Michael Scott Barnes

Novel radio‐frequency induction plasma processing techniques

A novel plasma source combining rf inductive drive and multipole plasma confinement has been constructed to process advanced semiconductor materials. Measurements show a linear dependence of density with input power. Ion current efficiencies of 1 A per 150–300 W of input power can be achieved in argon, with lower efficiencies in electronegative gases. Applying an rf bias to a substrate immersed in the plasma allows the sheath voltage to be controlled between 8 and 300 V. Insight into the rf induction process can be gained by a simple circuit model, which represents the induction process with a transformer. The physical quantities describing the transformer can be obtained from numerical calculation of the fields of the induction coil. This plasma source can etch thin films at rates exceeding 1 μm/min.

Monte Carlo‐fluid hybrid model of the accumulation of dust particles at sheath edges in radio‐frequency discharges

Particulate contamination (dust) has been observed to accumulate near the sheath‐plasma boundary in both radio‐frequency (rf) and direct‐current (dc) discharges. We have developed and applied a hybrid Monte Carlo‐fluid simulation of electron, ion, and charged dust transport in rf discharges to investigate the dynamics of particulate contamination. The processes governing the transport of charged dust in the model are drift of partially shielded particles in the electric field, collisions with the fill gases, and viscous ion drag arising from Coulomb interactions of particles with ions drifting and diffusing in the plasma. We find that negatively charged dust particles accumulate near the sheath‐plasma boundary, and that transport of the particles is dominated by ion drag.

Electron energy distribution function measurements in a planar inductive oxygen radio frequency glow discharge

A tuned, cylindrical Langmuir probe was used to measure current‐voltage traces in a planar, inductive oxygen, radio frequency glow discharge at several pressures ranging from 0.5 to 10 mT. The plasma potentials were determined from the zero crossings of the trace second derivatives. Positive ion densities were evaluated using orbit motion limited probe theory; electron densities were estimated by integrating the area under the unnormalized distribution function. By applying the Druyvesteyn formula to the digitized probe traces, the electron energy distribution functions were obtained. The distribution functions ranged from Maxwellian at 0.5 mT to almost Druyvesteyn‐like at 10 mT.

Ion kinetics in low-pressure, electropositive, RF glow discharge sheaths

Ion kinetics in low-pressure (e.g., 1 mtorr), electropositive, RF glow discharge sheaths are studied using a Monte-Carlo-based computer simulation. The numerical model integrates particle trajectories using a spatially nonlinear, time-varying model of the electric field in the RF sheath. A scaling relationship is then discussed, relating the normalized ion energy spread to the ratio of ion sheath transit time to the RF period. The scaled numerical data shows good agreement with existing numerical and experimental data. >

Optical ion energy measurements in a radio‐frequency‐induction plasma source

In situ, Fabry–Perot interferometry was used to study the translational dynamics of ions in a magnetically confined, radio‐frequency‐induction (RFI) plasma reactor. Radial ion motion was characterized through measurements of the Doppler profile of emission from Ar+ ions. Radial ion energies depend on the operating power, pressure, and magnetic‐field configuration. In a magnetically confined RFI plasma at 1000 W, ion energies increase from 0.08 to approximately 0.25 eV as the operating pressure is lowered from 13 to 0.18 mTorr. Complementary Langmuir probe studies of the plasma potential as well as its variation across the radius of the reactor illustrate the influence of electric fields on the radial motion of ions in the RFI system. These measurements illustrate that radially directed ion motion in the RFI reactor is significantly less than that reported previously for a divergent‐field electron cyclotron resonance system.

A Monte Carlo microtopography model for investigating plasma/reactive ion etch profile evolution

A two‐dimensional microtopography etch simulation using Monte Carlo methods is presented. This simulation investigates the topography of an arbitrary profile, periodic semiconductor surface after (ion assisted) plasma etching. The dependence of the topography on the etch chemistry, the ion energy, and the physical bombardment mechanism is discussed. For sputter etching, the degree of anisotropy is shown to be related to both the ion directionality and the sputter yield function. The potential for using this simulation to analyze microscopic properties of plasma etching is discussed.

Plasma‐Induced Damage in a Planar Inductively Coupled Etch Reactor

Plasma-induced damage produced during oxide etching has been characterized using physical (thermawave), chemical (total reflectance x-ray fluorescence, TXFR), and electrical (MOS capacitors) techniques. The system used in this study is a planar inductively coupled plasma reactor. In addition, results from a capacitively coupled parallel plate etch reactor are included for comparison. Plasma-induced damage is examined with respect to the inductive power, bias power, and gas chemistry. The planar inductive plasma reactor is shown to create significantly less damage compared to the parallel plate reactive ion etch reactor