1、Technology of Thin FilmThin-Film SputteringProcessesOutline1.Introduction 2.Plasmas,Discharges,and Arcs3.Physics of sputtering2Introduction Evaporation and sputtering are quite different An ionized gas or plasma rather than a vacuum environment,active electrodes that participate in the deposition pr
2、ocess,and low-temperature processing are among the features that distinguish sputtering from evaporation.Introduction evaporation and sputtering are quite different Target:cathode,several kV Substrate:anode Working gas:Ar,0.1-10Pa Visible glow discharge Schematics of simplified sputtering systems:(a
3、)DC,(b)RF.Introduction Evaporation and sputtering are quite different positive gas ions strike the cathode and physically sputter target atoms through momentum transfer to them.other particles(secondary electrons,desorbed gases,and negative ions)as well as radiation(X-rays and photons)are emitted fr
4、om the target.The electric field accelerates electrons and negatively charged ions toward the anode substrate where they impinge on the growing film.Introduction Application of Plasma Technology Deposition and removal(etching)of thin films as well as the modification of surfaces Microelectronics app
5、lications,automotive,optical coating,biomedical,information recording,waste management,and aerospace industriesOutline1.Introduction 2.Plasmas,Discharges,and Arcs3.Physics of sputtering4.DC,RF,Magnetron and reactive sputtering 7What is Plasma?What is Plasma?PDP TVFluorescent lightinglightingnorthern
6、 lightsSun99%of matter in the universePlasma Plasmas are ionized gases consisting of a collection of electrons,ions,and neutral atomic and molecular species FeatureQuasineutralConductive Nonthermal plasma：weekly ionized plasma,the temperature of ion is far below the temperature of electron.（eg：Fluor
7、escent lighting、sputtering process）Thermal plasma：highly ionized plasma,with high temperature of ion and high temperature of electron.（eg：Sun）Plasma Production of Plasma Gas discharge：gas ionize in electric field by collision between energic electron and gas molecular.Self-sustaining of plasma:the n
8、ew produced ions equal the ions that lost.Production and maintenance of Plasma 靶靶基片基片Glow discharge plasmaa plasma formed by the passage of electric current through a low-pressure gas.It is created by applying a voltage between two metal electrodes in a glass tube containing gas.。Neon_lamp_on_DCProd
9、uction and maintenance of Plasma normal glowabnormal dischargeTownsend dischargea tiny current flows initially due to the small number of charge carriers in the system.With charge multiplication,the current increases rapidly,but the voltage,limited by the output impedance of the power supply,remains
10、 constant.Townsend dischargethe characteristic(current vs.voltage)curve of a glow discharge in neon gas at a pressure of 1 torr,between two planar electrodes separated by 50 cm.Paschens Lawd:the distance between electrodesP:pressureA and B:constant At low values of Pd there are few electron-ion coll
11、isions and the secondary electron yield is too low to sustain ionization in the discharge.At high pressures there are frequent collisions,and since electrons do not acquire sufficient energy to ionize gas atoms,the discharge is quenchedApplication:selective sputteringProduction and maintenance of Pl
12、asma normal glowabnormal dischargeTownsend dischargewhen enough electrons produce sufficient ions to regenerate the same number of initial electrons,the discharge becomes self-sustaining.The gas begins to glow now and the voltage drops accompanied by a sharp rise in current.At this point normal glow
13、 occurs.Normal glow dischargeProduction and maintenance of Plasma Initially,ion bombardment of the c a t h o d e i s n o t u n i f o r m b u t concentrated near the cathode edges or at other surface irregularities.As m o r e p o w e r i s a p p l i e d,t h e bombardment increasingly spreads over the
14、 entire surface until a nearly uniform current density is achieved.A further increase in power results in both higher voltage and cathode current-density levels.The abnormal discharge regime has now been entered and this is the operative domain for sputtering and other discharge processes such as pl
15、asma etching.abnormal glow dischargeProduction and maintenance of Plasma At still higher currents,the cathode gets hotter.Now thermionic emission of electrons exceeds that of secondary-electron emission and low-voltage arcs propagate.Arcs have been defined as gas or vapor discharges where the cathod
16、e voltage drop is of the order of the minimum ionizing or excitation potential.Furthermore,the arc is a self-sustained discharge that supports high currents by providing its own mechanism for electron emission from negative or positive electrodes.A number of commercial PVD processes rely on arcs.Arc
