Abstract:
A method and apparatus for allowing the user of a power generator coupled to a time-varying load, to define an alternative reference impedance to enable on or more metrics to be provided relative to the alternative reference impedance. The metrics, for example, may provide indicia of performance of the power generator system. One illustrative embodiment provides a power delivery system that applies power to a plasma chamber to create a plasma therein; determines a reference impedance of the plasma at an operating condition; and controls the power delivery system based on the determined reference impedance.

Description:
PRIORITY 
       [0001]    This application claims priority to provisional application No. 61/141,823 entitled METHOD AND APPARATUS FOR ADJUSTING THE REFERENCE IMPEDANCE OF A POWER GENERATOR. 
     
    
     FIELD 
       [0002]    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 
       [0003]    Power generators are typically designed for optimal performance 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 
       [0004]    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. 
         [0005]    One illustrative embodiment includes a power generator, comprising a power delivery system configured to have a predefined reference impedance; a load, coupled to the power delivery system, having an operational impedance that is different than the predefined reference impedance of the power delivery system; and a performance assessor, coupled to the power delivery system, where the performance assessor is configured to receive information about the operational impedance of the load and is configured to assess operational efficiency of the power delivery system as it delivers power to the load, the assessed operational efficiency being relative to the operational impedance of the load. 
         [0006]    Another illustrative embodiment comprises a method of controlling a power generation system, comprising providing a power delivery sub-system having a predefined reference impedance; providing a load having an operational impedance different from the predefined reference impedance of the power delivery sub-system; delivering power from the power delivery sub-system to the load; and determining the operational efficiency of the power generation system with respect to the operational impedance of the load. 
         [0007]    These and other embodiments are described in further detail herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    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: 
           [0009]      FIG. 1  is a system-level block diagram depicting a representative embodiment of the disclosed power generation system coupled to a load; 
           [0010]      FIG. 2  is a block diagram depicting an exemplary embodiment of the performance assessor of the system depicted in  FIG. 1 ; and 
           [0011]      FIG. 3  is a flow diagram depicting a method for defining an alternative reference impedance of a power generator. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Reference is now directed to the drawings, where like or similar elements are designated with identical reference numerals throughout the several views. 
         [0013]    Referring to  FIG. 1 , a block diagram of the disclosed power generation system  100  is shown. A power generator  102  is electrically coupled to a load  106 . Coupled between the power generator  102  and the load  106  is a performance assessor  104 . Typically, but not always, some type of matching network (not shown) is used to match the load to the generator  102 . 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 generator  102 . 
         [0014]    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 power generator  102  and the performance assessor  104  may be realized by common components and may be within the same housing. Or the power generator  102  and the performance assessor  104  may be implemented and sold separately. 
         [0015]    Although not required, the power generator  102  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  102  includes a power supply configured to provide power from 30 Watts to 3 kW at frequencies around 13.56 MHz. It is certainly contemplated, however, that the power supply may provide other frequencies and power levels. One exemplary power supply that may be utilized to realize the power generator  102  is sold under the tradename PARAMOUNT by Advanced Energy Industries, Inc. of Fort Collins, CO. 
         [0016]    The measure of how close the load impedance is to the desired impedance can take many forms. Frequently it is expressed as a reflection coefficient, 
         [0000]    
       
         
           
             ρ 
             = 
             
               
                 Z 
                 - 
                 
                   Z 
                   o 
                 
               
               
                 Z 
                 + 
                 
                   Z 
                   0 
                   * 
                 
               
             
           
         
       
     
