Monica Scholten

On the Mechanism of ITO Etching: The Specificity of Halogen Acids

Tin-doped indium oxide films, prepared by dc magnetron sputtering, have been investigated with respect to their etching behavior in a large number of acids. The etch rate in acids other than the halogen acids is extremely low. The films dissolve at a rate convenient for practical use in concentrated aqueous solutions of halogen acids. Experiments in HCl solutions diluted with solvents with a low dielectric constant show that the undissociated halogen acid is the active agent for the etching process. A mechanism is proposed to explain the observed results

On the Mechanism of ITO Etching in Halogen Acids: The Influence of Oxidizing Agents

The etching process of polycrystalline tin-doped indium oxide (ITO) films in HCl solutions is investigated by kinetic and electrochemical experiments and the patterning characteristics are examined by scanning electron microscopy. The influence of oxidizing agents on the etching behavior is studied. A model is proposed in which ITO is first attacked by undissociated HCl molecules, forming a surface intermediate which is mobile on the surface. This intermediate can react with HCl molecules or with the oxidizing agent. The competition between these two reactions determines the kinetics and the patterning characteristics of the dissolution process. A kinetic rate law is derived that predicts the etch rate in FeCl 3 /HCl solutions. A good agreement between experimental and calculated values is obtained in a wide range of HCl and FeCl 3 concentrations.

(Photo)electrochemical characterization of tin‐doped indium oxide

Tin‐doped indium oxide (ITO) films, prepared by dc magnetron sputtering, were characterized by (photo)electrochemical measurements in aqueous H2SO4 solutions. Wavelength dependent photocurrent measurements were used to determine the optical band gap energy of these films. Electron excitation from the valence band to localized states in the band gap was observed. The presence of such energy levels resulted in an Urbach tail. Impedance measurements were used to determine the flatband potential and the charge carrier concentration of ITO. A change in the charge carrier concentration due to different deposition conditions resulted in a change of the resistivity and in a shift of the flatband potential. This shift could be explained by a Moss–Burstein shift of the optical band gap.

The etching of Ti-W in concetrated H2O2 solutions

Abstract The etching process of Ti-W alloys in concentrated H 2 O 2 solutions is characterized by analytical and microscopic techniques and kinetic experiments. The influence of the Ti-W composition, the composition of the solution and the process parameters on the rate and uniformity of etching is investigated. The kinetics exhibits a clear induction time, because of a top layer that contains oxygen and has a much higher titanium content than the bulk. Etching in pure H 2 O 2 solutions proceeds via surface oxides and is very sensitive to mass transport conditions. This causes a considerable scatter in the kinetic results and a very poor uniformity of etching over larger areas. Addition of a concentrated buffer to the H 2 O 2 solution results in a decreased etch rate, but the reproducibility and uniformity are greatly enhanced.

An electrochemical and X-ray photoelectron spectroscopic study into the mechanism of Ti + W alloy etching in H2O2 solutions

Abstract One of the most striking aspects of etching Ti + W alloys in aqueous H 2 O 2 solutions is the decrease in etch rate under improved mass transport conditions. This aspect was studied by X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. XPS results showed that Ti dissolves preferentially and that a W oxide film (WO x ) is formed at the surface during etching. The valence of W in this oxide is between IV and VI. The WO x film is thicker for a rotating Ti + W sample than for a stationary one. The electrochemical experiments showed that H 2 O 2 is reduced at the WO x covered surface. Intermediates of this reduction reaction (most probably OH . radicals) interact with WO x and enhance further oxidation into the soluble WO 5 2− ion. Removal of these intermediates by improved mass transport conditions and/or better supply of the stabilizing agent in H 2 O 2 solutions results in lower etch rates.