Junichi Tonotani

4.1: Low-Temperature-Processed IGZO TFTs for Flexible AMOLED with Integrated Gate Driver Circuits

We have reduced threshold voltage shift of IGZO TFTs processed at 200°C under bias-temperature stress of Vg = 20 V at 70°C for 2000 s to 0.22 V by optimizing IGZO deposition and annealing conditions. A flexible AMOLED display with integrated gate driver circuits has been demonstrated.

Measurement of Electron Density of Reactive Plasma Using a Plasma Oscillation Method

We measured the electron density of reactive plasma using a plasma oscillation probe and analyzed the mode change of power coupling during etching. The unique behavior of plasmas containing reactive negative ions is clarified. The change in the plasma reactor mode during silicon dioxide etching, from the inductive mode to the capacitive mode with increasing pressure, is investigated.

Effect of CHF3 Addition on Reactive Ion Etching of Aluminum Using Inductively Coupled Plasma

The role of CHF3 gas addition in reactive ion etching (RIE) processes using inductively coupled plasma for aluminum wirings were investigated. With increasing of the amount of CHF3 gas addition to the etching gas, the pattern profile changed from reverse to ordinary taper and the pattern width increased. It was considered that by adding CHF3 to the main etching gas, a larger amount of passivation layer deposited on the sidewall of the resist and Al pattern, which suppressed side etching of the pattern. To clarify the role of CHF3 addition, XPS, FT-IR and TDS analyses were carried out to study the structure of the passivation layer. Consequently, it is considered that the pattern sidewall is composed of AlF3, an organic polymerized film and a passivation layer including ammonium salt and B oxide. Due to the addition of CHF3 gas into the etching gas, AlF3 is additionally formed, which is deposited on the pattern sidewall, resulting in the change of the etched pattern profile and width.

Dry Etching of Cr2O3/Cr Stacked Film during Resist Ashing by Oxygen Plasma

Stacked films of chromium oxide and chromium (Cr2O3/Cr) have been commonly used as a photomask for the lithographic process of integrated circuit fabrication. It has been found, however, that the Cr2O3/Cr films were etched during the oxygen plasma ashing process, which is applied for the resist removal after the Cr2O3/Cr patterning. In order to solve this problem, we investigated the mechanisms of the Cr2O3/Cr film etching during the ashing process. As a result, it was found that the Cr2O3/Cr film is oxidized during the ashing process to generate CrOx (2≤x≤3) in which Cr has a higher valence than Cr2O3, and that the CrOx (2≤x≤3) evaporates. It was confirmed by means of a plasma shielding experiment that not only oxygen plasma but also oxygen radicals oxidize the Cr2O3/Cr. It has been found that keeping the photomask temperature below 200°C during the ashing process solves the Cr2O3/Cr etching problem.

Formation of Ammonium Salts and Their Effects on Controlling Pattern Geometry in the Reactive Ion Etching Process for Fabricating Aluminum Wiring and Polysilicon Gate

The role of N2 gas addition in the reactive ion etching (RIE) processes for aluminum wiring and polysilicon gate fabrication was investigated. With an increase in the amount of N2 gas added to the etching gas, the pattern profile changed from a reverse to an ordinary taper and the pattern width increased. By AES analysis, nitrogen was detected in the pattern sidewall passivation layer when N2 gas was added. Optical emission spectroscopy of the plasma revealed that hydrogen was supplied from the decomposition product of the photoresist in RIE of aluminum with BCl3/Cl2. XPS, FT-IR and TDS analyses were carried out to study the structure of the passivation layer. Consequently, it was confirmed that nitrogen combined with hydrogen to form N–H bonds in NH4+, and that NH4+ coupled with Cl-, AlCl4- and SiF62- during aluminum and polysilicon RIE, respectively. It was also found that ammonium salts were deposited on the pattern sidewall, and played a major role in controlling the etching profile and pattern width.

Behavior of incorporated nitrogen in plasma-nitrided silicon oxide formed by chemical vapor deposition

The behavior of nitrogen (N) atoms in plasma-nitrided silicon oxide (SiO2) formed by chemical vapor deposition (CVD) was characterized by physical analysis and from electrical properties. The changes in the chemical bonding and distribution of N in plasma-nitrided SiO2 were investigated for different subsequent processes. N–Si3, N–Si2O, and N2 are formed in a SiO2 film by plasma nitridation. N2 molecules diffuse out during annealing at temperatures higher than 900 °C. NH species are generated from N2 molecules and H in the SiO2 film with subsequent oxide deposition using O3 as an oxidant. The capacitance–voltage (C–V) curves of metal–oxide–semiconductor (MOS) capacitors are obtained. The negative shift of the C–V curve is caused by the increase in the density of positive fix charge traps in CVD-SiO2 induced by plasma nitridation. The C–V curve of plasma-nitrided SiO2 subjected to annealing shifts to the positive direction and that subjected to the subsequent oxide deposition shifts markedly to the negative direction. It is clarified that the density of positive charge fixed traps in plasma-nitrided SiO2 films decrease because the amount of N2 molecules is decreased by annealing, and that the density of traps increases because NH species are generated and move to the interface between SiO2 and the Si substrate with the subsequent oxide deposition.

Selective dry etching of La 2 O 3 /Si stacked film

Summary form given only: A stacked film structure of lanthanum oxide and silicon (La₂O₃/Si) is considered to be used in MOSFETs in the Nano-CMOS era since La₂O₃ is a promising high-k gate insulator. In the substrate contact formation process, La₂O₃ should be removed selectively against Si substrate. In order to examine the possibility of the selective dry etching of La₂O₃/Si stacked film, dry etching characteristics of La₂O₃ and Si were investigated. As a result, it was found that pure Ar sputtering as well as an addition of Cl₂, BCl₃ or CF₄ to Ar caused higher etching rate of Si than that of La₂O₃, which led to a low etching selectivity. In Ar plasma in a chamber with B contaminations, however, Si was not etched while La₂O₃ was etched with the etching rate about 2 nm/min. X-ray photoelectron spectroscopy revealed that B existed only on the etched Si surface, which was considered effective for preventing Si from being etched by Ar sputtering. As a conclusion, noble gas plasma, such as Ar plasma, with small amount of B fluxes to the etching surface enables the La₂O₃/Si selective etching.