Patent Application
20130252034
The invention relates to backup power systems and, in particular, to a backup power system using fuel cells.
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.
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.
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.
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.
An object of the invention is to integrate fuel cells into semiconductor fabs for backup power with a cost effective manner.
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.
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.
With reference to
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'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.
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.
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.
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.
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.
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.
