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`Page 4 of 14
`
`Spectroelectrochemical Studies of Indium
`Hexacyanoferrate Electrodes Prepared by
`the Sacrificial Anode Method
`KC. Ho, JC. BORescvssesvisvssininsnuntnineieinavisiininininenensen insite2334 <
`Modification of the Lithium Metal Surface
`by Nonionic Polyether Surfactants:
`Quartz Crystal Microbalance Studies
`M. Mori, % Naruoka, K. Naot, D. FAUlOux essecsesesessesessssesssceneesiesnsssecsseesesneesissvacsnnes2340
`Electrochemical Synthesis of Urea at Gas-Diffusion Electrodes.
`IV. Simultaneous Reduction of Carbon Dioxide and Nitrate
`Ions with Various Metal Catalysts
`M, Shibata, K Yoshida, N. Furteya cecssvessssssscsseeessesecssesessssenssesssvecessseessecesuessssveeesnvaeetsey2348
`Characterization of High-Surface-Area Electrocatalysts
`Using a Rotating Disk Electrode Configuration
`T.|. Schmidt, H. A. Gasteiger, G. D. Stab, P.M. Urban,
`
`D.M. Kol, RJ. BODO cccsssesevssvesessseessesisessnsssvestsessinsessasvensscnnensrssnersnssestasesesanen2354
`Water Electrolysis Using Diamond Thin-Film Electrodes
`N. Katsuki, B. Takahashi, M. Toyoda, T. Kurosu, M. lida,
`
`S. Wakita, ¥, Nishiki, 7 Shimamune ..ccccccsccccsssssvsesscsssssevsessusvessevssasestevinssesssssesseseee 2358
`
`The Mechanism of Electropolishing of Titanium
`in Methanol-Sulfuric Acid Electrolytes
`O. Piotrowski, C. Madore, D. LANGOML ....seessescssesessecssssesssessseesseseneesseesseessneesuescatessncensaves2362
`Electrochemical Behavior andSurface Morphologic Changes of Copper
`Substrates in the Presence of 2,5-Dimercapto-1,3,4-thiadiazole.
`In Situ EQCM and Phase Measurement Interferometric Microscopy
`Q. Chi, T. Tatsuma, M. Ozaki, T. Sotomutra, N. OVAMG vcsseecssessssesssesssesssecsssecsssssnscsssvsssssnse2369
`Super Dense Li€y as a High Capacity
`Li Intercalation Anode
`
`C. Bindra, V. A. Nalimova, D. E. Sklousky, Z. BeneS, J. B. Fisch?ieclceessseessssesssesssseensnns2377
`Photochemical and Photoelectrochemical Behavior
`of a Novel Ti09/Ni(OH)> Electrode
`R. Kostecki, T. Richardson, B MCLAPNON vecsescesssccssssesssssssssssssvussesesnssnanesssissesineesseee2380
`Quartz Crystal Microbalance Investigation
`of Electrochemical Calcium Carbonate Scaling
`C. Gabrielli, M. Keddam, A. Khalil, G. Maurin,
`H. Perrot, R. Rossel, M. ZAOUNE vooocccsescccsossesseseooesessassensusasessunasensasanasessusaneannansenee2386
`Passivity and Breakdown of CarbonSteelin Organic Solvent Mixtures
`of Propylene Carbonate and Dimethoxyethane
`DA. Shifler, J. Kruger, PJ. MOAN vvcccsccccssssssssssssssssesssssscessessssnivessssassessersssueesessssnsnrssceeve2396
`The Impact of the Operation Mode on Pattern
`Formation in Electrode Reactions.
`From Potentiostatic to Galvanostatic Control
`N. Mazouz, G. Fléitgen, K Krischer, L. G. Revvehidts..cccccccscccccscccssscsessnesnseernnsnvcee2404
`Influence of Nitrogen-Containing Precursors on the Electrocatalytic Activity
`of Heat-Treated Fe(OH), on Carbon Black for 0, Reduction
`R. Cité, G. Lalande, D. Guay, J. P. Dodelet, G. DENBS ceeossccescissccsescssssesssssssesunnseninnesses2411
`Study of the Structural Change Due to Heat-Treatment
`in High Resistivity Electroless NiPC Film
`Ti Osaka, T. Higashikawa, A. lizuka, M. Takai, M. Kim soocsccssccossccssscsssssnssunveueveveessee2419
`Prediction of Li Intercalation and Battery Voltages
`in Layered vs. Cubic Li,Co0,
`C. Wolverton, A, LUNGED ..essctsetssivissisesinsisesuesussssssesssuusssusssusssussneunnneee2424
`Gas Conversion Impedance: A Test Geometry Effect
`in Characterization of Solid Oxide Fuel Cell Anodes
`5: Primdabl, M. MOgOnSOM weosessessisssssstiviesiasiesissssseeassatunspusiisnssciannuenesee2431
`
`Page 4 of 14
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`

`

`.
