Review Chemical Vapor Deposition Enhanced by Atmospheric Pressure Non-thermal Non-equilibrium Plasmas** By Sergei E. Alexandrov and Michael L. Hitchman* Thisreviewgivesanoverviewofthecharacteristicsofvariousnon-thermal,non-equilibriumplasmasanddiscussesapplications ofAP-PECVDwithdielectricbarrierdischarges,coronadischarges,RFdischarges,andmicrowavedischarges. Keywords:Non-thermalplasmas,non-equilibriumplasmas,AP-PECVDprinciplesandapplications 1. Introduction Plasma enhanced chemical vapor deposition (PECVD) hasbeenwidelyusedformanydifferentapplications.These processes are distinguished from conventional, heat acti- vatedCVDprocessesbyelectricalenergyratherthanther- malenergybeingusedforinitiatinghomogeneousreactions for the production of chemically active ions and radicals that can participate in heterogeneous reactions which, in turn,leadtolayerformationonasubstrate.Themainpur- poseofusingaplasmaasasourceofenergyforCVDpro- cesses instead of heat is to overcome high deposition tem- peratures that can degrade many substrate materials. This goal is achieved through the use of non-equilibrium, non- thermal plasmas that are typically generated by electrical discharges in the gas phase at low pressure (LP). In such plasmas, the electron temperature is much higher than the gas temperature and inelastic collisions of the electrons with precursor molecules form chemically active species that participate in the reactions leading to film formation. In addition, surfaces in the plasma can be bombarded with theactivespecies,suchasions,electronsandphotons,lead- ing to changes in surface chemistry. PECVD processes based on this approach have been widely used for the de- positionofawiderangeofmaterialswithstandardandnov- elproperties.Inorganicelementsandcompoundsaswellas organicpolymershavebeendepositedbyPECVD. [1] TheuseofLP-PECVDhaslimitationsforvariousindus- trialapplications,though.Formanyindustrialproductsitis not practicable to use vacuum technology with load locks forlargescaleprocesses,andevenifitwerepracticablethe high capital and running costs of vacuum equipment can become prohibitive. As a result of these limitations, there has been considerable interest in recent years in the devel- opment of atmospheric pressure, non-thermal plasma sources suitable for use with CVD technologies. [2] In this paper we review some of the results achieved with atmo- spheric pressure PECVD (AP-PECVD) processes based ontheuseofnon-thermalplasmas. 2. Sources of Atmospheric Pressure, Non-thermal Plasmas Thevarioustypesofelectricaldischargethatcanbeused to generate non-thermal plasmas at atmospheric pressure have been recently reviewed. [3±6] These discharges occur in an appropriate gaseous atmosphere and are, typically, low frequency,dielectricbarriergloworfilamentarydischarges, as well as types of corona discharge, radio-frequency (RF) discharges in narrow gaps (which may include a dielectric barrier),ormicrowave(MW)discharges.Themainaspects ofthesedischargesandtheircommonfeaturesarethatthe electrical input power generates plasmas with highly ener- getic electrons, yet the gas molecules passing through the discharge generation region remain ªcoldº. Inelastic colli- sionsoftheenergeticelectronswithgasmoleculesproduce chemically active species such as free radicals, atoms and ions that can be involved in the chemical reactions leading tolayerdeposition. Chem. Vap. Deposition 2005, 11, 457±468 DOI: 10.1002/cvde.200500026  2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 457 ± [*] Prof.M.L.Hitchman DepartmentofPureandAppliedChemistry,UniversityofStrathclyde 295CathedralStreet,GlasgowG11XL(UK) E-mail:m.l.hitchman@strath.ac.uk Prof.S.E.Alexandrov DepartmentofElectronicMaterialsTechnology StPetersburgStatePolytechnicalUniversity 195251StPetersburg,PolytechnicalStr29(Russia) [**] We thank the European Commission - Project G5RD-CT-1999-00160 (Activated CVD for in-line coating of temperature sensitive parts, at atmospheric pressure) ± for financial support and the project partners forinterestingdiscussions.