Contains reports on eight research projects and a list of publications.National Science FoundationU.S. Air Force - Office of Scientific ResearchJoint Services Electronics Program Contract DAAL03-89-C-0001IBM CorporationHitachi CorporationSemiconductor Research CorporationNational Institutes of Healt

Cho, Jaeshin

Dubner, Andrew D.

Edell, David J.

Evans, Paul

Floro, Jerrold A.

Frost, Harold J.

Inglefield, Heather E.

Kahn, Harold

Liu, Yachin

Longworth, Hai P.

Ma, En

Melngailis, John

Miura, H.

Ro, Jaesang

Smith, David A.

Thompson, Carl V.

Tu, King-Ning

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Chapter 2. Microstructural Evolution in Thin FilmsChapter 2. Microstructural Evolution in Thin Films ofElectronic MaterialsAcademic and Research StaffProfessor Carl V. Thompson, Professor Henry i. Smith, Dr. Paul Evans, Dr. En Ma, Dr. John Melngailis, Dr.H. MiuraVisiting Scientists and Research AffiliatesDavid J. Edell,' Harold J. Frost, 2 David A. Smith, 3 King-N. Tu 3Graduate StudentsJaeshin Cho, S. Cooperman, Andrew D. Dubner, Jerrold A. Floro, H. Inglefield, Y-C. Joo, Harold Kahn,Yachin Liu, Hai P. Longworth, Jaesang RoTechnical and Support StaffCelia Slattery2.1 Coarsening of Particles ona Planar SubstrateSponsorNational Science FoundationProject StaffProfessor Carl V. Thompson, Yachin LiuVery small particles on a planar substrate canexchange material by atomic diffusion of the par-ticle constituent on the substrate surface. Thisgenerally leads to an increase in the average par-ticle size and spacing and can also lead to thedevelopment of restricted crystallographic orien-tations. This process can be very important in theearly stages of the formation of a thin film. Wehave developed a theory to describe the evolutionof particle sizes and orientations and are testingthis theory by experimentally characterizing particlecoarsening in model systems. We have shownthat Au particles on amorphous SiN membranesannealed in air undergo a coarsening processwhich is described well by the theory for interface-reaction-limited coarsening. We have also shownthat differences in the gaseous ambient stronglyaffect the coarsening rate.2.2 Epitaxial Grain GrowthSponsorsNational Science FoundationU.S. Air Force - Office of Scientific ResearchProject StaffJerrold A. Floro, H. Inglefield, Professor Carl V.ThompsonWe have demonstrated that grain growth in poly-crystalline films on single crystal substrates canlead to epitaxial films. This new approach toobtaining heteroepitaxial films can lead to ultrathinfilms with reduced defect densities compared tofilms deposited using conventional techniques. Inepitaxial grain growth, ultrathin polycrystallinefilms are deposited on single crystal substrates.When these polycrystalline films are heated to ele-vated temperatures, epitaxial grains with low film-substrate interface energies grow and consumemisoriented grains. Because the initial polycry-stalline films are deposited at low temperatures,fully continuous ultrathin films can be obtained.Conventional Volmer-Weber epitaxy which iscarried out at higher deposition temperatures cannot be used to obtain equivalently thin epitaxialfilms. We have developed kinetic analyses forepitaxial grain growth and are testing these ana-lyses through experiments on model systems,1 Harvard-MIT Health Sciences Program, Cambridge, Massachusetts.2 Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire.3 IBM Corporation, Thomas J. Watson Research Center, Yorktown Heights, New York.Chapter 2. Microstructural Evolution in Thin Filmsincluding Au and Ag films onExperiments on epitaxial grainviding a means of characterizinginterface energy, as a functiontation.mica and NaCI.growth are pro-the film-substrateof crystal orien-2.3 Modeling ofMicrostructural Evolution inThin FilmsSponsorsJoint Services Electronics ProgramContract DAAL03-89-C-0001National Science FoundationU.S. Air Force - Office of Scientific ResearchProject StaffProfessor Carl V.Jerrold A. FloroThompson, Harold J. Frost,We are developing analytic models for normal andsecondary grain growth in continuous thin films aswell as particle coarsening in discontinuous films.The effects of surface or interface energyanisotropy play especially important roles in theseprocesses. We have developed computer modelsfor film formation by crystal nucleation and growthto impingement under a variety of conditions. Wehave shown that topology and geometry of grainstructures strongly depend on the conditions offilm formation.We have also developed a computer model fortwo-dimensional grain growth. This simulationhas been modified to account for the importanteffects that the surfaces of a film have on graingrowth. We have shown that when