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`

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`
`-
`
`Addresschangu: Notineoiadung in addrrsshould besent
`bthe Cttuihtton Department, The Elecllochanitnl Society, tn.-_,
`'°5°"“"4=*"3M Penninm NJ08534-7396. use include
`tlemailinglabelorthenunterhomtlnmnilinglabelfiomyou;
`Previotislstieattiiejourndtoenstireproperirierrttit-,m(,.1_
`
`Spectroelectrochemicai Studies of indium
`liexacyanofen-ate Electrodes Prepared by
`the sacrificial Anode Method
`
`IC-C. Ha, ].-C Chen.....................................................; .............................
`Modification of the Lithium Metal Surface
`_' by Nonionic Polyether Surfactants:
`Quartz Crystal Microbalance Studies
`M Marl, if Namoka, K Nam‘, D. Fauleux ...................................................................... ..2340
`
`......................2334’ V
`
`Electrochemical Synthesis of Urea at Gas-Diflusion Electrodes.
`IV. Simultaneous Reduction of Carbon Dioxide and Nitrate
`Ions with Various Meta! Catalysts
`
`M. Sbibala, K Yosbida, N. Furuya .................................................................................. ..234’8
`
`Characterization of High-Surface-Area Electromtalysts
`Using a Rotating Disk Electrode Configuration
`7.'].Sc/2m1'dl,H.A. 6astet;ger,G.D..S‘tz'ib,RM. Urban,
`
`D. M. Kalb, R. 1. Bebm .........................................................
`Water iilectnolysis Using Diamond ‘thin-Film Electrodes
`Mlmi3~uki,E. TaIzabasIn',M. 7byoda,7.'Kums~u,Mlida,
`
`......................................... -2354
`
`S. Wakila, X Nisllilei, 7.‘ Sbimamune ................................................................................ .2358
`
`The Mechanism of Blectropoiishing of Titanium
`,
`in Methanol-Sulfuric Acid Electrolytes
`0. Px'om9u2.s'ln‘, C. Madore, D. Landolt ...............................................................................2362
`
`Electrochemical Behavior and Surface Morphologic Changes of Copper
`Substrates in the Presence of 2,5—Dimercapto-1,5,4-thiadiazole.
`In Situ EQCM and Phase Measurement Interferometric Microscopy
`
`Q. Cbi, 7.‘ Yéwuma, M. Ozakz‘, 7.’ Sotomura, IV. Oyama .................................................... .2369
`
`Super Dense Licz as a High Capacity
`Li intermlation Anode
`
`'
`
`C. Birzal-a, V.A Nalimom, D. E Slelowky, Z Benet, J. E Fitcber.....‘................................. ..2377
`Photochemical and Photoelectrochemicai Behavior
`
`of a Novel Tioz/Ni(0l-[)2 Electrode
`R. lmsteati, 7.’ Richardson, 1: Mclamon .......................................................................... ..2380
`
`Quartz Crystal Microbaianee lnvestigtion
`of Electrochemical Calcium Carbonate Scaling
`C. Gabrielli, M. Ieddam, A. Matti, G. Maurin,
`
`....................................................... .3386
`H. Pen-oi, R. Roster, M. Zialoune ............................
`Passivity and Breakdown of Carbon Steel in Organic Solvent Mixtures
`of Propylene Carbonate and Dimethoxyethanc
`D- 4- 3119785]. Kmger; R]. Moran ...................................................................................2396
`. The Impact of the operation Mode on Pattern
`Formation in Electrode Reactions.
