Abstract:
A method of reducing by-product deposition inside wafer processing equipment includes providing a chamber having a peripheral inner wall and placing a semiconductor wafer within the chamber. The method also includes placing a ring within the chamber proximate the peripheral inner wall and introducing a plurality of reactant gases into the chamber and reacting the gases. The method also includes introducing a heated gas into the chamber through the ring proximate the peripheral inner wall to increase the temperature of the peripheral inner wall.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [1]    1. This application is related to a co-pending application entitled Method to Reduce By-Product Deposition in Wafer Processing Equipment and Improved Apparatus, filed Jan. 7, 1998, having an attorney docket number of TI-23135  and a Ser. No. of 60/070,697.  
     
    
     
       TECHNICAL FIELD OF THE INVENTION  
         [2]    2. This invention relates generally to semiconductor manufacturing and more particularly to a method and system for reducing by-product deposition in wafer processing equipment.  
         BACKGROUND OF THE INVENTION  
         [3]    3. During the manufacture of semiconductor components, such as integrated circuits, memory chips, and the like, the failure of valves and pumps used in connection with wafer processing equipment is problematic. The failure is often caused by the deposition of by-products, such as by deposition of ammonium chloride (NH 4 Cl). In certain chemical vapor deposition (“CVD”) processes such as chloride-based ammonia reduction CVD processes, ammonium chloride (NH4Cl) is formed by reacting, for example, hydrogen chloride (HCL) with ammonia (NH 3 ). The resulting ammonium chloride may sublimate to a solid and stick to the inside of a wafer processing chamber wall or on the inside of associated valves and pumps. The build up over time of solidified ammonium chloride inside the valves and pumps may cause the valves to leak and the pumps to degrade, and the solidified ammonium chloride may also be transmitted into the process chambers, contaminating the manufacturing processes and reducing their yield.  
           [4]    4. One attempt at solving such a problem involves placing heaters around the wafer processing chamber or associated pump or conduits to maintain the produced ammonia chloride in a gaseous form to prevent sublimation to a solid form. However, in single wafer processing reactors for chemical vapor deposition of silicon nitride (SiCl 2 H 2  and NH 3   reaction) and titanium nitride (TiCl 4  and NH 3  reaction), process gases from a shower head flow into and through a chamber with high velocity and low temperatures. This flow removes a large amount of heat from inner walls of the reaction system. Because of the removal of heat from the inner walls, heating the outer walls may not be sufficient to prevent sublimation of ammonia chloride to a solid form.  
         SUMMARY OF THE INVENTION  
         [5]    5. Accordingly, a need has arisen for an improved method and system for reducing ammonium chloride deposition in wafer processing equipment. The present invention provides a method and system for reducing ammonium chloride deposition in single wafer processing equipment that addresses shortcomings of prior systems and methods.  
           [6]    6. According to one embodiment of the invention, a method of reducing by-product deposition inside wafer processing equipment includes providing a chamber having a peripheral inner wall and placing a semiconductor wafer within the swig chamber. The method also includes placing a ring within the chamber proximate the peripheral inner wall and introducing a plurality of reactant gases into the chamber and reacting the gases. The method also includes introducing a heated gas into the chamber through the ring proximate the peripheral inner wall to increase the temperature of the peripheral inner wall.  
           [7]    7. According to another embodiment of the invention, a method of reducing by-product deposition inside wafer processing equipment includes providing a chamber and placing a semiconductor wafer within the chamber. The method also includes connecting the chamber to a pump through a conduit and placing a heating element within the interior of the conduit to increase a temperature within the conduit. The method also includes introducing a plurality of reactant gases into the chamber and reacting the gases.  
           [8]    8. Embodiments of the invention provide numerous technical advantages. For example, in one embodiment of the invention, introduction of a heated gas through a ring along the periphery of the inner wall of a chamber inhibits solidification of by-products in water processing, such as ammonia chloride. Such inhibiting reduces degeneration of associated valves and pumps. In addition, the amount of solidified by-product contaminating the manufacturing process is reduced, which increases the yield of the manufacturing process.  
           [9]    9. Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [10]    10. For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:  
         [11]    11.FIG. 1 is a graph illustrating a sublimation curve for ammonia chloride;  
         [12]    12.FIG. 2A is a schematic block diagram illustrating a chemical vapor deposition reactor and associated equipment for wafer processing according to the teachings of the present invention;  
         [13]    13.FIG. 2B is a schematic cross sectional drawing of a ring for use in the reactor of FIG. 2A;  
         [14]    14.FIG. 3 is a schematic cross sectional drawing of another embodiment of a wafer processing reactor according to the teachings of the present invention;  
         [15]    15.FIG. 4 is a schematic cross sectional drawing of a pump and a conduit associated with a wafer processing reactor according to the teachings of the present invention; and  
         [16]    16.FIG. 5 is a schematic cross sectional diagram of a portion of a conduit according to the teachings of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [17]    17. Embodiments of the present invention and its advantages are best understood by referring to FIGS.  1  through  5  of the drawings, like numerals being used for like and corresponding parts of the various drawings.  
