Various Properties of Sputtered TaxAl1-x Films

Abstract

AbstractFilms of TaxxAl1-x have been prepared by diode sputtering from a target consisting of an Al mask placed on the face of a Ta target. The Ta target was 8″ in diameter while the Al mask was 0.125″ thick and machined with a grid-like shape. Films were deposited for a range of pressure, at a power of 300 watts, onto oxidized 100 mm diameter Si substrates that were placed on a planetary table beneath the target. The Al/Ta area ratio of the composite target was determined on the basis of the relative sputtering rates for these metals with the intent of producing a film composition with x = 0.5. The film composition was found to vary with argon pressure, going from 24 at.% Al at 4 mtorr to 72 at.% Al at 30 mtorr. This finding was quite unexpected. This result made it possible to deposit a wide range of film compositions from one composite target. The electrical resistivity has a broad maximum of,≈ 240 micro-ohm/cm between x=0.3 and 0.6. These results compliment and extend the earlier observations by Steidel \1] The as-deposited stress of the films varied from -400 to +150 MPa as x was decreased from 0.76 to 0.28. The temperature dependence of the film stress is hysteretic on the first cycle to 475 C. After the first cycle the films are driven more into tension by as much as 500 Mpa. The oxidation characteristics of one composition Ta0.66Al0.34 were characterized in some detail using a combination of electrical resistance, AES and XPS measurements. The results show that such films oxidize at temperatures in the 300 to 600C range via a diffusion-controlled process with an activation energy of 0.98 eV. Such films are substantially more oxidation-resistant than either ccα-or β-tantalum.