Simulation of an Ar/Cl₂inductively coupled plasma: study of the effect of bias, power and pressure and comparison with experiments

Abstract

A hybrid model, called the hybrid plasma equipment model, was used to study Ar/Cl2 inductively coupled plasmas used for the etching of Si. The effects of substrate bias, source power and gas pressure on the plasma characteristics and on the fluxes and energies of plasma species bombarding the substrate were observed. A comparison with experimentally measured etch rates was made to investigate how the etch process is influenced and which plasma species mainly account for the etch process. First, the general plasma characteristics are investigated at the following operating conditions: 10% Ar 90% Cl2 gas mixture, 5 mTorr total gas pressure, 100 sccm gas flow rate, 250 W source power, −200 V dc bias at the substrate electrode and an operating frequency of 13.56 MHz applied to the coil and to the substrate electrode. Subsequently, the pressure is varied from 5 to 80 mTorr, the substrate bias from −100 to −300 V and the source power from 250 to 1000 W. Increasing the total gas pressure results in a decrease of the etch rate and a less anisotropic flux to the substrate due to more collisions of the ions in the sheath. Increasing the substrate bias has an effect on the energy of the ions bombarding the substrate and to a lesser extent on the magnitude of the ion flux. When source power is increased, it was found that, not the energy, but the magnitude of the ion flux is increased. The etch rate was more influenced by a variation of the substrate bias than by a variation of the source power, at these operating conditions. These results suggest that the etch process is mainly affected by the energy of the ions bombarding the substrate and the magnitude of the ion flux, and to a lesser extent by the magnitude of the radical flux.

Fluorine–Silicon Surface Reactions during Cryogenic and Near Room Temperature Etching

“…Since their fluxes are a few orders of magnitude higher than the ion flux, it can be concluded that the surface is effectively converted to physisorbed SiF 4 molecules, which are very easily sputtered even by low energy ions. These observations are in line with basic ion-enhanced etching principles where a combination of chemical etching and ion sputtering yields a much higher etch rate than each process separately 36. Although direct sputtering of SiF 0-3 surfaces might thus not occur often in reality, as the surface is usually converted to SiF 4 during etching, figures 2 and 3 still give us important information on the behavior of the ions on the surface, like sputtering and incorporation yields.…”

“…For typical wafer processing plasmas, the flux of neutrals is usually 100 to 1000 times higher than the ion flux. 36 As a result, the surface is always heavily fluorinated before sputtering occurs. It can be noted from Indeed, because the layer of (physisorbed) SiF 4 molecules is easily removed by ion impact, the underlying SiF 0-3 layers can still be reached by ions.…”

“…Because the flux of neutrals is typically 1000 or more times larger than the ion flux under typical wafer processing conditions 36 , it is expected that an accumulated layer will again be formed before the next ion arrives on that surface site. Even though the sputter yields at 29 cryogenic and room temperature conditions are the same (see section 2), sputtering of the underlying Si layer might be slightly inhibited during cryoetching by the formation of this accumulated layer of physisorbed neutrals that assimilate a part of the ion energy and thus lower the chance for sputtering of the underlying silicon.…”

Formation of large-area GaN nanostructures with controlled geometry and morphology using top-down fabrication scheme

“…The initial increase was again attributed to the reaction-limited regime, whereas the decrease was attributed to lower ion energies due to the reduction in dc self-bias and ion-assisted desorption of reactive species at the substrate prior to the etch reactions. Despiau-Pujo et al 16 and Tinck et al 22 showed through simulation that ion fluxes increase with increase in ICP power. Ion flux (F ion ) in a collisionless sheath is given by the following relationship 16 :…”

Numerical Investigation of Ion and Radical Density Dependence on Electron Density and Temperature in Etching Gas Discharges

“…Neutral-neutral reactions [5] Ion-neutral reactions [5] CF4 discharge Electron collision reactions [2] Neutral-neutral reactions…”