Abstract:
Plasma generating devices, systems and processes are provided in which hybrid capacitively coupled plasma (CCP) and inductively coupled plasma (ICP) sources use a plurality of primary plasma generating cells embedded into large area electrode or elsewhere in communication with a plasma processing chamber. Plasma is generated and maintained by a shaped low-inductance element within each of a plurality of locally enhanced ICP micro-cells coupled to the chamber through a CCP electrode. The source is suitable for processing large diameter (300 mm and larger) semiconductor wafers and large area panels, including plasma screen displays.

Description:
[0001]    This application is related to commonly assigned U.S. patent application Ser. No. 11/694,354, filed Mar. 30, 2007, Ser. No. 11/563,399, filed Nov. 27, 2006, and Ser. No. 10/716,729, filed Nov. 19, 2003, by the applicant hereof, each expressly incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to the plasma and radical processing sources and reactors, and to plasma and radical processing systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    In plasma systems, non-uniformities have been reported in field-free plasmas, that is, in plasmas in which no magnetic field is present. For example, in systems having inductively coupled plasma (ICP) sources, such non-uniformities have been found during plasma assisted etching of large objects greater than 50 cm in length, when 13.56 MHz RF bias was applied. This non-uniformity was reduced at lower bias frequencies, but the cause has not been explained. Uniformity tolerances for integrated circuit manufacturing are becoming more stringent, while wafer size is projected to increase further. Therefore, process uniformity issues are especially important in the processing of large substrates. 
         [0004]    Plasma sources used for the processing of semiconductor wafers and some other substrates have evolved from those using simple DC ionization sources to complex RF sources that produce high-density, low energy plasmas. The RF sources include inductively coupled plasma (ICP) sources, and capacitively coupled plasma (CCP) sources. Design of these RF plasmas have traditionally involved the design of antenna and electrode configurations of a unitary source that creates or otherwise introduces bulk plasma in a plasma volume within a processing chamber. Antenna or electrode placement and shape, as well as various chamber properties, are design parameters that are varied to shape the bulk plasma. 
         [0005]    The most common inductively coupled plasma (ICP) sources include coils with a planar, cylindrical or dome-shaped geometry. Antennas with more complex shapes have been more recently described in patent literature, including combined, hybrid and dual-coil configurations, coils formed of multiple small solenoids, multiple spirals, multi-zone ICP enhanced PVD coils producing a torroidal plasma, coils designed as a transmission line, embedded coils, planar helicon antennas, 3D antennas, segmented antennas, parallel conductor antennas, etc. 
         [0006]    Capacitive coupling plasma (CCP) sources are often driven by a combination of at least two frequencies to achieve independent control of the ion flux and the ion energy impacting the electrodes. This has resulted in a widening of the range of frequencies that are used. A major attraction of dual-frequency excitation is an expectation of the ability to independently control ion flux and the ion energy. Typically in dual frequency systems, a wafer supporting electrode is at lower frequency of, for example, 13.56 MHz, while a second frequency, usually higher than the wafer bias frequency, is provided to give quasi-independent control of the plasma (ion) density and, to some extent, plasma uniformity. In some circumstances, a third frequency is added to further control the etching processes by modifying the ion energy distribution function at the substrate. This multiple frequency excitation produces additional electron heating mechanisms. It has been considered that the electron heating in the sheath is greatly enhanced by the combination of two frequencies, i.e., the heating produced is much larger than the sum of the two single contributions. 
         [0007]    With increased size of the wafer and the wafer supporting electrode, electromagnetic effects become important in capacitively coupled plasmas, and a significant amount of heating is provided by the inductive field as the discharge experiences a capacitive-to-inductive transition. Recent work on this subject has focused on two primary points: One group of studies has examined the influence of RF frequency on excitation and ionization changes that impact etch parameters, and provides guidance in the development of advanced plasma sources and processes capable of controlling the plasma and surface chemistry. Another group of studies has focused on non-uniformities introduced into the plasma by the skin effects and standing waves. This group of studies represents potential critical limitations to the practical implementation of high frequency sources for large-area processing. 
