Patent Publication Number: US-2023133101-A1

Title: Ion Source Gas Injection Beam Shaping

Description:
FIELD 
     Embodiments of the present disclosure relate to systems injecting gas into an ion source to shape the extracted ion beam. 
     BACKGROUND 
     Semiconductor devices are fabricated using a plurality of processes, some of which implant ions into the workpiece. Various ion sources may be used to create the ions. One such ion source is an indirectly heated cathode (IHC) ion source. An IHC ion source comprises a filament disposed behind a cathode. The cathode may be maintained at a more positive voltage than the filament. As current is passed through the filament, the filament emits thermionic electrons, which are accelerated toward the more positively charged cathode. These thermionic electrons serve to heat the cathode, in turn causing the cathode to emit electrons into the chamber of the ion source. The cathode is disposed at one end of a chamber. A repeller is typically disposed on the end of the chamber opposite the cathode. 
     In certain embodiments, the IHC ion source is configured to extract a ribbon ion beam, where a width of the ribbon ion beam is much larger than the height of the ribbon ion beam. Unfortunately, in many systems, due to non-uniformity of the plasma density within the ion source, the height of the extracted ion beam is not constant. For example, the height of the ribbon ion beam may be greater near the center of the extraction aperture, if the plasma density is greatest in the middle of the chamber. 
     Varying height of the ion beam may be problematic as it may cause non-uniformity in the implant dose. Therefore, in some ion implantation systems, additional components, such as lenses are used to correct for this issue. However, these additional components add cost and complexity. 
     Therefore, it would be beneficial if there was a system that could control the uniformity of the height of a ribbon ion beam being extracted from an ion source. 
     SUMMARY 
     An ion source for extracting a ribbon ion beam with improved height uniformity is disclosed. Gas nozzles are disposed in the chamber proximate the extraction aperture. The gas that is introduced near the extraction aperture serves to shape the ribbon ion beam as it is being extracted. For example, the height of the ribbon ion beam may be reduced by injecting gas above and below the ion beam so as to compress the extracted ion beam in the height direction. In some embodiments, the feedgas is introduced near the extraction aperture. In other embodiments, a shield gas, such as an inert gas, is introduced near the extraction aperture. 
     According to one embodiment, an ion source is disclosed. The ion source comprises a chamber comprising a first end, a second end and a plurality of walls connecting the first end and the second end, wherein one of the plurality of walls is an extraction plate having an extraction aperture having a width greater than its height; a plasma generator to generate a plasma within the chamber; a gas inlet in communication with gas channels; a supply channel in communication with the gas inlet to supply feedgas to the chamber; and gas nozzles disposed within the chamber near the extraction aperture, in communication with the gas channels to provide a flow of feedgas near the extraction aperture. In some embodiments, the plurality of walls comprises a bottom wall opposite the extraction plate and side walls that are adjacent to the extraction plate, and wherein the gas channels are disposed in the side walls. In some embodiments, the plurality of walls comprises a bottom wall opposite the extraction plate and side walls that are adjacent to the extraction plate, and wherein the gas channels comprise tubes disposed proximate an interior or exterior surface of the side walls. In some embodiments, the ion source comprises plate gas channels disposed in the extraction plate and in communication with the gas channels, wherein the gas nozzles are disposed on an interior surface of the extraction plate proximate the extraction aperture. In certain embodiments, the plurality of walls comprises a bottom wall opposite the extraction plate and side walls that are adjacent to the extraction plate, and wherein the gas nozzles are disposed on interior surfaces of the side walls proximate the extraction plate. In some embodiments, the extraction plate comprises a face plate and an extraction liner disposed between an interior of the chamber and the face plate, wherein the extraction liner is formed such that there is a gap between the extraction liner and the face plate, wherein the gap is in communication with the gas channels, and further comprising plate gas channels disposed in the extraction liner and in communication with the gap, wherein the gas nozzles are disposed on a surface of the extraction liner proximate the extraction aperture. In some embodiments, a dimension of the gas nozzles varies along the width of the extraction aperture to achieve an improved height uniformity of an extracted ribbon ion beam. In some embodiments, the plasma generator comprises an indirectly heated cathode (IHC). 
