纳米材料和纳米结构第七讲.ppt

1、第七讲,Physical Vapor Deposition物理气相沉积,纳米材料和纳米结构,Physical Vapor Deposition(PVD),Definition Film deposition by condensation from vapor phaseThree Steps of PVDGenerating a vapor phase by evaporation or sublimation Electron-beam evaporation Molecular-beam epitaxy Thermal evaporation Sputtering Cathodic ar

2、c plasma deposition Pulsed laser depositionTransporting the material from the source to the substrateFormation of film by nucleation and diffusion,ApplicationCoatings of electronic materialsInsulatorSemiconductorConductorSuperconductorNanometer scale multilayer structuresAdvanced electronic devicesA

3、brasion resistant coatings,Concerned Problems and ChallengesContamination at the interfaces or intermixingMulti-material systems involvedCost of equipment and maintenance Complexion of operationSystems Described in This SectionSputteringPulsed laser deposition,1 Sputtering（溅射）,1-1 Principle of Sputt

4、ering1-2 Sputtering System1-3 Preparing Multilayer Structures by Sputtering1-4 Current Status of Sputtering,1-1 Principle of Sputtering,Ejection of Atoms from the TargetEnergetic particles bombarding a target surface with sufficient energy(50 eV 1000 eV)TargetCathode,connected to a negative voltage

5、supplyComposed of the materials to be depositedSubstrateAnode May be grounded,floated,or biased,Glow Discharge Medium in Sputtering ChamberA gas or a mixture of different gases,most commonly Ar or HeIn reactive sputtering:introduce reactive gases such as O2 or N2 Pressure:a few mTorr to several hund

6、reds mTorrProcedureGeneration of positive ions:ionizing the sputtering gas by glow dischargeBombarding:accelerated positive ions to strike the target surface and remove mainly neutral atomsCondensation:neutral atoms leave the target and condense on the substrate surface,and form into thin films,An I

7、mportant Concept:Sputtering YieldA measurement of the efficiency of sputteringRatio of the number of emitted particles to the number of bombarding ones,1-2 Sputtering System,Typical Types of Sputtering SystemsDirect current(dc)diode sputteringUsed for sputtering conducting materialsRadio frequency(r

8、f)diode sputteringUsed for sputtering insulating materialsMagnetron diode sputtering Most commonly used todayPlasma be confined around the target surface by a magnet fieldAdvantages of using magnetron sputteringFeasibility of large cathode sizeHigh sputtering yieldLess bombardment to the substrate,用

9、于制备TiN/VN 多层膜的磁控溅射系统,氩气,流量表,流量控制阀,压力传感器,低温泵,低温泵,靶1,靶2,旋转衬底支架,衬底,流量表,阀门,流量表,流量控制阀1,流量控制阀2,主流量控制阀,质谱仪,阀门,锁定装置,Ways to reduce the damage and re-sputtering of growing filmDamage caused by negative ion effect and radiation enhanced diffusionImprovement methodUse high gas pressure:to reduce the energy of

10、the negative ionsUse off-axis sputtering:to avoid the substrate directly facing the cathode Disadvantage of off-axis sputtering:low deposition ratesmall deposition areaDeposition of magnetic materials:facing target sputtering systems,偏轴溅射系统示意图Schematic of off-axis sputtering system,可360度旋转的衬底支架,陶瓷加热

11、器,负离子撞击区,衬底,靶,溅射枪溅射源,屏蔽闸,空间屏蔽区,正面溅射系统示意图Schematic of the facing target sputtering system,衬底,靶,磁体,冷却水,氩气,1-3 Preparing Multilayer Structures by Sputtering,Types and Properties of Multilayer StructuresTypes of architecturesMetal/metalCeramic/ceramicMetal/ceramicSemiconductor/semiconductorStructural an

12、d physical propertiesWith structurally modulated architecturesWith compositionally modulated architecturesHigh interface volume fractionLarge intrinsic stressWith structural and/or compositional gradientExhibiting unique and enhanced electric,dielectric,magnetic,and mechanic properties,BaTiO3 Nanola

13、yer Ferroelectric Thin Film CapacitorsAdvantage:higher relative dielectric constantDisadvantage:high leakage currentElectrical properties strongly depending upon the processing condition,microcrystal structure,and choice of bottom electrodeAmorphous:low dielectric constant(16 at 105 V/cm),low leakag

14、e currentPolycrystalline:high dielectric constant(400 at 105 V/cm),high leakage currentAim of nanolayer structure BaTiO3 film capacitor:high dielectric constant and low leakage current,Realization and effectsSubstrate:Ru/SiO2/SiTechnique:rf magnetron sputtering,sputtering interruption between layers

15、 to change the substrate temperatures(680 C,60 C)Layer structure:n-cycle alternate layers of amorphous and polycrystalline BaTiO3(microcrystalline be obtained by annealing amorphous layer)Results obtainedLeakage current density be considerably reduced,and the effect becoming better with increasing c

16、ycle numberDielectric constant be two or three times higher than single amorphous layer but lower than a single polycrystalline layer,具有纳米多层结构的BaTiO3薄膜电容器横截面示意图,Nanolayer MoSi2/SiCSubstrate:single crystal silicon(sc-Si)Techniques:Magnetron sputtering for deposition of MoSi2rf sputtering for depositi

17、on of SiCMoSi2/SiC layered composites be prepared by cyclically passing the samples beneath the two targets with a speed(thickness of 10 nm/3 nm)Heat treatment or annealing:inducing recrystallization in the MoSi2/SiC multilayered filmProperties after annealing:Superior oxidation resistanceSignifican

