Abstract:
A technique for improving ion implanter productivity is disclosed. In one particular exemplary embodiment, the technique may be realized as a method for improving productivity of an ion implanter having an ion source chamber. The method may comprise supplying a gaseous substance to the ion source chamber, the gaseous substance comprising one or more reactive species for generating ions for the ion implanter. The method may also comprise stopping the supply of the gaseous substance to the ion source chamber. The method may further comprise supplying a hydrogen containing gas to the ion source chamber for a period of time after stopping the supply of the gaseous substance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This patent application claims priority to U.S. Provisional Patent Application No. 60/712,395, filed Aug. 31, 2005, which is hereby incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE DISCLOSURE  
       [0002]     The present disclosure relates generally to ion implantation and, more particularly, to a technique for improving ion implanter productivity.  
       BACKGROUND OF THE DISCLOSURE  
       [0003]     Ion implantation is a process for depositing chemical species into a substrate by direct bombardment of the substrate with high-energy ions. In semiconductor fabrication, ion implanters are used primarily for doping processes that alter the type and level of conductivity of target materials. A precise doping profile in an integrated circuit (IC) substrate and its thin-film structure is often crucial for proper IC performance. To achieve a desired doping profile, one or more ion species may be implanted in different doses and at different energies.  
         [0004]     Recently, carbon and oxygen ion implants have become more prevalent in the manufacture of IC devices. Such implants provide improved transistor performance.  
         [0005]     Carbon and oxygen ions are typically generated in a plasma-based ion source.  FIG. 1  shows a typical ion source  100  in an ion implanter. The ion source  100  comprises an ion source chamber  102  with conductive chamber walls  114 . At one end of the ion source chamber  102  there is a cathode  106  having a tungsten filament  104  located therein. The tungsten filament  104  is coupled to a first power supply  108  capable of supplying a high current. The high current may heat the tungsten filament  104  to cause thermionic emission of electrons. A second power supply  110  may bias the cathode  106  at a much higher potential than the tungsten filament  104  to cause the emitted electrons to accelerate to the cathode and so heat up the cathode  106 . The heated cathode  106  may then emit electrons into the ion source chamber  102 . A third power supply  112  may bias the chamber walls  114  with respect to the cathode  106  so that the electrons are accelerated at a high energy into the arc chamber. A source magnet (not shown) may create a magnetic field B inside the ion source chamber  102  to confine the energetic electrons, and a repeller  116  at the other end of the ion source chamber  102  may be biased at a same or similar potential as the cathode  106  to repel the energetic electrons. A gas source  118  may supply a reactive species (e.g., carbon dioxide, carbon monoxide, or oxygen, or a mixture of these gases) into the ion source chamber  102 . The gas source  118  is not limited to gas bottles or reservoirs, but may comprise, for example, an oven that heats up a substance to produce a desired gas. For implantation of carbon or oxygen ions, carbon or oxygen containing reactive species are required. The energetic electrons may interact with the reactive species to produce a plasma  10 . An extraction electrode (not shown) may then extract ions  12  from the plasma  10  for use in the ion implanter.  
         [0006]     Existing methods for generating carbon or oxygen ions are problematic. One significant problem is a limited lifetime of ion sources running carbon or oxygen containing reactive species. Reaction by-products can accumulate inside an ion source chamber within a few hours, reducing ion output or causing the ion output to become unstable. Replacement or maintenance of an ion source chamber results in an extended downtime for an ion implanter. In addition, carbon or oxygen ion generation in an ion source chamber tend to cause a negative impact on subsequent ion generation processes carried out in that ion source chamber. For example, in one ion source chamber, a ten-hour carbon run can lead to a 50% reduction in productivity of boron ions and a 10% reduction in productivity of phosphorous ions. It is believed that carbon or oxygen ion generation has a “poisoning” effect on interior walls of an ion source chamber. The “poisoning” effect can adversely change surface chemistry for subsequent reactions in the ion source chamber. For example, fractionation rate for certain reactive species may be reduced significantly.  
         [0007]     In view of the foregoing, it would be desirable to provide a technique for improving ion implanter productivity which overcomes the above-described inadequacies and shortcomings.  
       SUMMARY OF THE DISCLOSURE  
       [0008]     A technique for improving ion implanter productivity is disclosed. In one particular exemplary embodiment, the technique may be realized as a method for improving productivity of an ion implanter having an ion source chamber. The method may comprise supplying a gaseous substance to the ion source chamber, the gaseous substance comprising one or more reactive species for generating ions for the ion implanter. The method may also comprise stopping the supply of the gaseous substance to the ion source chamber. The method may further comprise supplying a hydrogen containing gas to the ion source chamber for a period of time after stopping the supply of the gaseous substance.  
         [0009]     In accordance with other aspects of this particular exemplary embodiment, the method may further comprise generating a plasma in the ion source chamber based on the one or more reactive species, thereby generating the ions.  