         [18]    18.FIG. 1 is a graph illustrating a sublimation curve for an example semiconductor processing by-product, ammonia chloride (NH 4 Cl). The illustrated graph indicates the temperature and pressure conditions at which ammonia chloride changes from a solid into a gas. For example, at 300 Pascals, which is an example pressure at which film formation occurs, ammonia chloride is a gas at temperatures above approximately 180° C. and is a solid at temperatures below approximately 180° C. This curve demonstrates the combination of pressure and temperatures at which ammonia chloride will take a gaseous or solid form, and therefore may be used to ascertain pressures and temperatures at which it is necessary to keep produced ammonia chloride to avoid solidification within a wafer processing system. Although a sublimation curve for ammonia chloride is presented, similar curves exist for other chemicals used in chemical vapor deposition processes.  
         [19]    19.FIG. 2A is a schematic diagram illustrating a chemical vapor deposition reactor  10  for use in accordance with one embodiment of the present invention. Reactor  10  includes a hermetically sealed chamber  12 , an inlet port  14  for introducing reactants into chamber  12 , a semiconductor support  16  for holding a substrate  18  in chamber  12 , and an outlet port  20  for evacuating chamber  12 . In this embodiment, reactor  10  is a single wafer processing reactor, which processes one wafer at a time. Chamber  12  has an inner peripheral wall  17 . Inlet port  14  is connected to a plurality of reactant gas stores  21  storing reactant gases  22 . Each gas store  21  includes a metering device  24  to control the introduction of reactant gases  22  into chamber  12 . Reactant gases  22  may be otherwise provided to chamber  12  without departing from the teachings of the present invention.  
         [20]    20. Inlet port  14  is connected to a “shower head” manifold  26  in chamber  12  for dispersing reactant gases  22  across a surface  28  of substrate  18 . Manifold  26  may be connected to a radio frequency source (not explicitly shown) for generating plasma to transfer energy to reactant gases  22  in chamber  12 .  
         [21]    21. Semiconductor support  16  may include clips or other suitable means for securing substrate  18  over manifold  26 . Substrate  18  may be a wafer, silicon slice, or any other work piece onto which thin films are deposited. A suceptor, or heater  32 , may be included as part of support  16  to transfer thermal energy to reactant gases at surface  28  of substrate  18 . Semiconductor support  16  may be formed from graphite. Heater  32  may be a radio frequency, resistive, or other suitable heater.  
         [22]    22. Outlet port  20  is connected to a vacuum pump  34  through a conduit  36 . Vacuum pump  34  evacuates and maintains chamber  12  at a desired pressure. An example of a desired pressure is in the range of 0.4 to approximately 8 torr; however, other suitable pressures may be maintained.  
         [23]    23. In chlorine-based ammonia reduction chemical vapor deposition, for example, reactant gases  22  may include silicon nitride utilizing dichlorosilane (SiCl 2 H 2 ), ammonia, titanium nitride (TiN), and tetrachloride (TiCl 4 ). Reaction of ammonia with hydrogen chloride (HCl) produced from the above reactants forms ammonia chloride (NH 4 Cl). Because of standard operating temperatures and pressures for reactor  10 , this formed ammonia chloride has a tendency to sublimate from gaseous form to a solid form and stick to the walls of chamber  12 , conduit  36 , pump  34 , and associated valves (not explicitly shown). This sublimation problem is particularly acute in single wafer processing systems utilizing shower head manifold  26 , because reactant gases  22  typically flow through shower head manifold  26  at low temperatures and high velocities, resulting in large heat losses within chamber  12  and along inner peripheral wall  17 . To combat the sublimation of formed ammonia chloride to a solid form and deposition of solid ammonia chloride within reactor  10 , pump  34 , conduit  36 , and other elements associated with reactor  10 , but particularly along inner peripheral wall  17  of reactor  10 , a ring  46  is provided within chamber  12 . Ring  46  introduces hot gases  52  along the periphery of inner peripheral wall  17  of chamber  12  to keep the temperature along inner wall  17  at a temperature sufficient to inhibit the produced ammonia chloride from sublimating to a solid form. The introduction of hot gases  52  within chamber  12 , and particularly along inner peripheral wall  17 , provides efficient convective heating that is more effective than heating the exterior of chamber  12 .  
