Abstract:
An ion source includes a first plasma chamber including a plasma generating component and a first gas inlet for receiving a first gas such that said plasma generating component and said first gas interact to generate a first plasma within said first plasma chamber, wherein said first plasma chamber further defines an aperture for extracting electrons from said first plasma, and a second plasma chamber including a second gas inlet for receiving a second gas, wherein said second plasma chamber further defines an aperture in substantial alignment with the aperture of said first plasma chamber, for receiving electrons extracted therefrom, such that the electrons and the second gas interact to generate a second plasma within said second plasma chamber, said second plasma chamber further defining an extraction aperture for extracting ions from said second plasma.

Description:
REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of U.S. Provisional Application Ser. No. 60/952,895 which was filed Jul. 31, 2007, entitled ELEVATED TEMPERATURE RF ION SOURCE, U.S. Provisional Application Ser. No. 60/952,916 which was filed Jul. 31, 2007, entitled HYBRID ION SOURCE/MULTIMODE ION SOURCE, and U.S. Provisional Application Ser. No. 60/981,576 which was filed on Oct. 22, 2007, the entirety of each being hereby incorporated by reference as if fully set forth herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to ion implantation systems, and more specifically to a system and method for utilizing a double plasma ion source for ion implantation. 
     BACKGROUND OF THE INVENTION 
     In the manufacture of semiconductor devices and further products, ion implantation systems are used to impart dopant elements into semiconductor workpieces, display panels, glass substrates, and the like. Typical ion implantation systems or ion implanters implant a workpiece with an ion beam of impurities in order to produce n-type and/or p-type doped regions, or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects a selected ion species into the workpiece to produce the desired extrinsic material properties. Typically, dopant atoms or molecules are ionized and isolated, accelerated and/or decelerated, formed into a beam, and implanted into a workpiece. The dopant ions physically bombard and enter the surface of the workpiece, and typically come to rest below the workpiece surface in the crystalline lattice structure thereof. 
     A typical ion implantation system is generally a collection of sophisticated subsystems, wherein each subsystem performs a specific action on the dopant ions. Dopant elements can be introduced in gas form (e.g., a process gas) or in a solid form that is subsequently vaporized, wherein the dopant elements are positioned inside an ionization chamber and ionized by a suitable ionization process. Over the last decade the so-called “Bernas-style” ion source has become generally accepted as an industry standard for both high and medium current ion implantation systems. For example, the ionization chamber is maintained at a low pressure (e.g., a vacuum), wherein a filament, for example is located within the ionization chamber and heated to a point where electrons are emitted from the filament. Negatively-charged electrons from the filament are then attracted to an oppositely-charged anode within the chamber, wherein during the travel from the filament to the anode, the electrons collide with the dopant source elements (e.g., molecules or atoms), which results in the separation of electrons from the source gas material, thereby ionizing the source gas and creating a plasma, i.e., a plurality of positively charged ions and negatively charged electrons from the dopant source elements. The positively charged ions are subsequently “extracted” from the chamber through an extraction slit or aperture via an extraction electrode, wherein the ions are generally directed along an ion beam path toward the workpiece. 
     Heated filament cathodes of the type described above typically degrade rapidly over time. As a result, a common variation to this style of ion source has been developed and deployed in commercial ion implantation systems, which employs an Indirectly Heated Cathode (IHC), wherein the electron emitter is a cylindrical cathode, typically 10 mm in diameter and 5 mm thick, positioned within the ionization chamber. This cathode is heated by an electron beam extracted from a filament located behind the cathode, thereby protected from the harsh environment of the ionization chamber. An exemplary IHC ion source is shown, for example, in commonly assigned U.S. Pat. No. 5,497,006, among other patents. 
     In the case of a filament cathode, the cathode heater power is typically on the order of a few hundred watts, and in the case of an IHC, typically on the order of one kilowatt. When operating with standard implantation gases such as boron trifluoride (BF 3 ), phosphine (PH 3 ) and arsine (AsH 3 ), typical maximum extracted ion beam currents are in the range of 50 to 100 mA, requiring a discharge power (cathode voltage times cathode current) of hundreds of watts. With these cathode heater powers and discharge powers, the walls of the ion source typically reach temperatures in excess of 400 degrees C. For operation with standard gases, these high wall temperatures are advantageous as condensation of phosphorus and arsenic on the walls is prevented, greatly reducing cross contamination when changing dopant species. 
