It was demonstrated that the deposition of Ta diffusion barriers under ultra-high vacuum conditions, without in situ O dosing, allowed for variations in the microstructure and in the concentration of chemical impurities which severely degraded barrier performance. The effects of deposition pressure, in situ O dosing at interfaces, H and O contamination, and microstructure upon the performance of electron-beam deposited Ta as a barrier to Cu diffusion were presented. Some 20nm of Ta, plus 150nm of Cu, were deposited under ultra-high vacuum (10-9 to 5 x 10-8torr) conditions, and high-vacuum (10-7 to 5 x 10-6torr) conditions, onto <100> Si. Auger depth profiling, secondary ion mass spectrometry, and forward recoil detection, together with scanning and transmission electron microscopy, were used to determine the electrical and structural changes which occurred in thin-film Ta diffusion barriers during annealing. Un-dosed high-vacuum deposited Ta barriers failed at 560 to 630C, while un-dosed ultra-high vacuum barriers failed at 310 to 630C. In the case of ultra-high vacuum Ta barriers, in situ O dosing during deposition at the Cu/Ta interface increased the failure temperatures by 30 to 250C, and decreased the range of failure temperatures to 570-630C. Un-dosed ultra-high vacuum Ta barriers exhibited no systematic relationship between failure temperature and deposition pressure, although there were correlations between breakdown temperature, O and H concentration, and microstructural variations.

Comparison of High Vacuum and Ultra-High Vacuum Tantalum Diffusion Barrier Performance against Copper Penetration. L.A.Clevenger, N.A.Bojarczuk, K.Holloway, J.M.E.Harper, C.Cabral, R.G.Schad, F.Cardone, L.Stolt: Journal of Applied Physics, 1993, 73[1], 300-8