     According to another embodiment, an ion implantation system is disclosed. The ion implantation system comprises the ion source described above, a mass analyzer and a platen. 
     According to another embodiment, an ion source is disclosed. The ion source comprises a chamber comprising a first end, a second end and a plurality of walls connecting the first end and the second end, wherein one of the plurality of walls is an extraction plate having an extraction aperture having a width greater than its height; a plasma generator to generate a plasma within the chamber; a gas inlet in communication with gas channels; gas nozzles disposed near the extraction aperture, in communication with the gas channels; and a second gas inlet in communication with a supply channel to supply feedgas to the chamber; wherein the supply channel and the gas channels are not in fluid communication with one another. In some embodiments, the plurality of walls comprises a bottom wall opposite the extraction plate and side walls that are adjacent to the extraction plate, and wherein the gas channels are disposed in the side walls. In some embodiments, the plurality of walls comprises a bottom wall opposite the extraction plate and side walls that are adjacent to the extraction plate, and wherein the gas channels comprise tubes disposed proximate an interior or exterior surface of the side walls. In some embodiments, the ion source comprises plate gas channels disposed in the extraction plate and in communication with the gas channels, wherein the gas nozzles are disposed on an interior surface of the extraction plate proximate the extraction aperture. In certain embodiments, the plurality of walls comprises a bottom wall opposite the extraction plate and side walls that are adjacent to the extraction plate, and wherein the gas nozzles are disposed on interior surfaces of the side walls proximate the extraction plate. In some embodiments, the extraction plate comprises a face plate and an extraction liner disposed between an interior of the chamber and the face plate, wherein the extraction liner is formed such that there is a gap between the extraction liner and the face plate, wherein the gap is in communication with the gas channels, and further comprising plate gas channels disposed in the extraction liner and in communication with the gap, wherein the gas nozzles are disposed on a surface of the extraction liner proximate the extraction aperture. In some embodiments, the ion source comprises a first gas container in fluid communication with the gas inlet and a second gas container in fluid communication with the second gas inlet. In some embodiments, the ion source comprises a gas container in fluid communication with a first mass flow controller and a second mass flow controller, wherein the first mass flow controller controls a flow rate through the gas inlet and the second mass flow controller controls a flow rate through the second gas inlet. In some embodiments, the flow rate through the gas inlet and the second gas inlet is independently controlled. In some embodiments, a dimension of the gas nozzles varies along the width of the extraction aperture to achieve an improved height uniformity of an extracted ribbon ion beam. In some embodiments, the plasma generator comprises an indirectly heated cathode (IHC). 
     According to another embodiment, an ion implantation system is disclosed. The ion implantation system comprises the ion source described above, a mass analyzer and a platen. 
    
    
     
       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    shows a block diagram of an ion source according to one embodiment; 
         FIG.  2    is a block of an ion implantation system that uses the IHC ion source of  FIG.  1   ; 
         FIG.  3 A  shows a cross-sectional view of the ion source according to one embodiment; 
         FIG.  3 B  shows the side walls of the ion source of  FIG.  3 A ; 
         FIG.  4 A  shows a cross-section view of the ion source according to another embodiment; 
         FIGS.  4 B- 4 C  show the extraction plate and side walls, respectively, of the ion source of  FIG.  4 A ; 
         FIG.  5 A  shows a cross-section view of the ion source according to a third embodiment; 
         FIG.  5 B  shows the extraction plate of the ion source of  FIG.  5 A ; and 
         FIGS.  6 A- 6 C  show a cross-sectional view of the ion source according to three additional embodiments. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    shows a cross-sectional view of an IHC ion source  10  that may be utilized to extract a ribbon ion beam with improved uniformity in the height direction. The IHC ion source  10  includes a chamber  100 , comprising two opposite ends, and walls  101  connecting to these ends. These walls  101  include side walls  101   a , an extraction plate  103  and a bottom wall  101   b  opposite the extraction plate  103 . Thus, the side walls  101   a  are the walls that are adjacent to the extraction plate  103  along the width direction. In certain embodiments, the side walls  101   a  and the bottom wall  101   b  may be an integral component. The two opposite ends are adjacent to the extraction plate  103  along the height direction. 
