Heon Chang Kim

Synthesis of Lithium-Cobalt Oxide Nanoparticles by Flame Spray Pyrolysis

Crystalline LiCoO2nanoparticles were synthesized from an aqueous solution of acetate compounds of lithium and cobalt by a flame spray pyrolysis, and characterized by TEM, XRD, and BET method. We investigated the evolution of LiCoO2nanoparticles from liquid droplets sprayed along the flame and observed disintegration of aqueous precursor droplets about 10μm into smaller fragments around 50 nm in the high temperature flame, as well as decomposition/oxidation of the precursor and coalescence/coagulation. We also examined effects of process variables such as molar concentrations of the precursors and flow rates of combustible gases on the particle size and crystal structure. The average particle diameter increased with an increase in the molar concentration of the precursor. Raising the maximum flame temperature by controlling the gas flow rates also led to an increase in the average diameter of the particles. The crystalline nanoparticles synthesized were nearly spherical, and their average primary particle diameters ranged from 11 to 35 nm.

Dually driven radio frequency plasma simulation with a three moment model

This article presents simulation results of a dually excited capacitive rf plasma reactor. A self-consistent three moment model is employed which is shown to accurately capture the ion flux and energy at the substrate. Self-dc biases at the powered electrodes are also self-consistently determined by relating surface charges through Gauss’ law. The simulation results of this rf triode system indicate that plasma density is predominantly determined by the primary electrode. Self-bias and ion bombardment energy at the secondary electrode both exhibit linear (logarithmic) dependency on the secondary rf power (frequency). This is qualitatively in good agreement with experimental results.

Simulation based plasma reactor design for improved ion bombardment uniformity

The geometric effects of plasma processing tools on the ion bombardment uniformity are studied through a plasma model that employs the first two and three moments of the Boltzmann equation for ions and electrons, respectively. The reactor considered is a parallel plate rf diode enclosed with insulators. The governing equations coupled with Poisson’s equation are self-consistently solved using a simplified 4th order accurate ENO scheme which determines the choice of stencils depending only on the characteristic direction. Reactor geometries are varied so as to improve the ion bombardment uniformity on the wafer while operating conditions are fixed. Two dimensional simulation results indicate that uniformity of ion bombardment impinging on the wafer can be improved by using a thicker insulating sidewall due to its higher impedance to rf currents. A longer electrode and a larger reactor diameter also improve the uniformity because sudden changes of electrical properties at the interface between electrode and...

On rapid computation of time periodic steady State in Simulation of capacitively coupled RF plasma

This paper proposes a methodology reducing the number of RF cycles necessary to reach time periodic steady-state solutions for efficient simulations of a three-moment plasma model. Our methodology employs a feedback control approach in conjunction with an implicit time integration scheme. Feedback gains are rigorously estimated by taking into account plasma responses during simulation. Through the one-dimensional simulation of a parallel plate capacitively coupled RF argon plasma, the proposed feedback control approach demonstrates its capability to dramatically reduce the number of RF cycles required to reach the time periodic steady state, resulting in several factors of speedup in simulation time. The simulation result showed that electrons emitted in a temporary cathodic sheath could acquire supersonic velocities and shocks could form near the corresponding sheath boundary as they enter a bulk plasma region.

Dust transport phenomena in a capacitively coupled plasma reactor

The effect of particulate size on the spatial distribution of dust in a plasma environment is investigated through the simulation of a dust transport model coupled with plasma and neutral models. The dust transport model takes into account all important factors affecting dust behavior (gravitational, electrostatic, ion drag, neutral drag and Brownian forces). A Lagrangian approach is employed for the simulation of the dust transport model, tracking the individual trajectory of each particulate by taking a force balance on the particulate. Trap locations, for dust particles of sizes ranging from a few nm to a few μm, are identified in an electropositive plasma. The simulation results show that dust particles are trapped at locations where the forces acting on them balance. While fine particles tend to be trapped in the bulk, large particles accumulate near bottom sheath boundaries and around material interfaces, such as wafer and electrode edges where a sudden change in electric field occurs. Overall, smal...

Phasing effects of dual RF voltage waves on plasma properties in a capacitively coupled plasma reactor

Summary form only given, as follows. In the plasma processing of electronic materials, it is common practice to control plasma density and ion bombardment energy by manipulating excitation voltage and frequency. In such applications, an appropriate combination of excitation frequency and RF power is required to accurately control ion flux and bombardment energy at the substrate surface. We investigate the effects of phase differences between excitation voltage waves simultaneously imposed, through blocking capacitors, on primary and secondary electrodes at the various combinations of commensurate frequencies by the simulations of a self-consistent, three-moment plasma model.