Abstract:
The present invention recognizes that reactions between processing liquids is a major source of residue which clogs gas delivery systems. To avoid reactions between or among vaporized processing liquids, an inventive gas delivery system provides parallel delivery of vaporized processing liquids. The gas delivery system may be configured using any conventional vaporizing mechanism such as bubblers or injection valves. Preferably, liquid precursors TEPO, TEOS and TEB are vaporized in parallel within three injection valves, the vaporized processing liquids then are flowed into a common line and delivered to a chemical vapor deposition chamber for processing semiconductor wafers. In the unlikely event the line becomes clogged, the line can be easily replaced. Most preferably a single source of carrier gas controlled by a single mass flow controller supplies carrier gas to all three injection valves.

Description:
FIELD OF THE INVENTION 
     The present invention relates to gas delivery systems for processing chambers, and specifically to a clog resistant gas delivery system for delivering vaporized liquid precursors; particularly triethylphosphate (TEPO) and tetraethyl orthosilicate (TEOS), to a chemical vapor deposition (CVD) chamber. 
     BACKGROUND OF THE INVENTION 
     CVD processing requires a number of vaporized processing liquids. These vaporized liquids are generated and supplied to a CVD chamber via a system of pipes (or “lines”) and vaporizing mechanisms known as a gas delivery system. Typically a separate vaporizing mechanism is provided for vaporizing each processing liquid, and is coupled to a source of processing liquid and a source of carrier gas. Each vaporizing mechanism and processing liquid source combination within a gas delivery system is referred to as a vaporization stage. Although a number of vaporizing mechanisms exist (e.g., bubblers, injection valves, etc.), most conventional gas delivery systems employ a plurality of injection valves for vaporizing processing liquids to be delivered to a CVD chamber. 
     A typical injection valve comprises a processing liquid inlet for receiving a pressurized processing liquid, a carrier gas inlet for receiving a pressurized inert carrier gas, and an outlet for delivering a vaporized processing liquid/carrier gas mixture. The injection valve is heated such that when the processing liquid is injected into the carrier gas, the heat and the low partial vapor pressure of the processing liquid in the carrier gas causes the processing liquid to vaporize. A high carrier gas pressure produces more processing liquid vaporization by lowering the partial vapor pressure of the processing liquid within the carrier gas. Accordingly, when designing a gas delivery system, maintenance of adequate carrier gas pressure is an important consideration, as is minimizing overall system size and complexity. 
     To achieve a low partial vapor pressure for each processing liquid while minimizing system size, conventional gas delivery systems are configured such that a carrier gas is delivered (via a mass flow controller) to a first injection valve, where it is used to vaporize a first processing liquid, forming a first vaporized processing liquid/carrier gas mixture. The first vaporized processing liquid/carrier gas mixture then is delivered to the carrier gas inlet of a second, consecutive injection valve where it is used to vaporize a second processing liquid. A mixture of the first and second vaporized processing liquids and the carrier gas then is delivered to the carrier gas inlet of a third consecutive injection valve, etc. These configurations provide a compact and cost effective system as they employ a single gas line, and a single carrier gas source controlled by a single mass flow controller to achieve vaporization within each of the various vaporization stages. Additionally, conventional gas delivery systems facilitate processing liquid vaporization as the entire mass flow of carrier gas is applied to each injection valve. 
     Despite their overall compact and efficient design, maintenance of conventional gas delivery systems is expensive due to injection valve clogging. A clogged injection valve can cause downtime not only of the chamber to which the clogged injection valve is coupled, but also of upstream and/or downstream chambers. In addition to costly chamber downtime, injection valves themselves are expensive, typically costing more than two thousand dollars to replace, exclusive of labor costs. Thus, considerable effort has been devoted to developing clog resistant gas delivery systems, and numerous advances have been achieved. 
     A particularly worthy advance is the recognition by Applied Materials, Inc., that alloys containing nickel react with the CVD processing liquid TEPO, causing residue formation and clogging, and the recognition that chromium can repress the nickel/TEPO reaction. Thus, gas delivery components made with less than 1% nickel and with 16-27% chromium significantly reduce clogging as described in commonly assigned U.S. Pat. No. 5,925,189 (application Ser. No. 08/568,193, filed Dec. 6, 1995). Despite such advances, clogging within gas delivery systems remains a problem, particularly when a gas delivery system must be configured with existing nickel-containing components. 
