Abstract:
A plasma process reactor is disclosed that allows for greater control in varying the functional temperature range for enhancing semiconductor processing and reactor cleaning. The temperature is controlled by splitting the process gas flow from a single gas manifold that injects the process gas behind the gas distribution plate into two streams where the first stream goes behind the gas distribution plate and the second stream is injected directly into the chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 10/127,104, filed Apr. 22, 2002, now U.S. Pat. No. 6,613,189, issued Sep. 2, 2003, which is a continuation of application Ser. No. 09/924,628, filed Aug. 8, 2001, now U.S. Pat. No. 6,383,334, issued May 7, 2002, which is a continuation of application Ser. No. 09/680,638, filed Oct. 6, 2000, now U.S. Pat. No. 6,299,725, issued Oct. 9, 2001, which is a continuation of application Ser. No. 09/026,246, filed Feb. 19, 1998, now U.S. Pat. No. 6,132,552, issued Oct. 17, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to process reactors used in fabricating semiconductor devices and, more particularly, to the control of the plasma temperature within the process reactor for improved reactor fabrication and maintenance operations. 
     Plasma process reactors are used for both etching and depositing material on the surface of the semiconductor substrate. In either case, a gas is injected into the chamber of the process reactor where it is ionized into a plasma for either etching or reacting with the surface of the semiconductor substrate to form a desired pattern thereon. It is important to control the gas distribution into the reactor, as well as to control the temperature of the gas in forming the plasma. Process reactors often use a thermally isolated dielectric plate to control the gas distribution into the reactor. The gases are injected into the chamber on the back side of the dielectric plate and pass through gas inlet holes in the plate to get into the reaction zone 
     The plate is thermally isolated because a back side gap is required to allow the process gases to flow behind the plate to the gas inlet holes. This makes the plate temperature and gas temperature difficult to control as the process puts a heat load on the plate. 
     Attempts have been made to control the temperature by controlling the temperature of the dielectric plate. Methods of adjusting or controlling the temperature have been performed by adjusting the back side gap to be as small as possible, by controlling the temperature of the reactor wall located behind it, or by cooling the dielectric plate, or any combination of the three. The heat transfer between the plate and the temperature control reactor wall occurs by conduction of the process gas as it flows through the narrow gap. The gas pressure, and not its flow rate, controls how much heat is transferred between the two surfaces. The plate temperature is controlled by the gas pressure, the reactor wall temperature, and the heat load on the plate from the process chamber. 
     A sample plasma process reactor  10  is depicted in the schematic diagram of FIG.  1 . Plasma process reactor  10  includes a plasma chamber  12  in which is positioned a substrate holder  14 . A semiconductor substrate  16  is placed on substrate holder  14 . A bias voltage controller  18  is coupled to substrate holder  14  in order to bias the voltage to counter the charges building up on semiconductor substrate  16 . An etching gas is provided through gas inlet  20 , which is ionized by inductor back side  22 . Placed upon inductor back side  22  is a plurality of inductor elements  24  that is controlled by a current  26 . Current  26  causes an induction current to flow that generates an ionizing field on the interior surface of inductor back side  22 . The plasma then passes through a gas distribution plate  28 , which is held in place with a vacuum seal via O-ring  30 , allowing a gas to pass through a plurality of apertures  32 . A second O-ring  34  is placed between the inductor back side  22  and gas distribution plate  28 . A vacuum is created by a vacuum pump  36  for evacuating material and pressure from plasma chamber  12 . A control gate  38  is provided to allow a more precise control of the vacuum, as well as the evacuated material. An outlet  40  removes the material from the vacuum for disposal. 
     In this example, gas distribution plate  28  is made of a silicon nitride material. In certain desired oxide etch processes, it is required that the gas distribution plate  28  be cooled below 80° C. This cooling is accomplished by cooling the reactor wall of plasma chamber  12  and is sometimes called a window in this plasma etch reactor. The reactor wall is cooled to about 20° C. and the process gas is run through the back side gap. Unfortunately, the temperature of the gas distribution plate  28  cannot be easily modified in this arrangement. The inability to control the temperature causes other problems during different stages of use of the process reactor. 
     One problem is that cleaning of the interior cannot be easily performed since the temperature is fixed as the gas distribution plate is thermally coupled to the reactor wall during cleaning. It is helpful to run the cleaning process at much higher temperatures than during the etching process, but such an effective cleaning temperature cannot be achieved since the temperature is controlled by the constant gas flow at the gas distribution plate. Another problem is that process modifications cannot be performed since only a set maximum temperature is possible and no higher temperature is available that would allow different processes to be performed that require hotter temperatures than those otherwise possible in a fixed-temperature reactor. 
     Accordingly, what is needed is a method and apparatus that overcome the prior problem of being unable to vary the temperature range of the process reactor for providing greater control over the process occurring in the processor reactor. The inability to vary the temperature range also hinders the cleaning ability of the reactor. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention, a plasma process reactor is disclosed that allows for greater control in varying the functional temperature range for enhancing semiconductor processing and reactor cleaning. The temperature is controlled by splitting the process gas flow from a single gas manifold that injects the process gas behind the gas distribution plate into two streams where the first stream goes behind the gas distribution plate and the second stream is injected directly into the chamber. By decreasing the fraction of flow that is injected behind the gas distribution plate, the temperature of the gas distribution plate can be increased. The increasing of the chamber temperature results in higher O 2  plasma cleaning rates of the deposits on the hotter surfaces. Additionally, where other processes would benefit from warmer gas distribution temperatures, the high gas flow allows higher temperatures to be achieved over the non-split flow of the prior art. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a plasma process reactor according to the prior art; 
     FIG. 2 is a schematic diagram of a plasma process reactor having a split fold plasma manifold and injector according to the present invention; 
