Abstract:
An ion implantation system of the kind including an ion source, an electrode plate, an extraction voltage supply, and a substrate holder is described. The electrode plate initially has an opening of about 6.35 mm which is enlarged to about 8.38 mm. The aperture is also tapered outwardly on a side thereof opposing the ion source. It has been found that such an electrode plate creates substantially lower suppression currents.

Description:
BACKGROUND OF THE INVENTION 
     1). Field of the Invention 
     This invention relates to an ion implantation system, its manufacture and its method of use. 
     2). Discussion of Related Art 
     Ion implantation systems are frequently used in the manufacture of integrated circuits on wafer substrates. An ion source generates ions and an extraction voltage supply is connected between an electrode plate and the ion source such that the ions are attracted to the electrode plate. An aperture is formed in the electrode plate through which the ions pass. The ions then pass through other components that accelerate the ions and deflect them before they are implanted into a wafer substrate held by a substrate holder. 
     One such a system is described in U.S. Pat. No. 4,283,631. It has been found that extremely high suppression currents result due to ions that collide with an electrode plate of the ion implantation system of the &#39;631 patent. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described by way of example with reference to the accompanying drawings wherein: 
     FIG. 1 is a cross-sectional side view of an electrode plate indicating modification of the electrode plate; and 
     FIG. 2 is a top plan view of an ion implantation system using the electrode plate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 of the accompanying drawings illustrates an electrode plate  10  which is modified according to the invention. The electrode plate  10  has first and second opposed sides  12  and  14  respectively. Before being modified, the electrode plate  10  has a circular aperture  16  extending from the first side  12  to the second side  14  therethrough. The aperture  16  has diameter D 1  of 6.35 mm. 
     The aperture  16  is modified in a lathe to an aperture  18  which is larger than the aperture  16 . The aperture  18  has a first section  20  extending from the first side  12  into the electrode plate  10 , and a second section  22  extending from the first section  20  to the second side  14 . 
     The first section  20  has a wall that extends at right angles relative to the first side  12  and has a diameter D 2  of 8.38 mm. It is generally preferred that the diameter D 2  be at least 7 mm more preferably at least 8 mm. The first section  20  extends for a length L 1  of 3.17 mm. It is generally preferred that the length L 1  be less than 4 mm. 
     The second section  22  extends from the first section  20  and has a wall at an angle other than at right angles relative to the second side  14 . As such, the second section  22  has a diameter D 3  at the second side  14  of 11.55 mm. It is generally preferred that the diameter D 3  be at least 2 mm larger than the diameter D 2 . 
     FIG. 2 illustrates an ion implantation system  30  according to an embodiment of the invention. The system  30  includes a mass analyzer  32 , an accelerator tube  34 , a quadrupole triplet  36 , deflection plates  38 , and a substrate holder  40 . 
     The mass analyzer  32  includes a high-voltage chamber  42 . One end of the accelerator tube  34  is attached to the high-voltage chamber  42 . An opposing end of the accelerator tube  34  is connected to ground. A high-voltage power supply  44  is connected between the end of the accelerator tube  34  connected to ground and the high-voltage chamber  42 . The high-voltage chamber  42  is held at a first voltage by the high-voltage power supply  44 . 
     The mass analyzer  32  further includes an ion source  50  and the electrode plate  10  located within the high-voltage chamber  42 . A vernier adjuster  51  is connected between the electrode plate  10  and the high-voltage chamber  42 . The vernier adjuster  51  maintains the electrode plate  10  at a second voltage which is lower than the first voltage of the high-voltage chamber  42 . The electrode plate  10  is located adjacent the ion source  50  with the first side (reference numeral  12  in FIG. 1) facing towards the ion source  50 . 
     The mass analyzers  32  further includes a holding chamber  52  located within the high-voltage chamber  42  for holding components that are connected to the ion source  50 . An extraction voltage supply  54  is connected between the high-voltage chamber  42  and the holding chamber  52 . The extraction voltage supply  54  maintains the holding chamber  52  at a third voltage which is different from the first voltage of the high-voltage chamber  42  and different from the second voltage of the electrode plate  10 . 
     The components of the mass analyzer  32  located within the holding chamber  52  include a source magnet power supply  58 , an arc power supply  60 , and a source gas  62 . The source gas  62  is connected to the ion source  50  to provide flow of a gas into the ion source  50 . The arc power supply  60  is connected between the holding chamber  52  and an ionizing filament of the ion source  50 . The arc power supply  60  maintains the ionizing filament of the ion source  50  at a fourth voltage which is different from the first, second, and third voltages. The source magnet power supply  58  is connected between the holding chamber  52  and the ion source  50  so as to create an axial magnetic field across a discharge region of the ion source  50 . The axial magnetic field is at a voltage potential which is different to a voltage potential of the electrode plate  10 . 
     In use, a gas flowing from the source gas  62  into the ion source  50  is ionized by the arc power supply  60 . The power supply  60  sustains an ion discharge by the filament of the ion source  50 . Ions generated by such ionization are attracted to the electrode plate  10  because of a voltage difference between the discharge region of the ion source  50  and the electrode plate  10 , and therefore because of a voltage difference between the ions and the electrode plate  10 . The ions move towards the electrode plate  10  and then pass through an aperture in the electrode plate  10 . An analyzer magnet  68  of the mass analyzer  32  deflects the ions towards an exit slit  70 . The ions then pass through the exit slit  70  and then experience a voltage drop as they pass through and are accelerated through the accelerator tube  34 . 
     The ions then pass through the quadrupole triplet  36  which is controlled by a quadrupole control  72 . The ions then pass through the deflection plates  38  which are controlled by a scanning system  74 . The scanning system  74  can apply a variable voltage to selected ones of the deflection plates  38  so that the ions are deflected onto a desired region of a substrate  76  which is held by the substrate holder  40 . By varying the voltages of the scanning system  74 , implantation locations of ions into the substrate  76  can be scanned across the substrate  76 . 
     Further details of the system  30  are described in U.S. Pat. No. 4,283,631, incorporated herein by reference. 
     The electrode plate  10  is initially unmodified and therefore has an aperture such as the aperture  16  in FIG.  1 . The electrode plate  10  is then removed from its location adjacent the ion source  50  and from the system  30 . The electrode plate  10  is then modified as discussed with reference to FIG. 1, i.e. so as to have the aperture  18 . The electrode plate  10  is then located back into its position adjacent the ion source  50  with the first side  12  facing toward the ion source  50 , and connected to the vernier adjuster  51 . 
     It has been found that the electrode plate  10  before being modified creates extremely high suppression currents through the arc power supply  60 . By modifying the electrode plate  10  as described with reference to FIG. 1, the suppression currents through the arc power supply  60  are dramatically reduced. 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive of the current invention, and that this invention is not restricted to the specific constructions and arrangements shown and described since modifications may occur to those ordinarily skilled in the art.