         [0008]    High-density magnetic-field-free plasma sources produce plasmas that are opaque to radio frequency (RF) fields when using frequencies in the 2-200 MHz frequency range. At these frequencies, a skin effect occurs by which plasma currents from a biased substrate flow to ground along reactor and electrode surfaces. In an ICP source with densities of from 10 11  to 10 12  cm −3  in argon, an RF skin effect has consequences. Magnetic probe measurements confirm that capacitively coupled RF fields are localized near the reactor surfaces where the skin-effect current flows. Further, RF wavelength and phase velocity along reactor surfaces have been found to be reduced by a factor of about 5 compared to the wavelength in free space. The effective RF wavelength, or wavelength of the applied RF actually measured on the electrode, has been shown to be about one fifth of the RF wavelength at the same frequency in free space. At 200 MHz, the free-space wavelength of 1.5 meters is reduced to an effective wavelength of about 0.3 meters, which is comparable to the dimension of a capacitive electrode or a 300 mm wafer. This can produce differences in voltage or current over the dimensions of a wafer, which can lead to spatial non-uniformities in plasma and plasma processing. Furthermore, the high frequency capacitive discharge can experience capacitive-to-inductive (E to H) transitions when the injected power, i.e. the voltage between the electrodes, is increased. When both the capacitive and inductive power are radially non-uniform, severe problems of process uniformity can result. 
         [0009]    Simulations of the RF discharges driven at various frequencies have been published showing that plasma density, ion current and plasma power are proportional to the square of the RF frequency that is driving the discharge, for constant RF voltage. Electron density is also predicted to scale linearly with increased pressure. Charged and neutral particle density has been examined to look for possible effects due to a capacitive-to-inductive transition in the energy deposition mechanism, and to explore CCP operation above the frequencies of 27 and 60 MHz. Multiple frequency excitation was shown to lead to new electron heating mechanisms. The electron heating in the sheath has been shown to be greatly enhanced by the combination of two frequencies, producing heating that is much larger than the sum of the two single contributions. It was observed that the higher frequencies drive the larger density in the central area of a plasma column in CCP, shifting the spatial distribution from one that is uniform to one that is highly peaked in the center. When combinations of two or more frequencies are coupled into the chamber, even at lower than VHF frequencies, products can be produced that have an effective portion in the VHF range sufficient to influence the plasma. 
         [0010]    Other approaches to improve non-uniformity in 300 mm systems and large area CCP sources have been described in publications, such as the suppressing of standing wave nonuniformity for large area rectangular CCP reactors. Electromagnetic effects also become important at high frequencies, for which significant heating is provided by the inductive field parallel to the electrode where the discharge experiences a capacitive-to-inductive transition when the high frequency voltage amplitude is raised. The electromagnetic effects of this lead to severe non-uniformity of the power deposition, which, in turn, can ruin process uniformity. 
         [0011]    There is a need to solve the problems of increased causes of non-uniformities in the processing of large area substrates. 
       SUMMARY OF THE INVENTION 
       [0012]    An objective of the present invention is to provide a plasma source for use in processing large area substrates. Another objective of the invention is to increase the uniformity of a plasma process in systems such as for plasma etching, plasma deposition and plasma cleaning. 
         [0013]    A further objective of the invention is to eliminate or at least reduce non-uniformity effects that are particularly experienced in the plasma processing of large area substrates, for example, 300 millimeter (mm) and 450 mm semiconductor wafers. 
         [0014]    More particular objectives of the invention include eliminating or reducing standing-wave effects and inductive edge-current effects in processing with CCP sources. 
         [0015]    Yet another objective of the invention is to effectively generate plasma in processing by using an ICP technique. 
         [0016]    A still further objective of the invention is to meet the above objectives without substantially increasing cost or technical complexity over that of current plasma processing systems. 
         [0017]    According to principles of the present invention, an Embedded, Multiple-Inductive, Large-Area Source (EMILA) is provided for plasma processing. The source has multiple primary sources of plasma. 
         [0018]    According to certain principles of the invention, an array of plasma generating cells, each a discrete plasma generating source, is disposed in a plasma processing chamber in communication with a plasma volume in which a large area substrate is supported for processing. The cells are spatially distributed in relation to the substrate so that plasma from each of the cells propagates into the processing volume at different, spaced-apart points, so that the density distribution of the plasma in relation to the substrate is more uniform than the distribution in the chamber would be were the plasma provided by a unitary, bulk plasma source. 
