Patent Publication Number: US-2009238972-A1

Title: Methods and apparatus for using reduced purity silane to deposit silicon

Description:
The present application claims priority to U.S. Provisional Patent Application No. 61/039,101, filed Mar. 24, 2008, and entitled “METHODS FOR USING REDUCED PURITY SILANE TO DEPOSIT AMORPHOUS AND MICROCRYSTALLINE SILICON”, (Attorney Docket No. 13326/L), which is hereby incorporated herein by reference in its entirety for all purposes. 
     The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/052,164, filed May 9, 2008 and entitled “METHODS AND APPARATUS FOR REDUCING THE CONSUMPTION OF REAGENTS IN ELECTRONIC DEVICE MANUFACTURING PROCESSES” (Attorney Docket No. 13543), which is hereby incorporated by reference herein in its entirety and for all purposes. 
     RELATED APPLICATIONS 
     Co-assigned U.S. patent application Ser. No. 11/565,400 filed Nov. 30, 2006, and entitled “DILUTION GAS RECIRCULATION”, (Attorney Docket No. 11402), is hereby incorporated herein by reference in its entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to electronic device manufacturing and is more particularly directed to the use of reduced purity silane for depositing silicon on a substrate, and the reclaim and recycle of reagent gases which are used in electronic device manufacturing processes. 
     BACKGROUND OF THE INVENTION 
     Some electronic device manufacturing processes may use large quantities of expensive reagents, and some of these reagents may be harmful and/or hazardous if released to the atmosphere. It is known to abate these reagents and their byproducts through the use of abatement systems which convert the reagents or their byproducts into less harmful and/or hazardous compounds. While the abatement of these reagents and their byproducts may address the issue of the harmful and/or hazardous nature of the reagents/byproducts, it does not address the fact that a significant quantity of expensive reagents may eventually be wasted when the reagents pass unused through a process chamber. 
     It is desirable to develop methods and apparatus which would reduce the amount of expensive reagents which are required to be produced and/or purchased for use in electronic device manufacturing processes. 
     SUMMARY OF THE INVENTION 
     In one aspect, a method of forming a silicon layer on a substrate is provided, including the steps providing a substrate; and introducing hydrogen and silane into a chamber containing the substrate such that a layer of silicon is deposited on the substrate; wherein the silane is less than about 99.999% pure. 
     In another aspect, a method for forming a silicon layer on a substrate is provided, including the steps: a) introducing hydrogen and silane into a deposition chamber containing a substrate such that a layer of silicon is deposited on the substrate; b) recovering silicon from an effluent stream which exits the deposition chamber; c) using the silicon recovered in step b) to produce silane; d) using the silane produced in step c) as at least a part of the silane which is introduced into the deposition chamber in step a). 
     In another aspect, a method for forming a silicon layer on a substrate is provided, including the steps: a) introducing hydrogen and silane into a deposition chamber containing a substrate such that a layer of silicon is deposited on the substrate; b) recovering silane from an effluent stream which exits the deposition chamber; c) introducing the silane recovered in step b) into a gas box which is adapted to supply gases to the deposition chamber; and d) supplying an amount of make-up silane to the deposition chamber sufficient to raise the purity of the combined recovered silane and make-up silane to at least a predetermined specification. 
     In another aspect, an apparatus for depositing silicon on a substrate is provided, including a deposition chamber; a source of silicon connected to the chamber; a source of hydrogen connected to the chamber; and a silicon separator adapted to receive an effluent stream produced by the deposition chamber and to provide silicon species suitable for use in producing silane. 
     In another aspect, an apparatus for depositing silicon on a substrate is provided, including: a deposition chamber; a source of silicon connected to the chamber; a source of hydrogen connected to the chamber; a hydrogen separator adapted to receive an effluent stream produced by the deposition chamber and to produce a recycled hydrogen stream; and a gas box which is adapted to receive the recycled hydrogen stream from the hydrogen separator and to provide recycled hydrogen to the deposition chamber. Numerous other aspects are provided in accordance with these and other aspects of the invention. Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic depiction of a substrate coating system of the invention adapted to reclaim and recycle hydrogen. 
         FIG. 1A  is a schematic depiction of a substrate coating system of the invention adapted to reclaim and recycle hydrogen. 
         FIG. 1B  is a schematic depiction of a substrate coating system of the invention adapted to reclaim and recycle hydrogen. 
         FIG. 1C  is a schematic depiction of a substrate coating system of the invention adapted to reclaim and recycle hydrogen. 
         FIG. 1D  is a schematic depiction of a substrate coating system of the invention adapted to reclaim and recycle hydrogen. 
         FIG. 2  is a schematic depiction of a substrate coating system of the invention adapted to reclaim and recycle hydrogen and silicon. 
         FIG. 3  is a schematic depiction of a substrate coating system of the invention adapted to reclaim and recycle hydrogen. 
         FIG. 4  is a schematic depiction of a substrate coating system of the invention adapted to reclaim and recycle hydrogen and silicon. 
         FIG. 5  is a schematic depiction of a substrate coating system of the invention adapted to reclaim and recycle hydrogen and silicon. 
         FIG. 6  is a flowchart depicting a method for coating silicon onto a substrate using silicon recovered from an effluent stream. 
         FIG. 7  is a flowchart depicting a method for coating silicon onto a substrate using recovered silicon and recovered hydrogen. 
         FIG. 8  is a flowchart depicting a method for coating silicon onto a substrate using recovered silicon and recovered hydrogen. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic device manufacturing processes may use large amounts of reagents, such as silane and hydrogen. A substantial portion of these reagents, which may be expensive and/or scarce, may pass from a process chamber unused, to be treated as waste. 
     In a typical substrate coating process prior to the invention, such as, for example, a solar panel coating process, silane and hydrogen gases may be introduced into a substrate coating chamber under substrate coating process conditions. Amorphous and microcrystalline silicon may be deposited in a chemical vapor deposition chamber, or other suitable process chamber, using silane and hydrogen as reagents. Similarly, silane and hydrogen may be used to form a single crystal silicon coating on an insulator. 
