Abstract:
An improved method and apparatus for managing an application of power with a power generator to a load, the apparatus comprising a power generator configured to apply power to the load; a controller coupled to the power generator, the controller configured to control a plurality of parameters to optimize operational performance of the power system in response to indicia of operational performance of the power system; and a performance assessor, coupled to the power generator and coupled to the controller, the performance assessor configured to provide the indicia of operational performance of the power system to the controller, where the indicia of the operational performance are relative to a plurality of metrics indicative of operational efficiency of the power system.

Description:
PRIORITY 
     This application claims priority to expired provisional application No. 61/141,957 entitled METHOD AND APPARATUS FOR CONTROLLING A POWER GENERATOR filed Dec. 31, 2008. 
    
    
     FIELD 
     The present disclosure relates generally to electrical generators. In particular, but not by way of limitation, the present disclosure relates to methods and apparatuses for managing an application of power with a power generator. 
     BACKGROUND 
     Power generators are typically designed to deliver power optimally into a specific load impedance, often referred to as a “reference impedance.” Typically, but not always, the reference impedance of power generators is 50 ohms. Operating into a load impedance close to the designed reference impedance typically results in the most efficient operation of the power generator, the highest output power capability, the lowest stress on the components internal to the generator, and zero (or near zero) reflected power (a measure of operational effectiveness) back to the generator from the load. 
     SUMMARY 
     Illustrative embodiments of the present disclosure are shown in the drawings and summarized below. These and other embodiments are more fully described in the Detailed Description section. It is to be understood, however, that there is no intention to limit the claims to the forms described in this Summary or in the Detailed Description. One skilled in the art can recognize that there are numerous modifications, equivalents, and alternative constructions that fall within the spirit and scope of this disclosure as expressed in the claims. 
     One illustrative embodiment includes a power system for applying power to a load comprising a power generator configured to apply power to the load, a controller coupled to the power generator, the controller configured to control a plurality of variable parameters to improve operational performance of the power system in response to indicia of operational performance of the power system, and a performance assessor, coupled to the power generator and coupled to the controller, where the performance assessor is configured to provide the indicia of operational performance of the power system to the controller, and where the indicia of the operational performance are relative to a plurality of metrics indicative of operational efficiency of the power system. 
     Another illustrative embodiment comprises a method for managing an application of power from a power system to a load, where the method comprises receiving a plurality of performance parameters from a user of the power system, controlling a gate bias voltage relative to a plurality of the received performance parameters, controlling a rail voltage relative to a plurality of the received performance parameters, and adjusting the gate bias voltage and adjusting the rail voltage to improve the operational performance of the power system. These and other embodiments are described in further detail herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various objects and advantages, and a more complete understanding, of the present disclosure are apparent and more readily appreciated by reference to the following Detailed Description and to the appended claims when taken in conjunction with the accompanying Drawings, wherein: 
         FIG. 1  is a system-level block diagram depicting an exemplary embodiment of the disclosed power generation system coupled to a load; 
         FIG. 2  is a block diagram depicting, in more detail, the exemplary embodiment of the disclosed power generation system of  FIG. 1 ; 
         FIG. 3  is a graphical representation illustrating a plurality of relationships between gate bias voltage, rail voltage, power dissipation and delivered power for an exemplary embodiment of the disclosed power generation system; 
         FIG. 4  is another graphical representation illustrating a plurality of relationships between gate bias voltage, rail voltage, power dissipation and delivered power for another exemplary embodiment of the disclosed power generation system; 
         FIG. 5  is another graphical representation illustrating a plurality of relationships between gate bias voltage, rail voltage, power dissipation and delivered power for another exemplary embodiment of the disclosed power generation system; 
         FIG. 6  is a graphical representation illustrating the relationships between gate bias voltage, rail voltage, and delivered power for an exemplary embodiment of the disclosed power generation system; 
         FIG. 7  is a graphical representation illustrating the relationships between gate bias voltage, rail voltage, and dissipated power for the exemplary embodiment of the disclosed power generation system; 
         FIG. 8  is a flow diagram depicting a method for controlling power delivered by the disclosed power generation system; and 
         FIG. 9  is another flow diagram depicting a method for controlling power delivered by the disclosed power generation system. 
         FIG. 10  is another flow diagram depicting a method for controlling power delivered by the disclosed power generation system. 
     