     Accordingly, a need exists for a clog resistant gas delivery system that can be easily and inexpensively repaired, should clogging occur, and that resists clogging regardless of component composition. 
     SUMMARY OF THE INVENTION 
     The present invention recognizes that processing liquids and/or contaminants within the various processing liquids react among themselves forming coagulates which clog gas delivery components. Specifically, the present inventors have discovered a reaction between TEOS and H 3 PO 4  (an impurity frequently found in TEPO, and a by-product of TEPO and nickel reactions) creates a residue responsible for most clogs within TEPO gas delivery systems. As used herein impurities are considered part of the processing liquid. For example, a processing liquid is referred to as comprising H 3 PO 4  whether H 3 PO 4  is a constituent of the liquid, or an impurity. 
     To substantially reduce or eliminate clogging an inventive gas delivery system is provided which routes gas delivery lines in a parallel format such that within each vaporization stage only a single processing liquid is present. The parallel gas delivery lines are joined, and the vaporized processing liquids are mixed within a gas line rather than within an injection valve or bubbler. Because vaporized processing liquids mixing occurs within a gas line, there are no small diameter orifices (such as those contained within injection valves or bubblers) which residue may clog. Further, in the unlikely event of clogging, the gas line can be easily and inexpensively replaced. 
     In its most preferred embodiment, the inventive gas delivery system comprises a single source of carrier gas and a single mass flow controller for supplying carrier gas to each vaporization stage, thus reducing the number of parts required to vaporize processing liquids in parallel. Generally, however, the present invention may be used to reduce clogging within any processing environment wherein mixed processing constituents form an undesirable reaction product that can clog the various components within a processing constituent delivery system. 
     Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic side elevational view of a vaporization stage comprising a conventional injection valve useful in describing the preferred embodiment of the invention; 
     FIG. 2 is a schematic diagram of an inventive gas delivery system, shown coupled to a processing chamber, a processing liquid source and carrier gas source; 
     FIG. 3 is a side elevational view of a foreline of the inventive gas delivery system of FIG. 2; and 
     FIG. 4 is a top plan view of an automated tool for semiconductor device fabrication which employs the inventive gas delivery system of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a diagrammatic side elevational view of a vaporization stage  10  comprising a conventional injection valve  11  useful in describing the preferred embodiment of the invention. In pertinent part, the conventional injection valve  11  comprises a processing liquid inlet  13  for inputting a processing liquid, a carrier gas inlet  15  for inputting an inert carrier gas, and an outlet  17  for outputting a vaporized processing liquid/carrier gas mixture. Within the injection valve  11 , the processing liquid inlet  13  terminates at an orifice  19  leading to a central region  21  where the processing liquid inlet  13 , the carrier gas inlet  15 , and the outlet  17  meet. The injection valve  11  is configured such that the relative sizes of the orifice  19  and the central region  21 , and the pressures, flow rates and relative direction of the processing liquid and carrier gas flow cause a pressure drop within the central region  21 , as is conventionally known in the art. This pressure drop causes processing liquid supplied to the processing liquid inlet  13  to vaporize as it passes from the processing liquid inlet  13 , through the orifice  19  to the central region  21 . In order to facilitate vaporization, the orifice  19  is small, and thus vulnerable to clogging. 
     Outside the injection valve  11 , the processing liquid inlet  13  is coupled to a liquid flow meter  23  of the vaporization stage  10  which controls the flow rate of processing liquid traveling to the injection valve  11 . The liquid flow meter  23  also is coupled via a line  27  to a source of processing liquid  25  within the vaporization stage  10 , which in turn is coupled to a source of pressurized helium  29 . 
     In operation, the pressurized helium forces the processing liquid from the processing liquid source  25  through the line  27  to the liquid flow meter  23 . The liquid flow meter  23  controls the flow rate of the processing liquid as it travels from the liquid flow meter  23  through the processing liquid inlet  13  and the orifice  19  to the central region  21  of the injection valve  11 . A pressurized carrier gas, such as helium, flows through the carrier gas inlet  15  into the central region  21 . 
     The processing liquid vaporizes and mixes with the carrier gas as the processing liquid enters the central region  21 , due to the pressure decrease experienced as the processing liquid travels from the orifice  19  to the central region  21 . The combined vaporized processing liquid/carrier gas flows from the injection valve  11  via the outlet  17 . As described below with reference to FIG. 2, the preferred embodiment of the inventive gas delivery system employs a plurality of conventional injection valves such as the injection valve  11  of FIG.  1 . 