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`Solid-State Science and Technology
`
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`Society Officers
`President
`Changes in the Environment of Hydrogen in PorousSilicon
`Gerard M. Blom
`with Thermal Annealing
`scarf _ rane10.2099, USA
`.
`riarc!
`anor,
`New Yor!
`,
`¥. H. Ogata, F. Kato, T. Tsubot, 7. SARRA ....ceccssseccceveccosssesessessecsessessecesnesecaniceennnasensnaneesey2439
`ticePresident
`Room Temperature Operating Solid-State Sensor for Chlorine Gas
`tehnwh
`ale E. Hall a
`,
`. Institute of Standards&TechnologyNational
`
`V, Naizei, S. SBIDQGG oes cceccscescssssesssessenssenesssveussesesvessstvesaveveassnscssensseacensaqaesseeseasenegeensaeesenes2445
`Gaithersburg, Maryland 20899, USA
`Incorporation of Cadmium Sulfide into NanoporousSilicon
`Vice-President
`by Sequential Chemical Deposition from Solution
`Carlton M. Osburn
`;
`.
`North Carolina State University
`M. Gros-Jean, R. Herin0, D. LinC0t wicsessecseessesseceeooresosennnnesnneeanenvasennnegnnnegnveennaeensee2448
`Raleigh, North Carolina 27695, USA
`Effect of the Gas-Phase Reaction in Metallorganic Chemical Vapor
`abTalbot
`sa:
`:
`:
`.
`.
`jan
`B.
`t
`Deposition of TiN from Tetrakis(dimethylamido)titanium
`Univesity of Califomia, San Diego
`JY, Yaar, M-¥, Park, SW. RCO ssessssssssssscssssersscessseseeessssssesessnnnsscesaneensssonensssssnsessssnsesse2453
`LaJolla, California 92093-0411, USA
`Fibrous and Porous Microstructure Formation
`Secretary
`.
`+
`Satine
`f
`;
`Robin A. Susko
`in 6H-SiC by Anodization in HF Solution
`IBM Corporation
`W. Shin, T. Hikosaka, W.-S. Seo, H. S. Abn, N. Sawaki, K. KOUMOL....ssscsssssssesssesesesssnsssen2456
`Endicott, New York 13760, USA
`.
`Treasurer
`. Dry Etching of SrS Thin Films
`W. D. Brown
`J. W. Lee, M. R. Davidson, B. Pathangey, P. H. Holloway, S. J. PEArtOM..secsssssseeseessseseneees2461
`University of Arkansas
`Fayetteville, Arkansas 72701, USA
`Tribochemical Reactions ofSilicon:
`Executive Director
`An In Situ Infrared Spectroscopy Characterization
`Roque J. Calvo
`V, A. Muratov, J. B. Olsen, B. M. Gallois, T. B. Fischer, J. C. Bean cessesessssosssssssssuiasesscsseseesee2465
`The Blectrochemical Society, Ine.
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`Pennington, NewJersey 08534-2896, USA
`and Deuterium in Titanium and TizAl
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`Photoluminescence Studies of Cadmium Selenide Crystals in
`Contact with Group III Trialkyl Derivatives
`BE. J. Winder, T. F. Kitech, A. B, BUAS ..ccsssescssessessecssssestecssesessesssnecsnnscnnecessnstnarensvasennecsanneess2475
`Reduction in Contact Resistance with In Situ 07
`,
`Plasma Treatment
`:
`.
`.
`K Yonekura, S. Sakamori, K. Kawai, H, MiyQta@..escccsssssssssessssseissesssvessssesssasessssseseD400
`Measurements of VOCs with a Semiconductor Electronic Nose
`.
