Abstract:
A high voltage insulator for preventing instability in an ion implanter due to triple junction breakdown is described. In one embodiment, there is an apparatus for preventing triple junction instability in an ion implanter. In this embodiment, there is a first metal electrode and a second metal electrode. An insulator is disposed between the first metal electrode and the second metal electrode. The insulator has at least one surface between the first metal electrode and the second metal electrode that is exposed to a vacuum that transports an ion beam generated by the ion implanter. A first conductive layer is located between the first metal electrode and the insulator. The first conductive layer prevents triple junction breakdown from occurring at an interface of the first electrode, insulator and vacuum. A second conductive layer is located between the second metal electrode and the insulator opposite the first conductive layer. The second conductive layer prevents triple junction breakdown from occurring at an interface of the second electrode, insulator and vacuum.

Description:
BACKGROUND 
       [0001]    This disclosure relates generally to ion implanters, and more specifically to a high voltage insulator that prevents instability in an ion implanter due to triple junction breakdown. 
         [0002]    A high voltage insulator is typically used in an ion implanter in locations along the beamline where there is a need for high voltage. For example, high voltage is necessary to extract an ion beam from an ion source. In particular, a high voltage insulator is used with an extraction system that receives the ion beam from the ion source and accelerates positively charged ions from within the beam as it leaves the source. Other locations where a high voltage insulator can be used in the beamline include an electrostatic lens that focuses the ion beam and an acceleration or deceleration stage that accelerates or decelerates the ion beam to a desired energy, respectively. 
         [0003]    Current high voltage insulator designs that are in use with a typical ion implanter are subject to triple junction breakdowns that lead to instability (e.g., high voltage instability, ion beam instability) and eventually failure of the implanter. A triple junction region in a high voltage insulator is the junction or region where three volumes having different electrical characteristics come together and thus the local electric field at the triple junction region is intensified due to the step change of the electrical characteristics at the triple junction region. The three volumes typically include a dielectric (e.g., insulator) that holds off high voltage, metal electrodes (e.g., metallic conductor), and a vacuum in the interior of the beamline. The dielectric and the metallic conductor together form the vacuum vessel to transport the ion beam and protect it from atmospheric pressure. An O-ring is sandwiched between the dielectric and the metallic conductor to provide a vacuum seal from atmospheric pressure. In addition, the O-ring allows the metallic conductor to be disassembled from the dielectric during the maintenance of the high voltage insulator. A vacuum seal interface gap is produced between the dielectric and the metallic conductor. The vacuum seal interface gap is a narrow or microscopic space containing many voids. The vacuum seal interface gap is located at exactly the same place where a triple junction region is located. 
         [0004]    During operation of the high voltage insulator, these voids formed in the vacuum seal interface gap or triple junction region not only have intensified local electric fields but also have poor vacuum pressure that promote electric discharge which makes the vacuum pressure even worse, triggering a secondary ionization. Eventually the secondary ionization will trigger a breakdown in a triple junction region that propagates along an inner surface of the dielectric until it reaches the opposite electrode and shorts out the power supply, resulting in ion implanter failure. 
         [0005]    Therefore, it is desirable to develop a high voltage insulator that can prevent triple junction breakdown that causes instability in an ion implanter. 
       SUMMARY 
       [0006]    In a first embodiment, there is an apparatus for preventing triple junction breakdown. In this embodiment, the apparatus comprises a first metal electrode and a second metal electrode. An insulator is disposed between the first metal electrode and the second metal electrode. The insulator has at least one surface between the first metal electrode and the second metal electrode that is exposed to a vacuum. A first conductive layer is located between the first metal electrode and the insulator. The first conductive layer prevents triple junction breakdown from occurring at an interface of the first electrode, insulator and vacuum. A second conductive layer is located between the second metal electrode and the insulator opposite the first conductive layer. The second conductive layer prevents triple junction breakdown from occurring at an interface of the second electrode, insulator and vacuum. 
         [0007]    In a second embodiment, there is an apparatus for preventing triple junction instability in an ion implanter. In this embodiment, the apparatus comprises a first metal electrode and a second metal electrode. An insulator is disposed between the first metal electrode and the second metal electrode. The insulator has at least one surface between the first metal electrode and the second metal electrode that is exposed to a vacuum that transports an ion beam generated by the ion implanter. A first conductive layer is located between the first metal electrode and the insulator. The first conductive layer prevents triple junction breakdown from occurring at an interface of the first electrode, insulator and vacuum. A second conductive layer is located between the second metal electrode and the insulator opposite the first conductive layer. The second conductive layer prevents triple junction breakdown from occurring at an interface of the second electrode, insulator and vacuum. 
