Microstructural characterization and inductively coupled plasma-reactive ion etching resistance of Y2O3-Y4Al2O9 composite under CF4/Ar/O2 mixed gas conditions.

In the semiconductor manufacturing process, when conducting inductively coupled plasma-reactive ion etching in challenging environments, both wafers and the ceramic components comprising the chamber's interior can be influenced by plasma attack. When ceramic components are exposed to long-term plasma environments, the eroded components must be replaced. Furthermore, non-volatile reactants can form and settle on semiconductor chips, acting as contaminants and reducing semiconductor production yield. Therefore, for semiconductor processing equipment parts to be utilized, it is necessary that they exhibit minimized generation of contaminant particles and not deviate significantly from the composition of conventionally used Al2O3 and Y2O3; part must also last long in various physicochemical etching environment. Herein, we investigate the plasma etching behavior of Y2O3-Y4Al2O9 (YAM) composites with a variety of mixing ratios under different gas fraction conditions. The investigation revealed that the etching rates and changes in surface roughness for these materials were significantly less than those of Y2O3 materials subjected to both chemical and physical etching. Microstructure analysis was conducted to demonstrate the minimization of crater formation. Mechanical properties of the composite were also analyzed. The results show that the composite can be commercialized as next-generation ceramic component in semiconductor processing equipment applications.

Low-Temperature, Universal Synthetic Route for Mesoporous Metal Oxides by Exploiting Synergistic Effect of Thermal Activation and Plasma.

Mesoporous metal oxides exhibit excellent physicochemical properties and are widely used in various fields, including energy storage/conversion, catalysis, and sensors. Although several soft-template approaches are reported, high-temperature calcination for both metal oxide formation and template removal is necessary, which limits direct synthesis on a plastic substrate for flexible devices. Here, a universal synthetic approach that combines thermal activation and oxygen plasma to synthesize diverse mesoporous metal oxides (V2O5, V6O13, TiO2, Nb2O5, WO3, and MoO3) at low temperatures (150-200 °C), which can be applicable to a flexible polymeric substrate is introduced. As a demonstration, a flexible micro-supercapacitor is fabricated by directly synthesizing mesoporous V2O5 on an indium-tin oxide-coated colorless polyimide film. The energy storage performance is well maintained under severe bending conditions.

Role of Oxygen in Amorphous Carbon Hard Mask Plasma Etching.

In the current and next-generation Si-based semiconductor manufacturing processes, amorphous carbon layer (ACL) hard masks are garnering considerable attention for high-aspect-ratio (HAR) etching due to their outstanding physical properties. However, a current limitation is the lack of research on the etching characteristics of ACL hard masks under plasma etching conditions. Given the significant impact of hard mask etching on device quality and performance, a deeper understanding of the etching characteristics of ACL is necessary. This study aims to investigate the role of oxygen in the etching characteristics of an ACL hard mask in a complex gas mixture plasma etching process. Our results show that a small change of oxygen concentration (3.5-6.5%) can significantly alter the etch rate and profile of the ACL hard mask. Through our comprehensive plasma diagnostics and wafer-processing results, we have also proven a detailed mechanism for the role of the oxygen gas. This research provides a solution for achieving an outstanding etch profile in ACL hard masks with sub-micron scale and emphasizes the importance of controlling the oxygen concentration to optimize the plasma conditions for the desired etching characteristics.

Correlation with the Microstructure and Synergistic Physiochemical Etching Resistance of Nanocomposites under Fluorine-Containing Plasma Conditions.

In the semiconductor fabrication industry, high-power plasma is indispensable to obtain a high aspect ratio of chips. For applications to ceramic components including the dielectric window and ring in the semiconductor etching chamber, the Y2O3 ceramics have attracted interest recently based on excellent erosion resistance. When a high bias voltage is applied in a plasma environment containing fluorine gas, both chemical etching and ion bombardment act simultaneously on the ceramic components. During this etching process, severe erosion and particles generated on the ceramic surface can have effects on overall equipment effectiveness. Herein, we report the outstanding plasma etching resistance of Y2O3-MgO nanocomposite ceramics under a CF4/Ar/O2 gas atmosphere; the erosion depth of this material is 40-79% of that of the reference materials, Y2O3 ceramics. In a robust approach involving effective control of the microstructure with different initial particles and sintering conditions, it is possible to understand the relationship between etching behavior and microstructure evolution of the nanocomposite ceramic. The results indicate that the nanocomposite with fine and homogeneous domain distribution can decrease particle generation and ameliorate its life cycle; accordingly, this is a promising alternative candidate material for ceramic components in plasma chambers.

Exploring the nonextensive thermodynamics of partially ionized gas in magnetic field.

Contrary to classical thermodynamics, which deals with systems in thermal equilibrium, partially ionized gases generally do not reach thermal equilibrium. Nonextensive statistical mechanics has helped extend classical thermodynamics to nonequilibrium ionized gas. However, the fundamental question on whether the statistics of non-Maxwellian electrons satisfy the laws of thermodynamics has not been resolved. Here, we verify the thermodynamic laws of reversible and adiabatic processes for a magnetically expanding ionized gas. Together with the experimental evidence of the non-Maxwellian electron distribution, the κ distribution, which measures the thermal equilibrium states, shows the Tsallis entropy to be nearly constant and the polytropic index to be close to adiabatic values along a divergent magnetic field. These results verify that the collisionless magnetic expansion of a nonequilibrium plasma is reversible and adiabatic, and an isentropic process is the origin of the high-energy tail of the energy distribution far downstream.

Crystalline silicon nanoparticle formation by tailored plasma irradiation: self-structurization, nucleation and growth acceleration, and size control.

