Abstract:
A method is provided for generating plasma using a plasma generator system. The method includes the steps of introducing energy and a reactant to a plasma generation apparatus of the plasma generator system for generating plasma, and expanding and inductively coupling the generated plasma. In another embodiment a plasma generation system is provided including a plasma generation apparatus for generating thermal plasma. The thermal plasma is received by a plasma treatment chamber external to the plasma generation apparatus. A pressure control system maintains a lower pressure in the plasma treatment chamber than in the plasma generation apparatus during plasma generation for causing the thermal plasma to expand within the plasma treatment chamber. An inductor system inductively couples the thermal plasma.

Description:
FIELD OF THE INVENTION  
         [0001]    The present disclosure relates to plasma processing, and particularly to inductive coupling of an expanding thermal plasma.  
         BACKGROUND OF THE INVENTION  
         [0002]    Deposition of coatings on substrates is performed using plasmas, such as thermal plasmas, expanding thermal plasmas (ETPs) and inductive coupling plasmas (ICPs). ETPs are produced by forming a thermal plasma under high pressure in an Upstream portion of an ETP source and providing the thermal plasma to a downstream portion of the ETP source. The downstream portion includes a low pressure chamber (having lower pressure than the upstream portion) which receives the thermal plasma and a reagent precursor injection. Inside the low pressure chamber the thermal plasma expands due to the relatively large pressure differential between the downstream and upstream portions of the ETP source. Reagents that are injected into the expanding thermal plasma dissociate due to chemical reactions, such as charge exchange and subsequent dissociative recombination reactions, between the thermal plasma and the reagent.  
           [0003]    Coatings deposited by individual ETP sources cover surfaces having a limited width typically less than 30 cm. Accordingly, multiple ETP sources are needed to coat large areas. The distribution of the energy level of the ETP is nonuniform, and is typically Gaussian shaped, resulting in a substantially Gaussian plasma density and a Gaussian deposition thickness profile. However, in most applications a uniform thickness profile for individual ETP sources is desired, particularly when multiple sources are used for coating a single surface.  
           [0004]    Furthermore, in ETP sources the energy at which ions bombard electrically floating substrates, such as polymer substrates, is extremely low and uncontrollable. The tendency of ETPs to have low ion energy may interfere with generation of coatings having good adhesion and/or high density.  
           [0005]    Attempts have been made to reduce pumping requirements and increase efficiency. These attempts include reducing the diameter orifice in a cascade plate of the ETP source for allowing ETP operation with a reduced plasma gas flow, which in turn reduces the ion flux that is needed for reagent dissociation and reduces deposition rate. Attempts have also been made to increase utilization by using a nozzle injector configured for intensive mixing of reagents and the expanding thermal plasma. However, the nozzle injector substantially confines the plasma, which tends to induce non-uniformities. Attempts have also been made to increase ion energy control by applying an independent bias voltage to the substrate to which deposits are being applied. However, this method does not function when processing electrically floating substrates, such as polymer substrates.  
           [0006]    Nonetheless, ETPs have relatively high charged particle densities, relatively low electron temperatures, and maintain an equilibrium between electron temperatures and ion temperatures, resulting in relatively low ion temperatures and bombardment energies, which is desirable for semiconductor applications and the prevention of damage to electronic devices. Although the low electron temperature of ETPs is considered to be advantageous, there exist nonobvious advantages for raising the electron temperature. While ETPs provide a reagent dissociation path based on charge exchange reactions followed by dissociative recombination reactions, which occurs at relatively low electron temperatures, the ETP&#39;s Te is too low for providing a reagent dissociation path based on electron impact dissociation reactions.  
           [0007]    Each path provides the ability for generation of specific chemical species, and the lack of the electron impact dissociation path limits the type of chemical species that can be generated, which limits contribution to the coating process and decreases efficiency of individual ETP sources. Thus, causing further demands are placed on the pumping process, including increases in gas and energy loads, the number of ETP sources required for large area uniformity and costs.  