     The silane typically used in such deposition processes may be at least 99.99999% pure, or “seven nines pure,” and such silane may be expensive and/or scarce. A problem associated with silane deposition processes, is that a significant amount of the hydrogen and silane which is introduced into the substrate coating chamber may pass through the substrate coating chamber unused. For example, In typical solar panel silicon deposition processes, less than about 20% of the silane introduced into the coating chamber may become consumed while coating silicon on one side of the glass. That translates into more than about 80% of the reagent silane being exhausted unused, e.g., wasted, from the chamber. Prior to the present invention unused hydrogen and silane have typically been treated as harmful and/or dangerous effluent and abated in a suitable abatement unit. Such an abatement unit may be a thermal abatement unit in which the effluent is heated and mixed with an oxidant to oxidize the effluent. 
     In light of the fact that silane may be expensive and more difficult to obtain in the future, and in light of the fact that some electronic device manufacturing fabrication plants may be located in relatively remote locations where it is difficult or expensive to truck or pipe in reagents, it would be desirable to avoid wasting these reagents, and/or to reduce the purity requirements of these reagents, so that only lesser amounts of perhaps cheaper reagents may need to be obtained from suppliers and lesser amounts may need to be treated as waste. 
     In one aspect, the present invention provides methods and apparatus for reclaiming hydrogen and/or silane for reuse as reagents in a substrate coating process. This may be accomplished by taking an effluent stream of unused reagents from the substrate coating chamber and scrubbing it to remove impurities. The scrubbed unused reagent stream may then be passed through a cold trap or a refrigerated chiller, for example, to further purify the unused reagent stream. Next, the unused reagent stream may be passed through a dryer to remove water which may be present in the unused reagent stream. The unused reagents may then be separated from each other and passed back to a gas box from which they may be supplied to the substrate coating chamber as a reagent. The unused reagents may be simply passed back to the gas box without being separated, as well. In an alternative aspect, the unused reagents may be introduced into a buffer tank rather than directly to the gas box. 
     In another aspect, the present invention provides methods and apparatus for reclaiming hydrogen for reuse as a reagent in a substrate coating process, and for reclaiming silicon for use in the manufacture of silane, which silane may then be used as a reagent in the substrate coating process. This may be accomplished by taking a stream of unused reagent from the substrate coating chamber and passing it through a silicon filter to remove silicon, silane, di-silane, tri-silane, and poly-silane from the unused reagent stream. In addition, to remove any dopants which may be present in the unused reagent stream, the unused reagent stream may be passed through a dopant filter, or an adsorption or absorption separation matrix. The unused reagent stream that has been passed through the filters may then consist primarily of hydrogen which may be passed to a gas box from which it may be sent to the substrate coating chamber for reuse. 
     In another aspect of the invention, methods and apparatus are provided to recycle hydrogen and silane for reuse in a process chamber. In this embodiment, at least a portion of the gasses which exit the substrate coating chamber as effluent may be diverted through a valve into a reclaim/recycle sub-system to form a recycle stream. The recycle stream may contain hydrogen and silane, in addition to possibly heavier impurities, such as dopant materials. 
     In another aspect of the invention, the diversion of the recycle stream from the effluent stream may be accomplished at different locations. Thus, in some aspects, the recycle stream may be diverted from the effluent stream between the outlet of the substrate coating chamber and the inlet of the blower-pump package. In other aspects, the recycle stream may be diverted from the effluent stream after a blower of the blower-pump package, but before a mechanical pump stack thereof. In yet other aspects, the recycle stream may be diverted from the effluent stream from a location between stages of the mechanical pump stack, before nitrogen is added to the effluent stream. 
     In some aspects of the invention where the recycle stream is diverted from the effluent stream before the blower-pump package, the reclaim/recycle sub-system may have one or more recycle blowers. These recycle blowers may be low pressure water cooled blowers, although non-water cooled blowers may be used. The recycle blowers may be lower tolerance blowers and may provide the benefits of less energy being needed to run the blowers and less heat being transferred to the gasses being moved by the blowers. In aspects wherein more than one recycle blower is used, the blowers may be staged so as to increase the pressure of the recycle stream while imparting a reduced amount of heat to the recycle stream. Any blowers or pumps which can increase the pressure of the recycle stream to, for example, between about 10 to about 40 p.s.i., about 20 to about 30 p.s.i. or about 10 to about 20 p.s.i., may be used. Other higher and lower pressures may be used. The recycle blowers may reduce or eliminate the transmission of any back pressure waves from the recycle stream to the effluent stream and the process chamber. In other aspects, where the recycle stream is diverted from the effluent stream after the blower, the recycle blowers may not be necessary. After the recycle stream has been diverted from the effluent stream, impurities in the recycle stream may be separated from the hydrogen and silane with a separation unit. In some aspects, the silane may also be separated from the hydrogen with a separation unit. 
     In some aspects of the invention, the recycle stream may be diverted from the effluent stream after the effluent stream has passed through the blower pump package. The gases, including unused hydrogen and silane, which exit a substrate coating process chamber may be at very low pressure, on the order of between about 1 and about 20 Torr. For this reason, a blower-pump package, which may consist of a blower and/or a mechanical pump stack, may be used to evacuate the gases from the substrate coating chamber, and pressurize them to a pressure at which the gases may be abated in an abatement unit. In a typical system, inert gas, e.g., nitrogen, may be added to the gases in order to increase the ease and efficiency of pumping hydrogen, which may be challenging to pump at low pressures. The nitrogen may be added before the mechanical pump or between stages of the mechanical pump. In such a case, nitrogen may also be recovered from the effluent stream and reused to assist pumping hydrogen. 
     In another aspect, the present invention may relieve the lack of silane supply by providing methods of manufacturing solar panels using silane which is less than seven nines pure. At least one specification of a less pure silane is silane which contains di- and/or tri-silane, in addition to silane. For example, a lower grade silane reagent of the invention may include up to about 1 wt. % di- and/or tri-silane, between about 1 wt. % and about 2 wt. % di- and/or tri-silane or up to about 5 wt. % di- and/or tri-silane. Additionally, the same or another lower grade silane reagent of the present invention may contain up to about 0.1 wt % dichlorosilane and/or trichlorosilane. By allowing the silane reagent to contain impurities, the purification process may be foreshortened and made less costly. 
