Abstract:
A highly reliable bulk chemical delivery system for high purity chemicals employing a manifold that ensures contamination free operation and canister change outs with a minimum of valves and tubing.

Description:
RELATED APPLICATIONS 
     This application is a Continuation-In-Part of application Ser. No. 09/013,327 filed Jan. 26, 1998, still pending, which is a CIP of Ser. No. 08/485,968, filed Jun. 7, 1995, now U.S. Pat. No. 5,711,354, which is a CIP of Ser. No. 08/345,244, filed Nov. 28, 1994, now U.S. Pat. No. 5,607,002, which is a CIP of Ser. No. 08/184,226, filed Jan. 21, 1994, now abandoned which is a CIP of Ser. No. 08/054,597, filed Apr. 28, 1993, now U.S. Pat. No. 5,465,766. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The field of the invention relates to chemical delivery systems, in particular manifolds and level sensing schemes for chemical delivery systems, and more particularly, a highly reliable bulk chemical delivery system for high purity chemicals employing a manifold that ensures contamination free operation and canister change outs with a minimum of valves and tubing. 
     BACKGROUND OF THE INVENTION 
     The chemicals used in the fabrication of integrated circuits must have a ultrahigh purity to allow satisfactory process yields. As integrated circuits have decreased in size, there has been a directly proportional increase in the need for maintaining the purity of source chemicals. This is because contaminants are more likely to deleteriously affect the electrical properties of integrated circuits as line spacing and interlayer dielectric thicknesses decrease. 
     One ultrahigh purity chemical used in the fabrication of integrated circuits is tetraethylorthosilicate (TEOS). The chemical formula for TEOS is (C.sub.2 H.sub.5 O).sub.4 Si. TEOS has been widely used in integrated circuit manufacturing operations such as chemical vapor deposition (CVD) to form silicon dioxide films. These conformal films are generated upon the molecular decomposition of TEOS at elevated temperatures and reduced pressures (LPCVD), or at lower temperatures in plasma enhanced and atmospheric pressure reactors (PECVD, APCVD). TEOS is typically used for phosphorous undoped and bottom doped interlayer dielectrics, intermetal dielectrics, sidewall spacers and trench filling applications. 
     Integrated circuit fabricators typically require TEOS with 99.999999+% (8-9&#39;s+%) purity with respect to trace metals. Overall, the TEOS must exhibit a 99.99+% purity. This high degree of purity is necessary to maintain satisfactory process yields. However, it also necessitates the use of special equipment to contain and deliver the high purity TEOS to the CVD reaction chamber. 
     Traditionally, high purity TEOS has been fed to the CVD reaction chamber from a small volume container called, an ampule. Historically, it was strongly believed ampules could not be metallic and that no metal should interface with the high purity TEOS or other source chemicals in the ampule. The use of metal ampules was spurned in the industry on the basis of the belief that high purity TEOS and other high purity source chemicals used in the semiconductor fabrication industry would pick up contamination from the metallic container in the form of dissolved metal ions. Thus, the industry used, almost exclusively, quartz ampules. 
     When these relatively small quartz ampules were emptied, they would simply be replaced with a full ampule. The ampules were not refilled in the fabrication area. The empty ampule was returned to the chemical manufacturer who would clean and refill the ampule. 
     Inconveniences resulting from the use of the quartz ampules are that they require frequent replacement due to their small size, which increases the potential for equipment damage. Furthermore, quartz ampules are subject to breakage, and have limited design versatility. Also, quartz has limited heat capacity making it difficult to control temperature of the ampule. Plus, the lack of effective quartz-to-stainless steel seals created significant leak problems. 
     In an attempt to solve the problem associated with quartz ampules, at least one supplier of ultrahigh purity chemicals, Advanced Delivery &amp; Chemical Systems, Inc., going against the belief in the industry that high purity source chemicals should not be placed in contact with metal, developed a stainless steel ampule. This ampule was used to directly supply high purity TEOS and other high purity source chemicals to semiconductor fabrication equipment. As with the quartz ampules, when it was empty it was not refilled, but rather returned to the supplier for cleaning and refilling. 
     There were still several problems with using the stainless steel ampule. Namely, because of the small size of the these ampules, they often required frequent replacement. Also, an optical sensor employing a quartz rod was used to detect when the high purity TEOS reached a low level inside the ampule. Unfortunately, optical sensors, which employ a light emitting diode and a photodetector in combination with a quartz rod, require a high degree of maintenance because they are subject to misalignment if jostled. Furthermore, the conditioning circuit of the sensor must be constantly tuned because the sensor is subject to calibration drift, which can cause false sensor output signals. These problems can result in allowing the ampule to run dry or causing the premature removal of a partial or full ampule. Another problem with optical sensors is that they are prone to breakage in transport and cleaning, requiring frequent replacement. Despite these problems, optical sensors were used over more reliable metallic float sensor systems because of the fears of contaminating the high purity chemical with metal particles and metal ions. 
     In an attempt to solve the problem of frequent replacement of stainless steel ampules, a larger five gallon stainless steel tank was developed to refill the smaller stainless steel ampule. This tank also used an optical level sensor to detect when the container had been depleted, despite all of the problems associated with optical level sensors. Like the ampule in the previous configuration, this tank was not refilled, but was rather returned to the supplier for cleaning and refilling. Due to the size and weight of the five-gallon tank, it is subject to more physical jarring than the smaller ampules when transported and changed out with empty canisters, thus causing a higher frequency of problems with the traditional optical sensors used to detect a low level of source chemical in the delivery system. 
     Furthermore, in this refill configuration a second optical sensor, with all of the problems associated with such sensors, was required in the ampule to signal when the ampule was full during the refilling process. This, in some cases, required another opening in the ampule which is undesirable, because this introduces additional potential for leaks and contamination points. 
     In an attempt to overcome the problems associated with the optical sensors, a metallic level sensor was employed to detect low levels of high purity chemicals in the five-gallon bulk container. The metallic level sensor generally consisted of a toroidal shaped float made of stainless steel held captive on a hollow shaft made of electropolished stainless steel. The float contained a fixed magnet. A digital reed relay was secured at a fixed position inside the shaft at an alarm trigger point. As the float travelled past the reed relay, the fixed magnet would change its state, thus causing a low level alarm condition to be signaled. A replacement tank would then be substituted. The digital magnetic reed relay used in the metallic float level sensor provided much more reliable detection of low source chemical levels in the remote tank, because the magnetic reed switch is a low maintenance mechanical switch and provides positive on/off switching. As before, the empty 5-gallon container was never refilled by the user. It was always returned to the chemical supplier for cleaning and filling. 
     A low level metallic float sensor has also been used more recently in the stainless steel ampule. Due to fears associated with contamination, however, the ampules were not refilled by the user and were only used in stand alone systems. As with the five-gallon tank, when the metallic level sensor indicated the high purity TEOS or other high purity source chemical level was low, the ampule was simply replaced with a full ampule. In no instance was a metallic level sensor used to detect the level of high purity TEOS or other high purity source chemical in an ampule when the ampule was used in any refill type system. Ampules used in refill type systems have not used a float-type sensor or any other sensor with movable parts. 
     The use of metallic level sensors has been spurned in ampules used in refill type systems because of the strong belief in the industry that sliding metal to metal contact will cause the shedding of metal particles and dissolution of metal ions, thus contaminating the high purity TEOS or other high purity source chemical employed in the delivery system. This belief exists despite the use of low level metal float sensors in stand alone stainless steel five-gallon tanks and in stainless steel ampules. This is because in the stand alone systems, the tank or ampule is exchanged with a replacement tank or ampule, respectively, following each use. Furthermore, following each use, the tank or ampule is cleaned before refilling for a subsequent use. Both the cleaning and refilling are accomplished at a remote location by the supplier of the source chemical. Therefore, the amount a metal float travels in a stand alone system is limited to one fill and drain cycle. On the other hand, in a refill system the ampule is periodically refilled from a remote bulk container after each time it is emptied. Further, in a refill system, the ampule is never completely drained of high purity TEOS or other high purity source chemical between each refilling. Thus, integrated circuit manufacturers and source chemical suppliers have had an unsubstantiated concern that with repeated fillings of the same ampule over a period of time, the metal ion concentration and metal particles in the ampule would increase to an unacceptable level. As a result of this concern, ampules that have been used in refill type systems have always been equipped with the optical sensors or with sensors with non-movable parts, despite the knowledge that metallic float level sensors were much more reliable in refill systems. 
     Because, as noted above, optical sensors require a high degree of maintenance and are subject to frequent failure, the reliability of the bulk chemical refill systems using optical sensors have been in question. When the optical sensor fails to detect a low or “empty” level, the ampule can be ran dry during the CVD process. As previously discussed, this could destroy the batch of wafers then in process or force their rework at a cost of thousands to tens of thousands of dollars. On the flip side, when the optical sensor fails to detect the high or “full” level during a refill cycle, the ampule can be overfilled potentially causing damage to costly equipment; wasting expensive high purity source chemical (high purity TEOS costs approximately $2,000/gal.); contaminating the fabrication area, which is typically a class 1 or class 10 clean room environment; contaminating or damaging other equipment in the clean room; ruining the wafers being processed; and causing severe personal safety concerns. In the past, to avoid these problems semiconductor equipment manufacturers have used refill systems with redundant optical level sensors to minimize the impact of sensor malfunctions, used other level sensor types, excluding float type sensors described, employed a timed refill, the refill of a small fixed volume or the refill of a measured mass of chemical. These refill systems suffer characteristic performance problems arising from: non-linearity of alternate sensor technology, uncertainty of the refill volume, the lack of a positive shut-off of the chemical fill, the risk of malfunction due to maladjustment of system components or the lack of level monitoring of the bulk chemical source. Therefore, a need exists for a reliable bulk chemical refill system for applications where a high degree of chemical purity must be maintained, and a high level or error free refill confidence must exist. 
     SUMMARY OF THE INVENTION 
     The present invention provides manifolds and level sensing schemes for chemical delivery systems, and more particularly, a highly reliable bulk chemical delivery system for high purity chemicals employing a manifold that ensures contamination free operation and canister change outs with a minimum of valves and tubing. The present invention substantially eliminates or reduces disadvantages and problems associated with previously developed level sensing schemes for chemical delivery systems. 
     Accordingly, it is an object of the present invention to provide a bulk chemical delivery system for among other chemicals, high purity chemicals of the type described above, but which uses a highly reliable manifold and method for using the manifold in a bulk chemical delivery system. 
     Through the unique set up of piping and valves and their method and sequence of operation, bulk canisters can be replaced without fear of contamination. This is especially useful in refillable high purity chemical bulk delivery systems. 
    