    
    
     DETAILED DESCRIPTION 
     Reference is now directed to the drawings, where like or similar elements are designated with identical reference numerals throughout the several views. 
     Referring to  FIG. 1 , a block diagram of the disclosed power generation system  100  is shown. A controller  102  is coupled to a power generator  104 . The power generator  104  is coupled to a load  106 . Coupled to the power generator  104  and to the controller  102  is a performance assessor  108 . Typically, but not always, some type of matching network (not shown) is used to match the load  106  to the power generator  104 . By correct design of the matching network (either internal or external to the generator), it is possible to transform the impedance of the load  106  to a value close to the reference impedance of the power generator  104 . 
     The illustrated arrangement of these components is logical; thus the components can be combined or further separated in an actual implementation, and the components can be connected in a variety of ways without changing the basic operation of the system. For example, the controller  102 , the power generator  104 , and the performance assessor  108  may be realized by common components and may be within the same housing. Or the controller  102 , the power generator  104  and the performance assessor may be implemented and sold separately. 
     Although not required, the power generator  104  may include a power supply configured to provide a range of power levels and frequencies to facilitate a variety of process applications including etch applications (e.g., silicon, dielectric, metal and strip) and deposition applications (e.g., PECVD, HDP-CVD, PVD, and PEALD). In one variation, the power generator  104  includes a power supply configured to provide power from 30 Watts to 3 kilowatts at frequencies around 13.56 MHz. It is contemplated, however, that the power supply may provide other frequencies and power levels. One exemplary power supply that may be used to realize the power generator  104  is sold under the trade name PARAMOUNT by Advanced Energy Industries, Inc. of Fort Collins, Colo. 
       FIG. 2  illustrates another embodiment of the disclosed power system. Controller  102  comprises a gate bias voltage controller  110  and a rail voltage controller  112 . Power generator  104  comprises a power amplifier  114  and power generation circuitry  116 . And performance assessor  108  comprises a delivered power assessor  118  and a dissipated power assessor  120 . While not required, the power amplifier  114  may comprise a field effect transistor, or FET. The power amplifier  114  is configured to receive a rail voltage signal, which supplies a DC voltage to the power amplifier  114 . The power amplifier  114  is also configured to receive a gate bias voltage signal, which delivers a DC offset value to the power amplifier  114 . 
     The illustrated arrangement of the components in  FIG. 2  is logical; thus the components can be combined or further separated in an actual implementation, and the components can be connected in a variety of ways without changing the basic operation of the system. For example, the controller  102 , including the gate bias voltage controller  110  and a rail voltage controller  112 , the power generator  104 , including the power amplifier  114  and power generation circuitry  116 , and the performance assessor  108 , including the delivered power assessor  118  and the dissipated power assessor  120  may be realized by common components and may be within the same housing. Or the controller  102 , including the gate bias voltage controller  110  and a rail voltage controller  112 , the power generator  104 , including the power amplifier  114  and power generation circuitry  116 , and the performance assessor  108 , including the delivered power assessor  118  and the dissipated power assessor  120 , may be implemented and sold separately. 
     One method for controlling the power delivered to the load  106  by the power generator  104  includes controlling gate bias voltage. The gate bias voltage delivers a DC offset to the power amplifier  114 . In the embodiment of  FIG. 2 , the gate bias voltage controller  110  performs this function. In typical embodiments, the gate bias voltage may be adjusted more quickly than the rail voltage. For example, in one embodiment, adjusting gate bias voltage from zero percent to 100 percent can be accomplished in approximately 1 microsecond. 
     Another method for controlling control the power delivered to the load  106  by the power generator  104  includes controlling rail voltage, the voltage at which the power amplifier  114  operates. In the embodiment of  FIG. 2 , the rail voltage controller  112  performs this function. In typical embodiments, it is difficult to adjust the rail voltage quickly. For example, in one embodiment, adjusting the rail voltage from zero percent to 100 percent can take approximately 2 milliseconds. 
     In several embodiments, both gate bias voltage and rail voltage are controlled concurrently to better manage the performance of the power system  100 . In doing so, the power delivery capability of the power generation system  100  is improved significantly. 