         [0019]    In particular embodiments according to these principles, an array of three, four or more cells, arranged in a line, or an array in which cells are disposed in more than one dimension, are preferred. The disposition of the cells is such as to introduce plasma into a processing space from a plurality of points to provide a capability of favorably affecting plasma uniformity in the volume of the processing chamber or in the vicinity of a large area substrate supported in the chamber for processing. 
         [0020]    In other embodiments, a plurality of cells that are spaced from each other and in communication with a processing volume of a chamber are differently controlled to supply plasma from different points to a processing volume of a chamber in a way that compensates for or otherwise varies the plasma from the different cells so as to achieve a desired affect on the distribution of the plasma in the chamber. Control of electrical power, RF frequency, gas flow rate or gas flow composition are examples of such different control. 
         [0021]    According to other principles of the invention, plasma generating cells are provided having inductive elements configured to concentrate plasma power within the cells using a novel 3D modification of a segmented antenna concepts to efficiently generate and inductively couple plasma into each cell. The cells can be used in combination with capacitive coupling to separately control plasma density and plasma potential. Differential control of different ones of such cells can be used to control plasma density distribution. 
         [0022]    According to certain embodiments of the invention, radical or plasma cells, or micro-cells, are embedded within a plasma processing chamber, for example in the top of a CCP chamber electrode or in some other extended chamber component. The cell sources can be powered, for example, by very high frequency (VHF) energy, which is typically considered as being in the 30-300 MHz range. For example, cells can be powered in the 50-100 MHz or 100-200 MHz frequency ranges, generating inductively coupled plasma within each cell. A top chamber electrode for a CCP source can be also biased at a lower frequency. The substrates can be placed on a grounded or biased substrate support electrode. A large surface area plasma slab or in-line plasma source can, for example, be produced with this structure, by appropriate arrangement of the multiple primary cells. 
         [0023]    The invention provides compensation for non-uniformity effects that are particularly experienced in the plasma processing of large area substrates. For example, compensation is provided for standing-wave effects and edge-inductive-coupling effects in CCP etchers, particularly in high frequency, dual frequency systems, and otherwise provides uniformly distributed gas or plasma for larger area substrate processing. Embodiments of the invention provide control of active species distribution within a processing chamber and separation of a primary plasma zone from a secondary processing zone. 
         [0024]    The invention is particularly useful with higher frequencies having corresponding wavelengths that are comparable to the electrode or wafer size. In such cases, electromagnetic effects can vary over the extended geometries. Such effects can become important and are believed to provide a significant amount of heating in a CCP source by producing an inductive field that results as the discharge experiences a capacitive-to-inductive transition when the high frequency voltage amplitude is raised. 
         [0025]    Embodiments of the invention can be formulated in several aspects of the plasma processing system, for example, in hybrid inductively and capacitively coupled plasma sources configured for localized high frequency ICP and global low frequency CCP, where they are useful for radial uniformity improvement in 300 mm-450 mm wafer etching and other large area plasma source processes. Embodiments of the invention are also useful in eliminating or reducing “standing wave” effects and “inductive edge” effects in CCP systems and other high frequency plasma sources. Embodiments of the invention can enhance dissociation of a working molecular gas. Embodiments can provide an ionization zone separate from a radical processing zone in a compact fashion. 
         [0026]    The invention allows control parameters, such as independent high frequency power and low frequency power, with independent control of the generation rate and the energy of the ions in the plasma. Gas flow rate control and geometrical disposition of micro-cell sources can provide control of processing uniformity. 
         [0027]    Embodiments of sources according to the invention have a hybrid but compact structure with inductive elements that are embedded into a main electrode of the capacitively coupled plasma (CCP) source and have geometries that produce inductively coupled plasma (ICP). The source can alternatively or in addition be embedded in other hardware parts within a processing chamber. 
