High conductivity copper-boron alloys obtained by low temperature annealing

The electrical behavior during annealing of copper films with a nominal concentration of 2 at.% boron has been investigated. The evolution of the resistivity of the film was monitored using an in situ technique, in which the film was ramp-annealed at constant ramp rates. At a temperature of 150-200 °C, the resistivity of the Cu(B) undergoes a first drop. This is followed by one or two such drops in resistivity, so that after completion of a ramp-anneal from 50 °C to 750 °C, the room temperature resistivity decreases from the initial value of 13 μΩ cm to 2.1 μΩ cm, close to that of bulk copper. Isothermal annealing of the film also leads to substantial decreases in resistivity, from 13 μΩ cm to 3 μΩ cm after annealing at 350 °C for 8 h and to 2.5 μΩ cm at 400 °C for 4 h. These results show that a dramatic reduction in resistivity of Cu(B) alloys takes place at temperatures below 400 °C, suggesting possible applications for silicon device interconnections.