Texture Evolution of Abnormal Grains with Post-Deposition Annealing Temperature in Nanocrystalline Cu Thin Films

Abstract

We have examined the evolution of abnormal grain growth texture with increasing post-deposition annealing temperature in nanocrystalline Cu films (20 nm thick) deposited on an amorphous SiNx (20 nm)/Si substrate. Texture is analyzed by a TEM-based orientation and phase mapping technique based on precession electron diffraction. The as-deposited film, which has an initial grain size of ~12 nm in diameter, already shows a signature of abnormal grain growth, exhibiting a bimodal grain size distribution. Texture is analyzed by calculating area fractions of major components. The overall texture of the as-deposited film is identified to be 〈110〉, but 〈100〉 grains occupy the largest fraction in the abnormally grown grain areas, followed by 〈111〉 grains. After annealing at 398 K, 573 K, and 773 K (125 °C, 300 °C, and 500 °C), the overall texture turns to 〈112〉. After annealing at 398 K (125 °C), abnormally grown grains have a major 〈112〉 component. The situation is similar for the film annealed at 573 K (300 °C). After annealing at 773 K (500 °C), the abnormal grain growth texture evolved into major 〈111〉. The 〈100〉 component found in the abnormal grain growth texture for the as-deposited film is clearly explained by elastic strain energy minimization and the 〈111〉 component for the as-deposited film and the film annealed at 773 K (500 °C) is explained by surface energy minimization. The development of the 〈112〉 texture obtained after annealing at 398 K and 573 K (125 °C and 300 °C) is not explained by either elastic strain energy minimization or surface energy minimization. We suggest that it is clarified by assuming that the Cu film system is perfectly elastic–plastic, which is associated with the Taylor factors.