Plasma-Enhanced-Polymerization Thin-Film as a Drift Barrier for Cu Ions

The barrier properties of divinyl siloxane-benzocyclobutene (DVS-BCB) films formed by plasma-enhanced polymerization were studied for ultralow-k porous silica (po-SiO) interlayer dielectrics. Time-dependent dielectric breakdown (TDDB) measurements of blanket Cu/BCB/Si metal–insulator–semiconductor (MIS) capacitors showed no polarity dependence of the bias-temperature stresses at 200 °C under 2 MV/cm, indicating that Cu ions hardly drifted into the BCB film with the positive bias stress. On the other hand, Cu/SiOC/Si MIS capacitors under the positively biased Cu showed a significant degradation in the TDDB lifetime compared with the negative bias case. The barrier effect of the thin BCB was confirmed from the TDDB measurements using Cu/BCB/ultralow-k-po-SiO/Si stacked MIS structures. The TDDB lifetime of the stacked MIS capacitor was improved more than 30-fold by the use of 15-nm-thick BCB on po-SiO. The electric field and temperature dependences of the TDDB lifetime of the stacked MIS structure indicated that the TDDB lifetime of po-SiO capped with 15-nm-thick BCB is longer than 10 years at 125 °C and 1.4 MV/cm. We conclude that the barrier property of BCB that is as thin as 15 nm is effective for preventing Cu ion drift into interlayer dielectrics.