Crystalline silicon nanoparticles at the nanometer scale have been attracting great interest in many different optoelectronic applications such as photovoltaic and light-emitting-diode devices. Formation, crystallization, and size control of silicon nanoparticles in nonharsh and nontoxic environments are highly required to achieve outstanding optoelectronic characteristics. The existing methods require high temperature, use of HF solution, and an additional process for the uniform redistribution of nanoparticles on the substrate and there are difficulties in controlling the size. Herein, we report a new self-assembly method that applies the controlled extremely low plasma ion energy near the sputtering threshold energy in rare gas environments as nonharsh and nontoxic environments. This method produces silicon nanoparticles by crystallization nucleation directly at the surface of the amorphous film via plasma surface interactions. It is evidently observed that the nucleation and growth rates of the crystalline silicon nanoparticles are promoted by the enhanced plasma ion energy. The crystalline silicon nanoparticle size is tailored to the nanometer scale by the plasma ion energy control.

Effect of Electron Energy Distribution on the Hysteresis of Plasma Discharge: Theory, Experiment, and Modeling.

Hysteresis, which is the history dependence of physical systems, is one of the most important topics in physics. Interestingly, bi-stability of plasma with a huge hysteresis loop has been observed in inductive plasma discharges. Despite long plasma research, how this plasma hysteresis occurs remains an unresolved question in plasma physics. Here, we report theory, experiment, and modeling of the hysteresis. It was found experimentally and theoretically that evolution of the electron energy distribution (EED) makes a strong plasma hysteresis. In Ramsauer and non-Ramsauer gas experiments, it was revealed that the plasma hysteresis is observed only at high pressure Ramsauer gas where the EED deviates considerably from a Maxwellian shape. This hysteresis was presented in the plasma balance model where the EED is considered. Because electrons in plasmas are usually not in a thermal equilibrium, this EED-effect can be regarded as a universal phenomenon in plasma physics.

Control of Size Uniformity of Cu Nanoparticle Array Produced by Plasma-Induced Dewetting.

The effects of plasma parameters such as plasma density, electron temperature, and sheath voltage on the uniformity of Cu nanoparticle arrays were investigated. These parameters were controlled by varying the pressure, RF power, and substrate bias voltage. A floating harmonic method was used to monitor the plasma parameters. Uniform nanoparticle arrays were produced when hole generation was increased by using a high ion.bombardment energy. As oppose to a low energy flux condition, where small and large nanoparticles coexisted due to a small number of holes, a larger number of holes was generated and distributed more uniformly during a high energy flux condition.

Probe diagnostics in the far scrape-off layer plasma of Korea Superconducting Tokamak Advanced Research tokamak using a sideband harmonic method.

Plasma characteristics in the far scrape-off layer region of tokamak play a crucial role in the stable plasma operation and its sustainability. Due to the huge facility, electrical diagnostic systems to measure plasma properties have extremely long cable length resulting in large stray current. To overcome this problem, a sideband harmonic method was applied to the Korea Superconducting Tokamak Advanced Research tokamak plasma. The sideband method allows the measurement of the electron temperature and the plasma density without the effect of the stray current. The measured plasma densities are compared with those from the interferometer, and the results show reliability of the method.

Mechanism of solid-state plasma-induced dewetting for formation of copper and gold nanoparticles.

Cu and Au nanoparticles were fabricated by plasma treatment on Cu and Au films at 653 K. The nanoparticles were formed by dewetting the metallic films using plasma. Scanning electron microscopy and transmission electron microscopy investigations showed that the plasma-induced dewetting of the Cu and Au films proceeded through heterogeneous hole nucleation and growth along the grain boundaries to lower the surface energy. The amount of energy transferred to surface atoms by one Ar ion was calculated to be 16.1 eV, which was sufficient for displacing Cu and Au atoms. Compared to thermally activated dewetting, more uniform particles could be obtained by plasma-induced dewetting because a much larger number of holes with smaller sizes was generated. The plasma dewetting process is less sensitive to the oxidation of metallic films compared to the annealing process. As a result, Cu nanoparticles could be fabricated at 653 K, whereas the thermally activated dewetting was not possible.

Two-dimensional-spatial distribution measurement of electron temperature and plasma density in low temperature plasmas.

A real-time measurement method for two-dimensional (2D) spatial distribution of the electron temperature and plasma density was developed. The method is based on the floating harmonic method and the real time measurement is achieved with little plasma perturbation. 2D arrays of the sensors on a 300 mm diameter wafer-shaped printed circuit board with a high speed multiplexer circuit were used. Experiments were performed in an inductive discharge under various external conditions, such as powers, gas pressures, and different gas mixing ratios. The results are consistent with theoretical prediction. Our method can measure the 2D spatial distribution of plasma parameters on a wafer-level in real-time. This method can be applied to plasma diagnostics to improve the plasma uniformity of plasma reactors for plasma processing.

Comparison of pressure dependence of electron energy distributions in oxygen capacitively and inductively coupled plasmas.

Electron energy distribution functions (EEDFs) were measured with increasing gas pressure in oxygen capacitively and inductively coupled plasmas. It was found that, in the capacitive discharge, abnormally low-energy electrons became highly populated and the EEDF evolved to a more distinct bi-Maxwellian distribution as the gas pressure was increased. This pressure dependence of the EEDF in the oxygen capacitive discharge is contrary to argon capacitively coupled plasma, where--at high gas pressure--low-energy electrons are significantly reduced due to collisional heating and the EEDF evolves to the Maxwellian. The highly populated low-energy electrons at high gas pressure, which was not observed in inductively coupled oxygen plasma, show that collisional heating is very inefficient in terms of the oxygen capacitive discharge. It appears that this inefficient collisional heating seems to be attributed to a low electric field strength at the center of the oxygen capacitive plasma.