FullPaper GrowthofNeodymiumOxideThinFilmsbyLiquid-Injection MOCVDUsingaNewNeodymiumAlkoxidePrecursor** By YimFunLoo, RichardJ.Potter, AnthonyC.Jones ,* HelenC.Aspinall, JeffreyM.Gaskell, PaulR.Chalker, LesleyM.Smith,and GaryW.Critchlow Thin films of neodymium oxide (Nd 2 O 3 ) have been deposited on Si(100) and GaAs(100) substrates by liquid injection MOCVD using the new neodymium alkoxide, [Nd(mmp) 3 ] (mmp=1-methoxy-2-methyl-2-propanolate, OCMe 2 CH 2 OMe). Thefilmsweregrownoverawiderangeofsubstratetemperatures(250±550C)andwerefoundtobeofhighpurity,withno detectablecarbon.ThefilmsexhibitedthecubicC-typeNd 2 O 3 phaseorwereamorphousdependingonsubstratetemperature. Keywords:Neodymiumoxide,neodymiumalkoxideprecursor,liquidinjectionMOCVD 1.Introduction Thecontinuousreductioninthedimensionsofmetal-ox- ide-semiconductor field-effect transistors (MOSFETs) in silicon integrated circuits, has forced the channel length and SiO 2 gate dielectric thickness to decrease rapidly. [1] However, as the dimensions of the SiO 2 layer approach 20±30,directelectrontunnelingeffectsandhighleakage currents present serious obstacles to future device reliabil- ity. [2] Theuseofmaterialswithahigherdielectricconstant (k) than SiO 2 allows an equivalent capacitance to be achieved in a physically thicker insulating layer, which should provide reduced leakage currents. There has thus been much recent research aimed at replacing the conven- tionalSiO 2 gatedielectricwithalternativehigh-k dielectric oxides or silicates, [2] suchasAl 2 O 3 , [3] ZrO 2 , [4] HfO 2 , [5] Zr- and Hf-silicate, [6,7] (HfO 2 ) x (Al 2 O 3 ) 1-x , [8,9] La 2 O 3 , [10] Pr 2 O 3 , [11] Y 2 O 3 , [12] Gd 2 O 3 , [12,13] andNd 2 O 3 . [14] The lanthanide, or rare-earth, oxides M 2 O 3 (M=La,Pr, Gd, Nd, etc.) are good insulators due to their large band- gaps(3.9eVforPr 2 O 3 ,5.6eVforGd 2 O 3 )andhighdielec- tric constants (Gd 2 O 3 k =16,La 2 O 3 k =27,Pr 2 O 3 k =26± 30). They also have good thermodynamic stability on sili- con, which makes them attractive materials for high-k di- electric applications. [2] Another attractive feature of some of the lanthanide rare-earth oxides (e.g., Pr 2 O 3 ,Gd 2 O 3 )is their relatively close lattice match to silicon, offering the possibility of epitaxial growth, eliminating problems re- latedtograinboundariesinpolycrystallinefilms,andsome rare earth oxides (e.g., Gd 2 O 3 ) can also be grown epitaxi- ally on GaAs(100), [15] to give an insulating and passivating oxidelayerwhichhaspotentialapplicationsinawiderange oftypeIII±Vphotonicandelectronicdevices. Neodymium oxide (Nd 2 O 3 ) has a number of properties which make it attractive for gate dielectric applications. These include, a capacitance density of 0.40±14 lFcm ±2 ,a high dielectric constant (k =12.64),ahighbreakdownfield strength (more than 1.510 6 Vcm ±1 ), a low dissipation factor(approximately0.0045),andalowtemperaturecoef- ficient of capacitance (approximately 350 ppmK ±1 ). [16] Nd 2 O 3 filmsalsohaveahighresistivity(10 12 ±10 13 X cm)in aconstantelectricfieldatroomtemperature. [17] Nd 2 O 3 filmshavemainlybeendepositedbyphysicalva- pordeposition(PVD)techniquessuchasultrahighvacuum vapor deposition [14,18,19] and electron-beam evaporation. [16] Metal±organicchemicalvapordeposition(MOCVD)hasa number of potential advantages over PVD, including a large-scale production capability, good composition con- trol,highfilmdensities,highdepositionrates,andexcellent conformal step coverage. Despite these advantages, there have been very few reports on the MOCVD of lanthanide oxides.TheMOCVDofLaAlO 3 [20] andGd 2 O 3 [21] hasbeen reported some time ago, whilst more recent reports de- scribetheMOCVDofProxide [22] andLa 2 O 3 . [23] Thereare alsoveryfewreportsonthegrowthofNd 2 O 3 byMOCVD, mainly due to the absence of suitable precursors with the appropriate stability, volatility, and decomposition charac- teristics.Neodymiumoxidewithacubicstructurehasbeen deposited by aerosol pyrolysis using neodymium tris-tri- 306 2004WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim DOI: 10.1002/cvde.200406313 Chem.Vap.Deposition 2004, 10,No.6 ± [*] Prof.A.C.Jones,Dr.Y.F.Loo,Dr.H.C.Aspinall,J.M.Gaskell DepartmentofChemistry,UniversityofLiverpool Liverpool,L693ZD(UK) E-mail:tjconsultancy@btconnect.com Dr.R.J.Potter,Prof.P.R.Chalker DepartmentofMaterialsScienceandEngineering UniversityofLiverpool Liverpool,L693BX(UK) Dr.L.M.Smith EpichemOxidesandNitrides PowerRoad,Bromborough,Wirral,Merseyside,CH623QF(UK) Dr.G.W.Critchlow InstituteofSurfaceScienceandTechnology UniversityofLoughborough Loughborough,Leicestershire,LE113TU(UK) [**] WearegratefultoEpichemLimitedforsupportofthiswork.