Intermetal dielectric process using spin-on glass for ferroelectric memory devices having SrBi_2Ta_2O_9 capacitors

摘要

The degradation behavior of integrated Pt/SrBi_2Ta_2O_9/Pt capacitors caused by hydrogen impregnation during the spin-on glass (SOG)-based intermetal dielectric (IMD) process was investigated. SOG was tested as an IMD since it offers better planarity for multilevel metallization processes compared to other 5i02 deposition methods. It was found that the SOG itself does not degrade the ferroelectric performance. Deposition of an under-layer of SiO_xN_y by plasma-enhanced chemical vapor deposition (PFCVD) using SiH_4 + N_2O + N_2 source gases and a SiO_(2-x) capping layer by another PECVD process using SiH_4 + N_2O source gases produced hydrogen as a reaction by-product. The hydrogen diffused into the SBT layer and degraded the ferroelectric performance during subsequent annealing cycles. A very thin (10 nm) Al_2O_3 layer grown by atomic layer deposition before the IMD process successfully blocked the impregnation of the hydrogen. Therefore, excellent ferroelectric performance of the SBT capacitors were maintained after the multilevel metallization process as well as passivation. The adoption of SOG in the IMD process greatly improved the surface flatness of the wafer resulting in a higher capacitor yield with very good uniformity in ferroelectric properties over the 8-in.-diameter wafer.