     One approach to source silane may be to capture silane at an earlier purification step to increase production yield and reduce cost. In the production of silane, the silane may be passed through a series of distillation columns, and the silane exiting each succeeding distillation column may be more pure than the silane which exited the preceding column. An acceptable purity of silane may be taken from an earlier one of these so-called fractional cuts of silane production. Such a lower grade of silane may be available at about 30% lower cost than seven nines silane and make possible a 30% higher production capacity. 
     In these and other aspects, a silane specification (sometimes referred to herein as a lower specification silane) may include 20 parts per million (ppm) nitrogen impurity in a silicon film made from the silane. The N 2  level of impurity in the silane reagent may be less than about 5%. In some other aspects, the N 2  level of impurity in the silane reagent may be less than about 1-3%. As discussed above, other impurity types and/or levels may be present in a lower specification silane reagent, such as, for example, di-silane, tri-silane, poly-silane and/or other silicon species such as, for example, SiF4. A silane specification may therefore include up to about 4000 ppm SiF 4 , up to about 3000 ppm SiF 4 , or up to about 2000 ppm SiF 4 . 
     In these and other aspects, water may be present in the silane reagent at less than or equal to about 10 ppm. In some other aspects, water may be present in the silane reagent at less than or equal to about 1 ppm. Other water amounts may be present. 
     In these and other aspects, dopant impurities in non-doped silicon films made from the silane may be acceptable at less than about 10 13 -10 14  dopant atoms/cc. Doped silicon films may contain about 10 19 -10 21  dopant atoms/cc. Other dopant levels may be employed. 
     Thus, in some aspects, the silane plant purification bottleneck may be removed by keeping the current purity targets for N 2  and halogens, and not limiting silane compounds such as, but not limited to, di-silane, tri-silane, dichlorosilane and trichlorosilane. In this way, silane production may be increased and silane cost may be decreased. 
     In additional aspects, the present invention provides methods for forming silicon layers on substrates such as glass or other insulators. In one step, a substrate may be provided. In another step, hydrogen and silane may be introduced into a chamber which may contain the substrate, such that an amorphous layer of silicon may be deposited on the substrate. The silane in this aspect may be less than or equal to about 99.999% pure, less than about 99.99% pure, less than about 99.9% pure, less than about 99% pure, less than 98% pure, and/or less than about 95% pure. In another similar aspect, the method differs in that the hydrogen and silane may be introduced into a chamber which contains the substrate such that a micro-crystalline layer of silicon is deposited on the substrate. 
       FIG. 1  is a schematic drawing of a substrate coating system  100  of the present invention adapted to reclaim and reuse hydrogen as a reagent in a substrate coating process. System  100  may include a substrate coating chamber  102  which may be used to coat substrates. For example, in the production of solar panels, it is common to coat a substrate such as glass with silicon to form a polysilicon coating on the glass. Substrates other than glass may be used, for example, metals, films, polymers, etc. System  100  may be used in coating processes which are employed in electronic device manufacturing other than solar panel manufacturing. 
     Substrate coating chamber  102  may be connected through conduit  104  and throttle valve  106  to blower package  108 . Blower package  108  may include low pressure water cooled blowers, although non-water cooled blowers may be used as well. The blowers may be lower tolerance blowers than the blowers typically used to evacuate process chamber effluent for the purpose of abatement, and may provide the benefits of less energy being needed to run the blowers and less heat being transferred to the gasses being moved by the blowers. In embodiments wherein more than one blower (optionally water cooled) may be used in blower package  108 , the blowers may be staged so as to increase the pressure of the recycle stream while imparting a reduced amount of heat to the recycle stream. Any blowers or pumps which can increase the pressure of the recycle stream to, for example, between about 10 to about 40 p.s.i., about 20 to about 30 p.s.i. or about 10 to about 20 p.s.i., may be used. Other higher and lower pressures may be used. The blowers may reduce or eliminate the transmission of any back pressure waves from downstream of the blower package  108  to upstream of the blower package  108 . Such back pressure waves may interfere with coating processes taking place in the substrate coating chamber  102 . 
     Blower package  108  may be connected through conduit  110  to wet scrubber  112 . Scrubber  112  may be, for example, a bubble tower, burr saddle, packed bed tower, or scrubbing tower. Any suitable wet scrubber may be used. 
     Scrubber  112  may be connected through conduit  114  to cold trap  116 . Cold trap  116  may include one or more refrigerated plates or other surfaces upon which gases which are to be removed from a gas stream may condense, the impurities thus condensing out of the recycle stream. In yet other embodiments, the separation unit may be a filter or a chilled ceramic or metal filter, such as, for example, a sintered nickel filter, and may be located downstream from the recycle blowers. Combinations of the foregoing separation units may also be used. 
     The cold trap  116  is capable of trapping and retaining particles and high molecular weight species. In embodiments which comprise a cold trap separator upstream from the recycle blowers, a remote plasma (not shown) may be used to clean the cold trap and the recycle blowers. If the cold trap is located downstream of the recycle blowers, a remote plasma may be used to clean the cold trap. The remote plasma generator may utilize either NF 3  or F 2  from the chamber clean cycle, or the NF 3  or F 2  may be from a different source. In some of these embodiments, the recycle stream may comprise two parallel streams (not shown), each of which pass through a cold trap/recycle blower set. In these embodiments, one cold trap/recycle blower set may be cleaned while the other set is being operated. The cold trap  116  may be adapted to be isolated and bypassed to facilitate maintenance (not shown). The two sets may be alternately cleaned and used. 
     In other alternative embodiments, instead of cryogenic or cold trap methods, high surface area packing, pressure swing adsorption, temperature swing adsorption, chemical, ceramic or metal filters may be used to polish (e.g., purify) reclaim gases. Single or double beds may be useful. 
     Scrubber  112  and cold trap  116  may be connected to a water treatment unit (not shown) through conduit  118 . Silicon species which may be present in the effluent which passes through a wet scrubber  112  may be recovered in such a water treatment unit. 