           [0008]    ICPs, on the other hand, are formed by ICP sources that include a low pressure chamber that receives a reagent precursor injection in a low pressure chamber, where the chamber is provided with at least one coil connected to an energy source. When energy is applied the at least one coil the Te increases and an electron impact dissociation path is achieved. However, ICPs, similar to ETPs, typically do not provide a uniform deposition over large areas. Further, in ICPs charged particle densities are typically low relative to ETPs, which limits the density of reagent fragments formed through dissociation reactions of reagents with energetic electrons, and thus results in low growth rates of coatings.  
           [0009]    Higher power ICPs have been attempted for generating higher charged particle densities, but high power stray capacitive power coupling typically develops, causing sputtering of reactor walls, and thus contaminating the coatings that are deposited. Also, as a result of the ICP plasma generation mechanism the electron temperatures are not generally lowered below a certain energy, thus limiting the plasma chemistry that can be achieved with the ICP source.  
           [0010]    Accordingly, there is a need for a system and method for uniformly distributing dissociated reagents over the surface of a substrate, thus forming a coating on a substrate.  
           [0011]    Furthermore, there is a need for a system and method for efficiently generating a high electron density plasma with a controllable electron temperature, such that ICP like high Tes can be combined with ETP like electron densities, resulting in high growth rates with controllable plasma chemistry based on both charge exchange and dissociative recombination paths and electron impact dissociation paths. Other advantages are described in greater detail below.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0012]    A method is provided for generating plasma using a plasma generator system. The method includes the steps of introducing energy and a reactant to a plasma generation apparatus of the plasma generator system for generating plasma, and expanding and inductively coupling the generated plasma.  
           [0013]    In another embodiment of the invention a plasma generation system is provided including a plasma generation apparatus for generating thermal plasma. The thermal plasma is received by a plasma treatment chamber external to the plasma generation apparatus. A pressure control system maintains a lower pressure in the plasma treatment chamber than in the plasma generation apparatus during plasma generation for causing the thermal plasma to expand within the plasma treatment chamber. An inductor system inductively couples the thermal plasma.  
           [0014]    In another embodiment of the invention a plasma generation system is provided including an apparatus for generating a plasma. An apparatus for receiving receives the generated plasma and provides for expansion of the generated plasma. An apparatus for inductively coupling inductively couples the generated plasma, wherein the apparatus for receiving and the apparatus for inductively coupling together form the generated plasma into an inductively coupled and expanded plasma.  
           [0015]    In still another embodiment of the invention a plasma generator system is provided including means for generating plasma by introducing energy and a reactant to the plasma generator system; and means for expanding and inductively coupling the generated plasma.  
           [0016]    In another embodiment of the invention an expanding inductively coupled plasma is provided. The plasma is generated by the method including the steps of introducing energy and a reactant to a plasma generation apparatus of a plasma generator system for generating plasma; and expanding and inductively coupling the generated plasma.  
           [0017]    In another embodiment of the invention an object having at least one surface is provided. The surface is treated using an expanding inductively coupled plasma, where the plasma is generated by the method including the steps of introducing energy and a reactant to a plasma generation apparatus of a plasma generator system for generating plasma; and expanding and inductively coupling the generated plasma. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a schematic diagram of a prior art ETP reactor;  
         [0019]    [0019]FIG. 2 is a schematic diagram of a prior art ICP reactor;  
         [0020]    [0020]FIG. 3 is a schematic diagram of a plasma source system in accordance with the invention; and  
         [0021]    [0021]FIG. 4 is a schematic diagram of a plasma source system in accordance with another embodiment of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    Superior plasma treatment is achieved in accordance with the present disclosure by combining inductive coupling with an expanding thermal plasma (ETP) system. The results achieved by the combination are superior to either ETPs or inductive coupling plasmas (ICPs) with respect to uniformity of deposition, electron and ion energy control, and efficiency. Shown schematically in FIG. 1 is a conventional ETP reactor  10 . The ETP reactor  10  includes an upstream portion  12  and a downstream portion  14 , where the upstream portion includes a plasma-generator  16 , and the downstream portion  14  includes a chamber  18 . The upstream portion  12  is similar to FIG. 2 of U.S. Pat. No. 4,871,580, issued to Schram et al. A substrate  20  is placed within the chamber  18 .  
