Strain in epitaxial CoSi2 films on Si (111) and inference for pseudomorphic growth

Abstract

The perpendicular x‐ray strain of epitaxial CoSi₂ films grown on Si(111) substrates at ∼600 °C was measured at temperatures from 24 up to 650 °C. At 600 °C, the perpendicular x‐ray strain is −0.86%, which is about the x‐ray strain that a stress‐free CoSi₂ film on Si(111) would have at that temperature. This result shows that the stress in the epitaxial CoSi₂ film is fully relaxed at the growth temperature. Strains in the film below the growth temperature are induced by the difference in the thermal expansion coefficient of CoSi₂ and Si, α_f−α_s=0.65×10⁻⁵/°C. Within experimental error margins, the strain increases linearly with decreasing temperature at a rate of (1.3±0.1)×10⁻⁵/C. The slope of the strain‐temperature dependence, obtained by assuming that the density of misfit dislocations formed at the growth temperature remains unchanged, agrees with the measured slope if the unknown Poisson ratio of CoSi₂ is assumed to be ν_f=1/3. These observations support three rules postulated for epitaxial growth.