    
     The above and other objects, features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features and wherein: 
     FIG. 1 is a schematic representation of a high purity chemical refill delivery system according to one embodiment of the present invention; 
     FIG. 2 is a front view of a control unit control panel according to one embodiment of the present invention; 
     FIG. 3 is a side view in partial cross section of a five-gallon high purity chemical container; 
     FIG. 4 is a schematic representation of a single level float control sensor in the “open” position of one embodiment; 
     FIG. 5 is a schematic representation of a single level float level sensor in the “closed” position of one embodiment of the present invention; 
     FIG. 6 is a side view in partial cross-section of a refillable ampule according to one embodiment of the present invention; 
     FIG. 7 is a top view of the ampule illustrated in FIG. 6; 
     FIG. 8 is a schematic side view in partial cross-section of a refillable ampule according to another embodiment of the present invention; 
     FIG. 9 is a side view of a metallic level switch assembly for a refillable container according to a preferred embodiment of the present invention; 
     FIG. 10 is a side view of metallic level switch assembly for a refillable container according to another embodiment of the present invention; 
     FIG. 11 is a side view of metallic level switch assembly for a bulk container according to one embodiment of the present invention; 
     FIG. 12 is a side view of a metallic level switch assembly for a bulk container according to another embodiment of the present invention; 
     FIG. 13 is a schematic diagram of typical prior art conditioning circuitry for interfacing an optical level sensor with existing semiconductor processing equipment; 
     FIG. 14 is an electrical schematic diagram of a prior art optical level sensor; 
     FIGS. 15,  15 A and  15 B are a schematic diagram of control circuitry for a control unit; 
     FIG. 16 is a front view of a manifold layout according to one embodiment of the present invention; and 
     FIG. 17 is a front view of a manifold layout for an embodiment of the present invention. 
     FIG. 18 is a schematic view of a manifold layout for the preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention are illustrated in the FIGUREs, like numerals being used to refer to like and corresponding parts of the various drawings. 
     A preferred embodiment of a high purity chemical refill system is described in connection with FIG.  1 . The system consists of three main functional components: a bulk canister  20  located in a remote chemical cabinet with a delivery manifold/purge panel  22 ; a refillable stainless steel ampule  30  to supply semiconductor fabrication equipment such as a CVD reactor with high purity TEOS or other high purity source chemicals; and a control unit  40  to supervise and control the refill operation and to monitor the level of the bulk container. 
     Bulk chemical refill system  18  has two basic modes of operation: a normal process operation and a refill mode of operation. Under normal process operation, refillable ampule  30  delivers high purity TEOS or other high purity source chemicals to semiconductor fabrication equipment fabrication equipment via outlet passage  32 . Outlet passage  32  is connected to the semiconductor processing equipment using conventional process connections. 
     In this embodiment the refillable ampule  30  incorporates an optical sensor  34  for communicating a low level signal to the CVD reactor through the conventional low level sensor/reactor interface circuit shown in FIG.  13 . When a low level signal is communicated to the fabrication equipment, the equipment will employ the signal in accordance with its normal conventional operation, such as its normal low level default procedure. 
     FIG. 2 illustrates a preferred arrangement of control panel  52  of control unit  42 . Control panel  52  contains five switches: a “MAIN POWER” on off switch, a “PUSH TO TEST INDICATORS” switch, an “ABORT FILL” switch, a “PUSH TO FILL” switch, and a “PUSH SONIC OFF” switch. The operation of these switches is described in detail in conjunction with FIGS. 15,  15 A and  15 B below. 
     Control panel  52  also includes a number of illuminated indicators to report the status of chemical levels in bulk container  20  and ampule  30 . The illuminated indicators include “BULK OK”, “BULK LOW”, “BULK EMPTY”, “AMPULE REFILLING”, “AMPULE NOT REFILLING”, “AMPULE HIGH—HIGH LEVEL”, and “AMPULE HIGH LEVEL”. 
     A preferred method of operation of control unit  40  during normal process operation is described in connection with FIG.  2 . During normal process operation, the level of source chemical in bulk container  20  should not change. Therefore, the “BULK OK” indicator should remain lit. However, if the “BULK LOW” or “BULK EMPTY” indicator came on during the last refill cycle, these indicators will remain illuminated until the bulk container  20  is replaced with a full container. The operation of the level sensors in bulk container  20  is explained in more detail below. 
     Throughout normal process operation, the “AMPULE NOT FILLING” indicator should remain on to indicate that the refill system is not in the refill mode. Because the level of high purity TEOS or other high purity source chemical in refillable ampule  30  changes throughout normal process operation, the “AMPULE HIGH” level indicator, which is illuminated upon completion of a refill cycle, will remain illuminated until the high purity TEOS or other high purity source chemical level in refillable ampule  30  falls below the “AMPULE HIGH” trigger point  41  of metallic level sensor  39 . 
     It should be noted that if the “AMPULE HIGH—HIGH” indicator was illuminated during the refill process, as with the “AMPULE HIGH” indicator, the “AMPULE HIGH—HIGH” indicator will remain on until the high purity source chemical in ampule  30  falls below the “HIGH—HIGH” trigger point  41   a  of metallic level sensor  39 . In such a case, the chemical level will fall through the “AMPULE HIGH” trigger region thus causing the “AMPULE HIGH” indicator to illuminate and then extinguish as described above. 
     The refill procedure is started either automatically or semiautomatically. The semiautomatic procedure begins by the operator manually configuring ampule  30  to the refill configuration. This is done by closing the outlet valve  36  on the ampule  30 . In addition, the operator would verify that the inlet valve  38  is closed. 
     Because the high purity TEOS or other high purity source chemical is supplied under pressure to some CVD reactors by an inert gas such as He during normal operation, the ampule  30  may need to be depressurized and a vacuum pulled to ease the high purity TEOS or other high purity source chemical transfer process. The depressurization and degassing process are accomplished using standard techniques utilized in the chemical vapor deposition art through passage  31 . After the depressurization step, the vacuum/pressurization valve  37  is closed. Inlet valve  38  is now opened to allow the flow of high purity TEOS or other high purity source chemical into ampule  30 . The pressurization would be unnecessary for other applications where pressurization of the headspace of ampule  30  would not present a problem. 
     The semiautomatic refilling process requires an operator to depress the “PUSH TO FILL” switch on control panel  52  of control unit  40  shown in FIG.  2 . Once the “PUSH TO FILL” switch is pushed, the control unit  40  opens a valve  42  in the refill line  44 . High purity TEOS or other high purity source chemical, depending on the application, then flows into the ampule  30  from the bulk container  20 . 
     Valve  42  is preferably a pneumatically activated valve. When a pneumatically activated valve is used for valve  42 , it is opened when a control pressure is supplied through passage  46  from control unit  40 . The control pressure used to open valve  42  can be nitrogen or other pressurization gas such as plant compressed dry air. The flow of a control pressure through passage  46  is controlled by solenoid valves in control unit  40 . The operation of these solenoid valves is described in detail below in conjunction with FIGS. 15,  15 A and  15 B. 
     Bulk container  20  is continuously pressurized with an inert gas such as helium; thus, when valve  42  is opened, inert gas forces the high purity source chemical from bulk container  20  through refill line  44  and to the ampule  30 . 