         [0008]    In a third embodiment, there is a method for preventing triple junction instability in an ion implanter. In this embodiment, the method comprises providing a first metal electrode; providing a second metal electrode; disposing an insulator between the first metal electrode and the second metal electrode, wherein the insulator has at least one surface between the first metal electrode and the second metal electrode that is exposed to a vacuum that transports an ion beam generated by the ion implanter; providing a first conductive layer located between the first metal electrode and the insulator, wherein the first conductive layer prevents triple junction breakdown from occurring at an interface of the first electrode, insulator and vacuum; and providing a second conductive layer located between the second metal electrode and the insulator opposite the first conductive layer, wherein the second conductive layer prevents triple junction breakdown from occurring at an interface of the second electrode, insulator and vacuum. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  shows a front view of a cross-section of a high-voltage insulator according to the prior art; 
           [0010]      FIG. 2  shows a more detailed schematic illustrating the triple junction regions of the high-voltage insulator of  FIG. 1 ; 
           [0011]      FIG. 3  shows a front view of a cross-section of a high-voltage insulator according to one embodiment of this disclosure; and 
           [0012]      FIG. 4  shows a more detailed schematic illustrating the triple junction regions of the high-voltage insulator of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Embodiments of this disclosure are directed to a high voltage insulator design that prevents triple junction instability in an ion implanter. In one embodiment, conductive layers or plates are placed between a dielectric (e.g., an insulator) and the metal electrodes (e.g., metallic conductor). With this design, one end of the insulator is joined to a first conductive layer to form a first triple junction using a joining technique that minimizes formation of the voids in the first triple junction region, while the first conductive layer is attached to the first metal electrode. A first O-ring is sandwiched between the first conductive layer and the first metal electrode to seal the vacuum from the atmospheric pressure. This forms a first vacuum seal interface gap at the space between the first conductive layer and the first metal electrode. Another end of the insulator is joined to a second conductive layer to form a second triple junction using a joining technique that minimizes formation of the voids in the second triple junction region, while the second conductive layer is attached to the second metal electrode. A second O-ring is sandwiched between the second conductive layer and the second metal electrode to seal the vacuum from the atmospheric pressure. This forms a second vacuum seal interface gap at the space between the second conductive layer and the second metal electrode. Because the vacuum seal interface gaps now are separated from the triple junction regions, gases that used to be trapped in the voids formed at the triple junction regions, are trapped in the spaces between the first conductive layer and the first metal electrode or between the second conductive layer and the second metal electrode having the same electric potential, and do not have an opportunity to initiate a breakdown that leads to failure of the ion implanter. 
         [0014]      FIG. 1  shows a front view of a cross-section of a high-voltage insulator  10  according to the prior art. The high-voltage insulator  10  shown in  FIG. 1  is for use in an ion implanter. In particular, the high voltage insulator  10  is used in an extraction system that extracts an ion beam from an ion source. Although the description that follows for the high voltage insulator  10  shown in  FIG. 1  and the insulator design that relates to this disclosure (see  FIGS. 3 and 4 ) is directed to an extraction system in an ion implanter, the scope of this disclosure is applicable to other components within the beamline of an ion implanter that need a high voltage. As mentioned above, other locations where a high voltage insulator can be used include an electrostatic lens, acceleration stage or deceleration stage. 
         [0015]    Referring back to  FIG. 1 , the high voltage insulator  10  includes a vacuum  12  formed within an insulator  14 , anode electrode  16  and a cathode electrode  18 . In one embodiment, the insulator  14  is a dielectric while the anode electrode  16  and the cathode electrode  18  are metal electrodes. As shown in  FIG. 1 , the insulator  14  separates the anode electrode  16  from the cathode electrode  18  in order to hold a high voltage that is necessary to extract ions from an ion source. Stress relief features  20 , which are metal components such as aluminum, reduce electrical stress at triple junction regions, which are interfaces where the vacuum  12 , insulator  14 , anode electrode  16  or cathode electrode  18  meet. In particular, the stress relief features  20  function to reduce the electric field that intensifies at the triple junction regions. O-rings  22  are positioned between the anode electrode  16  and one end of the insulator  14  and between the cathode electrode  18  and another end of the insulator to provide vacuum seals from atmospheric pressure  24 . The O-rings  22  are typically accommodated in a groove that allows assembly of the insulator  14  to the anode electrode  16  and cathode electrode  18  to be clamped tight by fasteners (not shown) while producing an appropriate compression for a vacuum seal. 