`Prom Potentiostatic to Caivnnostatic Control
`N Mazouz G. Havgen, K meter, 1. G. Iceure/ms............................................................24o4
`
`‘
`
`'“fl”°“°° °f Ni“'°2en-Containing Precursors on the lllectrocatalytic Activity
`-
`°f “°“'T"°3‘°d 1'40“): 0|! Carbon Black for 02 Reduction
`R. wré. G. lakmde. D. Guay, 1. 2 Dodelel, c. Dénés ........................................................2411
`Study of the Structural Change Due to Heat-Treatment
`in High Resistivity Electroless Nil’C Film
`T OW, T Higasbilzawa, A Itzu/ga, M. rm; M. Kim ....................................................-2419
`Prediction of Li lntercalation and Battery Voltages
`in Layered vs. Cubic Lixcooz
`5- Wdwfiofl, A Zmzger ...................................................................................................2424
`Gas Conversion Impedance: A Test Geometry Effect
`in Charaeterlntion of Solid oxide Fuel cell Anodes
`5- Pfimda/J1, M. Mogensen ................................................................................................2431
`
`"
`
`Page 4 of 14
`
`Page 4 of 14
`
`

`
`Solid-State Science and Technology
`
`Change in the Environment of Hydrogen in Porous Silicon
`with Therrnal Annealing
`if H. Ogata, R Mo, 1.‘ Ziuboi, T Sakka ...........................................................................2439
`
`Room Temperature Operating Solid-State Sensor for Chlorine Gas
`if Niizekl, S. siribata .......................................................'..................................................2445
`
`Incorporation of Cadmium Sulfide into Nanoporous Silicon
`by Sequential Chemical Deposition from Solution
`M. Gros—jaan, R. Herino, D. Léncot ..;.................................................................................24’48
`
`Elfect of the Gas-Phase Reaction in Metallorganic Chemical Vapor
`Deposition of ‘IN from ’l‘etrakis(dirnethylamido)titanium
`J.-I’. Yun, M.-if Park, S.—li'{ Rbee ...................................................................................... ..24'53
`Fibrous and Porous Microstructure Formation
`
`in 6H-Sic by Anodization in HF Solution
`W Shin, 7.‘ Hilzoealea, W-S. Sea, H. 5. Am, N. Sawalei, K Koumoto......................................2-456
`
`- Dry Etching of Srs Thin Films
`j. W Lee, M. R. Davidson, B. Patixmgey, P. H. Holloway, S. J. Pearton.............................. ..246I
`Trlhochernical Reactions of Silicon:
`An In situ Infrared Spectroscopy Characterization
`V.A. Muratov, ]. B. Olren, B. M. Gallarls, 73 E. Fischer; 1. 6. Bean ........................................2465
`
`High—Temper-ature Diffusion of Hydrogen
`.
`and Deuterium in Trtaniurn and 'l'i3Al
`S. Nailo, M. Yamamoto, M. Dar‘, M. Ifimura .................................................................... ..247I
`Photoluminescence Studies of cadmium selenide Crystals in
`Contact with Group III Trialkyl Derivatives
`E j. Winder, 7.’ E I(uedJ, A 3. Ellis ..................................................;.................................2475
`
`‘
`
`Reduction in Contact Resistance with in situ 02
`Plasma Treatment
`
`'
`
`1C Yonelzura, S. Sakamorl, K Itzzwal, H. Miyatalze............................................................ ..2480
`Measurements of vocs with a Semiconductor Electronic Nose
`
`M. c. Hm-fillo, 1. Getino, L Arés, 1. 1. Robla,
`
`I. Sayago, E ]. Gutr'e’n-ez ...................................................................................................2486
`Interface States Distribution in Electrical Stressed
`
`«
`‘
`Oxynitrided Gate-0xide
`S. Belkoucb, 7.‘ K Nguyen, L. M. landsberger; C. Aktrlb,
`
`6’. Jean, M. l(’aIJrt'zi ............................................................................................................2489
`
`Design of Injection Feed Multiwafer Low-Pressure
`Chemical Vapor Deposition Reactors
`1.. Zambov, C. Poporz, B. Ivamv .........................
`
`............................................................2494
`
`Aqueous KOH Etching of Silicon (1 10).
`Etch Characteristics and Compensation Methods for Convex Corners
`8. Kim, D.-i. D. Clio .........................................................................................................2499
`
`Amorphous Hydrogenated Silicon Films for
`Solar Dell Application Obtained with 55 kHz
`Plasma Enhanced Chemical Vapor Deposition
`
`B.G.Budaguan,AA.Sbercbenl2ov,D.A.5¥r3rabiIev,A.l{Sazonor;,
`
`A. G. Radoselirlry, V. D. Cbemomordic, A. A Popor/,1. W Meoelaar ....................................2508
`
`Dry Etch Patterning of l.aCaMn03 and Smco Thin Films
`j.j. Wang,].R. Clrildrmr,.‘>‘._].Pea11on,i«7S}Jargfi,IC!rl.Dabmen,
`
`E. S. Gillman, E]. Caaleu, R. Ram’, X Qian, L. Chen....................................................2512
`Growth Kinetics of Chemical Vapor Deposition
`of p-sic from (CH3)2SiCl2/Ar
`7.' Ikgo, M. Karmse, if Yasbrlmra, K Hashimotv..................
