Abstract:
An ion source includes an ion chamber housing defining an ion source chamber, the ion chamber housing having a side with a plurality of apertures. The ion source also includes an antechamber housing defining an antechamber. The antechamber housing shares the side with the plurality of apertures with the ion chamber housing. The antechamber housing has an opening to receive a gas from a gas source. The antechamber is configured to transform the gas into an altered state having excited neutrals that is provided through the plurality of apertures into the ion source chamber.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of prior U.S. application Ser. No. 12/328,096 filed Dec. 4, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     Ion implanters are commonly used in the production of semiconductor wafers. An ion source is used to create a beam of charged ions, which is then directed toward the wafer. As the ions strike the wafer, they impart a charge in the area of impact. This charge allows that particular region of the wafer to be properly “doped”. The configuration of doped regions defines their functionality, and through the use of conductive interconnects, these wafers can be transformed into complex circuits. 
     A block diagram of a representative ion implanter  1  is shown in  FIG. 1 . Power supply  2  supplies the required energy to the ion source  3  to enable the generation of ions. An ion source  3  generates ions of a desired species. In some embodiments, these species are mono-atoms, which are best suited for high-energy implant applications. In other embodiments, these species are molecules, which are better suited for low-energy implant applications. The ion source  3  has an aperture through which ions can pass. These ions are attracted to and through the aperture by electrodes  4 . These ions are formed into a beam  95 , which then passes through a mass analyzer  6 . The mass analyzer  6 , having a resolving aperture, is used to remove unwanted components from the ion beam, resulting in an ion beam having the desired energy and mass characteristics passing through resolving aperture. Ions of the desired species then pass through a deceleration stage  8 , which may include one or more electrodes. The output of the deceleration stage is a diverging ion beam. 
     A corrector magnet  13  is adapted to deflect the divergent ion beam into a set of beamlets having substantially parallel trajectories. Preferably, the corrector magnet  13  comprises a magnet coil and magnetic pole pieces that are spaced apart to form a gap, through which the ion beamlets pass. The coil is energized so as to create a magnetic field within the gap, which deflects the ion beamlets in accordance with the strength and direction of the applied magnetic field. The magnetic field is adjusted by varying the current through the magnet coil. Alternatively, other structures, such as parallelizing lenses, can also be utilized to perform this function. 
     Following the angle corrector  13 , the ribbon beam is targeted toward the workpiece. In some embodiments, a second deceleration stage  11  may be added. The workpiece is attached to a workpiece support  15 . The workpiece support  15  provides a variety of degrees of movement for various implant applications. 
     Referring to  FIG. 2 , a traditional ion source that may be incorporated into the ion implanter  1  is shown. The ion source shown in  FIG. 2  may include a chamber housing  10  that defines an ion source chamber  14 . One side of the chamber housing  10  has an extraction aperture  12  through which the ions pass. In some embodiments, this aperture is a hole, while in other applications, such as high current implantation, this aperture is a slot or a set of holes. 
     A cathode  20  is located on one end of the ion source chamber  14 . A filament  30  is positioned in close proximity to the cathode  20 , outside of the ion chamber. A repeller  60  is located on the opposite end of the ion source chamber  14 . 
     The filament  30  is energized by filament supply voltage  54 . The current passing through the filament  30  heats it sufficiently (i.e. above 2000° C.) so as to produce thermo-electrons. A bias supply voltage  52  is used to bias the cathode  20  at a substantially more positive voltage than the filament  30 . The effect of this large difference in voltage is to cause the thermo-electrons emitted from the filament to be accelerated toward the cathode. As these electrons bombard the cathode, the cathode heats significantly, often to temperatures over 2000° C. The cathode, which is referred to as an indirectly heated cathode (IHC), then emits thermo-electrons into the ion source chamber  14 . 
     The arc supply  50  is used to bias the ion chamber housing  10  positively as compared to the cathode. The arc supply typically biases the housing  10  to a voltage about 50-100 Volts more positive than the cathode  20 . This difference in voltage causes the electrons emitted from the cathode  20  to be accelerated toward the housing  10 . 
