Abstract:
A backup power system for industrial plants using purified hydrogen in critical processes. A smart valve at a hydrogen reservoir is used to steal hydrogen and divert the hydrogen to a fuel cell array providing backup power to critical processes. Before the fuel cell array comes online, backup power is provided by a battery array that can also supply backup power as the hydrogen supply is depleted.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to backup power systems and, in particular, to a backup power system using fuel cells. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the processing of semiconductor wafers, many processing steps occur at high temperature and low pressure, such as photolithography, chemical diffusion, thin film formation, oxidation and annealing. Critical processes often take place in ovens and reactors whose temperature and pressure must be kept stable to prevent mechanical stress in wafers whose value can be many tens of thousands of dollars per wafer. When critical processes, as well as operation of critical electronics, such as computers, controllers and data storage devices, are interrupted, an expensive loss can occur. For this reason, semiconductor fabs must have reliable backup power for the situation where primary power fails and critical wafer processes are at risk. 
         [0003]    A typical fab uses both battery and diesel backup power under control of a backup power controller. Such an arrangement is shown in U.S. Pat. No. 5,923,099 to A. Bilir. Within a second of primary power failure, backup batteries assume the load for critical processes. Within 30 seconds, sometimes longer, diesel generators can come online to supplement primary battery backup. 
         [0004]    One of the problems with use of battery backup is that batteries require frequent monitoring for readiness and must be kept charged. Moreover, battery shelf life is limited, even where the batteries are not frequently used. Moreover, when batteries are used to supply backup power until diesel power comes online, typically after a few minutes, the batteries are considered for replacement. Fuel cells have been suggested for use with batteries as fab backup power, or in lieu of batteries, but fuel cells are more expensive than batteries. Nevertheless, with improvements in fuel cell technology and adoption of fuel cells in experimental motor vehicles and indoor vehicles, such as forklifts and carts, the cost of fuel cells is diminishing. 
         [0005]    In the prior art, others have attempted to optimize the operating efficiency of fuel cells. For example, in U.S. Pat. No. 7,575,822 a method of operating a fuel cell is disclosed involving accounting for the cost of electricity versus the cost of fuel and then regulating fuel cell throughput accordingly. This patent recognizes that a semiconductor plant can be operated in this manner with fuel cells as primary or backup power. 
         [0006]    An object of the invention is to integrate fuel cells into semiconductor fabs for backup power with a cost effective manner. 
       SUMMARY OF INVENTION 
       [0007]    The above object has been satisfied with a backup power system for industrial plants that uses hydrogen as a process gas, preferably high quality purified hydrogen of the kind found in semiconductor manufacturing plants, including chip plants, LED plants and hydrogen-ready plants with purified hydrogen supplies. Such high quality hydrogen is stored in tanks or reservoirs for process use. A fuel cell array is arranged to provide backup power to critical processes in the plant by borrowing or stealing hydrogen from the process gas reservoir. The hydrogen reservoir must be sufficiently large so that it can operate the fuel cell array for a specified time or condition, as well as critical processes. In this manner, hydrogen becomes part of a hydrogen economy for operation of the plant since its cost is not distinguishable from the cost of running hydrogen consuming processes. As the cost of producing hydrogen becomes less, an integration of fuel cells with hydrogen consuming processes would allow the fuel cells to provide primary electrical power with other sources providing backup power. 
         [0008]    A power controller measures the quality of incoming line power. If the quality of A.C. power is below acceptable standards, such as having a low voltage or insufficient current, the controller generates a power failure signal that causes backup batteries to come online. At the same time fuel cells are started by diverting hydrogen from storage tanks that provide hydrogen to industrial processes that are maintained in the usual way. After a short time of running the industrial plant on backup batteries, the plant load is shifted to the fuel cells so long as hydrogen is available. Primarily, critical processes receive fuel cell power in order to conserve hydrogen. Other power needs can be met with diesel generators or other backup systems. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a plan view of a backup power system for an industrial plant in accordance with the invention. 
