Note: Descriptions are shown in the official language in which they were submitted.
10202530CA 02264371 l999-03- 18THIN FILM DEPOSITION METHODThis is a division of commonly owned Canadian Patent Application No. 2,146,369 ofNovember 10, 1993.FIELD OF THE INVENTIONThis invention relates generally to the deposition of a substantially uniform microwaveinitiated plasma over a relatively large area and more particularly to a method apparatus for thesimultaneous microwave initiated glow discharge chemical vapor deposition of uniform layersof thin ï¬lm material over a plurality of large area zones on an elongated web of microwavetransmissive substrate material. The microwave deposition assembly includes a linear, elongatedapplicator adapted to either radiate or transmit microwave energy via evanescent waves into theinterior of an enclosure maintained at sub-atmospheric pressure. In the most preferredembodiment, the thin ï¬lm material deposited upon the deposition surface of the web of substratematerial is an ultra-thin, transparent barrier layer for inhibiting the diffusion of oxygentherethrough. Speciï¬c processing parameters are enumerated herein.BACKGROUND OF THE INVENTIONOne application of microwave energy is to efï¬ciently create activated species fromgaseous precursors for use in plasma treatment processes, such as semiconductor etching andthin ï¬lm deposition. Previous microwave plasma deposition techniques, which illustrate the stateof the art and highlight both the problems encountered in increasing the energy uniformity andthe advantages provided by the microwave plasma generating structure and thin ï¬lm depositionapparatus of the instant invention, will be discussed in the following paragraphs.Commonly assigned, U.S. Patent Nos. 4,517,223 and 4,504,518 to Ovshinsky, et al.,both entitled "METHOD OF MAKING AMORPHOUS SEMICONDUCTOR ALLOYS ANDDEVICES USING MICROWAVE ENERGY" describe processes for the deposition of thin ï¬lmsonto small area substrates in a low pressure, microwave glow discharge plasma. As speciï¬callynoted in these Ovshinsky et al. patents, operation in the disclosed low pressure regimes not onlyeliminates powder and polymeric formations in the plasma, but also provides the most economicmode of plasma deposition. While these patents describe the revolutionary concept of operatingat low pressure and high energy density utilizing microwave energy, i.e., operating at thesubstantial minimum of the modiï¬ed Paschen curve, the problem of uniformity of the depositionof thin ï¬lms over large areas remained addressed.202530CA 02264371 l999-03- 182Turning now to microwave applicators for large area substrates, commonlyassigned U.S. Patent No. 4,729,341 of for "METHOD ANDAPPARATUS FOR MAKING ELECTROPHOTOGRAPHIC DEVICES" describes aFournier et al. low pressure microwave initiated plasma process for depositing a photoconductivesemiconductor thin film on a large area cylindrical substrate using a pair of radiativewaveguide applicators in a high power process. However, the principles of large areadeposition described therein are limited to cylindrically shaped substrates, such aselectrophotographic photoreceptors, and the teachings provided therein are not directlytransferable to elongated, generally planar substrates.While workers in the field have disclosed methods of processing thin filmsutilizing the high power of microwave sustained plasmas, previously microwave plasmatreatments have not been altogether appropriate for large surface area and/or lowpressure deposition. This is because of the non-uniformity of the plasma over anenlarged or elongated substrate due to the non-uniformity of the energy initiating theplasma. One attempt to provide greater large area uniformity was the use of a slowwave microwave structure. A problem that is inherent in slow wave structures,however is the very rapid decline of microwave coupling into the plasma as a functionof distance transverse to the microwave applicator. This problem has been addressedin the prior art by various structures that vary the spacing of the slow wave structurefrom the substrate to be processed. In this way the energy density at the surface of thesubstrate can be kept constant along the direction of movement of the substrate. Forexample, U.S. Patent No. 3,814,983 to Weissï¬och et al. for "APPARATUS ANDMETHOD FOR PLASMA GENERATION AND MATERIAL TREATMENT WITHELECTROMAGNETIC RADIATION" and U.S. Patent No. 4,521,717 to Kieser et al.for "APPARATUS FOR PRODUCING A MICROWAVE PLASMA FOR THETREATMENT OF SUBSTRATE IN PARTICULAR FOR THE PLASMAPOLYMERIZATION OF MONITORS THEREON", both address this problem byproposing various spatial relationships between the microwave applicator and thesubstrate to be processed. More particularly, Weissï¬och et al. discloses that in orderto obtain the uniform electric field intensity necessary for a plasma of uniform powerdensity along the full10202530CA 02264371 l999-03- 183structure at an angle with respect to the substrate. It should be apparent, however, thatinclination of the slow wave waveguide structure with respect to the substrate, to achieveuniformity. leads to an inefficient coupling of microwave energy into the plasma.Recognizing this deficiency, Kieser et al. described that the conditions resulting from superposing of two energy inputs. i.e., two microwave applicators, can be furtherimproved if the two slow wave applicators are set at an angle to each other such that theplanes normal to the medians of the applicators intersect at a straight line which extendsparallel to the surfaces of the substrate to be treated and at right angles to the directionof travel of the substrate. Moreover, Kieser et al. recommended that in order to avoid destructive interference of the wave ï¬eld patterns of the two applicators, the applicatorsshould be displaced from each other transversely of the direction of travel of the substrateby a distance equal to half of the space between the cross-bars of the waveguide. In thisway the microwave ï¬eld pattern is substantially suppressed.The problem of plasma uniformity and more particularly, energy uniformity wastreated by J. Asmussen and his co-workers, for example in T. Roppel. et al. "LOWTEMPERATURE OXIDATION OF SILICON USING A MICROWAVE PLASMA DISCSOURCE", J. Vac. Sci. Tgh. B-4 (January-February 1986) pp. 295-298 and M. Dahirneneand J. Asmussen "THE PERFORMANCE OF MICROWAVE ION SOURCE IMMERSEDIN A MULTICUSP STATIC MAGNETIC FIELD" J. Vac. Sci. Tech. B-4 (January-February 1986) pp. 126-130. In these, as well as other papers. Asmussen and his co-workers described a microwave reactor which they refer to as a microwave plasma discsource ("MPDS"). The plasma is reported to be in the shape of a disc or tablet, with adiameter that is a function of microwave frequency. A critical advantage claimed byAsmussen and his co-workers is that the plasma disc