Abstract:
Integrated voltage and current (VI) probe ( 18 ) for integration inside a transmission line ( 17 ) having inner ( 3 ) and an outer ( 4 ) conductors. Current probes, often implemented as loop antennas, can be coupled to the outer conductor. The probes can either be built onto the same panel or on different panels.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application claims priority and is related to U.S. provisional Ser. No. 60/360,016, filed on Feb. 28, 2002. The present application is related to U.S. provisional application Ser. No. 60/259,862, entitled “Capacitively coupled RF voltage probe”, filed on Jan. 8, 2001; and co-pending application 60/359,986, entitled “Portable VI probe,” filed on Feb. 28, 2002. The contents of all of those applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is directed to a method and a system for measuring voltage and current levels using an Integrated (i.e. in-line) Voltage and Current (VI) Probe. 
     2. Discussion of the Background 
     In the fabrication and processing of semi-conductor wafers, such as silicon wafers, a variety of different semiconductor equipment and processes can be utilized. For example, wafer processing techniques are known in the art and may include, for example, photolithography, ion beam deposition, vapor deposition, etching, as well as a variety of other processes. 
     In one method of wafer processing, plasma generators are used to process a wafer, for example by etching a layer formed on the surface of the wafer. In employing this technique, electrical power is coupled to the plasma generator from an electrical source. Typically, the electrical energy has a frequency in the radio frequency (RF) range. Control of the process is performed in part by measuring and monitoring the RF signal. The power input into the system can be determined by measuring the RF voltage (V) and the current (I) components of the RF power source coupled to the plasma generator. Thus, a common practice for measuring RF power is to install a sensor for monitoring current and voltage in series with the transmission medium coupling the RF power to the plasma generator. 
     Sometimes, however, the presence of the RF probes can itself disrupt the propagating electro-magnetic fields the probes are intended to measure. This may occur through reflections of the RF signal, for example, that are imposed by the implementation of the RF probe(s). Consequently, there exists a need for an integrated voltage and current probe to monitor a source of RF electrical power which minimally intrudes in the RF transmission line in which the probes are placed. 
     Moreover, the presence of RF probes can affect proven processes, which is entirely unacceptable to device manufacturers. As the probes are installed in the RF transmission structure outside the chamber and sometimes beyond the output of the match network, the above-identified problem can be further exacerbated when commercially available probes are utilized. Therefore, there exists a need for an integrated voltage and current probe to monitor a source of RF electrical power, which minimally affects a proven process. 
     SUMMARY OF THE INVENTION 
     A need exists for a voltage and or current probe which can be installed along a transmission line in a plasma generator and which will minimally perturb or impact the propagating electro-magnetic fields or the plasma process. 
     Therefore, an exemplary embodiment of this invention provides for an apparatus and a system for integrating the apparatus into a transmission line of a plasma generator. The apparatus can detect voltage and/or current within a transmission line while minimally impacting or perturbing the propagating electro-magnetic fields. This minimal impact arises from the voltage and current probes being placed within the existing chamber structure proximate the power coupling (or plasma) electrode. 
     Other objects, features and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will become readily apparent with reference to the following detailed description particularly when considered in conjunction with the accompanied drawings, in which: 
         FIG. 1A  is a perspective view of a voltage probe integrated into a transmission line; 
         FIG. 1B  is a perspective view of a voltage probe integrated into an inner conductor of a transmission line; 
         FIG. 2  is a side view of the various sections of the invention showing the integration of the voltage probe and the current probe; 
         FIG. 3  is a schematic view of the voltage and current probe constructed within an upper electrode structure; and 
         FIG. 4  is a schematic view of the voltage and current probe constructed within a lower electrode structure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1A , a transmission line  17  includes an inner conductor  3  and an outer conductor  4 . Each runs along the transmission line in an axial direction such that the inner conductor has a diameter substantially smaller than that of the outer conductor. 
     A non-limiting embodiment of an integrated VI probe  18  is shown broken away from the outer conductor of the transmission line. For example, the integrated VI probe can be attached, for example, as a panel, to the outer conductor  4  as shown by arrows  30 A,  30 B,  30 C and  30 D. Arrows  30 A,  30 B,  30 C and  30 D can, for example, represent fasteners (e.g., bolts, solder, adhesive) utilized to affix the VI probe panel  18  to a windowed section of the outer conductor  4  of RF transmission line  17 , wherein the VI probe panel  18  serves as the outer conductor. 