18、t hardness,MoSi2/SiC多层膜的剖面透射电镜图片Cross-sectional TEM image of MoSi2/SiC multilayered film,MoSi2/SiC多层膜退火前的电子衍射花样Electron Diffraction Pattern of MoSi2/SiC multilayered film before annealing,经过800C，1h退火处理的MoSi2/SiC多层膜的低放大倍数亮场电镜照片,Nanolayer Cu/NbSubstrate:(100)sc-SiTechniques:dc magnetron sputteringLaye

19、r thickness:(100 nm/100nm)Properties:High strengthSuperior thermal conductivitySuperior electrical conductivity,通过磁控溅射技术沉积的Cu/Nb多层膜的剖面透射电镜图像,Cu/Nb多层膜的电子衍射花样Electron diffraction pattern of Cu/Nb multilayer,1-4 Current Status of Sputtering,AdvantagesMost widely used sputtering methodWell-established c

20、oating techniques for microelectronic applicationsMany nanometer multilayer structures be prepared by sputteringShortcomingsMaterials system limitation:mainly conductors or nitridesDifficulty in control stoichiometry,low deposition rate etc.Be questionable to be used as the main coating tool in micr

21、oelectronics industry(although successful for SrTiO3,BaTiO3,and Ba1-xSrxO3),2-1 Principles of PLD2-2 Deposition of Nano-Scale Metal Oxide Thin Films2-3 Multilayer Structures Prepared by PLD2-4 Current Status of PLD,Pulsed Laser Deposition(PLD，脉冲激光沉积),2-1 Principles of PLD,Advantages and Properties o

22、f PLDSimplest deposition technique among all thin film growth techniquesStoichiometric removal of constituent species from targetVersatile deposition of a wide variety of materialsMetalsSemiconductorsNitridesDielectric materialsOxidesOrganic compounds/ploymersTernary compounds,Technical Description

23、of PLDBased on physical vapor deposition Impact of high-power short pulsed laser radiation on solid targetsRemoval of materials from impact zoneEquipment constituentHigh power laser:external energy source to vaporize target materialsVacuum chamber with a quartz windowTarget holder or multiple target

24、 holderSubstrate holder(with a heater)Integration with other type of evaporation sources,脉冲激光沉积系统（示意图）Schematic diagramof a PLD system,激光束,加热器,衬底,喷流,靶,2-2 Deposition of Nanoscale Metal Oxide Thin Films,ImportanceMetal oxides could exhibit versatile properties High temperature superconductivity Ferro

25、electricity Colossal magnetoresistivity Non-linear optical propertiesMetal oxides be recognized as possible candidates for next generation electronic materials due to their diverse properties,Substrates for Metal Oxide FilmsImportance:proper choice of substrate be essential for accomplishing perfect

26、 2-dimensional epitaxy of metal oxide heterostructuresRequirements for a good substrateGood in plane lattice matchThermal expansion coefficient close to that of filmAtomically smooth surfaceGood chemical compatibility with the film,Commonly used single crystal substratesYttria-stabilized zirconia(YS

27、Z)MgOLaAlO3SrTiO3NdGaO3(LaAlO3)0.3(Sr2AlTaO6)0.7Sapphire Surface treatment of substratesIon milling+in situ annealingIon milling+pre-depositionChemical etching+annealingSurface terminating,Initial Growth of Metal Oxide Films Observation and monitor techniquesIn situ:reflected high energy electron di

28、ffraction(RHEED),laser light scattering,real-time optical diagnosisEx situ:scanning tunneling microscope(STM),atomic force microscopy(AFM),cross-sectional transmission electron microscopy(TEM),X-ray diffractionGrowth ModeHighly depending upon the quality of substrateStranski-Krastanov mode(layer plu

29、s island growth)to Volmer-Weber mode(island growth)at a critical thicknessScrew-growth in thicker films,Layer plus island growth(Thickness Critical Thickness),Island growth(Thickness Critical Thickness),YBCO薄膜的早期生长模式及其转变,D.-W.Kim et al.,Physica C 313(1999)246,Characterizing multilayer thickness by X

30、-ray diffractionYBCO/PrBCO superlattice:a new man-made periodicityThe modulation thickness in superlattices is measured by the position of satellites peaks,given by D=(/2)/(sinn+1-sinn)D is the modulation thickness with D=dYBCO+dPrBCO;is the wavelength of X-ray source;n+1 and n are positions of the

31、nth and the(n+1)th satellite peaksThe satellite peaks up to the fourth order indicate atomically sharp and flat interfaces,Nominal Thickness2.4 nm/12 nm,Calculated Thickness14.6 nm,C.Kwon et al.,Appl.Phys.Lett.62(2004)1289,X-ray-2scan around(001)and(002)peaks of a YBCO/PrBCO superlattice,Characterin

32、g film thickness by low angle X-ray diffractionCharactering film thickness by STM,AFM,SEM,and TEM,C.Kwon et al.,Appl.Phys.Lett.62(2004)1289,A low angle X-ray reflection of a nominally 27.6 nm thick YBCO on NdGaO3,Superconductivity in a Unit-cell Thick YBCOAimed Questions:What is the minimum unit nee

33、ded for the occurrence of superconductivity?How essential is the interlayer coupling between Cu-O planes in determining the transition temperature?Way to the question:using superlattice structures as model system(possible coupling or other parameters can be changed artificially by interposing other materials in between the Cu-O planes or unit-cells)System Composing:Ultrathin YBCO layers+nonsuperco