     Metallic level sensor assembly  21  in ampule  30  contains a high level metallic level sensor  39 . Metallic level sensor  39  is preferably a dual level sensor capable of detecting two separate levels of source chemical in ampule  30 . However, metallic level sensor  39  can also be a single level sensor, or a multiple trigger point level sensor up to a continuous level sensor. In the preferred embodiment metallic level sensor  39  is a dual level sensor with two trigger points,  41  and  41   a.  Trigger point  41  is for detecting a “HIGH LEVEL” (full) condition in ampule  30 , and trigger point  41 ( a ) detects a “HIGH—HIGH LEVEL” condition in ampule  30 . 
     When the metallic level sensor  39  detects that the ampule  30  is full, it supplies a signal to the control unit  40  via cable  47 . In response to that signal control unit  40  closes pneumatic valve  42  without operator intervention. Simultaneously, control unit  40  signals an audible and visual alarm on control panel  52 . If the “HIGH LEVEL” trigger point  41  of metallic level sensor  39  should fail, the “HIGH—HIGH LEVEL” trigger point  41   a  of metallic level sensor  39  is in place and will trigger and instruct control unit  40  that the ampule  30  is full via cable  47  by an independent circuit within the control unit  40 . This “HIGH—HIGH” alarm is a fail safe feature that prevents overfilling the ampule  30  and stops refilling in case of electrical failure of the “HIGH LEVEL” alarm circuit and is described below in connection with FIGS. 15,  15 A and  15 B. Obviously, if metallic level sensor  39  is only a single level sensor, only a “HIGH LEVEL” condition can be detected, and no fail safe level detection is provided. Additionally, when the metallic level sensor  39  detects that the ampule  30  is at a low level, such as at trigger points described below, a signal may be supplied to the control unit  40  to open the pneumatic valve  42  with or without operator intervention. 
     Control unit  40  also interfaces with a metallic level sensor assembly  21  in bulk container  20  via cable  26 . The metallic level sensor  39  in the remote bulk container has its trigger points preferably set at 20% remaining source chemical and at 5% remaining source chemical. Depending on specific process requirements, however, other trigger points can be used. If the source chemical level falls below the first trigger point, which typically only occurs during the refilling sequence, a visual indication of “BULK LOW” on the control panel  52  of control unit  40  is produced. If the source chemical level falls below the second trigger point, a “BULK EMPTY” visual alarm on control panel  52  in addition to an audible alarm is produced in conjunction with an automatic termination of the refill sequence. 
     Control unit  40  can also be configured for manual shut off during the refill cycle. In such a configuration, the operator would terminate the refill cycle by manually depressing a button on control panel  52  upon acknowledging a visual or audible indication that the refillable ampule  30  is full. Similarly, a fully automatic start/automatic shut off configuration can be provided. This can be accomplished by replacing manual vacuum/pressurization valve  37  with an automatic valve preferably pneumatic, and placing a pressure sensor in the passage  31  to ampule  30 . The pneumatic valve and pressure sensor are then connected to control unit  40 . When a specified vacuum is pulled on ampule  30  at the beginning of the refill cycle to ease the flow of high purity source chemical into ampule  30 , the pressure sensor in passage  31  would signal control unit  40 . In response, control unit  40  would close the pneumatic valve  37  and simultaneously open pneumatic valve  42  in the refill line  44 , thus automatically initiating the refill process. 
     A particularly preferred bulk container  20  will now be described in connection with FIG.  3 . Bulk container  20  is made of 316L electropolished stainless steel to minimize the risk of contamination to the high purity source chemical contained within the tank. Bulk container  20  typically comes in a five-gallon capacity. However, larger capacity canisters can be used for bulk container  20 , including ten and twenty-gallon containers. Smaller containers may be used too, for example, one and two-gallon containers. Bulk container  20  is used to supply a bulk high purity source chemical such as high purity TEOS from a remote location to ampule  30 . The source chemical is delivered by continuous pressurization of the canister with inert gas such as helium for on demand refill of the refillable ampule  30 . The inert gas is supplied through the inlet valve  64 . Inlet valve  64  is connected to and communicates with passage  88  of the delivery/purge manifold  22  which is in communication with an inert gas source. The outlet valve  66  also connects to the refill line  44  by way of manifold  22 . Thus when container  20  is pressurized with helium gas or another suitable gas and pneumatic valve  42  is opened, high purity TEOS or other high purity source chemical is forced through outlet pipe  60 , outlet valve  66 , manifold  22 , refill line  44 , inlet valve  38  and into refillable ampule  30 . 
     In one embodiment, bulk container  20  is provided with a metallic level sensor assembly  21  including a metallic level sensor  39  preferably comprised of a two pole reed switch triggered by a metallic float  24 . It is understood that other types of triggers, such as a Hall effect sensor may be employed. The two-pole reed switch interfaces directly with control unit  40  through cable  26 . Metallic level sensor  39  preferably is a dual level sensor, in that it incorporates two reed switches. As with the metallic level sensor  39  in refillable ampule  30 , however, it can incorporate any desirable number of reed switches to detect one or more levels of source chemical. Further any number of separate metallic level sensors  39 , each employing their own metallic float  24  may be employed. 
     The principle of operation behind metallic level sensor  39  is described in connection with the single level metallic level sensor  39  illustrated in FIGS. 4 and 5. Metallic level sensor  39  is comprised of a toroidal shaped metallic float  24  made of stainless steel or other non-magnetic, chemically inert material. Alternatively, metallic float  24  is coated with a fluoropolymer or other chemically inert coating. The preferred construction material is 316L stainless steel. Metallic float  24  contains a fixed magnet  23  and is held captive on a hollow metallic shaft  28 . Shaft  28 , however, is sealed on its bottom and extending into ampule  30  to prevent high purity source chemical from flowing up into the shaft. Further, metallic shaft  28  is preferably made of electropolished 316L stainless steel or other chemically inert material. Alternatively, shaft  28  is made of a non-magnetic material coated with a fluoropolymer or other chemically inert material. Inside shaft  28 , a digital magnetic reed relay switch RS is secured in a fixed position at a predetermined alarm trigger point. This trigger point corresponds, for example, to the “BULK EMPTY” trigger set point. A ferrule  46  is permanently attached to one end of shaft  28  for attachment to the container. 
     Additional reed relay switches RS may be added within shaft  28  to form a multiple level detector. For example, if a second reed relay switch RS is added at second fixed trigger point within shaft  28  a dual level float sensor is created. Additional reed relay switches RS may be added for any number of additional levels of detection. 
     Retainer rings  27  are used to restrain the movement of the metallic float  24  so that upon filling of bulk container  20 , the float is restrained from sliding up the entire length of shaft  28 , and sliding back down the entire length of shaft  28  as bulk container  20  is drained. It should be noted that, if desired the upper retainer ring  27  may be eliminated in this configuration. Only the lower retainer ring  27  is necessary to prevent metallic float  24  from sliding off shaft  28 . Retainer rings  27  are also preferably constructed from 316 stainless steel, Kalrez.™. or other suitable, chemically inert material. 
     Metallic level sensor assembly  21  comprising shaft  28 , metallic float  24  and retainer ring  27  is preferably electropolished following assembly. In addition, the surface finish of all wetted metal parts is preferably Ra 20 or better prior to electropolishing. 
     Metallic level sensor  39  works as follows, when the liquid source chemical is above the upper retainer ring, the metallic float  24  remains at the top ring  74  in the “float up” position. As the liquid level drops, metallic float  24  moves down the shaft  28 . When the magnetic field from fixed magnet  23  latches the magnetic reed switch RS, metallic float  24  is in the “float down” position. When the magnetic reed switch is closed, the indicator circuit is completed. This output signal is transmitted through one of two wires  25  in cable  26  to an alarm circuit in control unit  40 . 