     Substantial improvements in throughput have been demonstrated for low energy boron implants, for example using large molecules such as decaborane (B 10 H 14 ) and octadecaborane (B 18 H 22 ). Discharge powers and plasma densities in such large molecule plasmas must be maintained at much lower levels than for standard implant gases in order to prevent dissociation of the molecules. Typically, extracted ion currents are 5 to 10 mA requiring only tens of watts of discharge power. Though the standard sources described above can run stably at these low powers with standard implant gases, problems are encountered when running decaborane or octadecaborane. In the case of the Bernas source, where the filament is in contact with the gas, the filament is attacked by the borane and a stable discharge cannot be maintained. In the case of the IHC, the discharge is much more stable, but thermal dissociation of the large molecules is unacceptably high. Dissociation occurs both on the hot cathode and on the walls, which are difficult to maintain at low temperature due to the high radiative power of the cathode. 
     The problems described above, encountered when operating with gases such as decaborane and octadecaborane, can be overcome by removing the electron source from the ionization chamber. One such solution is described in U.S. Pat. No. 6,686,595, wherein a conventional broad beam electron gun is mounted external to the ionization chamber and the electron beam is guided through an aperture into the ionization chamber. However, in this source configuration electron current injected into the ionization chamber is limited to tens of milliamps due to fundamental limitations of electron gun design. Since operation with standard implant gases at the standard ion beam currents of 50 to 100 mA requires electron currents of hundreds of milliamps to amps, this ion source configuration is not suitable for such operation. Indeed, this problem has become well recognized by the ion implant system manufacturers, and at least one solution has been described, as for example in U.S. Pat. No. 7,022,999, wherein it has been proposed to configure the ionization chamber in two discrete modes of operation: one mode for low electron current ionization applications; and one mode for high electron current ionization applications. Alternatively, an ion source configuration has been proposed in U.S. Patent Application Publication No. US 2006/0169915, wherein first and second electron sources are located at opposite ends of and arc chamber, with each electron source being energized in one of a so-called “hot” operating mode and a “cold” operating mode. 
     Accordingly, a need exists for an ion source which can operate with low source wall temperature and low discharge power for large molecule gases (so-called “molecular species”) and with high wall temperature and high discharge power for standard implant gases (so-called “monomer species”) in order to meet more of the needs of the ion implantation industry. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to providing a two plasma or double plasma ion source system and method for efficiently operating an ion source that can utilize large molecules, such as decaborane and octadecaborane as well as standard implantation gases such as BF 3 , PH 3  and AsH 3 . Consequently, the following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later. The present invention is directed generally toward an ion source for use in an ion implantation system, wherein the ion source incorporates two or more plasma chambers, such that the first plasma chamber is operative to generate electrons for injection into the second plasma chamber so that the second plasma chamber can efficiently and effectively generate ions for injection into an ion beam line of an ion implantation system. 
     According to one exemplary aspect of the invention, an ion source is provided, comprising: a first plasma chamber, referred to hereinafter as the electron source plasma chamber, and includes a plasma generating component for generating a plasma from the ionization of a first source gas. The ion source also comprises a second plasma chamber, referred to hereinafter as the ion source plasma chamber, into which electrons from the electron source plasma chamber are injected, creating a plasma from a second source gas. The ion source can include a high voltage extraction system including an electrode system configured to extract ions from the ion source plasma chamber via an extraction aperture formed therein. 
     In another exemplary aspect of the invention, a method is provided for ion generation, the method comprising: forming an electron source plasma in a first plasma chamber; extracting electrons from the plasma formed in the first plasma generating chamber so as to direct the extracted electrons into a second plasma chamber, whereby the extracted electrons generating a plasma within the second plasma chamber. The method further comprises extracting ions through an extraction aperture located in the second plasma chamber. 
     In yet another aspect of the invention, an ion implantation system is provided, including an ion source for injecting ions into an ion beamline for implantation into a workpiece. The ion source includes a first plasma chamber, (the electron source plasma chamber) for generating a plasma from ionization of a first source gas; and a second plasma chamber (the ion source plasma chamber, into which electrons from the electron source plasma chamber are injected, for generating a plasma from a second source gas. The ion implantation system further includes an extraction system including an electrode configured to extract ions from the ion source plasma chamber via an extraction aperture formed therein. 
