Abstract:
An improved deposition chamber ( 2 ) includes a housing ( 4 ) defining a vacuum chamber ( 18 ) which houses a substrate support ( 14 ). A set of first nozzles ( 34 ) have orifices ( 38 ) opening into the vacuum chamber in a circumferential pattern spaced apart from and generally overlying the periphery ( 40 ) of the substrate support. One or more seconds nozzle ( 56, 56   a ), positioned centrally above the substrate support, inject process gases into the vacuum chamber to improve deposition thickness uniformity. Deposition thickness uniformity is also improved by ensuring that the process gases are supplied to the first nozzles at the same pressure. If needed, enhanced cleaning of the nozzles can be achieved by slowly drawing a cleaning gas from within the vacuum chamber in a reverse flow direction through the nozzles using a vacuum pump ( 84 ).

Description:
This application is a continuation of and claims the benefit of U.S. application Ser. No. 09/023,500, filed Feb. 13, 1998, now U.S. Pat. No. 6,015,591, which is a divisional of U.S. application Ser. No. 08/571,618, filed Dec. 13, 1995, now U.S. Pat. No. 5,772,771, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     One of the primary steps in the fabrication of modern semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of gases. Such a deposition process is referred to as chemical vapor deposition (CVD). Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions can take place to produce the desired film. High density plasma CVD processes promote the disassociation of the reactant gases by the application of radio frequency (RF) energy to the reaction zone proximate the substrate surface thereby creating a plasma of highly reactive ionic species. The high reactivity of the released ionic species reduces the energy required for a chemical reaction to take place, and thus lowers the required temperature for such CVD processes. 
     In one design of high density plasma chemical vapor deposition (HDP-CVD) chambers, the vacuum chamber is generally defined by a planar substrate support, acting as a cathode, along the bottom, a planar anode along the top, a relatively short sidewall extending upwardly from the bottom, and a dielectric dome connecting the sidewall with the top. Inductive coils are mounted about the dome and are connected to a supply radio frequency generator. The anode and the cathode are typically coupled to bias radio frequency generators. A series of equally spaced gas distributors, typically nozzles, are mounted to the sidewall and extend into the region above the edge of the substrate support surface. The gas nozzles are all coupled to a common manifold which provides the gas nozzles with process gases, including gases such as argon, oxygen, silane, TEOS (tetraethoxysilane), silicon tetrafluoride (SiF 4 ), etc., the composition of the gases depending primarily on what type of material is to be formed on the substrate. The nozzle tips have exits, typically orifices, positioned in a circumferential pattern spaced apart above the circumferential periphery of the substrate support and through which the process gases flow. 
     The thickness of the deposited film is ideally, but in practice is never, perfectly uniform. Deposition uniformity is very sensitive to source configuration, gas flow changes, source radio frequency generator current, bias radio frequency generator currents, the nozzle height above the substrate support and the lateral position of the nozzle relative to the substrate support. Improvements in this deposition uniformity are hindered by several factors. For example, it is often preferable that the height of the nozzles above the substrate support surface be greater than it is. However, for practical reasons it is not feasible to position the nozzles through the dielectric dome. Also, adjusting the height of the nozzles above the substrate for each process condition is not practical unless the substrate is movable vertically. Furthermore, while increasing the distance between nozzle orifices and the substrate tends to improve the deposition uniformity, it adversely affects the gas efficiency, that is requires the use of more gas or more time. In addition, argon is commonly directed through the manifold and nozzles as part of the process gases, argon flow contributing to the effectiveness of sputtering rate and sputtering uniformity. However, the use of argon restricts the flexibility one has in varying the flow rate of the process gases through the nozzles. 
     Another factor affecting deposition is related to the cleanliness of the nozzle orifices. Some process gases, such as silane, can thermally disassociate and deposit silica on the inside of the nozzle orifices. In addition, some oxygen may diffuse back into the nozzle orifices and react with the process gases to create a deposit on the inside of the nozzle orifices. Attempts to “dry clean” the chamber (by keeping the chamber closed and injecting a cleaning gas, such as fluorine compounds, into the chamber) can create additional problems. For example, fluorine gas can partially react with deposited silica and create a porous material which expands and clogs up the orifices even worse. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved deposition chamber which uses a supplemental or second gas distributor, typically a nozzle, centered above the substrate support surface to enhance deposition thickness uniformity. Deposition thickness uniformity is also enhanced by equalizing the pressure of the process gases supplied to a series of gas distributors, also typically nozzles, fed by a common manifold. 
     The improved deposition chamber includes a housing defining a vacuum chamber. A substrate support is housed within the vacuum chamber. A plurality, typically 12, of first gas distributors, typically nozzles, have their orifices or other exits opening into the vacuum chamber in a circumferential pattern spaced apart from and generally overlying the circumferential periphery of the substrate support surface, as is conventional. With the invention, a second gas distributor is used and is positioned spaced apart from and generally overlying the center of the substrate support surface. The use of the second gas distributor to inject process gases into the vacuum chamber helps to improve deposition thickness uniformity over that which is achieved without the use of the second gas distributor. 