source is scalable with frequency:that is, at the normal microwave frequency of 2.45 gigahertz. the plasma disc diameteris 10 centimeters and the plasma disc thickness is 1.5 centimeters: but that the discdiameter can be increased by reducing the microwave frequency. In this way, the plasmageometry was said to be scalable to large diameters, potentially yielding a uniform plasmadensity over a large surface area. However, Asmussen, et al. only described a microwaveplasma disc source which is operational at 2.45 gigahertz, where the plasma confineddiameter is 10 centimeters and the plasma volume is ll8 cubic centimeters. This remains1015202530CA 02264371 l999-03- 184far from being a large surface area. In order to provide for the deposition onto largearea substrates, Asmussen et al. proposed a system operational at the lower frequency of 915 megahertz, which would provide a plasma diameter of approximately 40centimeters with a plasma volume of 2000 cubic centimeters. Furthermore, thedeposited material quality and deposition rate is dependent on excitation frequency. Themodulation of frequency to increase plasma dimensions comprises material quality andfilm deposition rate.Workers at Hitachi have described, for example in U.S. Patent No.4,481,229 to Suzuki et al., the use of electron cyclotron resonance (ECR) to obtain ahigh_power plasma having a relatively high degree of uniformity over a limited surfacearea. However, the Hitachi patent does not teach, nor even suggest a method by whichuniform large area plasmas may be achieved. Moreover, the use of ECR imposes theadded requirement of highly uniform magnetic field structures in the microwaveapparatus, and may be restricted in operation to only those very low pressure regimeswhere electron collision times are long enough to allow the ECR condition to beachieved.U.S. Patent Nos. 4,517,223 and 4,729,341 referred to above, describe thenecessity of using very low pressures in very high microwave power density plasmasin order to obtain high deposition rates and/or high gas utilization. However, therelationship between high deposition rates, high gas utilization, high power density, andlow pressure further limits the utility of slow wave structures and electron-cyclotronresonance methods. The limitations of the slow wave structure and of theelectron-cyclotron resonance methods were obviated by the method and apparatusdisclosed in commonly assigned U.S. Patent No. 4,893,584, to Doehler et al., "LARGEAREA MICROWAVE PLASMA APPARATUS". 'However, the apparatus of the âS84 patent, as well as the apparatus of theprior art, each suffer from a specific inherent design problem. That is, the prior artapparatus, due to their specific configuration, allow coating of the microwave radiatingapplicator isolating means (i.e. microwave window, protective cylinder, etc.) by thedeposition thereonto of material intended for the substrate web. In a continuous roll toroll process, this coating of the isolating means can cause reduced microwave efficiency1015202530CA 02264371 l999-03- 185at the intended deposition region, overheating of the isolating means and larger amounts of"downtime" due to the necessity of cleaning or replacing the isolating means.It would be commercially advantageous to create a deposition apparatus and method inwhich material could be deposited onto a continuous web of substrate material at multiple sitesupon the web during a single pass through the apparatus. This would allow for higher overallweb speed, and in the case of temperatures sensitive substrate materials, would allow formultiple cooling stages between deposition sites to prevent overheating and possible destructionof the web of substrate material.One particular application for the deposition of thin ï¬lm coatings onto an elongatedrelatively wide web of substrate material is for the food packaging industry. More particularly,there has recently arisen a desire to deposit thin ï¬lm oxygen and water vapor impermeablecoatings atop an elongated polymeric web to be employed for packaging and giving extendedshelf life to perishable foodstuffs. In order to accomplish this objective, researchers havepreviously developed thin ï¬lm SiCO coatings and have even suggested the signiï¬cance ofcontrolling the hydrogen content of that thin ï¬lm.More particularly, the importance of controlling the hydrogen content of prior art ï¬lmsfor the purpose of, inter alia, depositing oxygen impermeable ï¬lms has been discussed incommonly assigned U.S. Patent No. 4,737,379. As was noted therein, plasma depositedamorphous silicon hydrogen alloys, as well as alloys of silicon and hydrogen with one or moreof carbon, oxygen and nitrogen suffered from various shortcomings. The hydrogen content wasstrongly dependent upon the substrate temperature, that content decreasing at high temperaturesand increasing at low temperatures. The deleterious effect of hydrogenation on ï¬lm properties,such as oxygen and water vapor permeability, is a direct consequence of hydrogenâs role as achemical bond terminator. As such, hydrogen can disrupt the connectivity of the chemical bondnetwork of the deposited ï¬lm, thereby reducing its average atomic coordination number. Thesolution preferred by said â379 patent was to eliminate the presence of hydrogen for thefeedstock gases. This was at least partially due to the fact that thermally sensitive substrates,such as plastics, could not be heated sufï¬ciently to eliminate hydrogen bonding in the depositedthin ï¬lms. This inability to drive off hydrogen produced thin ï¬lms characterized by greatlydeteriorated properties which limited the utility of said ï¬lms. However, the recipes set forth inthe â379 patent fail to provide a ï¬lm which exhibits the type of oxygen and water vaporpermeation characteristics demanded by the food packaging industry.Therefore, there is a need in the art for a continuous, roll to roll deposition apparatus10152025CA 02264371 l999-03- 186which substantially eliminates coating of the microwave radiating applicator isolating means bydeposition material and allows for multiple simultaneous depositions upon a low temperature webof substrate material in a single pass through the apparatus. There also exists a need for thedeposition of thin ï¬lm oxygen and water vapor impermeable ï¬exible coatings atop a lowtemperature web of substrate material. These and other needs are met by the microwaveapparatus and deposition method described hereinbelow.BRIEF SUMMARY OF THE INVENTIONThere is disclosed and claimed in parent application No. 2,146,369 apparatus for theplasma enhanced chemical vapor deposition of thin ï¬lm material onto an elongated web ofsubstrate material utilizing a linear microwave applicator. More speciï¬cally, the apparatusincludes a deposition chamber which is capable of being evacuated, means for evacuating thedeposition chamber to sub atmospheric