Reactively sputtered RuO2 diffusion barriersE. Kolawa, F. C. T. So, E. TS. Pan, and MA. Nicolet Citation: Applied Physics Letters 50, 854 (1987); doi: 10.1063/1.98012 View online: http://dx.doi.org/10.1063/1.98012 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/50/13?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Analysis of leakage current mechanisms in RuO 2 – TiO 2 – RuO 2 MIM structures J. Vac. Sci. Technol. B 29, 01AC08 (2011); 10.1116/1.3534022 Reactively sputtered Ru–Si–O films J. Appl. Phys. 86, 1974 (1999); 10.1063/1.370996 Stress measurements of radiofrequency reactively sputtered RuO2 thin films J. Appl. Phys. 80, 822 (1996); 10.1063/1.362891 Summary Abstract: Reactively sputtered RuO2 and Mo–O diffusion barriers J. Vac. Sci. Technol. B 5, 1748 (1987); 10.1116/1.583631 Electronic structure of FeO and RuO J. Chem. Phys. 82, 5584 (1985); 10.1063/1.448593

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Reactively sputtered RU02 diffusion barriers E. Koiawa, F. C. T. So, E. T-S. Pan, and M-A. Nicolet CalijiJrnia Institute o/Technology, Pasadena. Calijbmia 91125

(Received 19 November 1986; accepted for publication 26 January 1987)

The thermal stability of reactively sputtered Ru02 films is investigated from the point of view of their application as diffusion barriers in silicon contact metallizations with an Al overlayer. Backscattering spectra of SilRu0 21 Al samples and electrical measurements on shallow junction diodes with (Si) ITiSi23 IRuOzl Al contacts both show that Ru02 films are effective diffusion barriers between Al and Si for 30-min annealing at temperatures as high as 600 0c.

Diffusion barriers are widely used in contact metalliza­tion schemes to preserve the integrity of shallow junctions during post-metallization processing. Refractory metalni­trides (e.g., TiN, W-N) \-4 have emerged as a leading class of materials for diffusion barrier purposes. These transition metal nitrides have attracted much interest because of their low resistivity and stability at high temperatures when in contact with a metal overlayer (e.g., AI, Au, Ag}. In con­trast, very little is known about the applicability of conduct­ing transition metal oxides as diffusion barriers. One reason for the scarcity of information is probably the fact that the most stable transition metal oxides are electrically insulat­ing. Recently, Ru02 films deposited by metalorganic chemi­cal vapor deposition have been investigated so far for diffu­sion barrier applications. 5 In this letter, we report on reactively sputtered Ru02 films and demonstrate that they are superior to TiN as diffusion barriers between Al and Si.

Substrates of < j 1 I > oriented !Hype 5i with 0.005 n em resistivity were used throughout the experiment to study the metallurgical interactions of the (Si) IRuOz I Ai system. The n 4.p shallow junctions for testing the performance of (Si)/TiSi2.3/RuOz/AI contacts were prepared on (100) oriented p-type Si with 10-20 n. cm resistivity. After an ini­tial growth of wet oxide of 4500 A, three photolithographic steps were followed to fabricate the junctions and metalliza­tions. The first mask defined the diffusion areas of 500 X 500 ;:tm2. The junctions were formed by implantation at room temperature of 7 X 1015 As/cm2 of 150 ke V into the diffu­sion openings through a 6oo-A-thick screen oxide formed previously by dry oxidation. Dopant activation and drive-in were accomplished subsequently by annealing the wafers at 1000·C for 30 min in an N2 ambient. The second mask was then applied to open contact windows of 300 X 300 Itm2 in the thin oxide with a buffered HF solution. Finally, a third mask was used to define the metallization area. The (Si) I TiSiz.3 IRuOz I Al contact pattern was then delineated by the lift-off technique. The completed diodes have junction depths of ~O.35 pm and As surface concentrations of about 3 X 1020 ern -.3, as indicated by the SUPREM simulation pro­gram.

The deposition of :films was performed in an rf sputter­ing system equipped with a diffusion pump and a cryogenic baffle. Magnetron-type circular cathodes (7 em diameter) were used as the sputtering source. Prior to loading into the sputtering system, the Si wafers were first slightly oxid.ized in an oxygen plasma and then etched in 1: 10 HF:H20 solu-

tion. The sputtering chamber was evacuated to a base pres­sure of about 1 X lO-' D Torr before deposition. To sputter the titanium silicide films, a composite TiSi2 target and pure argon were used. The films had a nominal composition of TiSi2.3' as determined by backscattering spectrometry, and were 300 A thick. Ru02 films were reactively sputtered in 10 mTorr of a 50% O2 and 50% Ne mixture with 500 W sput­tering power. The thickness of the films was 400 A. Alumi­num overlayers (2800 A for the Si/Ru02 I Al metallization samples, and 5000 A for diodes) were sputter deposited in argon. All metal films were deposited without breaking the vacuum in the sputtering system, The samples were then annealed in a vacuum furnace at ~! pressure below 5 X 10.- 7

Torr in the range of 50C~650 °C for 30 min. The thermal stability of contacts was analyzed by backscattering spec­trometry and electrical measurements.