     FIGS. 4 and 5 illustrate the use of a normally open magnetic reed switch RS. Alternatively, however, a normally closed magnetic reed switch can be used. In such a case, as the metallic float  24  travels pass the reed relay, the fixed magnet  23  will open the reed relay switch RS. Thus, the alarm condition is signaled either by opening the closed relay contacts or by closing the open reed relay contacts. 
     As discussed above, in the preferred embodiment, a dual level metallic sensor  39  is utilized. A dual level metallic sensor  39  is provided simply by securing a second digital magnetic reed relay switch RS at a desired alarm trigger point. The single metallic float  24  on shaft  28  can trigger both reed switches. If a dual level metallic sensor is used, four wires are found in cable  27  and are used to communicate the state of the switches to the control unit  40 . Preferably, the second trigger point should be set for 20% source chemical remaining. In the preferred embodiment, this corresponds to the “BULK LOW” trigger point. 
     A second sensor configuration could incorporate a fixed magnet  23  inside a float made of the same materials as metallic float  24  and attached to shaft  28  by means of a hinge. As the float swivels, it brings the fixed magnet into proximity of a reed relay switch RS and changes the state of the reed relay from open to closed or closed to open. 
     Refillable ampule  30  can now be described in connection with FIGS. 6 and 7. Refillable ampule  30  is preferably made from 316L electropolished stainless steel construction. Typically, ampule  30  has a 2.3 liter capacity, but can be provided in a wide range of sizes, including 1.3 liter, 1 gallon, 1.6 gallons, 2 gallons, and 5 gallons. The size of the ampule merely depends on process demands. 
     Vacuum/pressurization valve  37  permits refillable ampule  30  to be pressurized with an inert gas such as helium during normal process operation, which is typical of many CVD ampules. This valve also has the function of permitting the depressurization and application of a vacuum to ampule  30  prior to a refill sequence or removal of ampule  30  from the system  18 . 
     Outlet valve  36  connects refillable ampule  30  to a delivery line  32  that supplies liquid high purity TEOS or other high purity source chemical directly to the semiconductor processing equipment during normal process operation. Thus, during normal process operation, helium or other inert pressurizing gas is supplied through vacuum/pressurization valve  37  to pressurize ampule  30 . The pressure applied to the internal cavity of ampule  30  forces high purity TEOS or other high purity source chemical through hollow pipe  33  and outlet valve  36  to delivery line  32  that feeds a CVD reaction chamber. It should be noted that the entirety of pipe  33  is not shown on the drawing to allow the optical sensor assembly  45  to be seen. Normally the pipe  33  extends below the end of the optical sensor  34  to allow for proper operation of the system. 
     In the depicted embodiment, low level sensor  34  is an optical sensor. It is of the type commonly used with standard CVD processing equipment, and need not be explained in detail. An electrical schematic diagram of the optical sensor  34  is illustrated in FIG.  14 . Low level optical sensor  34  sends signals through cable  35  to an independent alarm module, the display panel for the reactor itself, or through a temperature controller, but not through control panel  40 . Because low level sensor  34  is an optical sensor in the present embodiment of the invention, it can interface with the semiconductor processing equipment, independent alarm module or temperature controller using the existing circuitry illustrated in FIG. 13 for interfacing a low level optical sensor with a reactor, independent alarm module, or temperature controller. 
     Inlet valve  38  is a manual shut-off valve for the refill line  44 . Valve  38  remains closed during normal process operation and is opened only during a refill sequence. In the fully automatic process this is an automatic valve, preferably pneumatically activated. 
     Metallic level sensor assembly  21  contains at least a single level metallic sensor level  39 . Preferably, however, metallic level sensor  39  is a dual level sensor for detecting “HIGH LEVEL” and “HIGH—HIGH LEVEL” respectfully. The metallic level sensor  39  of the metallic level sensor assembly  21  operates in the same manner as described in connection with FIGS. 4 and 5. Metallic level sensor  39  illustrated in FIG. 6 is a dual level sensor with trigger points at “HIGH LEVEL”  41  and “HIGH—HIGH LEVEL”  41   a.    
     A particularly preferred refillable ampule  30  is illustrated in FIG.  8 . The ampule  30  in FIG. 8 has two metallic level sensor assemblies  21 , each comprising a metallic level sensor  39 . The first  55  is for detecting high level conditions. As before, preferably metallic level sensor  39  is a dual level sensor as described in FIG.  6 . The second  58  detects a low level condition. Low level metallic level sensor  58  is a single level float sensor that signals the CVD reactor, an independent alarm module, or a temperature control unit that the source chemical level with in ampule  30  has reached a low level, terminating normal process operations. Cable  35  carries two wires. These two wires are used to interface with the semiconductor processing equipment. In particular, the two wires are connected across pins  1  and  2  of the interface circuitry depicted in FIG.  13 . When the metallic level sensor  39  is employed, pin  3  is left floating. 
     As is apparent from the above discussion, metallic level sensor assembly  21  can have a number of configurations. FIGS. 9-12 illustrate just a few of the available preferred configurations. 
     FIG. 9 illustrates a metallic level sensor assembly  21  for refillable ampule  30  comprising a metallic level sensor  39  with two trigger points a “HIGH LEVEL” trigger point  41  and a “HIGH—HIGH” level trigger point  41   a.    
     FIG. 10 illustrates a metallic level sensor assembly  21  for refillable ampule  30  comprising two metallic level sensors  39 . The first  49  is a dual level sensor as described in FIG.  9 . The second  50  detects a low level condition. Low level metallic level sensor  50  is a single level float sensor that signals the CVD reactor, an independent alarm module, or a temperature control unit that the source chemical level with in ampule  30  has reached a low level, terminating normal process operations. High level metallic level sensor  49  is a dual level float sensor with two trigger points a “HIGH LEVEL” trigger point  41  and a “HIGH—HIGH” level trigger point  41   a  as previously described. This configuration has an advantage in that only one hole must be provided in the lid  43  of ampule  30  for the source chemical level sensors, thus reducing the potential for contamination of source chemical. The cable  35  carries six wires. Four of these wires terminate in the control panel as indicated in FIGS. 15,  15 A and  15 B and two are used to interface with the semiconductor processing equipment. In particular, the two wires are connected across pins  1  and  2  of the interface circuitry depicted in FIG.  13 . When the metallic level sensor  39  is employed, pin  3  is left floating. 
     FIG. 11 illustrates a metallic level sensor assembly  21  for a bulk container  20  comprising a dual level metallic level sensor  39  with trigger points set at a “BULK EMPTY” trigger point and at a bulk full trigger point. The bulk full trigger point is used by the supplier of the high purity source chemical to fill bulk container  20  after cleaning and servicing the tank. 
     FIG. 12 illustrates a metallic level sensor assembly  21  for a bulk container  20  comprising a triple level metallic level sensor  39  with trigger points set to detect the following level conditions: “BULK EMPTY”, “BULK LOW”, and “BULK FULL”. Again, the bulk full trigger point is used by the supplier to the high purity source chemical to fill bulk container  20  after cleaning and servicing the tank. 
     The manner in which metallic level sensor assembly  21  is attached to ampule  30  is described in connection with FIGS. 8-12. A ferrule  46  is permanently attached to one end of shaft  28  for attachment of the metallic sensor assembly  21  to ampule  30 . Ferrule  46  is preferably constructed from 316L stainless steel, and the preferred method of attachment is welding. 
