Vitaly Kuzmenko

This study investigates the spatial distribution of the plasma sheath characteristics and radial non-uniformity of plasma parameters across the wafer in inductively coupled plasma etching tools for advanced microelectronic applications. The work focuses on the mechanisms controlling uniformity of hafnium oxide (HfO2) parasitic sputtering relevant for plasma-assisted atomic layer etching (ALE) with ultra-low energy ions. The study utilized a combination of hydrodynamic modeling for the plasma volume and a more detailed model for the plasma sheath near the wafer, incorporating field-dependent ion mobility. The developed models are based on parameters obtained by plasma diagnostics, and the results were validated in sputtering experiments. We show that sheath disturbance near the wafer edge systematically shifts the ion energy distribution to higher values, increasing sputtering rates at the periphery of the wafer for low-energy bombarding ions. Taking account of this effect is important in the development of monolayer-precision plasma technologies in microelectronics, such as ALE.

The selectivity of the reactive ion etching of silicon using a negative electron resist AR-N 7520 mask was investigated. The selectivity dependencies on the fraction of SF₆ in the feeding gas and bias voltage were obtained. To understand the kinetics of passivation film formation and etching, the type and concentration of neutral particles were evaluated and identified using plasma optical emission spectroscopy. Electron temperature and electron density were measured by the Langmuir probe method to interpret the optical emission spectroscopy data. A high etching selectivity of 8.0 ± 1.8 was obtained for the etching process. The optimum electron beam exposure dose for defining the mask was 8200 pC/m at 30 keV.

The possibilities of optimization of the two-step atomic layer etching process for HfO2 in conventional plasma etching tools were studied. The surface modification step was realized in Ar/CF4/H2 plasma, and the reaction between the modified layer and the surface was activated by Ar ion bombardment from the plasma in the second step. Investigation of the effects of activation step duration, DC bias during activation, and Ar plasma density was carried out. The mechanism of the etching process has been shown to involve fluorination of oxide during the modification step and subsequent removal of fluorine-containing particles at the activation step. An increase in parasitic sputtering rate and lower process saturation with the growth of DC bias during activation was demonstrated. The advantage of the ALE process in lower surface roughness over the conventional etching process was shown. Similar etching characteristics of HfO2 and ZrO2 suggest a similarity in the etching process for the mixed hafnium-zirconium oxide material.

This article discusses a method for forming black silicon using plasma etching at a sample temperature range from −20 °C to +20 °C in a mixture of oxygen and sulfur hexafluoride. The surface morphology of the resulting structures, the autocorrelation function of surface features, and reflectivity were studied depending on the process parameters—the composition of the plasma mixture, temperature and other discharge parameters (radical concentrations). The relationship between these parameters and the concentrations of oxygen and fluorine radicals in plasma is shown. A novel approach has been studied to reduce the reflectance using conformal bilayer dielectric coatings deposited by atomic layer deposition. The reflectivity of the resulting black silicon was studied in a wide spectral range from 400 to 900 nm. As a result of the research, technologies for creating black silicon on silicon wafers with a diameter of 200 mm have been proposed, and the structure formation process takes no more than 5 min. The resulting structures are an example of the self-formation of nanostructures due to anisotropic etching in a gas discharge plasma. This material has high mechanical, chemical and thermal stability and can be used as an antireflective coating, in structures requiring a developed surface—photovoltaics, supercapacitors, catalysts, and antibacterial surfaces.

Plasma was diagnosed using Langmuir probe and optical actinometry methods, and growth rates of films or etching of surfaces of functional layers from Ar/CF₄/H₂ plasma were investigated in a plasma etching setup. It was found that the deposition rate varies non-monotonically with the proportion of CF₄ in the plasma, and the film deposition process is replaced by the SiO₂ etching process. At high CF₄ proportions in the plasma, the deposition rate is determined by the concentration of fluorocarbon radicals in the plasma. Understanding the kinetics of the fluorocarbon film deposition process enables optimization of the atomic layer etching process.

Low-pressure inductively coupled plasma of gaseous CF₃Br has been studied by Langmuir probe and optical emission spectroscopy (actinometry) techniques. The electron temperature, electron and positive ion concentrations, and concentrations of fluorine- and bromine-containing radicals are determined. An explanation of the previously reported significant degradation of ultralow-k dielectrics during etching in this plasma is proposed.