         [24]    24.FIG. 2B illustrates a cross sectional view of ring  46  along the line  2 B- 2 B of FIG. 2A. As illustrated, ring  46  is generally circular and includes a plurality of apertures  48  for providing a hot gas into chamber  12  to heat inner wall  17  of chamber  12 ; however, ring  46  may take on any suitable configuration, particularly including configurations that conform to the shape of inner peripheral wall  17 . A hot gas conduit  50  provides a path for hot gases  52  to flow into ring  46 . Hot gases  52  may include any suitable gas for introduction into chamber  12 , including hot purge gases that may be available from other steps of the semiconductor wafer processing process. Particularly suitable gases include hydrogen and nitrogen, because these gases will not interact with reactant gases  22 . Although purge gases may be particularly useful, other gas sources may be utilized without departing from the teachings of the present invention. Thus, the introduction of hot gases along inner peripheral wall  17  increases the temperature of peripheral wall  17  to an extent that would otherwise be difficult using conventional techniques and overcomes heat loss associated with reactant gases  22  flowing through shower head manifold  26  at low temperatures and high velocity. Such increase in temperature inhibits sublimation of produced by-products, such as ammonia chloride, and therefore reduces degradation of associated valves and pumps in addition to reducing contamination of the manufacturing process.  
         [25]    25.FIG. 3 illustrates a cross sectional schematic of another embodiment of the present invention. A reactor system  110  is analogous to reactor system  10 ; however, instead of utilizing ring  46  to provide hot gases  152  to the interior of a chamber  112 , hot gases  152  are provided directly through a conduit  146  to the underside of a semiconductor support  116 , which in this example is heater  32 . The provided hot gases  152  flare outward towards an inner wall  117  near connection of chamber  112  to an outlet port  120 .  
         [26]    26. The provision of hot gases  152  underneath semiconductor support  116  is particularly useful in heating a conduit  136  and preventing sublimation of by-products, such as ammonia chloride, to a solid form within a conduit  136  in addition to preventing sublimation of ammonia chloride to a solid form within chamber  112 . Hot gases  152  may include any suitable gas for introduction into chamber  112 , including hot purge gases that may be available from other steps of the semiconductor wafer processing process. Particularly suitable gases include hydrogen and nitrogen, because these gases will not interact with reactant gases  122 . This introduction of hot gases  152  may be combined with the introduction of hot gases  52 , as illustrated in FIG. 2A.  
         [27]    27.FIG. 4 illustrates another embodiment of the present invention. Illustrated in FIG. 4 is a reactor  210  analogous to reactor  10 , illustrated in FIG. 1. Attached to reactor  210  is a conduit  236  leading to a pump  234 . Conduit  236  receives gases from a reactor such as reactor  210  through application of negative pressure by pump  234 . Disposed within conduit  236  is a heating element  250 . Heating element  250  increases the temperature within conduit  236  and pump  234 . In particular, heating element  250  increases the temperature of an inner wall  232  of conduit  236  and an inner wall  238  of pump  234 . Increasing the temperature of inner walls  232  and  238  of conduit  236  and pump  234 , respectively, inhibits solidification of, for example, ammonia chloride on inner walls  232  of conduit  236  and  238  of pump  234 . Heating element  250  may be any suitable heater for increasing the temperature within conduit  236  or pump  234 ; however, according to one embodiment of the invention, heating element  250  is a tungsten halogen lamp.  
         [28]    28. The introduction of a heating element within the interior of conduit  236  allows more effective heating than heating the exterior of conduit  236 . This more effective heating prevents sublimation of by-product gases to a solid form and therefore reduces degradation of associated valves and pumps in addition to reducing contamination of the manufacturing process. The introduction of a heating element into conduit  236  may be combined with the techniques described in conjunction with FIGS. 2A,  2 B, and  3  to further prevent sublimation of by-product gas.  
         [29]    29.FIG. 5 illustrates a schematic cross sectional diagram of a portion of a conduit  336  suitable for use with the present invention. According to the embodiment illustrated in FIG. 5, conduit  336  receives hot hydrogen  352  through a conduit  350  from a hot hydrogen source (not explicitly shown). In addition to heating an inner wall  332  of conduit  336  and an inner wall  338  of a pump  334 , hot hydrogen gas  352  provides a hydrogen passivation for, for example, ammonia chloride. Hydrogen passivation of ammonia chloride inhibits formation of ammonia chloride from its constituent elements. Therefore, in addition to preventing the solidification of by-products such as ammonia chloride, use of hot hydrogen  352  prevents the formation of both gas and solid ammonia chloride. To further inhibit the formation of by-products such as ammonia chloride by hydrogen passivation, a platinum catalyst  360  and a heater  354  may be disposed within conduit  332  to generate free hydrogen radicals. In addition, heater  354  may also be added to facilitate generation of free hydrogen radicals The existence of free hydrogen radicals more efficiently inhibits the formation of ammonia chloride and therefore inhibits formation of solid ammonia chloride on inner walls  332  and  338 .  
         [30]    30. Although the present invention and its advantages have been described in detail, it should be understood the various changes, substitutions, and alterations can be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.