     Metallic level sensor assembly  21  is attached to ampule  30  using ferrule  46  in conjunction with clamp  61 . Clamp  61  is preferably a flange clamp of the type used for sanitary piping. Clamp  61  is used to clamp flange surface  62  of ferrule  46  against a mating flange surface on a pipe  63  extending out of the top of ampule lid  43 . Clamp  61  is tightened around ferrule  46  and the mating flange on pipe  63  by tightening knob  65 . A teflon O-ring  67 , which is interposed between the mating flange surfaces, is compressed as clamp  61  is tightened, thereby providing leak tight seal. 
     Alternatively, metallic level sensor assembly  21  can be attached to ampule  30  by welding a threaded connector plug to shaft  28 . The threaded connector plug would then be threaded into a mating female connector on lid  43  of ampule  30 . 
     The operation of control unit  40  will now be described in connection with FIGS. 1,  2 ,  15 ,  15 A and  15 B. 
     Connection to the 110 V.A.C. 60 Hz. Plant Power is made via a standard U-ground male plug of the AC Cord Set CS 1 . Cord set CS 1  plugs into the filter assembly L 1 . Filter L 1  provides line conditioning for both incoming and outgoing transients and connects the AC power to the main power switch SW 1 . Filter L 1  also provides the chassis ground connection. 
     Main power switch SW 1 , is a Double Pole Double Throw (DPDT) toggle switch located on the upper left-hand corner of the control panel  52  of the control unit  40 . Both the hot and neutral sides of the AC line are switched ON and OFF. Switched AC power is connected to the Fuse F 1  through main power switch SW 1 . Fuse F 1  is ¾ AMP, 3 AG size (¼″.times.{fraction (11/4)}″), standard blow fuse mounted inside control unit  40 . 
     Conditioned, switched, and fused AC power is connected to the AC input of the linear power supply PS 1 . Power supply PS 1  is located inside the control unit  40  and provides regulated 24 V.D.C. power for the control unit  40  circuitry. 
     The “BULK LOW” circuit  83  will be described first. 
     When the level of source chemical in bulk container  20  is above the “LOW LEVEL” trigger point, float  24  is floated up and the “BULK LOW” sensor reed switch RS 1 , is open and the “BULK LOW” indicator LED 1  is off. (It should be noted that the reed switches are only shown in representative form as being inside the control panel. In reality the reed switches are in respective containers in the metallic level sensor assemblies  21 .) 
     When the level of product in bulk container  20  goes below the “LOW LEVEL” trigger point, float  24  floats down and the “BULK LOW” sensor reed switch RS 1 , is closed and the “BULK LOW” indicator LED 1  is turned on. 
     With respect to the “BULK EMPTY” circuit  85 , when the level of product in bulk container  20  is above the “EMPTY LEVEL” trigger point, float  24  is floated up and the “BULK EMPTY” sensor reed switch RS 2  is open, and the control relay RY 1  coil (pins  2  to  7 ) is deenergized. When RELAY RY 1  is deenergized, the normally open contacts (N.O.) (pins  8  to  6 ), are open, and the “BULK EMPTY” indicator LED 2  is off. When relay RY 1  is deenergized, the normally closed (N.C.) contacts (pins  8  to  5 ) are closed and the “BULK OK” indicator LED 3  is on. When relay RY 1  is deenergized, the N.C. contacts (pins  1  to  4 ) are closed and the refill circuit is made. 
     When the level of product in the Bulk Container goes below the “EMPTY LEVEL” trigger point, the float  24  floats down and the “BULK EMPTY” sensor reed switch RS 2  is closed, and the control relay RY 1  coil (pins  2  to  7 ) is energized. When relay RY 1  is energized, the N.O. contacts (pins  8  to  6 ) close and the “BULK EMPTY” indicator LED 2  is turned on. When relay RY 1  is energized, the N.C. contacts (pins  8  to  5 ) open and the “BULK OK” indicator LED 3  is turned off. When relay RY 1  is energized, the N.C. contacts (pins  1  to  4 ) open and the refill circuit is broken. 
     The ampule “HIGH—HIGH LEVEL” circuit  86  is now described. 
     When the level of product in the ampule  30  is below the “HIGH—HIGH LEVEL”, the float  24  of dual level metallic level sensor  39  is floated down with respect to the “HIGH—HIGH LEVEL” trigger point  41   a,  and the ampule  30  “HIGH—HIGH” sensor reed switch RS 3  is open. Thus, the control relay RY 2  coil (pins  2  to  7 ) is deenergized. When relay RY 2  is deenergized, the N.O. contacts (pins  8  to  6 ) are open and the “AMPULE HIGH—HIGH” indicator LED 4  is off. When relay RY 2  is deenergized, the N.O. contacts (pins  8  to  6 ) are open and the N.O. coil of air control valve V 1  is deenergized and valve V 1  is open. When relay RY 2  is deenergized, the N.C. contacts (pins  1  to  4 ) are closed and the refill circuit is made. 
     When the level of product in ampule  30  goes above the “HIGH—HIGH LEVEL” trigger point  41   a,  the float  24  of dual level metallic level sensor  39  floats up with respect to the “HIGH—HIGH LEVEL” trigger point  41   a,  and the ampule  30  “HIGH—HIGH” sensor reed switch RS 3  is closed. Thus, control relay RY 2  Coil (pins  2  to  7 ) is energized. When relay RY 2  is energized, the N.O. contacts (pins  8  to  6 ) close and the “AMPULE HIGH—HIGH” indicator LED 4  is turned on. When relay RY 2  is energized, the N.O. contacts (pins  8  to  6 ) close and the N.O. coil of control solenoid valve V 1  is energized and valve V 1  closes, stopping the refill cycle. When relay RY 2  is energized, the N.C. contacts (pins  1  to  4 ) open and the refill circuit is broken. 
     With respect to the “AMPULE HIGH” circuit  87 , when the level of product in ampule  30  is below the “HIGH LEVEL” trigger point  41 , the float of dual level float sensor  39  is floated down with respect to the “HIGH LEVEL” trigger point  41 , and the “AMPULE HIGH” sensor reed switch RS 4  is open. Thus, the control relay RY 3  coil (pins  2  to  7 ) is deenergized. When relay RY 3  is deenergized, the N.O. contacts (pins  8  to  6 ) are open and the “AMPULE HIGH” indicator LED 5  is off. When relay RY 3  is deenergized, the N.C. contacts (pins  1  to  4 ) are closed and the refill circuit is made. 
     When the level of source chemical in the ampule  30  goes to or above the “HIGH LEVEL” trigger point  41 , the float  24  of dual level metallic level sensor  39  floats up and the “AMPULE HIGH” sensor reed switch RS 4 , is closed and the control relay RY 3  coil (pins  2  to  7 ) is energized. When relay RY 3  is energized, the N.O. contacts (pins  8  to  6 ) close and the “AMPULE HIGH” indicator LED 5  is turned on. When relay RY 3  is energized, the N.C. contacts (pins  1  to  4 ) open and the refill circuit is broken. 
     Refill circuit  82  is now described. Before the refill cycle begins, the “PUSH TO FILL” switch SW 2  is open, the “ABORT FILL” switch SW 3  is closed, the control relay RY 4  coil (pins  2  to  7 ) is deenergized, the N.C. contacts (pins  8  to  5 ) are closed and the “AMPULE NOT FILLING” indicator LED 7  is on, the N.O. contacts (pins  8  to  6 ) are open and the “AMPULE REFILLING” indicator LED 6  is off, the N.O. contacts (pins  8  to  6 ) are open and the N.C. coil of air control valve V 2  is deenergized, and solenoid valve  12  is closed. When the N.C. solenoid valve V 2  is closed, there is no control pressure supplied to pneumatic valve  42  through passage  40 . 
     To start the refill cycle, the “PUSH TO FILL” switch SW 2  is momentarily pushed closed, the coil of control relay RY 4  (pins  2  to  7 ) is energized through the N.C. contacts of SW 3 , RY 1  (pins  1  to  4 ), RY 2  (pins  1  to  4 ), RY 3  (pins  1  to  4 ). As RY 4  energizes, N.O. contacts (pins  1  to  3 ) close. This energizes relay RY 4  and latches it in the energized state. “PUSH TO FILL” switch SW 2  may now be released. 
     The refill cycle continues with RY 4  energized, the N.C. contacts (pins  8  to  5 ) are open and the “AMPULE NOT FILLING” indicator LED 7  is turned OFF. Also, the N.O. contacts (pins  8  to  6 ) are closed, and the “AMPULE REFILLING” indicator LED 6  is turned on. Finally, the N.O. contacts (pins  8  to  6 ) are closed and the N.C. solenoid valve V 2  is energized and the valve is opened. When the N.C. solenoid valve V 2  is opened, control pressure is supplied through passage  46  to pneumatic valve  42 , opening pneumatic valve  42 . Source chemical from bulk container  20  can now flow through refill line  44  to ampule  30 . 
     The end of the refill cycle occurs in one of six (6) ways: 
     MODE 1: Control pressure failure: Pneumatic valve  42  closes, ending the refill cycle. 
     MODE 2: Power Failure: The N.C. solenoid valve V 2  is de-energized and solenoid valve V 2  is closed. When the N.C. solenoid valve V 2  is closed, no control pressure is supplied through passage  46  to pneumatic valve  42 . Thus, pneumatic valve  42  closes, ending the refill cycle. 