     The cold trap  116  may be connected through conduit  120  to dryer  122 . The dryer  122  may be a molecular sieve dryer, or any other suitable dryer. The dryer  122  may be a single or a multiple bed dryer. 
     The dryer  122  may be connected through conduit  124  to blower  126 . Blower  126  may be similar to a blower used in the blower package  108 . Blower  126  may be connected through conduit  128  to oil filter  130 . Oil filter  130  may be used to trap any oil, contaminant, lubricant reaction products, and or any other high vapor pressure material which may be imparted to the reagent stream from blower stack  126 . 
     Oil filter  130  may be connected through conduit  132  to gas box  134 . Alternatively, oil filter  130  may be connected through conduit  132  to a buffer tank (not shown). 
     The gas box  134  may be used to mix reagent and other gases for introduction through conduit  136  into substrate coating chamber  102 . The gas box  134  may be configured such that it is connected to reagent sources, such as silicon source  138 A and hydrogen source  135 B and other gas sources (not shown). The reagent and other gases may be introduced into the gas box through mass flow controllers (not shown) which may form part of the gas box  134 , so that precise mass flow rates of reagent and other gases may be introduced into the substrate coating chamber  102 . 
     The substrate coating chamber  102  may also be connected to blower pump stack  138  through conduit  140  and isolation valve  142 . The blower pump stack  138 , which may be comprised of one or more blowers (not shown in  FIG. 1 ) and one or more mechanical pumps (not shown in  FIG. 1 ) may be connected through conduit  144  to abatement tool  146 . 
     The abatement tool  146  may be a burn wet abatement tool, or an electro-thermal abatement unit, etc. Any abatement tool which is effective to abate chamber cleans, which may contain fluorine species, may be used. The abatement tool  146  may be connected through conduit  148  to a house exhaust system (not shown), further abatement treatment on (not shown), or to the atmosphere. 
     System controller  150  may be connected through communication lines (or communication network)  152  to the gas box  134 , valve  142 , the valve  106 , the composition sensor  154  and pressure control sensor  156 . System controller  150  may be any microcomputer, microprocessor, process logic controller, logic circuit, a combination of hardware and software, or the like. Communication lines/network  152  may be an Ethernet network, a standard communication bus or signal connector cables. Any suitable communication link may be used. Sensor  154  may be a quadrupole mass spectrometer residual gas analyzer (QMS RGA) sensors, Fourier Transform Infrared (FTIR) sensors, chemiluminescence sensors, or any other sensors suitable for detecting hydrogen, silane, and or other species. 
     The following description of the operation of system  100  uses a process for coating silicon on a substrate as an example. It should be understood, however, that the invention is not limited to coating silicon on a substrate, but, rather, may be used in any electronic device manufacturing process where a reagent may pass unused through a process chamber. Examples include deposition applications for solar panels, liquid crystal displays, organic light emitting diodes, film, and nanomanufacturing, etc. In addition, the invention may be used for process chambers which may be used to etch patterns to remove unwanted materials and/or to clean surfaces, etc. 
     In operation, the substrate coating chamber  102  may be operated in at least two modes. In a first mode, the substrate coating chamber  102  may perform a coating process whereby a substrate may be coated with silicon, for example. During this mode, excess silane and hydrogen reagents may pass from the coating chamber  102  as effluent, and it may be desirable for reclaim and recycle the reagent gases. In a second mode, the substrate coating chamber  102  may be cleaned with a plasma, such as a fluorine plasma, for example. During clean modes, it may be desirable to simply abate effluent which passes from the coating chamber  102 . 
     In the first mode, the deposition mode, the gas box  134  may receive hydrogen and silane gases from silane source  135 A and hydrogen source  135 B. Silane source  135 A and hydrogen source  135 B may be cylinders, facility supplies, or any other suitable supplies of silane and hydrogen. The gas box  134  may in turn supply precise amounts of silane and hydrogen gases to the substrate coating chamber  102 , using mass flow controllers (not shown), for example. 
     During the coating process, the pressure in the substrate coating chamber  102  may be regulated by a pressure control subsystem comprising pressure gauge  156 , controller  150 , valve  106 , blower package  108 , and the introduction of gases to the process chamber  102  from the gas box  134 . The blower package  108  may provide a source of vacuum through conduit  104 . During the deposition mode, the valve  142  may be in a closed position so that effluent silane and hydrogen do not pass to the abatement tool  146 . Instead, during the coating process, the effluent hydrogen and silane gases may be evacuated from the coating chamber  102  for reclaim and recycling by blower package  108  through conduit  104 , throttle valve  106  and conduit  110 , and passed into scrubber  112 . 
     The effluent hydrogen and silane reagents may optionally contact water in scrubber  112  or staged cryogenic filters or cold traps (not shown in  FIG. 1 ) which may have the effect of removing silane, di-silane, tri-silane, poly-silane and/or other silicon species such as, for example, SiF4 from the gas stream. In addition, scrubber  112  or optional staged cryogenic filters or cold traps may remove dopants which may exist in the effluent gas stream. The silane, di-silane, tri-silane, poly-silane, dopants and/or other silane species may exit the scrubber in scrubber medium through conduit  118 . The remaining gas stream may then pass through conduit  114  into cold trap  116 . The cold trap  116  may have the effect of removing any remaining particles, water, silane, di-silane, tri-silane, poly-silane, dopants and/or other silane species which may remain in the gas stream. The effluent gas stream may then pass from the cold trap  116  through conduit  120  into dryer  122 , where the gas stream may be dried to less than about 2 ppm water. Blower  126  may then motivate the gas stream to move from dryer  122  through conduits  124 ,  128  and oil filter  130  where any oil or other high molecular weight and/or high vapor pressure species which may have been imparted to the gas stream from blower  126  and/or blower package  108  may be removed. At this stage, the gas stream may be a hydrogen gas stream which may then be supplied to gas box  134  for reuse as a reagent in the substrate coating process conducted in substrate coating chamber  102 . 
