Doosik Kim

Three-dimensional simulation of an inductively coupled plasma reactor

A three-dimensional finite element fluid model and a corresponding simulation tool have been developed for studying azimuthal asymmetries and their effect on etch uniformity in inductively coupled plasma (ICP) reactors. For silicon etching with chlorine in an ICP reactor with a planar coil, four different cases were examined: (a) uniform power deposition without a focus ring, (b) uniform power deposition with a focus ring, (c) nonuniform power deposition without a focus ring, and (d) nonuniform power deposition with a focus ring. When etching is ion driven, the power deposition profile is most important for etch uniformity, because azimuthal nonuniformities in the ion production rate can persist even down to the wafer level. For uniform power deposition, the effect of asymmetric pumping becomes more important. A focus ring can play an important role in alleviating azimuthal nonuniformities, especially in the nonuniform power deposition cases. Gas inlets pointing parallel to the wafer plane introduce only ...

SiO2 etching in inductively coupled C2F6 plasmas: surface chemistry and two-dimensional simulations

Abstract A surface chemistry model was developed to understand the mechanism of etching or deposition on silicon dioxide surfaces exposed to a high density C2F6 plasma. The surface chemistry model in combination with a gas phase plasma chemistry model was implemented in the Modular Plasma Reactor Simulator (MPRES) to study oxide etching and uniformity under typical processing conditions. Simulation results on etch rate and uniformity as a function of operating conditions were consistent with experimental data. The transition from polymerization to etching as the ion bombardment energy (bias power) was increased was also captured by the simulation. Under low pressure conditions (several mtorr) the ion flux peaked at the wafer center while the neutral flux peaked at the wafer edge. Under such conditions, the oxide etch rate was highest at the edge. This supports the conclusion that, at such low pressures, oxide etching is ion driven but neutral dominated.

Simulation of a two-dimensional sheath over a flat wall with an insulator/conductor interface exposed to a high density plasma

The structure of the two-dimensional (2D) sheath over a flat, electrically inhomogeneous wall exposed to a high density plasma was investigated by a fluid model. The wall consisted of a floating semi-infinite insulator in contact with a semi-infinite conductor biased by a negative dc voltage. The difference in sheath potential over the two materials resulted in a 2D sheath over the insulator/conductor interface. The ion flux was higher on the conductor side of the interface at the expense of the flux on the insulator side. The spatial extend and magnitude of the ion flux disturbance scaled with the difference in the sheath thickness over the two different materials. The ion impact angle along the surface increased progressively as the material interface was approached. Sheath distortion was exacerbated when the electron temperature was decreased or the bias potential was made more negative.

Experimental and theoretical study of ion distributions near 300 μm tall steps on rf-biased wafers in high density plasmas

We present an experimental and theoretical study of ion fluxes, energy distributions, and angular distributions close to 300 μm tall “steps” on rf-biased wafers in high-density argon plasmas. This feature size is important in the etching of microelectromechanical systems. The theory and data show good agreement in most of the trends in the ion distributions as our sampling point approaches the foot of the step: (1) the ion flux decreases, (2) the ions move away from vertical, turning towards the step, and (3) the widths of the double-peaked ion energy distributions become narrower. The theory predicts that the hot neutral flux near the foot of the step is comparable to the ion flux. These hot neutrals may have important effects on the etching process.

Simulation of a two-dimensional sheath over a flat insulator–conductor interface on a radio-frequency biased electrode in a high-density plasma

A combined fluid/Monte Carlo (MC) simulation was developed to study the two-dimensional (2D) sheath over a flat insulator/conductor interface on a radio-frequency (rf) biased electrode in a high-density plasma. The insulator capacitance increased the local impedance between the plasma and the bias voltage source. Thus, for uniform ion density and electron temperature far away from the wall, the sheath potential over the insulator was only a fraction of that over the conductor, resulting in a thinner sheath over the insulator. The fluid model provided the spatiotemporal profiles of the 2D sheath electric field. These were used as input to the MC simulation to compute the ion energy distribution (IED) and ion angular distribution (IAD) at different locations on the surface. The ion flux, IED, and IAD changed drastically across the insulator/conductor interface due to the diverging rf electric field in the distorted sheath. The ion flux was larger on the conductor at the expense of that on the insulator. Bot...

Plasma molding over deep trenches and the resulting ion and energetic neutral distributions

A two-dimensional fluid/Monte Carlo simulation was developed to study plasma molding over deep trenches and the resulting ion and energetic (fast) neutral distributions, with emphasis on neutral beam sources. Plasma molding occurs when the sheath thickness is comparable to or smaller than the trench width. Using the electric field profiles predicted by the self-consistent fluid simulation, ions and energetic neutrals (resulting mainly by ion neutralization on the sidewall) were followed by the Monte Carlo simulation. The dominant energetic species at the bottom of a high aspect ratio trench were neutrals. A thin sheath (compared to the trench width), favored a larger energetic neutral flux at the bottom, at the expense of neutral energy and directionality. A relatively thick sheath produced neutrals of higher directionality at the expense of neutral flux. Neutral energy and directionality both increased by increasing the sheath potential.

Simulation of plasma molding over a ring on a flat surface

A fluid/Monte Carlo simulation model was developed to study plasma molding over an axisymmetric feature (a ring) resting on an otherwise planar surface in contact with a high-density rf plasma. The two-dimensional (r,z) time-dependent sheath potential, and ion density and flux profiles were predicted with a self-consistent fluid simulation. The trajectories of ions and energetic neutrals (resulting mainly by ion neutralization on the cylindrical sidewalls of the ring) were then followed with a Monte Carlo simulation, in an effort to obtain their energy and angular distributions on the substrate surface. When the sheath thickness was comparable to the size of the ring, strong radial electric fields deflected oncoming ions toward the sidewalls of the ring. The ion density was lower in the cylindrical well formed by the ring, compared to outside, resulting in a locally thicker sheath and a smaller spread in the double-peaked ion energy distributions at the bottom of the well. The ion impact angle increased p...

Energy and angular distributions of ions and neutrals extracted from a slot in contact with a high-density plasma

The energy and angular distributions of ions and neutrals extracted from a two-dimensional slot in contact with a high-density Ar plasma were investigated. A combined fluid/Monte Carlo simulation was developed to follow the trajectories of ions and fast neutrals through the sheath and out the slot. The energy and angular distributions reflect the strong disturbance of the sheath when the slot size is comparable to the sheath thickness.