`M. C. Horrillo, ]. Getino, L. Arés, J. I. Robla,
`-
`1, Seayaago, FJ. GUGrreZeeesssscssssesssssseesnsnesessseessssesceseuescnnnieccesscssssssscnnvesisussecssansaessaneeetty2486
`Interface States Distribution in Electrical Stressed
`Oxynitrided Gate-Oxide
`S. Belkouch, T: K. Nguyen, L. M. Landsberger C. Aktib,
`C. Jecarn, M. KADVIZ ooesceecescssesesseeesssesssesesvecssneesssecsssscessseeaseessnnessanecenneenasenseascasunecasassnnsseays2489
`Design of Injection Feed Multiwafer Low-Pressure
`Chemical Vapor Deposition Reactors
`L. ZaMbOV, C. POPOV, B. LVAMOV vessecsecsessseccseeseesssressecsvseseasnesesnneaneeassessassuseanssacensennennneey2494
`Aqueous KOH Etching ofSilicon (110).
`Etch Characteristics and Compensation Methods for Convex Corners
`B. Kirra, Devi. D. CBO cessessssessssesssvessssessesevesnesesssecsssecssvacesisessneceancessnscessvenniasesancssaneessiseranases2499
`.
`\
`Amorphous Hydrogenated Silicon Films for
`Solar Cell Application Obtained with 55 kHz
`Plasma Enhanced Chemical Vapor Deposition
`B. G. Budaguan,A. A. Sherchenkov, D. A. Stryabilev, A. ¥. Sazonov,
`,
`A. G. Radosel’sky, V. D. Chernomordic, A. A. Popov,J. We. MOISCQAE as..eesistssensensnsse2508
`Dry Etch Patterning of LaCaMn03 and SmCo Thin Films
`J.J. Wang, J. R. Childress, 8. J. Pearton, F Sharifi, K H. Dabmen,
`.
`.
`.
`.
`E.S. Gillman, EJ. Cadieu, R. Rani, X. R. Qian, L. WMecssieereseeesnscesseessesssnnnseesennvees2512
`Growth Kinetics of Chemical Vapor Deposition
`of B-SiC from (CH3)2SiC12/Ar
`T. Tago, M. Kawase, ¥. Yoshihara, K Hashim0t0....seereonpeseesveneensssesnensesseseceeeeuenneansensees2516
`
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`- Page 5 of 14
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`Page 5 of 14
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`

`

`Divisions and Groups
`
`Battery Division
`Curtis F Holmes, Chairman
`Subbarao Surampudi, Vice-Chairman
`James S. Symanski, Secretary
`Esther S. Takeuchi, 7reasurer
`Mark D.Allendor, Advisor
`Corrosion Division
`
`Martin W. Kendig, Chairman
`PatrickJ. Moran,Vice-Chairman
`Clive R. Clayton, Secrelary-Treasurer
`Robert S. Alwitt, Advisor
`
`Dielectric Science and Technology Division
`R.L. Opila, Chaérman
`RK. Ulrich, Vice-Chairman
`C. Reidsema-Simpson,Secretary
`Henry G. Hughes, Treasurer
`Hisham Z. Massoud, Advisor
`
`Electrodeposttion Diviston
`_ John Dukovic, Chairman
`Thomas P. Moffat, Vice-Chairman
`Madhav Datta, Secretary-Treasurer
`Mark D. Allendorf, Advisor
`Electronics Division
`Hisham 7. Massoud, Chairman
`Janet L. Benton,First Vice-Chairman
`Richard B. Fair, Second Vice-Chairman
`CorL, Claeys, Secretary
`‘ThomasJ. Shaffner, 7reasurer
`Katsumi Niki, Advisor
`
`Energy Technology Division
`Kimio Kinoshita, Chairman
`Margaret A. Ryan, Vice-Chairman
`Robert B. Swaroop,Secretary
`Thomas F Fuller, Treasurer
`Walter van Schalkwijk, Advisor
`
`Fullerenes Group
`Karl Kadish, Chairman
`P.\. Kamat,Vice-Chairman
`S.R. Wilson,Secretary
`Shekhar Subramoney, Treasurer
`William H. Smyrl, Advisor
`
`High Temperature Materials Division
`Mark D.Allendorf, Chairman
`Steven J. Visco, Senfor Vice-Chairman
`Steven L, Russek,Junior Vice-Chairman
`Femando Garzon,Secrefary-Treasurer
`John P. Dismukes, Advisor