     Deposition thickness uniformity is also improved by supplying the process gases to the manifold at a plurality of positions. The supply of the process gases to the manifold is done in a manner so that the process gases are supplied to the gas distributors at the same pressure. This is done to ensure an equal flow rate from each of the first gas distributors. 
     The exits of the gas distributors are preferably sized to permit effective dry cleaning operations. In some situations dry cleaning operations may not be effective to clean the inside surfaces of the exits. In such situations enhanced cleaning of the gas distributors can be achieved by selectively connecting a vacuum pump to the gas distributors and slowly drawing the cleaning gas within the vacuum chamber in a reverse flow direction from the chamber, through the gas distributors and from the system through the vacuum pump. 
     A primary advantage of the invention is that by independently supplying process gases to the second (or upper) gas distributor, a more uniform deposition thickness can be achieved under a variety of operating conditions, which result in a change in the distribution of the process gases through the first or lower gas distributors. 
     It has been found that a second gas distributor with a single exit is effective for use with 8-inch (20 cm) substrates. However, for larger substrates, such as 12-inch (30 cm) substrates, one or more second gas distributors having a plurality of exits will likely provide the best deposition thickness uniformity. 
     Other features and advantages of the invention will appear from the following description in which the preferred embodiment has been set forth in detail in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross-sectional view showing a deposition chamber made according to the invention; 
     FIG. 1A is a simplified view of an alternative embodiment of the center nozzle of FIG. 1 having three orifices finding particular utility for use with larger diameter (e.g., 12-inch or 30 cm) substrates; 
     FIG. 2 is an exaggerated view illustrating the characteristic M-shaped, deposition thickness variation plot of the prior art; 
     FIG. 3 illustrates an improvement in the deposition thickness variation plot of FIG. 2 using the apparatus and method according to the invention; 
     FIG. 4 is a schematic diagram illustrating a pair of equal length gas feed lines used to supply the manifold with the process gases at equal pressures; and 
     FIG. 5 is a schematic diagram illustrating how a cleaning gas within the chamber can be drawn back through the nozzles using a vacuum pump. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a deposition chamber  2  comprising a housing  4 , the housing including a dielectric dome  6  surrounded by RF inductive coils  8 . Coils  8  are powered by a source RF generator  10  through a matching circuit  12 . Chamber  2  also includes a substrate support  14  having a substrate support surface  16  within the vacuum chamber  18  defined within housing  4 . Surface  16  is used to support a substrate  20  within chamber  18 . Substrate support  14  acts as a cathode and is connected to a bias RF generator  22  through a matching circuit  24 . The top  25  of housing  4  acts as an anode and is electrically biased by a second bias RF generator  26  through a matching circuit  28 . A generally cylindrical sidewall  30  of housing  4  connects the bottom  32  of housing  4  to dielectric dome  6 . Process gases, typically including deposition gases such as silane, TEOS, silicon tetrafluoride (SiF 4 ) and any other reactive deposition gas which has a short lifetime in chamber  18 , as well as process gases such as argon, are introduced to vacuum chamber  18  through a series of 12 equally spaced nozzles  34 . As suggested in FIG. 4, nozzles  34  are arranged in a ring-like pattern and are all fluidly coupled to a gas manifold  36 . Each nozzle  34  has an orifice  38  at its distal end. The orifices  38  of nozzles  34  are arranged above the periphery  40  of substrate support  14  and thus above the periphery  42  of substrate  20  since the two peripheries are generally aligned. Vacuum chamber  18  is exhausted through an exhaust port  44 . 
     The above-described structure of deposition chamber  2  is described in more detail in U.S. patent application Ser. No. 08/234,746 filed Apr. 26, 1994, the disclosure of which is incorporated by reference. 
     FIG. 2 illustrates a typical deposition thickness variation plot  46  for a conventional deposition chamber as described above. The average thickness is shown by base line  48 . As can be seen by this plot  46 , there is a relatively steep increase in thickness at end points  50  and  52  of plot  46  corresponding to the periphery  42  of substrate  20 . The center  54  of plot  46  also dips down substantially as well. 
     The present invention improves upon plot  46  through the use of a center nozzle  56  coupled to a second gas source  58  through a second gas controller  60  and a second gas feed line  62 . See FIGS. 1 and 4. Center nozzle  56  has an orifice  64  positioned centrally above substrate support surface  16 . Orifice  64  is positioned at least twice the distance from surface  16  as are orifices  38  of nozzles  34 . Using center nozzle  56  permits the modification of deposition thickness variation plot  46  from that of FIG. 2 to exemplary plot  68  of FIG.  3 . Exemplary deposition thickness variation plot  68  is flat enough so that the standard deviation of the deposition thickness is about 1 to 2% of one sigma. This is achieved primarily by reducing the steep slope of the plot at end points  50 ,  52  and raising in the low point at center  54  of plot  46 . 