     The system  100  may also recertify the reclaimed hydrogen. Thus, gas sensor  154  may be located in line to provide the controller  150  with information regarding the chemical make-up of the recycle gases through communication network  152 . The process controller may then, if necessary, command the gas box  134  through communication network  152  to cause virgin or make-up hydrogen feed stocks to be added to the hydrogen recycle gas to bring the gas up to a predetermined specification for use in the substrate coating process chamber. In addition to continuous recertification, recertification may be done in a batch process where the recycle gases are stored prior to remixing with new feed stocks (not shown). 
     Sensor  154  may optionally be eliminated. The purity of the hydrogen stream in conduit  132  over the course of the deposition, and then the clean cycles, may either be calculated, or may be known through experience. The controller  150  may therefore be programmed to command the gas box  134  to mix in an appropriate amount of make-up hydrogen without the use of a real time sensor  154 . 
     The silane, di-silane, tri-silane, poly-silane and/or other silane species which may flow through conduit  118  may be collected using filters, for example, and may be used as precursor materials for silane production (not shown). Any suitable method or apparatus for separating the silane, di-silane, tri-silane, poly-silane and/or other silane species from the scrubber medium may be used. 
     In the second mode, the cleaning mode, the substrate coating chamber may be cleaned with a plasma from a remote plasma source (not shown). This plasma clean may be motivated by blower pump stack  138  to move through conduit  140 , valve  142  and conduit  144  into abatement tool  146 , where the plasma clean may be abated. From the abatement tool  146 , the abated plasma clean may pass through conduit  148  into a house scrubber (not shown), further abatement (not shown), or to the atmosphere. During the cleaning mode, the valve  106  may be in a closed position. 
       FIG. 1A  is a schematic drawing of an alternative configuration of the substrate coating system  100  of  FIG. 1 , substrate coating system  100 A. System  100 A may be similar to the system  100  of  FIG. 1  with the exception of the connection between the blower package  108  and the substrate coating chamber  102 , and the inclusion of a control system. Instead of the blower package  108  being connected directly to the substrate coating chamber  102 , as depicted in  FIG. 1 , the blower package  108  may be connected through conduit  158  and three way valve  160  to conduit  140 . Conduit  140  may be a vacuum line which connects blower pump stack  138  to the substrate coating chamber  102 . Controller  150  may be connected through signal lines  152  to the sensor  154 , the gas box  134 , the valve  142 , and the three way valve  160 . 
     In operation, system  100 A may operate similarly to system  100  of  FIG. 1 , with the exception that during the coating or deposition mode, unused reagent gases may not pass into conduit  104  as the reagent gases may in the system  100  of  FIG. 1 . Instead, the reagent gasses may pass into conduit  140 , and then be diverted by valve  160  through conduit  158  into blower package  108 . During the chamber clean mode, the valve  160  may be configured such that the chamber clean may pass through conduit  140  into blower pump stack  138 . 
     The controller  150  may determine whether the substrate coating chamber  102  is in the clean mode or in the deposition mode, and may appropriately configure three way valve  160 . 
       FIG. 1B  is a schematic drawing of an alternative configuration of a substrate coating system  100 B of the present invention. The system  100 B may be similar to the system  100 A, with the exception of a location of the blower package  108  connection to the conduit  140 . Whereas, in  FIG. 1A  the blower package  108  is depicted as connected to the conduit  140  prior to the blower pump stack  138 , in  FIG. 1B , the blower package  108  is depicted as connected to conduit  140  through valve  160  between the blower  138 A and the mechanical pump stack  138 B components of the blower pump stack  138 . In an alternative embodiment, blower package  108  may be eliminated, because the system  100 B may rely on the blower  138 A to prevent back pressure waves from passing through to the substrate coating chamber  102 . 
     In operation, the system  100 B may operate similarly to the system  100 A of  FIG. 1A , with the following exceptions. In embodiments wherein blower package  108  is eliminated, blower  138 A may provided the motive force for effluent to move through valve  160  and conduits  158 ,  110  to wet scrubber  112 . 
       FIG. 1C  is a schematic drawing of an alternative configuration of a substrate coating system  100 C of the present invention. The system  100 C may be similar to the system  100 B of  FIG. 1B , with the following exceptions. Whereas in  FIG. 1B  the optional blower package  108  is depicted as connected to conduit  140  between the blower  138 A and the mechanical pump stack  138 B components of the blower pump stack  138 , in  FIG. 1C  the optional blower package  108  is connected to conduit  140 A through valve  160  between mechanical pumps  138 B′,  138 B″ of mechanical pump stack  138 B. 
     As will be discussed in more detail below with respect to  FIG. 3 , an inert gas such as nitrogen, for example, may typically be added to the effluent gas stream before, or as, it passes through the mechanical pump stack in order to facilitate the pumping of hydrogen (not shown). The addition point of the inert gas may be before any of the mechanical pumps  138 B′,  138 B″. Note that, although only two mechanical pumps  138 B′,  138 B″ are shown in  FIG. 1C , either more or fewer mechanical pumps may be employed. 
     In operation, the system  100 C may operate similarly to the system  100 B of  FIG. 1B . 
       FIG. 1D  is a schematic drawing of an alternative configuration of a substrate coating system  100 D of the present invention. The system  100 D of  FIG. 1D  may be similar to the system  100 B of  FIG. 1B  and the system  100 C of  FIG. 1C , with the following difference. In the system  100 D, the optional blower package  108  may be connected to the conduit  140 A downstream from the blower pump stack  138 . 
     In operation, the system  100 D may operate similarly to the systems  100 B and  100 C. 
       FIG. 2  is a schematic drawing of a substrate coating system  200  depicting another embodiment of the present invention. System  200  may include a substrate coating chamber  202  which may be used to coat substrates. The substrate coating chamber  202  may be similar to the substrate chamber  102  of  FIG. 1 . The substrate coating chamber  202  may be connected through conduit  204  and valve  206  to blower package  208 . The valve  206  may be a throttle valve. Blower package  208  may be similar to blower package  108  of  FIG. 1 . 
