半导体物理学半导体 (4).pdf

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1、Growth of Semiconductor Materials Czochralski method01PVD03Epitaxial Growth、MBE02CVD、MOCVD04PLD、ALD05Sol-gel、spin-coating、roll-to-roll06Magnetron sputtering07Czochralski methodIn 1916,the Polish scholar Czochralski proposed a method of growing crystals from the melt through a pulling equipment.The i

2、ndustry referred to it as the Czochralski method or the CZ method.Melting raw materialSeed-onNeckingFinishingShoulderDimeter growthProcess of Czochralski methodFirst,the high-purity polysilicon raw materials are melted in an environment of high temperature(1420)、vacuum(1000 Pa)with an inert gas(Ar)a

3、nd strong magnetic field(0.1 0.5 T),and then the polysilicon is grown into a single crystal with a certain atomic arrangement period through the processes of seed-on、necking、shoulder、diameter growth and finishing.Epitaxial growthEpitaxy1）Basic concepts of epitaxy：A process whereby a thin,single-crys

4、tal layer of material with thickness,conductivity type,resistivity and lattice structure that meets the requirements is grown on the surface of a single-crystal substrate along its original crystal orientation.2）R o l e o f e p i t a x y i n semiconductor production:Achieve sudden changes in impurit

5、y concentration and optimize the performance of substrate material.Molecular Beam Epitaxy(MBE)Molecular Beam Epitaxy(MBE)Definition：Under ultra-high vacuum(10-9-10-11Torr),the molecular beams of the films constituent elements are directly sprayed onto the substrate surface,thereby forming an epitaxi

6、al film on it.Molecular Beam Epitaxy(MBE)Molecular Beam Epitaxy(MBE)Features：1）Strictly control the growth process and rate;2）Ultra-high vacuum physical deposition process,which dont need to consider the conveying process and the intermediate reaction,and the shutter can be used for instantaneous co

7、ntrol of growth and interruption;3）MBE is a kinetic process that can grow thin films that are difficult to grow under ordinary thermal equilibrium;4）The low temperature of the substrate reduces the effect of thermal expansion on lattice mismatch and the self-doped diffusion of the substrate layer to

8、 the epitaxial layer;Molecular Beam Epitaxy(MBE)Molecular Beam Epitaxy(MBE)Features：5）Low growth rate(1 s per atomic layer),which is easy to precise control of film thickness,structure,composition,especially suitable for growing superlattice;6）Equipped with a variety of surface analysis instruments,

9、helpful to scientific research.Physical Vapor Deposition（PVD）Physical Vapor Deposition,PVDDefinition：The process of vaporizing the material source-solid or liquid surface into gaseous atoms,molecules or parts by ionization under vacuum conditions,and then depositing it on the substrate surface to fo

10、rm a film.Process characteristics:The deposition temperature is low,the principle is simple,and it can be used to deposit various films.But the adhesion and compactness of the deposited films are not as good as that of CVD-deposited films.Applications：Deposit thin films of metal、alloy films、ceramics

11、、semiconductors.Features：Physical adsorption Growth rate is much faster than that of epitaxial growth Heterogeneous growth Thickness range:Typical thin films：nm-m Thicker films can also be grownThe physical principle of PVDPhysical Vapor Deposition（PVD）E-beam evaporation(1)Working principle:When the

12、 electron beam accelerated and focused by high pressure bombards the surface of the evaporation source in a vacuum,since the kinetic energy of the electron beam is almost completely converted into heat energy,it can reach a high temperature of 3000 C in an instant,enough to melt the evaporation sour

13、ce and be evaporated to the substrate surface to form a thin film.Physical Vapor Deposition（PVD）Magnetron Sputtering Add magnetic device on the basis of DC sputtering and RF sputteringSputtering Magnetron SputteringE Target Surface B Target Surface Only affected by electric field in cathode dark spa

14、ce Secondary electron:Only affected by magnetic field in negative glow region Oscillation up and down,lateral driftPhysical Vapor Deposition（PVD）Various targetTarget positionOperation interfaceSputtering Magnetron SputteringPhysical Vapor Deposition（PVD）Basic process3 volatility criteria that CVD mu

