Annealing of thin Zr films on Si1-xGex (0≤x≤1): X-ray diffraction and Raman studies
Résumé
X-ray diffraction experiments have been combined to Raman scattering and transmission electron microscopy data to analyze the result of rapid thermal annealing applied to Zr films, 16 or 80 nm thick, sputtered on Si1-xGex epilayers (0≤x≤1). The C49 Zr(Si1-xGex)2 is the unique phase obtained after complete reaction. ZrSi1-xGex is formed as intermediate phase. The C49 formation temperature Tf is lowered by the addition of Ge in the structure. Above a critical Ge composition close to x=0.33, a film microstructure change was observed. Films annealed at temperatures close to Tf are continuous and relaxed. Annealing at T>Tf leads to discontinuous films: surface roughening resulting from SiGe diffusion at film grain boundaries occurred. Grains are ultimately partially embedded in a SiGe matrix. A reduction in the lattice parameters as well as a shift of Raman lines are observed as T exceeds Tf. Both Ge non-stoichiometry and residual stress have been considered as possible origins of these changes. However, as Ge segregation has never been detected, even by using very efficient techniques, it is thought that the changes originate merely from residual stress. The C49 grains are expected to be strained under the SiGe matrix effect and the shift of the Raman lines would indicate the stress is compressive. Some simple evaluations of the stress values indicate that it varies between -0.3 and -3.5 GPa for 0≤x≤1 which corresponds to a strain in the range [-0.11, -1.15 %]. X-ray and Raman determinations are in good agreement.
Domaines
Matériaux
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