`
`Industrial Electrolysis and
`Electrochemical Engineering Division
`James M. Fenton, Chairman
`Clifford W. Walton, Vice-Chairman
`P.C. Foller, Secretary-Treasurer
`Robert $. Alwitt, Advisor
`
`Iuminescence and Display Materials Division
`Alok M. Srivastava, Chairman
`Comelis R. Ronda, Vice-Chairman
`V. Butchi Reddy, Secretary
`Lauren Shea, Treasurer
`Walter van Schalkwijk, Advisor _
`
`Organic and Biological Electrochemistry Division
`Franklin A Schultz, Chairman
`Jean Lessard, Vice-Chairman
`KatsumiNiki, Secrelary-Treasurer
`Hisham Z. Massoud, Advisor
`
`Physical Electrochemistry Division
`Shimshon Gottesfeld, Chairman
`Andrzej Wieckowski, Vice-Chairman
`Johna Leddy, Secretary-Treasurer
`Katsumi Niki, Advisor
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`Sensor Division
`Petr Vanysek, Chairman
`PeterJ. Hesketh, Vice-Chairman
`Joseph R. Stetter, Secrelary-Teasurer
`John P. Dismukes, Advisor
`
`Page6 of 14
`
`Gravitational Stress-Induced Dislocations in Large-DiameterSilicon
`Wafers Studied by X-Ray Topography and Computer Simulation
`H. Shimizu, 8, Isomae, K. Minowa, T. Satoh, T. SUZURG vesssssiessssinsessesssssuseessusessseesseressst2523
`Boron in Polycrystalline Si,,Gey_,. Films.
`Phase Diagram andSolid Solubility
`D. Mangelinck, P-B. Hellberg, S.-L. Zhang, FM. @'HEUTE ..essessssssessssninsseesssesesssesnen2530
`Enhanced Diffusion of Boron in Si during
`Doping from Borosilicate Glass
`M, Miphe....ssssosssersssscsssvnsessscsssssseesnsssresensnssessonnessscsansccsssanesonssanaaussocosasessonsssssaressneasansonves2534
`Barrier Properties of Very Thin Ta and
`TaN Layers Against Copper Diffusion
`M. T. Wang, ¥. C. Litt, Mo C. CQ vescscesesssessssecssseseseessseeesnssssessssesseerssennseessessnseesvassuneesneds2538
`Investigation of Boron Penetration Through Thin Gate
`Dielectrics Including Role of Nitrogen and Fluorine
`M. Navi, S. T. DURDQM ceesceseescesvesvecrsssessesnesnesssavessesseseeaveseesesnesnassanesesieuesneesaeusanennesensnenees2545
`
`Evaporation of Oxygen-Containing Species
`from Boron-DopedSilicon Melts
`S. Maeda, M. Kato, K. Abe, H. Nakanishi,
`
`K. Hoshikawe,, K. TerasBtrnd vesvessessessvssvsssssvsvvssversssvsnvsseessenseesspeucensarsaseesaseusaeeseearsnsansavessaes 2548
`Electric Properties of [(Zr02)9g(Ce02)p219,9(Ca0)94 Solid Solution
`. K-t. Kawamura, K. Watanabe, Y. Nigara,
`
`A. Kama, 7. Kawada, J. Mizusari..cecccceccccccccccscesvssessesssvevesesvessavenssssesnsvescevessassnesecserseeses2552
`
`Chemical Reactions in Plasma-Assisted Chemical Vapor
`Deposition of Titanium
`Y. Obshita, Ko WAIGMADE ceececescecccssssesessecsessesessvesesesscssesesssesvsveavsrcessvavereavayeavansusasasevsnesessees 2558
`
`High Temperature Barrier Electrode Technology for High
`Density Ferroelectric Memories with Stacked Capacitor Structure
`5. Onishi, M. Nagata, S. Mitarai, Y. Ito, J. Kudo, K. Sakiyama,
`
`S. B. Desu, H. D. Bhatt, D. B Vijay, ¥. Hwang...sessuceuresnecnnecanessieraeearessesanecanesssecsvensen2563
`Irregular Surface and Porous Structure of Si0Films Deposited
`at Low Temperature and Low Pressure
`E N. Dulisev, L. A. Nenasheva, L. L. VASIpCU0....ccccsssesessessssssssssscectssesssiesssssesessessessessesesnees 2569