     MODE 3: ABORT FILL: If an operator presses the “ABORT FILL” switch SW 3 , which is a push-button switch, the refill circuit  82  is broken. Control relay RY 4  de-energizes, N.O. contacts (pins  8  to  6 ) open, and N.C. solenoid valve V 2  is de-energized, cutting off the flow of control pressure to pneumatic valve  42  and ending the refill cycle. 
     MODE 4: BULK EMPTY: If the level of product in the bulk container  20  goes below the “EMPTY LEVEL” trigger point, the float of dual level float sensor  24  floats down with respect to the “EMPTY LEVEL” trigger point, and the “BULK EMPTY” sensor reed switch RS 2  closes. As a result, the control relay RY 1  coil (pins  2  to  7 ) is energized, N.C. contacts (pins  1  to  4 ) open, and the refill circuit  82  is broken. This causes control relay RY 4  to de-energize, N.O. contacts (pins  8  to  6 ) to open, and N.C. solenoid valve V 2  is de-energized, closing solenoid valve V 2 . When the N.C. solenoid valve V 2  closes, no control pressure is supplied through passage  46  to pneumatic valve  42 . Thus, pneumatic valve  42  closes, ending the refill cycle. 
     MODE 5: AMPULE HIGH—HIGH: If the level of source chemical in ampule  30  goes above the “HIGH—HIGH LEVEL” trigger point  41   a,  the float of dual level float sensor  39  floats up with respect to the “HIGH—HIGH LEVEL” trigger point  41   a,  and the “HIGH—HIGH” sensor reed switch RS 3  closes. In turn, the coil of control relay RY 2  (pins  2  to  7 ) is energized, the N.O. contacts (pins  8  to  6 ) close, and the N.O. solenoid valve V 1  is energized, closing the valve. When the N.O. solenoid valve V 1  is closed, no control pressure can be supplied through passage  46  to pneumatic valve  42 , thus ending the refill cycle. Additionally, when relay RY 2  is energized, the N.C. contacts (pins  1  to  4 ) open, and the refill circuit  82  is broken. As a result, control relay RY 4  de-energizes, N.O. contacts (pins  8  to  6 ) open, N.C. solenoid valve V 2  is de-energized, causing solenoid valve V 2  to close. When N.C. solenoid valve V 2  is closed, no control pressure can be supplied through passage  46  to pneumatic valve  42 , thus ending the refill cycle. 
     MODE 6: AMPULE HIGH: If the level of source chemical in the ampule  30  goes to or above the “HIGH LEVEL” trigger point  41 , the float of dual level float sensor  39  floats up with respect to “HIGH LEVEL” trigger point  41 , and the “AMPULE HIGH” sensor reed switch RS 4  closes. In turn, the coil of control relay RY 3  (pins  2  to  7 ) is energized. When relay RY 3  is energized, the N.C. contacts (pins  1  to  4 ) open, and the refill circuit  82  is broken. As a result, control relay RY 4  deenergizes, N.O. contacts (pins  8  to  6 ) open, N.C. solenoid valve V 2  is de-energized, causing the valve to close. When the N.C. solenoid valve V 2  is closed, no control pressure is supplied to pneumatic valve  42 , ending the refill cycle. 
     Sonic circuit  84  is now described in connection with FIGS. 2,  15 ,  15 A, and  15 B. When the “MAIN POWER” switch SW 1  is first turned ON, the sonic circuit  84  will self-test and an audible signal will be heard. The sonic transducer S 1  is powered by the circuit through the N.C. contacts (pins  8  to  5 ) of relay RY 4 , through the N.C. contacts (pins  8  to  5 ) of relay RY 5 , and through Diode D 17 . The Operator presses the “PUSH SONIC OFF” switch SW 4  to silence the audible signal. 
     When the “PUSH SONIC OFF” switch SW 4  is momentarily closed, the Control relay RY 5  coil (pins  2  to  7 ) is energized. As a result, N.C. contacts (pins  8  to  5 ) open, and the audible signal is turned off. Also, N.O. contacts (pins  1  to  3 ) close. When relay RY 5  is energized, N.O. contacts (pins  1  to  3 ) are latched. “PUSH SONIC OFF” switch SW 4  may now be released and the audible signal will stay off. 
     At the start of the refill cycle, control relay RY 4  energizes. In turn, N.C. contacts (pins  1  to  4 ) and N.C. contacts (pins  8  to  5 ) open, de-energizing and un-latching control relay RY 5  and simultaneously removing power from the contacts of RY 5  connected to the sonic transducer S 1 . Therefore, the audible signal still remains off. 
     At the end of the refill cycle, control relay RY 4  de-energizes. In addition, N.C. contacts (pins  8  to  5 ) close and, through the N.C. contacts (pins  8  to  5 ) of RY 5 , energize the sonic transducer Si so that a audible signal is sounded. 
     At the Operator&#39;s discretion, the Sonic audible signal may be silenced by pressing the “PUSH SONIC OFF” switch SW 4 . When SW 4  momentarily closes, control relay RY 5  energizes and latches as described above. In turn, N.C. contacts (pins  8  to  5 ) open and de-energize the sonic transducer S 1 . Also, N.O. contacts (pins  1  to  3 ) close, energizing and latching relay RY 5  in the energized state. “PUSH SONIC OFF” switch SW 4  may now be released and the audible signal will stay OFF until the next refill cycle ends. 
     When the “PUSH TO TEST INDICATORS” switch SW 5  is momentarily pressed, test circuit  86  is completed and power is connected to LED 1 , LED 2 , LED 3 , LED 4 , LED 5 , LED 6 , LED 7 , and sonic transducer S 1 , thus energizing all of these indicators. 
     Each Diode anode of test circuit  86  is connected in parallel to the direct drive Diode anode of the various indicator circuits. This blocks any potential false circuit paths. 
     Diodes D 9 , D 14 , D 19 , D 20 , D 22 , D 23  are connected in parallel across their respective relay coils with their cathodes toward the positive power supply line. When a coil that has been energized is deenergized, the magnetic field that is created, quickly collapses and creates a transient voltage of opposite polarity to the energizing voltage across the coil terminals. Diodes D 9 , D 14 , D 19 , D 20 , D 22 , D 23  provides a discharge path in its forward biased direction for this transient voltage and dissipates the stored energy. This configuration tends to protect the contacts of the switch that energizes the coil from high voltage spikes that may cause arc damage and also contributes to a quieter overall electrical environment. 
     FIG. 16 illustrates a partial view of a chemical cabinet  69  having two manifolds  22  therein. Each manifold  22  connects up to a separate bulk container  20 . Manifold  22  contains six valves: process isolation valve  70 , carrier gas isolation valve  71 , container bypass valve  72 , low pressure vent valve  73 , emergency shut off valve  74 , and vacuum supply valve  75 . Obviously chemical cabinet  69  can have one or more manifolds in it depending on process requirements. 
     A particularly preferred manifold arrangement is depicted in FIG.  17 . The difference between the manifold in FIG.  16  and the one in FIG. 17 is that a block valve  76  contains both a container bypass valve  72  and a refill line isolation valve  70 . Thus, block valve  76  is substituted for separate valves  70  and  72  of FIG.  16 . As a result of this modification, high purity source chemical is prevented from being trapped in the passage  89  of refill line  44  illustrated in FIG.  16 . This is because passage  89  is effectively removed from the manifold with the use of block valve  76 . Thus, the manifold configuration of FIG. 17 further reduces the risk of introducing contamination to the system. 
     A most preferred embodiment of manifold  22  is depicted in FIG.  18 . In this embodiment, in addition to employing a process isolation block valve  76  for the canister bypass valve  72  and the process line isolation valve  70 , a vacuum/pressure block valve  91  is used for the low pressure vent valve  73  and the carrier gas isolation valve  71 . Again, as with the embodiment depicted in FIG. 17, the basic operation of the manifolds are the same. Thus, the description of the operation of the manifold for various processes applies to all three depicted embodiments. 
     Manifold  22  is preferably used to isolate the refill line  44  when the bulk container  20  is replaced with a fresh tank. This helps prevent contamination of the system. Thus, the preferred manifold  22 , is not required for operation of refill system  18 . Naturally, if a manifold is not used, bulk canister input valve  66  will need to be attached to a regulated source of inert gas and bulk canister output valve  64  will need to be connected to refill line  44 . 
     Process isolation valve  70  is interposed in refill line  44  between the inlet valve  38  of ampule  30  and the outlet valve  66  of bulk container  20 . When process isolation valve  70  is closed, the portion of process line  44  down stream from valve  70  is isolated from the atmosphere during subsequent replacement of bulk tank  20 . Carrier gas isolation valve  71  is interposed in carrier gas line  77  between the inlet valve  64  of bulk container  20  and the carrier gas supply source. 
