Sputtered Cr and Reactively Sputtered CrN_x Serving as Barrier Layers Against Copper Diffusion

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