         [0016]    The high voltage insulator  10  of  FIG. 1  operates by maintaining a high voltage across the insulator  14 , anode electrode  16  and cathode electrode  18  in order to extract ions from an ion source in the form of an ion beam. The ion beam moves through the vacuum  12  keeping its polarity because atmospheric pressure from the atmosphere  24  is sealed off. 
         [0017]    Although the high voltage insulator  10  of  FIG. 1  utilizes stress relief features  20  to reduce the electric field at the triple junction regions, these features are not very effective and eventually breakdown will occur at the triple junction regions and lead to failure of the ion implanter. The root cause for the breakdown at the triple junction regions in the high voltage insulator  10  is due to a first vacuum seal interface gap formed between the insulator  14  and the anode electrode  16  at one end and a second vacuum seal interface gap formed between the insulator  14  and the cathode electrode  18  at the other end, which are both located at the exactly same places where the triple junction regions are located. As mentioned above, the vacuum seal interface gap is a narrow or microscopic space that contains many voids, which are also in the triple junction regions. Because of the extreme aspect ratio of the vacuum seal interface gaps, the volume associated with the voids formed in each vacuum seal interface gap are poorly evacuated. From the perspective of the overall vacuum system used in the ion implanter, the volume associated with these voids are so small that trapped gas that slowly leaks out is essentially a negligible gas load that does not significantly increase pressure. 
         [0018]    From the perspective of the high voltage triple junctions, the inventors have ascertained that this situation exposes a critical weakness in the conventional design of the high voltage insulator  10 . In particular, if high voltage operation is initiated as soon as possible after vacuum conditions have been established, then the gas in this trapped volume will still be slowly leaking out, but creating very local high pressures in exactly the worst place having the local electric field intensified (i.e., triple junction regions). Such local pressures may reach the Paschen minimum where the mean free path of charged particles is just sufficient to allow them to gain enough energy to initiate a secondary ionization. Consequently, breakdown occurs across the channel formed in the triple junction regions between the insulator  14  and the anode electrode  16  or cathode electrode  18 , despite the presence of the relief features  20 . Furthermore, the local vacuum pressure in the triple junction regions rises due to the outgassing associated with the breakdown, which in turn fuels the secondary ionization and the breakdown. 
         [0019]    The result of this positive feedback loop is that this initial breakdown causes the insulator  14  to develop a carbonized layer that is a resistive conductor. This initiates “tracking” because the tip of such a carbonized region will cause an electric field concentration at the triple junction regions, resulting in the breakdown propagating along the inner surface of the insulator  14  until it reaches the opposite electrode (i.e., anode electrode  16  and cathode electrode  18 ) and shorts out the power supply leading to failure of the ion implanter. 
         [0020]      FIG. 2  shows a more detailed schematic illustrating the triple junction region of the high-voltage insulator  10  shown in  FIG. 1 . As shown in  FIG. 2 , a vacuum seal interface gap  26  is formed at each triple junction region  28 . During a high voltage operation, the local electric field is intensified in the vacuum seal interface gaps  26  due to the step change of the electrical characteristic in the triple junction regions  28  that cause an electric field concentration in the gaps  26 . This intensified electric field in each localized vacuum seal interface gap  26  detaches the charged particles (absorbed gases, deposited contaminants) from one surface of the vacuum gap  26 , which impinge with sufficient energy on the other surface of the gap to trigger a secondary emission of charged particles leading to positive feedback. 
         [0021]    As mentioned above, gas trapped in the space associated with the vacuum seal interface gaps  26  will slowly leak out and create a very high pressure in this volume. Such local pressures may reach the Paschen minimum where the mean free path of the charged particles is just sufficient to allow them to gain enough energy to initiate a secondary ionization in the localized vacuum seal interface gaps  26 . Consequently, breakdown occurs across the vacuum seal interface gaps  26  and the local vacuum pressure in the gaps rises due to the outgassing associated with the breakdown, which in turn fuels the secondary ionization and the breakdown. This initial breakdown results in the consequential breakdown that propagates along the inner surface of the insulator  14  until it reaches the opposite electrode (i.e., anode electrode  16  or cathode electrode  18 ). 
         [0022]    The inventors to this disclosure have discovered that effects from triple junction breakdown can be avoided by separating the triple junction regions  28  from the vacuum seal interface gaps  26 .  FIG. 3  shows a schematic of a high voltage insulator  30  according to one embodiment of this disclosure that separates the triple junction regions from the vacuum seal interface gaps. As shown in  FIG. 3 , the high voltage insulator  30  includes a first conductive layer  32 A between one end of the insulator  14  and the anode electrode  16  and a second conductive layer  32 B between the opposite end of the insulator and the cathode electrode  18 . 