     In the preferred embodiment,  12  identical nozzles  34  are used in the regions surrounding periphery  40  of substrate support  14 . Orifices  38  have a diameter of about 0.014 inch (0.36 mm) and a depth or throat of about 0.020 inch (0.51 mm). It has been found that enlarging the orifice diameter and limiting the depth or throat of orifice  38  is important in ensuring that cleaning gases defuse back into the nozzles during dry clean operations. Such consideration may not be as necessary when the nozzle cleaning system described with reference to FIG. 5 is used. 
     To help ensure that equal amounts of processing gases pass through each orifice  38 , it is useful to provide the processing gases at the same pressure to each nozzle  34 . To help do so, the processing gas is provided to manifold  36  at opposite sides of the manifold as shown in FIG.  4 . Manifold  36  is supplied by a pair of gas feed lines  70 ,  72 , which are coupled to a first gas controller  74  and a first gas source  76  as shown in FIG.  4 . Gas feed line  70 ,  72  are constructed so as to be of equal lengths and equal diameters to provide equal resistance to fluid flow for the processing gases entering manifold  36 . Other ways for helping to ensure the same amount of processing gas flows through nozzles  34  could be used. For example, manifold  36  could be modified so that it is actually two manifolds, an outer manifold (not shown) coupled to one or more of the gas feed lines  70 ,  72  and having openings (not shown) opening into a inner manifold (not shown) to which first nozzles  34  are mounted. The openings coupling the outer and inner manifolds could be smaller adjacent the entrances of gas feed lines  70 ,  72  and larger away from those entrances to help equalize the flow rates to first nozzles  34 . 
     While deposition chamber  2  is suitable for dry cleaning operations, the system shown with reference to FIG. 5 can be used to help ensure proper cleaning of the nozzles. A process gas valve  78  is used along common gas feed line  80  operates as a final valve so to isolate vacuum chamber  18  from first gas controller  74  during cleaning operations. Downstream of process gas valve  78 , that is between the process gas valve  78  and manifold  36 , is a cleaning gas line  82  coupling a vacuum pump  84  to common gas feed line  80  through a flow control valve  86  and a shutoff valve  88 , valves  86 ,  88  acting as a flow control assembly  90 . For cleaning nozzles  34 , valve  78  is closed, a cleaning gas is introduced into vacuum chamber  18 , shutoff valve  88  is opened and flow control valve  86  is operated to permit vacuum pump  84  to slowly draw the cleaning gas into nozzles  34  through orifices  38 , back through manifold  36  and along line  82  through the operation of vacuum pump  84 . In this way, cleaning of the insides of nozzles  34  is not left to the ability of the cleaning gases to diffuse into the interior of the nozzles through their orifices  38  but rather are actively, albeit slowly, drawn through the orifices and into the nozzles by vacuum pump  84 . 
     In use, the operator can affect or control the deposition thickness uniformity occurring on substrate  20  by controlling the discharge of process gases through center nozzle  56  independently of the passage of the same or different process gases through nozzles  34 . Thickness uniformly is also enhanced by helping to equalize the flow through each orifice  38  into vacuum chamber  18 , preferably by delivering the gases to the manifold  36  using two or more gas feed lines  70 ,  72 , each gas feed line exhibiting a common fluid flow resistance from a common gas source  76 . After a period of time, it may be desired to clean deposition chamber  2  using various cleaning gases within vacuum chamber  18 . Orifices  38  and the remainders of the interiors of nozzles  34  can be effectively cleaned by using vacuum pump  84 , typically a roughing pump, to slowly draw the cleaning gases in a retrograde or reverse manner through orifices  38  and into the interiors of nozzles  34 , into manifold  36  and finally from chamber  2 . 
     In the preferred embodiment maximum flexibility is achieved using two gas controllers  60 ,  74  and two separate gas sources  58 ,  76  since this permits both the composition and rate of gas flow through nozzles  34 ,  56  to be independently varied. If the same gas composition is to be used for nozzles  34 ,  56 , a single gas source, a single gas controller and a flow divider could be used to supply the gas to lines  62 ,  80 . 
     The above-described embodiment has been designed for substrates  20  having diameters of 8 inches (20 cm). Larger diameter substrates, such as substrates having diameters of 12 inches (30 cm), may call for the use of multiple center nozzles  56   a  as illustrated in FIG.  1 A. In such embodiments the deposition thickness variation plot would likely have a three-bump (as in FIG.  3 ), a four-bump or a five-bump shape. The particular shape for the deposition thickness plot would be influenced by the type, number, orientation and spacing of center nozzles  56 A and orifices  64 . 
     Modification and variation can be made to the disclosed embodiment without departing from the subject of the invention as defined in the following claims. For example, center nozzle  56  could be replaced by a shower head type of gas distributor having multiple exits. Similarly, nozzles  34  or nozzles  56   a  could be replaced by, for example, a ring or ring-like structure having gas exits or orifices through which the process gases are delivered into chamber  18 .