     Low pressure vent valve  73  is interposed in vacuum line  78 , which is communicated to both the carrier gas line  77  and refill line  44 . Container bypass valve  72 , however, is interposed in the line between refill line  44  and low pressure valve  73 . This line is both pressurized or evacuated dependent on the states of LPV and CGI. 
     Emergency shut off valve  74  is a normally closed valve, preferably a pneumatic valve. Thus, any loss in system air pressure will immediately close the valve. Typically emergency shut off valve  74  is controlled by the facility emergency gas pad shut off control system. The use of pneumatically activated normally closed valves in the manifold and on the bulk canister inlet and outlet enables all valves to act as emergency shut-off valves. Thus, when the ESO condition is activated, the pneumatic supply to the valves will be cut off, closing all valves. Vacuum supply valve  75  is disposed in a venturi loop  99  so that when it is opened, vacuum is supplied to vacuum supply lines  78 . 
     During normal operation the manifold  22  is left in the delivery configuration. Pneumatic valve  42  in the refill line  44  is used to control the refilling operation. In the delivery configuration the emergency shutoff valve  74  is open, the carrier gas isolation valve  71  is open, the process line isolation valve  70  is open, the vacuum gas shutoff valve  75  is closed, the low pressure vent valve  73  is closed, the canister bypass valve  72  is closed, the bulk canister inlet valve  64  is open and the bulk canister outlet valve  66  is open. 
     To change the bulk canister  20 , the following preferred procedure is used to prevent contamination of the high purity chemical being delivered. First the high purity chemical must be evacuated from the manifold and the bulk canister  20  depressurized and isolated. Next the manifold should be purged. After purging, the depleted bulk canister should be disconnected and removed. Then the new full bulk canister  20  should be installed and connected. The connections for the full bulk canister should be tested for leaks. The manifold should then be purged and the new bulk canister  20  placed in service. 
     To evacuate the high purity chemical remaining in the manifold  22  and to isolate, depressurize and shut off the bulk canister  20 , the following procedure is presently preferred. (It should be noted that unless otherwise expressly noted, the emergency shutoff valve  74  should open throughout all of the following procedures.) Ensure that the canister bypass valve  72  is closed, which it should be in the delivery configuration. Then close the process line isolation valve  70 . Next close the bulk canister outlet valve  66 . Close the carrier gas isolation valve  71  and open the vacuum gas shutoff valve  75  and the low pressure vent valve  73 . Wait until the manifold pressure gauge  92  reads approximately zero psia, which takes approximately four minutes. 
     Close the bulk canister inlet valve  64 . Close the low pressure vent valve  73  and open the carrier gas isolation valve  71  and the canister bypass valve  72 . Open the canister outlet valve  66  and wait approximately a half a minute or until the bulk canister pressure equalizes with the pressurizing gas. Close the bulk container bypass valve  72 , the bulk canister outlet valve  66  and the carrier gas isolation valve  71 . Open the bulk canister inlet valve  64 . The foregoing steps should preferably be repeated a number of times, most preferably a minimum of five times. Finally the bulk canister inlet valve  64  should be closed. 
     To purge the manifold prior to disconnecting the depleted canister  20 , the following steps should preferably be followed. Open the canister bypass valve  72  and the low pressure vent valve  73 . Wait approximately 30 seconds to maximize the evaporation of the residual high purity chemical in the manifold. Close the low pressure vent valve  73  and open the carrier gas isolation valve  71 . Wait approximately 4 seconds and then close the carrier gas isolation valve  71 . Open the low pressure vent valve for approximately 10 seconds and then close it again. Repeat the steps of closing the low pressure vent valve  73 ; opening the carrier gas isolation valve  71 ; waiting approximately 4 seconds and then closing the carrier gas isolation valve  71 ; and, opening the low pressure vent valve for approximately 10 seconds and then closing it again preferably a minimum of nineteen times. Then close the vacuum gas shutoff valve  75  and wait approximately three seconds. Then open the low pressure vent valve  73  for approximately five seconds. 
     To disconnect and remove the depleted bulk canister  20 , the following steps are preferred. Open the carrier gas isolation valve  71  to keep a positive pressure of the pressurizing gas, preferably helium, on the manifold. Open the canister inlet and outlet valves  64  and  66 . With a suitable tool, support the canister outlet valve  66  to prevent rotation, and then loosen the canister outlet valve  66  connection and disconnect the canister outlet tubing  79 . In a similar fashion, disconnect the canister inlet tubing  88 . The pressurizing gas should be flowing freely out of the canister inlet and outlet tubing  88  and  79  throughout the operation and until the new canister is connected. This prevents atmospheric contamination of the manifold. Disconnect the level sensor cable, unfasten the safety chains and straps and carefully remove the depleted bulk canister  20  from the enclosure. 
     To install a full bulk canister  20 , the following steps should preferably be performed. Carefully place the bulk canister in the enclosure and reconnect the safety strap and chain. Connect the canister inlet valve  66  and outlet valve  64  connections to the outlet and inlet tubing  88  and  79  reversing the procedure used to disconnect them from the depleted bulk canister  20 . Connect the level sensor cable and close the carrier gas isolation valve  71 . 
     Before moving to the next step, a test for leakage should be performed. Open the vacuum gas shutoff valve  75  and the low pressure vent valve  73 . After approximately 10 seconds, close the low pressure vent valve  73  and open the carrier gas isolation valve  71 . After a few seconds, preferably four, close the carrier gas isolation valve  71  and the vacuum gas shutoff valve  75 . Using an appropriate leak tester, check the inlet and outlet canister connections for leaks. If none appear, the manifold should be purged and then set for normal operation. 
     To purge the manifold, with the canister inlet and outlet valves  64  and  66  closed, the canister bypass valve  72 , the vacuum gas shutoff valve  75  and the low pressure vent valve  73  should first be opened. After approximately 10 seconds, the low pressure vent valve  73  should be closed. Open the carrier gas isolation valve  71  for approximately four seconds and then close it. Repeat the opening and closing of the low pressure vent valve  73  and the carrier gas isolation valve  71  preferably a minimum of nineteen times. Open the low pressure vent valve  73  for approximately 15 seconds to ensure that vacuum has been pulled on the manifold and then close it. Close the vacuum gas shutoff valve  75  and the carrier bypass valve  72 . 
     To place the manifold  22  in the normal operating configuration, slowly open the carrier gas isolation valve  71 . Then slowly open the canister inlet valve  64  and then the canister outlet valve  66 . Adjust the pressure regulator to the desired delivery pressure and open the process line isolation valve  70 . 
     In addition, the manifold  22  can be used to purge and evacuate the refill line  44  as well. To accomplish this, the purge and evacuation cycles would be performed with the process line isolation valve open and the pneumatic valve  42  closed. Also, if desired, additional parts of the system can be evacuated and purged by merely opening downstream valves to the final point that is desired to be purged. The suggested times for purging and evacuating should be extended to allow for the vacuum to be completely pulled on the lines being evacuated and purged. 
     While the bulk chemical refill system of the present invention has been described in connection with high purity TEOS, the system has application with many other high purity source chemicals, as a person of ordinary skill in the art would recognize. A non-exclusive list of the various high purity source chemical that might be used in the chemical refill system of the present invention is contained in Table 1. 
     
