Abstract:
An apparatus and process for recovering a desired gas such as xenon difluoride, xenon, argon, helium or neon, from the effluent of a chemical process reactor that utilizes such gases alone or in a gas mixture or in a molecule that becomes decomposed wherein the chemical process reactor uses a sequence of different gas composition not all of which contain the desired gas and the desired gas is captured and recovered substantially only during the time the desired gas is in the effluent.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present patent application claims the benefit of prior U.S. Provisional Patent Application Ser. No. 61/298,949 filed Jan. 28, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     There is a need to discriminate and effectively collect process gas containing high value desired gases, such as noble gases (Kr, Xe) from a source or effluent gas that is available on an intermittant and variable flow basis. It is very important that the apparatus to collect the desired gas not in any way interfere with the performance of the process equipment, such as a chemical process reactor to which the collection system is attached. Effluent gas from semiconductor processes, such as etching, typically are diluted at the process pump and then transferred through a gas manifold after the pump into a common effluent gas manifold that eventually goes to an abatement or scrubbing system. This comingling of effluent gases eventually dilutes the process effluent stream of interest making it very difficult to efficiently process to remove the species of interest, i.e., the desired gas, for recovery. 
     Gases which are either unacceptable as pollutant effluents or sufficiently valuable to recover are known to be recovered from waste streams from chemical processes. See U.S. Pat. No. 7,261,763. 
     Rare gases are recovered from effluents for packaging and transport to refinement and recycling. See U.S. Pat. No. 7,294,172 and U.S. Pat. No. 7,169,210. 
     Etchant gases from semiconductor processing are known to be recovered because of global warming potential. See U.S. Pat. No. 7,258,725. 
     Rare gas collection from effluent of semiconductor processing is known. See U.S. Pat. No. 6,605,134. 
     Recycle of perfluorocarbons (PFCs) from semiconductor processing is known. See U.S. Pat. No. 6,277,173. 
     Xenon recovery systems are known. See U.S. Pat. No. 7,285,154. 
     Xenon sensors are known. See US2006/00211421. 
     However, these processes do not address the discrete collection of the desired gas from other effluent gases passing through a chemical process effluent system in sequence and avoidance of upset conditions of such chemical process during the discrete collection of the desired gas. These and other advantages are obtained by the present invention which will be set forth in greater detail below. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is an apparatus for recovering a desired gas from the effluent of a chemical process reactor that utilizes two or more gas compositions in sequence, comprising;
         (a) a chemical process reactor provided with one or more lines for introducing two or more separate gas compositions into the chemical process reactor;   (b) a process controller for controlling the introduction of the separate gas compositions in the chemical process reactor;   (c) an effluent line from the chemical process reactor capable of removing effluents of the two or more separate gas compositions introduced into the chemical process reactor;   (d) a check valve in the effluent line allowing removal of the effluent from the chemical process reactor and preventing any substantial flow of effluent to the chemical process reactor;   (e) a recovery line capable of removing a desired gas from the effluent line;   (f) an automatic valve in the recovery line;   (g) a process controller capable of controlling introduction of two or more gas compositions in sequence into the chemical process controller and capable of controlling the operation of the automatic valve in the recovery line so that the automatic valve is open during at least a portion of the time when the desired gas is in the effluent line as a part of a gas composition, where the process controller is capable of generating and receiving process signals by signal connections with the chemical process reactor and the automatic valve; and,   (h) a compressor in the recovery line capable of removing the desired gas from the effluent line in sufficient flow to close the check valve in the effluent line.       

     The present invention is also a process for recovering a desired gas from the effluent of a chemical process reactor that utilizes two or more gas compositions in sequence, comprising;
         (a) Introducing two or more gas compositions in sequence into the chemical process reactor, including the desired gas, through an inlet to the chemical process reactor;   (b) Removing an effluent from the chemical process reactor including the two or more gas compositions and the desired gas in sequence in an effluent line;   (c) Passing the effluent through a check valve having a crack pressure setting;   (d) Removing a portion of the effluent from the effluent line upstream of the check valve, which portion of the effluent contains a substantial portion of the desired gas, wherein the removal closes the check valve, such removal conducted through a recovery line controlled by an automatic valve;   (e) Controlling the operation of the automatic valve by a process controller in signal communication with the automatic valve, wherein the process controller at least monitors the introduction of the two or more gas compositions into the chemical process reactor or its inlet by signal communication with one or more of the chemical process reactor or its inlet; and,   (f) Opening the automatic valve to recover the gas composition containing the desired gas from the effluent line during at least a portion of the time when the desired gas is in the effluent line as a part of a gas composition.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic illustration of an embodiment of the present invention for collecting a desired gas in a discrete manner from a chemical process reactor effluent. 