         [0000]    where ρ is the reflection coefficient of the impedance Z with respect to the desired impedance Z 0 . The magnitude of the reflection coefficient (|ρ|) is a very convenient way to express how close the impedance Z is to the desired impedance Z 0 . Both Z and Z 0  are in general complex numbers. 
         [0017]    Other measures may be used for this purpose. Such other measures, for example, include without limitation, minimum reflected power or maximum delivered power. 
         [0018]    Some types of loads, like a plasma for example, can be unstable when configured to operate at the power generator&#39;s reference impedance at a particular power level. In such circumstances, the reflected power will not be at or near zero because the load&#39;s impedance is not matched to the power generator&#39;s reference impedance. Under such circumstances, it has been found to be desirable to assess the power generator&#39;s operational efficiency relative to the load&#39;s impedance rather than relative to the power generator&#39;s reference impedance. 
         [0019]    The performance assessor  104 , in many embodiments, is configured to receive input from the user of the power generation system  100  defining the operational impedance at the load. The performance assessor  104  is configured to substitute the operational impedance of the load (as input by the user) for the reference impedance of the power generator  102 , thereby enabling use of standard performance measurement techniques with respect to the load&#39;s operational impedance rather than the power generator&#39;s  102  reference impedance. Thus, an alternative reference impedance may be defined, with respect to which metrics of operational efficiency (such as reflected power) may be used to assess performance of the power generator system as depicted in  FIG. 1   
         [0020]    Referring to  FIG. 2 , depicted is an embodiment of an exemplary performance assessor  204  that may be used to realize the performance assessor  104  referenced in FIG.  1 . As depicted, a coupler  108  in this embodiment is coupled between the power generator  102  and the load  106 , and a controller  110  is coupled to the coupler and is disposed so as to receive a user input. It should be recognized that the depiction of these components is logical; thus the components can be combined or further separated in an actual implementation. Moreover, the construction of these functional components, in light of this specification, is well known to one of ordinary skill in the art. 
         [0021]    The coupler  108  is configured to measure one or more characteristics (e.g., forward and reflected voltage) of the power that is applied to the load  106 . In many implementations, the coupler  108  is realized by a directional coupler. And one of ordinary skill in the art will appreciate that the coupler  108  may include a transducer, electronics, and processing logic (e.g., instructions embodied in software, hardware, firmware or a combination thereof). U.S. application Ser. No. 12/116,375 entitled System, Method, and Apparatus for Monitoring Power, which is incorporated herein by reference, includes a disclosure of exemplary techniques for monitoring power. 
         [0022]    As shown, the controller  110 , in this embodiment is configured to receive input data from a user of the system as well as the measurements (e.g., forward and reflected voltage) from the coupler  108 . In many implementations, the controller  110  is generally configured to enable a user to redefine the reference impedance so that one or more characteristics of the power applied to the load (e.g., forward and reflected power) may be calculated with respect to the redefined reference impedance. 
         [0023]    The controller  110  may be realized by hardware, software, firmware or a combination thereof. It should also be recognized that the functionality of the controller may be realized by components within a generator (e.g., generator  102 ), within a performance assessor that is separately housed from a generator, or may be distributed among components within both a generator and a performance assessor. And in some implementations, the controller  110  is coupled to a display and is configured to display characteristics (e.g., reflected power) of the power that is applied to a load (e.g., load  106 ) 
         [0024]    In many modes of operation, delivered power may be considered to be independent of the chosen reference impedance. For exemplary purposes, assume that it is desirable to deliver 3000 Watts into a load having a complex impedance of 60+j10 ohms. A 50 ohm-based measurement system will calculate the load reflection coefficient as follows: ρ=(60+j10−50)/(60+j10+50)=(10+j10)/(110+j10)=0.0984+j0.082, with the forward power equal to: 1/(1−|ρ|̂2)*3000=3050 Watts, and thus the reflected power is 50 Watts. 
         [0025]    If the reference impedance is changed (e.g., by the user) to 60+j10, the forward power will equal the delivered power (3000 W) and the reflected power is 0. Thus, the user may define the reference impedance so that reflected power is approximately zero when a desirable impedance is provided to the generator. 
         [0026]    In many implementations, the controller  110  uses a 2 by 2 complex matrix to convert the signals measured by the coupler  108  to the forward and reflected voltages from which forward and reflected power as well as load impedance is calculated by the controller  110 . This matrix, for example, may include coefficients that are determined with a calibration procedure for every coupler. 
         [0027]    The relationship between the operational load impedance and the generator reference impedance may be characterized as follows: Pforward — 1−Preflected — 1=Pdelivered=Pforward — 2−Preflected — 2, where Pforward — 1 and Preflected — 1 is the split for the generator reference impedance, and Pforward — 2−Preflected — 2 is the split for the load&#39;s operational impedance. 
         [0028]    Referring now to  FIG. 3 , depicted is a flow diagram illustrating a method  300  for defining an alternative reference impedance of a power generator with respect to which metrics of operational efficiency (such as reflected power) may be used to assess performance of a power generator system (e.g., system  100 ). As depicted, the method  300  begins at block  302 . At branch  304 , the method determines whether the load  106 , when coupled to the power generator  102 , will be stable under the desired operating conditions, for example, at a specified fixed power delivery level. In one embodiment, the system user provides stability information to the system. If the load  106 , operating at desired conditions, will be stable, then the method progresses to block  306  where the system calculates operational performance and efficiency with respect to the reference impedance of the power generator, for example, 50 ohms. 
         [0029]    If the load  106 , operating at desired conditions, will not be stable, then the method progresses to block  308 , where the user sets the operational impedance of the load to be the impedance value upon which system performance and efficiency will be referenced. Next, at block  310 , the system calculates both forward power delivered by the power generator to the load, and reflected power, reflected by the load back to the power generator. At block  312 , the exemplary method then adjusts performance of the system adjusting parameters, including delivered power, so as to arrive at a desired metric of performance (e.g., reflected power). For example, parameters may be adjusted to minimize reflected power. It should also be recognized that parameters may be adjusted so as to arrive at a desired balance between system stability and power-delivery performance. The process of calculating and adjusting repeat until a desired state of operation (e.g., a desired or predetermined efficiency) is reached, or until operation of the system ceases. 
         [0030]    In conclusion, the present application discloses, among other things, a method and apparatus for defining an alternative reference impedance of a power generator, with respect to which metrics of operational efficiency (such as reflected power, among others) may be used to assess performance of the power generator system. 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.