Impact Energy Distribution Research Articles

Angular ion and neutral energy distribution in a collisional rf sheath

A numerical study on the ion and neutral angular impact energy distribution at the rf-driven electrode of a reactive ion etcher is presented. The calculations for the ions are performed using a Monte Carlo method that includes charge exchange and elastic scattering. The contribution of both collision processes to the angular ion impact energy distribution is studied. For the case that charge exchange is the only collision process, the Monte Carlo results can be checked against those of a method based on a spatially uniform and time independent collision rate. In that case, both methods yield the same ion impact energy distribution. The position, velocity, and propagation angle of the energetic neutrals created in collisions of ions with the background gas are stored. These are used as input data for a separate code that follows the evolution of the angular neutral energy distribution, taking into account (multiple) neutral elastic scattering. From the ion and neutral distributions, the number of neutrals per ion, the average impact energy, and the energy-weighted average impact angle have been derived. It is shown that these parameters are well described by simple expressions. Finally, the sputter yield is calculated. The results show that the contribution of the angular distributions of both ions and neutrals to the yield can be neglected.

A study of dry etching mechanisms in CL2 by ion energy analysis at the rf-electrode

A quantitative experimental study on the etching mechanisms of Si, SiO2, Ti, and TiSi2 in Cl2 reactive ion etching is reported. The ion impact energy distribution and the ion current density have been measured in situ at the rf-electrode of a parallel plate reactor, together with the relevant etch rates. The ion transport through the collisional rf-sheath has been simulated using a Monte Carlo method. A separate method has been used to calculate the energy distribution of bombarding neutrals. This way the contribution of ions and fast neutrals to the sputter yield in Cl2 RIE plasmas was established. The quantitative approach has been tested against etch results in Ar plasmas in which merely physical sputtering occurs and for which well-defined experimental results are available from the literature.

Measurement of ion impact energy and ion flux at the rf electrode of a parallel plate reactive ion etcher

An experimental study on the ion impact energy distribution and the total ion flux at the driven electrode of a parallel plate reactive ion etcher is presented. Results are shown for 13.56 MHz discharges in Ar, Ar/H2, N2, O2, Cl2, and SF6/He over a pressure range of 0.3–40 Pa. The ion impact energy distribution consists of a collision-free part and a collision-induced part. It is observed that in Ar, N2, O2, and Cl2 the collision-induced part contains single and double peaks at regular energy intervals. This peaked structure is attributed to charge exchange processes in the sheath. Both the collision-free part and the collision-induced part of the ion impact energy distribution are well described by a model based on a constant sheath width, a sinusoidal sheath voltage, and a power law for the electric field in the sheath. The only adjustable parameter in the model is the sheath thickness. The sheath thickness has also been determined independently from the total ion current density using the Child–Langmuir law. The obtained values are in good quantitative agreement with each other and with the observed optical sheath thickness, demonstrating the overall consistency of the present approach.

Impact ionization coefficient and energy distribution function at high fields in semiconductors

Impact ionization coefficients in semiconductors are numerically calculated following Keldysh’s method [Sov. Phys. JETP 21, 1135 (1965)]. This requires deriving expressions for an energy-dependent mean free path l(ε) and an energy-dependent impact ionization scattering rate rii(ε). In the derivation of rii(ε), a nonparabolic ε-k relation as well as a smooth transition from the phonon-assisted impact ionization to the phononless impact ionization are considered. Numerically calculated impact ionization coefficients for electrons and holes in Ge, Si, and GaAs agree very well with experimental data. The calculated Keldysh energy distribution function is also compared with the standard Maxwellian distribution. The average mean free path l̄, which is a function of the electric field, has values within the range often quoted in the literature.

A Method for Non-Intrusively Determining ion Impact Current Density and Energy Distribution in Capacitively Coupled RF Plasmas

ABSTRACTThe dependence of ion current density on the sheath voltage and thickness, and ion energy distributions as functions of the pressure and sheath voltage amplitude have been calculated using a self-consistent computer code, ISHEATH. The current density is found to obey an approximate power law dependence on the amplitude of the sheath voltage, Vs, and the sheath thickness, d, and, when charge exchange collisions are considered, on the collision parameter α ΞNgas · σcx ·d. The ion energy distribution (IED) is found to mainly depend on α: for α ≃l there is only a slight (≃10%) change from the collisionless case; for a ≤ 10 the IED is peaked at an energy which is much less than the time-average sheath potential.

A visco-elastic polymer as an aid in injury management and prevention in equine athletes

During an eighteen month period, thirty-four equine athletes competing at international levels of dressage, 3-day eventing, jumping and competitive driving were studied as to the amount and distribution of impact energy and vibration associated with their activity, and the nature and extent of current or preexisting injury. The group was then evaluated as to recovery and returned to service after the use of a visco-elastic polymer foot pad. They were followed throughout an entire competition season, and further analyzed for recurrence of injury. In the group studied, 94% had relief of locomotor abnormality and returned to competition. There were no recurrence of injury in any horses studied during this season.

Analyzing statistical variability of fracture properties

A recently developed statistical analysis is applied to the estimation of lower-bound Charpy V-notch impact energies. Scatter of the impact-energy-absorption data, at any given temperature, is described using a two-parameter Weibull distribution, with the parameters allowed to vary with temperature. Values for the parameters are obtained using standard linear-regression techniques. As a result, the analysis naturally yields the temperature dependence of the pth percentile of the impact-energy distribution. Data with both large and small scatter are analyzed using this procedure.

Ion impact desorption mechanisms and energy distributions

A computer simulation study was made for the desorption of adsorbed layers from surfaces under energetic particle bombardment. The calculations were made on the basis of the binary collision approximation using the numerical program MORLAY. Primary particles are H, He and Ar and the adsorption layers are H, D, O and N on various metal surfaces. Desorption cross-sections are calculated for primary energies between 300 eV and 1 keV and the various processes which can lead to the release of an adsorbed particle are studied. Energy distributions of the desorbed species are also calculated and compared to the energy distributions of sputtered bulk material. In most cases desorbed particle distributions exhibit a much slower exponential decrease than sputtered substrate particles. Thus a considerable amount of desorbed species has relatively high energies up to a sizeable fraction of the projectile energy. This can be of importance for the penetration of desorbed particles through the boundary layer of a fusion plasma.

Heat flow—from the early earth's history to the present

A simple model for the thermal evolution of the Earth, which considers the effects of impact energy partitioning and distribution, gravitational or chemical differentiation, including core segregation, radioactive heat production and mantle convection, has been proposed. It has been shown that the melting proceeded from the surface towards the deeper zones of the primitive Earth. It is likely that the maximum gravitational energy corresponding to the end of core segregation occurred around 2000 m.y.B.P, assuming that the process was of long, duration.