         [0028]    Advantages of the invention include a compact assembly embedded in a CCP electrode or elsewhere in a chamber. Dual frequency operation, with independent control of flux and the energy of species is provided, such as separate control of high frequency power and low frequency power. Localized ICP performance can provide increased plasma density and improved gas dissociation, along with a reduction of the “standing wave” effects and “inductive edge” effects in CCP in a high frequency plasma source. An ionization zone separate from a radical processing zone can also be achieved in a compact fashion. 
         [0029]    In practicing the invention, commercial EM or modeling software is available and can be used to optimize device design in 3D space for specific processor configurations. Interference and control of neighboring micro-cells, may be resolved by persons skilled in the field and in part may be learned by practice of the invention. 
         [0030]    The invention is useful in large plasma sources and related technologies, including, for example, CCP plasma etch systems (dual frequency), activated neutral gas etch and deposition systems, PECVD or other CVD systems, plasma cleaning systems, surface and polymer modification plasma systems, and surface reaction systems. 
         [0031]    These and other objectives and advantages of the present invention will be more readily apparent from the following detailed description, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1A  is a circuit diagram of a planar segmented antenna of varying cross-section. 
           [0033]      FIG. 1B  is a diagram a modification of the planar segmented antenna of  FIG. 1A  folded in a concentric 3D arrangement to form a microcell. 
           [0034]      FIG. 2  is a cross-sectional diagram of an embodiment of the microcell of  FIG. 1B . 
           [0035]      FIGS. 3A-3E  are illustrations of opening patterns of the cell of  FIG. 2 . 
           [0036]      FIG. 4  is an equivalent circuit representation of the cell of  FIG. 2 . 
           [0037]      FIG. 5  is an isometric diagram of a section of an array micro-cell plasma sources. 
           [0038]      FIG. 6  is diagram similar to  FIG. 5  illustrating an alternative embodiment of an alternative array of the micro-cell sources. 
           [0039]      FIG. 7  is a representative cross-sectional diagram of the arrays of  FIGS. 5 and 6 . 
           [0040]      FIGS. 8A and 8B  are 3D graphs of simulations of surface current density and current and B-field vectors, respectively. 
           [0041]      FIG. 9  is an isometric diagram of the microcell of  FIG. 2 . 
           [0042]      FIG. 10  is a cross-sectional diagram of an alternative embodiment of the microcell of  FIG. 2 . 
           [0043]      FIG. 11  is an isometric diagram similar to  FIG. 9  illustrating a cell having a J-antenna configuration. 
           [0044]      FIG. 12  is an isometric assembly similar to  FIG. 6  showing cells having an alternative antenna configuration. 
           [0045]      FIGS. 13A-E  are diagrams showing various plasma source cell arrays. 
           [0046]      FIG. 14  is a disassembled isometric diagram of a plasma source microcell array. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    Certain aspects of the present invention can be understood by reference to the principles of the segmented antenna (SEGA) disclosed in applicant&#39;s commonly assigned US patent application, Pub. No. 2005/0103445, hereby expressly incorporated by reference herein. Certain embodiments of the SEGA utilize a conductor that has a variable cross-section, which creates low and high impedance portions of the inductive element that provide different current densities through the different portions of the conductor. This approach provides the ability to pre-design the inductive antenna to localize RF power distribution deposited into plasma by magnitude and geometrical configuration. 
         [0048]      FIG. 1A  is a circuit diagram illustrating a 2D-planar segmented antenna  20  having a narrow portion  21  of small cross-section connected in series with a wide portion  22  having a relatively large cross-section, or a plurality of alternating small and large cross-section portions connected in series, across an RF generator  23 . The narrow portion  21  has a high inductance and concentrated current surrounded by strong magnetic fields near the conductor surface, while the wide portion  22  has a relatively low inductance and more distributed current surrounded by relatively weak and magnetic fields close to the conductor surface. By shaping the portions  21  and  22  of the antenna  20  as concentric cylinders to conduct a central outgoing inner current within a concentric return outer current, as illustrated in  FIG. 1B , a cavity  24  is created within the conductor of the antenna  20 , forming a micro-cell  25 . Considering the much higher RF current density in an axial conductor  21 , plasma will be created by intense concentric RF magnetic fields around the axial conductor. After passing through the axial portion  21  of the conductor of the antenna  20 , the RF current follows a return current path through the large area cylindrical portion  22 . 
