Influence of texture on the growth of ternary silicide thin films

Smeets, Dries1; Detavernier, Christophe1; De Keyser, Koen1; Comrie, Craig M.2; Theron, Chris C.2; Vantomme, Andre1 1Belgium; 2South Africa

The influence of texture on the kinetics during growth of thin films has long been neglected. Alloying a metal film that is used to grow a silicide can influence this texture and thus allows a study of the relation between texture and growth properties.
In this work we have investigated the growth and texture of ternary Co_1-xNi_xSi₂ as a function of Ni concentration. Real time sheet resistance, laser light scattering, X-ray diffraction (XRD) and Rutherford backscattering spectrometry measurements were performed to investigate the kinetics and thermodynamics during the growth, while the texture of the thin films was contemplated using XRD pole figure measurements and electron backscatter diffraction images.
The activation energy for the initial, nucleation-controlled growth of the disilicide film, drops off linearly from 2.7 ± 0.2 eV for a pure CoSi₂ layer to 2.1 ± 0.2 eV for a metal film containing 40% Ni. The observed trend is consistent with the dependence of the free energy of formation for the disilicide phase on the Ni concentration.
The effective activation energy (E_D) for the diffusion process during CoSi₂ growth is 2.3 ± 0.2 eV, which is almost 0.3 eV higher than the average for the Ni containing films (2.02 ± 0.8 eV). Despite the lower activation energy for the diffusion process, the overall diffusion process is significantly slower for Ni containing films. This apparent contradiction is explained by the large difference in pre-exponential factor (D₀) for the Arrhenius relation (D=D₀exp(-E_D/kT)) of the diffusion coefficient. With respect to the Ni containing films, D₀ is 2 to 3 orders of magnitude larger for the pure CoSi₂ film. Both results are explained on the basis of the texture of the disilicide thin films. The larger density of highly defected, high angle grain boundaries in the Ni containing films is responsible for the lower activation energy, while the larger grain size and corresponding lower density of grain boundaries in these films results in a smaller pre-exponential factor.
The combination of complementary experimental techniques in real time and the thorough analysis of the texture of the thin films after growth thus reveals a strong correlation between the texture of these thin films and their diffusion controlled growth.

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