納米材料和納米結(jié)構(gòu)七講課件

1、第七講Physical Vapor Deposition物理氣相沉積納米材料和納米結(jié)構(gòu)第七講Physical Vapor Deposition納米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 evapor

2、ation Sputtering Cathodic arc plasma deposition Pulsed laser depositionTransporting the material from the source to the substrateFormation of film by nucleation and diffusionPhysical Vapor Deposition (PVDApplicationCoatings of electronic materialsInsulatorSemiconductorConductorSuperconductorNanomete

3、r scale multilayer structuresAdvanced electronic devicesAbrasion resistant coatingsApplicationConcerned Problems and ChallengesContamination at the interfaces or intermixingMulti-material systems involvedCost of equipment and maintenance Complexion of operationSystems Described in This SectionSputte

4、ringPulsed laser depositionConcerned Problems and Challen1 Sputtering（濺射）1-1 Principle of Sputtering1-2 Sputtering System1-3 Preparing Multilayer Structures by Sputtering1-4 Current Status of Sputtering1 Sputtering（濺射）1-1 Principle of SputteringEjection of Atoms from the TargetEnergetic particles bo

5、mbarding a target surface with sufficient energy (50 eV 1000 eV) TargetCathode, connected to a negative voltage supplyComposed of the materials to be depositedSubstrateAnode May be grounded, floated, or biased1-1 Principle of SputteringEjGlow Discharge Medium in Sputtering ChamberA gas or a mixture

6、of different gases, most commonly Ar or HeIn reactive sputtering: introduce reactive gases such as O2 or N2 Pressure: a few mTorr to several hundreds mTorrProcedureGeneration of positive ions: ionizing the sputtering gas by glow dischargeBombarding: accelerated positive ions to strike the target sur

7、face and remove mainly neutral atomsCondensation: neutral atoms leave the target and condense on the substrate surface, and form into thin films Glow Discharge Medium in SputtAn Important Concept: Sputtering YieldA measurement of the efficiency of sputteringRatio of the number of emitted particles t

8、o the number of bombarding ones An Important Concept: Sputteri1-2 Sputtering SystemTypical Types of Sputtering SystemsDirect current (dc) diode sputteringUsed for sputtering conducting materialsRadio frequency (rf) diode sputteringUsed for sputtering insulating materialsMagnetron diode sputtering Mo

9、st 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 substrate1-2 Sputtering SystemTypical 用于制備TiN/VN 多層膜的磁控濺射系統(tǒng)氬氣流量表流量控制閥壓力傳感器低溫泵低溫泵靶1靶2旋轉(zhuǎn)襯底支架襯底流量表閥門流

10、量表流量控制閥1流量控制閥2主流量控制閥質(zhì)譜儀閥門鎖定裝置用于制備TiN/VN 多層膜的磁控濺射系統(tǒng)氬氣流量表流量控制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 the negative ionsUse off-axis sputtering: to avo

11、id the substrate directly facing the cathode Disadvantage of off-axis sputtering:low deposition ratesmall deposition areaDeposition of magnetic materials: facing target sputtering systemsWays to reduce the damage and 偏軸濺射系統(tǒng)示意圖Schematic of off-axis sputtering system可360度旋轉(zhuǎn)的襯底支架陶瓷加熱器負(fù)離子撞擊區(qū)襯底靶濺射槍濺射源屏蔽閘

12、空間屏蔽區(qū)偏軸濺射系統(tǒng)可360度旋轉(zhuǎn)的襯底支架陶瓷加熱器負(fù)離子撞擊區(qū)襯正面濺射系統(tǒng)示意圖Schematic of the facing target sputtering system襯底靶磁體冷卻水氬氣正面濺射系統(tǒng)襯底靶磁體冷卻水氬氣1-3 Preparing Multilayer Structures by SputteringTypes and Properties of Multilayer StructuresTypes of architecturesMetal/metalCeramic/ceramicMetal/ceramicSemiconductor/semiconductor

13、Structural and 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 properti

14、es1-3 Preparing Multilayer StruBaTiO3 Nanolayer 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: l

15、ow dielectric constant (16 at 105 V/cm), low leakage currentPolycrystalline: high dielectric constant (400 at 105 V/cm), high leakage currentAim of nanolayer structure BaTiO3 film capacitor: high dielectric constant and low leakage currentBaTiO3 Nanolayer FerroelectricRealization and effectsSubstrat

16、e: Ru/SiO2/SiTechnique: rf magnetron sputtering, sputtering interruption between layers 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 obtainedLeaka

17、ge current density be considerably reduced, and the effect becoming better with increasing cycle numberDielectric constant be two or three times higher than single amorphous layer but lower than a single polycrystalline layer納米材料和納米結(jié)構(gòu)七講課件具有納米多層結(jié)構(gòu)的BaTiO3薄膜電容器橫截面示意圖具有納米多層結(jié)構(gòu)的BaTiO3薄膜電容器橫截面示意圖Nanolayer

18、MoSi2/SiCSubstrate: single crystal silicon (sc-Si)Techniques:Magnetron sputtering for deposition of MoSi2rf sputtering for deposition 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 annea

19、ling: inducing recrystallization in the MoSi2/SiC multilayered filmProperties after annealing:Superior oxidation resistanceSignificant hardness Nanolayer MoSi2/SiC MoSi2/SiC多層膜的剖面透射電鏡圖片Cross-sectional TEM image of MoSi2/SiC multilayered film MoSi2/SiC多層膜的剖面透射電鏡圖片MoSi2/SiC多層膜退火前的電子衍射花樣Electron Diffra