     A magnetic field is preferably created in the direction  62 , typically by using magnetic poles  86  located outside the chamber. The effect of the magnetic field is to confine the emitted electrons within magnetic field lines. The emitted electrons, electro-statically confined between cathode and repeller, take the spiral motions along the source magnetic field lines, thus effectively ionize background gases, forming ions (as shown in  FIG. 3 ). 
     Vapor or gas source  40  is used to provide atoms or molecules into the ion source chamber  14 . The molecules can be of a variety of species, including but not limited to inert gases (such as argon or hydrogen), oxygen-containing gases (such as oxygen and carbon dioxide), nitrogen containing gases (such as nitrogen or nitrogen triflouride), and other dopant-containing gases (such as diborane, boron tri-fluoride, or arsenic penta-fluoride). These background gasses are ionized by electron impact, thus forming plasma  80 . 
     At the far end of the chamber  14 , opposite the cathode  20 , a repeller  60  is preferably biased to the same voltage as the cathode  20 . This causes the emitted electrons to be electro-statically confined between cathode  20  and repeller  60 . The use of these structures at each end of the ion source chamber  14  maximizes the interaction of the emitted electrons with the background gas, thus generating high-density plasmas. 
       FIG. 3  shows a different view of the ion source of  FIG. 2 . The source magnet  86  creates a magnetic field  62  across the ion chamber. The cathode  20  and repeller  60  are maintained at the same potential, so as to effectively confine the electrons, which collide with the background gas thus generate the plasma  80 . The electrode set  90  is biased so as to attract the ions to and through the extraction aperture  12 . These extracted ions are then formed into an ion beam  95  and are used as described above. 
     An alternative embodiment of an ion implantation system, plasma immersion, is shown in  FIG. 4 . The plasma doping system  100  includes a process chamber  102  defining an enclosed volume  103 . A platen  134  is positioned in the process chamber  102  to support a workpiece  138 . In one instance, the workpiece  138  comprises a semiconductor wafer having a disk shape, such as, in one embodiment, a 300 millimeter (mm) diameter silicon wafer. The workpiece  138  may be clamped to a flat surface of the platen  134  by electrostatic or mechanical forces. In one embodiment, the platen  134  may include conductive pins (not shown) for making connection to the workpiece  138 . 
     A gas source  104  provides a dopant gas to the interior volume  103  of the process chamber  102  through the mass flow controller  106 . A gas baffle  170  is positioned in the process chamber  102  to uniformly distribute the gas from the gas source  104 . A pressure gauge  108  measures the pressure inside the process chamber  102 . A vacuum pump  112  evacuates exhausts from the process chamber  102  through an exhaust port  110  in the process chamber  102 . An exhaust valve  114  controls the exhaust conductance through the exhaust port  110 . 
     The plasma doping system  100  may further include a gas pressure controller  116  that is electrically connected to the mass flow controller  106 , the pressure gauge  108 , and the exhaust valve  114 . The gas pressure controller  116  may be configured to maintain a desired pressure in the process chamber  102  by controlling either the exhaust conductance with the exhaust valve  114  or a process gas flow rate with the mass flow controller  106  in a feedback loop that is responsive to the pressure gauge  108 . 
     The process chamber  102  may have a chamber top  118  that includes a first section  120  formed of a dielectric material that extends in a generally horizontal direction. The chamber top  118  also includes a second section  122  formed of a dielectric material that extends a height from the first section  120  in a generally vertical direction. The chamber top  118  further includes a lid  124  formed of an electrically and thermally conductive material that extends across the second section  122  in a horizontal direction. 
     The plasma doping system may further include a source  101  configured to generate a plasma  140  within the process chamber  102 . The source  101  may include a RF source  150 , such as a power supply, to supply RF power to either one or both of the planar antenna  126  and the helical antenna  146  to generate the plasma  140 . The RF source  150  may be coupled to the antennas  126 ,  146  by an impedance matching network  152  that matches the output impedance of the RF source  150  to the impedance of the RF antennas  126 ,  146  in order to maximize the power transferred from the RF source  150  to the RF antennas  126 ,  146 . 
     The plasma doping system  100  also may include a bias power supply  148  electrically coupled to the platen  134 . The bias power supply  148  is configured to provide a pulsed platen signal having pulse ON and OFF time periods to bias the platen  134 , and, hence, the workpiece  138 , and to accelerate ions from the plasma  140  toward the workpiece  138  during the pulse ON time periods and not during the pulse OFF periods. The bias power supply  148  may be a DC or an RF power supply. 