     Blower package  208  may be connected through conduits  210 ,  210 ′ and oil filters  212 ,  212 ′ to separation systems  214 ,  214 ′. Oil filters  212 ,  212 ′ may be similar to oil filter  130  of  FIG. 1 . Although two separation systems  214 ,  214 ′ are shown in  FIG. 2 , it is to be understood that fewer or more separation systems may be used (e.g., 1, 3, 4, etc.). 
     Separation system  214  may include isolation valves  216 ,  218 ; dopant separator  220 ; and silicon separator  222 . Isolation valves  216 ,  218  may be used to isolate separation system  214  from system  200 . Dopant separator  220  may be an absorption separation matrix or an adsorption separation matrix. Alternatively, the dopant separator  220  may be replaced with a dopant filter (not shown). Similarly, the silicon separator  222  may be an absorption separation matrix or an adsorption separation matrix, or, alternatively, silicon separator  222  may be a silicon filter. A suitable filter may be a honeycomb ceramic matrix which is coated with silicon. The ceramic may be an yttria doped alumina. Separation system  214 ′ may be similar to separation system  214 . 
     Separation systems  214 ,  214 ′ may be connected to blower  224 . Blower  224  may be connected through conduit  226  and oil filter  228  to gas box  230 . Gas box  230  may be connected through conduit  232  to substrate coating chamber  202 . 
     Substrate coating chamber  202  may also be connected through conduit  234  and isolation valve  236  to pump stack  238 . Pump stack  238  may be connected through conduit  240  to abatement tool  242 . Abatement tool  242  May be connected through conduit  244  to a house exhaust system (not shown), further abatement treatment (not shown), or to the atmosphere, etc. 
     Controller  246  may be connected, through communication network  248  to the gas box  230 , the valve  236 , the valve  206 , the composition sensor  250  and pressure sensor  252 . 
     Although not shown, the system  200  may be modified in a manner similar to the manner in which the system  100  may be modified to form system  100 A. Such a modification may include connecting the blower package  208  to the effluent conduit  234  through a three way valve (not shown) located between the throttle valve  236  and the pump stack  238 , for example, which would be adapted to divert gas flow between the pump stack  238  and the blower package  208 , depending upon whether the chamber was in a clean mode or a deposition mode, respectively. The controller may be used to control the three way valve (not shown) so that chamber cleans may be directed to the abatement tool  242 , while effluent reagents may be directed to blower package  208  for reclaim and recycling. Analogously, the system  200  may also be modified in manners similar to the manners in which the system  100  may be modified to form the systems  100 B,  100 C, and  100 D. 
     In operation, substrate coating chamber  202  may operate similarly to substrate coating chamber  102  of  FIG. 1 , with the exception that in the deposition mode the unused reagents may not be passed through a wet scrubber, a cold trap, and a dryer, as they are in system  100  of  FIG. 1 . Instead, the unused reagents (and any dopants) may be passed from blower package  208  through conduits  210 ,  210 ′, through oil filters  212 ,  212 ′ and into separation systems  214 ,  214 ′. 
     Separation systems  214 ,  214 ′ may remove dopants from the unused reagent gas stream with dopant separators  220 ,  220 ′, which, as described above, may be absorption or adsorption separation matrices. The dopants may be collected, separated if necessary, and reused as dopants. 
     Separation systems  214 ,  214 ′ may remove silicon compounds from the unused gas stream using silicon separation units  222 ,  222 ′. Silicon separators  222 ,  222 ′ may remove silicon, silane, di-silane, tri-silane, and poly-silane through mechanisms of absorption, adsorption, and/or filtration. The silicon, silane, di-silane, tri-silane, and poly-silane which may be removed from the unused reagent gas stream may be collected and sent, or sent directly, to a silane manufacturing facility, which may supply silane to the gas box  230  for use as a substrate in substrate coating chamber  202 . 
     The net result of the unused reagent gas stream passing through separation systems  214 ,  214 ′ may be that the unused reagent gas which flows from the separation systems  214 ,  214 ′ into blower  224  may include high purity hydrogen gas. The high purity hydrogen gas may flow through conduit  226  and oil filter  228  (where any oil or other high molecular weight contaminant introduced into the hydrogen gas by blower  224  may be removed), and into gas box  230 . 
     The remainder of the system  200  of  FIG. 2 , including recycle of hydrogen through conduit  226 , may operate similarly to the system  100  of  FIG. 1 . 
       FIG. 3  is a schematic depiction of a substrate coating system  300  of the present invention. The system  300  may be similar to the system  100  of  FIG. 1 , with the following exceptions. In system  300 , the oil filter  130  may not be connected through conduit  132  to gas box  134  as it is in the system  100  of  FIG. 1 . Instead, the oil filter  130  may be connected through the conduit  132  to separation unit  302 . The separation unit  302  may be a membrane separator which may be adapted to separate hydrogen gas from an inert gas. Any suitable separator may be used. The separation unit  302  may be connected through conduit  304  to the gas box  134  and through conduit  306  to an inert gas source  308 . The inert gas source  308  may be connected through the conduit  310  to the gas box  134 , and through conduit  312  to pump stack  138 . 
     In operation, the system  300  may operate similarly to the system  100  of  FIG. 1 , with the following exceptions. In the system  300 , inert gas may be introduced into the gas box  134  from the inert gas source  308  through the conduit  310 . The inert gas may be nitrogen, helium, argon, etc. or any other suitable inert gas. The inert gas may be used to cool the substrate coating chamber  102 . An additional benefit may be more efficient utilization of reagents such as silane and hydrogen. The inert gas may pass with the unused reagents through the system until the inert gas enters conduit  132  with otherwise highly pure hydrogen gas. The inert gas/hydrogen gas mixture may then enter separation unit  302  which may separate the hydrogen gas from the inert gas. The hydrogen gas may then pass from the separation unit  302  through the conduit  304  and into the gas box  134 . The inert gas may pass from the separation unit  302  through the conduit  306  into the inert gas source  308 , from which it may be sent through the conduit  310  into the gas box  134 . 
     In addition, the inert gas source  308  may supply inert gas to the mechanical pumps (not shown) of the pump stack  138  through conduit  312 . 
