Abstract:
A segmented electrode apparatus for use in plasma processing in a plasma chamber or as part of a plasma processing system. The apparatus is composed of a plurality of electrode segments each having an upper surface, a lower surface and a periphery. The lower surfaces of the electrode segments define an electrode segment plane. Further included in the electrode is a plurality of displaceable insulating ring assemblies with a conductive shielding layer in each of them. Each assembly has an insulating body with an upper and lower portion and surrounds a corresponding one of the electrode segments at the electrode segment periphery. Each insulating ring assembly is arranged adjacent another insulating ring assembly and is displaceable with respect thereto and to the corresponding electrode segment. Also included in the electrode apparatus is a plurality of displacement actuators connected to the chamber and to the plurality of insulating ring assemblies at the insulating body upper portions. The displacement actuators are used to displace at least one of the insulating ring assemblies relative to the corresponding one of the electrode segments so as to cause the lower portion of at least one insulating body to move in a direction perpendicular to the electrode segment plane.

Description:
This a Continuation of International Application No. PCT/US01/41311, which was filed on Jul. 10, 2001 and claims priority from Provisional U.S. application Ser. No. 60/218,040, which was filed Jul. 13, 2000, the contents of both of which are incorporated in their entirety herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention pertains to electrodes, and in particular to adjustable segmented electrodes used in plasma processing of workpieces such as semiconductor wafers. 
     In semiconductor manufacturing, plasma reactor chambers are used to remove or deposit material on a workpiece (e.g., semiconductor substrate) in the process of making integrated circuit (IC) devices. A key factor in obtaining the highest yield and overall quality of ICs is the uniformity of the etching and deposition processes. 
     A problem that has plagued prior art plasma reactors is the control of the plasma to obtain uniform workpiece etching and deposition. In plasma reactors, the degree of etch or deposition uniformity is determined by the uniformity of the plasma properties. The latter is dictated by the design of the overall system, and in particular the design of the electrodes used to create the plasma in the interior of the reactor chamber. 
     One approach to improving etch and deposition uniformity has been to use a segmented electrode.  FIG. 1  is a plan view of one type of prior art segmented electrode  800 . Electrode  800  is circular in shape and comprises a central electrode segment  806 , and four arcuate-shaped outer electrode segments  810  surrounding the central electrode segment. Electrode segments  806  and  810  are made of a conducting material, such as aluminum or aluminum covered with silicon on the front surface facing the plasma. Each electrode segment  806  or  810  is electrically connected to a RF power supply (not shown) that provides power to the electrode segment. Though nominally identical, the RF signal being applied to one electrode segment is likely to differ from that being applied to adjacent electrode segments in power (voltage or current or both at the same time), frequency, phase, or even waveform. Even the phase difference in RF between adjacent sub-electrodes (i.e., electrode segments) can be sufficient to cause electrical discharging between electrode segments when the dielectric separation between them is small. 
     Accordingly an insulating structure  816  supports and separates respective electrode segments  806  and  810  to prevent electrical communication (e.g., discharging) between the segments when RF power is supplied to the segments. Insulating structure  816  is typically non-adjustable and made of a ceramic material or glass. 
     Unfortunately, even with a segmented electrode such as electrode  800  of  FIG. 1 , etch and deposition non-uniformities can occur when processing a workpiece. In particular, when plasma etching a substrate with a segmented electrode, it is expected that regions underneath the insulating structure  816  have a different etch or deposition rate than regions directly underneath the sub-electrodes. The overall non-uniformity is typically-up to 10% for a 200 mm capacitively coupled plasma chamber with an unsegmented plasma electrode. A successful implementation of a segmented electrode for a capacitive plasma chamber is expected to achieve non-uniformity less than about 5% when a partition shown in  FIG. 1  is used, due to the smaller dimensions of the sub-electrodes. However, there are a number of issues that need to be addressed when a partitioned plasma electrode is used for a capacitively coupled plasma chamber, such as a discharge between adjacent sub-electrodes and RF interference among sub-electrodes. 
     There are several U.S. patents pertaining to segmented electrodes used in plasma processing. These include U.S. Pat. Nos. 4,885,074, 5,565,074 and 5,733,511. The segmented electrodes disclosed in these patents are not adjustable in position. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention pertains to electrodes, and in particular to adjustable segmented electrodes used in plasma processing of workpieces such as semiconductor wafers. 