`
`.............................................25I6
`
`- Page 5 of 14
`
`
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`Philip ltemrdr
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`North Carolina State University
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`University ol Calilornll. San Diego
`Ialolla. Califomia 92093-041 1. USA
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`lobinA.Susko
`IBM Corporation
`Endioott, New York 13760. USA
`fieaturcr
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`University of Arltansrrs
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`Executive Direrarr
`
`'
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`

`
`Divisions and Groups
`
`ta:-my mmm
`Curtis E Holmes. Cbnitman
`Subbaraosurampudi, WOI~(MI'mIM
`James S S/maiski, Secretary
`Fslher S. Talteuchl, Mwunr
`Milk D. Allcndorf, Ada/iaor
`
`Corrosion Division
`Marlin W. Ktndlg, Chairman
`Patrick]. Moran, Vt‘aL(.ta:'rman
`Clive ll." Clayton, Seauaryirmwer
`Roben & Alwitt, Adzuw
`
`Dielectric science and Technology Division
`IL L Opilz, damn
`it K Ulrich. liascbairman
`C. lleidsam-sin'gson,sawIaoy
`Henry 6. Hughes, Illwurer
`Hlslum Z Masoud, Adam-
`
`Blecirodepofliloii Division
`
`Ilnotnas P. l/olfat, lizectaimian
`Madhav Dam, .9aoeIaay7l-comer
`Mark D. Allendmi. Advimr
`Electronics Division
`Hisham 7, Massoud, alairman
`Janet L Benton, Fin‘! We-Cbainnan
`Ridtanl B. Fall‘. Second Vice-Gunman
`(‘or L C1aey:,Szaular_y
`Thomas]. Shnllhei; Tlmnmr
`Katsuml Niki, Aabbor
`
`Energy Tednlology Division
`lfimio Kinmhila. avairman
`Margaret M Ryan. Via-duirman
`Robert ll. Smmop, Sazetmy
`Thomas E Fulbc Ilwuur
`Waller van Schalkwijlt, Mu'a7r
`
`Fuller-mes Group
`Karl Kadish, drainnan
`P. V. Katnll. Wat-(.'bu:’rman
`S. R. Wilson, Saaefmy
`shekhu Sulnamonq, Ylwmr
`William ll. Smyll, Adviser
`
`lligb Teiupenun Materials Division
`Mail: D. Allzndod. abaimm
`Steven]. Vlsoo,Sailor Va-(.‘bairman
`Slum l.. Rusehjuntbr Vim-(.‘baz'nnan
`Femando Gama. krwmy-Timmy
`john I’. Dlsmultes, Mum-
`
`lnlusirlal Eleclmbcis and
`Hcdrocbuniul Engiuuriig mam
`Janus M. Fenton. azairman
`Clifiotd W. Walton, Woe-daalrmau
`12 t‘. Fol|en5'aa'eIa:y-Trmirer
`Robert S. Alwltt. Adwimr
`
`luminescence and Display Materials Division
`Molt M. Stivastavn. mdrman
`Carells R. Rofllii. Wahchairman
`li Butch! lledrly.Sa:rniary
`Laulen Shea, lhnmw
`walvemn Sdulkwijk, Muisor _
`
`Organic and Biological Blectroabernlstrypiusmg
`Franklin A Schultz, (Jainmm
`Jeln 152111., Woo-aninnm
`Knsumi Niki. Saamry-Iimmw
`I-iislnm 7. Massoud, Aalaiiur
`
`Pbysiul Blectrocbanistoy Division
`Shimshun Gomeslekl. dniman
`Andml Wleckowsld, Wm-(.‘bainnan
`Johna ledily, Saaelaiy-Imwzrar
`Iiamml Niki. Aalzlibr
`Sensor Division
`Petr Vanysek, daairman
`Peter} Hdwlh. Viaedminnan
`1089911 It Stem. Secretaiy-mamm
`John B Dlsmllkfi. Aduirar
`
`Page 6 of 14
`
`Gravitational Stress-Induced Dislocations in Large-Diameter Silicon
`Wafers Studied by x-Ray Topography and Computer Simulation
`H. Sbimizu, S. lsomae, K Minowa, 7.’ Satob, 7? Suzuki .................................................. ..-.2523
`
`Boron in Polycrystalline SixGe1_x Films.