         [0023]    The plasma-generator  16  receives a reactant, such as gases including Argon, Xenon, Helium, other noble gases, Nitrogen and/or Hydrogen gas, through an inlet  22 . Energy is applied to the plasma generator via an energy source  21 , such as for producing arcs and/or discharges within the plasma-generator  16 . The arcs and/or discharges act upon the reactant to produce a plasma. Pressure is maintained within the plasma-generator  16  that is suitable for producing a thermal plasma. In an exemplary plasma-generator, ions and electrons of the thermal plasma have a temperature of 1 eV, and the charge density is 10 15  cm −3  or higher. The plasma-generator  16  is further provided with a nozzle through which the thermal plasma exits the plasma-generator  16  for passing through an inlet  24  and then into the chamber  18 .  100251  The chamber  18  is maintained at a pressure that is lower than the pressure maintained in the plasma-generator  16  for allowing the thermal plasma to expand into an expanding thermal plasma  50 . In the chamber  18 , the ETP  50  cools rapidly and the electrons and ions start to recombine, after which the expansion shocks, i.e., expansion speed goes from supersonic speed to subsonic speed, and the electron temperature (Te) drops, such as to 0.1-0.3 eV, and the charge density is around 10 12  cm −3 .  
         [0024]    A reagent, such as a material formed of gas, liquid and/or solids, e.g., silanes, methanes, other hydrocarbons, fluorocarbons, deuterated carbons, deuterated silanes, alcohols, acrylates, epoxies, organosilanes, chlorosilanes, fluorosilanes, aminosilanes, organosilicones, metal organic precursors, metal chlorides, metal fluorides, water, oxygen, hydrogen, nitrogen, ammonia, carbon dioxide, carbon monoxide or a suitable combination thereof, is injected into the chamber  18  via a port, such as injection inlet  26 , causing precursor dissociation to occur mainly through charge exchange and subsequent dissociative recombination reactions between the reactant ions and the reagent ions. The reagent dissociation products are transported along with the expansion at high drift velocity, thus generating a convective flux of reactive species, which arrives at the surface of the substrate  20 , resulting in deposition of a coating  34  on the substrate.  
         [0025]    The ETP  50  is an equilibrium plasma in which electron temperature substantially equals ion temperature, where the electron temperatures and ion temperatures are relatively low, such as 0.1 eV. Ion density of the ETP  50  has a Gaussian distribution resulting in a coating  34  on the substrate  20  having a Gaussian shaped deposition profile that is non-uniform in thickness and density.  
         [0026]    [0026]FIG. 2 shows a conventional ICP reactor  200  having at least one chamber  202  including a vacuum chamber under low pressure conditions, such as under 10 Torr, in communication with a substrate  220  to which a reagent is introduced, through a port  206 , such as a ring injector, a shower head or another type of inlet. A reactant gas, such as Argon, Helium or other noble gas, may also be introduced through port  206  or another port (not shown). At least one coil  204  is disposed within the at least one chamber  202 , or looped around the at least one chamber  202  or a passageway connected thereto, where typically a portion of a surface with which the at least one coil  204  (particularly when the at least one coil is not insulated) is in contact is formed of a dielectric material.  
         [0027]    The at least one coil is connected between ground and a power source (not shown). Energy provided by the power source is applied to the at least one coil  204  for causing an electric discharge, i.e. to generate a plasma. An inductively coupled plasma  250  is thus generated within the chamber  202 . Precursor dissociation occurs through an electron impact dissociation path generating a flux of reactive species, which arrives at the surface of the substrate  220  resulting in deposition of a coating  224  on the substrate.  
         [0028]    The ICP plasma is a non-equilibrium plasma, where the Te may be significantly higher than the ion temperature, such as where the ion temperature is 0.1 eV and the electron temperature is higher than 1 eV. With the at least one electric coil  204  strategically positioned in an annular formation within the at least one chamber  202 , the ion density of the ICP formed has an off axis high (not along axis  226 ) distribution, typically resulting in the coating  224  having an off-axis high deposition profile on the substrate  220 , and the coating  224  being non-uniform in thickness and density. Specifically, the density and thickness of the coating  224  is increased in an annular area about a central axis  226 .  
