文本課件文稿教程ald of metal oxide and nitride thin films

1、Atomic Layer Deposition ofMOxide and Nitride Thin FilmsA thesis presentedbyJill Svenja BeckertoThe Department of Chemistry and Chemical Biologyin partial fulfillment of the requirements for the degree ofDoctor of Philosophyin the subject ofChemistryHarvard University Cambridge, Massachusetts Decembe

2、r 2002© 2002 Jill Svenja Beckers.Atomic Layer Deposition of MOxide and Nitride Thin FilmsAbstractAdvisor: Prof. Roy G. GordonJill Svenja BeckerWith the continued miniaturization of thin film devices, growth techniques arerequired that deposit conformal films with atomic layer control. In this t

3、hesis, atomiclayer deposition (ALD) techniques were developed to achieve conformal and atomiclayer controlled film growth.Reactors were constructed and optimized for testingpotential precursors and deposition processes.Several methods of volatilization anddelivery into the reactor were studied and o

4、ptimized. All of the ALD methods are basedon sequential, self-limiting surface reactions.The research included developing newchemistries and new precursors for ALD, optimizing and characterizing film growth andevaluating properties of ALD films. This thesis is based on experimental work carriedout d

5、uring the years 1999-2002 at Harvard. It will first review ALD in general. Then,the growth and properties of films of moxides and nitrides will be described. Theself-limiting film growth mechanism in ALD ensures excellent film conformality anduniformity over large areas, and atomic level composition

6、 and thickness control.Avariety of electronic films have been deposited by ALD. In this thesis, ALD depositionand material characterization of two groups of films will be examined: (i) insulatingfilms and (ii) conductive films. In every case atomic layer controlled growth was shownto occur.In the pr

7、esent work, the deposition of silver-colored, conductive tungstennitridebarrierfilmsbyALDusinganovelprecursor,bis(tert-butylimido)bis(dimethylamido)tungsten,(t-BuN)2(Me2N)2W, andammoniaatlow- iii -substrate temperatures (250-350 oC) is reported. The basic bulk properties of these filmswere investiga

8、ted, as well as their performance as a barrier to the diffusion of copper.The thesis also deals with a new type of ALD reaction, using trimethylaluminumand tris(tert-butoxy)silanol, that deposits dozens of monolayers in cycles less than half aminute long, resulting in a deposition rate more than 100

9、 times faster than previouslyknown ALD reactions for silica nanolaminates. In addition, new deposition processes formsilicates for hafnium, zirconium, lanthanum and yttrium from malkylamidesand tris(alkoxy)silanols are reported.Using malkylamide precursors and ammonia, films of pure insulating nitri

10、desof hafnium and zirconium were prepared and characterized. The ALD of thin films ofHf3N4 and Zr3N4 using homoleptic tetrakis(dialkylamido)m(IV) complexes andammonia at low substrate temperatures (150-250 C) is reported. Hafnium and zirconiumoxynitride (HfOxNy and ZrOxNy) dielectrics were also made

11、 by ALD using, homoleptictetrakis(dimethylamido)m(IV), water and ammonia at low substrate temperatures(200-250 oC). The basic bulk properties of these films were investigated, as well as theirelectrical properties for the application of these materials as gate dielectrics.- iv -AcknowledgementsI wou

12、ld like to thank my advisor, Professor Roy G. Gordon, for his guidance inthis work. His expertise, extensive knowledge of the literature, and unwavering scrutinyhave made this thesis possible. I am grateful for having had the opportuto try myhand at several different projects, and am deeply satisfie

13、d with the vast amount of newideas and concepts I acquired in the process.I would also like to thank the other members of my thesis committee, ProfessorCharles M. Lieber and Professor William N. Lipscomb for their contributions to mywork. Gratitude also extends to the helpful administrative staff at

14、 Harvard, as well as tomy fellow students for making my stay that much more enjoyable.This work was supported in part by the National Science Foundation and theNatural Science and Engineering Research Council of Canada.My husband, Drew, deserves very special thanksforhispatienceandunderstanding duri