`Phase Diagram and Solid solubility
`D. Mangelindz, R-E. Hellberg S.-L Zlumg, E M. d’Heurle ................................................2530
`
`Enhanced Diffusion of Boron in Si during A
`.
`Doping from Borosilicate Glass
`M. Miyalee........................................................................................................................ "253-I
`
`Barrier Properties of Very 'I‘hin Ta and
`TaN Layers Against Copper Diffusion
`
`M. 73 Wang, K 6. Lin, M. C. Cben .................................................................................... ..2538
`
`Investigation of Boron Penetration Through Thin Gate
`Dielectrics Including Role of Nitrogen and Fluorine
`
`M. Navt,_.S‘. 7.‘ Dunbam......................................................................................................2545
`Bvaporation of Oxygen-Containing Species
`from Boron-Doped Silicon Melts
`S. Maeda, M. Kato, K Abe, H. Naéanisbi,
`
`K Hosbiéawa, K krasbima ............................................................................................ .2548
`
`Of [(Z1'02)0.8(Ce02)o_2]0_9(Ca0)0'_1 solid Solution
`Electric
`- K-1'. mwamura, K Watanabe, K Nigara,
`
`A mm, 7.’ lmwada, J. Mizusabi............................................ ...............................; ........_2552
`chemical Reactions in Plasma-Assisted Chemical Vapor
`Deposition of Titanium
`if Obsbila, K Watanabe ....................................................................................................2558
`
`High Temperature Barrier Electrode Technology for High
`Density Fer-roelectric Memories with Stacked Capacitor Structure
`
`.1 Onisbi, M Nagala, s. Mitami, K Ito, 1. Kudo, K Salziyama,
`
`...................................................... ..2563
`S B. Dam, H. D. Bbalt D. R Vijay, If Hwang..........
`Irregular surface and Porous structure of Sioz Films Deposited
`at Low Temperature and Low Pressure
`
`1? N. Dultteu L A Nenasbwa, L. L Vas1'.’yeva .................................................................. .2569
`Electron Field Emission from Chemical Vapltr Deposited
`Diamond Films
`
`A N. Obraztsav, 1. Yu. Pavlovsky, A R Volkou, E. V Rakova, .1 R Nagovitsyn ....................2572
`Si0F Film Deposition Using FSi(0C2H5)3 Gas in a Helicon
`Plasma source
`
`Yzm, H.-Y Cbmzg,'l(-M. lee, D.-C. Kim, C.—K Cboi.................................................. ..2576
`
`Growth of Ill-Nitrides on no, LiGa0z, and mm, Substrates
`J. D. Macltenzieg S. M. Donovan, C. R. Abematlry, S. j. Pear-km,
`
`R H. Holloway, R. Limret, J. Zawda, B. (lbai ..................................................................258!
`
`.........-2535
`
`Copper Dry Etching with C12/Ar Plasma Chemistry
`1- W lee. K 0. Peru. R. Cbildress, s. 1. Pearton, I-.' Sbarfi, R Ren .......................