17、Structure of a DC glow dischargePlasma sheaths Immersion of a floating electrode(Vf)into a plasma(Vp)causes it to charge negatively,because of the disparity(in mass,velocity,and energy)between electrons and ions.Positive space charge layer shields the negative surface.A plasma sheath of potential Vs
18、(Vs=Vp-Vf)that envelops the electrode and repels electrons.Voltage distribution across DC glow discharge.Note cathode sheath is wider than anode sheath.Plasma sheathsOutline1.Introduction 2.Plasmas,Discharges,and Arcs3.Physics of sputtering4.DC,RF,Magnetron and reactive sputtering 28Energic partical
19、Sputtered atomcollisionPHYSICS OF SPUTTERINGWhen ions bombard the target,When ions bombard the target,is it true that atoms of is it true that atoms of target must be sputtered?target must be sputtered?vLow energy of Incident ion(10-2eV or less)：depositionvMedium energy of Incident ion(10-2eV-104 eV
20、)：sputteringvHigh energy of Incident ion(104 eV and up)：implantationPHYSICS OF SPUTTERING Nuclear stopping have main role in low energy;Electronic stopping have main role in high energyStopping power is defined as the retarding force acting on the particle during the interaction with materialsPHYSIC
21、S OF SPUTTERINGSelf-sustained dischargeSelf-sustained dischargeDepiction of energetic-particle bombardment effects on surfaces and growing filmsWhen one ion bombard the target,how many atoms of target would fly out?Sputter Yieldsfactors：Incident ion（energy、angle of incident、species）Target（species、cr
22、ystallographic、temperature）Effect of energySputter-yield values for Al as a function of energy W h e n a n g l e o f i o n incidence reachs 60o 70o,obtain the SmaxAngle of ion incidenceKind of ions：Strong inverse variation between S and sublimation energyEffect of periodic table溅射产额溅射产额升华热的倒数升华热的倒数C
23、rystallographic effects.Target temperatureOutline1.Introduction 2.Plasmas,Discharges,and Arcs3.Physics of sputtering4.DC,RF,Magnetron and reactive sputtering 42eeeeeeeeeeeeeeeeDC sputtering:also known as diode or cathodic sputteringDC supplyDC sputteringDC sputtering有效溅射产额有效溅射产额（150eV Ar离子）离子）相对沉积速率
24、相对沉积速率放电电流放电电流平面二极（平面二极（3000V）Effect of pressure and current由曲线由曲线A和和B确定确定的沉积速率的沉积速率典型溅射条件典型溅射条件Ar 气压（气压（mTorr）Low P：MFP of collision is large,ionization efficiencies are low and current is low.Increase P would improve current.High P：the sputtered atoms undergo increased collisionalscattering and ar
25、e not efficiently deposited.DC sputteringEffect of pressure and currentInfluence of working pressure and current on film deposition rates in nonmagnetron sputteringDC sputteringEffect of pressure and currentdVIpkR)(R：depositionk(p):coefficient relative to PV：voltageI：currentd:the cathode-anode gap d
26、istanceDC sputteringEffect of pressure and currentadvantage：Appealing simplicitydisadvantage：Film deposition rate are too low(e.g.a few hundred A/min at most for many metals)Need high working pressure(e.g.10Pa）Need conductive targetDC sputteringEffect of pressure and currentAdvantage:The discharge c
27、an be maintained at low pressures Disadvantage:Nonuniform plasma densityDC sputteringTriode SputteringWhen the filament is heated to high temperatures,thermionic emission and injection of electrons into the plasma increase the gas-ionization probability.eeeeeeeeeeeeeeee13.56MHz射频电源射频电源+阻抗匹配阻抗匹配阻抗匹配器
28、阻抗匹配器RF sputteringBelow 1MHz DC sputtering conditions essentially prevail at both electrodes,which alternate as cathodes and anodes.Above 1MkHz electrons oscillating in the glow region acquire enough energy to cause ionizing collisions.no need to rely on secondary electrons emitted from the cathode
29、to sustain the discharge At radio frequencies,voltage can be coupled through any kind of impedance so that the electrodes need not be conductors.RF sputtering that electrons are considerably more mobile than ions and have little difficulty in following the periodic change in the electric field.Targe
30、t Self-BiasRF sputteringIn cycling electrical field,electrode draw e l e ctro n a n d i o n respectively to change its potential.The time of electrode as anode less than 1%,which causes the avg.potential move down.Voltage from RF supplyVoltage on the targetIon currentSelf-biasEletron currenta large
31、value of As is very effective in raising the target sheath potential while minimizing ion bombardment of substrate.Electrode area effects are also important in plasma-etching processesVt：target voltage；Vs：substrate voltage;As:target area；As：substrate areaRF sputteringElectrode-Size Effectseeeeeeeeee
32、eeeeeReactive gasReactive sputteringe.g.Reactive sputteringTarget poisoningMetal sputtering modeCompound sputtering modeReactive sputtering Sputtering yield of compound far below that of metalReactive sputtering In order to resort metal mode from compound mode,needs Qr Qr*Gas flow control could be t