15、ng the years it took to complete this work.- v -Table of ContentsPrefaceAbstract Acknowledgements Table of Contents Glossary of TermsSymbols and Abbreviationsiii v vi ix xChapter 1. Introduction11.1 An Introduction to Thin Films1.2 Thin Film Process Steps1.3 Future of Thin Film Growth1.4 Thesis Over

16、view1.5 References and Notes137911Chapter 2. Atomic Layer Deposition122.1 Introduction2.2 Alternative ALD Names2.3 ALD Cycle2.4 ALD Reactors2.5 ALD Processing Window2.6 ALD Precursors2.7 Limitations of ALD1213141722232828302.8s2.9 References and NotesChapter 3. Thin Film Characterization313.1 Introd

17、uction3.2 Film Adhesion3.3 Rutherford Backscattering Spectroscopy3.4 High-Resolution Transmission Electron Microscopy3.5 Surface Morphology3.5.A Atomic Force Microscopy3.5.B Scanning Electron Microscopy31323235383940- vi -3.6 Ellipsometry3.7 X-Ray Diffraction3.8 X-Ray Reflectivity3.9 Quartz Crystal

18、Microbalance3.10 Electrical Characterization3.10.A Resistivity3.10.B Insulating Properties3.11 References and Notes4345465354545658Chapter 4. Atomic Layer Deposition of Tungsten Nitride & Tungsten594.1 Introduction4.2 Experimental Methods4.2.A Synthesis of Tungsten Precursor4.2.B ALD of Tungsten

19、 Nitride4.2.C Characterization of Films4.3 Results and Discussion59636365686983844.4s4.5 References and NotesChapter 5. Rapid Vapor Deposition of Silica Nanolaminates865.1 Introduction5.2 Experimental Methods5.2.A Deposition of Silica Films5.2.B Characterization of Films5.3 Results and Discussion868

20、88890901021035.4s5.5 References and NotesChapter 6. Vapor Deposition of MSilicates1066.1 Introduction6.2 Experimental Methods6.2.A Synthesis of Precursors1061091091101111111161176.2.B ALD of MSilicates6.2.C Characterization of Films6.3 Results and Discussion6.4s6.5 References and Notes- vii -Chapter

21、 7. Insulating Hafnium and Zirconium Nitrides1187.1 Introduction7.2 Experimental Methods7.2.A Precursors7.2.B ALD of Hafnium and Zirconium Nitride7.2.C Characterization of Films7.3 Results and Discussion1181191191201251251331347.4s7.5 References and NotesChapter 8. Hafnium and Zirconium Oxynitrides1

22、358.1 Introduction8.2. Experimental Methods8.2.A ALD of Hafnium and Zirconium Oxynitrides8.2.B Characterization of Films8.3 Results and Discussion1351371371381391421438.4s8.5 References and NotesAppendix A.1144A.1 System Automation144Appendix A.2147A.2.1 IntroductionA.2.2 Results and DiscussionA.2.3

23、 Source of MaterialA.2.4 X-Ray Data DetailsA.2.5 References and Notes147147151151153- viii -Glossary of TermsDiode. A semiconductor device, which conducts electric current run in one direction only. This is the simplest kind of semiconductor device, it has two terminals and a single PN junction. One

24、 diode can be used as a half-wave rectifier or four as a full-wave rectifier.Dielectric. A substance in which an electric field may be maintained with near-zero power dissipation, i.e., the electrical conductivity is near zero. A dielectric material is an electrical insulator. In a dielectric, elect

25、rons are bound to atoms and molecules, hence there are few free electrons.Dielectric Constant k. The dielectric constant (k) of a substance is the measure of the relative effectiveness of that substance as an electrical insulator.Epitaxy. The growth of one crystal on a crystal face of another crysta

26、l, such that the crystalline structures have a well-defined orientation.Index of refraction. The ratio of the speed of light in a vacuum to the speed of light in a medium under consideration. Also called refractive index.MOSFET (m-oxide semiconductor field-effect transistor).A semiconductordevice th