     The plasma doping system  100  may further include a shield ring  194  disposed around the platen  134 . As is known in the art, the shield ring  194  may be biased to improve the uniformity of implanted ion distribution near the edge of the workpiece  138 . One or more Faraday sensors such as an annular Faraday sensor  199  may be positioned in the shield ring  194  to sense ion beam current. 
     The plasma doping system  100  may further include a controller  156  and a user interface system  158 . The controller  156  can be or include a general-purpose computer or network of general-purpose computers that may be programmed to perform desired input/output functions. The controller  156  also can include other electronic circuitry or components, such as application-specific integrated circuits, other hardwired or programmable electronic devices, discrete element circuits, etc. The controller  156  also may include communication devices, data storage devices, and software. For clarity of illustration, the controller  156  is illustrated as providing only an output signal to the power supplies  148 ,  150 , and receiving input signals from the Faraday sensor  199 . Those skilled in the art will recognize that the controller  156  may provide output signals to other components of the plasma doping system  100  and receive input signals from the same. The user interface system  158  may include devices such as touch screens, keyboards, user pointing devices, displays, printers, etc. to allow a user to input commands and/or data and/or to monitor the plasma doping system via the controller  156 . 
     In operation, the gas source  104  supplies a primary dopant gas containing a desired dopant for implantation into the workpiece  138 . The gas pressure controller  116  regulates the rate at which the primary dopant gas is supplied to the process chamber  102 . The source  101  is configured to generate the plasma  140  within the process chamber  102 . The source  101  may be controlled by the controller  156 . To generate the plasma  140 , the RF source  150  resonates RF currents in at least one of the RF antennas  126 ,  146  to produce an oscillating magnetic field. The oscillating magnetic field induces RF currents into the process chamber  102 . The RF currents in the process chamber  102  excite and ionize the primary dopant gas to generate the plasma  140 . 
     The bias power supply  148  provides a pulsed platen signal to bias the platen  134  and, hence, the workpiece  138  to accelerate ions from the plasma  140  toward the workpiece  138  during the pulse ON periods of the pulsed platen signal. The frequency of the pulsed platen signal and/or the duty cycle of the pulses may be selected to provide a desired dose rate. The amplitude of the pulsed platen signal may be selected to provide a desired energy. With all other parameters being equal, a greater energy will result in a greater implanted depth. 
     Note that in both systems, gas is supplied to the chamber, which is used to create the ions that are then implanted in the wafer. Traditionally, these gasses include either elemental gasses, such as hydrogen, argon, oxygen, nitrogen, or other molecules, including but not limited to carbon dioxide, nitrogen tri-fluoride, diborane, phosphorus tri-fluoride, boron tri-fluoride, or arsenic penta-fluoride. 
     As described above, these gasses are ionized to produce the desired ions for implantation. For ion source applications, in order to maximize the generation of a specific ion species, several variables must be controlled, including source gas flow, arc current, ion source materials, wall temperature, and others. Similarly, for plasma implantation applications, factors are used to generate a uniform charged species over the wafer region. Factors, such as source antenna design, pressure, power, target bias voltage, wall/target temperature, and others, are modified to produce the desired ion distribution. 
     One factor that has not been fully exploited is controlling the characteristics of the incoming source gas. As stated above, different types of gasses are used, depending on the application. However, once a gas is selected, no other modifications are made to that source gas. It would be beneficial to control the composition of the ion species and their spatial distribution by varying the characteristics of the source gas. 