     When attached, the VI probe panel  18  should be within the transmission line, as shown in  FIGS. 1A through 4 , proximate to the plasma processing electrode in a space sufficiently large to accommodate the size of the probe. Typically, the latitudinal and longitudinal dimensions of the probe are on the order of one centimeter and the thickness is on the order of a millimeter. Once installed, the probe should not alter the geometric configuration of the transmission line or the material properties of the conductors. Thus, the intrinsic impedance of the transmission line is to remain substantially constant or constant. 
     Voltage and current probes  19  and  20 , respectively, with electrical leads  19 A,  19 B,  20 A and  20 B can mounted upon the VI probe panel  18  using techniques conventional in the art. For example, in a plasma processing environment, lead  19 A can be directly coupled to the capacitively coupled electrode and lead  19 B can be coupled to the outer conductor  4  of RF transmission line  17 . Alternatively, the pair of leads  19 A,  19 B can be replaced with a standard electrical connector such as, for example, a SMA connector or a BNC connector. For example, lead  20 A can be coupled to the loop antenna and lead  20 B can be coupled to the outer conductor  4  of RF transmission line  17 . Alternatively, the pair of leads  20 A,  20 B can be replaced with a standard electrical connector such as, for example, a SMA connector or a BNC connector. The construction and calibration of VI probes are well known to those skilled in the art of voltage-current diagnostics. For example, VI probe construction and calibration is described in detail in pending U.S. application Ser. No. 60/259,862 filed on Jan. 8, 2001, and U.S. Pat. No. 5,467,013 issued to Sematech, Inc. on Nov. 14, 1995; each of which is incorporated herein by reference in its entirety. 
     In  FIG. 1A , voltage and current probes,  19  and  20 , respectively are shown mounted to a single VI probe panel  18 . Alternatively, each probe can be mounted to separate panels, for example, a pair of VI probe panels can be oriented on diametrically opposing sides of RF transmission line  17 , to which a voltage probe is fabricated on a first panel and a current probe is fabricated on a second, opposing panel. Desirably, transmission line  17  is mounted within a process chamber (not shown). 
       FIG. 1B  shows the same voltage probe discussed above integrated onto an inner conductor  3  of a transmission line. Voltage probe  119  comprises electrical leads  119 A and  119 B, wherein lead  119 A is coupled to voltage probe electrode  108  or an electrode ring and exits the transmission line through outer conductor  4 . Voltage probe electrode  108  can be a ring electrode as shown in  FIG. 1B , or alternately, can comprises a plate electrode in close proximity to the inner conductor. 
       FIG. 2  represents an alternate embodiment of an implementation of a VI probe in a RF transmission line  17 . The RF transmission line  17  includes various sections including sections  17 A,  17 B and  17 C as shown. Section  17 A can represent the output transmission line of an impedance match network, section  17 C can represent the input transmission line to a plasma reactor, and section  17 B can represent a transmission line section within which a voltage and current probe are mounted. Section  17 B can be, for example, mounted between sections  17 A and  17 C using standard flanges (e.g., CF flanges, KF flanges) and the characteristic impedance of the overall transmission line (sections  17 A,  17 B and  17 C) can be preserved. Desirably, sections  17 B and  17 C are mounted within the chamber. 
     Outer conductor  4 B is the area on the transmission line  17  in which the probes have been installed. The outer conductor  4 B contains access areas  27 ,  28  through which the probes attach to and exit from the outer conductor. The outer conductor  4 B surrounds its corresponding part of the inner conductor  3 B. In the illustrated embodiment, the various elements of the voltage and current probe are attached to the inner surface of the outer conductor. The voltage and current probes comprise similar elements as described with reference to  FIG. 1 . The voltage probe comprises a voltage probe electrode  19  that is connected to first and second leads  19 A and  19 B. At least one of the leads  19 A and  19 B is connected to one of the conductors (e.g., the outer conductor  4 B) and acts as a ground reference. The pair of leads  19 A,  19 B, however, can be replaced with a standard electrical connector such as, for example, a SMA connector or a BNC connector. The current probe comprises a loop antenna  20  to which a lead  20 A is coupled. A second lead  20 B is coupled to the outer conductor  4 B. The pair of leads  20 A,  20 B can be replaced with a standard electrical connector such as, for example, a SMA connector or a BNC connector. The VI probe construction and calibration is performed in a manner equivalent to the VI probe of  FIG. 1A  and described in detail in pending U.S. application Ser. No. 60/259,862 filed on Jan. 8, 2001, and U.S. Pat. No. 5,467,013 issued to Sematech, Inc. on Nov. 14, 1995. 
