Post-cleaning effect on a HfO₂ gate stack using a NF₃/NH₃ plasma

The effects of dry cleaning of a HfO₂ gate stack using NF₃ only and a NF₃/NH₃ gas mixture plasma were investigated. The plasma dry cleaning process was carried out after HfO₂ deposition using an indirect down-flow capacitively coupled plasma (CCP) system. An analysis of the chemical composition of the HfO₂ gate stacks by XPS indicated that fluorine was incorporated into the HfO₂ films during the plasma dry cleaning. Significant changes in the HfO₂ chemical composition were observed as a result of the NF₃ dry cleaning, while they were not observed in this case of NF₃/NH₃ dry cleaning. TEM results showed that the interfacial layer (IL) between the HfO₂ and Si thickness was increased by the plasma dry cleaning. However, in the case of NF₃/NH₃ dry cleaning using 150 W, the IL thickness was suppressed significantly compared to the sample that had not been dry cleaned. Its electrical properties were also improved, including the low gate leakage currents, and reduced EOT. Finally, the finding show that the IL thickness of the HfO₂ gate stack can be controlled by using the novel NF₃/NH₃ dry cleaning process technique without any the significant changes in chemical composition and metal-oxide-semiconductor (MOS) capacitor characteristics.