     FIG. 3 is a schematic diagram of a top plan view of a gas distribution ring providing the secondary gas flow into the chamber; 
     FIG. 4 is an alternative embodiment of the gas flow ring used in the plasma process reactor of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A high density plasma process reactor  100  is depicted in the schematic diagram of FIG.  2 . The reactor may have multiple plasma sources where one source is for etching layers in a semiconductor substrate while the other source is for depositing a polymer. Reactor  100  is a low pressure reactor that operates at or below 50 milliTorr. Low pressure reactors are desired, as they avoid microscopic loading, where features of the same size etch more slowly in dense patterns than in sparse patterns. The reactor  100  has separate controls for top and bottom power. The top power is for energizing high density plasma sources and the bottom power or bias source is for directing the plasma process for etching and for directing a polymer for depositing. The high density plasma process reactor  100  is modeled after an LAM 9100 TCP (transferred coupled plasma) etcher and an Applied Materials HDP 5300. High density plasma is defined as plasma having an ion density greater than 1×10 10  per centimeter 3  in a plasma generation zone. Typically, high density plasmas range in ion density from 10 11  to 10 13  per cm 3 . 
     Reactor  100  increases the range of process results capable of being obtained, as well as improves the ability to clean the chamber by adding a second process gas flow inlet that avoids gas passing through the gas distribution plate on the back side of the reactor. Reactor  100  is similar in construction to that of the prior art reactor  10  in FIG.  1 . Reactor  100  includes a chamber  112  in which is placed a substrate support platform  114  that holds a semiconductor substrate  116 . A plurality of semiconductor substrates  116  can be placed upon substrate support platform  114 . The bottom bias source is controlled by voltage supply  118  that either grounds substrate support platform  114  or holds it at a selected voltage to attract the plasma generated within reactor  100 . A first process gas inlet  120  is provided that feeds process gas within a chamber formed by reactor back side  122  and gas distribution plate (or dielectric)  128 . Gas distribution plate  128  further includes a dielectric layer  129 , placed on the reactor back side  122  of gas distribution plate  128 . 
     A plurality of inductive power sources  124 , which is controlled by power supply  126 , is mounted to the reactor back side  122  for inductively coupling energy to form the plasma that is emitted through apertures  132  in gas distribution plate  128 . A first O-ring  130  is used to seal gas distribution plate  128  in place within chamber  112  and a second O-ring  134  is used to form the chamber between reactor back side  122  and gas distribution plate  128 . A vacuum is created by a vacuum pump  136  for evacuating material and pressure from plasma chamber  112 . A control gate  138  is provided to allow a more precise control of the vacuum, as well as the evacuated material. An outlet  140  removes the material from the vacuum for disposal. Reactor  100  further includes a second process gas inlet  142  as well as an auxiliary oxygen inlet  144 ; both inlets provide gas flow into chamber  112  and thus bypass gas distribution plate  128 . By splitting the process gas flow into chamber  112  via first process gas inlet  120  and second process gas inlet  142 , the fractional flow decreases that flows behind the gas distribution plate  128 , thus allowing the temperature of gas distribution plate  128  to increase. Inlets  120 ,  142 , and  144  can be controlled by a mechanical valve (not shown) that is electronically controlled to open and close at different times. 
     The second process gas inlet  142  actually feeds into a distribution ring  146  (FIG.  3 ). In the embodiment of FIG. 2, a pair of distribution rings  146 ,  148  are placed within the reactor, one above semiconductor substrate  116  and another substantially coplanar to semiconductor substrate  116 . In using distribution ring  146 , it is an annular ring with gas vents that point downwardly towards semiconductor substrate  116 . The distribution ring  146  is annular and thus provides a radial gas flow symmetrical to the semiconductor substrate  116 . The alternative distribution ring  148 , which may be used in tandem with the first ring, has jets  150  that direct the gas flow upward and radially inward for uniform distribution to semiconductor substrate  116 . 
     The use of the additional inlet valves allows reactor  100  to improve its cleaning ability, as well as provide process modifications. When the process gas is 100% injected through the side, the cooling of the dielectric layer  129  on gas distribution plate  128  diminishes and the O 2  plasma can now clean deposits from the gas distribution plate  128 , because it is thermally uncoupled from the reactor back side  122  during the cleaning step. Further, residue such as fluorocarbon polymers is quickly and more efficiently cleaned off of gas distribution plate  128  because of the higher temperature. 
     Process modifications are possible now in that if conditions require high gas flows to occur, but also require a warmer gas distribution plate, the split flow allows the plate to operate at higher temperatures than the prior method of just passing process gas through gas distribution plate  128 . 
     Importantly, the change in gas temperature is inversely-proportional to the change in pressure within chamber  112 . Accordingly, by reducing the pressure behind gas distribution plate  128 , the temperature of the gas flow can increase by bypassing gas distribution plate  128 . 
     FIG. 3 is a bottom plan view of a second inlet gas distribution ring  146 . Distribution ring  146  includes an annular gas vent  152  that has a plurality of holes  154  distributed around the inner perimeter. The holes can be directed to point either perpendicular to the plane of distribution ring  146  or to point slightly inwardly radially towards the axis of the annular gas vent  152 . An inlet connector  156  is provided to attach distribution ring  146  to the interior of chamber  112 . FIG. 4 depicts an alternative embodiment of the distribution ring  146 . In this embodiment, distribution ring  146  has a square or polygonal shaped gas vent  158 . A plurality of holes  154  is provided along the bottom surface of gas vent  158 . Again, an inlet connector  156  is provided to connect distribution ring  146  to the second process gas inlet  142  within chamber  112 . Either ring of FIG. 3 or FIG. 4 can be placed in the position of distribution ring  146  in FIG.  2 . Additionally, either ring can be placed in a position of distribution ring  148  having jets  150  that are substantially coplanar with the semiconductor substrate  116 . 
     Referring back to the cleaning operation used to clean plasma process reactor  100 , the oxygen is introduced at a partial pressure shown in Table I below: 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                   
                   