     An Integrated VI probe can be built onto a transmission line within a plasma reactor. In a first embodiment, as shown in  FIG. 3 , a plasma generator  100  includes a plasma processing electrode  2 , a match network  1 , and a “transmission line” formed of (1) a conductor (acting as an inner conductor  3 ) between the electrode  2  and the match network  1  and (2) an electrode housing (acting as an outer conductor  4 ). An exemplary plasma reactor comprising a plasma processing electrode, to which RF power is applied, is described in U.S. Pat. No. 5,900,103 issued to Tokyo Electron Ltd. on May 4, 1999, which is incorporated herein by reference in its entirety. A match network  1  is employed to optimize the transfer of power from a RF source to plasma through a plasma processing electrode  2  by matching the output impedance of the RF source to the load impedance which includes the plasma. In general, an impedance match is obtained when the output impedance of the match network  1  is the complex conjugate of the load impedance. The interesting feature is that the characteristic impedance of the structure following the output of the match network  1  and including the plasma is not generally 50 Ohms. In fact, this impedance is usually very small. Therefore, when a VI probe is arranged within the electrode structure as shown in  FIG. 3 , it maximally complies with the designed characteristic impedance of the system and, hence, it minimally perturbs the propagating electro-magnetic fields. Such a system design can minimize any impact on the proven process in the plasma processing system while providing reliable measurement of the RF voltage and current. 
       FIG. 3  also shows a schematic view of the connection between the probes and the outer conductor that are analogous the structures shown in  FIGS. 1A ,  1 B and  2 . In  FIG. 3 , the voltage probe  19  and the current probe  20  are attached to the outer conductor in such a way as to be substantially close to one another. Alternately, they can be mounted on opposite sides of the outer conductor. In general, a voltage probe measures a voltage between a capacitively couple plasma electrode and a grounded housing. Similarly, the current probe  20  can be implemented as a loop antenna that captures at least a fraction of the azimuthal magnetic flux from the “transmission line”. 
     The voltage probe  5  and the current probe  6  are installed onto the inner surface of the outer conductor. As described above, the construction and calibration of the voltage and current probes are described in detail in pending U.S. application Ser. No. 60/259,862 filed on Jan. 8, 2001, and U.S. Pat. No. 5,467,013 issued to Sematech, Inc. on Nov. 14, 1995. 
     As shown in  FIG. 4 , a similarly effective result can be accomplished by having the voltage probe  19  and the current probe  20  installed onto the lower electrode structure. Here,  FIG. 4  presents a second embodiment of an Integrated VI probe built into a “transmission line” for a lower electrode  2  of a plasma generator using structures analogous to those shown in  FIGS. 1 and 2 . In  FIG. 4 , the voltage probe  19  and the current probe  20  are built into the RF path between the lower electrode  2  and the match network  1 . The probes can be mounted on opposite sides of the outer conductor as shown, on the same side, or on adjacent sides. As discussed above, the implementation of voltage and current probes using the structures described in  FIGS. 1 and 2 , and shown in  FIG. 4 , can be expected to minimally perturb the propagating electro-magnetic fields by not introducing (1) substantive changes in the characteristic impedance of the RF transmission line and, hence, (2) additional reflections. Therefore, such probes will reduce any impact on proven process in the plasma processing system. 
     At least one detector can be coupled to each probe in order to detect a voltage and/or current being transmitted on the transmission line to which the probes are connected. Such a detector can be an oscilloscope or an A/D device coupled to a computer to provide the voltage and/or current to the computer in periodic samples. 
     As would be understood by one of ordinary skill in the art, the voltage and current probes may be integrated into a transmission line separately. Thus, a current probe may be used without a voltage probe and vice versa. 
     Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.