         FIG. 2  is a partial section of  FIG. 1  showing an alternate valve arrangement using three-way valve  20 A. 
         FIG. 3  is a partial section of  FIG. 1  showing an embodiment with a buffer tank  31  downstream of the compressor  28  and upstream of the guard bed  30 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     There is a need to discriminate and effectively collect process gas containing high value materials such as noble gases (Kr, Xe, He, Ne, Ar, Rn) as a desired gas from a source gas or effluent gas, which desired gas is available on an intermittant and/or variable flow basis, in contrast to the continuous flow of effluent gases from a process, such as a chemical process reactor exemplified by a semiconductor process reactor. It is desirable that the apparatus to collect the desired gas not interfere with the performance of the process equipment, i.e., chemical process reactor, to which the collection system is attached. This idea enables collecting the desired gas by connecting to the control system, i.e., process controller or computer, and process exhaust using an automatic valve that is actuated at the appropriate times. An alternate approach is to utilize an onboard sensor after the chemical process reactor, such as in the effluent line from the chemical process reactor. The sensor would detect the presense of the species of interest, such as a desired gas exemplified by xenon, and activate the process controller to initiate recovery or collection of such gas. Actuation of the automatic valve is controlled by logic based on measurement of key process parameters. The system includes process equipment that provides vacuum and capacity needed to collect and store the desired gas. Such equipment creates an appropriate level of capacity, such that a steady flow of desired gas contained in an effluent gas can be metered into an enrichment system, such as a vacuum swing adsorption system (VSA), temperature swing adsorption system (TSA), or pressure swing adsorption system (PSA). 
     This invention addresses a need for a method to efficiently collect valuable vented desired gases (such as xenon) from multiple process effluent streams that contain the desired gas on, preferably, an intermittent basis. The method comprises a system for monitoring/measuring the process parameters, logic for control, an automatic valve to divert the gas when selected, a check valve, a vacuum system, and storage volume. The interface operates by utilizing a pressure difference between the recovery gas manifold or recovery line and the normal waste gas manifold or effluent line after the process pumps/compressors. Upon receiving a signal from the process controller, an automatic valve, such as a solenoid valve is opened. The reduced pressure within the recovery line forces closure of a check valve in the effluent line. This now diverts the effluent gas toward the recovery line. The system also contains process logic to selectively signal when the species of interest or desired gas is present, as well as to shut-off flow, if the species of interest or desired gas is not present, or another species is present that could cause disruptions to the downstream recovery system. The process logic can also compensate for the time required for the species of interest or desired gas, such as xenon, to travel from the chemical process reactor to the recovery line or automatic valve. This is accomplished by an adjustable delay in the opening and closing of the automatic valve. 
     The interface with the chemical process reactor may comprise a tee to tap into the effluent line, a shutoff valve, an analytical port (optional), a flex line to reduce vibrational coupling and stresses, a pressure gauge (optional), solenoid valve, and a manual shutoff valve to enable isolation of the chemical process reactor from the recovery system. 
     Effluent gas from semiconductor or chemical process reactor, such as etching, typically are diluted at the process pump and then transferred through a gas manifold or effluent line after the pump into a common effluent gas manifold that eventually goes to an abatement or scrubbing system. This comingling of effluent gases eventually dilutes the process effluent compositions and the desired gas of interest, making it very difficult to efficiently process to remove the species of interest or desired gas for recovery. Thus, it is preferable that the desired gas of interest be segregated from the other effluent streams prior to arrival in the common header. For this to be accomplished the desired gas of interest is diverted towards the recovery system between the process chambers and entrance to the common header. Furthermore, this diversion must be performed in a manner that prevents any interference with the flow of process gases through the chemical process reactor. Such disruptions could cause failures in the manufacturing process that could lead to yield losses. Thus, the waste gas collection system should be transparent to the chemical process reactor. This invention enables efficient and timely transfer of effluent gas, which contains the species of interest or desired gas for recovery. Furthermore, it performs this transfer in a manner that essentially does not interfere with the processing within the chemical process reactor. 