`Electron Field Emission from Chemical Vapor Deposited
`Diamond Films
`A. N. Obraztsov, |. Yu. Pavlousky, A. P. Volkov, B. V. Rakova, 8, P. NagovitsyMt cores2572
`SiOF Film Deposition Using FSi(OC2H5)3 Gas in a Helicon
`Plasma Source
`
`S.-M. Yun, H.-Y. Chang, K.-M. Lee, D.-C. Kitt, C.-K. ObObcesssceccsssscsccsssssesssvessssssssessssssssvessess 2576
`Growth of III-Nitrides on ZnO, LiGa0, and LiAl02 Substrates
`J. D. MacKenzie, S. M. Donovan, C. R. Abernathy, 8. J. Pearton,
`PH. Holloway, R. Linares, J. Zavada, B. Cbd: ....cccsccscsssssssssssssssassssesesesvessesssssassussseeeeeiee 2581
`Copper Dry Etching with Cl/Ar Plasma Chemistry
`J. W. Lee, ¥. D. Park, J. R. Childress, S. J. Pearton, F Shariff, FROM osccccsscvvveeseeeeveceenseee2585
`Impact of Iron Contamination and Roughness Generated
`in Ammonia Hydrogen Peroxide Mixtures (SC1) on 5 nm Gate Oxides
`S. De Gendt, D. M. Knotter, K. Kenis, PW. Mertens, MoM. Heysciccccsscsosssssssssssennvsennee2589
`Impact of High-Temperature Dry Local Oxidation
`‘
`on Gate Oxide Quality
`P Belltttli, N. ZOPTo.ceecseesseessseesnsssssssesssvissesseusssssniasessssssvenssianessansessensnanieuseeesssee2595
`Detection of Metallic Contaminants onSilicon by Surface
`Sensitive Minority Carrier Lifetime Measurements
`G. J. Norga, M. Platero, K. A. Black, A. J Reddy,
`J Michel, L. C. Kitmerling ...essossscsscsssvsessssunessssesisssssssssssssssssssiasssssnsssisnassuseenesss2602
`INSEPUCHIONS 10AUKBOPS ..ecceorsisssssseriussesiesseesossssissssssesusssesessssceessssussnsussiunesanesss566
`
`Page 6 of 14
`
`

`

`Barrier Properties of Very Thin Ta and TaN Layers
`Against CopperDiffusion
`M.T. Wang,Y. C. Lin, and M. C. Chen*
`Department of Electronics Engineering, National Chiao-Tung University, Hsinchu, Taiwan
`
`ABSTRACT
`
`Diffusion barrier properties of very thin sputtered Ta and reactively sputtered TaN films used as a barrier layer
`between Cu and Si su strates were investigated using electrical measurement and materials analysis. The Cu/Ta/p*-n
`junction diodes with the Ta barrier of 5, 10, and 25 nm thicknesses were able to sustain a 30 min thermal annealing at
`temperatures up to 450, 500, and 550°C, respectively, without causing degradation to the device's electrical characteris-
`tics. The barrier capability of Ta layer can be effectively improved by incorporation of nitrogen in the Ta film using reac-
`tivesputtering technique. For the Cu/TaN/p*-n junction diodes withthe TaNbarrier of5, 10, and 25 nm thicknesses, ther-
`malstabilitywas able to reach 500, 600, and 700°C,respectively. Wefound that failure of thevery thinTa andTaNbarriers
`wasnot related to Ta silicidation at the barrier/Si interface. Failure of the barrier layer is presumably due to Cu diffu-
`' sion through the barrier layer during the process of thermal annealingvia local defects, such as grain boundaries and
`stress-induced weak points.
`
`of ultrathin (less than 30 nm) Ta and TaN films using the
`electrical measurements as well as material analyses. As
`the device dimensions move to 0.25 um and below, it
`becomes inappropriate to use a barrier thicker than 30 nm.
`Thebarrier thickness should be reduced to lower the resist-
`ance of the total line interconnect and/orvia.