         [0010]     In accordance with further aspects of this particular exemplary embodiment, the gaseous substance may comprise reactive species selected from a group consisting of carbon dioxide (CO 2 ), carbon monoxide (CO), oxygen (O 2 ), and any type of hydrocarbon.  
         [0011]     In accordance with additional aspects of this particular exemplary embodiment, the method may further comprise generating a plasma in the ion source chamber based on the hydrogen containing gas, thereby reconditioning the ion source chamber.  
         [0012]     In accordance with another aspect of this particular exemplary embodiment, the hydrogen containing gas may comprise one or more materials selected from a group consisting of phosphine (PH 3 ), ammonia (NH 3 ), arsine (AsH 3 ), methane (CH 4 ), and hydrogen (H 2 ). The hydrogen containing gas may further comprise a sputtering agent, such as one or more inert gases.  
         [0013]     In accordance with yet another aspect of this particular exemplary embodiment, the period of time for supplying the hydrogen containing gas is determined based at least in part on an amount of time during which the gaseous substance is supplied to the ion source chamber.  
         [0014]     In accordance with still another aspect of this particular exemplary embodiment, the method may further comprising the steps of: stopping supplying the hydrogen containing gas to the ion source chamber after the period of time, and supplying a second gaseous substance to the ion source chamber after stopping supplying the hydrogen containing gas. The period of time may be determined based at least in part on a composition of the second gaseous substance. The second gaseous substance may comprise one or more boron containing reactive species. Alternatively, the period of time for supplying the hydrogen containing gas may be determined based on one or more endpoint detection methods selected from a group consisting of mass spectrometry, residual gas analysis, emission spectroscopy, and absorption spectroscopy.  
         [0015]     In another particular exemplary embodiment, the technique may be realized as a method for improving productivity of an ion implanter having an ion source chamber. The method may comprise supplying a gaseous substance to the ion source chamber, the gaseous substance comprising one or more reactive species for generating ions for the ion implanter. The method may also comprise stopping the supply of the gaseous substance to the ion source chamber. The method may further comprise supplying a chlorine containing gas to the ion source chamber for a period of time after stopping the supply of the gaseous substance.  
         [0016]     In accordance with other aspects of this particular exemplary embodiment, the chlorine containing gas may comprise one or more materials selected from a group consisting of chlorine (Cl 2 ), hydrochloride (HCl), boron trichloride (BCl 3 ) and indium trichloride (BCl 3 ).  
         [0017]     In yet another particular exemplary embodiment, the technique may be realized as a method for improving productivity of an ion implanter having an ion source chamber. The method may comprise supplying the ion source chamber with a gaseous mixture of a hydrogen containing gas and one or more reactive species. The method may also comprise generating a plasma in the ion source chamber based on the gaseous mixture, wherein the plasma contains ions generated from the one or more reactive species for use in the ion implanter, and wherein the plasma further removes one or more compounds from the ion source chamber.  
         [0018]     In accordance with other aspects of this particular exemplary embodiment, the gaseous mixture may further comprise a sputtering agent, such as one or more inert gases.  
         [0019]     In accordance with further aspects of this particular exemplary embodiment, the hydrogen containing gas may comprise one or more materials selected from a group consisting of phosphine (PH 3 ), ammonia (NH 3 ), arsine (AsH 3 ), and hydrogen (H 2 ).  
         [0020]     In accordance with additional aspects of this particular exemplary embodiment, the hydrogen containing gas may account for 5-40% of a volume of the gaseous mixture.  
         [0021]     In another particular exemplary embodiment, the technique may be realized as a method for improving productivity of an ion implanter having an ion source chamber. The method may comprise supplying a gaseous substance to the ion source chamber, the gaseous substance comprising one or more reactive species for generating carbon ions for the ion implanter. The method may also comprise stopping the supply of the gaseous substance to the ion source chamber. The method may further comprise supplying a hydrogen containing gas to the ion source chamber for a period of time after stopping the supply of the gaseous substance, the hydrogen containing gas also comprising at least one sputtering agent. The method may additionally comprise generating a plasma based on the hydrogen containing gas, wherein the plasma removes one or more metal compounds from the ion source chamber.  
         [0022]     The present disclosure will now be described in more detail with reference to exemplary embodiments thereof as shown in the accompanying drawings. While the present disclosure is described below with reference to exemplary embodiments, it should be understood that the present disclosure is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present disclosure as described herein, and with respect to which the present disclosure may be of significant utility. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     In order to facilitate a fuller understanding of the present disclosure, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present disclosure, but are intended to be exemplary only.  
         [0024]      FIG. 1  shows a typical ion source in an ion implanter.  
         [0025]      FIG. 2  shows a flow chart illustrating an exemplary method for improving ion implanter productivity in accordance with an embodiment of the present disclosure.  