     Another problem this collection apparatus solves is that it enables collection of gas streams or desired gas simultaneously from many process chambers, that may only be processing with the desired gas of interest in an intermittent manner. The interface performs this function by receiving signals from any chemical process reactor or its effluent line and determining when the desired gas of interest for recovery is present in the effluent gas stream. Furthermore, if there happens to be species which the recovery system does not want to accept during intervals of the process, it is possible to program it via additional signals from the chemical process reactor and pre-determined timing to discriminate against these portions of the effluent stream from being diverted to the recovery system. 
     The normal flow of process gas is through the chemical process reactor to a process pump located on the effluent line of the chemical process reactor. These pumps can be many types, including: turbomolecular, cryogenic, and diffusion type pumps to achieve high vacuums. These pumps are then backed up using mechanical pumps, which compress the effluent gas for exhausting. At the mechanical pump, nitrogen dilution is typically performed to lower the flammability limits of the effluent gas, to dilute the effluent gas below lethal dose levels (LDLs), to help cool the process pump as it operates, as well as to seal the pumps to prevent leaks. There may be other reasons for adding nitrogen dilution. At this point, the effluent gas then traverses through a gas manifold to a larger exhaust gas manifold, where effluent gases from many processes comingle. In order to efficiently recover high valued species, such as desired gases exemplified by xenon, from an effluent gas, it is desirable to divert the effluent gas containing the species of interest or desired gas away from this collection manifold and towards the recovery system. The reasons for performing this diversion include: presence of species of interest (desired gas) at high enough concentrations to enable efficient recovery, reduction of contaminants from other processes that could poison or reduce collection efficiency, and reduction of the overall volume of effluent gas to the recovery system to a volume more manageable for the size of the recovery system. 
     The challenge to placing a diversion system onto the effluent line of a chemical process reactor is that the diversion system should not compromise the process underway within the chemical process reactor(s). Any interference with gas flow has the potential to disrupt pressures, gas flow, and pumping efficiencies. These could lead to process disruptions, which could result in loss of product yield. Thus, it is desirable that the reactor interface perform in a transparent manner to the chemical process reactor. Another challenge is that oftentimes chemical process reactors perform many types of duties. Some of these may include the species (desired gas) desired for recovery, and at other times the species of interest (desired gas) may not be part of the effluent gas stream. During these times, it is not desirable to collect and process the effluent gas, because it can lead to inefficiencies. Another challenge is that during the flow of process gas containing the species of interest (desired gas), there might be present other species, that because of safety or risks to the recovery system, it is inappropriate to collect. Oftentimes these species are destroyed during the process and it is only necessary to exclude them from the collection process during various points of the process recipe. Finally, there are often multiple chemical process reactors present, and each is utilizing the desired gas intended for recovery at intermittent time intervals. Thus, it is desirable to have the capability to independently perform desired gas diversion at each chemical process reactor towards the collection header for the recovery system. 
     This reactor interface invention addresses each of the aforementioned challenges for enabling efficient recovery of desired gas from a process effluent gas stream. 
     There are many options potentially available for placing the system onto a chemical process reactor for diverting process effluent gas to a recovery system. The method pursued in this invention attached the interface upstream to a ball check valve located on the atmospheric side of the exhaust effluent pump. In normal operation, the effluent gas flows from the pump at a pressure slightly above atmospheric pressure (0.04 psig). This ball check valve only enables flow of gas in the direction from the exhaust pump to the effluent gas manifold. The reactor interface is connected in via a tee in between the process pump and the ball check valve. The interface consists of pressure gauge (optional), an automatic (solenoid or pneumatically actuated) valve, and a shut-off valve to enable safe closure of the line from the recovery system, when maintenance is required. An electrical reactor interface controller is attached to the automatic (solenoid, etc.) valve to open/close the valve, when effluent gas containing the species (desired gas) to be recovered is present within the effluent stream. Just before the reactor interface unit, a shutoff valve, analytical port, and flex hosing may be attached to the tee to facilitate servicing and to reduce vibrational coupling between the chemical process reactor and the recovery system. 