       
    
    
     DESCRIPTION 
       [0010]    With reference to  FIG. 1 , an industrial plant is symbolized by an automated machine  33  for processing semiconductor wafers  34 . Such processing occurs using many different machines that perform diverse functions in the plant. For purposes of simplicity, only one machine  33  is shown that may receive wafers  34  for deposition of one or more thin films and then exit the machine in wafer stack  36 . Thin film deposition involves processes that have critical parameters, such a temperature and such processes are deemed to be critical processes because the operation cannot be interrupted without damage to wafers. Moreover, certain ovens and reactors must be maintained at certain temperatures and pressure conditions to avoid damage to wafers and are included among factory critical processes, even when not processing substrates. For example, in deposition of thin films by chemical vapor deposition, the preferred temperature for deposition is usually above 750° C. at the substrate. If the substrate falls below the preferred temperature, deposition may occur elsewhere in the reactor, for example in a showerhead or a liner plate, thereby contaminating the reactor. Similarly, deposition occurs under very low pressure conditions and so vacuum pumps must continue to run during deposition. For this reason, reactors and ovens must be kept under appropriate power and are deemed critical processes. 
         [0011]    During normal operating conditions A.C. power from a utility arrives at an industrial plant at a power controller  13  on power line  11 . The controller monitors power quality by measurement of voltage and current; as well as other parameters. Normal limits for voltage and current are established by calibration. Normal power is sent through a normal feed path  15  to an interface  17  which&#39;converts normal power, if necessary, to appropriate power for particular equipment, such as machine  33 . Very frequently the interface  17  will be distributed within various pieces of equipment. For example, a reactor may have an A.C. to D.C. converter for providing a desired level of D.C. voltage and current for operations. Power sent to a machine  33  and power within machine  33  is reported to a process monitor  31  that is part of a computer  37  that logs data for storage on a disc  39  and displayed on a video display  38  for an operator. In the event that power arriving at the industrial plant is outside of normal limits, a power failure signal is generated by the power controller  13 . This signal goes to battery array  19 , diesel generator  27 , as well as blocking the normal feed path  15  using power controller  13 . Battery array  19  is adequate for supplying backup power to critical processes through interface  21  for several hours. 
         [0012]    The power failure signal is also reported to process controller  41  which reports the condition to computer  37 . Process controller  41  uses the power failure signal to operate a smart meter  43  connected to hydrogen reservoir  35 . The hydrogen reservoir  35  sends purified hydrogen gas to smart meter.  43  via pipe  42  where the hydrogen is diverted, or stolen, for use in fuel cells  23 . 
         [0013]    The smart meter  43  has the capability of diverting gas flow to the fuel cells via pipe  46  on command of the power controller  13 , as well as continuously monitoring flow rates to the fuel cells and to industrial processes in equipment  33  fed via pipe  44 , then reporting usage to process monitor  31  which, in turn, reports to computer  37 . The fuel cells require a few minutes to develop full voltage and adequate current, as reported to a process monitor  31  and computer  37 . 
         [0014]    When full voltage and adequate current for backup is achieved, computer  37  sends a signal to the process controller  41  which then notifies the power controller  13  to shut down battery  19 , allowing fuel cells  23  to provide power through interface  25  to machine  33  through interface  25 . A typical industrial plant may require as much as 2 kW of backup power, sometimes more, for critical processes. To generate 1 kW a fuel cell array will typically require 16 SLPM (standard liters per minute) and 27 SLPM for 2 kW. A corresponding volume of purified hydrogen for at least several hours of operation is required in the hydrogen reservoir  35 , in addition to the regularly consumed volume of purified hydrogen for processes. The entire backup load of the industrial plant may be one MW or more. Non critical processes are backed up by diesel generator  27  which is started upon receipt of a power failure signal from power controller  13 . Interface  29  adjusts diesel output power to appropriate levels. The output of generator  27  goes to power interface  29  which, like power interface  17  may be distributed and provide A.C. power resembling power in the normal feed path  15 . Such power is handled in the industrial plant in the same manner as normal power. 
         [0015]    Process monitor  31  is a controller that monitors the progress of critical processes and controls the schedule of such processes. During a power failure no new critical processes need be started. On the other hand, ongoing processes, including cassette to cassette processing may continue. Equipment  33  is shown to have an input wafer cassette  34  and an output cassette  36  wherein a batch of wafers is processed usually using the same recipe. When a batch is finished, no new batches are started in order to conserve hydrogen, although the temperature and vacuum conditions of the equipment  33  is maintained for readiness after the power failure. 
         [0016]    If hydrogen starts to run low in the hydrogen reservoir  35 , the process controller  41  notifies power controller  13  to switch back to backup battery array  19 . A graceful shutdown of processes ensues if normal A.C. power has not been restored.