27、at can serve as a switch to process and store information.n-type semiconductor. Example: Phosphorus (P), the donor impurity, has one more valence electron than Si, thus creating a negative electron that can move in the conduction band. Hence the term n-type semiconductor.p-type semiconductor. Exampl

28、e: Boron (B), the acceptor impurity, has one less valence electron than Si, thus creating a positive hole in the valence band. Hence the term p- type semiconductor.- ix -Symbols and AbbreviationsÅngstrom (10-8 cm or 10-10m) atomic force microscopy atomic layer deposition atomic layer epitaxyatm

29、ospheres (1 atm = 760 Torr) boiling pointdegrees centigrade cathode ray tubechemical vapor deposition dynamic random access memory gas chromatographyhourshigh aspect ratiohigh-resolution transmission electron microscopy integrated circuitLangmuirs (10-6 Torr·sec)Å AFM ALD ALEatm bp ºC

30、 CRT CVDDRAM GCh HARHRTEM ICL LCR MBEMEMSmicron MOSFET MLnm ppb ppm psi PVD QCM RBSRMSSc SCCM SEM SFM SLM STP TEM TFEL UHV XPS XRD XRRinductance, capacitance, molecular beam epitaxymicro electro-mechanical systems µ (10-6 m)(meter)m-oxide semiconductor field-effect transistormonolayernanometer

31、(10-9 m) parts per billion parts per millionpounds per square inch physical vapor deposition quartz crystal microbalanceRutherford backscattering spectrometryroot mean square ( x 2 )sticking coefficientstandard cubic centimeter per minute scanning electron microscopy scanning force microscopystandar

32、d liters per minutestandard temperature (0 ºC) and pressure (1 atm) transmission electron microscopythin film electroluminescent ultra high vaccumX-ray photoelectron spectroscopy X-ray diffractionX-ray reflectivity- x -To my friends and family.- xi -Chapter 1. Introduction1.1 An Introduction to

33、 Thin FilmsThin film technology is simultaneously one of the oldest arts and one of thenewest sciences. Involvement with thin films dates to the mages of antiquity wherethey were first used for decorative purposes. Consider the ancient craft of gold beating,which has been practiced continuously for

34、at least four millennia.1 Thin films are stillused today for decorative or protective purposes: to form conductors, resistors, and othertypes of films in microelectronic circuits; to form photovoltaic devices for conversion ofsolar energy to electricity; and for many other applications. A thin film

35、might be made ofany kind of material, including ms, moxides, mnitrides or mixed materials.The term thin film does not have a precise definition. In general, it refers to athree-dimensional film less than about 100 µm thick and as thin as a few nanometers. Athin film is a liquid or a solid such

36、that one of the dimensions of the film, the filmsthickness, is smaller than the other two dimensions, by several orders of magnitude.Typically thin films are made by deposition of individual atoms or molecules, while thickfilms are made by deposition of particles.Examples of thick film techniques ar

37、epainting, silk screening, spin-on glass coating, and plasma spraying.The thick filmtechniques are important and relatively inexpensive, but they do not offer as much controlof the material quality as do thin film techniques. Note that films deposited by a thin filmtechnique can be thicker than thos

38、e deposited by a thick film technique.1 This thesisdiscusses systems of a thin solid film on a (solid) substrate (backed films) rather thanunsupported films (foils).- 1 -IntroductionFor a thin film to be useful, it should possess all or most of the followingproperties: (a) It should be chemically st

39、able in the environment in which it is to be used;(b) it should adhere well to the surface it covers (the substrate); (c) it should have auniform thickness; (d) it should be chemically pure or ofcontrolled chemicalcomposition; (e) it should have a low density of imperfections.In addition to thesegen

40、eral characteristics, special properties might be required forcertain applications.Table 1.1 divides these properties into five basic categories and gives examples of typicalapplications within each category.Examination of this table shows that the range of thinfilm applications is very broad.Often,

41、 multiple properties are obtainablesimultaneously.1Table 1.1 Thin film Applications.Thin film propertyTypical ApplicationsOpticalReflective/antireflective coatings Interference filtersDecoration (color, luster) Memory discs (CDs) WaveguidesElectricalInsulation ConductionSemiconductor devices Piezoel