         [0029]    A first embodiment of an exemplary ETP-ICP reactor  300  configured for generating an expanding thermal plasma and inductively coupling the generated ETP according to the invention is shown schematically in FIG. 3. The ETP-ICP reactor  300  includes an upstream portion  312  and a downstream portion  314 , where the upstream portion  312  includes a plasma-generator  316 , and the downstream portion  314  includes a chamber  318 . A substrate  320  is mounted in communication with the chamber  318 , and may be mounted within the chamber  318 . The ETP-ICP reactor  300  receives at least one of a reactant and a reagent which is processed within the ETP-ICP reactor  300  for treating the substrate.  
         [0030]    Similar to the ETP reactor  10  shown in FIG. 1, the plasma-generator  316  receives a reactant, such as Argon, Helium, other noble gases, Nitrogen and/or Hydrogen gas, through a port  322  such as a ring injector, a nozzle injector, a flash evaporator, a shower head or another type of inlet. Energy is applied to the plasma generator via an energy source  321 . For example, the energy applied may be in the form of radio frequency (RF) energy, microwaves, direct electrical current or voltage, or alternating electrical current or voltage, such as for producing arcs and/or discharges within the plasma-generator  316 . The energy applied may be of direct current form or have a continuous or pulsed waveform, where parameters of the waveform, such as waveform type (sinusoidal, square, triangular, trapezoidal, etc.); frequency; duty cycle; etc., are selected for obtaining the desired result. The arcs and/or discharges act upon the reactant to produce a plasma.  
         [0031]    Pressure is maintained within the plasma-generator  316  that is suitable for producing a thermal plasma. For example, the pressure may be maintained at near atmospheric pressures or atmospheric pressure, such as&gt;100 Torr. In an exemplary plasma-generator, ions and electrons of the thermal plasma have a temperature of 1 eV, and the charge density is 10 15  cm −3 . The plasma-generator  316  is further provided with a nozzle through which the thermal plasma exits the plasma-generator  316  for passing through an inlet  324  and then into the chamber  318 .  
         [0032]    The ETP-ICP reactor  300  differs from the ETP reactor  10  of FIG. 1 in that the chamber  318  is provided with an inductively coupling (IC) system  330 . The I/C system  330  includes an apparatus for generating an electromagnetic force, such as at least one electric coil, and a power source for energizing the apparatus, such as by supplying electrical energy of continuous or pulsed waveform, where parameters of the waveform, such as waveform type (sinusoidal, square, triangular, trapezoidal, etc.); frequency; duty cycle; etc., are selected for obtaining the desired result.  
         [0033]    The chamber  318  is maintained at a pressure that is lower than the pressure maintained in: the plasma-generator  316  for allowing the thermal plasma to expand into an expanding thermal plasma. In the example provided, the pressure maintained in the chamber  318  is 20-200 mTorr and the expansion occurs supersonically. In the chamber  318  the ETP cools rapidly and the electrons and ions start to recombine, after which the expansion shocks. In the I/C ETP  350 , as a result of the inductive coupling of electrical power into the expanding thermal plasma, the Te drops less than in the ETP reactor of FIG. 1, and thus will be larger than 0.1-0.3 eV, and the charge density is around 10 12  cm −3  or larger.  
         [0034]    A reagent such as a material formed of gas, liquid and/or solids, e.g., silanes, methanes, other hydrocarbons, fluorocarbons, deuterated carbons, deuterated silanes, alcohols, acrylates, epoxies, organosilanes, chlorosilanes, fluorosilanes, aminosilanes, organosilicones, metal organic precursors, metal chlorides, metal fluorides, water, oxygen, hydrogen, nitrogen, ammonia, carbon dioxide, carbon monoxide, or a suitable combination thereof, is injected into the chamber  318  via a port, such as injection inlet  326 , thus causing dissociation to occur both through charge exchange and subsequent dissociative recombination reactions between the reactant ions and the reagent, and through electron impact dissociation reactions between the inductively heated electrons and the reagent.  
         [0035]    The apparatus for generating the electromagnetic force may be provided within the chamber  318 , integrated within walls of the chamber  318  or provided outside of the walls of the chamber  318 . For example, the apparatus may include at least one free standing insulated electric coil supported by a dielectric support, integrated within walls of the chamber  318  or wound around the walls of the chamber  318 . Typically, a portion of a wall of the chamber  318  or other surface with which the at least one coil is in contact (particularly when the at least one coil is not insulated) is formed of a dielectric material. Other portions of walls of the chamber may be formed of dielectric or conductive materials.  