`In this study, we investigated the thermal stability of
`ultrathin Ta and TaN barrier layers in a Cu metallization
`system. Properties of these barrier layers were evaluated
`by electrical measurement as well as material analyses.
`The results of this study might be useful for Cu metalliza-
`tion in ultralarge-scale integrated (ULSI) multilevel inter-
`connects applications.
`
`Introduction
`Copper (Cu) has attracted much attention in deep sub-
`micron mutlilevel interconnection applications because of
`its low bulkresistivity (1.68 © cm), excellent electromi-
`gration resistance,’? and acceptability of deposition by
`electroless as well as chemical vapor deposition (CVD).**
`Unfortunately, Cu diffuses fast in silicon,silicide, as well
`as oxide, and forms Cu-Si compoundsat temperatures as
`low as 200°C,resulting in degradation of device character-
`istics.*” Moreover, it has poor adhesionto interlevel dielec-
`tric and drifts through oxide underfield acceleration.*
`Therefore, a diffusion barrier between Cu and its underly-
`ing layers is considered as a prerequisite for Cu to be use-
`ful in silicon integrated circuit applications,
`Various materials have been studied as a diffusion bar-
`rier between Cu and Si substrate, as well as Cu and dielec-
`tric layer. Refractory metals have been recognized as an
`attractive class of materials becauseof their high thermal
`stability and good electrical conductivity."Sputtering of
`nitride-based diffusion barriers, such as WN4 TiN,
`TiWN,"*" and TaN,"to be used in Cu/barrier/Si and
`Cu/barrier/SiO, structures, has attracted extensive atten-
`tion. Tantalum (Ta) forms no compound with copper; thus,
`Cu/Ta/Si, structure is expected to be stable at high tem-
`peratures.”*” In addition, because Ta has a low formation
`enthalpy (AH) with nitrogen, and tantalum nitride (TaN)
`has a high melting point of 3087°C as well as a more dense
`microstructure, Cu/TaN/Si structure is also expected to be
`thermally stable at elevated temperatures.”* In this work,
`we investigate Ta and TaN as a diffusion barrier in Cu
`metallization system.
`It was reported that a Ta film of 50 nm thickness acting
`as a diffusion barrier between a Cu and Si structure
`retained the integrity of the Cu/Ta/Si structure at temper-
`atures up to 600°C for 30 min.”It was also reported that a
`TaN film of 100 nm thickness was able to act as an effec-
`tive diffusion barrier between Cu and Si substrate at
`750°C for 60 min.”* Moreover, it was found that an Ar* ion
`bombardment during deposition of Ta resulted in a dense
`Ta film with low resistivity, and thus the barrier effective-
`ness of Ta film was significantly enhanced.2? Although
`these studies have provided much valuable information
`for the application of Ta film as a diffusion barrier, never-
`theless, little study has been made on the evaluation of
`barrier effectiveness with respect to the devices’electrical
`characteristics, which is believed to-be more sensitive to
`barrier degradation than the material property.'* Moreover,
`though a numberofdata are already published on the ther-
`malstability of Ta and TaNfilms thicker than 30 nm using
`the characterization techniques of material analysis, no
`comparative study has been made on the thermal stability
`* Electrochemical Society Active Member.
`2538
`
`Experimental
`The Cu/Ta/p*-n and Cu/TaN/p*-n junction diodes were
`fabricated for the study of Ta and TaNbarrier capability.
`The starting materials were 4-in., (100)-oriented, n-type
`silicon wafers with 4-7 Q cm nominal resistivity. After
`RCA standard cleaning, the wafers were thermally oxi-
`dized at 1050°C in steam atmosphere to grow a 500 nm
`oxide layer. Diffusion regions with areas 500 < 500 and
`1000 Xx 1000 4m* were defined on the oxide-covered
`wafers using the conventional photolithographic tech-
`nique. The p*-n junctions with junction depths of 0.3 »m
`were formed by BF; implantation at 40 keV to a dose of
`3 x 10" cm™followed by furnace annealing at 900°C for
`30 min in N, ambient,
`After the junctions were formed, the wafers were pre-
`pared for Ta or TaN barrier layer deposition. In this study,
`a de magnetron Sputtering system with a base pressure of
`I-2 X 10°* Torr and with no intentional substrate heating
`and bias was used. The Ta films were sputtered using a Ta
`target in Ar ambientat a pressure of 7.6 mTorr, while the
`TaNfilms were reactively sputtered using the same Tatarget
`in an Ar/N, gas mixture at the same pressure of 7.6 mTorr.