     SUMMARY 
     An ion source includes an ion chamber housing defining an ion source chamber, the ion chamber housing having a side with a plurality of apertures. The ion source also includes an antechamber housing defining an antechamber. The antechamber housing shares the side with the plurality of apertures with the ion chamber housing. The antechamber housing has an opening to receive a gas from a gas source. The antechamber is configured to transform the gas into an altered state having excited neutrals that is provided through the plurality of apertures into the ion source chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a block diagram of a representative high-current ion implanter tool; 
         FIG. 2  illustrates a traditional ion source used in ion beam applications; 
         FIG. 3  shows the major components of the traditional ion source of  FIG. 2 ; 
         FIG. 4  illustrates a plasma immersion system; 
         FIG. 5  shows a first embodiment of a gas injection system used in an ion beam application; 
         FIG. 6  shows a second embodiment of a gas injection system used in an ion beam application; 
         FIG. 7  shows a third embodiment of a gas injection system used in an ion beam application; 
         FIG. 8  shows a fourth embodiment of a gas injection system used in an ion beam application; 
         FIG. 9  shows an embodiment of a gas injection system used in a plasma immersion system; and 
         FIG. 10  shows a second view of the gas injection system of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 5  illustrates a first embodiment of a gas injection system used in an ion beam application. Traditionally, gas source  40  is in direct fluid communication with source chamber  14 . However,  FIG. 5  illustrates the components of the gas injection system according to a first embodiment. In this embodiment, gas source  40  may be in communication with a mass flow controller (MFC)  220 . The MFC is responsible for regulating the flow of gas from gas source  40  to a desired flow rate. The output of the MFC is in fluid communication with adjustable bypass valve  210  and remote plasma source  200 . The outputs from the adjustable bypass valve  210  and the remote plasma source  200  then join together and are in fluid communication with the source chamber  14 . 
     The remote plasma source  200  can be of any suitable type. However, those sources having a wide operating range with high-density plasma and/or excited neutral species generation capability are preferred. In one embodiment, a microwave plasma source (Electron cyclotron resonance-type) is used, which can operate at pressures between 10 −6  and 10 −1  torr, generating high-density, highly-charged ionized species and/or highly-excited neutral species. In a second embodiment, a microwave plasma source, such as ASTRON® manufactured by MKS Instruments, is used, which can operate at pressures between 10 −1  torr and atmospheric pressure, while generating defragmented or excited neutrals. In other embodiments, a second indirectly heated cathode (IHC) ion source is used to create the heavy neutrals and ionized species, which are then supplied to the ion source  14 . In other embodiments, a helicon source, an inductively-coupled plasma (ICP) source, a capacitively-coupled plasma source, a hollow-cathode (HC) source, or a filament-based plasma source can be used. The term “remote plasma source” is intended to encompass any device capable of transforming molecules to an altered state. Altered states include not only plasma, but also ions, excited neutrals, and metastable molecules. As is well known, ions are simply atoms or molecules with an electrical charge associated with them, such as BF 2   + . Excited neutrals refer to atoms or molecules, which are still neutral in charge. However, these atoms or molecules have one or more electrons in an excited energy state. Finally, metastable molecules refer to molecule configurations which can be created, such as B 2 F 4  or B 4 F 5 . However, these molecules may not remain in those configurations for long periods of time, as they are likely to recombine or breakdown into more common molecular configurations. Each of these altered states; plasma, ions, excited neutrals and metastable molecules are of interest. Therefore, it is not a requirement that the remote plasma generator actually create a plasma as its output. 
     When the remote plasma source  200  is enabled, the molecules from the source gas  40  pass through the MFC  220  and enter the plasma source. Based on the type of remote plasma source and its operating parameters, the source gas can be altered. In certain cases, source gas is acted upon to produce excited neutrals, metastable molecules or ionic molecules. In other cases, the source gas is defragmented into atomic and/or smaller molecular species. In yet other embodiments, the source gas combines to generate heavier or metastable molecules. 
     If maximum extraction current of a specific ion species is required, the source gas injection can be tuned accordingly in order to optimize (or maximize) the concentration of that specific ion in the source chamber  14 . As an example, by operating the remote plasma source at low-pressure and high-power, the production of excited neutrals is promoted. As these excited neutrals are introduced into the source chamber  14 , the production of mono-atomic ions and/or multiply-charged ions will be enhanced and, as a result, the extraction of mono-atomic and/or multiply-charged ion current is increased. 
