Preparation of W-W 2 B composites from W-BN powders and properties of W-B-N barrier for copper metallization

Sintered composites of W-W ₂B were prepared from W-BN powders mixture using hot pressing technique that initiated reaction between W and BN at temperatures above 1973 K when BN decomposes and forming boron reacts with W powder to form tungsten boride. Fully densified W-W ₂B solid sputtering targets were prepared with the composition range W-Xwt% B (1 < X < 5). The thermal stability of reactively magnetron sputtered tungsten boron nitride (W-B-N) thin films has been investigated as a diffusion barrier between Cu and Si during subsequent annealing between 623 and 823 K. All the as-deposited W-B-N thin films were amorphous, except the film sputtered with 40% N ₂, which showed some crystalline peaks, indexed potentially as WB. Sputtered W-B-N layer is very effective for preventing the fast diffusion of Cu atoms during the high-temperature annealing. Barrier properties of W-B-N is studied by measuring resistivity of top Cu layer by annealing of the Cu/W-B-N/Si thin film stack. Cu layer resistivity on Si changes from 3 and 150 μΩ-cm from room temperature to K due to the formation of Cu ₃Si compound. When the WBN barrier is present, no resistivity change was observed. X-ray diffraction, and electrical property analysis show that the W-B-N barriers do not react with Si during an annealing in vacuum at 823 K for 30 min and prevent interdiffusion of Cu atoms at 623-823 K for 30 min, which is the better result for the thermal stability of a diffusion barrier compared to conventional TaN barrier.