John Howard Keller

New precision technique for measuring the concentration versus depth of hydrogen in solids

A method for the measurement of the concentration of hydrogen versus depth in solids using the 1H+15N resonant nuclear reaction is discussed. This method has a typical depth resolution of 50–100 A, can be used to a depth of several microns, and can measure hydrogen in concentrations of one part per thousand or greater.

Plasma potentials of 13.56‐MHz rf argon glow discharges in a planar system

The plasma potential of 13.56‐MHz low‐pressure argon glow discharges has been measured for various modes of applying the rf power in a geometrically asymmetric planar system. The plasma potential is determined from the energy distribution of positive ions incident on the grounded electrode. The voltages on the excitation electrode (target electrode) are carefully measured and the capacitive sheath approximation is used to relate these measured voltages to the measured plasma potential. This approximation is successful in most of the situations encountered in this low‐pressure (20 mTorr) relatively low‐power density regime. The effects of superimposing dc voltages on the excitation electrode are discussed.

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.

Inductive plasmas for plasma processing

With the need for high plasma density and low pressure in single wafer etching tools, a number of inductive etching systems have been and are being developed for commercial sale. This paper reviews some of the history of low-pressure inductive plasmas, gives features of inductive plasmas, limitations, corrections and presents uses for plasma processing. The theory for the skin depth, rf coil impedance and efficiency is also discussed.

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 study of CClF3/H2 reactive ion etching damage and contamination effects in silicon

A comprehensive characterization of the damage and contamination produced in silicon by CC1F3/H2 reactive ion etching is presented. This highly selective SiO2‐to‐Si reactive ion etching process unfortunately produces all three of the deleterious damage‐contamination layers that can result from dry etching exposure; viz., CC1F3/H2 reactive ion etching produces a residue layer on the Si surface, a permeated layer at the Si near‐surface, and a layer of damaged Si. Various post‐RIE‐exposure, surface‐recovery approaches are evaluated in this report. The results indicate that in order to restore the surface to a device‐quality state, it is not sufficient to simply eliminate surface contamination. Damage incurred in the silicon bonding must be restored or removed. The latter can be accomplished by suitable treatments such as wet chemical silicon etch or silicide formation.

New and possible future trends in inductively coupled plasmas (ICPs) for semiconductor processing

ICPs have become one of the dominant high-density plasma sources for etching. More variations of ICP etch sources are currently being developed and inductive systems for high-density plasma deposition are also being developed. In addition, helicon inductive sources are being developed in single loop and spiral antenna configurations. In the future these two fields may merge to combine the optimum features of both systems. The physics of low-pressure ICP systems will be discussed. Experimental effects of multipole magnetic fields near the rf coil will be described as they relate to low pressure and electronegative gases.