                 PRESSURE AT GAS 
                   
               
               
                   
                 FLOWS 
                 DISTRIBUTION PLATE 128 
                 CHAMBER 
               
               
                 GASES 
                 (sccm) 
                 (Torr) 
                 PRESSURE (mTorr) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 C 2 HF 5   
                 15 
                 30-40 
                 5-50 
               
               
                 N 2   
                 5 
               
               
                 CHF 3   
                 15 
               
               
                 CH 2 F 2   
                 15 
               
               
                   
               
             
          
         
       
     
     The approximate temperature behind the gas distribution plate  128  is T 128 =80° C. For another example, if the gas flow is split equally (50/50) between the gas distribution plate  128  and the second process gas inlet  142 , the pressure behind gas distribution plate  128  is between 15-20 Torr, with a temperature approximately T 128 =110° C. As the flow increases at the second process gas inlet  142 , the temperature can increase from 50° to 250° C. Table II provides the values for when the flow is either 100% through first process gas inlet  120  or second process gas inlet  142 : 
     
       
         
               
               
               
             
           
               
                 TABLE II 
               
               
                   
               
               
                 PRESSURE 
                 100% through Inlet 120 
                 100% through Inlet 142 
               
               
                   
               
             
             
               
                 Behind Gas 
                 30-500 mTorr 
                 5-500 mTorr 
               
               
                 Distribution 
               
               
                 Plate 128 
               
               
                 In Chamber 
                  5-500 mTorr 
                 5-500 mTorr 
               
               
                   
               
             
          
         
       
     
     The chamber pressure is independent of the pressure behind gas distribution plate  128 . The pressure for 100% of the flow through first process gas inlet  120  is dependent on O 2  flow rates shown in Table I. 
     The present invention may be employed to fabricate a variety of devices such as, for example, memory devices. These other devices are not necessarily limited to memory devices but can include applications, specific integrated circuits, microprocessors, microcontrollers, digital signal processors, and the like. Moreover, such devices may be employed in a variety of systems, such systems including, but not limited to, memory modules, network cards, telephones, scanners, facsimile machines, routers, copying machines, displays, printers, calculators, and computers, among others. 
     Although the present invention has been described with reference to a particular embodiment, the invention is not limited to the described embodiment. The invention is limited only by the appended claims, which include within their scope all equivalent devices or methods which operate according to the principles of the invention as described.