pressure, and an elongated web of substrate materialdisposed in the deposition chamber so that the deposition surface thereof substantially enclosesa ï¬rst interior volume of the chamber. The volume enclosed by the web of substrate materialdefines a ï¬rst plasma region. The apparatus also includes means for introducing a precursormixture of deposition gases into the ï¬rst plasma region, a ï¬rst linear, non-evanescent applicatorfor the substantially uniform introduction of microwave energy from a source into the ï¬rstdeposition region for disassociating the precursor gas mixture into a plasma of activated speciesand depositing the mixture of activated species onto the substrate. The linear applicator isoperatively disposed adjacent to the non-deposition surface of the substrate. The precursormixture of gases is substantially conï¬ned by the disposition of the web of substrate materialrelative to the linear applicator, whereby the associated precursor mixture is substantiallyprevented from depositing on the linear applicator.The apparatus also includes means for isolating the microwave radiating applicator fromthe low pressure deposition region. The additional isolating means is formed from a materialthrough which microwave energy can be radiated from the applicator means into the vessel andis conï¬gured into a shape substantially optimized to withstand the1015202530CA 02264371 l999-03- 187pressure differential to which it may be exposed. In this manner, the thickness of theisolating means may be minimized and a substantially unifomi plasma operation may beperformed along the surface of the elongated web of substrate material disposed in thedeposition chamber. The isolating means is preferably eylindrically or hemiâcy1indricallyshaped so as to encapsulate at least that portion of the applicator means which extendsinto the vessel. though other generally smoothly curved surfaces may be employed withequal success. A vacuum seal is disposed between the cylindrically shaped isolatingmeans and the vessel wall, so that a pressure differential may be maintained between theinterior and the exterior of the cylindrically-shaped isolating means. Accordingly,pressure (vacuum) maintaining means is provided to maintain the pressure (vacuum) ofsaid vessel disposed exteriorly of said cylindrically-shaped isolating means at a pressureapproximating that required for plasma operation near the minimum of a modifiedPaschen curve. The thickness of the circumferential wall of the isolating means isdesigned to withstand that pressure differential which exists between the exterior andinterior thereof.The applicator preferably takes the form of an elongated waveguide which includesat least one aperture for substantially uniformly radiating microwave energy therefrom intothe interior of the vacuum vessel. It is to be understood that the size of the apertures maybe periodic or aperiodic. and the size of the aperture may be equal to or less than onewavelength of the microwave energy. In other embodiments, a plurality of apertures arespacedly positioned along the longitudinal extent of the waveguide. Here, as above. thesize and spacing of the apertures may be either periodic or aperiodic.An elongated substrate web is adapted to be continuously moved past thelongitudinal extent of the waveguide. It is preferred that the substrate web is operativelydisposed within a near ï¬eld distance of said applicator. The applicator is adapted tosubstantially uniformly radiate microwave energy from the waveguide over a dimensiongreater than one wavelength of the microwaves and, preferably, greater than twelveinches. The applicator may further include shutter means adapted to ensure that asubstantially uniform density of microwave energy is emitted from the aperture meansalong the entire longitudinal extent thereof.The apparatus preferably further includes applicator cooling means. The cooling1015202530CA 02264371 l999-03- 188means may be a flux of air adapted to flow about the interior of the isolating means. In anotherpreferred embodiment, the cooling means may include a concentric enclosure formed interiorlyof and shaped similarly to said isolating means so as to define a conduit between said isolatingmeans and said concentric enclosure. It is into this conduit that a coolant ï¬uid, examples ofwhich include water, oils or freon, is adapted to flow. The ability to utilize thin isolating meansinsures that said isolating means can be thermally cooled to a sufficiently low temperature thatrelatively high power microwave energy can be introduced into the vacuum vessel and excite ahigh electron density plasma without the heat which is associated therewith cracking saidisolating means.The invention as disclosed and claimed herein provides, in a method of depositing, byplasma assisted chemical vapor deposition, an oxygen and water vapor barrier coating atop atemperature sensitive substrate for a precursor gaseous mixture which includes at least asiliconâcontaining gas and an oxygen-containing gas; the method characterized by the improvedsteps of: performing a plasma pretreatment of the low temperature substrate prior to themicrowave deposition step; and introducing a sufficient flow rate of oxygen-containing gas intothe precursor mixture to eliminate the formation of siliconâhydrogen bonds in the depositedcoating.These and other objects and advantages of the instant invention will become apparentfrom the Detailed Description, the Drawings and the Claims which follow hereinafter.BRIEF DESCRIPTION OF THE DRAWINGSFig. 1 is a schematic cross-sectional view of a first embodiment of the depositionapparatus, speciï¬cally illustrating the elements operatively disposed therein for effecting theuniform microwave plasma deposition on an elongated substrate; this figure illusnates anembodiment of the instant invention having a single plasma deposition region, employing a singlegas manifold and a single elongated microwave applicator;Fig. 2 is a schematic cross-sectional view of a second embodiment of the depositionapparatus of the instant invention, this embodiment employing a single deposition region, asingle elongated microwave applicator, and two gas manifolds, the first of which is adapted tointroduce the precursor gaseous mixture and the second of which is adapted to introduce anon-depositing gas mixture to effectuate plasma pretreatment of the deposition surface of theelongated web of substrate material;Fig. 3 is a schematic cross-sectional view of a third embodiment of the depositionapparatus of the instant invention, this apparatus employing two deposition regions, two1015202530CA 02264371 l999-03- 189elongated microwave applicators and two precursor gas mixture injection manifolds;Fig. 4 is a schematic cross-sectional view of a fourth embodiment of the depositionapparatus, this embodiment employing two elongated microwave applicators and three gasmanifolds, two of which are adapted to introduce precursor gaseous mixture into the depositionregions and a third adapted to introduce a non-depositing gas mixture for the plasmapreâtreatment of the deposition surface of the elongated web of substrate material;Fig. 5 is a cross-sectional view of a portion of the apparatus, speciï¬cally depicting aradiative linear microwave applicator unit operatively attached interiorly of the depositionchamber;Fig. 6 is a fragmentary perspective view illustrating a ï¬rst embodiment of the radiativemicrowave applicator with spacedly disposed discrete apertures formed through one of the widerfaces thereof;Fig. 7 is a fragmentary perspective view illustrating a second embodiment of the radiativemicrowave applicator with a single elongated aperture formed through one of the wider facesthereof and shutter means disposed thereover; andFig. 