     To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an isometric perspective view of an exemplary ion source in accordance with one aspect of the present invention; 
         FIG. 2  illustrates a cross sectional perspective view of an exemplary ion source in accordance with one aspect of the present invention; 
         FIG. 3  is a flow chart of an exemplary method for creating and extracting ions from an ion source according to another exemplary aspect of the invention; and 
         FIG. 4  is a schematic of an exemplary ion implantation system utilizing an exemplary ion source according to another aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed generally towards an improved ion source apparatus used in ion implantation. More particularly, the system and methods of the present invention provide an efficient way to ionize large molecule ionization gases for the production of molecular ion implantation species, such as, for example: carborane; decaborane; octadecaborane and icosaboranes, as well as standard ionization gases for the production of monomer ion implant species, such as boron trifluoride, phosphine and arsine. It will be understood that the foregoing list of ion implantation species is provided for illustrative purposes only, and shall not be considered to represent a complete list of the ionization gases that could be used to generate ion implant species. Accordingly, the present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It should be understood that the description of these aspects are merely illustrative and that they should not be taken in a limiting sense. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident to one skilled in the art, however, that the present invention may be practiced without these specific details. 
     Referring now to the figures,  FIGS. 1 and 2  illustrate a simplified exemplary ion source  100  in accordance with the present invention, wherein the ion source  100  is suitable for implementing one or more aspects of the present invention. It should be noted that the ion source  100  depicted in  FIG. 1  is provided for illustrative purposes and is not intended to include all aspects, components, and features of an ion source. Instead, the exemplary ion source  100  is depicted so as to facilitate a further understanding of the present invention. 
     The ion source  100 , for example, comprises a first plasma chamber  102  situated adjacent a second plasma chamber  116 . The first plasma chamber  102  includes a gas source supply line  106  and is a configured with a plasma generating component  104  for creating a plasma from a first source gas. A source gas is introduced into the first plasma chamber  102  by the gas supply line  106 . The source gas can comprise at least one of the following: inert gases such as argon (Ar) and xenon (Xe), standard ion implantation gases such as boron trifluoride (BF 3 ), arsine (AsH 3 ) and phosphine (PH 3 ), and reactive gases such as oxygen (O 2 ) and nitrogen trifluoride (NF 3 ). Once again, it will be understood that the foregoing list of source gases is provided for illustrative purposes only, and shall not be considered to represent a complete list of the source gases that could be delivered to the first plasma chamber. 
     The plasma generating component  104  can comprise a cathode  108 /anode  110  combination, wherein the cathode  108  may include a simple Bernas-type filament configuration, or an indirectly heated cathode of the type illustrated in  FIGS. 1 and 2 . Alternatively, the plasma generating component  104  may include an RF induction coil antenna that is supported having a radio frequency conducting segment mounted directly within a gas confinement chamber to deliver ionizing energy into the gas ionization zone, for example, as disclosed in commonly assigned U.S. Pat. No. 5,661,308, which is hereby incorporated by reference in its entirety. 
     The first, or electron source, plasma chamber  102  defines an aperture  112  forming a passageway into a high vacuum region of an ion implantation system, i.e. a region wherein pressure is much lower than the pressure of the source gas in the first plasma chamber  102 . The aperture  112  provides a pumping aperture for maintaining source gas purity at a high level, as will be further discussed hereinbelow. 
     The electron source plasma chamber  102  also defines an aperture  114  forming an extraction aperture for extracting electrons from the electron source plasma chamber  102 . In a preferred embodiment, the extraction aperture  114  is provided in the form of a replaceable anode element  110  as illustrated in  FIG. 2 , having an aperture  114  formed therein. As such, it will be recognized by those of skill in the art that the electron source plasma chamber  102  can be configured to have a positively biased electrode  119  (relative to the cathode  108 ) for attracting electrons from the plasma in a so-called non-reflex mode. Alternatively, the electrode  119  can be biased negatively relative to the cathode  108  to cause electrons to be repelled back into the electron source plasma chamber  102  in a so-called reflex mode. It will be understood that this reflex mode configuration would require proper biasing of the plasma chamber walls, together with electrical insulation and independent biasing of the electrode  119 . 
     As previously stated, the ion source  100  of the present invention also includes a second, or ion source chamber  116 . The second ion source plasma chamber  116  includes a second gas source supply line  118  for introducing a source gas into the ion source plasma chamber  116  and is further configured to receive electrons from the electron source plasma chamber  102 , thereby creating plasma therein via the collisions between the electrons and the second source gas. The second source gas can comprise any of the gases listed above for the electron source plasma chamber  102  or any large molecule gases such as carborane (C 2 B 10 H 12 ), decaborane (B 10 H 14 ), and octadecaborane (B 18 H 22 ) or an icosadecaborane. Once again, it will be understood that the foregoing list of source gases is provided for illustrative purposes only, and shall not be considered to represent a complete list of the source gases that could be delivered to the second plasma chamber  116 . 