     FIG. 2 is a schematic diagram of an inventive gas delivery system  31 . The gas delivery system  31  is shown coupled between a source of carrier gas, a helium gas source  33 , and a processing chamber  35 . In the example of FIG. 2, the processing chamber  35  is a CVD chamber configured to deposit silicon dioxide; the silicon dioxide is deposited by flowing TEOS, TEPO and tetraethel borate (TEB) into the processing chamber  35 . The gas delivery system  31 , therefore, comprises three processing liquid vaporization stages  10   a-c . Preferably each vaporization stage comprises an injection valve like the conventional injection valve  11  of FIG. 1, however other vaporization means (e.g., other injection valves, bubblers, etc.) can be employed. 
     The first stage  10   a  comprises a first injection valve  11   a  coupled to a source of liquid TEB  25   a  via a first liquid flow meter  23   a , the second stage  10   b  comprises a second injection valve  11   b  coupled to a source of liquid TEOS  25   b  via a second liquid flow meter  23   b , and the third stage  10   c  comprises a third injection valve  11   c  coupled to a source of liquid TEPO  25   c  via a third liquid flow meter  23   c . Each source of processing liquid  25   a-c  is coupled to a source of pressurized helium  29   a-c  (which may comprise a plurality of sources  29   a-c , as shown, or may comprise a single source). 
     The outlet  17   a  of the first injection valve  11   a , the outlet  17   b  of the second injection valve  11   b , and the outlet  17   c  of the third injection valve  11   c  join at a foreline  37 . Thus, vaporized TEB, TEOS and TEPO are maintained separately within each stage  10   a-c  of the gas delivery system  31 . Each stage  10   a-c  of the gas delivery system  31  therefore is free of the processing liquid reactions discovered by the present inventors, and the resultant residue that plagues conventional gas delivery systems. Specifically, H 3 PO 4 , which is both an impurity found in TEPO and a by-product of the reaction between TEPO and nickel (e.g., the nickel found in various stainless steel components of the gas delivery system  31 ), does not meet and react with TEPO until the H 3 PO 4  reaches the foreline  37 . Residue formed by the TEPO/H 3 PO 4  reaction does not clog the foreline  37  as the passageway through the foreline  37  does not contain small diameter regions and/or small orifices like those found in processing liquid vaporization means such as bubblers and injection valves. The foreline  37  preferably is configured with a large diameter (preferably at least ¼ inch, and most preferably between ⅜ and ½ inch) to further reduce the possibility of clogging. Nonetheless, because the foreline  37  is a simple pipe, it can be quickly and inexpensively cleaned or replaced should clogging occur. 
     The preferred gas delivery system of FIG. 2 supplies carrier gas to each vaporization stage via a single carrier gas source  33  controlled by a single mass flow controller  39 , and thereby minimizes parts and conserves space. Specifically, after the flow controller  39 , the gas delivery system  31  branches in three with a first branch  41   a  coupling to the carrier gas inlet  15   a  of the first injection valve  11   a , a second branch  41   b  coupling to the carrier gas inlet  15   b  of the second injection valve  11   b , and a third branch  41   c  coupling to the carrier gas inlet  15   c  of the third injection valve  11   c . Thus, carrier gas from a single carrier gas source  33  flows to and vaporizes processing liquid within each stage  10   a-c  of the inventive gas delivery system  31 . 
     In operation, helium, an inert carrier gas, flows from the gas source  33  into the flow controller  39 , and the flow controller  39  is set at a first flow rate. As the carrier gas flows into each branch  41   a-c  the mass flow rate within each branch  41   a-c  drops to one third of the first flow rate. Alternatively, the branches  41   a-c  can be configured (e.g., by varying tubing diameter, or by increasing/decreasing the number and degree of bends in each branch, etc.) so that a higher carrier gas flow rate is directed to processing liquids having lower vaporization rates (e.g., TEOS and TEPO). 
