Abstract:
A liner ( 102 ) for an arc chamber ( 100 ) of an ion implanter. The arc chamber ( 100 ) comprises a liner ( 102 ) on the inner surface ( 104 ) of the arc chamber ( 100 ) that extends the life of the arc chamber ( 100 ). The liner ( 102 ) comprises a one piece portion ( 102   a ) that covers the bottom and long sidewalls of the arc chamber ( 100 ) and two end plates ( 102   b ) for covering the end walls of the arc chamber ( 100 ). When the liner ( 102 ) wears out it is replaced at a significantly reduced cost compared to replacing the entire arc chamber ( 100 ).

Description:
This application claims priority under 35 USC § 119(e)(1) of provisional application No. 60/152,165 filed Sep. 2, 1999. 
    
    
     FIELD OF THE INVENTION 
     The invention is generally related to the field of ion implanters for semiconductor fabrication and more specifically to ARC chambers in ion implanters. 
     BACKGROUND OF THE INVENTION 
     In semiconductor processing, various regions of a semiconductor wafer are modified by implanting dopants, such as boron, phosphorus, arsenic, antimony and the like, into the body of the wafer to produce regions having varying conductivity (e.g., source and drain regions, channel adjusts, etc.). As the density of the semiconductor devices increases, stricter control of the areas to be implanted is required. Thus, ion implanters have been developed to accurately implant dopants into small areas. 
     In an ion implanter, an ion beam of the desired chemical species is generated by means of a current applied to a filament within an ion source chamber. One of the more common types of source is the Freeman source. In the Freeman source, the filament, or cathode, is a straight rod that can be made of tungsten or tungsten alloy, or other known source material such as iridium, that is passed into an arc chamber whose walls are the anode. The ions are extracted through an aperture in the arc chamber by means of a potential between the source chamber, which is positive, and extraction means. The size and intensity of the generated ion beam can be tailored by system design and operating conditions; for example, the current applied to the filament can be varied to regulate the intensity of the ion beam emitted from the ion source chamber. 
     A top view of a prior art arc chamber  10  is shown in FIG.  1 . Arc Chamber  10  typically comprises molybdenum or tungsten and is fitted with an exit aperture  12  and with means  14  for feeding in the desired gaseous ion precursors for the desired ions. Arc chamber  10  includes a filament end  18  for inserting a filament and a repeller end  16 . When power is fed to the filament, the filament temperature increases until it emits electrons that bombard the precursor gas molecules, breaking up the gas molecules so that a plasma is formed containing the electrons and various ions. The ions are emitted from the arc chamber  10  through the exit aperture  12  and selectively passed to the target. 
     The inner contour of arc chamber  10  is carefully designed and must be extremely accurate for proper operation. Unfortunately, the inner surface of the arc chamber  10  is damaged over time by the plasma. The surface of the arc chamber wears away. Sputtered deposits of tungsten or molybdenum from the chamber walls create an inefficiency in the extraction of positively charged ions from the source ACR chamber. After a time of 3-6 months, the arc chamber becomes unusable and must be replaced. Replacement ARC chambers cost on the order of $3000-$6000 and up. Thus, there is a desire to minimize this cost. 
     SUMMARY OF THE INVENTION 
     The invention is an arc chamber for an ion implanter. The arc chamber comprises a liner that extends the life of the arc chamber. When the liner wears out it is replaced at a significantly reduced cost compared to replacing the entire arc chamber. 
     An advantage of the invention is providing an arc chamber with an extended life versus the prior art. 
    