       FIG. 4  is a schematic depiction of a substrate coating system  400 . System  400  may be similar to the system  200  of  FIG. 2 , with the following exceptions. In system  400 , the oil filter  228  may not be connected through the conduit  226  to the gas box  230  as it is in system  200  of  FIG. 2 . Instead, the oil filter  228  may be connected through conduit  402  to separation unit  404 . The separation unit  404  may be similar to the separation unit  302  of  FIG. 3 . The separation unit  404  may be connected through conduit  406  to the gas box  230 . The separation unit  404  may also be connected through the conduit  408  to inert gas source  410 . The inert gas source  410  may be connected through conduit  412  to gas box  230 . The inert gas source  410  may also be connected through conduit  414  to the blower pump stack  238 . 
     In operation, the system  400  may operate similarly to the operation of the system  200  of  FIG. 2 , with the following changes and additions. In the system  400 , inert gas may be introduced into the gas box  230  from the inert gas source  410  through the conduit  412 . As in the system  300  of  FIG. 3 , the inert gas may be nitrogen, helium, argon, etc. or any other suitable inert gas. The inert gas may have the same effects on the system  400  as the inert gas has on the system  300  of  FIG. 3 . As in the system  300 , the inert gas may pass with the unused reagents through the system until the inert gas enters the conduit  402  with hydrogen gas. The inert gas/hydrogen gas mixture may then enter the separation unit  404  which may separate the hydrogen gas from the inert gas. The hydrogen gas may then pass from the separation unit  404  through the conduit  406  into the gas box  230 . The inert gas may pass from the separation unit  404  through the conduit  408  into the inert gas source  410  from which the inert gas may be sent through the conduit  412  into the gas box  230 . The inert gas may also pass through conduit  414  to the blower pump stack  238  to facilitate the pumping of hydrogen. 
     The system  400 , like the system  100 , may also recertify the reclaimed hydrogen. Thus, gas sensor  250  may be located in line to provide the controller  246  with information regarding the chemical make-up of the recycle gases through communication network  248 . The process controller may then, if necessary, command the gas box  230  through communication network  248  to cause virgin hydrogen feed stocks to be added to the hydrogen recycle gas to bring the gas up to a predetermined specification for use in the substrate coating process chamber. In addition to continuous recertification, recertification may be done in a batch process where the recycle gases are stored prior to remixing with new feed stocks (not shown). 
       FIG. 5  is schematic depiction of a substrate coating system  500  of the present invention. The system  500  may be similar to the system  300  of  FIG. 3 , with the following differences. System  500  may not employ the wet scrubber  112  and cold trap  116  to separate silane and other silicon species from the effluent stream. Instead, coating system  500  may employ pump  501  to move the effluent stream through staged cold traps or cryogenic filters  502  which may remove heavier silicon species, such as di-silane, tri-silane, and SiF 4  from the stream, while leaving silane in the stream. The resulting effluent stream may contain silane, hydrogen and inert gas when it enters cryogenic separator  504 . The cryogenic separator  504  may comprised liquid nitrogen chilled plates, or any other cryogenic separator capable of separating silane from hydrogen and/or nitrogen. The cryogenic separator  504  may separate silane from hydrogen and an inert gas such as nitrogen, flowing silane through conduit  506  to the gas box  134  and hydrogen/inert gas through conduit  508  into separation unit  302 . Although not shown, conduits  506 ,  508  may incorporate pumps to facilitate the movement of the gas streams therein. Conduit  506 , may also be connected to sensor  510 . Sensor  510  may be similar to sensor  154 , and may be connected to controller  150  through network  152 . 
     Although only one pump  502 , staged cold traps  502  and cryogenic separator  504  are depicted in  FIG. 5 , it should be understood that more than one pump  502 , staged cold traps  502  and cryogenic separator  504  may be used in parallel so that one set may be taken out of service for maintenance without interrupting operation of the coating system  500 . 
     In some embodiments, the separation unit may be a cryogenic separator, which is capable of separating the impurities from the silane and hydrogen, and also of separating the silane from the hydrogen. The cryogenic separator may be located downstream of the recycle blowers. In other embodiments, the separation unit may be a cold trap separator, which may be located upstream or downstream from the recycle blowers. 
     In operation, coating system  500  may operate in a manner similar to the manner in which coating system  300  operates, with the following differences. A coating chamber effluent stream may pass through pump  501  into staged cold traps  502  and cryogenic separator  504 . The staged cold traps  502  may be arranged to remove successively lighter molecules from effluent stream so that di-silane and tri-silane may be removed first, then SiF 4  may be removed. The cryogenic separator  504  may separate the coating chamber effluent stream into a silane stream which may be channeled through conduit  506  to the gas box  134 , and a hydrogen/inert gas stream which may be channeled through conduit  508  to separation unit  302 . The operation of coating system  500  with respect to the hydrogen/inert gas stream following the separation unit  302  may operate in a manner similar to the operation of coating system  300 . 
     As discussed above, the silane stream which may flow through conduit  506  to the gas box  134 , may not be sufficiently pure to meet a predetermined silane specification for use in the substrate coating chamber  102 . Sensor  510  may determine the composition of the silane stream flowing through conduit  506  and report such composition to the controller  150 . The controller  150  may then calculate an amount of virgin silane which needs to be added to the recycle silane and the gas box  134  to add a sufficient amount of silane from silane source  135 A to bring the resulting silane/virgin silane mixture up to the predetermined specification. 
     Sensor  510  may optionally be eliminated. The purity of the silane stream in conduit  506  over the course of the deposition, and then the clean cycles, may either be calculated, or may be known through experience. The controller  150  may therefore be programmed to command the gas box  134  to mix in an appropriate amount of make-up silane without the use of a real time sensor  510 . 
