Patent Publication Number: US-2003234372-A1

Title: Ion source of an ion implantation apparatus

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to an ion implantation apparatus used in fabricating semiconductor devices. More particularly, the present invention relates to an ion source of an ion implantation apparatus.  
       [0003] 2. Description of the Related Art  
       [0004] One of the basic techniques in the fabricating of semiconductor devices is an ion implantation process of implanting impurities in a silicon substrate. In particular, the ion implantation process collide ions having high energy with the substrate, thereby physically filling the substrate with the ions. An ion implantation apparatus used for performing the ion implantation process comprises an ion source for generating the ions to be implanted into the substrate.  
       [0005] Generally, as shown in FIG. 1, the ion source comprises an arc chamber  12  in which the ions are generated. A filament  14  through which electric current flows is disposed within the arc chamber  12 . A reflector  16  is located on a side of the chamber  12  opposite the filament  12  and negative electric current flows through the reflector  16 . An inlet port  18  extends through a tungsten base plate  13  of the arc chamber  12 , and a gas supply pipe  20  for supplying source gases into the arc chamber  12  is connected to the inlet port  18 . As is also shown FIG. 1, the inlet port  18  consists of one large opening having a diameter of about 10 mm. Therefore, various problems occur.  
       [0006] First, the mobility of the gas molecules is poor because the gases can only be supplied into the arc chamber  12  through the large opening of the inlet port  18  at a relatively small velocity. This, in turn, leads to a low probability of reactant gases colliding with thermal electrons emitted from the filament  12 .  
       [0007] Second, the gases are not supplied uniformly in the arc chamber  12  and concentrate in front of the inlet port  18 , as shown at FIG. 1. This prevents plasma from being formed. Accordingly, the ionization efficiency in the arc chamber  12  is low, meaning that a large amount of the gases is used during the implantation process.  
       [0008] Third, a large amount of residual substances is deposited on the base plate  13  and, in particular, on the gas inlet port  18  during the ionization of the source gas because the base plate is made of tungsten. As the ionization process proceeds, the amount of deposition is increased. Finally, the opening of the inlet port  18  is gradually choked and the gases are not smoothly supplied into the arc chamber  12 .  
       SUMMARY OF THE INVENTION  
       [0009] An object of the present invention to provide an ion source of an ion implantation apparatus, that performs with a high degree of ionization efficiency.  
       [0010] It is another object of the present invention to provide an ion source of an ion implantation apparatus, that use a relatively small amount of gas to produce an ion beam.  
       [0011] It is still another object of the present invention to provide an ion source of an ion implantation apparatus, that uniformly supplies the gases into an arc chamber thereof.  
       [0012] In accordance with an aspect of the present invention, an ion source comprises an arc chamber having a gas line through which the gases are supplied, a first electrode installed on an inner wall of the arc chamber, and a second electrode installed on an inner wall of the arc chamber opposite the first electrode. A spray nozzle is connected with the gas line and has a plurality of minute holes so that the gases are uniformly sprayed toward the arc chamber at a high velocity.  
       [0013] According to another aspect of the present invention, the spray nozzle is made of boron nitride or ceramic to prevent residual substances from being deposited thereon in the arc chamber. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014] Additional objects, features and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments thereof when taken together with the accompanying drawings in which:  
     [0015]FIG. 1 is a schematic view of a conventional ion source of an ion implantation apparatus;  
     [0016]FIG. 2 is a schematic view of an ion implantation apparatus comprising an ion source according to an embodiment of the present invention;  
     [0017]FIG. 3 is a sectional view of the ion source shown in FIG. 2;  
     [0018]FIG. 4 is a perspective view of a spray nozzle of the ion source shown in FIG. 3;  
     [0019]FIG. 5 is a sectional view of an ion source according to another embodiment of the present invention; and  
     [0020]FIG. 6 is a perspective view of the base plate of the ion source shown in FIG. 5. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0021] The present invention will now be described more fully hereinafter with reference to the attached figures.  
     [0022] Referring to FIG. 2, the ion implantation apparatus includes an ion source  110  for forming an ion beam by ionizing reactant gases, an analyzer  130  for removing undesired impurities from the ion beam, an accelerator  140  for accelerating the ion beam with energy in a range of 2 KeV to 200 KeV, and an ion implantation chamber  150 .  
