Sputtered Cr and reactively sputtered CrNx serving as barrier layers against copper diffusion

The barrier capability of sputter deposited Cr and reactively sputter deposited CrNx films against Cu diffusion in a structure of Cu/barrier/p(+)n junction diodes was investigated by means of thermal annealing at elevated temperatures in conjunction with electrical measurements and material analysis. For a 500 Angstrom thick barrier layer, the barrier capability of a pure Cr layer was limited to temperatures up to 500 degrees C, while CrNx films sputter deposited in a gas mixture of Ar and N-2 showed improved barrier capabilities. With Ar/N-2 flow rates of 24/6 to 24/12 standard cubic centimeters per minute, the deposited CrNx films possessed a much improved barrier capability. In particular, the Cu/CrNx (24/9)/p(+)n junction diodes were capable of sustaining 30 min of thermal anneal at temperatures up to 700 degrees C without degradation of the diodes' electrical characteristics. The failure of Cu/Cr/p(+)n and Cu/CrNx/p(+)n junction diodes under extreme thermal treatment was presumed to arise from two mechanisms: grain boundary diffusion for lightly nitrogen doped CrNx and pure Cr barriers, and localized defect (microcrack) diffusion for excessively nitrogen doped CrNx barriers.