`The flow rates of Ar and N,into the sputtering chamber
`were 24 and 6 scem, respectively, for making the Ar/N, gas
`mixture.” Prior to each sputter deposition, the target was
`cleaned by presputtering with the shutter closed for 10 min.
`The Ta and TaN films were deposited at a sputtering
`powerof 200 W to a thickness of 25, 10, and 5 nm sepa-
`rately. The deposition rates of Ta and TaN films were
`determined to be 2.94 and 2.07 nm/min, respectively. After
`the barrier layer deposition, Cu films of 200 nm thickness
`were deposited on the barrier metal using the same sput-
`tering system without breaking the vacuum.Finally, Cu
`patterns were defined and etched using dilute (5 vol %)
`HNO), while Ta and Tanitrides were etched using SF,/N,
`Plasma for the preparation of Cu/Ta/p*-n and Cu/TaN/p*-
`n diodes. For comparison, the thermal stability of Cu/p*-n
`diodes without a barrier layer as well as Ta/p*-n and
`TaN/p*-n diodes without a Cu overlayer wasalso investi-
`J. Electrochem. Soc., Vol. 145, No. 7, July 1998 © The Electrochemical Society, Inc.
`
`°
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`
`

`

`
`
`J. Electrochem. Soc., Vol. 145, No. 7, July 1998 © The Electrochemical Society, Inc.
`
`2539
`
`Cu/Ta(25nm)/p'-n
`
`Cu/Ta(10nm)/p*-n
`
`Cu/Ta(Som)/p*-n
`
`(%)
`Frequency
`
`gated. The schematic cross sections of these differently
`metallized p*-n junction diodes are illustrated in Fig. 1.
`To investigate thermal stability of the Cu/Ta/p*-n and
`Cu/TaN/p*-n diodes, the diodes were thermally annealed at
`various temperatures ranging from 200 to 800°C for 30 min
`in N, ambient. Leakage current was measured at a reverse
`bias of —5 V using an HP-4145B semiconductor parameter
`analyzer; the measured diodes have an active area of 500 x
`500 or 1000 X 1000 ym, and at least 30 diodes were meas-
`ured in each case. For material analysis, unpatterned sam-
`ples of barrier/Si, Cu/barrier/Si, and Cu/barrier/SiO,/Si
`structures were also prepared. These samples were processed
`in the same process run with the patterned samples of junc-
`tion diodes except a numberof thicker Ta and TaN samples
`of Ta/Si and TaN/Si specialized for X-ray diffraction (XRD)
`analysis. Sheet resistance of the multilayer structures was
`measured using a four-point probe. XRD analysis using a
`30 keV copper Ka radiation was used for phase identifica-
`tion. Scanning electron microscopy (SEM) was employed
`to observe surface morphology and microstructure.
`Results and Discussion
`Electrical measurements.—Barrier capability of thin Ta
`and TaN films was investigated by evaluating the thermal
`stability of Cu/Ta/p*-n and Cu/TaN/p*-n junction diodes
`LA
`10° 10107104 19°10103 107104107104105104107=10710107104 10° 10410"
`using electrical measurements. We analyzed the distribu-
`tions of leakage current density for the annealed diodes
`and related the results of electrical measurements to other
`results obtained by sheet resistance measurement, XRD
`analysis, and SEM observation.
`Cu/Ta/p*-n junction diodes.—Figure 2 illustrates the sta-
`tistical distributions of reverse bias leakage current densi-
`ty measured at —5 V for the Cu/Ta(25 nm)/p*-n, Cu/Ta
`(10 nm)p*-n, and Cu/Ta(5 nm)/p*-n junction diodes
`annealed at various temperatures. The Cu/Ta(25 nm)/p*-n
`diodes remained stable after annealing at temperatures up
`to 550°C but suffered moderate degradation in electrical
`characteristic at 600°C; annealing at 650°C resulted in
`severe degradation (Fig. 2a). For the Cu/Ta(10 nm)/p*-n
`diodes, the diodes remained stable after annealing at tem-
`
`
`
` ZY
`
`Leakage Current Density (A/cm?)