     For example, currently, source gasses, such as boron triflouride, are supplied to an ion source chamber. This gas is ionized by the indirectly heated cathode, thereby producing various ion species, such as BF 2   + , BF + , F + , B x F y   +  and B + . In the current disclosure, the source gas is supplied to a remote plasma source, preferably operating at high power and low pressure. This remote plasma source then produces either excited fragmented neutrals, or various fragmented ionized species. These various species are then supplied to the ion source chamber  14 . Since the composition and energy levels of the supplied gas have been modified, the output of the ion source is similarly affected, thereby creating more ions of a particular species. In this example, more small ionic species, such as B +  and BF +  are created. 
     In other embodiments, the production of heavier ions, such as dimmers, trimers or tetramers is desired. The remote plasma source may be operated at much higher pressure, thereby causing molecules to combine into heavier neutral species or metastable molecules. These excited heavy molecules and metastable molecules are then supplied to the ion source chamber  14 . 
     For example, currently, source gasses, such as arsenic and phosphorus, are supplied to a ion source chamber  14 . To create heavier species, the chamber must be operated at low power, and typically the output current is quite low. According to one embodiment, these source gasses can be supplied to the remote plasma source  200 , operating at a much higher pressure than used to create monoatomic species, to create these heavier neutral species, such as As 2 , As 3 , P 2 , P 3  and P 4 . These heavier species are then supplied to the ion course chamber  14 , where they are ionized and extracted into an ion beam. Since the concentration of heavier species is increased through the use of a remote plasma source, the resulting ion beam possesses a greater current. 
     While the above description highlights the use of the remote plasma source  200  exclusively, the disclosure is not limited to this embodiment. The use of an adjustable bypass valve  210  allows the mixing of molecular source gas and the output from the remote plasma source  200 . The resultant mixture can be adjusted such that the ratio of the molecular source gas and the output of the remote plasma source can be finely controlled to achieve the desired effect. 
       FIG. 6  illustrates a second embodiment of a gas injection system, usable with the ion source chamber of  FIG. 3 . In this embodiment, two different source gasses are each in communication with a separate mass flow controller (MFC)  320 ,  325 . These MFCs  320 ,  325  are each in fluid communication with a remote plasma source  300 ,  305  and an adjustable bypass valve  310 ,  315 , respectively. Through use of the MFCs, the flow rate of each source gas can be controlled. Additionally, through the use of adjustable bypass valves, the ratio of injected molecular source gas and source gas in altered states can be varied for each source gas independently. Additionally, more than 2 source gasses can be utilized by replicating the structure shown in  FIG. 6 . Finally,  FIG. 6  shows a completely flexible system which allows the injection of Source Gas A, excited Source Gas A, Source Gas B, and excited Source Gas B. Each can be supplied in varying amounts, where each flow rate is completely independent of the other rates. However, not all of the illustrated components are required. For example, assume that in a particular embodiment, only Source Gas A and both states of Source Gas B are required. In this case, it is possible to eliminate remote plasma source  300  and adjustable bypass valve  310 . Alternatively, if Source B is only required in its excited state, adjustable bypass valve  315  can be eliminated. 
     In some embodiments, two separate source gases allow for specialized components. For example, one source gas, bypass valve and remote plasma source can be dedicated to n-type dopants, while the second set of components is dedicated to p-type dopants to avoid potential cross-contamination and/or improve serviceability. 
       FIG. 7  illustrates another embodiment suitable for use with the ion source chamber  14  of  FIG. 3 . In this embodiment, a common remote plasma source  330  is utilized, whereby flows from both source gasses can enter a single plasma source. This deliberate reaction of two source gasses (which can be elemental or compound gasses) may be used to produce a new compound gas, which is then injected into the ion source chamber  14 . 
     By doing so, desired molecules that are derived from the combination of multiple different gasses within the vacuum and environment of the source area and/or remote plasma area can be created. In other words, different gasses are fed into the vacuum environment or plasma chamber, so that they can react to create desired molecules. These molecules may be advantageous for specific purposes, such as implantation, deposition, or use in cleaning. The formation of molecules can be tailored by manipulating the plasma conditions via various control mechanisms, such as magnetic fields, flow, pressure, or electrical fields and/or properties, to create the desired effect. Thus, the formation of new or enhanced molecules could be realized and directly put to use in the process. One example of this would be to use two source gasses to introduce Hydride and Fluoride, which then combine to create HF, which is one of the more common molecules. 