     For example, a first control loop may be utilized that controls the gate bias to produce the required output power, for example, delivered power or forward power. Alternatively, the first control loop may limit the delivered power at a user-defined maximum power (e.g., maximum reflected power), or at a user-defined maximum current drawn from the DC power supply. 
     And a second, independent loop may be utilized to adjust the rail voltage to achieve an improved (e.g., optimal) rail voltage. The adjustment of the rail voltage (e.g., to improve and/or optimize the rail voltage) may use a variety of rules, including: (1) maintaining at least a minimum bias value (defined by the user) by dropping the rail voltage if the bias value drops below the desired minimum bias, up to a user-defined minimum rail voltage; (2) maintaining a desired rail voltage (again, defined by the user) if the bias is between a minimum and maximum desired (i.e., user-defined) bias voltage and the power amplifier  114  dissipation is below a maximum desired (user-defined) power amplifier  114  dissipation value; (3) maintaining a maximum desired (user-defined) power amplifier  114  dissipation if the control loop needs to drop the rail voltage below the desired rail voltage in order not to exceed the maximum desired power amplifier  114  dissipation; (4) maintaining a desired (user-defined) bias voltage by manipulating the rail voltage if the power amplifier  114  dissipation is between the desired maximum and absolute maximum (as defined by the user); and (5) maintaining absolute maximum power amplifier  114  dissipation by dropping the rail voltage. 
     The above-disclosed set of rules for controlling the gate bias voltage and the rail voltage result in an apparatus and method for controlling a power generation system that may use significantly less silicon to achieve a desired (user-defined) power profile and frequency range. The disclosed apparatus and method prolongs the life of devices by operating close to the maximum efficiency. Additionally, the disclosed apparatus and method allow achievement of a very broad power profile and a wider frequency range of operation than what would otherwise be possible. Moreover, the disclosed method and apparatus can, at a given power level, closely maintain a desired rail voltage from which it is easy to change the output power quickly. 
     Depicted in  FIG. 3  is a case where the load impedance is such that dissipation of the power amplifier  114  stays below an unacceptable dissipated power level. As illustrated, the loop will keep the rail voltage at a desired value (e.g., 150 V) and simply increase the gate bias until the desired output power is achieved. In this case, the generator  102  can go from zero to full power in approximately one microsecond. 
     Dissipation is normally highest when the bias level is such that the generator is around half-power. If the requested power is such that the dissipation is high, the rail voltage control loop, in many modes of operation, will reduce the rail voltage to keep the dissipation under control, as illustrated in  FIG. 4 . 
     Optimum efficiency is approximately along a constant high gate bias line. In many modes of operation, the control loop adjusts the rail voltage so that the gate bias stabilizes at this high value while avoiding the range of unacceptable dissipated power. As illustrated in  FIG. 4 , the rail voltage starts at a high level, but then is adjusted downward to avoid the area of unacceptable dissipated power. The rail voltage ultimately converges at a point where the desired delivered is met. 
     An additional feature of many embodiments of the disclosed apparatus and method for controlling a power generator is that it ensures that the generator will operate in the same setting (rail voltage, gate bias voltage) every time that the generator is given the same set point for the same load impedance. 
     The gate bias control loop is much faster than the rail voltage control loop. This allows the gate bias loop to “punch through” areas of high dissipation quickly (i.e., sufficiently fast enough to avoid the harmful effects of operating at unacceptably high dissipation levels) if a high output power is requested, as illustrated in  FIG. 5 . Even though the rail voltage control loop will try to decrease the rail voltage when in the unacceptably high dissipation area, the rail voltage control loop it is too slow, relative to the gate bias control loop, to affect the rail voltage if the generator stays in the high dissipation area for only a short time. 
       FIGS. 6 and 7 , viewed together, provide additional insight into the operation of the disclosed system and method. In general there is a continuum of solutions to achieve a desired output power. For example, looking at  FIGS. 6 and 7  together, it is apparent that 1 kilowatt delivered power can be produced at the three points listed. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Illustrating a Continuum of Solutions 
               
