PROPERTIES OF REACTIVELY SPUTTER-DEPOSITED TA-N THIN-FILMS

We deposited Ta-N films by reactive r.f. sputtering from a Ta target w ith an N-2,-Ar gas mixture. Alloys over a composition range 0-60 at.% N have been synthesized. We report on their composition, structure and electrical resistivity before and after vacuum annealing in the tempe rature range 500-800 degrees C. We found that the film growth rate dec reases with increasing ratio of the nitrogen flow rate to the total Ao w rate, while the nitrogen content in the films first increases with t he N-2 partial flow rate and then saturates at about 60 at.%. B.c.c.-T a, Ta2N TaN and Ta5N6 appear in succession as the nitrogen content ris es, with Ta2N being the only single-phase film obtained. The atomic de nsity of the films generally increases with the nitrogen content in th e film. Transmission electron micrographs show that the grain size dec reases from about 25 to 4 nm as the nitrogen concentration increases f rom 20 to 50 at.%. The Ta2N phase can exist over a wide range of nitro gen concentration from about 25 to 45 at.%. For as-deposited films an amorphous phase exists along with polycrystalline Ta2N in the center p ortion of that range. This phase crystallizes after vacuum annealing a t 600 degrees C for 65 min. A diagram of stable and metastable phases for Ta-N films based on X-ray diffraction and transmission electron mi croscopy results is constructed. The resistivity is below 0.3 m Omega cm for films with 0-50 at.%N and changes little upon vacuum annealing at 800 degrees C.