     The extraction plate  103  has a height, width and a thickness. The extraction plate  103  includes an extraction aperture  140  that passes through the extraction plate  103  in the thickness direction. Ions are extracted through the extraction aperture  140 . The extraction aperture  140  may be much larger in the width direction, also referred to as the X direction, than in the height direction, also referred to as the Y direction. The Z direction is defined along the thickness of the extraction plate  103  and is defined as the direction of travel for the ribbon ion beam. For example, the extraction aperture  140  may be greater than 3 inches in the width direction and less than 0.3 inches in the height direction. 
     In certain embodiments, the extraction plate  103  may comprise a face plate  103   a  and an extraction liner  103   b , wherein the extraction liner  103   b  is disposed between the interior of the chamber  100  and the face plate  103   a . The extraction liner  103   b  may be a replaceable component. In certain embodiments, the face plate  103   a  and the extraction liner  103   b  are both constructed from tungsten, although other suitable materials may be used. 
     The walls  101  of the chamber  100  may be constructed of an electrically conductive material and may be in electrical communication with one another. A cathode  110  is disposed in the chamber  100  at a first end  104  of the chamber  100 . A filament  160  is disposed behind the cathode  110 . The filament  160  is in communication with a filament power supply  165 . The filament power supply  165  is configured to pass a current through the filament  160 , such that the filament  160  emits thermionic electrons. Cathode bias power supply  115  biases filament  160  negatively relative to the cathode  110 , so these thermionic electrons are accelerated from the filament  160  toward the cathode  110  and heat the cathode  110  when they strike the back surface of cathode  110 . The cathode bias power supply  115  may bias the filament  160  so that it has a voltage that is between, for example, 200 V to 1500 V more negative than the voltage of the cathode  110 . The cathode  110  then emits thermionic electrons from its front surface into chamber  100 . 
     Thus, the filament power supply  165  supplies a current to the filament  160 . The cathode bias power supply  115  biases the filament  160  so that it is more negative than the cathode  110 , so that electrons are attracted toward the cathode  110  from the filament  160 . The cathode  110  is in communication with an arc voltage power supply  111 . The arc voltage power supply  111  supplies a voltage to the cathode relative to the chamber  100 . This arc voltage accelerates the thermionic electrons emitted at the cathode into chamber  100  to ionize the neutral gas. The current drawn by this arc voltage power supply  111  is a measurement of the amount of current being driven through the plasma  150 . In certain embodiments, the walls  101  provide the ground reference for the other power supplies. 
     In this embodiment, a repeller  120  may be disposed in the chamber  100  on the second end  105  of the chamber  100  opposite the cathode  110 . 
     The repeller  120  may be in electrical communication with a repeller power supply  123 . As the name suggests, the repeller  120  serves to repel the electrons emitted from the cathode  110  back toward the center of the chamber  100 . For example, in certain embodiments, the repeller  120  may be biased at a negative voltage relative to the chamber  100  to repel the electrons. For example, in certain embodiments, the repeller  120  is biased at between 0 and -150V relative to the chamber  100 . In certain embodiments, the repeller  120  may be floated relative to the chamber  100 . In other words, when floated, the repeller  120  is not electrically connected to the repeller power supply  123  or to the chamber  100 . In this embodiment, the voltage of the repeller  120  tends to drift to a voltage close to that of the cathode  110 . Alternatively, the repeller  120  may be electrically connected to the walls  101 . 
     In certain embodiments, a magnetic field  190  is generated in the chamber  100 . This magnetic field is intended to confine the electrons along one direction. The magnetic field  190  typically runs parallel to the walls  101  from the first end  104  to the second end  105 . For example, electrons may be confined in a column that is parallel to the direction from the cathode  110  to the repeller  120  (i.e. the x direction). Thus, electrons do not experience electromagnetic force to move in the x direction. However, movement of the electrons in other directions may experience an electromagnetic force. 