     A first aspect of the invention is a segmented electrode apparatus for use in a plasma chamber having a wall. The apparatus comprises a plurality of electrode segments each having an upper surface, a lower surface and a periphery. The electrode segments are supported in place relative to the plasma chamber wall by an electrode segment support member connected to each of the electrode segments and to the chamber wall. The lower surfaces of the electrode segments define an electrode segment plane. Further included in the electrode is a plurality of displaceable insulating ring assemblies. Each assembly has an insulating body with an upper portion and a lower portion and surrounds a corresponding one of the electrode segments at the electrode segment periphery. Each insulating ring assembly is arranged adjacent another insulating ring assembly and is displaceable with respect thereto and to the corresponding electrode segment. Also included in the electrode is a first plurality of displacement actuators connected to the chamber wall and to the plurality of insulating ring assemblies at the insulating body upper portions. The displacement actuators are used to displace at least one of the insulating ring assemblies relative to the corresponding one of the electrode segments so as to cause the lower portion of at least one insulating body to move in a direction perpendicular to the electrode segment plane (e.g., toward the plasma). 
     A second aspect of the invention is a plasma processing system for processing a workpiece. The system comprises a plasma chamber having an interior region capable of supporting a plasma, a workpiece support for supporting the workpiece, and the segmented electrode as described above, arranged within the plasma chamber adjacent the workpiece support. The system can further include a plurality of RF power supplies connected to corresponding electrode segments, and a control system electronically connected to the plurality of RF power supplies, for controlling the RF power delivered to the plurality of electrode segments. 
     A third aspect of the invention is a method of processing a workpiece with a plasma formed in a process chamber from a gas enclosed therein. The plasma chamber has a segmented electrode with electrode segments that define an electrode segment plane. The electrode segments are separated by adjustable insulating ring members having an insulating body with an upper portion and a lower portion. The workpiece resides on a workpiece support adjacent the segmented electrode. The method comprising a first step of providing RF power to each of the electrode segments, thereby forming within the plasma chamber the plasma with a plasma density profile. The next step is adjusting one or more of the insulating bodies such that the lower portion of the one or more insulating bodies is translated in a direction perpendicular to the electrode segment plane, so as to adjust the plasma density profile. The last step is processing the workpiece with the plasma having the adjusted plasma density profile. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a plan view of a prior art segmented electrode showing the electrode segments with the insulating structure between the segments; 
         FIG. 2  is a schematic diagram of a plasma processing system according to the present invention having a segmented electrode according to the present invention; 
         FIG. 3  is a plan view of an embodiment of the segmented electrode of the present invention; 
         FIG. 4  is a cross-sectional diagram of the segmented electrode of  FIG. 3  incorporated into the plasma chamber of the plasma processing system of  FIG. 2 , showing a portion of the chamber side wall and upper wall; and 
         FIG. 5  is a close-up cross-sectional view of the segmented electrode shown in  FIG. 4 , illustrating the movement of insulation ring assemblies relative to one another. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention pertains to electrodes, and in particular to adjustable segmented electrodes used in plasma processing of workpieces such as semiconductor wafers. 
     With reference to  FIG. 2 , there is shown a plasma processing system comprising a plasma chamber  20  as a vacuum processing chamber adapted to perform plasma cleaning of a workpiece W, such as a silicon wafer. Workpiece W has an upper surface WS. Chamber  20  has sidewalls  22 , an upper wall  24  and a lower wall  26  that enclose an interior region  30  capable of supporting a plasma  36 . Chamber  20  includes within region  30  a workpiece support  40  arranged adjacent lower wall  26  for supporting workpiece W while the workpiece is processed in chamber  20 . Workpiece W may be, for example, a semiconductor substrate on which patterns have been formed, where the patterns correspond to product devices at any point of the process cycle used to manufacture a semiconductor device. Workpiece W can also be a bare semiconductor substrate that needs to be plasma cleaned in preparation for processing. 
