Blasco, Nicolas

Deduytsche, Davy

Detavernier, Christophe

Devloo-Casier, Kilian

Rampelberg, Geert

Schaekers, Marc

English

Ghent University Academic Bibliography

 Plasma-enhanced atomic layer deposition of thin vanadium nitride layers as a copper diffusion barrier  Geert Rampelberga,*, Kilian Devloo-Casiera, Davy Deduytschea, Marc Schaekersb, Nicolas Blascoc, Christophe Detaverniera  a Ghent University, Krijgslaan 281 (S1), 9000 Ghent, Belgium b IMEC, Kapeldreef 75, B-3001 Leuven, Belgium c Air Liquide Electronics US, L.P., 46401 Landing Parkway, 94538, Fremont, CA, USA   Transition metal nitrides are well known for their superior characteristics such as high temperature stability, hardness, corrosion resistance and metallic resistivity [1]. In microelectronics TiN and TaN have been extensively investigated for their use as diffusion barriers for copper interconnects [2]. In the same group of materials vanadium nitride (VN) is known as a strongly coupled superconductor with a room-temperature resistivity near 100μΩcm [3]. Thin films of VN are mainly deposited by reactive sputtering, high temperature nitridation of metallic vanadium layers and chemical vapour deposition. The latest reported applications include supercapacitors and diffusion barriers [4,5].   In this work, vanadium nitride layers were grown by plasma-enhanced atomic layer deposition (PE-ALD) using Tetrakis(EthylMethylAmino)Vanadium (TEMAV) as metal-organic precursor and ammonia plasma as reactant. A saturated and linear growth regime was achieved at a deposition temperature of 150°C, resulting in a growth rate of 0.07nm per ALD cycle (Fig. 1). Variation of the plasma power did not have much influence on the growth characteristics. X-ray photoelectron spectroscopy (XPS) confirmed the stoichiometric VN composition (49.6% V and 47.7% N), with only a minor oxygen impurity fraction of approximately 3% (Fig. 2). Moreover, x-ray diffraction (XRD) indicated that the as deposited films were crystalline with a structure closely related to δ-VN (fcc) (Fig. 3). At optimized conditions the resistivity was as low as 200μΩcm for films thicker than 20nm, while for a 3nm thick film the resistivity only increased to 320μΩcm (Fig. 4), indicating film continuity. Post-ALD annealing to 825°C lead to further reduction of the resistivity, from 200μΩcm to approximately 145μΩcm in N2 ambient and 95μΩcm in a mixture of H2 and N2. Decreasing the deposition temperature lead to a reduced growth rate and a slightly higher resistivity. It should be noted that the thermal ALD process using the same precursor in combination with exposure to standard NH3 vapor instead of NH3 plasma resulted in similar growth rates, but the resistivity of these films was a factor of 50 higher. XPS indicated that in this case an oxygen-rich composition was present, close to V2NO2.  A thin PE-ALD VN layer of 5nm proved to be effective as a diffusion barrier for copper (Fig. 5). In-situ XRD was used to monitor the reaction between a sputtered Cu film and the underlying HF-cleaned Si substrate. Without an intermediate barrier, fig. 5a shows the formation of Cu3Si at 230°C and the melting of this silicide phase at 820°C. A similar experiment was performed on a sample with a 5nm PE-ALD VN barrier in between the sputtered Cu and the HF-cleaned Si substrate. The in-situ XRD graph shows how the VN barrier effectively delays interaction between Cu and Si up to a temperature of 720°C (fig. 5b).   References 1. M. Wittmer, J. Vac. Sci. Technol. A 3, 4 (1985). 2. C. Lee, Y.-L. Kuo, JOM, 59, 1, 44-49 (2007). 3. J. Zadanski, R. Vaglio, G. Rubino, K.E. Gray, M. Russo, Phys. Rev. B, 32, 5 (1985). 4. D. Choi, G.E. Blomgren, P. N. Kumta, Adv. Mater., 18, 1178-1182 (2006). 5. X.-P. Qu, M. Zhou, T. Chen, Q. Xie, G.-P. Ru, B.-Z. Li, Microelectronic Engineering, 83, 236-240 (2006).  * corresponding author e-mail:  Geert.Rampelberg@UGent.be    Figure 1: Vanadium nitride film thickness as a function of the number of PE-ALD cycles for various deposition temperatures. A growth rate of 0.07nm per cycle is extracted for a deposition temperature of 150°C.     Figure 2: X-ray photoelectron spectroscopy of the plasma-enhanced and thermal ALD processes.     Figure 3: X-ray diffraction of the as deposited PE-ALD VN layers (150°C deposition temperature) reveals a polycrystalline structure, closely related to δ-VN.      Figure 4: Resistivity of the PE-ALD VN films as a function of film thickness for various deposition temperatures. The black line shows the trend for the 150°C depositions.     Figure 5: In-situ x-ray diffraction as a function of temperature shows how Cu diffuses into the Si substrate and forms Cu3Si. (a) 50nm PVD Cu on Si reacts at 230°C, (b) 50nm PVD Cu with a 5nm PE-ALD VN on Si is stable up to 700°C.   

Plasma-enhanced atomic layer deposition of thin vanadium nitride layers as a copper diffusion barrier

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Plasma-enhanced atomic layer deposition of thin vanadium nitride layers as a copper diffusion barrier

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