         [0036]    One end of the at least one coil is typically connected to ground, and the other to a power source, such as RF/AC power supply  332  and RF/AC matching network  333 . Energy, such as electric or RF energy is applied to the at least one coil causing an inductive coupling effect on the I/C ETP  350 . Typically, when operating in a start-up mode, energy is applied to the at least one coil once the thermal plasma enters the chamber  318 , after which energy is applied to the apparatus as the thermal plasma flows into the chamber  318 , although other energy application timing schedules may be used. The energy applied may have a continuous or pulsed waveform, where parameters of the waveform, such as waveform type (sinusoidal, square, triangular, trapezoidal, etc.); frequency; duty cycle; etc., are selected for obtaining the desired results.  
         [0037]    The inductive coupling effect causes precursor dissociation to occur through an electron impact dissociation path (in addition to the charge exchange followed by dissociative recombination reactions that occur in a regular ETP) generating a flux of reactive species, and the Te of at least a portion of electrons in the plasma to be raised to a relatively high Te. Once affected by the inductive coupling, the I/C ETP  350  becomes a non-equilibrium plasma, wherein the ion temperature and the electron temperatures may vary relative to one another.  
         [0038]    Accordingly, the Te is not completely limited by the ion temperature, and is able to rise, even when the ion temperature does not. Application of energy to the I/C system  330  changes the electric field, causing movement of electrons, increasing the kinetic energy of the electrons and increasing Te. The heavier-ions do not react to the change,d electric field. Thus, the kinetic energy and temperature of electrons in the chamber  318  are increased without changing the energy level or temperature of ions in the chamber  318 .  
         [0039]    In a conventional ETP reactor, the thermal plasma rapidly cools in the chamber and electrons loose energy based on the expansion, and are not effective in electron impact dissociation reactions. Further, once recombination begins at least a portion of the electrons and ions are lost. In the apparatus shown by FIG. 3, activation of the added I/C system  330  causes the electrons to heat up without heating the heavier ions. A spectrum of Tes is generated including relatively low Tes, such as approximately equal to 0.1 eV and relatively high Tes greater than 1 eV. The Te spectrum generated typically includes a Te of 0.3 eV having highly useful properties for generating more electrons, ions and thus plasma.  
         [0040]    First and second sets of chemical species are generated via the dissociative recombination path and the electron impact dissociation path, respectively. The dissociation products are transported along with the expansion at high drift velocity, thus generating a convective flux of reactive species, which arrives at the surface of the substrate  320 , resulting in deposition of a coating  334  on the substrate  320 .  
         [0041]    Furthermore, the increase in heat causes ionization to occur again, and results in an increase in ion density relative to an ETP only plasma. Accordingly, the increase in Te is proportional to increased ion density. Furthermore, the increase in Te provides the ability to do non-equilibrium chemistry, and to perform high temperature chemistry on a low temperature substrate.  
         [0042]    A further advantage to the increased Te is that an increased sheath voltage is built in front of the substrate that the I/C ETP  350  is in contact with as a result of “Child&#39;s Law”. Ions impacting the substrate are accelerated across this sheath due to the increased voltage. Accordingly, ion acceleration and bombardment energy are increased, which causes increased penetration and implantation of ions into the substrate  320  to form a mixed interface between the substrate  320  and the coating  334  being deposited for providing increased adhesion of the coating  334  to the substrate  320 . If porous openings exist in the coating  334  as it is being deposited, ion bombardment fills in the openings, producing a higher density coating.  
         [0043]    In an embodiment of the invention, the at least one electric coil of the I/C system  330  includes at least one coil having at least one turn that is mounted strategically in a substantially annular formation within the chamber  318  for applying an off axis, substantially annular bias to the ion density and the deposition profile, resulting in a substantially annular bias to the deposition density and thickness. The strategic placement of the at least one electric coil  330  provides for compensation for the Gaussian distribution of the deposition profile obtained with I/C ETP  350 .  
