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

Abstract

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.