formation ofgrain boundary surface grooves leads to stagnationof normal grain growth, lognormal grain size dis-tributions with average grain size two to threetimes the film thickness result. This is in agree-ment with well-established experimental observa-tions. We have also successfully modeledabnormal grain growth caused by anisotropy of thesurface energy of grains.2.4 Properties of GrainBoundaries in Zone MeltedSilicon Thin FilmsSponsorIBM CorporationProject StaffDr. Paul Evans, David A. Smith,ThompsonProfessor Carl V.We are using zone melting recrystallization (ZMR)of thin silicon films on oxidized silicon wafers toprepare thin film bicrystals in order to study theelectronic properties of grain boundaries in silicon.We are correlating electronic properties with struc-tural features, as revealed using high resolutionelectron microscopy. We have found that in thesesamples, (100) tilt boundaries with tilts up to 25.5degrees are electrically inactive. This surprisingresult indicates that even polycrystalline ZMR filmsmight be useful for silicon-on-insulator (SOI)majority carrier devices.2.5 Kinetics of Thin FilmSilicide FormationSponsorsHitachi CorporationIBM CorporationProject StaffProfessor Carl V. Thompson, Dr. EnMiura, King-N. TuMa, Dr. H.Currently, there is considerable interest in the useof refractory metals or refractory metal silicides asinterconnects, as gate materials in MOS devicesand for low contact resistance diffusion barriers atmetal-silicon contacts in integrated circuits. Onemethod of silicide formation is through thereaction of metallic thin films with silicon sub-strates or polycrystalline silicon films. This appli-cation raises fundamental questions about the rateand products of thin film metal-silicon reactions.There are four critical parameters in analysis andmodeling of these reactions: (1) interdiffusivities,(2) free energy changes, (3) surface energies, and(4) interface reaction constants. Of these, the firsttwo parameters are fairly well understood and pre-dictable. The purpose of this project is to developa better understanding and predictive capability forthe last two parameters. Surface energies arebeing determined through silicide precipitationexperiments and the kinetics of thin film reactions24 RLE Progress Report Number 133are being studied through thermal, TEM, and x-rayanalysis of reactions in multilayer thin films.We have used differential scanning calorimetry,transmission electron microscopy, electron beammicroanalysis, and thin film x-ray diffractometry tostudy the thermodynamics and kinetics of reac-tions in multilayer thin films. In Pt/amorphous-Si(Pt/a-Si), Ni/a-Si, V/a-Si and Ti/a-Si multilayers,amorphous silicides are the first phases to form,even though these phases are thermodynamicallystable only if crystalline silicide formation iskinetically suppressed.We have demonstrated that calorimetric analysis ofmultilayer films can be used to detect and analyzecrystalline silicide nucleation during reactions inmultilayers. Evidence for crystal nucleation hasbeen observed in the cases listed above as well asin Co/a-Si and Ni/Al multilayers in which crystal-line phases are the first phases to form. We haveaccumulated experimental and theoretical evidencewhich suggests that nucleation is preceded byinterdiffusion and that it is the kinetic constraintsof these sequential processes which govern phaseselection during interfacial reactions.We have also observed explosive reactions inmultilayer metal/a-Si films and fully crystallineNi/Al multilayers. These reactions can propagatein a room temperature ambient at velocities over20 meters per second. This self-rapid-thermal-annealing process results in homogeneous filmscomposed of the stable high temperature productphase.2.6 Reliability andMicrostructures ofInterconnectsSponsorsJoint Services Electronics ProgramContract DAAL03-89-C-0001Semiconductor Research CorporationProject StaffJaeshin Cho, Harold Kahn, Hai P. Lonfessor Carl V. Thompsongworth, Pro-We are developing new techniques which allowstatistical characterization of failure of contact viasand interconnects for integrated circuits. We areusing these techniques to correlate failure ratesand mechanisms with microstructures of intercon-nect lines, contact diffusion barriers and via plugs.Chapter 2. Microstructural Evolution in Thin FilmsWe are also investigating techniques for control-ling microstructures in order to improve contactand interconnect reliability, especially under condi-tions which can lead to electromigration.We have recently shown that in interconnect lineswith uniform microstructures, increasing the grainsize results in an increase of both the median timeto electromigration-induced failure and