Scalability of plasma enhanced atomic layer deposited ruthenium films for interconnect applications J. Swerts, S. Armini, L. Carbonell, A. Delabie, A. Franquet, S. Mertens, M. Popovici, M. Schaekers, T. Witters, Z. Tökei, G. Beyer, S. Van Elshocht, V. Gravey, A. Cockburn, K. Shah, and J. Aubuchon Citation: Journal of Vacuum Science & Technology A 30, 01A103 (2012); doi: 10.1116/1.3625566 View online: http://dx.doi.org/10.1116/1.3625566 View Table of Contents: http://scitation.aip.org/content/avs/journal/jvsta/30/1?ver=pdfcov Published by the AVS: Science & Technology of Materials, Interfaces, and Processing
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Scalability of plasma enhanced atomic layer deposited ruthenium films for interconnect applications J. Swerts,a) S. Armini, L. Carbonell, A. Delabie, A. Franquet, S. Mertens, M. Popovici M. Schaekers, T. Witters, Z. To¨kei, G. Beyer, and S. Van Elshocht IMEC, Kapeldreef 75, 3001- Leuven, Belgium
V. Gravey and A. Cockburn Applied Materials Belgium, Kapeldreef 75, 3001- Leuven, Belgium
K. Shah and J. Aubuchon Applied Materials, Bowers Avenue, California
(Received 7 April 2011; accepted 20 July 2011; published 2 September 2011) Ru thin films were deposited by plasma enhanced atomic layer deposition using MethylCyclopentadienylPyrrolylRuthenium (MeCpPy)Ru and N2/NH3 plasma. The growth characteristics have been studied on titanium nitride or tantalum nitride substrates of various thicknesses. On SiO2, a large incubation period has been observed, which can be resolved by the use of a metal nitride layer of 0.8 nm. The growth characteristics of Ru layers deposited on ultrathin metal nitride layers are similar to those on thick metal nitride substrates despite the fact that the metal nitride layers are not fully closed. Scaled Ru/metal nitride stacks were deposited in narrow lines down to 25 nm width. Thinning of the metal nitride does not impact the conformality of the Ru layer in the narrow lines. For the thinnest lines the Ru deposited on the side wall showed a more granular structure when compared to the bottom of the trench, which is attributed to the C 2012 American Vacuum Society. plasma directionality during the deposition process. V [DOI: 10.1116/1.3625566]
I. INTRODUCTION Electrochemical deposition of Cu for interconnect metallization traditionally uses physical vapor deposition (PVD) of a Cu seed layer on top of a PVD Ta/TaN barrier to conduct the current. However, the step coverage limitations of the PVD technique compromise its use in future technology nodes.1 To meet the resistivity specifications (Cu < 7 lOhm.cm) in lines with sub-25 nm critical dimension (CD), thicknesses of less than 3 nm are required for the barrier layer.1 Barriers grown by atomic layer deposition (ALD) combined with seedless Cu electroplating is one of the metallization routes explored for sub-25 nm line CD’s. However, compatibility with seedless electroplating seriously limits the choice of materials. Among the different candidates, Ru layers have been identified as very promising to act as nucleation layers for direct Cu plating.2 Furthermore, high electromigration resistance has recently been demonstrated for Cu metallization using a CVD Ru-liner showing that Ru is a valuable replacement for the conventional Ta (Ref. 3). The deposition by thermal ALD has been examined using various Ru chemistries such as Ru(EtCp)2 (Ref. 4), RuCp2 (Ref. 5), Ru(thd) (Ref. 6), (MeCpPy)Ru (Ref. 7), (EtCpPy)Ru (Ref. 8), and Ru(tBu-Me-amd)2(CO)2 (Ref. 9). The latter uses NH3 as co-reactant whereas all the others use O2. The use of O2 in an ALD process around 300 C is not compatible in a dual damascene flow since it can oxidize the a)
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J. Vac. Sci. Technol. A 30(1), Jan/Feb 2012
Cu interconnect leading to a too high via resistance. Furthermore, all the thermal Ru processes have been shown to be very surface dependent. Large incubation times or bad adhesion is found when growing Ru on Si or Si oxides substrates. When grown on metal nitride layers such as TiN (Ref. 4) or WN (Ref. 9), less incubation and good adhesion has been observed. The incubation could be further reduced by using a plasma pretreatment of the substrates7 or using plasma enhanced atomic layer deposition (PE-ALD). For the Ru(EtCp)2/NH3 plasma chemistry, a much shorter incubation period on TiN substrates was found than in the thermal O2-based ALD process.4 Unfortunately, the same PE-ALD process does not sufficiently reduce the very large incubation period for Si oxide. Islandlike growth resulted in noncontinuous layers for thicknesses < 5 nm, which makes it not usable for future interconnect nodes.10 As such, the use of plasma is not sufficient to enable Ru growth on Si oxides and ensure adhesion. Therefore, a growth enabling layer like metal nitrides is a must when depositing Ru by ALD on Si oxides. When the Ru would be integrated in a dual damascene flow, the growth enabling layer will also be deposited on top of the Cu and as such increase the via resistance. For that reason, it is important to minimize its thickness. Moreover, because of space limitations in the case of line widths below 25 nm for future interconnects, thicknesses of the adhesion layer needs to be scaled down to