         [0044]    Deposition profiles  336  (corresponding to the deposition profile for coating  34  shown in FIG. 1) for a coating produced by an ETP only plasma, and  338  (corresponding to the deposition profile for coating  224  shown in FIG. 2) for a coating produced by an ICP only plasma are shown schematically by dotted lines. Coating  334  has a profile that is a combined deposition profile resulting from the Gaussian distribution ion density of the I/C ETP  350  combined with the off-axis high ion distribution effect of the I/C system  330 . The combined deposition profile of coating  334  is substantially uniform, resulting in substantially uniform density and thickness of the coating  334  on the substrate  320 , as is schematically shown in FIG. 3.  
         [0045]    Parameters of the ETP-ICP reactor  300  may be selected and/or controlled to obtain the desired combined deposition profile of coating  334  for achieving deposition uniformity. Exemplary parameters, such as parameters described in “High-rate Deposition of Abrasion Resistant Coatings Using a Dual-source Expanding Thermal Plasma Reactor” by M. Schaepkens, S. Selezneva, P. Moeleker, and C. D. Iacovangelo, J. Vac. Sci. Technol. A21(4), July/August 2003, include downstream operating pressure, working distanced between plasma source and substrate, precursor flow rate into the expanding argon plasma beam, and cathode-to-anode distance in the ETP source. Other parameters may include the amount and type of energy applied to the I/C system  330 , configuration of the I/C system  330 , strategic placement of the I/C system  330 , the number of coils and windings used for the at least one coil. For example, a larger number of turns yields a higher change in density of ions and a higher electron temperature.  
         [0046]    [0046]FIG. 4 shows an ETP-ICP reactor  400  that is substantially the same as the ETP-ICP reactor  300  shown in FIG. 3, except that an I/C system  430  is positioned along inlet  424 , i.e., along the path of the thermal plasma and proximate the thermal plasma as it flows to chamber  318 . I/C system  330  (not shown) may also be included.  
         [0047]    The I/C system  430  includes an apparatus for generating an electro-magnetic force, such as at least one coil, and a power source for energizing the apparatus. In the embodiment shown, the at least one coil is wound around an outer surface of the inlet  424 , so that plasma passes through the at least one coil before entering the chamber  318 . The at least one coil  430  may further (or alternatively) be disposed within the inlet  424 , such as insulated and positioned within the inlet  424  and/or wound along an inner wall of the inlet  424 . Typically, a portion of a wall of the inlet  424  or other surface with which the at least one coil is in contact (particularly when the at least one coil is not insulated) is formed of a dielectric material. Other portions of walls of the inlet  424  may be formed of dielectric or conductive materials.  
         [0048]    One end of each coil is typically connected to ground, and the other to a power source, such as RF/AC power supply  332  and RF/AC matching network  333 . Electric or RF energy is applied to the at least one coil causing an inductive coupling effect on the I/C ETP  350 . Other configurations for the I/C system  430  are envisioned. For example, the apparatus for generating the electromagnetic force may be integrated within the inlet  424 .  
         [0049]    The I/C ETP  350  generated by the ETP-ICP reactors  300  and  400  according to the disclosure are particularly useful for thin film deposition on surfaces for a large variety of applications, including surface glazing in the automotive, transportation, architectural glass replacement, semiconductor, photovoltaics, optical media, flat panel display and lighting industries. An array of ETP-ICP reactors may be used to achieve a uniform deposition profile using a high density plasma to uniformly provide functional coatings for large surface areas of surfaces formed of glass, metal, silicon and plastic (including polycarbonates). Examples of functional coatings that can be applied to the surface are abrasion resistant coatings, moisture and/or oxygen barrier coatings, ultraviolet absorbing coatings, infrared reflecting coatings and/or other transparent optical coatings (e.g., coatings that have more than 20% light transmission in the 400 nm to 700 nm range).  
         [0050]    The I/C ETP  350  may further be used for other applications including treating a surface to etch, roughen, heat and/or clean the surface. In certain cases of this application it is not required to inject a reagent into the expanding inductively coupled plasma, but instead the ionized reactant gas may be used.  
         [0051]    The described embodiments of the present disclosure are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present disclosure. Various modifications and variations can be made without departing from the spirit or scope of the present disclosure as set forth in the following claims both literally and in equivalents recognized in law.