42、ectric devicesMagneticMemory discsChemicalBarriers to diffusion or alloying Protection against oxidation/corrosion Gas/liquid sensorsMechanicalWear-resistant coatings HardnessAdhesion MicromechanicsThermalBarrier layers Heat sinks- 2 -IntroductionAdditional functionality in thin films can be achieve

43、d by depositing multiplelayers of different materials. For example, optical interference filters consist of tens oreven hundreds of layers alternating between high and low indexes of refraction.For most applications, a thin film must adhere well to its underlying substrate.Because the film is inhere

44、ntly fragile, it must depend on the substrate for structuralsupport. To attain that support, the film must be bound to the substrate by strong forces.The bonding forces may be chemical in nature; that is, a chemical reaction at the interfacecan connect the film to the underlying material. For exampl

45、e, when a moxide isdeposited on glass, the oxide lattices of the moxide and glass blend at the interface,forming a thin zone of intermediate composition. In these cases the bonding energiesbetween the film and the substrate are of the same magnitudes as chemical bonds, in therange of 250 to 400 kJ/m

46、ol.2 This makes for a robust film.1.2 Thin Film Process StepsAll thin film processes contain the four (or five) sequential steps shown inFigure 1.1.A source of film material is provided, the material is transported to thesubstrate, deposition takes place, sometimes the film is subsequently annealed,

47、 andfinally it is analyzed to evaluate the process. The results of the analysis are then used toadjust the conditions of the other steps for film property modification. Additional processcontrol and understanding are obtained by monitoring the first three steps during filmdeposition.3The source of t

48、he film-forming material may be a solid, liquid, vapor, or gas.Solid materials need to be vaporized to transport them to the substrate, and this can be- 3 -IntroductionSupply RateUniformityStructure and CompositionSupply RateFig. 1.1 Thin film process steps. In all steps process monitoring is valuab

49、le.done by heat or by an energetic beam of electrons, photons (laser ablation), or positiveions (sputtering). These methods are categorized as physical vapor deposition (PVD). Inother cases, the source material is supplied as a gas or as a liquid having sufficient vaporpressure to be transported at

50、moderate temperatures. Thin film processes that use gases,evaporating liquids, or chemically gasified solids as source materials are categorized aschemical vapor deposition (CVD). In both PVD and CVD contamination and supply rateare the major source-material issues. Contamination is also an issue in

51、 the transport anddeposition steps. Supply rate is important because film properties vary with depositionrate and with the ratio of elements supplied to compound films.In the transport step, the major issue is uniformity of arrival rate over thesubstrate area. The factors affecting this uniformity a

52、re very different, depending onwhether the transport medium is a high vacuum or a fluid. (Here we arking aboutgaseous fluids rather than liquid fluids.) In a high vacuum, molecules travel from the- 4 -Analysisstructure composition propertiesAnnealingDepositionsubstrate conditions reactivity of sourc

53、e materialenergy inputTransportvacuum fluid plasmaSourcesolid liquid vapor gasIntroductionsource to the substrate in straight lines, whereas in a fluid there are many collisionsamong molecules during the transport step. Consequently, in a high vacuum, uniformityof source-material arrival rate at the

54、 substrate is determined by geometry, whereas in afluid it is determined by gas flow patterns and by diffusion of the source moleculesthrough the other gases present.Often, the high-vacuum processes are equated withphysical vapor deposition, and the fluid-flow processes are equated with chemical vap

55、ordeposition. However, this is not always a valid association. Although many physicaldeposition processes do operate in a high vacuum, others like laser ablation andsputtering often operate at higher pressures characteristic of a fluid. Similarly, althoughmost chemical deposition processes operate a

56、t fluid pressures, chemical beam epitaxyoperates in a high vacuum.The high-vacuum transport medium has the important advantage of clear accessto the deposition surface. This allows energy input from an ion beam and allows the useof analytical techniques involving electron beams, such as electron diffraction and Augerspectroscopy. On the other hand, the fluid medium has the advantage that it functions atatmospheric pressure or at easi