     Chamber  20  includes a segmented electrode  50  arranged within interior region  30  adjacent workpiece support  40 . Segmented electrode  50  has an upper surface  50 U facing away from workpiece support  40  and a lower surface  50 L facing towards workpiece support  40 . Segmented electrode  50  serves to further divide plasma chamber interior region  30  into a first section  32 U between upper chamber wall  24  and upper electrode surface  50 U, and a second section  32 L between lower electrode surface  50 L and lower chamber wall  26 . Plasma  36  is formed in second section  32 L of interior region  30 . Plasma  36  ideally has a plasma density (i.e., number of ions/volume, along with energy/ion) that is uniform, unless the density needs to be tailored to account for other sources of process non-uniformities. The density of plasma  36  has a density profile referred to herein as a “plasma density profile.” 
     Referring to  FIG. 3  together with  FIG. 2 , segmented electrode  50  comprises a plurality of electrode segments  52  (e.g.,  52 A,  52 B, . . .  52 N) and an insulating structure  54  comprising a plurality of insulating ring assemblies  56  surrounding the electrode segments. Electrode segments  52  are preferably planar (i.e., plate-like). Segmented electrode  50  of the present invention is discussed in greater detail below. 
     Electrode segments  52  are electrically connected to respective RF power supplies  62  (e.g.,  62 A,  62 B, . . .  62 N) of an RF power supply system  60 . respective RF power supplies  62  (e.g.,  62 A,  62 B, . . .  62 N). Each RF power supply  62  has an associated match network MN (e.g., MNA, MNB, . . . MNN) for controlling the amplitude and phase of the RF power delivered to a respective electrode segment  52 . By adjusting the RF power amplitude and phase delivered to each electrode segment  52 , the plasma density profile can be adjusted. This adjustment is preferably done to optimize the uniformity of the plasma density profile. The regions in plasma  36  that lie between workpiece support  40  and insulating ring assemblies  56  are indicated by R. 
     With continuing reference to  FIG. 2 , plasma processing system  12  further includes a gas supply system  80  in pneumatic communication with plasma-cleaning chamber  20  via one or more gas conduits  82 , for supplying gas in a regulated manner to form plasma  36 . Gas supply system  80  supplies such gases as chlorine, hydrogen-bromide, octafluorocyclobutane, and various other fluorocarbon compounds, and for chemical vapor deposition applications, includes silane, ammonia, tungsten-tetrachloride, titanium-tetrachloride, and the like. 
     The plasma processing system also includes a vacuum system  90  pneumatically connected to chamber  20  for evacuating interior region section  32 L to a desired pressure [1 to 1000 mTorr]. The precise pressure depends on the nature of plasma  36  and of the desired processing operation. 
     Further included in the plasma processing system  12  is a workpiece handling and robotic system  94  in operative communication with chamber  20  for transporting workpieces W to and from workpiece support  40 . In addition, a cooling system  96  in fluid communication with segmented electrode  50  is preferably included for flowing a cooling fluid to and from the segmented electrode. 
     Plasma processing system  12  further includes a main control system  100  to which RF power supply system  60 , gas supply system  80 , vacuum pump system  90  and workpiece handling and robotic system  94  are electronically connected. Also connected to control system  100  are the displacement actuator control units, introduced below. 
     In a preferred embodiment, main control system  100  is a computer having a memory unit MU having both random-access memory (RAM) and read-only memory (ROM), a central processing unit CPU (e.g., PENTIUM™ processor from Intel Corporation), and a hard disk HD, all electronically connected. Hard disk HD serves as a secondary computer-readable storage medium, and can be, for example, a hard disk drive for storing information corresponding to instructions for control system  184  to carry out the present invention, as described below. Control system  100  also preferably includes a disk drive DD, electronically connected to hard disk HD, memory unit MU and central processing unit CPU, wherein the disk drive is capable of accepting and reading (and even writing to) a computer-readable medium CRM, such as a floppy disk or compact disk (CD), on which is stored information corresponding to instructions for control system  100  to carry out the present invention. It is also preferable that main control system  100  have data acquisition and control capability. A preferred control system  100  is a computer, such as a DELL PRECISION WORKSTATION 610™, available from Dell Corporation, Dallas, Tex. Control system  100  is used for controlling the operation of system  12  in the plasma processing of a workpiece, as described below. 
