EVOLUTION OF MICROSTRUCTURE IN NANOCRYSTALLINE MO-CU THIN-FILMS DURING THERMAL ANNEALING

The evolution of microstructure in Mo-Cu thin films during annealing has been investigated by in situ sheet resistance measurements, ex situ x-ray diffraction, and in situ hot-stage as well as conventional transmission electron microscopy. Mo-Cu thin films, deposited on various glass substrates by magnetron sputtering at similar to 30 degrees C, were supersaturated solid solutions of Cu in Mo with a nanocrystalline microstructure. The as-deposited films had large compressive residual stresses owing to the low homologous deposition temperature and low Ar pressure during deposition. Annealing results showed two distinct sets of microstructural changes occurring in the temperature ranges between similar to 300 and 500 degrees C, and similar to 525 and 810 degrees C. In the lower-temperature range, anisotropic growth of nanocrystallites was accompanied by stress relaxation without any observable phase separation. At temperatures greater than similar to 525 degrees C, the metastable solid solution collapsed and Cu precipitated at the grain boundaries. Increasing temperature resulted in the coarsening of Cu precipitates and simultaneous growth of Mo grains. At temperatures greater than similar to 700 degrees C, phase separation and grain growth approached completion. (C) 1995 American Institute of Physics.