8 is a fragmentary perspective view illustrating a second embodiment of the linearradiative microwave applicator in which the spacedly disposed apertures are formed along thelongitudinal extent of one of the narrower faces thereof.DETAILED DESCRIPTION OF THE INVENTIONThere is disclosed herein an apparatus for the simultaneous plasma enhanced chemicalvapor deposition of thin film material onto multiple portions of an elongated web of substratematerial utilizing a linear microwave applicator. Deposition occurs within an evacuateddeposition chamber. By maintaining the vessel, at sub atmospheric pressures, it is possible tooperate the plasma at a pressure approximately that required for operation near the minimum ofthe modified Paschen curve. Low pressure operation also allows for a longer mean free pathof travel for the plasma excited species, thereby contributing to overall plasma uniformity. Inthis way, it is possible for the microwave deposition apparatus to sustain a uniform plasmareaction upon a substrate disposed within the near field distance of the microwave source.Fig. 1, illustrates, in schematic cross-section, a first embodiment of a microwavedeposition apparatus 1 for sustaining a substantially uniform microwave plasma over a relativelywide web of substrate material. As used herein, the term "wide" refers to a body having awidth dimension greater than one microwave wavelength, and preferably1015202530CA 02264371 l999-03- 1810greater than twelve inches. The apparatus 1 includes, inter alia, a vacuum vesseldeposition chamber 2, the walls of which are preferably fomted of a durable, corrosionresistant material such as stainless steel. The vacuum vessel deposition chamber 2 furtherincludes a pump-down port 3 adapted for suitable connection to a vacuum pump formaintaining the interior of the vacuum vessel deposition chamber 2 at an appropriate sub-atmospheric pressure. The vacuum pump is further adapted to remove reaction productsfrom the interior of said vessel 2.The vessel 2 further includes at least one process gas input line connected to aprocess gas input manifold 9, which manifold 9 is operatively disposed so as to uniformlydistribute processed gases into the interior of said reaction vessel 2, and specifically intothe plasma deposition region 12 thereof. The process gas input manifold 9 is operativelydisposed between a pair of process gas containment means 11 and between at least twosections of the web of substrate material which define the deposition region 12. Incombination, the web of substrate material and the process gas containment means 11contain the process gas introduced by the manifold 9 into the plasma region 12 of thevacuum vessel deposition chamber 2.During operation, the web of substrate material is drawn from payoff roll 5 andguided by guide rollers 8 toward the deposition region. Guide rollers 8 may be variabletension rollers to relieve stress upon the web of substrate material as it passes through thedeposition chamber. After passing along one or more guide roller 8. the web of substratematerial is passed between the linear microwave applicator 4 and the process gas injectionmanifold 9. The web of substrate material is then passed around chill roller 7, againpassing gas port 9, around additional guide rollers 8. and collected upon take-up roll 6.The sections of the web of substrate material extending between guide roller 8 and chillroller 7 create an enclosed plasma deposition region 12. The precursor gas mixtureinjected front gas manifold 9 interacts with the microwave energy supplied by theelongated microwave applicator 4 to create energized species in deposition region 12.Deposition therefore occurs on both the section of substrate material leading toward andmoving away from chill roller 7. Because plasma deposition is inherently a hightemperature process, temperature sensitive substrates must be intermittently cooled so thatdestruction thereof is avoided. This cooling is accomplished by chill roller 7. Cooling1015202530CA 02264371 l999-03- 1811the web of substrate material allows for a longer overall exposure time to the plasmadeposition. The apparatus of Fig. 1 allows for high deposition rates and good process gasutilization by allowing for deposition on at least two discrete portions of the web ofsubstrate material on a single pass.The microwave deposition apparatus 1 further includes a microwave applicator unit4 which extends at least partially into the interior of said vacuum vessel depositionchamber 2. The microwave applicator unit 4 is adapted to radiate microwave energy froma source thereof, into the interior of said vacuum vessel deposition chamber 2 forinitiating and maintaining a plasma of the process gases introduced into said vessel 2through a process gas manifold 9. The specifics of the microwave applicator unit 4including the microwave applicator and microwave applicator isolating means will bediscussed in detail hereinbelow. ITurning now to Fig. 2, there is shown a schematic cross-sectional view of a secondembodiment of the microwave deposition apparatus - This secondembodiment is similar to the microwave deposition apparatus of the first embodiment(Fig. 1) with the exception of the addition of a deposition surface pretreatment zone. Theinstant inventors have surprisingly found that microwave pretreatment of the depositionsurface of the web of substrate material enhances the barrier properties of the depositedthin film. This microwave pre-treatment is preferably a plasma pre-treatment and mostpreferably an argon plasma pre-treatment. The argon plasma pre-treatment of thedeposition surface of the web of substrate material occurs in a plasma pre-treatment zone13. The argon is injected into the plasma pre-treatment zone 13 by pre-treatment gasmanifold 14. The injected argon interacts with the microwaves from the linear microwaveapplicator 4 thereby pretreating the deposition surface of the web of substrate material.In order