Complete prevention of reaction at HfO2/Si interfaces by 1 nm silicon nitride layer

When hafnium oxide (HfO2) is directly deposited on Si by the RF sputtering method, Hf silicide is formed and post-deposition anneal (PDA) at 400 °C transforms Hf silicide to Si suboxide plus Hf suboxide. The leakage current density for the 〈aluminum (Al)/HfO2/Si(1 0 0)〉 diodes without PDA is high due to the high density interface states near the Fermi level (0.86 eV above the Si valence band maximum, VBM) and minute conduction channels. PDA at 400 °C eliminates the interface states and the conduction channels, and improves the characteristics of the HfO2 layer, but interface states are newly formed at 0.53 eV above the VBM, resulting in still high leakage current density. Silicon nitride (SiN) layers formed by Si nitridation using N2-plasma generated by the low energy electron impact method possess a high nitrogen atomic concentration ratio, N/(N + O) of 0.65. When a 1.0 nm SiN layer is inserted between HfO2 and Si, interfacial reaction is completely prevented, resulting in a smaller effective oxide thickness, EOT of 1.4 nm. In spite of the smaller EOT, the leakage current density is nearly the same as that with no SiN layer, possibly due to the prevention of the formation of the conduction channels. PDA at 400 °C improves HfO2 characteristics without causing the interfacial reaction, leading to a decrease in the leakage current density.