         [0049]    By application of RF power from generator  23  to the antenna  20  configured as in  FIG. 1B , plasma will be produced within the cavity  24  of the micro-cell  25  under appropriate process conditions, for example, by applying RF power at an operating frequency of between approximately 50-100 MHz at an argon gas pressure of 20 to 100 s of mTorr, although other frequencies and pressures may be appropriate for particular processes. A micro-cell  25  is illustrated in schematic cross-section in  FIG. 2 . The micro-cell  25  includes the central conductor  21  surrounded by the outer conductor  22 , which can be formed by a metallic plate  50 , defining the cavity  24  between the conductor portions  21  and  22 . An insulator  26  is provided to separate the conductor portions  21  and  22  and support the outer conductive plate  22 . A tapered or reduced cross-section axial conductor section  27  may be optionally provided to further concentrate the magnetic field in the zone where plasma is created. This provides additional enhancement of plasma production due to the increased current density flowing in the narrowed conductive section  27  of the conductor portion  21 . This concept of power concentration can be referred to as “locally-enhanced inductive coupling” (LEIC). 
         [0050]    Plasma formed in the micro-cell  25  propagates out of the cavity  24  through appropriate openings  28  that communicate with the process volume  30  of a processing chamber. The outlets  28  of the micro-cell  25  can have a variety of shapes and dimensions, some of which will be more appropriate than others, depending on overall chamber and process design. The outlets  28  should be selected to provide a transition from the axial conductor geometry to the cavity geometry.  FIGS. 3A-E  show several options for outlet openings  28 . These outlets  28  can also have an impact on, and can be designed to adjust, the total inductance and load of the antenna  20 . For example, viewed from the volume  30  on the chamber side, the configuration in  FIG. 3A  provides continuous conductive connections  29   a  between central conductor  21  and the outer cavity conductor  22  in the form of several radial spikes  31 . In  FIG. 3B  spikes  32 ,  33  are not continuous, but are separated by a gap  34  and are coupled capacitively. In  FIG. 3C , two pair  28   a ,  28   b  of ½ circular openings are provided. In  FIG. 3D , spiral opening  28   c , and in  FIG. 3E , circular openings  28   d  and  28   e  are provided to define interconnects  29   b  and  29   c , respectively, between conductor portions  21  and  22 . 
         [0051]    The continuity of the plate  22  that forms the main electrode, or of such other structure that forms the surface that face the process volume  30  of the chamber, should provide minimal pattern transfer into the bulk plasma or towards the wafer. The shapes of the openings  28  can affect this. The micro-cell sources  25  can be embedded into a one-piece main electrode, which can be a large cross-section conductor  22  for all of the cells. The micro-cell sources  25  can alternatively be individual single sources attached to a main body “electrode” or “holder”. An equivalent circuit for example of such a configuration is shown in  FIG. 4 , in which a lead  38 , which may include, for example, a coaxial cable or a suitable matching network, from the generator  23  to a micro-cell  25  is shown as feeding the axial inductance (La) of inner conductor  21 , which connects to a radial (outlet) inductance (Lr) representing, for example, conductor portions  29  and  22 , a plasma resistive load (Rp) in the chamber  24 , a connection capacitance (Cc) which can be present from the conductors, and a micro-cell resistive load (Rc). This represents a serial resonant circuit with maximum current at a resonance frequency. According, the theoretical resonance in the RF magnetic fields will be a result of the total inductance Lc=La+Lr and connection capacitance (Cc). 
         [0052]    To provide uniform plasma, several micro-cells  25  can be embedded in a single large electrode  40 , as illustrated in  FIG. 5 . The micro-cells  25  can be arranged also in one-line fashion, as it is shown in  FIG. 6 . These micro-cells are usually of the same geometry, but need not all have the same geometry. The cells of the same or different geometries may be energized differently. The differences can be selected to compensate for various non-uniformity effects to improve overall uniformity or otherwise shape the uniformity. 