     One or more gas containers  108  may be in communication with the chamber  100  via a gas inlet  106 . Each gas container  108  may include a mass flow controller (MFC)  107  so as to regulate a flow of gas from each gas container. 
     An extraction power supply  170  may be used to bias the walls  101  of the IHC ion source  10  relative to the rest of the components in the beam line. For example, the platen  260  (see  FIG.  2   ) may be at a first voltage, such as ground, while a positive voltage is applied to the IHC ion source  10  such that the IHC ion source  10  is more positively biased than the platen  260 . Thus, the voltage supplied by the extraction power supply  170 , referred to as the extraction voltage, determines the energy of the ions that are extracted from the IHC ion source  10 . Further, the current supplied by the extraction power supply  170  is a measure of the total extracted beam current. 
     In certain embodiments, there is a feedback loop between the cathode bias power supply  115  and the extraction power supply  170 . Specifically, it may be desirable to maintain the extracted beam current at a constant value. Thus, the current supplied from the extraction power supply  170  may be monitored and the output of the cathode bias power supply  115  may be adjusted to maintain a constant extraction current. This feedback loop may be performed by the controller  180 , or may be performed in another manner. 
     A controller  180  may be in communication with one or more of the power supplies such that the voltage or current supplied by these power supplies may be monitored and/or modified. Additionally, the controller  180  may be in communication with the MFCs  107  of each gas container  108  so as to regulate a flow of each gas into the chamber  100 . The controller  180  may include a processing unit, such as a microcontroller, a personal computer, a special purpose controller, or another suitable processing unit. The controller  180  may also include a non-transitory storage element, such as a semiconductor memory, a magnetic memory, or another suitable memory. This non-transitory storage element may contain instructions and other data that allows the controller  180  to perform the functions described herein. For example, the controller  180  may be in communication with the cathode bias power supply  115  to allow the IHC ion source  10  to vary the voltage applied to the cathode relative to the filament  160 . The controller  180  may also be in communication with the repeller power supply  123  to bias the repeller. Further, the controller  180  may be able to monitor the voltage, current and/or power supplied by the cathode bias power supply  115 . 
       FIG.  2    shows an ion implantation system using the IHC ion source  10  of  FIG.  1   . Disposed outside and proximate the extraction aperture of the IHC ion source  10  are one or more electrodes  200 . 
     Located downstream from the electrodes  200  is a mass analyzer  210 . The mass analyzer  210  uses magnetic fields to guide the path of the extracted ribbon ion beam 1. The magnetic fields affect the flight path of ions according to their mass and charge. A mass resolving device  220  that has a resolving aperture  221  is disposed at the output, or distal end, of the mass analyzer  210 . By proper selection of the magnetic fields, only those ions in the extracted ribbon ion beam 1 that have a selected mass and charge will be directed through the resolving aperture  221 . Other ions will strike the mass resolving device  220  or a wall of the mass analyzer  210  and will not travel any further in the system. 
     A collimator  230  may disposed downstream from the mass resolving device  220 . The collimator  230  accepts the ions from the extracted ribbon ion beam 1 that pass through the resolving aperture  221  and creates a ribbon ion beam formed of a plurality of parallel or nearly parallel beamlets. The output, or distal end, of the mass analyzer  210  and the input, or proximal end, of the collimator  230  may be a fixed distance apart. The mass resolving device  220  is disposed in the space between these two components. 
     Located downstream from the collimator  230  may be an acceleration/deceleration stage  240 . The acceleration/deceleration stage  240  may be referred to as an energy purity module. The energy purity module is a beam-line lens component configured to independently control deflection, deceleration, and focus of the ion beam. For example, the energy purity module may be a vertical electrostatic energy filter (VEEF) or electrostatic filter (EF). Located downstream from the acceleration/deceleration stage  240  is a platen  260 . The workpiece is disposed on the platen  260  during processing. 