         [0026]      FIG. 3  shows a flow chart illustrating another exemplary method for improving ion implanter productivity in accordance with an embodiment of the present disclosure.  
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0027]     Embodiments of the present disclosure may improve productivity of an ion implanter by reducing or eliminating ion source chamber poisoning. An ion source chamber may be cleaned or reconditioned with a hydrogen containing gas or a chlorine containing gas between ion generation processes. A variety of endpoint detection methods may be employed to know when to stop the cleaning process. Alternatively, a hydrogen containing gas may be mixed with or act as a diluent for one or more ion-generating reactive species, such that the ion source chamber is cleaned or reconditioned concurrently with an ion generation process. As a result, the ion source may become more productive in generating ions since a cleaning of the ion source chamber is less frequently required. When cleaning of the ion source chamber is required, it may be carried out more effectively and more efficiently.  
         [0028]     Referring to  FIG. 2 , there is shown a flow chart illustrating an exemplary method for improving ion implanter productivity in accordance with an embodiment of the present disclosure.  
         [0029]     In step  202 , an ion source chamber may be provided in an ion implanter. Preferably, the ion source chamber may be a plasma-based device such as, for example, the ion source chamber  102  shown in  FIG. 1 , although other types of ion source chambers (including non-plasma-based) are also contemplated.  
         [0030]     In step  204 , a first reactive species may be supplied to the ion source chamber. The first reactive species may comprise one or more ion-generating species as well as one or more diluent gases. For generation of carbon ions, the ion-generating species may comprise, for example, carbon dioxide (CO 2 ), carbon monoxide (CO), methane (CH 4 ), or a combination thereof. For generation of oxygen ions, the ion-generating species may comprise, for example, oxygen (O 2 ), carbon dioxide (CO 2 ), carbon monoxide (CO), or a combination thereof. Inert gases such as argon (Ar) and krypton (Kr) may be used as the diluent gases. According to one embodiment, the supply of the first reactive species may be achieved with a CO 2  flow of approximately 1.5-6.0 sccm combined with an Ar flow of approximately 0.1-2.0 sccm. “sccm” stands for “standard cubic centimeters per minute.” 
         [0031]     In step  206 , ions (e.g., carbon ions or oxygen ions) for use in the ion implanter may be generated based on the first reactive species. In a plasma-based ion source chamber, a number of techniques may be employed to generate a plasma from the first reactive species. For example, a plasma may be generated in an arc chamber like the ion source chamber  102  shown in  FIG. 1 . Alternatively, electrical power (e.g., RF or microwave) may be capacitively or inductively coupled into the ion source chamber to generate the plasma. Ions may then be extracted from the plasma for use in the ion implanter.  
         [0032]     In step  208 , the supply of the first reactive species may be stopped, thereby halting ion generation in the ion source chamber. A hydrogen containing gas may then be supplied to the ion source chamber. The hydrogen containing gas may comprise one or more materials including, for example, phosphine (PH 3 ), ammonia (NH 3 ), arsine (AsH 3 ), and/or hydrogen (H 2 ). The hydrogen containing species may function mainly as a cleaning agent for the ion source chamber. In addition, one or more sputtering agents such as inert gases (e.g., argon or krypton) may be included in the hydrogen containing gas. Ions generated from the sputtering agents may sputter contaminant particles off the ion source chamber walls and extraction optics.  
         [0033]     In step  210 , a cleansing reaction may be created in the ion source chamber based on the hydrogen containing gas. The cleansing reaction may be created based on a technique that is similar to or different from the one used to generate ions in step  206 . Preferably, the cleansing reaction may be created by generating a plasma from the hydrogen containing gas. The cleansing reaction may involve an interaction of the hydrogen containing gas with deposits accumulated in the ion source chamber due to the ion generation in step  206 . The cleansing reaction may further involve a sputtering process, wherein particles of one or more sputtering agents (e.g., argon or krypton) may bombard the deposits off the ion source chamber walls. The cleansing reaction may be maintained for a specified period of time to remove unwanted deposits from the ion source chamber and/or to re-condition the ion source chamber.  
         [0034]     In step  212 , the supply of the hydrogen containing gas may be stopped, and a second reactive species may be supplied to the ion source chamber to generate ions. The second reactive species may or may not be the same as the first reactive species.  
         [0035]     The specified period of time for maintaining the cleansing reaction in step  210  may be determined based on the type of the first reactive species and the length of the ion generation process in  206 . For example, a longer ion generation process in  206  with a relatively more contaminant first reactive species (e.g., CO 2 ) may require a longer cleansing reaction in step  210 . The specified period of time for maintaining the cleansing reaction may also depend on the type of the second reactive species. According to one embodiment, it is typical to run the cleaning for 15-60 minutes. Some reactive species are more sensitive to ion source chamber poisoning than others. For example, generation of carbon ions has a significant impact on a subsequent generation process of boron ions (e.g., approximately 50% reduction in beam current), compared to a moderate impact on a subsequent generation process of phosphorous ions (e.g., approximately 10% reduction in beam current) and a negligible effect on a subsequent generation process of arsenic ions. Therefore, after running carbon containing reactive species, if the next process generates boron ions, it may take longer to re-condition the ion source chamber than if the next process generates phosphorous ions.  
