Katsuhisa Yuda

Controlling the Amount of Si-OH Bonds for the Formation of High-Quality Low-Temperature Gate Oxides for Poly-Si TFTs

Lowering process temperatures for polysilicon Thin-Film-Transistors (TFTs) has given rise to new worries about the quality of TFT gate oxides. Specifically, the presence of large amounts of Si-OH bonds in gate oxides has become a matter of concern. We discuss methods for suppressing the formation of Si-OH bonds during Chemical Vapor Deposition (CVD) of Low-Temperature Processed (LTP) gate oxides. In various kinds of CVD techniques, the use of Remote-Plasma Enhanced CVD (RPCVD is shown to be efficacious for the suppression. The control of the reaction between the silicon source gas and the oxygen source gas is also shown to be effective. We also show that decreased amounts of Si-OH bonds in LTP-CVD gate oxides result in desirable decreases in both leakage current and fixed oxide charge densities, and that the amount of Si-OH bonds can be used as an index of gate oxide quality.

Reliability improvement in low-temperature processed poly-Si TFTs for AMLCDs

Low-temperature processed polysilicon thin-film-transistors have shown negative threshold voltage shift under gate bias stress. This shift was produced as a result of the positive charge created by water penetration and by the subsequent field activated chemical reaction in the gate oxide. Thermal desorption mass spectrometry (TDS) measurements reveal that dissociation of Si-OH bonds with hydrogen-bonded water in the oxide may be a fundamental contributor to the creation of the positive charge. As a preventative measure, we used hydrogenation to dissociate the Si-OH bonds beforehand, and in this way we have been able to obtain stable TFTs that can be applied to drivers for AMLCDs.<<ETX>>