to pass the deposition surface of the web of substrate material past pre-treatmentzone 13, the guide rollers 8 on the payoff roll 5 side of the deposition apparatus 1 mustbe moved to the opposite side of the microwave applicator vis a vis the depositionapparatus of Fig. 1. In addition, another roller 15 must be added to the system. Thisadditional roller 15 can be either a guide roller or a quench roller as required. It ishypothesized that this pretreatment process promotes the adherence of the coating to theweb and possibly even affects the growth kinetics thereof.1015202530CA 02264371 l999-03- 181')Turning now to Fig. 3, illustrated therein is a schematic cross-section of a thirdembodiment of the microwave deposition apparatus . This thirdembodiment is similar to the first embodiment of Fig. 1 except for the inclusion of anadditional deposition region 12 which includes an additional chill roller 7, an additionalgas manifold 9, an additional guide roller 8, and an additional linear microwave applicator4. Also, the embodiment of Fig. 3 includes a microwave barrier 16 which reduces oreliminates the interaction of microwaves from the linear applicators 4. This embodimentprovides for very high deposition rates. due to the dual depositionregions 12 which allow deposition on at least four discreet portions of the web ofsubstrate material during a single pass. This higher deposition rate allows for fasterthroughput of the web of substrate material, for a given deposited thin film thickness.This higher throughput speed reduces the temperature rise of the web of substrate materialat any given deposition zone by reducing the time of exposure to the deposition plasmaand allowing the web of substrate material to pass over cooling rollers betweendepositions.Alternatively, the first deposition region of the microwave deposition apparatus ofFig. 3 may be used as a plasma pre-treatrnent region. In this instance, the deposition zone12 which is closest to the pay off reel 5 would be used as a plasma pre-treatrnent zone13, as in Fig. 2, by providing a non-depositing gas or gaseous mixture, such as argon, inthe first gas manifold 9. This alternative embodiment would reduce any microwave lossesencountered by the deposition apparatus of Fig. 2 due to the plasma pre-treatmentmicrowave energy load by providing a separate linear microwave applicator for each ofthe plasma pre-treatrnent and plasma deposition zones.Turning now to Fig. 4, there is depicted therein a cross-sectional schematicrepresentation of a fourth embodiment of the microwave deposition apparatus .This embodiment combines both the dual deposition regions 12 of theembodiment of Fig. 3 and the plasma pretreatment region 13 of the embodiment of Fig.2. Therefore, this embodiment allows for both high deposition rate/high throughput andplasma pre-treatment of the deposition surface of the web of substrate material forenhancement thereof.As is illustrated in Fig. 5, the microwave applicator unit 4 comprises a1015202530CA 02264371 l999-03- 1813substantially rectangular waveguide 42 having an open end portion 44 at the terminal endportion thereof extended into the vessel 2. The open end portion is adapted to avoidstanding waves. It is to be understood that the applicator unit 4 may alternatively besealed at the terminal end thereof. The waveguide means 42 includes a plurality ofapertures fortned through a wider face thereof. The apertures are dimensioned and spacedto provide for the uniform radiation of microwave energy therefrom.Illustrated in greater detail in Fig. 6, is a fragmentary perspective view of themicrowave applicator unit rectangular waveguide 42 having the terminal end portion 44,and a plurality off spacedly disposed apertures, 46, 48, 50, 52 and 54 formed through awider face thereof. As is illustrated therein, apertures 46 and 48 are blocked bymicrowave absorbing material to prevent microwave energy from radiating therefrom. Itis to be understood that the density of the microwave energy radiated by the microwaveapplicator waveguide 42 can be distributed in a desired, controllable manner simply byblocking and partially unblocking various ones of the apertures. In Fig. 8, a secondmicrowave applicator embodiment is depicted only differing from the Fig. 6 embodimentby the formation of said apertures through one of the narrower rectangular faces of thewaveguide. Experiments have demonstrated that it is possible to maintain plasmauniformity over large area substrates, while increasing the amount of microwave energyintroduced into the chamber by forming the apertures in the narrow waveguide face. Thisis believed to be due to the fact that current nodes are convergent along the narrower faceas the microwaves travel through the rectangular waveguide structure.The instant inventors have found that the size of the apertures is of greatsignificance, in that the leak rate of microwaves through any one of said apertures isstrongly dependent upon the size of that aperture. While the size of the apernire may beeither larger or smaller than a wavelength of microwave energy, in the embodiment ofFig. 6, it is preferred that the aperture be the size of. or smaller than one wavelength ofmicrowave energy. Additionally, the inventors have found that by partially unblockingthe apertures, the apparatus 1 is capable of sustaining a plasma which is substantiallyuniform.Referring now to Fig. 7. a third embodiment of the microwave applicatorwaveguide 142 has an open end portion 144 thereof and a single elongated. rectangular10I5202530lCA 02264371 2002-08-2714aperture 146. larger than a wavelength of microwave energy. fonned through substantiallythe entire length and width dimension of a wider face thereof. The open end portion isadapted to avoid standing wave problems, though a sealed end portion may be employedfor a given application. The waveguide 142 allows microwave energy to radiate from theentire aperture 146. though without more. the concentration of microwave energy isgreatest at the end of the aperture nearest the source of microwave energy. Theconcentration of the microwave energy, and consequently the density of the plasma maybe regulated by employing at least one elongated either straight or sligptly curved metallicmicrowave shutter 150 operatively affixed to said microwave waveguide 142 by a singleconnection 152 consisting of, for example. a pin 153 through a channel 155, on the sideof said waveguide nearest to the source of microwave energy. Disposed at the oppositeend of said elongated aperture 146. and along the edges of said aperture. are dielectricinsulator blocks 154 fabricated from. for example glass or teï¬oy The dielectric insulatorblocks 154 are adapted to form an insulating barrier between the waveguide 142 and themicrowave shutter 150. This is necessary since the microwave shutter 150 may begrounded to the waveguide means 142 only at the connection 152. Additional contactbetween the shutter 150 and the waveguide 142 will cause a so called "sizzling" ground.i.e., an arcing contact.The waveguide embodiments shown and discussed in detail in connection withFigs. 