     The second, or ion source, plasma chamber  116  defines an aperture  117  aligned with the extraction aperture  114  of the first plasma chamber  102 , forming a passageway therebetween for permitting electrons extracted from the first plasma chamber  102  to flow into the second plasma chamber  116 . Preferably, the ion source plasma chamber  116  is configured to have a positively biased electrode  119  for attracting electrons injected into the ion source plasma chamber  116  in a so-called non-reflex mode to create the desired collisions between electrons and gas molecules to create ionization plasma. Alternatively, the electrode  119  can be biased negatively to cause electrons to be repelled back into the ion source plasma chamber  116  in a so-called reflex mode. 
     An extraction aperture  120  is configured in the second plasma chamber  116  to extract ions for formation of an ion beam for implantation. 
     It is important to note that in one embodiment the second plasma chamber  116  is biased positively with respect to the first plasma chamber  102  utilizing an external bias power supply  115  ( FIG. 2 ). Electrons are thus extracted from the electron source plasma chamber  102  and injected into the ion source plasma chamber  116  where collisions are induced in the second plasma chamber  116  between the electrons provided by the first plasma chamber  102  and the supply gas supplied to the second plasma chamber  116  via the second gas source supply line  118 , to create a plasma. 
     It should be noted that the first plasma chamber  102  and the second plasma chamber  116  can have three open boundaries: a gas inlet (e.g., a first gas supply inlet  122  and a second gas supply inlet  124 ), an opening to a high vacuum area (e.g., pumping aperture  112  and extraction aperture  120 ) and a common boundary apertures  114  and  117  forming the common passageway between the first and second plasma chambers,  102  and  104 , respectively. In one embodiment the area of the common boundary apertures  114  and  117  is kept small compared to the apertures  112  and  120  into the high vacuum region, i.e. first plasma chamber aperture  112  and second plasma chamber aperture  120  for reasons that will be discussed hereinbelow. 
     In one exemplary ion source configuration in accordance with the present invention, the ion source of the present invention comprises components of a standard IHC ion source of the type manufactured and sold by Axcelis Technologies, of Beverly, Mass., wherein the ion source plasma chamber includes a standard arc chamber, configured with a standard anode, extraction system and source feed tube. The internally heated cathode element of the standard IHC source is removed and replaced with a small electron source plasma chamber mounted in its place, which contains components similar to a standard IHC ion source of the type manufactured and sold by Axcelis Technologies, including an arc chamber, a standard internally heated cathode element and a source feed tube. 
     Both plasma chambers also share a magnetic field oriented along the extraction aperture, provided by a standard Axcelis source magnet, depicted by reference numeral  130 . It is well known that the ionization process (and in this case the electron generating process) becomes more efficient by inducing a vertical magnetic field in the plasma generating chamber. As such, in one embodiment electromagnet members  130  are positioned outside of the first and second plasma chambers,  102  and  116  respectively, preferably along the axis of the shared boundary therebetween. These electromagnet elements  130  induce a magnetic field that traps the electrons to improve the efficiency of the ionization process. 
     In one embodiment the electron source chamber  102  is thermally isolated from the ion source plasma chamber  116  via an insulative member  126  positioned therebetween, with the only power coupled to the ion source plasma chamber  116  being a small amount of radiative power, typically on the order of 10 W, provided from the cathode  108  through the common boundary aperture formed by apertures  114 ,  117 , and the discharge power associated with the electron current injected into the ion source plasma chamber  166 , typically 10 W for a decaborane or octadecaborane discharge. The low amount of power coupled to the ion source plasma chamber  116  facilitates maintaining the wall temperatures in chamber  116  low enough to prevent dissociation of large molecule gases. The electron source chamber  102  also is electrically isolated from the ion source plasma chamber  116  by the insulative member  126 . 
