Mechanism about improvement of NiSi thermal stability for Ni/Pt/Si(1 1 1) bi-layered system
Introduction
Nickel silicide has become an attractive candidate material for use in future complementary metal-oxide semiconductor (CMOS) device generations because of its sheet resistance independence of line-width, low resistivity and relatively low consumption of Si [1], [2], [3], [4]. The major drawback to use nickel silicide is its poor thermal stability, and NiSi is thermally stable only up to a temperature of 750 °C thereafter the high resistivity phase NiSi2 starts to nucleate [5]. In the past few years, much work has been done to improve the stability of NiSi films [6], [7], [8], [9], [10].
In this report, we find that due to the presence of a thin interlayer of Pt, a NiSi–PtSi solid solution is formed when the samples are annealed at high temperatures, and the NiSi2 nucleation is postponed by 100 °C. We will show effects of the Pt interlayer on the activation energy for the NiSi2 nucleation and investigate the mechanism about the improved NiSi thermal stability for the samples with the Pt interlayer.
Section snippets
Experimental details
An 8 nm thin interlayer of Pt and a 100 nm top layer of Ni were sequentially evaporated on the Si(1 1 1) substrates by e-gun, forming a Ni/Pt/Si bi-layered sample. The base pressure of the vacuum chamber was 1.3×10−6 Pa and during the deposition, the pressure of the vacuum chamber was better than 3.9×10−6 Pa. The deposition rates were 0.4 Å/s for Pt and 2 Å/s for Ni. To make a comparison, a 100 nm-thick Ni film without Pt interlayer was also deposited on Si(1 1 1) substrate with the same experimental
Result and discussion
The XRD patterns of Ni/Si samples annealed at different temperatures were shown in Fig. 1. From Fig. 1(a), it can be seen that the polycrystalline NiSi films were formed on Si(1 1 1) substrates after annealing at 740 °C. When the annealing temperature reached 800 °C, only peaks corresponding to NiSi2 were present (Fig. 1(b) and its inset), indicating that the transition from NiSi to NiSi2 had been completed at this temperature. For Ni/Pt/Si samples, however, strong NiSi peaks with the preferred
Conclusion
We introduce a thin interlayer of Pt between the Ni films and Si substrates, improving the thermal stability of NiSi by 100 °C, and find that the Ni0.945Pt0.055Si solid solution is formed during the reaction through XRD patterns and AES profile. The solid solution and its preferred orientation Ni0.945Pt0.055Si(1 0 0)||Si(1 1 1) seem to account for the enhancement of the thermal stability of NiSi in Ni/Pt/Si samples, by increasing the interfacial energy change and decreasing the driving force |ΔG|
Acknowledgements
This work was supported by the National Natural Science Foundation of China.
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