     Adjustable Segmented Electrode 
     In  FIGS. 3 and 4 , segmented electrode  50  is shown to have five segments  52 A- 52 D. Though five total electrode segments are shown for the sake of illustration, it will be apparent that two or more segments are generally possible. It will also be apparent that a segmented electrode  52  according to the present invention can have virtually any shape. In  FIG. 3 , Electrode segment  52 A is shown as a circular central electrode with a perimeter  52 AP, while segments  52 B- 52 E are arcuate-shaped electrodes arranged around the perimeter  52 AP. Electrode segments  52 B- 52 E also each have a corresponding perimeter  52 BP- 52 EP. Electrode segments  52 A- 52 E also have respective upper surfaces  52 AU- 52 EU (see  FIG. 3 ) and corresponding lower surfaces. An exemplary segmented electrode to which the present invention can be applied is described in U.S. Provisional Patent Application No. 60/175,284, filed Jan. 10, 2000, entitled “Segmented electrode apparatus and method for plasma processing,” the entire disclosure of which is incorporated by reference herein. Generally, each electrode segment  52  has a perimeter  52 P, an upper surface  52 U and a lower surface  52 L. 
     Each electrode segment  52  includes a port  120  that allows for electrical connection with one of RF power supplies  62 . Ports  120  also allow for pneumatic communication between chamber interior  30  and gas supply system  80  via gas conduit  82 , and if necessary, fluid communication with cooling system  96  through conduits  122 . The latter also serve as electrode support members for supporting electrode segments  52  within chamber interior region  30  and holding the segments fixed relative to chamber  20 . Plasma chamber  20  has openings  126  in upper wall  24  through which conduits  122  extend (see FIG.  1 ). Each opening  126  is preferably surrounded with a dielectric insulator  126 D to prevent an undesirable electrical connection forming through chamber  20 , which is typically made of a conducting material. 
     Arranged between electrode segments  52  is insulating structure  54 , mentioned above. With reference now also to  FIG. 4 , insulating structure  54  comprises individual insulation ring assemblies  56  (e.g.,  56 A- 56 E) surrounding each electrode perimeter  52 P (e.g.,  52 AP- 52 EP). 
     With continuing reference to  FIG. 4 , each insulation ring assembly  56  comprises an insulating body  128  having an inner portion  130 O adjacent the corresponding electrode segment periphery  52 P (e.g., periphery  52 CP of electrode segment  56 C), an outer portion  1300  opposite the inner portion, an upper portion  130 U and a lower portion  130 L. Upper portion  130 U preferably is formed so as to extend over a small portion of upper surface (e.g.,  52 CU) of the corresponding electrode segment (e.g.,  52 C) near periphery  52 P. In a preferred embodiment of the present invention, upper portion  130 U is made of a first dielectric material and lower portion  130 L made of a second dielectric material. A preferred material for upper portion  130 U is quartz, while a preferred material for lower portion  130 L is alumina. The material constituting lower portion  130 L is preferably a material compatible with the particular plasma processing to be performed in plasma processing system  12 . Upper and lower portions  130 U and  130 L can be formed as separate ring structures joined together to form integral insulating bodies  128 . 
     Each insulation ring assembly  56  further includes a conducting shield  140  embedded within insulating body  128  and arranged so as to shield the corresponding electrode segment from electrical interference from adjacent electrode segments. Each shield  140  is connected to ground (here, upper chamber wall  24 ) via a ground wire  144 . Each insulation ring assembly  56  preferably further includes a seal  150  between insulating body  128  and the corresponding electrode segment perimeter (e.g.,  52 CP of electrode segment  52 C) the top insulation ring and the outer radius of the electrode. Each seal  150  preferably resides in a cut-out  156  in inner portion  1301  of a respective insulating body  128 . Seals  150  serve to isolate plasma chamber upper interior section  32 U from plasma chamber lower interior section  32 L. This could allow, for example, for the flow of cooling fluid over upper surfaces  52 U (e.g.,  52 AU- 52 EU) of each electrode segment  52  (e.g.,  52 A- 52 E). For those electrode segments adjacent chamber sidewall  22 , an additional seal  150  and corresponding cut-out  156  is provided in outer portion  1300  of insulating body  128  to seal the gap between the chamber sidewall and insulating body  128 . 