15、st meet(a)Formation of crystal nucleus;(b)Grain aggregation;(c)Form a continuous film At the deposition temperature,the reactant must have a sufficiently high vapor pressure In addition to the deposited material,the reaction product must be volatile The deposits itself must have a sufficiently low v

16、apor pressureChemical Vapor Deposition(CVD)chemical reaction of gas mixtureClassificationu Atmospheric pressure chemical vapor deposition（APCVD)u Low pressure chemical vapor deposition(LPCVD)u Plasma enhanced chemical vapor deposition PECVD）u ICP-CVDChemical Vapor Deposition(CVD)AdvantagesDisadvanta

17、gesApplicationsAPCVDSimple reactorLow reaction temperatureFast deposition ratePoor step coveragePoor uniformitySevere particle contaminationLow temperature oxide layerLPCVDGood uniformityGood step coverageMass productionHigh growth temperatureLow deposition rateSiO2Si3N4Polysilicon,Tungsten Silicon

18、etc.PECVDLow growth temperatureFast deposition rateControlled stressHigh pinhole densityparticle contaminationPoor Stoichiometric ratioSiO2Si3N4Amorphous siliconICPCVDLow growth temperature High breakdown voltageLow deposition rateLow deposition rateSiO2Si3N4SiCFeaturesPrinciplesl Wide range of appl

19、ication,almost all compounds and alloy semiconductors can be grown;l Very suitable for growing various heterostructure materials;l Ultra-thin epitaxial layer can be grown,and a very steep interface transition cab be obtained;l Growth is easy to control；l High purity materials cab be grown；l The larg

20、e-area uniformity of the epitaxial layer is good；l Large-scale production is possible.Metal-organic Chemical Vapor Deposition(MOCVD)Metal-organic Chemical Vapor Deposition(MOCVD)Comparison of CVD and PVDChemical Vapor Deposition(CVD)ItemsPVDCVDMaterial sourceVapors of forming films,reactive gasesCom

21、pound vapors containing elements of films,reactive gasesActivation methodConsumption of evaporation heat,ionization,etc.Activation energy,high temperature chemical free energyPreparation temperature250 2000 (Evaporation source)25 Suitable temp.(Substrate)150 2000 （Substrate）Deposition rate20-250m/h2

22、5-1500m/hApplicationsDecoration,electronic and optical filmMaterial refining,surface protection,electronic filmFilm materials that can be preparedAll solids(C,Ta,W are difficult to be prepared),halides and thermally stable compoundsMetals other than alkali metals and alkaline earth metals(Ag and Au

23、are difficult to be prepared),carbides,nitrides,and oxidesBasic Principles1.Interaction between laser radiation and target2.Dynamics of melted substances3.Deposition of molten material on the substrate4.Nucleation and formation of thin film on the substrate surfacePulsed Laser Deposition (PLD)Proces

24、s Mounting target and substrate Adjust laser parametersPump the chamber to a vacuum of 10-5 PaTurn on the heating device and insert gasIntroduce laser for depositionTurn off the instrumentPLD SystemPulsed Laser Deposition (PLD)Process Problems to be solved：1)It is not easy to prepare large-area film

25、s2)Micron-submicron scale particle exists on the film surface,and the uniformity of the prepared film is poor.3)The composition of the target film of some materials is not consistent.For multi-component compound films,if certain cations have a high vapor pressure,the stoichiometric growth of the fil

26、m cannot be guaranteed at high temperatures.Pulsed Laser Deposition (PLD)Atomic Layer Deposition(ALD)Basic PrinciplesALD is a method by which gas-phase precursor are alternately passed into the reactor and chemically adsorbed and react on the substrate and form a deposited film.When the precursors r

27、each the surface of the substrate,they will chemically adsorb on the surface and undergo surface reactions.The surface reaction of ALD has self-limiting,namely chemical adsorption self-limiting(CS)and sequential reaction self-limiting(RS)processes.In fact,this self-limiting feature is the basis of A