`Impact of Iron Contamination and Roughness Generated
`in Ammonia Hydrogen Peroxide Mixtures (SC!) on 5 nm Gate Oxides
`S. De Gendt, D. M Knotfer, K lens, 2 WMerIens, M M. Hgrns......................................-2589
`Impact of High-Temperature Dry local oxidation
`on Gate oxide Quality
`-
`2 Beuuttx; N. mm’..........................................................................................................-2595
`' Detection of Metallic Contaminants on Silicon by Surface
`Sensitive Minority Carrier Lifetime Measurements
`6.]. Norga, M. Platero, KA. Black, 11.]. Redajl,
`1. Midiel, L. c. Iemerhng ..................................................................................................2602
`
`Instructions toAuthors .......................................................................................................566‘
`
`Page 6 of 14
`
`

`
`Barrier Properties of Very Thin To and pTaN Layers
`Against Copper Diffusion
`C
`
`M. 1; Wang, Y. c. Lin, and M. c. Chen’
`Department of Electronics Engineering, National Chiao-Tung University, Hsinchu, Taiwan
`
`ABSTRACT
`Diflusion barrier properties of very thin sputtered Ta and reactively sputtered 'I‘aN films used as a barrier layer
`strates were investigated using electrical measurement and materials analysis. The Cu/‘I‘a/p -n
`junction diodes with the 'l‘a 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 chara
`cteris-
`' ties, The barrier capability of Ta la er can be effectively imp
`_
`_
`roved by incorporation of nitrogen in the la film using reac-
`C}i'i,/'l‘aN/p’-n junction diodes with the TaNbarrier of5, 10, and 253 nm thicknesses, ther-
`tive sputtering technique. For the
`mal s
`ability was able to reach 500, 600, and 700°C, respectively. We found that failure of the very thin Ta and 'I'aN baniers
`_ was not 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 annealing via 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 pm and below, it
`becomes inappropriate to use a barrier thicker than 30 nm.
`The barrier thickness should be reduced to lower the resist-
`ance of the total line interconnect and/or via.
`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.
`.
`
`Experimental
`The Cu/Ta/p*-n and Cu/TaN/p‘-n junction diodes were
`fabricated for the study of Ta and 'I‘aN_barrier capability.
`The starting materials were 4-in., (100)-oriented, n-type
`silicon wafers with 4-7 .0 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 X 500 and
`1000 X 1000 um’ were defined on the oxide-covered
`wafers using the conventional photolithographic tech-
`nique. The p‘-n junctions with junction depths of 0.3 amp
`were formed by BF,‘ implantation at 40 keV to a dose of
`3 X 10” crn“ 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 dc magnetron sputtering system with a base pressure of
`1-2 X 10" ’I‘orr and with no intentional substrate heating
`and bias was used. The Ta films were sputtered using a Ta
`target in Ar ambient at a pressure of 7.6 mTorr, while the
`TaN films were reactively sputtered using the same Ta target
`in an Ar/N, gas mixture at the same pressure of 7.6 m'Ibn'.
`The flow rates of Ar and N, into the sputtering chamber
`were 24 and 6 sccm, respectively, for making the Ar/N2 gas
`mixture." Prior to each sputter deposition, the target was
`cleaned by presputtering with the shutter closed for 10 min.
`The 'I‘a and TaN films were deposited at a sputtering
`power of 200 W to a thickness of 25, 10, and 5 nm sepa-
`rately. The deposition rates of ’I‘a 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 'I‘a and Ta nitrides 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 was also investi-
`J. Electrochem. Soc., Vol. 145, No. 7, July 1998 © The Electrochemical Society, Inc.
`
`Introduction
`Copper (Cu) has attracted much attention in deep sub-
`rnicron mutlilevel interconnection applications because of
`its low bulk resistivity (1.68 ufl 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 compounds at temperatures as
`low as 200°C, resulting in degradation of device character-
`istics.°;" Moreover, it has poor adhesion to interlevel dielec-
`tric and drifts through oxide under field 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 because of their high thermal
`stability and good electrical conductivity.“‘" Sputtering of
`nitride-based diffusion barriers, such as WN,“ ‘I‘iN,"
`'l‘iWN,“""' and '1‘aN,“'” to be used in Cu/barrier/Si and
`Cu/barrier/Si0, structures, has attracted extensive atten-
`tion. Tantalum (Ta) forms no compound with copper; thus,
`Cu/'I‘a/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 Ia and TaN as a difiusion barrier in Cu
`metallization system.
`It was reported that a 'l‘a film of 50 nm thickness acting
`as a diffusion barrier between a Cu and Si structure
`retained the integrity of the Cu/'l‘a/Si structure at temper-
`atures up to 600°C for 30 min." It was also reported that a
`
`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." 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
`
`'
`
`‘ Electrochemical Society Active Member.
