Diffusion of silicon in titanium dioxide thin films with different degree of crystallinity: Efficiency of TiO2 and TiN barrier layers

• Quantitative determination of the silicon diffusion in TiO2 thin films with different microstructure.
• Physical sense of the diffusion constants – interrelationship with the crystalline structure.
• Different growing modes foreordained by the films deposition rate and gas nature.
• Depth profiling by high-precision Rutherford backscattering spectrometry (RBS).
• Comparison of the barrier thermal stability of TiO2/Si interface with one of the best known anti-diffusion barriers –TiN/Si.

Two kinds of reactively sputtered titanium dioxide films with columnar and fine-grained structures were investigated as diffusion barriers, preventing the silicon diffusion. The only differences in the deposition conditions were the oxygen percentage concentration (OC) in the discharge, kept for 10% and 30% of the total working pressure. The resulting films were found to have different thicknesses being 800 and 240 nm for 10% and 30% OC, respectively. The films were studied by X-Ray diffraction spectrometry (XRD) and their composition by Rutherford Backscattering Spectrometry (RBS). In order to describe the diffusion processes, the two batches were annealed up to temperature of 800 °C. The diffusivity from 300° to 800 °C is D(m2/s)=2.43.10−18exp[−(15kJ/mol)/(RT)] andD(m2/s)=2.36.10−18exp[−(18.4kJ/mol)/(RT)] for (10% OC) and TiO2 (30% OC), respectively. The physical meaning of the derived diffusion parameters are discussed in view of the crystalline peculiarities of the obtained films. Arrhenius plots show clearly that higher activation energy is characteristics for films with better-packed crystallites. These results are compared with known diffusion barrier layer such as TiN.

Arrhenius plot of silicon diffusivity in TiO2 (10% OC*), TiO2 (30% OC) and TiN layers. In general this plot shows the thermal stability of a given interface. The TiO2 films deposited by higher oxygen concentration in the discharge show about 75% lower diffusivity, an expected result inasmuch as TiO2 (30% OC) layers have more densely packed structure with slightly larger grain size. Otherwise, the TiO2 (10% OC) films show different texture consisting of columns separated by voids. The difference in the diffusion activation energy (EA) in those two cases is obviously due to the partial participation of a surface diffusion in the voids of this layers. *OC means relative oxygen concentration in the discharge. For example, 30% OC means 3 sccm O2 plus 7 sccm Ar.Figure optionsDownload high-quality image (118 K)Download as PowerPoint slide