       
         
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 Aluminum Tri-sec-Butoxide 
               
               
                   
                 Borazine 
               
               
                   
                 Carbon Tetrachloride 
               
               
                   
                 Chloroform 
               
               
                   
                 Dichloroethylene 
               
               
                   
                 Dichloromethane 
               
               
                   
                 Diethylsilane 
               
               
                   
                 Isopropoxide 
               
               
                   
                 Hexafluoroacetylacetonate- 
               
               
                   
                 Copper (I)-Trimethylphosphine 
               
               
                   
                 Silicon Tetrachloride 
               
               
                   
                 Tetrakis (Diethylamino) titanium 
               
               
                   
                 Triethylphosphite 
               
               
                   
                 Titanium Tetrachloride 
               
               
                   
                 Trimethylorthosilicate 
               
               
                   
                 Tetramethylcyclotetrasiloxane 
               
               
                   
                 Trichloroethane 
               
               
                   
                 Trimethylphosphite 
               
               
                   
                 Trimethylborate 
               
               
                   
                 Titanium N-Butoxide 
               
               
                   
                 Titanium 
               
               
                   
                 Tantalum Ethoxide 
               
               
                   
                 Triethylborate 
               
               
                   
                 Triethylphosphate 
               
               
                   
                 Trimethylphosphate 
               
               
                   
                 Titanium Ethoxide 
               
               
                   
                 Titanium N-propoxide 
               
               
                   
                 Titanium Isobutoxide 
               
               
                   
                 Tris (Trimethylsiloxy) Boron 
               
               
                   
                 Tris (Trimethylsilyl) Phosphate 
               
               
                   
                   
               
             
          
         
       
     
     Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as described by the appended claims.