         [0053]    The individual micro-cells  25  are preferably powered by a high frequency electromagnetic field from a 50 to 100 MHz supply  23 , through the power splitter  42  configured to deliver an appropriate portion of the total RF power to each cell  25 , as illustrated in  FIG. 7 . In each of the RF delivery lines for each cell  25 , a high pass filter  44  is connected in series to prevent low frequency current from flowing into the high frequency supply  23 . The electrode  22  can be powered by low frequency power from a LF power supply  45  that is connected to it through a low pass filter  47 . With two generators  23  and  45 , both plasma density and ion energy can be controlled independently, plasma density by HF (or VHF) and energy by LF or relatively lower frequency than the HF. The micro-cell plasma, however, will operate independently whether LF is applied or not. Process gas can be fed through gas distribution channels formed in the electrode plate  22 , or through some other convenient structure. 
         [0054]    In  FIGS. 8A and 8B  show simulation results of one micro-cell  25  with a spherical shape cavity and an enhanced axial RF power configuration of the type that would be produced by the axial conductor  21  of  FIG. 2  which has the reduced axial conductor section  27 .  FIG. 8A  shows surface currents on the surfaces of the axial conductor  21  and of the outer conductor  22  formed of the walls of cavity  24  in the block  50 . The current density is the highest in narrow portion  27  of the axial conductor  21 . The B-field magnitude is shown in crossing a horizontal plane  35  with its maximum localized closely to axial conductor  21 . The induced HF plasma current magnitude is shown in a radial-axial plane  36 .  FIG. 8B  shows the directions and magnitude of peak current density in the plasma within the cavity  24  of a cell  25 . 
         [0055]    Common or separate gas inlets can be connected to each local plasma micro cell  25  by a gas distribution system, which can be incorporated into the main electrode body  50 . One or more gases can be used, and different gases can be introduced into different cells. This provides the advantage that each gas can be excited into a plasma state prior to mixing with other gases in the main chamber, or at-least at significantly reduced concentrations of other gas components. The EMILIA source provides the ability to control uniformity by different control of parameters in different cells  25 , such as by varying HF power or gas flow rate due to have a desired effect on the plasma downstream in the main chamber. 
         [0056]      FIG. 9  is a three-dimensional view of an axially-symmetric microcell  25 , similar to that of  FIG. 2 , having an outlet opening  28  configured as the openings  28   d  and  28   e  of  FIG. 3   e . The single micro-cell  25  contains primary plasma volume within cavity  24  embedded in the main body formed of the plate  50 , which is made of metal, for example aluminum or an aluminum alloy, having good surface conductivity. Alternatively, the plate  50  can be formed of an insulator material and coated with an electrically-conductive film. The openings  28   d ,  28   e  can be formed in an outlet plate  51  that is metallic and electrically connected to the inner conductor  21 . 
         [0057]    The plate  51  is shown as isolated from the main body  50  by an insulating coating or insulator plate  52 , which forms the connection capacitance (Cc) in  FIG. 4  between the plate outlet  51  and the main body  50 . Inclusion of the connection capacitance (Cc) can be provided in another way, for example, as shown  FIG. 10 , as a gap  53  between the surface of the cavity surface in main electrode body  50  and the outlet plate  51 , such as can be formed by a cylindrical flange  54  extending from the output plate  51 . This capacitively connects the inductive element  21  to the main electrode body  50 . Main electrode body  50  is well grounded at high frequency through a high pass filter  55  to ground, which also maintains a good connection with the ground of the lead  38  ( FIG. 9 ) that supplies HF input to the inner conductor  21 . In  FIG. 9 , the conductor  21  that forms the axial inductive element is insulated from the main electrode body  50  by insulation  26 . Within the main electrode body  50 , distribution channels  57  and  58  for operating gas and cooling medium, respectively, are incorporated. 
         [0058]    An alternative inductive element  21  is shown in  FIG. 11  in a shape of the J-antenna  61 . The connection capacitance (Cc) in series can be provided by including an insulating layer  62  between J-antenna  61  and the surface of the micro-cell cavity wall formed of the main body  50 . The cavity  24  can have a rectangular cross section, as shown. Other cross-sectional shapes can be used, of which circular, oval, elliptical, or various polygonal shapes are examples. The shape can be selected to optimize plasma generation inside micro-cell  25 . Enhanced radiation for the J-antenna  61  can be provided by incorporating a reduced cross-section portion  63 , for example the semicircular cutout portion  63  of the J-antenna  61 . Other shapes for the inductive element  21  can be used. For example, multiple part inductive elements  65  can be assembled, for example, in a cavity having a linear configuration, such as is shown in  FIG. 12 . Here, several J-antennas are assembled into a single conductor in linear cavity  66 . 