     The height of the extracted ribbon ion beam is improved by directing a gas toward the extraction aperture  140 . The gas flow serves to reduce the height of the extracted beam. This may be achieved in a plurality of different ways. 
     In the embodiment shown in  FIGS.  3 A- 3 B , the IHC ion source  10  may comprise gas channels  141  that terminate in gas nozzles  142  located at or near the interface between the side walls  101   a  and the extraction plate  103 .  FIG.  3 A  shows a cross-sectional view of the IHC ion source  10 , while  FIG.  3 B  shows the side walls  101   a  of the ion source according to this embodiment. In this embodiment, as best seen in  FIG.  3 A , a feedgas is disposed in gas container  108 . This feedgas enters the chamber  100  via the gas inlet  106 . The flow rate of the feedgas is controlled by the MFC  107 . The gas inlet  106  may be in communication with one or more supply channels  143  that supply the feedgas to the interior of the chamber  100 . In certain embodiments, the supply channels  143  may be disposed on the bottom wall  101   b . In other embodiments, the supply channels  143  may be disposed on one or more of the side walls  101   a . 
     Additionally, the gas inlet  106  may be in communication with one or more gas channels  141  that are disposed inside the walls  101 . For example, the gas channels  141  may be created by machining one or more channels in the side walls  101   a . In another embodiment, the gas channels  141  may be created by providing tubes that are disposed along an interior or exterior surface of the side walls  101   a . In both embodiments, the gas is directed toward the end of the side walls  101   a  nearest the extraction plate  103 . 
     In this embodiment, the gas channels  141  terminate at the top surface of the side wall  101   a  proximate the interface between the side wall  101   a  and the extraction plate  103 . The gas channels  141  may be disposed within the side walls  101   a . Thus, in this embodiment, as shown by arrow  144  in  FIG.  3 A , the feedgas exits the gas channels  141  via gas nozzles  142  in the side walls  101   a  and flows along the interior surface of the extraction plate  103  before reaching the extraction aperture  140 . For example, as shown in  FIG.  3 B , a plurality of gas nozzles  142  may be arranged on the interior surfaces of the side walls  101   a  on either side of the extraction plate  103 , where the extraction plate  103  meets the side walls  101   a . The gas channels  141  terminate at the top surface of the side walls  101   a  in a horizontal groove  146  that extends along the side walls  101   a  in the X direction. The gas nozzles  142  are each in communication with the horizontal groove  146 . Further, the size of each gas nozzle  142  may be same in some embodiments. In other embodiments, the gas nozzles  142  may vary and be dimensioned based on the amount of height adjustment that is to be performed. For example, if the height of the extracted ribbon ion beam 1 is greatest at the center of the extraction aperture  140 , the gas nozzles  142  that are aligned with the center of the extraction aperture  140  may be larger than other gas nozzles  142 . In this way, more gas flows through these larger nozzles and constrains the extracted ribbon ion beam 1. Note that in this embodiment, the extraction plate  103  is unchanged. 
     Note that if a tube is used to carry the feedgas along an interior or exterior surface of the side walls  101   a , that tube may terminate in the horizontal groove  146 . 
     In a related embodiment, the supply channels  143  may be eliminated. In this embodiment, the feedgas to be ionized enters through the gas nozzles  142 . 
       FIGS.  4 A- 4 C  show a second embodiment.  FIG.  4 A  shows a cross-sectional view of the IHC ion source  10 ,  FIG.  4 B  shows the extraction liner  103   b  and  FIG.  4 C  shows the side walls  101   a  of the ion source according to this embodiment. 
     In this embodiment, as best seen in  FIG.  4 A , a feedgas is disposed in gas container  108 . This feedgas enters the chamber  100  via the gas inlet  106 . The flow rate of the feedgas is controlled by the MFC  107 . The gas inlet  106  may be in communication with one or more supply channels  143  that supply the feedgas to the interior of the chamber  100 . In certain embodiments, the supply channels  143  may be disposed on the bottom wall  101   b . In other embodiments, the supply channels  143  may be disposed on one or more of the side walls  101   a . 