6 and 7 are of the type generally known as "leaky" microwave structures in thatmicrowave energy is allowed to leak or radiate therefrom through a plurality of apertures.Alternatively, though not illustrated herein, the microwave applicators may be slow wavemicrowave structures. The slow wave structure delivers a signiï¬cant part of microwaveenergy by means of evanescent waves. This type of slow wave structure was discussedhereinabove with reference to the Wgissï¬ggh, gt gl, and Kiggr, eg al, patents. Themicrowave energy apparatus 1 substantially obviates the shortcomings inherent in slowwave structures, i.e., the rapid decline in applied energy coupled to the plasma as aftmction of distance along the direction transverse to the microwave structure. Thisshortcoming is substantially obviated herein by, inter alia, isolating the microwaveapplicator from the plasma region, thereby allowing the applicator to sustain a moreuniform plasma.1015202530CA 02264371 l999-03- 1813Returning now to Fig. 5, the microwave applicator unit 4 further comprises means60 for isolating the microwave waveguide 42 from the deposition chamber 2. Theisolating means 60 is preferably fabricated from a dielectric material which is substantiallytransparent to microwave energy. A preferred material from which said isolating means60 may be fabricated is quartz, though it is to be understood than many other materialsmay be employed with equal success. The isolating means 60 should further beconfigured in a shape designed to optimize its ability to withstand forces due to thepresence of a pressure differential. In this manner, the thickness of the isolating meansmay be minimized to provide for effective thermal cooling whereby high microwavepower densities may be employed without deleteriously effecting the isolating means. Tothis end, a preferred shape for said isolating means is cylindrical or hemi-cylindrical asto encapsulate at least that portion of the waveguide 42 which extends into the vacuumvessel 2.A cylindrical or hemiâcylindrically shape is preferred to for example a planarshape, because a cylinder may be made thinner than a planar shape due to the strengthinherent in a cylinder. Thus, a thin cylinder is capable of withstanding pressures whichwould require a much thicker planar plate. Additionally, a thick plate cannot bemaintained at a uniform, relatively low temperature, as can a thin cylinder. Thus, a planarplate may be subject to themtal degradation, in a microwave plasma apparatus particularlyat elevated power levels. By contrast, the thin cylindrical isolating means 60 may beuniformly cooled, and thus does not experience thermal degradation, and therefore doesnot impose practical limitations upon the amount of power which may be applied.Additionally, the waveguide 42 should be operatively disposed within the isolationmeans 60 and spaced from the circumferential wall thereof. So disposed, the waveguide42 may extend partially through the vacuum vessel 2, without being directly exposed ofthe plasma regions 12 or 13 contained therein.The cylindrical isolating means 60 of Fig. 5 is configured so as to be coextensivewith at least one dimension of the vacuum vessel 2, and protrude through at least a firstand second wall portion of said vacuum vessel 2. The cylindrical isolating means 60 isfixed through the walls of the vacuum vessel 2 by means of two collar fittings 62 and 64which are preferably mutably joined to the stainless steel vessel 2. Collar ï¬tting 621015202530CA 02264371 l999-03- 1816comprises an open end portion 66 extending from a connection ï¬ange 68 affixed directlyto a side wall of the vacuum vessel 2, and includes an opening 70 coâextensive with thecircumference of the cylindrical isolating means 60 and adapted to receive cylindricalisolating means 60. Open end portion 66 extends from said connection ï¬ange 68. and isadapted to receive at least two O-rings 72, 74, which O-rings 72, 74 are adapted to effecta vacuum and water barrier between the interior of said vacuum vessel 2 and outsideambient conditions. Between O-rings 72, 74 is disposed a cooling channel 73 throughwhich a cooling medium such as water may be circulated to maintain the O-rings at auniformly low temperature. The O-rings 72, 74 are preferably adapted to maintain thevacuum and water seal at substantially elevated temperatures, i.e., temperatures in excessof 100° Centigrade.The cylindrical isolating means 60 passes through opening 70, connection flange68, and the open end portion 66. In this way, O-rings 72, 74 are urged against the outsidecircumference of said cylindrical isolating means 60. The compression of the O-rings 72,74 against the cylindrical isolating means 60 results in an air tight, water tight seal. It isimportant to note that the location of O-rings 72, 74 is well outside the plasma region 12of the apparatus 1. This is noteworthy because by keeping the O-rings out of the plasmaregion 12, they are not exposed to the excessive temperatures associated with microwaveplasmas, i.e., temperatures in excess of 500° Centigrade. Had the O-ring seals beenlocated within the plasma region, as shown in the aforementioned U.S. Patent No.4,729,341, special (and costly) high temperature resistant seals would have been required.greatly increasing the complexity and cost of the apparatus 1.The cylindrical isolating means 60 may extend beyond the outside terminal edgeof said open end portion 66. This portion of the cylindrical isolating means 60 must thusbe equipped with microwave containment means 80. The microwave containment means80 is typically fabricated from a metal microwave containment canister operatively affixedaround the outside circumference of the cylindrical isolating means 60. and in electricalcontact with said open end portion 66 by grounding ï¬ngers 82. The microwavecontainment canister is fabricated so as to be coextensive with that portion of cylindricalisolating means 60 which extends beyond the open end portion 66. Additionally, themicrowave containment means 80 further includes an open end portion 84 over which is1015202530CA 02264371 l999-03- l8l7disposed a metallic microwave blocking mesh 86 adapted to contain stray microwavestherewithin. The mesh 86 is also adapted to allow for the passage of a flux of coolingair through the cylindrical isolating means 60. Alternatively, and as is illustrated inphantom in Fig. 5, the opened end portion 84 of the microwave containment canister 80may be attached to a dummy load adapted to absorb excess microwave radiation. Thisembodiment is particularly useful at high power levels, where excess reflected microwaveenergy causes reflection modes which may degrade the uniformity of the microwaveplasma.The vacuum vessel 2 is further adapted to receive the cylindrical isolating means60 through at least a second wall portion thereof, preferably the wall portion opposite thewall portion upon which collar fitting 62 is mounted. Collar fitting 64 is disposed on saidopposite wall position, substantially in line with collar fitting 62. Collar ï¬tting 64comprises an open end portion 90 extended from a connection ï¬ange 92. Connectionï¬ange 92 is affixed directly to the opposite wall position and includes an opening 94 co-extensive with the circumference of the cylindrical isolating means 60. The open endportion 90 extends from the connection flange 92, and is adapted to receive at least twoO-rings 96. 