Effect of Plasma Pretreatment on Fixed Charge at the Silicon Nitride/Silicon Interface

The effect of plasma treatment prior to hydrogenated amorphous silicon nitride (a-SiN:H) deposition on the a-SiN:H/Si interface was studied. NH3, NH3+N2, and NH3+H2 were used as source gases for plasma treatments. Nitridation of silicon surfaces after plasma treatment was observed by X-ray photoelectron spectroscopy (XPS). Fourier transform infrared spectroscopy (FTIR) measurement revealed that the stoichiometry of the thin nitrided layer varied depending on the source gas. After the plasma treatment and subsequent a-SiN:H deposition on the silicon substrate, capacitance–voltage (C–V) characteristics of the metal–insulator–semiconductor (MIS) structure were measured. As a result, it was found that the interface trap density (DIT) of the plasma-treated sample decreased compared with that of the nontreated sample, whereas the type of source gas did not affect DIT. On the other hand, flatband voltage (VFB) of MIS structure shifted along with the type of source gas, and this phenomenon indicates that the fixed charge at the a-SiN:H/Si interface depends on the stoichiometry of the thin nitrided layer. Finally, the passivation effect of plasma treatment was evaluated quantitatively on the basis of the extended Shockley–Read–Hall (SRH) theory.