     Additionally, the gas inlet  106  may be in communication with one or more gas channels  141  that are disposed inside the walls  101 . For example, the gas channels  141  may be created by machining one or more channels in the side walls  101   a . In another embodiment, the gas channels  141  may be created by providing tubes that are disposed along an interior or exterior surface of the side walls  101   a . In both embodiments, the gas is directed toward the end of the side walls  101   a  nearest the extraction plate  103 . 
     In this embodiment, the gas channels  141  terminate at the top surface of the side wall  101   a  proximate the interface between the side wall  101   a  and the extraction plate  103 . The gas channels  141  may be disposed within the side walls  101   a . As shown in  FIG.  4 C , the gas channels  141  terminate at the top surface of the side walls  101   a  in a horizontal groove  146  that extends along the X direction. 
     In this embodiment, the horizontal grooves  146  in the side walls  101   a  are in communication with a corresponding horizontal plate groove  147  in the extraction plate  103 , as shown in  FIG.  4 B . The horizontal plate groove  147  is in communication with a plurality of plate gas channels  145 , which are disposed within the extraction plate  103 . In certain embodiments, the horizontal plate groove  147  and the plate gas channels  145  are disposed in the extraction liner  103   b . The horizontal plate groove  147  may be positioned such that it overlaps the horizontal groove  146  in the side walls  101   a  when assembled. In this way, the gas channels  141  in the side walls  101   a  supply feedgas to the horizontal groove  146 , which is coupled to the horizontal plate groove  147 . The feedgas then enters the plate gas channels  145  in the extraction plate  103 . The feedgas then exits the plate gas channels  145  through gas nozzles  142 . The gas nozzles  142  are located on the interior surface of the extraction plate  103 , near the extraction aperture  140 , such as within 0.25 inches. In some embodiments, the gas nozzles  142  may be located within 0.1 inches of the extraction aperture  140 . In this embodiment, the gas nozzles  142  are closer to the extraction aperture  140  than the embodiment shown in  FIGS.  3 A- 3 B  and may be more effective at shaping the extracted ribbon ion beam 1. The dimensions of the various gas nozzles  142  may be as described above. 
     Note that if a tube is used to carry the feedgas along an interior or exterior surface of the side walls  101   a , that tube may terminate in the horizontal groove  146  or in the horizontal plate groove  147 . 
     In a related embodiment, the supply channels  143  may be eliminated. In this embodiment, the feedgas to be ionized enters through the gas nozzles  142 . 
       FIGS.  5 A- 5 B  show another embodiment.  FIG.  5 A  shows a cross-sectional view of the IHC ion source  10 , while  FIG.  5 B  shows the extraction liner  103   b . In this embodiment, as shown in  FIG.  5 A , the extraction liner  103   b  is formed such that there is a gap  148  between the top surface of the side walls  101   a  and the face plate  103   a . A hole  149  in the extraction liner  103   b  allows fluid communication between the gas channels  141  and the gap  148 . 
     The gap  148  is in communication with a plurality of plate gas channels  145 , which are disposed within the extraction liner  103   b . In this embodiment, the horizontal groove  146  may not be present. Rather, the gas channels  141  may be aligned with the hole  149  to allow feedgas to flow directly into the gap  148 . Other aspects of this embodiment may be similar to those described with respect to the embodiment shown in  FIGS.  4 A- 4 B . 
       FIGS.  3 A,  4 A and  5 A  all show the gas channels  141  and the supply channel  143  in communication with the same gas inlet  106 . However, in other embodiments, there may be two gas inlets, where the flow of gas entering each gas inlet may be independently controlled using separate mass flow controller (MFC)  107 . In this way, the flow rate of the gas introduced near the extraction aperture  140  may not be related to the flow rate of feedgas used for ionization. 
