Solid State Phenomena Vol. 314

Abstract: Tetramethylammonium hydroxide (TMAH) is a metal-free strong alkaline solution which can etch poly-Si. The concentration of dissolved gas as well as the concentration of TMAH affects etching rate of poly-Si. The detailed kinetics of poly-Si etching in TMAH solution is investigated in this study. The effect of water and TMAH concentration on the etching kinetics of poly-Si was investigated by using various concentrations of TMAH solution. It is found that H₂O in TMAH solution plays an important role in etching poly-Si. Presence of dissolved CO₂ and O₂ in TMAH solution tends to inhibit etching of poly-Si. The concentration of dissolved CO₂ and O₂ in TMAH were reduced by Ar bubbling, thereby the poly-Si etching rate increased.

Abstract: In this atomic-scale study on technologically relevant group IV semiconductors, Ge and SiGe, we relate surface chemistry, in particular the nature of surface oxides, to wet etching kinetics. ICP-MS quantification of Ge in HCl solution containing H₂O_­2 as the oxidizing agent showed that the Si bulk concentration strongly impacted the etching kinetics. Post operando synchrotron XPS provided insight into the surface oxide chemistry involved in the etching process: a non-homogeneous porous layer with a depletion of Ge components at the outer surface due to pull out effects.

Abstract: 3 formulated etchants were prepared and their etch rates were measured using blanket wafers in order to confirm that the etching reactions on Si_1-XGe_X and Si are controllable. Si_1-XGe_X selective etching with those formulations was also verified using the wafers which had Si_1-XGe_X and Si multi-stacked structures. Cross-sectional transmission electron microscope (TEM) images suggested that the formulations were usable for Si_1-XGe_X selective etching processes.

Abstract: GaN based electronic devices have gained great success in the arena of high-frequency and high-power applications. A high-quality GaN MOS structure has the potential to enable new device designs and higher device performance, thereby bringing the success of GaN electronics to a new level. This paper discusses results of the work on GaN MOS structures show that with adequate surface preparation samples featuring interface trap density down to the ~ 10¹⁰ eV^-1cm^-2 range can be formed.

Abstract: Group III–V compound semiconductors are attracting attention as new channel materials that have higher carrier mobility than Si. However, defects easily occur at the interface between the semiconductor and insulator film, which degrades performance. In an earlier study, we demonstrated that the interfacial properties of InP are degraded by the growth of In₂O₃ and that In₂O₃ grows better in water than in air. Therefore, it is necessary to suppress the growth of In₂O₃ to improve the interfacial properties of InP. In this work, we focused on functional water, which can be controlled by adjusting the water conditions, and investigated the growth behavior of In₂O₃ in functional water. As a result, we found that the growth is suppressed in the low-pH range and in hydrogen water. It is important that H⁺ ions reduce OH⁻ ions, which contributes to the reaction with InP.

Abstract: Indium gallium arsenide (InGaAs) is one of the candidate materials to overcome the physical limitation of Si due to its excellent electrical properties. The effect of surface oxidation on the etching characteristics of InGaAs surface in acidic solutions were investigated. InGaAs surfaces was etched in HCl/H₂O₂/H₂O (CPM) and HNO₃/H₂O₂/H₂O (NPM), while there was no thickness change in diluted HCl or HNO₃. The CPM-treated InGaAs surface had a lower etching rate than the NPM-treated one, while etching rate of oxidized layer was higher in diluted HCl than in HNO₃. NaCl added in the NPM acts as an etching inhibitor for InGaAs and the etching rate was significantly suppressed. It is thought that Cl⁻ anion inhibits the formation of hydroxyl radical (OH∙) or consumes OH∙ in acidic solution, inhibiting surface oxidation of InGaAs and suppressing its material loss.

Abstract: In this work, we characterized the wet chemical atomic layer etching of an InGaAs surface by using various surface analysis methods. For this etching process, H₂O₂ was used to create a self-limiting oxide layer. Oxide removal was studied for both HCl and NH₄OH solutions. Less In oxide tended to remain after the HCl treatment than after the NH₄OH treatment, so the combination of H₂O₂ and HCl is suitable for wet chemical atomic layer etching. In addition, we found that repetition of this etching process does not impact on the oxide amount, surface roughness, and interface state density. Thus, nanoscale etching of InGaAs with no impact on the surface condition is possible with this method.

Abstract: VPC (Vapor Phase Cleaning) is studied to etch various types oxide film using a mixture of HF gas and H₂O vapor. We focused on controlling the amount of gas molecules adsorbed on the oxide surface and investigated the H₂O amount included in oxide films, which will contribute to the oxide etching reaction. We have verified that selective etching between different oxide films can be achieved by controlling the gas adhesion amount by varying process parameters and utilizing the different amounts of H₂O in the oxide films for several deposition methods.

Abstract: Silicon nitride is commonly etched by hot orthophosphoric acid. Hot diluted hydrofluoric acid is hereby used as an alternative. Nonetheless, in presence of silicon surfaces, some corrosion has been evidenced, degrading significantly active areas during the STI (Shallow Trench isolation) integration. Oxygen in hot deionized water or hot HF generates this corrosion and selecting a relevant chemical oxide before dispensing hot diluted HF is key in solving the concern.

Abstract: Wet etching of Si₃N₄ was conducted in superheated water at 160 °C with different additives type and concentration. In general, etching rate of Si₃N₄ increased with the pH of solution. However, it is difficult to fully explain the Si₃N₄ etching behavior just with the pH of solution. The OH^- concentration (or pH) in superheated water at 160 °C are different from the pH of solution at room temperature. Therefore, the OH^- concentrations in superheated water at 160 °C were calculated using van't Hoff equation, equilibrium constant equations, mass and charge balance equations. The calculated OH^- concentration at 160 °C showed better correlation with Si₃N₄ etching rate than that of initial pH of solution.