X-ray study of strains and dislocation density in epitaxial Cu/Ni/Cu/Si(001) films

The strain state of epitaxial Cu(50 Angstrom)/Ni(t(Ni))/Cu(2000 Angstrom)/Si(001) films as a function of the nickel film thickness (30 Angstrom less than or equal to t(Ni) less than or equal to 2000 Angstrom) has been studied using Bragg diffraction and grazing-incidence diffraction with a synchrotron x-ray source. For 30 Angstrom less than or equal to t(Ni) less than or equal to 150 Angstrom both the in-plane and out-of-plane nickel strains show a phenomenological (1/t)(2/3) power dependence, which is significantly different from the 1/t law commonly accepted in the literature. The Matthews' theory, including the effect of the copper capping layer, is used to account for the equilibrium strains of the nickel layer. The 500 and 2000 Angstrom films show larger strains than that predicted by the theory, consistent with other studies. The ratio of the nickel in-plant to out-of-plane strains is -1.18 +/- 0.05, very close to the expected nickel bulk value of -2c(12)/c(11) = -1.28. [S0163-1829(99)12743-7].