       FIGS.  6 A- 6 C  show three embodiments where the gas inlets are separate. These embodiments correspond to the embodiments of  FIGS.  3 A,  4 Aand  5 A , respectively. 
     As described above, the flow rate of gas from gas container  108  is controlled by MFC  107 . The gas then passes through gas inlet  106  and enters the gas channels  141 . In  FIG.  6 A , the gas channels  141  terminate near the interface between the side walls  101   a  and the extraction plate  103 , as described above with respect to  FIG.  3 A . In  FIG.  6 B , plate gas channels  145  are disposed in the extraction plate  103 , as described above with respect to  FIG.  4 A . In  FIG.  6 C , the plate gas channels  145  are disposed in the extraction liner  103   b , as described above with respect to  FIG.  5 A . 
     However, in these embodiments, a second gas inlet  116  is used to supply the feedgas to the chamber  100 . Specifically, the feedgas may be stored in second gas container  118 . The flow rate of the feedgas is controlled by second MFC  117 . The feedgas enters via second gas inlet  116 . The second gas inlet  116  is in communication with the supply channels  143 . Thus, the flow rate of gas through the two gas inlets may be separately controlled. 
     In these embodiments, the gas channels  141  and the supply channels  143  are completely separated such that there is no fluid communication between the supply channels  143  and the gas channels  141 . 
     While  FIGS.  6 A- 6 C  show two different gas containers, it is understood that one gas container may be in communication with both MFCs such that gas from a single gas container is used to supply gas to both the supply channels  143  and the gas channels  141 . In other words, MFC  107  may be used to regulate the flow of gas through the gas nozzles  142 , while second MFC  117  is used to independently control the flow of feedgas into the chamber  100  through supply channels  143 . In this way, the two flow rates can be separately controlled and optimized for their respective functions. 
     In certain embodiments, the use of two separate gas inlets allows the use of two different gasses. For example, a feedgas may be provided in second gas container  118 . A shield gas, different from the feedgas, may be stored in gas container  108 . The shield gas may be an inert species, such as argon or xenon. 
     Further, while  FIGS.  6 A- 6 C  show the supply channels  143  being disposed on the bottom wall  101   b  of the ion source, it is understood that the position of the supply channels  143  may be modified. For example, the supply channels  143  may enter the chamber  100  via a side wall  101   a . 
     The above describes the ion source as being an IHC ion source. However, other ion sources may also be used with the gas nozzles  142  For example, magnetized DC plasma sources, tubular cathode source, Bernas ion source and inductively coupled plasma (ICP) ion sources may also use gas channels and gas nozzles. Thus, the extraction plate may be used with an ion source having a variety of different plasma generators. 
     In operation, a gas, which may be the feedgas for the embodiments shown in  FIGS.  3 A,  4 A and  5 A , or a shield gas for the embodiments shown in  FIGS.  6 A- 6 C , is supplied to the gas channels  141 . The gas travels through the gas channels  141  and exits through the gas nozzles  142 . The gas flowing near the extraction aperture  140  tends to compress the ribbon ion beam that this being extracted through the extraction aperture  140 . To improve the uniformity of the height of the extracted ion beam, the flow rate may be different at different portions of the extraction aperture  140  along the X dimension. For example, larger gas nozzles may be employed in regions where the height of the extracted ion beam is traditionally greatest. In some embodiments, such as those shown in  FIGS.  6 A- 6 C , the flow rates of gasses through the gas nozzles  142  may be regulated using the MFC  107 , independent of the flow rate of the feedgas, which is controlled by second MFC  117 . 
     The present system has many advantages. The ability to flow a gas, either the feedgas or a shield gas, near the extraction aperture may facilitate shaping of the ribbon ion beam as it is being extracted. Specifically, the flow may compress the flow of ions in the height direction. Traditionally, ribbon ion beams that are extracted from ion sources may be non-uniform in height as a result of plasma shape and the chemistry inside the ion source. By compressing or blocking the flow of some of the ions to account for common non-uniform profiles, an extracted ribbon ion beam having better uniformity in the height direction may be achieved. 
     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 andaccompanying 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.