     Adding multiple gasses and manipulating the conditions of the reaction within the chamber could allow the tailored formation of molecules that might otherwise be unstable, toxic, pyrophoric, dangerous, or have other characteristics that make them inconvenient to store and transport in bulk. Thus, in this embodiment, these molecules are only generated for point of use and for a desired effect. 
     Again, as described above, all of the components shown in  FIG. 7  need not be present. For example, if Source Gas A and Source Gas B are only excited in a combined state, there is no need to include separate remote plasma sources  300 ,  305 . Alternatively, if there is no need to inject the molecular form of one of the source gasses, the corresponding bypass valve can be eliminated. 
     The path length between the remote plasma sources  300 ,  305 ,  330  and the source chamber  14  is an important consideration. Should the path by too long, any metastable, excited or defragmented species would recombine prior to entering the ion source chamber  14 . Several techniques can be employed to minimize the recombination of species exiting the remote plasma source. In certain embodiments, the physical distance between the remote plasma source and the ion source chamber is minimized. In other embodiments, a localized magnetic confinement scheme is utilized so that the energized electrons and ions can be delivered to the source chamber. In yet another embodiment, an orifice located proximate the output of the remote plasma source is used to provide the necessary pressure difference for different operating conditions. 
     The gas injection system of  FIGS. 5-7  is primarily intended to be used in conjunction with the existing ion source in an ion beam system. Thus, the gas injection system is used to alter the gas before it enters the ion source chamber  14 . Thus, the injected gas can be in different neutral conditions in terms of energy, configuration and fragmentation, since the ion source is used to then ionize the incoming gas. 
       FIG. 8  shows another embodiment for use with an ion beam application. In this embodiment, a second chamber, known as an antechamber  400 , is use to excite source gasses before they enter the ion source chamber  14 . Gas from one or more gas sources  40  enter the antechamber  400 . The antechamber  400  may have indirectly heated cathode  420 , with a filament  430  on one end and a repeller  460  on the opposite end. While  FIG. 8  shows repeller  460  on the left end of the antechamber, and repeller  60  on the right end of the ion source, this is not a requirement. For example, the repeller  460  of the antechamber and the repeller  60  of the ion source can be on the same side of their respective chambers. The same source magnet  86 , used to confine electrons and ions within the source chamber  14 , may also be used to provide the same function in the antechamber  400 , if the antechamber and the ion source chamber are aligned, as shown in  FIG. 8 . 
     As mentioned above, gas flows into the antechamber  400 , where it is treated to form excited neutrals as well as some ions. These excited molecules are then fed into the ion source chamber  14  via small openings or holes  450  on the top side of the antechamber. Note that in this embodiment, the top side of the antechamber also serves as the bottom of the ion source chamber  14 . Thus, excited, defragmented and/or heavy neutrals enter the ion source chamber  14  after being treated in the antechamber  400 . Also, since the electric fields are parallel in the ion source chamber  14  and the antechamber  400 , a common magnetic field, such as that created by source magnet  86 , can be used to confine the electrons, which are essential for ion source operation, in both chambers. 
     In certain embodiments, the holes  450  connecting the antechamber to the ion source chamber  14  are extremely small, such as 0.5 mm. In this way, the pressure in the antechamber  400  can be significantly different from that in the ion source chamber. As described above, by creating a remote plasma source, the formation of desired species can be optimized. For example, to produce heavier and metastable species, the antechamber is kept at a much higher pressure than the ion source chamber  14 , such as at about 100-500 mTorr. This enables heavier excited neutral species, such as P 2  and P 4  to be created. These molecules are then allowed to pass into the ion source chamber  14 , through the small holes connecting the chambers to be ionized. 
     Alternatively, high power and low pressure is used to create mono-atomic species. For example, boron tri-fluoride can be supplied to the antechamber  400 . The cathode  420  in the antechamber  400  serves to break the gas into a variety of ionic species and excited neutrals. These species are then fed into the ion source chamber where they are further broken down before being extracted as an ion beam. By pre-treating the gas, the concentration of specific charged ions, e.g. B + , is increased, resulting in an increased ion beam current for specific species. 