         [0059]    As is shown in  FIG. 5 , a plurality of individual cells  25  can be arranged into matrix or array producing large area electrode  40  for use as a large area plasma source. Several arrays of multi-cell source configurations are presented in  FIGS. 13   a - 13   e , which shows rectangular grids ( FIGS. 13A and 13B ), hexagonal arrangements ( FIG. 13C ), linear arrangements ( FIG. 13D ) and circular, arcuate or polygonal arrangements ( FIG. 13E ), for example. 
         [0060]      FIG. 14  illustrates an example of a simplified assembly  70  of a section of a plasma source formed of an array of microcells  25  in the pattern of  FIG. 13B . The assembly  70  can be made of a limited number of parts that each form common components for a plurality of the microcells that are shown in detail in  FIG. 9 . For example, an insulation layer  71  can form the insulators  26  of a plurality of cells  25  of the array  70 . A common block  72  can form a plurality of the main bodies  50  of the cells  25 . A single insulator sheet  73  can form the insulators  52 . A single piece of conductive metal  75  can form an assembly of multiple outlet plates  51  and corresponding axial conductors  21  of plural microcells  25  of the array. Vacuum sealing can be done by methods known in the art. In the simplest case, sealing O-rings can be used. 
         [0061]    The frequency range of the RF power is preferably approximately from 50 MHz to 100 MHz, but the possible frequencies are not limited by this range. Frequency much higher, up to 500 MHz for example, and in special cases up to 1 GHz, can be utilized. The high frequency RF power is supplied through the power splitter  42  to deliver a portion of the HF power to each cell, as described in  FIG. 7 , where high pass filters  44  are shown connected in series in the delivery lines for each cell  25  to prevent low frequency current from flowing into high frequency supply  23 . Also main body electrode  50  is grounded through the high-pass filter, and ideally to the ground of the lead  38  ( FIG. 4 ). The main electrode  50  is powered by low frequency power from LF power supply  45  in series with the low pass filter  47  so that both plasma density and ion energy can be controlled independently: plasma density by HF and energy by LF. With this method, the micro-cells  25  will operate with no LF power connected. 
         [0062]    The optimal tapered shape of the axial conductor  21  can be determined by EM simulation and by experimentation to adjust the optimal plasma load inside micro-cells. Radial or outlet inductance can also be varied to tune the total inductance of the source. The various outlet openings  28  shown in  FIG. 3  can be changed to vary the total inductance of the load. 
         [0063]    Depending on dimensions of the cell cavities  24  and the exciting frequency, the operating pressure will range from tens mTorr to hundreds mTorr. Very high frequency operation is suitable for a pressure range of from several Torr to sub atmospheric pressure. It is likely that even atmospheric operation at 1 GHz or above may be achieved. 
         [0064]    Common or separate gas inlets can be used for the different micocells. A gas distribution system can be incorporated into the block  72  of which the main electrode bodies  50  are formed. One or more gases can be used, and different gases can be supplied to different microcells  25 , which will allow each gas to be excited into a plasma state without mixing with another gas, or at-least mixing at a significantly reduced concentration, and interacting in the main reaction chamber. 
         [0065]    The EMILA source described above provides control of uniformity by the design, HF power control, and flow rate control to control plasma downstream using individual local micro-cell plasma sources. In some embodiments, an array of plasma generating microcells  25 , even of identically configured and controlled cells, properly distributed adjacent a processing chamber, can produce a plasma of greater uniformity over a large area substrate of 300 mm or larger than would be produced by a unitary RF plasma source, or one that uses one or more large coupling element, to produce a bulk plasma in the processing chamber. In other embodiments, control of electrical and gas parameters among different cells of a plural cell array can be employed to enhance or otherwise favorably affect the uniformity of the plasma. 
         [0066]    Although only certain exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.