Yasunari Okamoto

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.

Influence of Preferred Orientation in Indium Tin Oxide.

We investigated the electrical and optical properties, the chemical composition, the surface morphology and the crystallinity of sputtered Sn-doped In 2 O 3 films deposited on different substrate positions. Both the electric conductivity and the optical transparency are related to the free carrier density and moreover the preferred crystal orientation. The former relation is attributed to the Burstein-Moss effect and the latter suggests the Sn doping mechanism.

Effects of Nitrogen Doping in the Insulational Character of Anodically Oxidized Films of Tantalum

The effects of nitrogen doping as a terminator in an anodically oxidized film of tantalum have been investigated. In the oxide film of nitrogen-free tantalum, the electric leakage current abruptly increased with the applied voltage. It is well-known as the Poole-Frenkel effect [1] [2]. After annealing at 623K in a hydrogen atmosphere, the leakage current increased. On the other hand, in the oxidized films of nitrogen-doped tantalum the leakage current increased in proportion to the applied voltage, but it was very small as compared with the nitrogen-free oxide. Moreover the leakage current decreased after annealing. The decrement strongly depended on the amount of doped nitrogen.