     Within each vaporization stage  10   a-c  processing liquid is vaporized as described with reference to FIG.  1 . Thus, a mixture of vaporized TEB and helium flows from the first injection valve  11   a &#39;s outlet  17   a  to the foreline  37 , a mixture of vaporized TEOS and helium flows from the second injection valve  11   b &#39;s outlet  17   b  to the foreline  37 , and a mixture of vaporized TEPO and helium flows from the third injection valve  11   c &#39;s outlet  17   c  to the foreline  37 . The mixture of TEB, TEOS, TEPO and helium flows through the foreline  37  to the processing chamber  35  where the chamber pressure and temperature causes the TEB, TEOS and TEPO to react forming a silicon dioxide layer on a substrate (not shown) positioned within the processing chamber  35 . Because the foreline  37  has no small diameter orifices (i.e., is unrestricted) any residue formed by the mixture of TEB, TEOS and TEPO will not clog the foreline  37 . 
     FIG. 3 is a side elevational view of the foreline  37  of the inventive gas delivery system of FIG.  2 . The present inventors believe that the inventive gas distribution system achieves more uniform concentrations of vaporized processing liquids, and superior mixing among the vaporized processing liquids and the carrier gas, because the vaporized processing liquids intermingle for the first time within a larger diameter region (e.g., within the ½ inch foreline  37  rather than within the ¼ inch lines directly coupled to each injection valve output  17   a-c ). To increase turbulence and mixing within the foreline  37 , the vaporized processing liquids preferably are introduced to the foreline  37  in a spaced relationship as shown in FIG.  3 . The configuration of FIG. 3, with the injection valve outlets  17   a-c  entering the foreline  37  from the sides thereof, is preferred as an inline liquid monitor  42  can be coupled below the outlets  17   a-c . In this manner any residue which forms drops onto the inline liquid monitor  42  allowing the inline liquid monitor  42  to detect when the foreline  37  should be cleaned or replaced. Inline liquid monitors are well known in the art. Accordingly, a suitable inline monitor will be readily apparent to those of ordinary skill in the art. Although the outlets  17   a-c  are shown coupling the foreline  37  at the same level, they may alternatively couple the foreline  37  at varied levels. 
     FIG. 4 is a top plan view of an automated tool  43  for fabricating semiconductor devices. The tool  43  comprises a pair of load locks  45   a ,  45   b , and a first wafer handler chamber  47  containing a first wafer handler  49 . The first wafer handler chamber  47  is operatively coupled to the pair of load locks  45   a ,  45   b  and to a pair of pass-through chambers  51   a ,  51   b . The pair of pass-through chambers  51   a ,  51   b  are further coupled to a second wafer handler chamber  53  (e.g., a transfer chamber), containing a second wafer handler  55 , and to a plurality of processing chambers  57 ,  59 . Most importantly, the second wafer handler chamber  53  is coupled to the processing chamber  35  of FIG. 2 which is further coupled to the inventive gas delivery system  31 . The entire tool  43  is controlled by a controller  61  (which comprises a microprocessor and a memory—not shown) having a program therein, which controls semiconductor wafer transfer among the load locks  45   a ,  45   b , the pass-through chambers  51   a ,  51   b , and the processing chambers  57 ,  59 ,  35 , and which controls processing therein. 
     The controller program and the overall configuration of the tool  43  is designed for optimal productivity. A clogged gas delivery system within such a tool is particularly costly, as it can affect the productivity of the entire tool  43 , including the plurality of processing chambers contained therein. Thus, by employing the inventive gas delivery system  31 , the value of the automated semiconductor processing tool  43  increases significantly. 
     The foregoing description discloses only the preferred embodiments of the invention, modifications of the above disclosed apparatus and method which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, the inventive gas delivery system can be advantageously employed to reduce clogging due to any number of processing liquids. The invention is neither limited to the delivery of merely three processing liquids nor to the delivery of the specific processing liquids described, nor is the invention limited to liquid sources. That is, the present invention may be used to reduce clogging within any processing environment wherein mixed processing constituents form an undesirable reaction product that can clog the various components within a processing constituent delivery system. Further, it will be understood that the exemplary gas delivery system of FIG. 2 may contain additional components (e.g., valves, flow meters, etc.), and the various components of the gas delivery system can be made with reduced nickel content and increased chromium content to further reduce residue formation. Finally, although the benefits of the inventive gas delivery system are most dramatic when used with injection valves, other vaporization mechanisms (e.g., bubblers, etc.) may be employed. 
     Accordingly, while the present invention has been disclosed in connection with the preferred embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.