         [0036]     The specified period of time for maintaining the cleansing reaction in step  210  may also be controlled based on a variety of endpoint detection methods such as, for example, mass spectrometry (MS), residual gas analysis (RGA), and/or emission/absorption spectroscopy. That is, while running a cleansing reaction, the reaction itself (e.g., plasma) and/or the reaction products (e.g., residual gases) may be monitored in substantial real-time to determine the presence and amount of contaminants in the ion source chamber. Once the amount of a contaminant has dropped below a predetermined level or become undetectable, an endpoint for the cleansing reaction may have been reached. For example, according to one embodiment, a mass spectrum may be taken of the plasma during a cleansing reaction that follows a carbon operation. An oxygen peak at mass/charge =16 may be a good indication of how well the cleaning is going for a subsequent boron operation. Once the oxygen peak has been sufficiently reduced, the cleansing reaction may be stopped and the boron operation may be started.  
         [0037]     According to embodiments of the present disclosure, a chlorine containing gas may be used as a cleaning agent in place of the hydrogen containing gas described above. That is, after running ion generation in an ion source chamber, a chlorine containing gas may be flowed into the ion source chamber to generate a plasma. The plasma may react with unwanted compounds or deposits and remove them from the ion source chamber. The chlorine containing gas may comprise, for example, chlorine (Cl 2 ), hydrochloride (HCl), boron trichloride (BCl 3 ), or a combination thereof. In addition, one or more inert gases may be included in the chlorine containing gas as a sputtering agent.  
         [0038]      FIG. 3  shows a flow chart illustrating another exemplary method for improving ion implanter productivity in accordance with an embodiment of the present disclosure.  
         [0039]     In step  302 , an ion source chamber may be provided in an ion implanter. Preferably, the ion source chamber may be a plasma-based device such as, for example, the ion source chamber  102  shown in  FIG. 1 , although other types of ion source chambers (including non-plasma-based) are also contemplated.  
         [0040]     In step  304 , a mixture of a hydrogen containing gas and a reactive species may be supplied to the ion source chamber. The hydrogen containing gas and the reactive species may be fed to the ion source chamber concurrently, sequentially, or pre-mixed. The reactive species may comprise one or more ion-generating species as well as one or more sputtering agents such as, for example inert gases (e.g., argon or krypton). Typically, the mixture may comprise a greater amount of the reactive species than the hydrogen containing gas. According to one embodiment, the mixture may include 83% carbon dioxide, 8.5% argon, and 8.5% hydrogen, wherein the percentage is based on the respective flow rates of the three gases. According to another embodiment, carbon dioxide and hydrogen may be pre-mixed and supplied to the ion source chamber at a flow rate of approximately 1.0-6.0 sccm, while argon may be supplied at a flow rate of approximately 0.1-2.0 sccm.  
         [0041]     In step  306 , a plasma may be generated from the gas mixture to generate ions while maintaining a benign ion source chamber condition. In the plasma, the reactive species may generate ions for use in the ion implanter, while the hydrogen containing gas is mainly responsible for cleaning the ion source chamber. In addition, particles created from one or more inert gases in the gas mixture may sputter deposits off the ion source chamber walls and extraction optics. The simultaneous cleaning of the ion source chamber during ion generation may keep the ion source running longer before any maintenance is required.  
         [0042]     Although the exact reasons for or mechanisms behind ion source “poisoning” are not fully understood in the art, it is believed that one contributing factor may be an accumulation of compounds that are formed as a by-product between ion-generating reactive species (e.g., oxygen) and certain metals (e.g. tungsten) inside the ion source chamber. For example, in an ion source chamber that uses a tungsten cathode and/or has a tungsten wall, it is believed that tungsten oxide (WO 3 ) or other tungsten compound(s) are formed during carbon operation. The accumulation of tungsten compound(s) may be particularly detrimental to a subsequent boron operation, because it is believed that a heated tungsten wall puts BF 3  molecules into an exited state and helps them to break up more easily. A tungsten wall masked with tungsten compounds such as WO 3  will reduce boron fractionation. Therefore, one effect of a hydrogen containing gas or a chlorine containing gas or a reducing agent may be to remove the metal compound(s) (e.g., WO 3 ) from the ion source chamber. It should be noted, however, that embodiments of the present disclosure or the scope of the claims are not limited to the above-described theory.  
         [0043]     The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, 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.