33、aken out by measuring deposition rate,active gas pressure and target voltage.Qr*Qr*Hysteresis effectsReactive sputteringeeeeeeeeeeeeeeeeMagnetron sputteringMagnetic fieldElectrons are forced to drift in a cycloidal hopping motion along the tunnel track lengthMagnetron sputteringFeaturesHigh depositi
34、on rateLow operating pressureLow substrate temperatureMagnetron sputteringtargetMagnetron sputteringMagnetronShape Cylindrical-Post Magnetron Planar target Rotary targetMagnetic line balanced magnetron Unbanced magnetronMagnetron sputteringCylindrical-Post MagnetronPlanar targetadvantge：simpledisadv
35、antge：Uneven sputtering靶材刻蚀横截面靶材刻蚀横截面Planar targetRotary magnetronadvantage：High usage(90%)；disadvantage：Hard preparationRotary magnetron旋转靶长旋转靶长3.86 mRotary magnetronMagnetronShape Cylindrical-Post Magnetron Planar target Rotary targetMagnetic line balanced magnetron Unbanced magnetronMagnetron spu
36、tteringUBMSUBMSCFUBMSOutline1.Introduction 2.Plasmas,Discharges,and Arcs3.Physics of sputtering4.DC,RF,Magnetron and reactive sputtering5.Pulsed dc/mid-frequency sputtering6.Bias sputtering7.Ion beam sputtering 77Why to use the Pulsed dc/mid-frequency sputtering?Oxides and non-conducting systems pro
37、vide increased challenges to reactive sputter deposition due to:The higher reactivity of oxygen(than,for example,nitrogen)leading to higher reactive gas coverages onthe target surface.Formation of an insulating layer over the entire target surface causing the discharge to extinguish.The formation of
38、 insulating regions on the target surface giving rise to arc formation resulting in:The ejection of liquid metal droplets.Damage to the power supply.Discharge extinguish阳极等离子鞘层阳极等离子鞘层Arc formation during dc reactive puttering of Al in Ar/O2Al PlasmaSubstrate AlPlasmaAl2O3Image chargeAccumlated charg
39、eEffects of arcs during dc reactive magnetron sputtering of insulatorsSEM images of metal droplets,due to arcing at the target,embedded in Al203 layers deposited by reactive dc magnetron sputteringArc spot on the target(diam.12 um)Mechanism of metal droplets formationEffects of arcs during dc reacti
40、ve magnetron sputtering of insulatorsdropletDroplet formation during deposition:Tio.5Alo.5N/steelHow to deal with the problem of arc?How to deal with the problem of arc?JEtbrb0Arc would be avoid by neutralization in period of tbtt AlPlasmaAl2O3Image chargeAccumlated charge0rbEJThe permittivity of fr
41、ee spaceThe relative dieletric constant of particleBreakdown field for the particle The discharge current densityPeriod time of arc(tb)TAC sppulyPulsed dcmid-frequencyMethod of neutralizationNormal sputteringCharge neutralizationgDC vs.Pulsed DCDC sputteringPulsed DC sputteringWhat is the Pulsed dc/
42、mid-frequency sputtering?mid-frequency voltage waveforms：DC pulsed Voltage waveforms：T10150kHz10300kHzTTT Mid-frequency sputtering：TkHztTtTbb52112频率The discharge current density:1 mA/cm2Breakdown field Eb(SiO2):3X105 V/cmdieletric constant：3.7e.g.reactive sputtering SiO2:Period of Arc:tb=100 usPulse
43、d DC sputtering：Te.g.反应溅射沉积反应溅射沉积SiO2:Period of Arc:tb=100 uskHztTtTtTTbbb10111频率btT The discharge current density:1 mA/cm2Breakdown field Eb(SiO2):3X105 V/cmdieletric constant：3.7Application of mid-frequency and pulsed DC sputteringmid-frequency sputtering：TSputtering in half period,low efficient.中
44、频电源中频电源bipolar pulsed dc sputtering：Using One target and hige deposition rate；TTTTvvioneApplication of mid-frequency and pulsed DC sputteringbipolar pulsed dc sputtering：TAdjust the pulse time,control the sputtering rate of two target,adjust the content of coating中频电源中频电源孪生靶孪生靶TApplication of mid-fr
45、equency and pulsed DC sputteringOutline1.Introduction 2.Plasmas,Discharges,and Arcs3.Physics of sputtering4.DC,RF,Magnetron and reactive sputtering5.Pulsed dc/mid-frequency sputtering6.Bias sputtering7.Ion beam sputtering 96Bias sputtering：in sputtering process，apply bias voltage between the substra
46、te and plasma,in order to attract the ions flow to subtrate.无偏压溅射无偏压溅射Bias voltge偏压溅射偏压溅射Ta film bias voltage could change the resistance,hardness,dielectric constant,index of refraction,density and adhesion of thin film.Important method for adjusting the sturcture and properties of thin film什么是离子束溅
47、射什么是离子束溅射?Outline1.Introduction 2.Plasmas,Discharges,and Arcs3.Physics of sputtering4.DC,RF,Magnetron and reactive sputtering5.Pulsed dc/mid-frequency sputtering6.Bias sputtering7.Ion beam sputtering 1004.Ion beam sputtering4.Ion beam sputteringdvantages:lower pressure operation well-controlled ion
48、energies decreased gas scattering during transport independent control of process variables(sometimes)minimize e-bombardment heating.Disadvantages:broad area depositionis difficult with most designs(except for recent linear anode layer ion sources)ion current density at target generally lower reliability generally poorer contamination can be a problem.Linear ion sourceFor large aera deposition
