the glitch is eliminated. 
     In each of the embodiments shown in  FIGS. 4-6 , the extraction power supplies, suppression power supplies, switching devices and modulators constitute a biasing system. Specifically, in  FIG. 4 , the biasing system may include the extraction power supply  154 , the suppression power supply  153 , the electrode power supply  155 , switching devices  410   a - c  and controller  420 . In  FIG. 5 , the biasing system may include the extraction processing power supply  554   a , the extraction cleaning power supply  554   b , the suppression processing power supply  553   a , the suppression cleaning power supply  553   b , the electrode processing power supply  555   a , the electrode cleaning power supply  555   b , the switching devices  510   a - c  and the controller  520 . In  FIG. 6 , the biasing system may include the extraction power supply  654 , the suppression power supply  653 , the modulator  660 , the switching devices  610   a - b  and the controller  620 . In each of these configurations, the biasing system is configured to periodically stop the ion beam from striking the suppression electrode  114   a  during the cleaning mode. When the ion beam  210  is stopped, the biasing system is configured to ground the suppression electrode  114   a  and the ion source chamber  102  to remove any charge built up on these components. Furthermore, in embodiments that also include a glitch detector, the biasing system may be used to temporarily stop the ion beam during the processing mode to remove the detected glitch. This may be done by grounding the ion source chamber  102  and suppression electrode  114   a , so as to remove the charge build up, as is done during the cleaning mode. 
     The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.