     Upstream to the recovery system, a compressor is present on the recovery gas line. The pressure within the recovery line is held at a pressure below the normal discharge pressure of the exhaust effluent pump, typically the recovery line is at less that 1 atmosphere. When the automatic (solenoid, etc.) valve is activated open to begin gas diversion to the recovery system, the reduced pressure causes the ball check valve to shut gas flow off to the primary effluent gas manifold, and divert it to the recovery gas manifold system. Process effluent gas then flows out of the exhaust effluent pump and towards the recovery system for processing. When the process signal is given to stop flow of gas to the recovery system, this releases the ball within the ball check valve and enables flow of gas again from the chemical process reactors to the effluent gas manifold. 
     The materials of construction of the reactor interface should able to withstand process temperatures up to 100° C. This is preferable, because the temperature of the effluent gas as it departs the vacuum pump may be close to this temperature. 
     Because there may be situations where the effluent stream contains undesirable materials, the electronic controller is equipped with process logic capability that enables shut-off of the gas diversion, when these species are present. This can be done in a number of ways, including; the use of process sensors and on-line process analyzers. Another methodology adopted is the use of process signals from the chemical process reactor and comparison against a threshold to determine when these species are present. Using a combination of signals from the chemical process reactor and analytical is another approach to addressing this issue. Signals from the effluent line are also possible. 
     The apparatus and process of the present invention will now be described in one embodiment with reference to the figures. 
     In  FIG. 1 , two or more gas compositions are introduced in a prescribe sequence through an inlet  11  into a semiconductor chemical process reactor  10  to assist in the performance of various steps of semiconductor fabrication, including etching of a semiconductor substrate  14  mounted on a platen  12  and/or cleaning of the inside surface of the reactor  10  of by-product inadvertent depositions. The substrate  14  may be one or more semiconductor wafers such as a “boat” or carrier of a series of wafers stacked on their edge. The substrate  14  is introduced into the reactor  10  through a load lock  15  from a load chamber  16 . The reactor  10  and the inlet  11  can be controlled and or monitored by signal connections  99  and  98  to a process controller  94 . For instance, the process controller can monitor the reactor  10  through signal connection  99 , adjust its temperature, control plasma conditions and maintain pressures to set parameters. 
     Likewise, the flow of various gas compositions can be monitored and/or controlled by signal connection  98  to the process controller  94 , such that a sequence of gas compositions are introduced into the reactor  10  through the inlet  11 , including at least one gas composition containing a desired gas in elemental form or molecular form. An example would be the introduction of xenon difluoride, as an etch gas, where the xenon difluoride is decomposed under the conditions in the reactor  10 , and the xenon is desired to be recovered for reuse and recycling, as a desired gas in the effluent of the reactor  10 . 
     Effluent from the reactor  10  can pass through an optional second load lock  17  into a exhaust effluent pump/compressor  19  and an effluent line  18 . The effluent continues through a check valve  20  that prevents backflow of effluent towards the reactor  10 . The check valve  20  is set with a minimum cracking pressure, which represents the pressure at which it will open to allow flow and below which it will close to prevent backflow toward the reactor  10 . 
     In another configuration, rather than using a check valve to divert gas, a three-way valve  20 A, shown in  FIG. 2 , could also be employed to divert the effluent gas towards the recovery system. This method for diverting the waste gas may not be preferred to the check valve approach, because there exists the possibility that pressure spikes could occur in the effluent line, which could impact the pressure within the process reactor. However, for processes that are not as sensitive to changes in pressure and flow, this method for diversion may be acceptable. 
     Effluent that passes through the check valve  20  is sent in line  22  to an abatement, scrubbing and vent system  23  to decompose, burn or sorb toxic, hazardous, corrosive or global warming gases, before the residual effluent gases are vented. 
     A recovery line  24  is connected to the effluent line  18  upstream of the check valve  20 . The recovery line  24  is controlled by an automatic valve  26 , which may be a pneumatic actuated valve or an electric solenoid valve or similar automatic valve capable of operating upon a pneumatic, electrical or other signal sent by a recovery system process controller  104 , which may not necessarily be connected to the process controller  94 , such recovery system process controller communicating with the automatic valve  26  through signal connection  95 . Process controller  94  and recovery process controller  104  can be discrete or their functionality may be combined in one controller for various embodiments of the present invention. 