     [0023] Referring to FIG. 3, the ion source  110  has an arc chamber  112  in which the reactant gases are ionized. A filament  114  is installed on an inner wall of the arc chamber  112  and thermal electrons which provide the bases for generating ions is emitted from the filament  114 . The filament  114  is connected with a source of external power (not shown). A reflector  116  is installed on the inner wall of the arc chamber  112  opposite the filament and negative current flows through the reflector  116 . A gas spray nozzle  120  is installed on a base plate  113   a  of the arc chamber  112 . An exit aperture  118  for the ion beam is formed in a front plate  113   b  of the arc chamber  112  which is located opposite the base plate  113   a.    
     [0024] The gas spray nozzle  120  is connected with a gas line  180 . Referring to FIG. 4, the gas spray nozzle  120  has a plurality of minute spray holes (about 0.5 mm in diameter) so that reactant gases are uniformly sprayed toward the inside of the arc chamber  112  at a high velocity. The reaction gases are supplied into the arc chamber  112  through the gas spray nozzle  120  from a gas source (not shown) and are ionized by thermal electrons emitted from the filament  114 .  
     [0025] The reactant gases, including impurities such as arsenic (As), phosphorus (P), boron (B), and argon (Ar) are supplied to the inside of the arc chamber  112  from the gas source through the gas spray nozzle  120 . Thermal electrons are emitted from the filament  114  when electric current flows therethrough. The thermal electrons collide with the reactant gases, thereby ionizing the reactant gases. The ionized reactant gas (or ion beam) is emitted from the arc chamber  112  through the exit aperture  118  of the arc chamber  112 . The emitted ions are accelerated in the accelerator  140  so that the ions have a predetermined energy. Then the emitted ions are used in an ion implantation process.  
     [0026] The thermal electrons move toward the walls of the arc chamber  112  due to the electric potential difference between the arc chamber  112  and the filament  114 . During this movement, the thermal electrons collide with the reactant gases and ionize them. The reactant gas flows in the arc chamber  112  with a high velocity because the reactant gas was forced through the minute holes of the gas spray nozzle  120 . The reactant gas molecules have a great deal of mobility because the velocity of the reactant gas is relatively high. Therefore, the probability of the reactant gases and the thermal electrons colliding is correspondingly high. And, the ionization efficiency is also high because the reactant gases are supplied to the inside of the arc chamber  112  as a shower or spray.  
     [0027] Also, as was discussed above, a great amount of substances is deposited on the prior art base plate, in particular, on the inlet port, while the reactant gases are ionized because the conventional base plate is made of tungsten. On the other hand, the gas spray nozzle  120  of the present invention is made of boron nitride or ceramic to prevent the substances from being deposited on the inlet port. Accordingly, the gases are supplied smoothly in the ion source of the present invention without the inlet being chocked even over a long period of use.  
     [0028] In FIG. 5, an ion source  110   a  includes the same components (i.e., an arc chamber  112   a,  a filament  114 , and a reflector  116 ) as the ion source  110  shown in FIG. 3. These components have the same functions and construction as previously stated in FIG. 3, and will not be explained in further detail. Unlike the ion source  110  shown in FIG. 3, a base plate of the arc chamber  112   a  has spray holes  119 .  
     [0029] Referring to FIG. 5 and FIG. 6, the spray holes  119  are formed at a groove  118  of the base plate  113   a ′. In view of the beam slit shape, the spray holes  119  are wholly elliptical. A spray nozzle  120   a  may be weld-connected with the groove  118  formed at a bottom side of the base plate  113   a.  The spray nozzle  120   a  serves to connect a gas line  180  with the spray holes  119  formed at the base plate  113   a ′. The width “b” of a gas-outlet port of the spray nozzle  120   a  is greater than the width “a” of a gas-inlet port connected to the gas line  180 .  
     [0030] For example, gas supplied through the gas line  180  passes the spray nozzle  120   a  to be uniformly sprayed to the inside of the arc chamber  112   a  through the spray holes  119  formed at the base plate  113   a ′. As a result, it is possible to obtain the same effect as described in the foregoing embodiment. The base plate is made of, for example, tungsten (W).  
     [0031] Finally, although the present invention has been shown and described with respect to the preferred embodiment thereof, the present invention is not so limited. Rather, various modifications and changes may be made thereto without departing from the true spirit and scope of the invention as defined by the appended claims.