The RuOz films tested in this study were single phase as indicllted by x-ray diffraction with Read camera with resis­tivity of about 120 11ft em. The spectra of Fig. 1 show that within the resolution of back scattering spectrometry, there is no change in a SilRu02 I Al sample before and after an­nealing at 650 "C for 30 min. The electrical characteristics of a shallow n+ p junction with the (Si)/TiSi23 /Ru02 /Al contact scheme are presented in Fig. 2. The dc characteris­tics of the diodes prior to any heat treatment show a reverse leakage current density of about 3 X 10 - K A cm - 2.

f::2 z ::J o u '61 :::: 4~ o . ...1 I ~ I (9 i ~ I ~2 I­<{ U (j) :,c u « co

Si (III)

--as-deposited •• ·650"C/30min.

0.6 0.8 1.0 12 14 ENERGY (MeV)

RU!

FIG. 1. Backscattering spectra of Si/RuO" I A1 sample before and 'lfter an­nealing <1t 650 "C for 30 min.

854 AppL Phys. Lett. 50 (13), 30 March 1987 0003-6951/87/130854-02$01.00 @ 1 S87 American Institute of Physics 854

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~ Si/'Ti Si~.3/Ru02/AI ,- as-deposited ••• 600oCl30 min I

'. --- 650"C/30min ,

/ , i ' . / I

! , , ,

j 0" , ! :l./ . . .

l(pAl

IOO/div

v (V)

/.Ll~I!I$

..-Vi i : .-~

O.5/div o I.O/div

1 . . I . . . .

I (j.lA) . . . 0. 55/di'l. .

o

FIG. 2. Electrical characteristics ofdimles with the Si/TiSi"/Ru02 IAl metallizatioJl before and after annealing at 600 and 650 <C for 30 min.

After annealing at 600 °C for 30 min, the leakage current remains constant but the forward voltage drop rises slightly. The diodes subjected to heat treatment at 650 °C for 30 min were all shorted. However, back scattering spectra do not show any signs of reactions between the layers at this tem­perature. Scanning electron microscopy was used to eluci­date the failure mechanism of the diodes. To see the Ru02

surface, the Al overlayer was selectively etched in a HClIHNOJ solution. The as-deposited sample exhibits very smooth surface morphology. For samples annealed at 650°C for 30 min, the presence oflocaIized pits and fractures was observed OIl the Ru02 surface. Diode failures can be con­nected with diffusion of Al through these weak spots. Inter­diffusion through these spots is probably too small to be de­tected by backscattering spectrometry.

Electrical measurements on pn shallow junction diodes with Si/TiSi2 ! Al contacts reported previously6 showed that the device junctions were an shorted after annealing for 30

855 Appl. Phys. Lett, Vol. 50, r'lio. i 3,30 March i 987

min at 400 "C. This indicates that the presence of a RuOz diffusion barrier enhances dramatically the thermal stability ofthe SiiTiSi2 / Ai contact. It is also interesting to note that even such a thin tUm of Ru02 like 400 A is able to act as a good diffusion barrier. For comparison, previous reports (such as those by Ting and Wittmer l and Nygren et aC) showed that the shallow junctions with Si/Ti(TiSi2 )/

TiN/ Al are not stable after annealing at 400-550 °C for 30 min (increasing leakage) and at 475 ·C for 30 min, respec­tively.

This study shows that sputtered Ru02 has very interest­ing properties in terms of application of this material as dif­fusion barriers in very large scale integration technologyo

The authors gratefully acknowledge technical assis­tance from R, Garris, help in scanning electron microscopy analysis from Rindge Shima, and manuscript preparation by A. Collinwood. Financial support from the Army Research Office under contract number DAAG29-85-K-Ol92 is also gratefully acknowledged.

'e. Y. Ting and M. Wittmer, Thin Solid Films 96, 327 ( 1983). "S. Kanamori, Thin Solid Films 136,195 ([985). 'n. P. Katteluso E. Kolawa, K. Affolter, and M-A. Nicolet, 10 Vac. Sci. T echnoL A 3, 2246 (J (85).

4H. P. Kattelus and M-A. Nicolet, in DljJusiofl Phenomena in Thin Films, edited by D. Gupta and P. So Ho (Noyes, New Jersey, in press).

'M. L. Green, M. E. Gross, L. E. Papa, K. J. Schnoes, and D. Brasen, J. Electfochem. Soc. 132, 2077 (1985).

"e, Y. Ting and M. Wittmer, J. App!. Phys. 54, 937 (19H3). .. 7S. Nygren, R. Buchta, V. SusUlfsson, H. Norstrom, P. Wiklund, M. Os­tling, and C. S. Petersson, in Proceedings a/11th Nordic Semiconductor Meeting (Espoo, Finland. 1984), p. 271.

Kolawa et al. 855

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