98 which are adapted to effect a vacuum and water barrier between thevacuum vessel 2 and the surrounding ambient conditions. Between O-rings 96, 98 isdisposed a cooling channel 97, through which a cooling medium such as water may becirculated so as to maintain the O-rings at a uniformly low temperature. The O-rings 96,98 like O-rings 72, 74 are adapted to withstand elevated temperatures. The cylindricalisolating means 60 is passed through opening 94, through connection ï¬ange 92 and openend portion 90 whereby O-rings 96, 98 are urged against the outside circumferential edgeof said cylindrical isolating means 60. The compression of said O-rings is the mechanismby which an air tight. water tight seal is effected. Also, O-rings 96, 98, like O-rings 72,74, are well out of the plasma region 20. and therefore not subjected to degradationthereby.By effecting an air-tight, water tight seal around the outer circumference of thecylindrical isolating means 60, it is possible to maintain the vacuum vessel 2 atsubstantially sub-atrnospheric pressures, while the interior of the cylindrically isolatingmeans 60 is maintained at atmospheric pressures, and is directly exposed to ambient1015202530CA 02264371 l999-03- 1818conditions. This is in fact an advantage in the operation of the apparatus 1. Bymaintaining the vacuum vessel at subâatrnospheric pressures, it is possible to operate theapparatus 1 at a pressure approximating that required for operation near the minimum ofa modified Paschen curve. Additionally, the low pressures allow for a longer mean freepath of travel for the plasma species, thereby contributing to overall plasma uniformity.Since the interior of the cylindrical isolating means 60 is exposed to ambient conditions,a flux of cooling air may be maintained therethrough so as to prevent the excessiveheating which may be associated with microwave plasmas. Alternatively, a microwavetransmissive cooling medium such as silicon oil may be circulated within the cylinder tomaintain a uniform, cool temperature. The cylindrical isolating means 60, extendingbeyond the open end portion 90 must be sheathed within a metallic microwavecontainment means 100, of the type described hereinabove. The microwave containmentmeans 100 is disposed adjacent to connection plate 102 which affects a connectionbetween the microwave waveguide 42, and a source of microwave energy.Another form of substrate pretreatment, which may be used with or without plasmapretreatment, is a thermal bake-out of the substrate material. This bake-out may beaccomplished by providing a heat generator (i.e. coil, lamp etc.) in the apparatus such thatthe substrate passes nearby before any plasma pretreatment or deposition occurs. See. forexample, heater 300 in Fig. 1. This bake-out of the substrate is thought to drive off waterfrom the bulk of the substrate, thereby reducing the water vapor transmission rate of thecoated product.Finally, although enclosure of the deposition plasma region 12 within the folds ofthe web of substrate material 10 is highly effective in preventing the deposition of coatingmaterial onto the quartz isolation tube, a web of microwave transmissive material on pay-out roller 200 (Fig. 1) may be operatively positioned interiorly of said deposition chamber1 so as to slowly move about the surface of the isolation means of the linear microwaveapplicator 4 and be wound about the take-up roller 201. When the microwavetransmissive web is coated with an excess thickness of depositing barrier material, therollers are indexed and a clean portion of the web is allowed to collect the unwantedbuildup. In this manner, even at extremely high rates of deposition, no coating isdeposited onto the outer surface of the isolation means (the quartz tube). Accordingly,1015202530CA 02264371 l999-03- 1819the deposition process can proceed for long periods of time and is specifically adapted forvolume production.EXAMPLE 1A microwave deposition apparatus 1 as described hereinabove with reference toFig. l was employed to fabricate a clear silicon based thin ï¬lm oxygen permeation barrierlayer coating upon an elongated web of polyester substrate material. The exact steps bywhich the above described apparatus 1 was used to fabricate such coatings will be detailedhereinbelow.An elongated roll of 0.5 mil (12 micron) thick 30 cm wide polyester was used asthe substrate for the instant example. The roll of polyester substrate was loaded onto thepayout roller of apparatus 1 described hereinabove with reference to Fig. 1. After placingthe substrate onto the payout roller 5, the apparatus 1 was closed and sealed so as toeffect an air tight seal between the interior of the vessel and the surrounding ambientconditions. The interior of the vessel was then evacuated to a pressure of approximately20 to 25 millitorr. Thereafter. the interior of said chamber was purged in an argon gasenvironment for a period of approximately one-half hour. After purging for approximatelyone-half hour, the chamber was evacuated to a background pressure of approximately 3to 4 millitorr. Thereafter, preferred feedstock gases were introduced to the interior of saidchamber through said input gas manifold 9 according to the following recipe:GAS FLOW RATEsin. 