Failure Mechanism of 5 nm Thick Ta–Si–C Barrier Layers Against Cu Penetration at 750–800°C

Abstract

Ta–Si–C amorphous films 5nm thick were found applicable as a diffusion barrier against Cu penetration for sub- 65nm integrated circuit processing. The failure mechanisms of such a barrier were still unknown and were explored in this study. Ta–Si–C films were prepared by magnetron cosputtering using TanormalSi2 and C targets on p-type Si(100) substrate. Failure mechanisms were explored by Auger electron spectroscopy, X-ray diffraction, transmission electron microscopy, and four-point probe measurement on annealed films. In a sandwiched scheme Si∕Ta–Si–C (50.3emnm)∕Cu , the failure temperatures 750 (18 atom % C) and 800°C (24 atom % C) were demonstrated. Deterioration of Ta–Si–C barriers arose from local nucleation of TanormalSi2 crystallites, providing short paths for copper penetration. Carbon addition significantly inhibited the formation of TanormalSi2 and increased the failure temperature of the barriers. From the understanding of the failure mechanism a possible solution is proposed to research thinner barriers (such as 2nm ) to meet the 2016 International Technology Roadmap for Semiconductors.

Low-Resistivity Ru-Ta-C Barriers for Cu Interconnects

“…Although Ta 34 Si 47 C 18 also has superior performance, the resistivity of as-deposited Ta 34 Si 47 C 18 is 349 lX cm, while that of the 900°C-annealed film is 210 lX cm. 12 However, the resistivity of as-deposited Ru 77 Ta 15 C 7 in this study is 143 lX cm, while that of 900°C-annealed film is as low as 20 lX cm. Laurila et al 13 showed that the resistivity of Ta 53 C 47 is 210 lX cm, and 7-nm-thick TaC fails at 550°C for 30 min.…”

The Inhibition of Enhanced Cu Oxidation on Ruthenium∕Diffusion Barrier Layers for Cu Interconnects by Carbon Alloying into Ru

“…30 The effect of C on inhibition of Cu oxidation.-The fact that the Cu 2 O XRD peak is less intense for the Cu/Ru/Ta 0.44 C 0.19 N 0.37 / Si sample indicates that C doped in the TaN layer may inhibit Cu oxidation. Although C-containing barrier, such as WCN, 31 Ta-Si-C, 32 Ru-WCN mixed layer 33 have been reported as good barrier, but the 1f, it can be seen that the RuC film is more effective than the TaCN film for the inhibition of Cu 2 O formation. The in-situ XRD results also indicate that by alloying C in the Ru layer, the thermal stability of the whole system is improved, with the failure temperatures of about 740 • C, higher than that of the samples shown in Fig.…”

“…30 The effect of C on inhibition of Cu oxidation.-The fact that the Cu 2 O XRD peak is less intense for the Cu/Ru/Ta 0.44 C 0.19 N 0.37 / Si sample indicates that C doped in the TaN layer may inhibit Cu oxidation. Although C-containing barrier, such as WCN, 31 Ta-Si-C, 32 Ru-WCN mixed layer 33 have been reported as good barrier, but the C effect on the Cu oxidation was not studied. We further alloyed C into the Ru layer and studied the effect of C on the Cu oxidation.…”

Comparative Study of Cu Diffusion in Ru and Ru-C Films for Cu Metallization

“…A similar observation has been reported in a Cu/Ta-Si-C/Si system where the native oxide layer was clearly revealed in TEM micrographs even the Si wafer was thoroughly cleaned by a standard RCA procedure before loading into the sputtering chamber. 27 Nevertheless, it has been reported that the Cu can diffuse much more rapidly into SiO 2 , with the diffusivity of 1.2 ϫ 10 −11 cm 2 s −1 . 28 The formation of Cu 3 Si was also observed in the Cu/Si system with a native oxide layer of 1.5 nm in thickness after annealing at 600°C.…”