         [0023]    With this configuration, one end of the insulator  14  is joined to the conductive layer  32 A using a joining technique to form the first triple junction at the joint between the insulator  14  and the conductive layer  32 A. The joining technique minimizes formation of the voids in the first triple junction region while the conductive layer  32 A is attached to the anode electrode  16 . An O-ring  22  is sandwiched between the conductive layer  32 A and the anode electrode  16  to seal the vacuum from the atmospheric pressure. This forms a first vacuum seal interface gap at the space between the conductive layer  32 A and the anode electrode  16 . Another end of the insulator  14  is joined to the conductive layer  32 B using a joining technique to form a second triple junction at the joint between the insulator  14  and the conductive layer  32 B. The joining technique minimizes formation of the voids in the second triple junction region while the conductive layer  32 B is attached to the cathode electrode  18 . Another O-ring  22  is sandwiched between the conductive layer  32 B and the cathode electrode  18  to seal the vacuum from the atmospheric pressure. This forms a second vacuum seal interface gap at the space between the conductive layer  32 B and the cathode electrode  18 . 
         [0024]      FIG. 4  shows a more detailed schematic illustrating the triple junction regions of the high-voltage insulator of  FIG. 3 . As shown in  FIG. 4 , a first triple junction region  36 A is formed at the joint between the insulator  14  and the conductive layer  32 A. A first vacuum seal interface gap  34 A is formed in the space between the conductive layer  32 A and the anode electrode  16 . A second triple junction region  36 B is formed at the joint between the insulator  14  and the conductive layer  32 B. A second vacuum seal interface gap  34 B is formed in the space between the conductive layer  32 B and the cathode electrode  18 . Thus, the triple junction regions  36 A and  36 B are now separated from the vacuum seal interface gaps  34 A and  34 B, respectively. 
         [0025]    Because there is no microscopic gap between the conductive layers  32 A and  32 B and the insulator  14 , and the gaps between the conductive layers  32 A and  32 B and the insulator  14  are smaller than the molecular size of gases, the joints between the conductive layers and the insulator  14  also seal the vacuum from atmospheric pressure. Since the triple junction regions  34 A and  34 B are formed at the joint between the conductive layers  32 A and  32 B and the insulator  14  there is no gap at the triple junction regions any more, which greatly reduces the local electric field at the triple junction regions. 
         [0026]    In one embodiment, the conductive layers  32 A and  32 B are formed by doping metal particles into the insulator  14 . As an example, the metal particles can include aluminum. The metal particles are doped into the insulator  14  by using well-known doping techniques. In another embodiment, the conductive layers  32 A and  32 B are deposited on the insulator  14  using well-known deposition techniques. In another embodiment, the conductive layers  32 A and  32 B are bonded onto the insulator  14  so that there is no trapped void volume. Gluing (e.g., applying an epoxy) is only one example of an approach that can be used to bond the conductive layers  32 A and  32 B to the insulator  14 . Those skilled in the art will recognize that other joining techniques may be used to join the conductive layers  32 A and  32 B to the insulator  14  at an atom level without a microscopic gap produced between the conductive layers and the insulator  14 . 
         [0027]    Each of the above-described techniques for forming the conductive layers  32 A and  32 B has a commonality in that the insulator  14  and the conductive layers are joined together in the atomic level to form the triple junction so that there is no microscopic gap between the insulator  14  and the conductive layers. 
         [0028]    Because the triple junction regions in the extraction system of  FIGS. 3 and 4  are separated from the vacuum seal interface gaps that are formed in the space between the conductive layer  32 A and the anode electrode  16  and the space between the conductive layer  32 B and the cathode electrode  18 , the gases that used to be trapped at the triple junction regions now are trapped in the space  34 A between the conductive layer  32 A and the anode electrode  16  and the space  34 B between the conductive layer  32 B and the cathode electrode  18 ; there is no microscopic gap at the triple junctions  36 A and  36 B. Because the conductive layer  32 A and the anode electrode  16  or the conductive layer  32 B and the cathode electrode  18  have the same electrical potential, the trapped gases have no opportunity to initiate a secondary ionization and trigger a triple junction breakdown that will cause voltage or ion beam instability and subsequent failure of an ion implanter. 
         [0029]    It is apparent that there has been provided with this disclosure a high voltage insulator that prevents instability in an ion implanter due to triple-junction breakdown. While the disclosure has been particularly shown and described in conjunction with a preferred embodiment thereof, it will be appreciated that variations and modifications will occur to those skilled in the art. Therefore, it is to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.