     In one embodiment, the ion source plasma chamber  116  is configured with an extraction aperture  120  having an area of approximately 300 mm 2  (5 mm×60 mm). The electron source chamber  102  is also configured with a pumping aperture  112  of total area of approximately 300 mm 2 . The common boundary aperture formed by apertures  114  and  117  shared by the two plasma chambers in one embodiment has an area on the order of 30 mm 2  (4×7.5 mm). In this configuration, operating with an argon gas source coupled to the electron source plasma chamber  102  and a decaborane or octadecaborane gas source coupled to the ion source plasma chamber  116 , extracted ion beam currents of approximately 5 mA are easily obtained through the extraction aperture  120 . Under these conditions, argon discharge currents and voltages in the electron source chamber  102  on the order of typically 0.2 A @ 40v have yielded 0.1 A electron current injected into the ion source plasma chamber  116  (with a voltage setting of 100V on the bias power supply  115 ). In the same physical configuration, switching to phosphine as a gas source in the ion source plasma chamber  116 , increasing the electron source plasma discharge parameters to 5 A @ 60V enables the electron current injected into the ion source plasma to increase to 3 A at a setting of 120V on the bias supply, with ion beam currents in excess of 50 mA extracted through the extraction aperture  120 . 
     As previously noted, the choice of the areas of the electron source plasma chamber pumping aperture  112  and ion source plasma chamber extraction aperture  120 , is preferably large compared to the common boundary aperture created by apertures  114  and  117 , which results in relatively high gas purity in each chamber,  102  and  116 . Referring to the above example, argon flows into the ion source plasma chamber  116  through the 30 mm 2  common extraction aperture  114  and out through the 300 mm2 extraction aperture  120 . As a result, argon density in the ion source plasma chamber  116  is only 10% of that in the electron source plasma chamber  102 . By the same reasoning, the density of the second gas, supplied to the ion source plasma chamber  116  via gas supply line  118 , which can flow into the electron source plasma chamber  102 , is only 10% of that in the ion source plasma chamber  116 . In a typical application, argon density in the electron source plasma chamber  102  and second gas density in the ion source plasma chamber  116  are approximately equal such that each plasma chamber gas is about 90% pure. 
     As a result of the foregoing ion source hardware configurations, the inventor has recognized that the formation of molecular ion species such as decaborane (B 10 H 14 ) or octadecaborane (B 18 H 22 ) ions within a second plasma chamber  116  utilizing electrons from the first plasma chamber  102  can avoid the typical ion source contamination problems associated with a cathode, for example, while the power dissipation attributes of such hardware can enable low electron current ionization applications typically associated with molecular species ionization, as well as high electron current ionization applications typically associated with monomer species ionization. 
     As illustrated in  FIG. 3 , the method  200  in accordance with the present invention begins at  202  by supplying a first gas through the gas supply line  106  to the first plasma chamber  102  that is in a vacuum condition (see  FIG. 1 ) and a second gas through the second gas source supply line  118  to the second plasma chamber  116  that is also in a vacuum state (see  FIG. 1 ). The ion source  100  ( FIG. 1 ), for example, comprises the first plasma chamber  102  containing the first gas configured with a plasma generating component  104  ( FIG. 1 ) for producing a plasma from the first gas. 
     At  204 , a plasma generating component  104  (see  FIG. 1 ) is energized to create a plasma in the first plasma chamber  102  (see  FIG. 1 ) from interaction of the plasma generating component  104  and the first source gas (e.g., argon). For example, the plasma may be created by a DC discharge with a discharge current of 0.4 amps and a discharge voltage of 60 volts. At  206  electrons are extracted from the plasma created in the first plasma chamber  102  (see  FIG. 1 ) and injected into the second plasma chamber  116  (see  FIG. 1 ) through the common boundary area formed by apertures  114  and  117  formed in the first and second plasma chambers  102  and  116 , respectively, allowing fluid communication therebetween (e.g., fluids comprising electrons, ions, and plasma). The second gas within the second plasma chamber  116 , supplied via gas line  118 , is impacted by the electrons extracted from the first plasma chamber  102  (see  FIG. 1 ), thus forming a second plasma in the second plasma chamber  116  (see  FIG. 1 ), at  208 . Finally, ions are extracted from the plasma in the second plasma chamber  116  (see  FIG. 1 ) through an extraction aperture  120  ( FIG. 1 ) at  210 . 