`2538
`
`Page 7 of 14
`
`Page 7 of 14
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`

`
`F
`
`
`
`J. Electrochem. Soc., Vol. 145, No.7, July 1998 © The Electrochemical Society Inc.
`
`2539
`
`CI!/TI(2Snn)/p’-n
`
`CIIfI'a(I0nm)Ip'-n
`
`C,“-,(,,__),P.__
`
`100
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`
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`
`gated. The schematic cross sections of these differently
`metallized p“-n junction diodes are illustrated in Fig. 1.
`Th investigate thermal stability of the Cu/I‘a/p*-n and
`Cu/'I'a.N/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 um, and at least 30 diodes were meas-
`ured in each case. For material analysis, unpattemed 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 nm with the patterned samples of junc-
`tion diodes except _a number of thicker ‘Ia and 'I‘aN samples
`of 'I‘a/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
`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/pf-n junction diodes.-—Figure 2 illustrates the sta-
`tistical distributions of reverse bias leakage current densi-
`ty measured at -5 V for the Cu/'I‘a(25 nm)/P‘-n, Cu/'I‘a
`(10 nm)p*-n, and Cu/Ta(5 nm)/pl-n junction diodes
`annealed at various temperatures. The (hi/'I‘a(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/'l‘a(10 nm)/p"-n
`diodes, the diodes remained stable after annealing at tem-
`
`
`
`Cu/p*-n diode
`
`'
`
`Ta or TaN (50nm)
`
`'
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`- <:= sio,
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`Ta/pf-n or TaN/p‘-n diode
`
`C"
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`Ta or TaN
`10, and 25 nm)
`
`(5.
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`Cu/I‘alp*-ll or Cu/TaN/p*-n diode
`
`Fig. ‘I. Schematic cross sections of la) Cu/p"n,,ll3l liflfflel’/P""I
`and (cl Cu/barrier/p‘-n iunclion diodes.
`‘
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`Page 8 of 14
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`Leakage Current Density (A/cm’)
`
`Fig. 2. Histogram: showin the distributions of reverse bias
`leakage current density for fol Cu/'[ol25 nml/p*-n, (bl Cu/To
`(I0 nm}/p"-n, and (c) Cu/Ta(5 nm)/p‘-n iunction diodes annealed
`at various temperatures.
`
`peratures up to 500°C, while a number of diodes suflered
`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 d:'odes.—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 'I‘a-N films, respectively,
`decreased and increased as the nitrogen concentration in _
`the Ta—N films was increased; moreover, the bcc-Ta, 'I‘a,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/'l‘aN/Si is thermally very
`stable.” The superiority of TaN films in thermal stability
`over the pure Ta film was also reported."
`Figure 3 shows the statistical distributions of reverse
`for the Cu/TaN/p‘-n junction -
`bias leakage current density
`diodes of different TaN barrier thickness annealed at var-
`ious temperatures. For the diodes with a 25 nm thick TaN
`barrier, the devices remained stable after armealing 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 TaN layer. For the diodes with a 10 nm thick TaN
`barrier, the devices suffered moderate degradation
`annealing at 650°C and degraded severely after annealing
`at 700°C (Fig. 3b). For the Cu/'I‘aN(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
`
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`Page 8 of 14
`
`

`
`2540
`
`J. Electrochem. Soc., Vol. 145, No. 7, July 1998 © The Electrochemical Society, Inc.
`
`Cu/p‘-n
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`Leakage Current Density (A/cm‘)
`Fig. 3. Histograms showing the distributions of reverse bias
`leakage current densi
`for (al Cu/'l'aN[25 nm)/p*-n, (bl Cu/'|'aN
`(I0 nm)/p*-n, and c) Cu/TaN(5 nml/p*-n iunction diodes
`annealed at various temperatures.
`
`Leakage Current Density (A/cmz)
`Fig. 4. Histograms showing the distributions of reverse bias leak-
`age culrent density for (a) Cu/p‘-n, (bl 'l’a[50 nm)/p*-n, and {cl
`'|'aN[5O nm)/p*-n junction diodes annealed at various temperatures.
`
`of barrier effectiveness for Ta and 'l‘aN films of difierent
`thickness are summarized in Table I. The results show that
`the barrier capability of a Ta layer can be substantially
`improved by incorpora