`Fig. 2. Histograms showing
`thedistributions of reverse bias
`leakage current density for fa) Cu/Ta(25 nm)/p*-n,
`(b) Cu/Ta
`(10 nm}/p*-n, and(c) Cu/Ta(5 nm)/p*-n junction diodes annealed
`at various temperatures.
`
`peratures up to 500°C, while a numberof diodes suffered
`moderate degradation after annealing at 550°C; however,
`about 50% of the diodes survived even after annealing at
`600°C (Fig. 2b). As for the Cu/Ta(5 nm)/p*-n diodes, they
`started to show degradation after annealing at 500°C
`(Fig. 2c). This indicates that
`thermal stability of the
`Cu/Ta/p*-n junction diodes may be severely degraded by
`reducing the Ta barrier layer thickness below 5 nm.
`
`Cu/TaN/p*-n junction diodes—The barrier properties of
`Ta can be significantly improved by adding impurities,
`such as N and O, to the Ta film."®”*If solubility limit of the
`impurity is exceeded, solute atoms in the Ta grain are
`expected to be segregated to the grain boundaries,result-
`. ing in obstruction of the fast paths for copper diffusion.It
`was reported that the grain size and atomic density of
`reactively sputtering deposited Ta-N films, respectively,
`decreased and increased as the nitrogen concentration in
`the Ta_N films was increased; moreover, the bec-Ta, Ta,N,
`TaN, and Ta,N, phase appeared in succession with the
`increase of the nitrogen content.’’ In addition, TaN is
`chemically inert to Si and Cu, and it has been reported
`that the contact system of Cu/TaN/Si is thermally very
`stable.“ The superiority of TaN films in thermalstability
`over the pure Ta film wasalso reported.”
`Figure 3 showsthe statistical distributions of reverse
`bias leakage currentdensity for the Cu/TaN/p*-n junction »
`diodes of different TaN barrier thickness annealed at var-
`ious temperatures. For the diodes with a 25 nm thick TaN
`barrier, the devices remainedstable after annealing at tem-
`peratures up to 700°C. After annealing at 750°C, though
`many devices failed, more than half of the tested diodes
`still survived (Fig. 3a). This feature of failure is probably
`related to the Cu diffusion through localized defects in the
`annealed TaNlayer. For the diodes with a 10 nm thick TaN
`barrier, the devices suffered moderate degradation after
`annealing at 650°C and degraded severely after annealing
`at 700°C (Fig. 3b). For the Cu/TaN(5 nm)/p*-n diodes, the
`5 nm TaN film was proved to be an effective barrier
`against Cu diffusion at temperatures up to 500°C. As the
`annealing temperature was raised to 550°C, the diodes
`started to show degradation (Fig. 3c). Comparative results
`
`
`
`Cu/p*-n diode
`
`Ta or TaN (50nm)
`
`
`
`Ta/p*-n or TaN/p*-n diode
`
`Cu
`
`Ta or TaN
`(5, 10, and 25 nm)
`
`
`
`
`
`>
`
`
`
`
`
`Cu/Ta/p*-n or Cu/TaN/p*-n diode
`Fig. 1. Schematic cross sections of (a) Cu/p*-n, (b) barrier/p*-n,
`and {c) Cu/barrier/p*-n junction diodes.
`
`Page 8 of 14
`
`Page 8 of 14
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`

`

`J. Electrochem. Soc., Vol. 145, No. 7, July 1998 © The Electrochemical Society, Inc.
`
`CwTaN(2S5nm)/p*-n
`
`CwTaN(10nm)/p*-n
`
`Cu/TaN(5nm)/p*-n
`
`Cu/p*-n
`
`3
`
`Ta(50om)/p’-n
`
`TaN(SOnm)/p*-n
`
`(c,)
`
`As-deposited eoB&BESS
`
` Frequency
`(%)
`
`2540
`
`
`
`Frequency(%)
`
`S
`
` 10710*30710%10% 10410—401074
`
`
`10° 107107}0*10% 1010
`3
`10*10%104109
`1010410710107 10107
`10101010107 10" 103
`10710*10"30%107 307 107
`
` °-2*ese
`
`Leakage Current Density (A/cm?)
`Fig. 3. Histograms showing the distributions of reverse bias
`leakage current density
`for (a) Cu/TaN(25 nm