thelognormal standard deviation in the time to failure.The net result, in large populations of lines, is littleor no change in the time to the first failure. Wehave explained these results in terms of a "failureunit model" in which grain boundaries are taken tobe the individual units which are responsible forthe reliability of a line. The successful applicationof this model indicates the importance of the prop-erties of individual grain boundaries in controllinginterconnect reliability.This interpretation is further supported by theobservation that interconnects with bimodal grainsize distributions (leading to grain size discontinui-ties) have greatly reduced reliabilities. On theother hand, lines which are completely free ofgrain boundary triple junctions have greatlyimproved reliabilities compared to lines with com-parable grain sizes but also with triple junctions.We are now investigating the development ofelectromigration-induced damage in lines withindividual grain boundaries of controlled types andlocations. This will allow characterization of thefailure mechanisms and rates for the fundamentalunits that control the reliability of interconnectsystems.2.7 Focused Ion Beam InducedDepositionSponsorIBM CorporationProject StaffDr. John Melngailis, Andrew D. Dubner, JaesangRo, Professor Carl V. ThompsonIt is now possible to produce ion beams withdiameters as small as 500 A. This permits use offocused ion beams for high spatial resolutionimplantation, sputtering and deposition. In prin-cipal, the latter can be used in integrated circuitmask repair or high resolution direct writing ofinterconnects. We are investigating the mechan-isms of ion-beam-induced chemical vapor deposi-tion from metal-bearing gases.Chapter 2. Microstructural Evolution in Thin Films2.8 Protective Coatings forIntegrated Circuits in an invitro EnvironmentSponsorNational Institutes of HealthProject StaffDavid J. Edell, Professor Carl V. ThompsonWe are investigating the use of various coatingmaterials to prevent Na diffusion into integratedcircuits to be used in biomedical applications. Weare correlating processing conditions, microstruc-tural characteristics and diffusion barrier propertiesto develop standard methodologies for depositionand characterization of protective coatings.2.9 PublicationsCammarata, R.C., C.V. Thompson, C. Haydelden,and K.N. Tu. "Silicide Precipitation and SiliconCrystallization in Nickel Implanted AmorphousSilicon Thin Films." J. Mater. Res. 5: 2133(1990).Cho, J., and C.V. Thompson. "Electromigration-Induced Failures in Interconnects with BimodalGrain Size Distributions." J. Electron. Mater.19: 1207 (1990).Clevenger, L.A., and C.V. Thompson. "ExplosiveSilicidation in Nickel/Amorphous-Silicon Mul-tilayer Thin Films." J. App. Phys. 67: 2894(1990).Clevenger, L.A., and C.V. Thompson. "NucleationLimited Phase Selection During Reactions inNickel Amorphous-Silicon Multilayer ThinFilms." J. Appi. Phys. 67: 1325 (1990).Clevenger, L.A., C.V. Thompson, R.R. De Avillez,and E. Ma. "Nucleation Controlled PhaseSelection in Vanadium/Amorphous-SiliconMultilayer Thin Films." J. Vac. Sci. Tech. A 8(3): 1566 (1990).De Avillez, R.R., L.A. Clevenger, C.V. Thompson,and K-N. Tu. "Quantitative Investigation ofTitanium/Amorphous-Silicon Multilayer ThinFilm Reactions." J. Mater. Res. 4: 593 (1990).Frost, H.J., C.V. Thompson, and D.T. Walton."Simulation of Thin Film Grain Structures: I.Grain Growth Stagnation," Acta Metall. Mater.38: 1455 (1990).Jiran, E., and C.V. Thompson. "Capillary Instabili-ties in Thin Films." J. Electron. Mater. 19: 1155(1990).Kim, H.-J., and C.V. Thompson. "The Effects ofDopants on Surface- Energy- Driven SecondaryGrain Growth in Silicon Films." J. Appl. Phys.67: 757 (1990).Ma, E., and C.V. Thompson. "Self-PropagatingExplosive Reactions in AI/Ni Multilayer ThinFilms." Appi. Phys. Lett. B7: 1262 (1990).Thompson, C.V. "Grain Growth in Thin Films."Ann. Rev. Mater. Sci. 20: 245-68 (1990).Thompson, C.V., J. Floro, and H.I. Smith."Epitaxial Grain Growth in Thin Metal Films."J. Appl. Phys. 67 (9): 4-99 (1990).ThesesCho, J. Effect of Microstructure of AluminumAlloys on the Electromigration-Limited Reli-ability of VLSI Interconnects, Ph.D. diss. Dept.of Mater. Sci. and Eng., MIT, 1990.Dubner, A.D. Mechanisms of Ion Beam InducedDeposition. Ph.D. diss. Dept. of Mater. Sci.and Eng., MIT, 1990.Jiran, E. Capillary Instabilities in Thin, Solid Films.Ph.D. diss. Dept. of Mater. Sci. and Eng., MIT,1990.26 RLE Progress Report Number 133

Microstructural Evolution in Thin Films of Electronic Materials

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Microstructural Evolution in Thin Films of Electronic Materials

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