     In a preferred embodiment, each insulation ring assembly further includes a displacement actuator  160  placed adjacent seal  150  in a cut-out  156  (see  FIG. 5 ) in upper portion  130  of insulating body  128 . Displacement actuator  160  is located adjacent seal  150  so that seal  150  tightly engages the perimeter of the corresponding electrode segment  52  when the displacement actuator is activated. Displacement actuators  160  are electronically connected to a displacement actuator control unit  162 , which is electronically connected to and controlled by main control system  100 . Displacement actuators  160  are preferably piezoelectric transducers, though other known actuators can also be employed. Displacement actuators  160  are constructed and operated to expand in the X-direction. When contracted by a signal from control unit  162 , actuators  160  cause the pressure of seal  150  against segment  52  to diminish in order to allow body  128  to be moved in the Y-direction. 
     Each insulation ring assembly  56  preferably further includes an inner bellows  164  attached to inner portion  1301  of insulating body  128  and upper surface  52 U of the corresponding electrode segment  52  so as to form a seal between each insulating body and the corresponding electrode segment. 
     In addition, each insulation ring assembly  56  further includes an outer bellows  166  attached to upper surfaces of upper portions  130 U of adjacent insulating bodies  128 . For those insulating bodies  128  adjacent chamber wall  22 , outer bellows  166  are attached to upper surfaces of upper portions  130 U and to the chamber sidewalls  22 . Outer bellows  166  form a seal between adjacent insulating bodies  128 , or between an insulation body and chamber wall  22 , even when one of the insulating bodies moves relative to an adjacent insulation body or the chamber wall, as described below. 
     For those processes where some contamination is tolerable, the bellows can be entirely removed, in which case walls  22  and  24  serve as the primary vacuum enclosure. When bellows are used and the segmented electrode is composed of concentric rings, each bellows will be connected between two rings or between the outer ring and wall  22 , as shown. However, when the upper electrode is further segmented in the azimuthal direction, as in  FIGS. 1 and 3 , walls  22  and  24 , which can be fabricated from the same material piece, must also include ribs that outline or partition the layout of electrode segments and extend downward between plates  196 . Therefore, the bellows would be attached between insulation ring assemblies and the respective wall and/or ribs surrounding the assemblies. 
     With reference now also to  FIG. 5 , each insulation ring assembly  56  further includes displacement actuators  170  connected to upper chamber wall  24  and to corresponding upper portions  130 U of insulating body  128 . Displacement actuators  170  serve to adjust the position of insulating ring assemblies  56  in the Y-direction, or vertically. Displacement actuators  170  are electronically connected to a displacement actuator control unit  180  through conduit  122 . Displacement actuator control unit  180  is also electronically connected to and controlled by main control system  100 . Displacement actuators  170  are preferably piezoelectric transducers, though other known actuators can also be employed. 
     Further, each insulation ring assembly  56  includes displacement actuators  190  arranged on outer portion  130  of insulating body  128 . Displacement actuators  190  can be embedded into insulating body  128 . Each set of displacement actuators  190  carries at the side thereof remote from insulating body  128 , a thin flat plate member  196  that interfaces with other plate members  196  of adjacent insulating bodies  128 . Displacement actuators  190  are active in the X-direction so that adjacent plate members  196  can be made to be loosely or tightly engaged (i.e., interfaced). When loosely engaged, or not engaged, members  196  can slide over one another so that the positions of insulating bodies  128  can be adjusted (i.e., displaced in the Y-direction).  FIG. 5  shows a state in which plates  196  are not engaged. When members  196  are tightly engaged, i.e. pressed against one another, seals  150  on the opposite side of the respective insulating bodies are pressed between the respective electrode segment and the electrode body to form a tight seal. In other words, displacement actuators  190  control the degree of engagement between adjacent insulating ring assemblies for the purposes of varying the relative displacement of the assemblies. 
     Displacement actuators  190  are electronically connected to a displacement actuator control unit  200  through conduit  122 . Displacement actuator control unit  200  is also electronically connected to and controlled by main control system  100 . Displacement actuators  170  are preferably piezoelectric transducers, though other known actuators can also be employed. 