180 SCCMco, 500 SCCMo, 500 SCCMAr 400 SCCMA general range of gases for this four component mixture would be about 100to 200 SCCM Si}L, 300-700 SCCM 0,, 300-700 SCCM CO, and 300-700 SCCM Ar.After initiating the flow of these feedstock gases into the interior of the vacuumvessel, a microwave plasma was initiated at a frequency of 2.45 GHz and at a power ofapproximately 5 kilowatts. The elongated web of substrate material was passed through1015202530CA 02264371 l999-03- 1820the deposition region 12 of the apparatus 1 at a rate of about 20 m/min. During theoperation of the microwave plasma, a ï¬ux of cooling air was directed through thecylindrical isolating means 60 so as to maintain a uniform low temperature. Thereafter,microwave plasma was extinguished, and the flow of process gases to the vacuum vessel2 was terminated.After extinguishing the plasma and terminating the ï¬ow of process gases to thevacuum vessel 2, the interior of the reaction vessel was purged with argon, and thereaction vessel was vented to ambient conditions. Thereafter, the reaction vessel wasopened and the substrate was removed for examination which revealed a uniform, clear,silicon based, thin film, oxygen permeation barrier coating on the web of substrate 10.Tests indicate that the deposited film has the chemical composition SiO_, wherex=l.8â2. Oxygen permeation tests on a coated substrate having a 200 A thin filmdeposited thereon show an O2 permeation of l cmâ/m2/day at room temperature and 0%relative humidity.In order to obtain the impressive oxygen and water vapor imperrneabilitybehavior described herein, it was necessary to devise a method of eliminating hydrogenfrom the deposited ï¬lm taking into account the low melting point of the PET substrate.In this regard, both the effect of increased oxygen concentration in the precursor gaseousmixture was studied and the chemical bonds responsible for water vapor diffusion werestudied by conducting IR spectroscopy on sample ï¬lms deposited on crystalline siliconwafers. Table A summarizes the relationship of Si-H concentration versus water vaportransmission and the precursor mixture.A perusal of Table A will demonstrate that the Si-H concentration and thewater vapor transmission decreases with the increase of oxygen concentration in theprecursor gaseous mixture. It is, of course, well established that Si-H bonds readily reactwith water. Accordingly, it is not surprising that Si-H bonds in the deposited films willabsorb, react with and create a transmission pathway for the water vapor. The conclusionto be drawn is that the relatively poor water vapor permeation properties shown insamples 1 and 2 were due to the presence of Si-H bonds in the films and that increasedoxygen concentration in the precursor mixture eliminated those Si-H bonds and increasedthe imperrneability of the films. Note that the further increase of oxygen concentration1015202530CA 02264371 1999-03- 1821in the precursor beyond that indicated in Sample 3, failed to improve the water barrierproperties. Of course, the plasma treatment process detailed hereinabove further improvedthe barrier properties of the deposited film.TABLE ASAMPLE FEEDSTOCK Si-H H20 VAPORNo. GASES BOND TRANS. RATE(SCCM) CONTENT (gm/mâ-24 hrs.)SiH,, CO2 Ar 0, 38°C. 100% RHl 220 750 450 275 0.5% 262 220 400 450 400 Trace 1 13 150 500 450 500 None 7EXAMPLE 2A microwave deposition apparatus 1 as described hereinabove with referenceto Fig. 2 was employed to fabricate a second clear silicon based thin film oxygenpermeation barrier layer coating upon an elongated web of polyester substrate material.A roll of 0.5 mil (12 micron) thick 30 cm wide polyester was again used as the substrate.The roll of polyester substrate was loaded onto the payout roller of apparatus 1 describedhereinabove with reference to Fig. 2. After placing the substrate onto the payout roller5. the apparatus 1 was closed and sealed so as to effect an air tight seal between theinterior of the vessel and the surrounding ambient conditions. The interior of the vesselwas then evacuated to a pressure of approximately 20 to 25 millitorr. Thereafter, theinterior of said chamber was purged in an argon gas environment for a period ofapproximately one-half hour. After purging for approximately oneâhalf hour, the chamberwas evacuated to a background pressure of approximately 3 to 4 millitorr. Thereafter.feedstock gases were introduced to the interior of said chamber through said input gasmanifold 9 according to the following recipe:1015202530CA 02264371 l999-03- 1822GAS FLOW RATESiH., 300 SCCM0, 900 SCCMHe 100 SCCMA general range for this three component mixture would be about 200-400SCCM SiI~l,,, 800-1000 SCCM 0,, and O-200 SCCM He.Additionally, 400 SCCM of Ar was introduced to the plasma pretreatment zone13 through gas manifold 14. After initiating the flow of these gases into the interior ofthe vacuum vessel, microwave plasmas were initiated at a frequency of 2.45 GHz and ata power of approximately 6 kilowatts for Ar plasma pretreatment and 5 kilowatts forplasma deposition. The elongated web of substrate material was passed through I h eplasma pretreatment region 13 and deposition region 12 of the apparatus 1 at a rate ofabout 20 m/min. During the operation of the microwave plasma, a flux of cooling air wasdirected through the cylindrical isolating means 60 so as to maintain a uniform lowtemperature. Thereafter, microwave plasma was extinguished, and the flow of processgases to the vacuum vessel 2 was terminated.After extinguishing the plasma and terminating the flow of process gases to thevacuum vessel 2, the interior of the reaction vessel was purged with argon. and thereaction vessel was vented to ambient conditions. Thereafter, the reaction vessel wasopened and the substrate was removed for examination which revealed a uniform, clear,silicon based, thin film, oxygen permeation barrier coating on the web of substrate 10.Tests indicate that the deposited film has the chemical composition SiO,, wherex=l.8-2. Permeation tests on a coated substrate having a 150 A thin film depositedthereon show an 0, transmission rate of less than 1 cmâ/mâ/day at room temperature and0% relative humidity and a water vapor transmission rate of less than 1 g/mz/day at 38°C and 100% relative humidity.While the speciï¬c examples of the method of depositing high barrier coatingsby microwave plasma enhanced CVD recited herein above are described with referenceto ï¬at rolls of substrate material and the apparatus as described herein itshould be noted that the present method is useful for depositionof high barrier coating onto10CA 02264371 l999-03- 1823substrates of any shape, by any machine which is capable of deposition onto the desiredsubstrate. Other types of substrates which would benefit from a coating of high barriermaterial would be those such as plastic bottles, jars or other plastic containers in whichthe material to be stored is sensitive to water or oxygen. Of specific interest is coatingthe interior of plastic bottles or jars for storage of food or beverages. As long as the basicmicrowave deposition steps are present (i.e. such as thermal bake-out, plasmapretreatment, microwave PECVD of high barrier coating etc.). the shape and/or size of thesubstrate and/or portion of the substrate to be coated is irrelevant.While the invention has been described in connection with preferredembodiments and procedures, it is to be understood that it is not intended to limit theinvention to the described embodiments and procedures. On the contrary it is intendedto cover all alternatives, modifications and equivalence which may be included within thespirit and scope of the invention as defined by the claims appended hereinafter.
