A model of capacitively coupled radio-frequency methane/hydrogen plasmas for III-V semiconductor etching applications

Abstract

A model has been developed which follows electrons and ions through assumed time varying potentials in a radio-frequency methane/hydrogen plasma. The system modelled is relevant to a low-pressure (10-90 mTorr) plasma used in the etching of GaAs surfaces. To understand the etching process, a knowledge of the flux and energy distributions of all species at the surface is required and as a first stage it is necessary to derive the spatial ionization distribution function. Inelastic and elastic collisions with neutral gas molecules are included in the model and the results give realistic electron energy distribution functions (EEDFs). These EEDFs are found to be insensitive to the inclusion of rotational modes of excitation, but vary significantly when vibrational modes of excitation are included. The EEDF is seen to change greatly with spatial position between the electrodes. Results also suggest that the form of the spatial ionization distribution function is identical for all ion species, though different in magnitude. Ion fluxes predicted at the anode are in broad agreement with experiment and are most affected by the ionization cross sections used in the simulation. Neutral fluxes to the surface are seen to make a major contribution to the particle flux, especially at the higher pressures. The secondary electron emission coefficient, though having a significant effect on the electron energy distribution function, has little effect on the mass distribution of the flux deposition on the substrate surface.

Electron plasma parameters and ion energy measurement at the grounded electrode in an rf discharge

“…Taking into account the processes described in the phenomenological model [4], the double hump shape of the IEDs can be explained. The model is referring to a large range of bias voltages (up to 500 V) which leads to a multi-peak distribution.…”

“…In highly asymmetric rf discharges with a large electrode area ratio the ion bombardment is confined to the smaller electrode (called the 'cathode'), which exhibits a large negative self-bias voltage almost approaching the amplitude of the rf signal. The particle fluxes upon the cathode from an rf discharge were intensively studied [1][2][3][4][5]. Investigations undertaken for two distinctive cases showed that:…”

“…The maximum and the minimum energy occur when the ion crosses the sheath during the maximum and the minimum potentials. If an ion takes many rf cycles to cross the sheath, its energy will depend on the average sheath potential [3,4].…”

Study of fundamental processes affecting the structure of the cathode zone of nitrogen/titanium dc discharge

“…If we want our consideration to be more exact, then we should take into account the dependence of the cross section Q ex (λ) and τ av on the particle energy and the energy structure of fluxes J (x). These problems are considered by Layberry et al [14] where useful formulae are proposed. The above dependences limit the analytical assessment of the I (λ, x, x).…”