     The recovery line can be vibration isolated form the effluent line  18  by a flexible line section  21  that prevents vibrations from being transmitted either from the effluent line to the recovery line  24  or from the recovery line  24  to the effluent line  18 . Recovery line can also be manually closed off from the effluent line, for instance for service, my manual shutoff valve  25 . 
     A compressor  28  is situated in the recovery line  24  to remove effluent from the effluent line  18  when automatic valve  26  is open. The compressor  28  is capable of reducing the pressure of the recovery line  24  and thus the effluent line  18 , so that check valve  20  closes. The pressure differential across check valve  20  must be higher than the cracking pressure of the check valve  20 . In this manner the entire effluent gas flow in effluent line  18  may be diverted into recover line  24 . This would occur typically when the desired gas is in the gas composition of the effluent in the effluent line during the sequence of introduction of gas compositions into the reactor  10  when the desired gas is introduced into the reactor or in a phase time delayed from such introduction when the desired gas is being exhausted from the reactor  10  in the effluent line  18 . This timing, sequence and delayed, phased time to discretely remove and recover the desired gas from the effluent&#39;s overall substantially continuous flow is monitored and/or controlled by the process controller  94  through its signal connections  96 ,  98  and  99  and the recovery system process controller  104  and its signal connection  95  to the automatic valve  26 . As stated above, these controllers may be discrete or their functions combined in one controller. Monitoring the composition of the effluent stream is also possible. 
     When automatic valve  26  is open and the desired gas is removed through compressor  28 , the gas is then passed through a sorptive guard bed  30  to remove corrosive, toxic, hazardous or global warming class gas constituents that may be included in the desired gas, along with other gases, such as inert gases exemplified by nitrogen. In an embodiment of the present invention, shown in  FIG. 3 , a buffer tank  31  is situated downstream of compressor  28  and upstream of guard bed  30 . The buffer tank  31  moderates any pressure variances as different reactors  10  feed the desired gas to line  24 , so that the beds  40  and  42  see feed gas of a substantially constant pressure. The desired gas then passes through a check valve  32  in line  34  and is alternately subjected to selective sorptive separation in parallel switching sorptive separation beds  40  and  42 , alternatively on feed sorption and countercurrent depressurization and purge by alternate passage through one of either valve  36  or  38 . In the case of xenon being the desired gas in a carrier gas of nitrogen, the nitrogen is typically least strongly adsorbed on adsorbents, such as: activated carbon, zeolites and aluminas and passes through the beds  40  or  42  unadsorbed, while the xenon is adsorbed on the adsorbent in the beds  40  and  42 . Just before xenon breakthrough in the downstream end of the beds that are on feed, such as near line  44  or  46  respectively, that bed on feed is taken off feed by closing valve  36  or  38  respectively, and valve  48  or  50  respectively. The bed that has finished feed, is then depressurized countercurrently through valves  64  or  66 , respectively, through lines  68  and  70  and is compressed in additional compressor  72  through line  74  to surge tank  76  to collect the gas and mix it for uniformity. This gas contains enriched desired gas, such as xenon, relative to the gas in line  24 . The compressed desired gas, e.g. xenon, is further compressed in additional compressor  78  and can be recycled to the reactor  10 , taken to further processing or stored in one or more storage containers  90  and  92  through check valve  84  and, alternately and respectively, valves  86  and  88 . Preferably, while one container of the two containers  90  and  92  is being filled, the other container is being removed for remote processing and an empty container is being connected to line  82  to be filled when the remaining container is full. 
     In addition to recovering the sorbed desired gas, such as xenon, from the beds  40  and  42  by countercurrent depressurization, it is also contemplated to further remove the sorbed desired gas by evacuation conducted by compressor  72 . Further or alternatively, desired gas can be desorbed from the beds  40  and  42  by a carrier gas, such as inert gases, exemplified by nitrogen introduced through line  58  and alternatively valves  60  or  62 , depending on which bed  40  or  42  is on depressurization mode to purge the desired gas from the sorbent in the beds  40  and  42 . 
     The unrecovered and unsorbed gas constituents of the gas mixture, diminished in desired gas that passes substantially unsorbed through beds  40  and  42 , are removed through valves  48  and  50 , respectively, to be returned in line  52 , valve  54  and line  56  to the effluent line  22  to be treated in the abatement and vent system  23  to decompose, burn or sorb toxic, hazardous, corrosive or global warming gases, before the residual effluent gases are vented.