       FIG. 6  is a flow chart depicting a method  600  of the invention for forming a silicon layer on a substrate. In step  602 , hydrogen and silane are introduced into a chamber containing a substrate under process conditions adapted to form a silicon layer on the substrate. In step  604 , silicon is recovered from an effluent stream which exits the chamber. As explained above, a majority of the silane which is introduced into the chamber may typically exit the chamber as effluent, in the forms of silicon species such as, e.g., silane, di-silane, tri-silane, and poly-silane, and/or other silicon species, etc. The method  600  may be practiced on, but is not limited to, coating systems  100 ,  100 A,  100 B,  100 C,  100 D,  200 ,  300 ,  400  and  500 . In step  606 , the silicon species is/are used to produce silane for use as a reagent in the coating chamber. Any known or yet to be discovered methods for producing silane from the silicon species precursors may be used. In step  608 , the silane produced from the recovered silicon species is provided to a gas box which, in turn, introduces the silane into the deposition chamber. In optional step  610 , hydrogen is recovered from the deposition chamber effluent stream. The hydrogen may be processed, such as, for example, by filtering, drying, etc. It is to be understood that although this example is presented in the form of a deposition system, the chamber may be used to perform any suitable process where unused reagents or elements exit from the chamber in an effluent stream. In optional step  612 , the recovered hydrogen is provided to the gas box from which the recovered hydrogen may be introduced into the silicon coating chamber. Alternatively, the recovered hydrogen may be used to produce methane. The methane may then be introduced, with or without hydrogen, into the silicon coating chamber along with silane. 
       FIG. 7  is a flow chart depicting another method  700  of the invention for forming a silicon layer on a substrate. Method  700  may be similar to method  600 , with the addition of the following steps. In step  702 , the chemical composition of the hydrogen which is recovered from the effluent stream which exits the deposition chamber in step  610  is tested for composition and/or purity. Any suitable sensor may be used to determine the composition and/or purity of the recovered hydrogen, including a quadrupole mass spectrometer residual gas analyzer (QMS RGA) sensors, Fourier Transform Infrared (FTIR) sensors, chemiluminescence sensors, or any other sensors suitable for detecting hydrogen. In step  704 , virgin hydrogen of a known purity is added to the recovered hydrogen so that the combined recovered hydrogen and virgin hydrogen meets a minimum predetermined composition/purity. By virgin hydrogen is meant hydrogen which has not been recovered from the silicon deposition process. A microcomputer, microprocessor, process logic controller, logic circuit, a combination of hardware and software, or the like may be used to determine the amount of virgin hydrogen which needs to be added to the recovered hydrogen in order to bring the combined hydrogen to the predetermined minimum specification. 
       FIG. 8  is a flow chart depicting another method  800  of the invention for forming a silicon layer on a substrate. Method  800  may be similar to method  600 , with the addition of the following steps. In step  802 , the chemical composition of the silane produced from the recovered silicon is tested for composition and/or purity. Any suitable sensor may be used to determine the composition and/or purity of the recovered silane, including a quadrupole mass spectrometer residual gas analyzer (QMS RGA) sensors, Fourier Transform Infrared (FTIR) sensors, chemiluminescence sensors, or any other sensors suitable for detecting silane. In step  804 , virgin silane of a known purity is added to the silane produced from the recovered silicon, as described above, so that the combined silane produced from the recovered silicon and virgin silane meets a minimum predetermined composition/purity. By virgin silane is meant silane which has not been produced from the recovered silane. A microcomputer, microprocessor, process logic controller, logic circuit, a combination of hardware and software, or the like may be used to determine the amount of virgin silane which needs to be added to the silane produced from the recovered silicon in order to bring the combined hydrogen to the predetermined minimum specification. 
     Some of the foregoing and other embodiments may include using waste heat from the abatement and or substrate coating process to drive refrigerated chillers or for cogeneration; recycling waste hydrogen, and or waste heat, and or waste SiO 2  to an on-site glass manufacturing plant for process use; using waste residual F 2  to etch substrate in the substrate factory to improve adhesion and remove trace metals from the surface via metal halide vaporization at high temperatures; using the blower and first stages on the conventional pump stack to boost the reclaim stream pre-inert (e.g., nitrogen) dilution, which would save capital cost of recycle blowers; and the entire system can be integrated as an optimal system rather than operated as individual components. In gigawatt solar plants, silane, hydrogen and nitrogen may be kept as liquids, not gases. Coolant streams which themselves need to be re-chilled may be passed through heat exchangers in the liquid silane, hydrogen and nitrogen tanks to cause those compounds to boil off for use, and to re-chill the coolant. In addition the abatement system compressors and pumps create heat which can be used to run chillers or create steam and/or electricity. 
     The present invention may be combined with processes whereby effluent may be taken from the post blower-pump package, after inert gas has been added, and hydrogen and silane then separated from the effluent. 
     The foregoing description discloses only exemplary embodiments of the invention. Modifications of the above disclosed apparatus and methods which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For example, in the systems  300  and  400 , the unused reagent gas may pass through a vacuum line and three-way valve as the unused reagent gases do in system  100 A. Such modified systems may have control systems which divert effluent from the process chamber to either be recycled or abated depending upon whether the process chamber is in a deposition or in a chamber clean mode. 
     Following separation from impurities, and/or separation of silane from hydrogen, the reclaimed hydrogen and silane, or mixture of hydrogen and silane may then be sent to one or more of 1) separate feed tanks on gas pads (e.g., pads where reagent gases are stored); and 2) a gas box (e.g., mixing box) where the reclaimed gases may be mixed in real time with new feed stocks. In those embodiments where silane is separated from hydrogen, silane may be recompressed to a liquid for storage and blending back to the substrate coating process chamber. 
     If silane has been recompressed to a liquid and stored, the tank&#39;s internal gas regenerator heat exchanger may be used to thermally separate silane from heavier di- and tri-silane. The di- and tri-silane would become a tank bottom. Lower vapor pressure impurities may be removed from the tank bottom and the di- and tri-silane may be recycled to a silane plant as feedstock. 
     Finally, new silane and hydrogen may be added to the reclaimed mixture and the reclaim may be added to a buffer volume (e.g., a volume of gas which may be used to damp difference between the inflow and the outflow of the electronic device manufacturing process.) 
     Mass flow controllers and/or mass flow meters and throttle valves may be used by the process controller to control the composition and flow of gases into the process chamber and/or the flow of gases out of the process chamber, and the pressures of the gases in different locations of the system. 
     Accordingly, while the present invention has been disclosed in connection with exemplary 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.