28、LD.Repeating this self-limiting reaction can form the desired film.Equipment SchematicAtomic Layer Deposition(ALD)The ALD process of Al2O3 thin filmRegion-selective deposition of Al2O3Typical ALD deposition process-TiO2 depositionAtomic Layer Deposition(ALD)Comparison with other technologiesMethodAL

29、DMBECVDSputterEvaporPLDThickness uniformityFilm densityStep coverOInterface qualityOOAmount of raw materialsLow temperature depositionODeposition rateIndustrial applicabilityNote：Very good:Good:Changeable:O Poor:Atomic Layer Deposition(ALD)Sol-Gel methodBasic ConceptsThe sol-gel method is a kind of

30、inorganic liquid phase synthesis,which refers to using metal organic or inorganic compounds,go through the process of solution,sol,and gel,and then form in the state of sol or gel,and then undergo drying and heat treatment to make products in different forms.Sol refers to a liquid in which colloidal

31、 particles are dispersed and suspended,that is,multiple systems formed by solid particles with a size between 1-100 nm dispersed in a medium.These solid particles are generally composed of 103-109 atoms,called colloids.Gel refers to the internal structure of a grid,with solids containing liquid in t

32、he gaps between the grids.When the sol is subjected to a certain effect(such as temperature change,stirring,chemical reaction or electrochemical equilibrium,etc.),the new viscosity of the system increases to a certain degree,and a frozen substance between solid and liquid can be obtained.The colloid

33、al particles are aggregated into a three-dimensional space network structure,which meshes all or part of the medium.It is a very viscous substance,which is a gel.Spin-CoatingBasic ConceptsThe spin coating method is also called homogenization because of the high viscosity of the fluid used and its co

34、lloidal shape.A typical spin-coating process is mainly divided into three steps:(i)glue dispensing,(ii)high-speed rotation,and(iii)drying(solvent volatilization).First,the glue drop is to inject the spin coating onto the surface of the substrate,and then spread it on the substrate through high-speed

35、 rotation to form a uniform film,and then remove the remaining solvent by drying,and finally obtain a film with stable performance.For various spin coating liquids with different viscosities and wettability,there are two commonly used methods for dispensing glue,namely static dispensing and dynamic

36、dispensing.The high-speed rotation and drying in the spin coating method are the key steps to control the film thickness,structure and other properties.Preparation of PZT thin film by sol-gel methodSol-Gel methodPb(CHCOO)2 3H2OCH3COOHZn(NO3)4 5H2OHO(CH2)2OCH3Ti(OC4H9)4HO(CH2)2OCH3Stir&AzeotropyStir&

37、AzeotropyStir&AzeotropyStirPZT SolAcetylacetoneEthylene glycolStirPZT precursor solution StirPt/Ti/SiO2/Si Substrate PZT wet filmPZT Inorganic film PZT ferroelectric filmSpin-coating 4000 rpmPretreatment at 400 C for 5minAnnealing at 600-750 C for 5minRepeat BubbleThere is a problem with the tip of

38、the nozzle or the barbed Center vortex patternEquipment exhaust speed is too highWhen spraying glue,the glue liquid deviates from the center of the substrateSpin coating time is too longAcceleration is too high Radial stripesGlue jetting speed is too highEquipment exhaust speed is too highThe static

39、 time before coating is too longThe speed or acceleration of the homogenizer is set too highSmall particles are left on the surface of the tabletThere are particles in the glueGlue is not covering the substrateInsufficient amount of glueUnsuitable uniform accelerationCenter haloInappropriate trayNoz

40、zle off center of substrateSpin-CoatingInfluence of spin coating parameters on filmBasic PrinciplesRoll-to-Roll processing is a process of preparing nanoscale electronic devices in large quantities on a roll of very thin plastic or metal.The process is similar to nanoimprint lithography,but the Kunz

41、i allows printing patterns on a larger substrate at a faster speed.Advantages：Cheap equipment,low substrate cost,high volume productionDisadvantages：Available equipment is limited and challenging for defect recoveryRoll-to-roll processProcess principleComposition of process equipmentRoll-to-roll processProcess principleSchematic of roll-to-roll making RFID steam sensorUsing roll-to-roll process to make photovoltaic cellsRoll-to-roll process