     Thus, the present invention describes a “double plasma ion source.” It will be understood that this double plasma ion source described can be incorporated for use into an ion implantation system, as illustrated in the exemplary ion implantation system  300  of  FIG. 4 . The ion implantation apparatus  300  (also referred to as an ion implanter) is operably coupled to a controller  302  for controlling the various operations and processes implemented on the ion implantation apparatus  300 . In accordance with the present invention, the ion implantation apparatus  300  includes the double plasma ion source assembly  306  described hereinabove for producing a quantity of ions for generating an ion beam  308  traveling along an ion beam path P, for implantation of the ions to a workpiece  310  (e.g., a semiconductor workpiece, display panel, etc.) held on a workpiece support platen  312 . The ions can be formed from inert gases such as argon (Ar) and xenon (Xe), standard ion implantation gases such as boron trifluoride (BF 3 ), arsine (AsH 3 ) and phosphine (PH 3 ), reactive gases such as oxygen (O 2 ) and nitrogen trifluoride (NF 3 ), and large molecule gases such as decaborane (B 10 H 14 ), and octadecaborane (B 18 H 22 ). 
     The ion source assembly  306 , comprises a first plasma chamber  314  (e.g., a plasma chamber or arc chamber) and a second plasma chamber  316 , wherein the first plasma chamber  314  is configured with a plasma generating component  318 , which can include a cathode  108  (see  FIG. 2 ) and an anode  110  (see  FIG. 2 ) for generating a plasma from a first gas introduced into the first plasma chamber  314  via a first gas feed line  322  from a first gas supply  301 . The plasma generating component  318  can in the alternative comprise an RF induction coil, for example. The first gas can comprise at least one of the following: inert gases such as argon (Ar) and xenon (Xe), standard ion implantation gases such as boron trifluoride (BF 3 ), arsine (AsH 3 ) and phosphine (PH 3 ), and reactive gases such as oxygen (O 2 ) and nitrogen trifluoride (NF 3 ). 
     A second plasma chamber  316  is situated in fluid communication with the first plasma chamber  314  via a common boundary aperture  326  formed between the first and second plasma chambers,  314  and  316 , wherein the second plasma chamber  316  contains a second gas introduced by a second gas feed line  328  from a second gas supply  320 . The second gas can comprise at least one of the following: inert gases such as argon (Ar) and xenon (Xe), standard ion implantation gases such as boron trifluoride (BF 3 ), arsine (AsH 3 ) and phosphine (PH 3 ), reactive gases such as oxygen (O 2 ) and nitrogen trifluoride (NF 3 ), and large molecule gases such as decaborane (B 10 H 14 ), and octadecaborane (B 18 H 22 ). 
     The second plasma chamber  316  is preferably biased positive with respect to the first plasma chamber  314  by a bias power supply  332 , enabling the extraction of electrons from the first plasma chamber  314  for injection into the second plasma chamber  316 . When the extracted electrons collide with the second gas in the second plasma chamber  316  they create a plasma in the second plasma chamber  316 . An extraction aperture  334  is provided in the second plasma chamber  316  to extract ions from the plasma formed therein. 
     The ion implantation system  300  further comprises an extraction electrode assembly  331  associated with source assembly  306 , wherein the extraction electrode assembly  331  is biased to attract charged ions from the source assembly  306  for extraction through the extraction aperture. A beamline assembly  336  is further provided downstream of the ion source assembly  306 , wherein the beamline assembly  336  generally receives the charged ions from the source  306 . The beam line assembly  336 , for example, comprises a beam guide  342 , a mass analyzer  338 , and a resolving aperture  340 , wherein the beam line assembly  336  is operable to transport the ions along the ion beam path P for implantation into workpiece  310 . 
     The mass analyzer  338 , for example, further comprises a field generating component, such as a magnet (not shown), wherein the mass analyzer  338  generally provides a magnetic field across the ion beam  308 , thus deflecting ions from the ion beam  308  at varying trajectories according to a charge to mass ratio associated with the ions extracted from the source  306 . For example, ions traveling through the magnetic field experience a force that directs individual ions of a desired charge to mass ratio along the beam path P and deflects ions of undesired charge to mass ratios away from the beam path P. Once through the mass analyzer  338 , the ion beam  308  is directed though a resolving aperture  340 , wherein the ion beam  308  may be accelerated, decelerated, focused or otherwise modified for implantation into the workpiece  310  positioned within an end station  344 . 
     Although the invention has been described with respect to certain preferred embodiments, it is obvious that equivalent alterations and modifications can and will occur to others skilled in the art upon the reading and understanding of this specification and annexed drawings. In particular regard to various functions performed by the above described components (assemblies, devices, circuits, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more other features of the other embodiments as may be desired and advantageous for any given application.