     With continuing reference to  FIG. 5 , several key parameters associated with the present invention are now discussed. The distance that lower portion  130 L of insulation ring assembly  128  protrudes into section  32 L of interior  30  is given by DP. This parameter is a measure of how far beyond an electrode segment plane P (defined by lower surfaces  52 L of electrode segments  52 ) lower portion  130 L of insulating body  128  extends. The overall spacing between electrode segments  52  is S. The width of each insulating body  128  as measured across the portion of the insulating body between adjacent electrode segments (i.e., in the X-direction) is DT. When lower portion  130 L is made of a dielectric material different from upper portion  130 U, the thickness of the lower portion (measured in the Y-direction) is DB. In a preferred embodiment, the values for DB and DT are the same for all of the electrode segments, but in general this need not be the case. The gap between adjacent electrode segments is denoted by DG. Thus, S˜DG+2DT, in the case where DT is the same for each insulating ring assembly  56 . 
     Where upper portion  130 U and lower portion  130 L are made of different materials, the upper portion provides electrical insulation between adjacent electrode segments  52 . Further, conducting shield  140  preferably resides in upper portion  130 U and does not extend into lower portion  130 L. Selection of the material for lower portion  130 L and its corresponding dimensions are chosen such that electrical insulation from adjacent electrodes is preserved. However, the material should allow for segmented electrode  50  to match the impedance of the RF power being fed to electrode segments  52 . Thus, the materials used for upper portion  130 U and lower portion  130 L could be the same, depending on the design requirements of the particular system  12 . In addition, the material should be compatible with the plasma process to be carried out. In some cases, it can be necessary to relax the necessity of trying to impedance match with plasma  36 . If the material used for lower portion  130  is not compatible with the plasma processing to be carried out, then the value of DP should be less than DB to prevent contamination. 
     The parameters DT, DG and DP are design parameters, since they are designed into segmented electrode  50  and cannot be readily changed. The value of DG should be as small as possible, but not so small as to restrict the relative motion between the adjacent insulating bodies  128 . Typical ranges for the above-described parameters are 0&lt;DP&lt;8 mm, 2&lt;DT&lt;10 mm, and 1&lt;DB&lt;10 mm. DP can have a value of 0 because the lower surface of each lower portion  130 L can be flush with the lower surface of the adjacent electrode  52 . Like many semiconductor processing techniques, the optimum parameter values can best be determined empirically by performing experiments that take into account the RF power levels, the gases used to form the plasma, the impedance match between the RF power feed and the electrode segments, the particular process to be performed, and the like. Empirical data can also be stored in control system  100  in memory unit MU as a database for setting the control parameters. 
       FIGS. 4 and 5  show one insulation ring assembly  56  displaced relative to another. Note that electrode segments  52  do not move, but rather only one or more of insulating ring assemblies  56  are translated in the Y-direction via the activation of displacement actuators  170 , thereby introducing of a small portion of insulating ring assembly  56  (i.e., lower portion  130 L of insulating body  128 ) below plane P. The presence of this extra dielectric material changes the dielectric constant in regions R. As noted above in the “Background of the Invention” section, the plasma can have slight variations in plasma density in these regions due to the presence of the insulating structure between the electrode segments. This translates into non-uniform etching or deposition when processing a workpiece. By slightly changing the position of insulating rings, thus the equivalent dielectric constant in this manner, the slight variations (up to about 8%) in plasma density can be smoothed out. This, in turn, results in more uniform processing of the workpiece. 
     Method of Adjusting Segmented Electrode 
     With continuing reference to  FIGS. 4 and 5 , if one insulating ring assembly  56  needs to be adjusted, then displacement actuators  160  and  190  are activated by first and second electronic signals, respectively, from displacement actuator control units  162  and  200 , respectively. This causes displacement actuators  160  and  190  to contract inwardly in the X-direction, leaving plate members  196  of adjacent insulating bodies loosely engaged so that one plate member can slide past another in the Y-direction. Then, a third electronic signal from displacement actuator control unit  180  activates displacement actuators  170  to expand or contract along the Y-direction to place insulating ring assembly  56  in a desired vertical position. Once so positioned, displacement actuator control units  162  and  200  send fourth and fifth electronic signals to displacement actuators  162  and  190 , respectively, to expand outwardly in the X-direction. This causes seals  150  to tightly engage electrode segment perimeters  52 P, and causes plate members  196  of adjacent insulating ring assemblies  56  to tightly engage one another. 
