STRESS STABILIZATION OF BETA-TANTALUM AND ITS CRYSTAL-STRUCTURE

We studied the relationship between Ta crystal structures and the stress stability of Ta under heating. The stress in Ta which was sputter deposited on SiC was unstable and changed more than 2 x 10(9) dyn/cm2 to the compressive side during heating at 200-degrees-C for 30 min in air. In contrast, the stress in Ta which was sputter deposited on SiC whose surface was modified by Ar sputtering was very stable, and the stress change was less than 1.5 x 10(8) dyn/cm2 even after 6 h of heating at 200-degrees-C. The x-ray diffraction patterns of the Ta revealed that stable Ta was strongly (002) oriented beta-Ta, and that unstable Ta was randomly oriented beta-Ta with some alpha-Ta. We found that amorphizing the SiC surface or inserting a thin amorphous interlayer enhanced growth of strongly (002) oriented beta-Ta.