             
          
           
               
                   
                 Bias 
                 Rail voltage 
                 Delivered power 
                 Dissipated power 
               
               
                   
                   
               
             
          
           
               
                   
                 −1 
                 200 
                 1000 
                 1100 
               
               
                   
                 0 
                 110 
                 1000 
                 300 
               
               
                   
                 3 
                 80 
                 1000 
                 250 
               
               
                   
                   
               
             
          
         
       
     
     The trajectories, shown in  FIGS. 6 and 7 , illustrate how the control loops adjust the power between 50 W and 1500 W. Starting from the very left point, the bias voltage is increased rapidly until 1500 W is achieved at 0.5 V gate bias and 150 V rail voltage. Notice that rail voltage is slightly below 150 V rail because, in this example, the desired dissipation is set at 250 W, so the rail voltage is decreased a bit. Once the generator is at 1500 W, the rail voltage control loop decreases the rail voltage to attempt to get to the desired dissipation of 250 W and the desired gate bias of 2.5 V (it does not achieve the latter objective). When the power set point is changed to 50 W, the bias voltage is again rapidly decreased until the output power is 50 W. At this point the rail voltage is increased back to the desired 150 V. 
     In operation, embodiments of the disclosed control system comprise two control loops (gate bias and rail voltage) to achieve the desired objective. The gate bias control loop (fast loop) looks at the delivered power, and at two protection parameters that require high speed control: reflected power and supply current. This control loop adjusts the gate bias to achieve the desired power (also referred to as “set point”) subject to the condition that the reflected power and supply current remain below their (user-defined) maximum limits. 
     In the gate bias control loop, if operation is below the set point and below any of the limiting values, the bias voltage will be increased until operation reaches the set point. Otherwise the control loop will decrease the gate bias voltage until operation of the power system is at the set point or at the defined maximum reflected power or at the maximum drain current. Once at least one of those conditions is met, the gate bias control loop stops operation unless there is a change in operational condition of the system. 
       FIG. 8  is a flow diagram illustrating the method for controlling gate bias voltage. The method of control loop  800  begins at block  802 . Next at block  804 , three parameters are measured: the difference between the delivered power and the desired delivered power, also referred to as the “delivered power error;” the reflected power; and the drain current. At block  806  an adjustment to the gate bias voltage is calculated, based on the measured delivered power error, to achieve required delivered power. At block  808  an adjustment to the gate bias voltage is calculated, based on the measured reflected power, to achieve the maximum reflected power. At block  810  an adjustment to the gate bias voltage is calculated, based on the measured drain current, to achieve the maximum drain current. The desired delivered power, maximum reflected power and maximum drain current are set by the user (not shown) prior to operation of the power generation system. At block  812  the three adjustments calculated in blocks  806 ,  808  and  810 , are compared, and the calculated adjustment having the smallest magnitude will be implemented. At branch  814 , the method determines whether one (or more) of the desired delivered power (or set point), maximum reflected power or maximum drain current are met. If so, the method stops at block  816 . If not, then the method returns to block  804  to go through the control loop again. 
     The second, rail voltage loop (slow loop) handles the dissipation limit loop and acts as an optimizer, trying to achieve as close as possible to the desired rail voltage, desired gate bias voltage and desired dissipation. It receives three inputs: (1) the gate bias voltage (which is controlled by the fast loop); (2) the dissipated power; and (3) the previous value of the rail voltage. 
     This method optimizes the rail voltage to try to achieve: (1) no more than the maximum dissipation; (2) preferably no more than the minimum dissipation; (3) a bias voltage (as set by the first loop); (4) a minimum bias value; and (5) a minimum rail voltage. 
       FIG. 9  is a flow diagram illustrating the method for controlling rail voltage. The method of control loop  900  begins at block  902 . Next at block  904 , two parameters are measured: the gate bias voltage, and the dissipated power. At branch  906  the control loop determines whether the dissipated power is greater than the maximum allowed dissipated power (an unacceptable condition, except for short periods of time). If the dissipated power is greater than the maximum dissipated power allowed, then the control loop progresses to block  980  where an adjustment to the rail voltage is calculated based on the difference between the measured dissipated power and the maximum allowed dissipated power. At block  910  an adjustment to the rail voltage is calculated, based on the previous value of the rail voltage. At block  912  the two adjustments calculated in blocks  908  and  910  are compared, and the calculated adjustment having the smallest magnitude will be implemented. 
     If at branch  906 , the dissipated power is not greater than the maximum allowed dissipated power, then the control loop progresses to branch  914 . At branch  914 , the control loop determines whether the measured dissipated power is less than the minimum allowed dissipated power. If it is, the control loop progresses to branch  916  and determines whether the gate bias is greater than the minimum allowed gate bias. If it is, then the control loop progresses to branch  918  to determine whether the previous rail voltage is less than the minimum desired rail voltage. If it is, then the control loop progresses to block  920  to calculate an adjustment to the rail voltage based on the difference between the previous rail voltage and the desired minimum rail voltage. The control loop next progresses to block  922  where it calculates an adjustment to the rail voltage based on the previous rail voltage. Next, in block  924 , the control loop compares the two calculated adjustments and implements the larger of the two. 
     If any of branches  914 ,  916  or  918  are answered in the negative, then the control loop progresses to block  926  whereby the rail voltage is adjusted based simply on the previous value of the rail voltage. 
     Finally, as depicted in  FIG. 10 , a method for controlling the power generation system  1000  is illustrated. The method begins at block  1002 , and then branches to blocks  800  and  900  concurrently. Block  800  corresponds to the method for controlling gate bias voltage as described above and depicted in  FIG. 8 . Block  900  corresponds to the method for controlling rail voltage as described above, and as depicted in  FIG. 9 . At branch  1004 , the method determines whether the power generation system is presently optimized for the given performance parameters, as established by the user, under the present circumstances. If the power generation system is optimized for the given performance parameters, then the method stops at block  1006 . If the power generation system is not optimized, then the method branches out from block  1004  to return to the beginning of the method to repeat the steps accordingly until such time that the power generation system is operating at the desired operational parameters. 
     In conclusion, the present application discloses, among other things, a system, an apparatus and a method for controlling the application of power with a power generator. Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the disclosure herein, its use, and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the claims to the disclosed exemplary forms. Many variations, modifications, and alternative constructions fall within the scope and spirit of the present disclosure as expressed in the claims.