20、ction Pattern of MoSi2/SiC multilayered film before annealingMoSi2/SiC多層膜退火前的電子衍射花樣經(jīng)過800C，1h退火處理的MoSi2/SiC多層膜的低放大倍數(shù)亮場(chǎng)電鏡照片經(jīng)過800C，1h退火處理的MoSi2/SiC多層膜Nanolayer Cu/NbSubstrate: (100) sc-SiTechniques: dc magnetron sputteringLayer thickness: (100 nm/100nm)Properties:High strengthSuperior thermal conductiv

21、itySuperior electrical conductivityNanolayer Cu/Nb通過磁控濺射技術(shù)沉積的Cu/Nb多層膜的剖面透射電鏡圖像通過磁控濺射技術(shù)沉積的Cu/Nb多層膜的剖面透射電鏡圖像Cu/Nb多層膜的電子衍射花樣Electron diffraction pattern of Cu/Nb multilayerCu/Nb多層膜的電子衍射花樣1-4 Current Status of Sputtering AdvantagesMost widely used sputtering methodWell-established coating techniques for

22、 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 microelectronics indust

23、ry (although successful for SrTiO3, BaTiO3, and Ba1-xSrxO3) 1-4 Current Status of Sputter2-1 Principles of PLD2-2 Deposition of Nano-Scale Metal Oxide Thin Films2-3 Multilayer Structures Prepared by PLD2-4 Current Status of PLDPulsed Laser Deposition (PLD，脈沖激光沉積) Pulsed Laser Deposition (PLD，脈2-1 Pr

24、inciples of PLDAdvantages and Properties of PLDSimplest deposition technique among all thin film growth techniquesStoichiometric removal of constituent species from targetVersatile deposition of a wide variety of materialsMetalsSemiconductorsNitridesDielectric materialsOxidesOrganic compounds/ployme

25、rsTernary compounds2-1 Principles of PLDAdvantagTechnical Description 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 mater

26、ialsVacuum chamber with a quartz windowTarget holder or multiple target holderSubstrate holder (with a heater)Integration with other type of evaporation sourcesTechnical Description of PLD脈沖激光沉積系統(tǒng)（示意圖）Schematic diagramof a PLD system激光束加熱器襯底噴流靶脈沖激光沉積系統(tǒng)激光束加熱器襯底噴流靶2-2 Deposition of Nanoscale Metal Oxi

27、de Thin FilmsImportanceMetal oxides could exhibit versatile properties High temperature superconductivity Ferroelectricity Colossal magnetoresistivity Non-linear optical propertiesMetal oxides be recognized as possible candidates for next generation electronic materials due to their diverse properti

28、es2-2 Deposition of Nanoscale MSubstrates for Metal Oxide FilmsImportance: proper choice of substrate be essential for accomplishing perfect 2-dimensional epitaxy of metal oxide heterostructuresRequirements for a good substrateGood in plane lattice matchThermal expansion coefficient close to that of

29、 filmAtomically smooth surfaceGood chemical compatibility with the filmSubstrates for Metal Oxide Fil Commonly used single crystal substratesYttria-stabilized zirconia (YSZ)MgOLaAlO3SrTiO3NdGaO3(LaAlO3)0.3 (Sr2AlTaO6)0.7Sapphire Surface treatment of substratesIon milling + in situ annealingIon milli

30、ng + pre-depositionChemical etching + annealingSurface terminating Commonly used single crystal Initial Growth of Metal Oxide Films Observation and monitor techniquesIn situ: reflected high energy electron diffraction (RHEED), laser light scattering, real-time optical diagnosisEx situ: scanning tunn

31、eling 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 plus island growth) to Volmer-Weber mode (island growth) at a critical thicknessScre

32、w-growth in thicker films納米材料和納米結(jié)構(gòu)七講課件Layer plus island growth(Thickness Critical Thickness)YBCO薄膜的早期生長模式及其轉(zhuǎn)變D.-W. Kim et al., Physica C 313 (1999) 246Layer plus island growthIslandCharacterizing multilayer thickness by X-ray diffractionYBCO/PrBCO superlattice: a new man-made periodicityThe modulati

33、on 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 nth and the (n+1)th satellite peaksThe satellite peaks up to the f

34、ourth order indicate atomically sharp and flat interfaces Characterizing multilayer thicNominal Thickness2.4 nm/12 nmCalculated Thickness14.6 nmC. Kwon et al., Appl. Phys. Lett. 62 (2004) 1289X-ray -2scan around (001) and (002) peaks of a YBCO/PrBCO superlatticeNominal ThicknessCalculated ThCharacte

35、ring film thickness by low angle X-ray diffractionCharactering film thickness by STM, AFM, SEM, and TEMC. Kwon et al., Appl. Phys. Lett. 62 (2004) 1289A low angle X-ray reflection of a nominally 27.6 nm thick YBCO on NdGaO3Charactering film thickness bySuperconductivity in a Unit-cell Thick YBCOAime

36、d Questions:What is the minimum unit needed 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

37、changed artificially by interposing other materials in between the Cu-O planes or unit-cells)System Composing: Ultrathin YBCO layers + nonsuperconducting PrBCO layers2-3 Examples of Multilayer Structures Prepared by PLDSuperconductivity in a Unit-ceC. Kwon et al., Superlattices and Micro structures 29 (2005) 169Resistive transition of 1, 2 and 4 unit-cell thick YBCO layers sandwichedbetween (Y1-xPrx)Ba2Cu3O7 adjacent layers with x=1 and 0.6C. Kwon et al., Superlattices C. Kw