    
     This and other advantages will be apparent to those of ordinary skill in the art having reference to the specification in conjunction with the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a top view diagram of a prior art arc chamber; 
     FIGS. 2A-2D are a top view and three side views, respectively, of an arc chamber having a liner according to the invention; 
     FIG. 3 is a top view of a portion of the liner according to an embodiment of the invention; 
     FIG. 4 is a diagram of a first end plate portion of the liner according to an embodiment of the invention; 
     FIG. 5 is a diagram of a second end plate portion of the liner according to an embodiment of the invention; 
     FIG. 6 is a diagram of an end plate portion of the liner according to an alternative embodiment of the invention; and 
     FIG. 7 is a diagram of a portion of the liner according to another alternative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     An arc chamber  100  according to the invention is shown in FIGS. 2A-2D. FIG. 2A is a top view, FIGS. 2B,  2 C, and  2 D are side views. Arc chamber  100  includes a removable liner  102  that covers the inner surface  104  of arc chamber  100 . 
     Arc chamber  100  may be similar in construction to prior art arc chambers. Arc Chamber  100  may be fitted with an exit aperture (not shown) and with means  114  for feeding in the desired gaseous ion precursors for the desired ions. The arc chamber  100  also includes means  118  for inserting a filament and means  116  for a repeller. The repeller is a solid plate that repels the positive ion charge and plasma field. 
     Arc chamber  100  may comprise molybdenum or tungsten as in the prior art. Alternatively, arc chamber  100  may comprise addition materials, for example graphite, that are not currently used due to their interaction with the plasma. The liner  102  prevents the interaction of the arc chamber inner walls with the plasma, thus allowing the use of other materials. Some new products are even sensitive to molybdenum. The liner  102  of the invention allows the extended use of molybdenum in these new products. The material chosen for arc chamber  100 , however, must still be able to withstand the high temperature requirements of an ion source. 
     Arc chamber  100  differs from prior art arc chambers in that the inner wall  104  is extended inward the width of liner  102 . For example, a prior art arc chamber may be used. The inner wall of the prior art arc chamber is milled out a distance equal to the width of the liner. This may be on the order 0.06 of an inch ±0.04 inches. Then liner  102  is inserted. Alternatively, arc chamber  100  may be fabricated with an inner space extended by the thickness of the liner. 
     Liner  102  consists of a one-piece three-sided portion  102   a  (shown in FIG. 3) and two end plates  102   b  and  102   c,  as shown in FIGS. 4 and 5. The two end plates  102   b  and  102   c  are inserted at the ends of arc chamber  100 . End plate  102   b  is inserted at the filament end of the arc chamber and includes apertures  120  for the insertion of a filament. End plate  102   c  is inserted at the repeller end and includes an aperture  122  for the insertion of a repeller. Apertures  120  and  122  are designed to match those in arc chamber  100  and the filament and repellant to be used. If different filament or repeller configurations are to be used, then the apertures should be adjusted accordingly. For example, FIG. 6 shows an alternative end plate  202   b  that may be used in place of both end plates  102   b  and  102   c.  End plate  202   b  includes an aperture  232 . Then, the one-piece portion  102   a  is inserted. One piece portion  102   a  has two bends in order to cover the longer two sidewalls of inner wall  104  and the bottom surface  105  of arc chamber  100 , as shown in FIG.  3 . The bends are designed to match the surface of arc chamber  100  and are preferably 85°. One piece portion  102   a  holds the two end plates  102   b  in place. Tension in one-piece portion  102   a  holds it in place. One piece portion  102   a  also includes portion  150 . An aperture  124  is included in liner  102   a  for feeding desired gases to the chamber and is designed to match means  114  in arc chamber  100 . The liner  102  creates a seal that prevents outgassing. It prevents the interaction of the arc chamber inner wall  104  from the plasma. 
     An alternative liner portion  202   a  is shown in FIG.  7 . Liner portion  202   a  could replace liner portion  102   a.  Liner portion  202   a  includes two additional apertures  228  and  230 . Apertures  228  and  230  are for auxiliary gas inlets. 
     Liner  102  may be fabricated using, for example, tungsten. Molybdenum may also be used if the product is not sensitive to molybdenum. Other materials having the electrical characteristic to contain an ionic plasma field may alternatively be used. Liner  102  is a thin sheet of material. The thickness may be on the order of 0.06 inch. 
     The inner wall  104  of arc chamber  100  may also contain two divots  106 . The divots  106  may be used to insert pliers to install and/or remove liner  102 . The divots  106  are preferably centered in each of the opposing longer sidewalls of inner wall  104  as shown in FIG.  2 A. 
     In operation, when the liner  102  wears out, it is removed and replaced. The liner  102  is much less expensive to fabricate. Thus, the cost of replacing the liner  102  is much less expensive than replacing the entire arc chamber. Current arc chambers can cost in excess of $3000-$6000, whereas a liner is expected to cost under $100. Thus, even with the one time cost of milling, significant reduction in expense can be obtained. Furthermore, old arc chambers that have been removed due to the erosion of the inner surface may now be reused by milling out the surface and inserting a liner  102 . 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.