     While the above description utilizes a indirect heated cathode (IHC) ion source as the antechamber, other types of plasma sources may be used to create the antechamber. For example, traditional bernas-style ion sources, hollow-cathode style sources or filament based ion sources may also be used. In other embodiments, other types of plasma sources as described earlier can be used. 
     In other embodiments, ion implantation is performed using plasma immersion. Altered source gas injection can be used for plasma immersion implantation, as well. As shown in  FIG. 4 , source gas enters the process chamber  102  via a conduit near the top of the volume. It is then converted to plasma using antennae  126 ,  146 , and diffuses above the wafer. Baffles  170  serve to disperse the plasma relatively uniformly within the chamber  102 . For these implantation applications, controlling the plasma uniformity and the deposition pattern is critical to achieve acceptable implant uniformity. However, asymmetries from plasma generation and plasma confinement make it difficult to attain this goal for some applications, especially for low-energy applications. In addition, asymmetric pumping can add additional non-uniformity to the system. 
     In order to compensate for this uniformity, gas injection locations  510  can be added to the process chamber  102 .  FIG. 9  shows the addition of several remote plasma sources  500 . These remote plasma sources can be of the types described above in reference to ion beam implantation system. Each remote plasma source receives a source gas, such as from a central reservoir. This gas is then altered to create plasma, ions, excited neutrals and metastable molecules. As described above, different pressures and power levels can be used to create different characteristics, depending on the specific species desired. These altered states can then be injected into the process chamber  102 . In  FIG. 9 , 4 side injection locations are shown. However, this is only one embodiment; a greater or lesser number of injection locations can also be provided. Note that the preferred injection locations are along the side of the process chamber  102 , near the antenna  126 , as shown in  FIG. 10 . This allows the effect from planar antenna  126  to excite the injected gas into a plasma, thereby helping to improve the uniformity over the workpiece. In certain embodiments, the rate of excited gas flow into each of the gas injection locations is the same, but only the power on each remote plasma source  500  is adjusted. However, if asymmetrical gas injection is desired, a mass flow controller (MFC) can be located between the source gas reservoir and each of the remote plasma sources  500 . Thus, the uniformity of the plasma and that of the neutrals within the chamber can be improved. 
     Although  FIG. 9  shows the output of the remote plasma source being directly in communication with the injection locations, this is not a requirement of the present disclosure. For example, any of the configurations shown in  FIGS. 5-7  can be used in conjunction with the system of  FIG. 9 . In other words, a mix of source gas and altered molecules (as shown in  FIG. 5 ) can be supplied to one or more injection locations. Similarly, a mixture of two gasses and their altered versions (as shown in  FIG. 6 ) can also be supplied to one of more injection locations. Finally, the configuration shown in  FIG. 7  can also be used to supply gasses to one or more injection locations. The components for these configurations can be replicated for each injection location. Alternatively, one such set of components may be shared for two or more injection locations. 
     In another embodiment, shown in  FIG. 10 , the gas injection location  520  located on the top of the process chamber  102  is supplied with molecules from a remote plasma source  500   e . The use of a remote plasma source to pre-treat the gas can be used to compensate for fundamental asymmetries caused by the plasma source and/or confinement. A remote plasma source  500   e  supplies gas to this injection location. This remote plasma source can be any suitable device, such as those described above. 
     In operation, gas source  104  supplies one of more gasses to one or more remote plasma sources  500 . These remote plasma sources excite the source gas as described above. The altered gas is then fed into the plasma chamber  102  via injection locations  510 . In some embodiments, different rate flows are required at each injection location, so separate MFCs are used for each injection location. In certain embodiments, the altered gas to be supplied to the injection locations is the same, and therefore only one remote plasma source is used to supply gas to all injection locations, where the flow rate at each location is controlled by an independent MFC. In other embodiments, the altered gas to be supplied to each injection location may differ. For example, it may be desirable to inject more heavy species near the outer edge of the plasma chamber  102 , as these species do not diffuse as readily as lighter ions. In this scenario, more than one remote plasma source  500  may be used. 
     While this disclosure describes specific embodiments disclosed above, those of ordinary skill in the art will recognize that many variations and modifications are possible. 
     Accordingly, the embodiments presented in this disclosure are intended to be illustrative and not limiting. Various embodiments can be envisioned without departing from the spirit of the disclosure.