Stabilization of intermediate NiSi phase in NiPt/Si(001) and Ni/Pt/Si(001) nanodimensional film compositions

Complete text of publication follows. Currently NiSi is the most favorable low resistivity (ρν ∼ 10νΩ x cm) interconnect material in semiconductor technology. The increase of the thermal stability of NiSi and prevention of transition of this phase to high-resistivity NiSi2 is a topical problem of material science. The goal of present study is to investigate the influence of Pt on the development of thermally activated solid state reactions and on the thermal stability of NiSi in [(Ni+x at.%Pt)30 nm]/Si(001) and Ni(30 nm)/Pt(2;6 nm)/Siepi(50 nm)/Si(001) nanodimensional film compositions, where x=0.73; 3.35; 8.24; 19. The samples were produced by magnetron sputtering from mosaic target of NiPt with different content of Pt and also by layer-by-layer deposition of Ni and Pt on Si(001) substrate at room temperature. Annealing of samples were carried out in vacuum (∼ 10-3 Pa) and in nitrogen atmosphere in the temperature range of 450-900 deg C for 30 seconds. Solid state reactions were characterized by methods of X-ray diffraction, Secondary Neutral Mass Spectrometry (SNMS - SPECS, INA-X type), Transmission Electron Microscopy (TEM) and resistometry. During annealing the thermally activated solid state reactions began by formation of intermediated silicide phases. It is show that the presence of the intermediate Pt layer stabilizes the NiSi phase and hinders the formation of NiSi2 phase. It is established that in samples, regardless of Pt concentration, during annealing in vacuum the solid state reaction begin at 450 deg C with formation of intermediate NiSi and Ni2Si phases. By the increasing of Pt content the NiSi→NiSi2 transition shifts in side of more high temperatures. During annealing of samples in nitrogen atmosphere at 450 deg C only NiSi phase formation was observed. In samples with small Pt content (0.73; 3.35 at.%) the annealing at 700 deg C is accompanied by start of phase transition of NiSi to Ni2Si. In samples with large content of Pt (8.24; 19 at.%) the NiSi remains stable up to the temperature of 900 deg C, which is in 150 deg C higher than in samples of Ni(30 nm)/Si(001) without alloying of Pt. It is confirmed by the low value of electric resistance. The presence of the Pt in the grain and interphase boundaries can explain the detection of small amount of the PtSi phase by XRD. On the other hand these can not be observed by TEM or SNMS. It was shown recently [1] that the diffusion intermixing in Co/Si systems started with fast (triple junctions/grain boundary) diffusion of the Si into the Co layer. After some incubation time Si atoms appeared and enriched on the Co surface and acted as a reservoir for back-diffusion into the Co layer from the Co surface through the slower grain boundaries. Thus, assuming similar Si diffusion mechanisms in Ni/Si system, formation of different PtxSiy phase in the grain boundaries or at the interphase boundaries can take place and the Si enrichment at the free surface can also be explained.