     Method of Operating Plasma Processing System 
     With reference now to  FIG. 1 , a method of operating plasma processing system  12  according to the present invention is now described. First, a predetermined set of instructions (e.g., a computer program) is loaded (e.g., via computer readable medium CRM and disk drive DD) and stored in main control system  100  in memory unit MU or on hard drive HD. The instructions include steps for implementing a user-defined recipe for plasma processing of workpiece W. Next, control system  100  sends an electronic signal to workpiece handling and robotics system  94  to initiate the loading and unloading of workpiece W to and from workpiece support  40 . Control system  100  then sends an electronic signal to gas supply system  80  to initiate purging of plasma chamber  20  with a purge gas (e.g., nitrogen) supplied by gas supply system  80 . Next, control system  100  sends another electronic signal to vacuum system  90  to maintain a predetermined pressure in plasma chamber  20 . Typical operating pressures in chamber  20  range from 1 to 100 mTorr, but can also significantly deviate from this range, depending on the plasma process. 
     In the next step of the operation, control system  100  sends another electronic signal to gas supply system  80  to regulate the flow of gases from which plasma  36  can be formed, such as those gases mentioned above, from the gas supply system to plasma chamber  20 . Next, control system  100  sends another electronic signal to RF power supply system  60 , which provides RF power to electrode segments  52  via corresponding RF power supplies  62  and match networks MN. This results in the formation of plasma  36  within interior section  32 L of plasma chamber  20 . The preferred frequency for RF power supply system  60  driving electrode segments  52  is preferably in the megahertz range. 
     In the next step of the operation, control system  100  sends electronic signals to actuator control units  162 ,  180  and  200  to adjust the position of one or more of insulating ring assemblies  56  in the manner described above to change the plasma density profile of plasma  36  to match, or at least approach, a desired plasma density profile. The desired plasma density profile can be a uniform profile, or a non-uniform profile that provides a particular plasma processing characteristic, for example etch or deposition characteristic. The desired profile can be predetermined as an idealized one, or can be chosen from one of the plasma density profiles available based on the available operating conditions using information stored in memory unit MU of control system  100 . 
     In arriving at forming a plasma density profile that approaches or matches a desired plasma density profile, it can be preferred, or even necessary, to process a test substrate, or multiple substrates. This data can be compared to data stored in memory unit MU pertaining to a variety of possible plasma states, and can be used to determine the state of plasma  36 . This then provides direction as to setting the operating parameters of system  12 , including the design parameters DB, DG and DT, and control variable DP so that this measured plasma density profile is altered to match or approach a desired plasma density profile. In this case, after the test substrate or substrates are processed and evaluated, the above steps are repeated in processing the substrate to be processed with the newly formed plasma density profile. 
     In the meantime, control system  100  sends another electronic signal to cooling system  96  so that the flow of cooling fluid to segmented electrode  50  is adjusted to maintain electrode segments  52  at a controlled temperature during operation when processing workpiece W. This step is optional and may not be required for certain plasma processes. 
     When plasma processing of workpiece W is complete, control system  100  sends another electronic signal to vacuum system  90 , which adjusts the pressure of interior region  30  of chamber  20  to a setting where unloading of workpiece W can be performed. Finally, control system  100  sends an electronic signal to workpiece handling and robotics system  94 , which removes workpiece W from reactor chamber  20 . 
     In further accordance with the invention, a segmented electrode apparatus could include both the movable insulating ring assemblies, as described above, and movable electrode segments, as disclosed in co-pending Provisional U.S. application Ser. No. 60/175,284, filed Jan. 10, 2000, the entire disclosure of which is incorporated herein by reference. 
     The many features and advantages of the present invention are apparent from the detailed specification and thus, it is intended by the appended claims to cover all such features and advantages of the described method which follow in the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those of ordinary skill in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described. Moreover, the method and apparatus of the present invention, like related apparatus and methods used in the semiconductor arts that are complex in nature, are often best practiced by empirically determining the appropriate values of the operating parameters, or by conducting computer simulations to arrive at best design for a given application. Accordingly, all suitable modifications and equivalents should be considered as falling within the spirit and scope of the invention.