Chlorine plasma and polysilicon etch characterization in an inductively coupled plasma etch reactor

Abstract

Measurements of the plasma properties versus location, pressure and power have been made in chlorine plasmas using a compensated Langmuir probe. The locations included a plane 1 cm below the window on which the inductively coupled plasma source rests (power deposition plane) and 1 cm above the wafer electrode (wafer plane). The pressures were varied between 1 and 25 mTorr and the RF power was varied between 200 and 900 W at 13.56 MHz. Spatial profiles of the electron and positive ion densities indicate that the plasma source efficiently heated electrons where the source induced electric fields were most intense. This caused a large variation in the electron average energy (T e ) both along the diameter of the power deposition plane and between the power deposition and wafer planes.Where T e was largest, n e was found to be smallest and vice versa. Spatial profiles of the electron density and T e at the wafer plane were dramatically more uniform. In addition, a comparison between polysilicon etch profiles on 150 mm wafers and plasma characteristics at the wafer plane revealed that the ion density always peaked on axis while the etch rate tended to peak at the radial edge.

Comparison between fluid simulations and experiments in inductively coupled argon/chlorine plasmas

“…Figures 9 and 10 show how the spatial distribution of electrons and negative ions changes with pressure. With increasing pressure, we observe that power absorption and distribution of electrons become more localized below the quartz window, as previously reported [40]. It should also be noted that several other processes might occur when changing the pressure.…”

“…The measured density displays a maximum near 17 mTorr at 3.7 × 10 10 cm −3 . A similar dependence was observed by Khater and Overzet [40] when operating with a pure chlorine discharge. They observed that this dependence on pressure varies at different axial positions.…”

On the applicability of self-consistent global model for the characterization of Cl2/Ar inductively coupled plasma

“…In our opinion, such phenomenon can be explained as follows. First, the literature gives several experimental confirmations that, in both Cl 2 and Ar ICPs, real EEDFs are close to Maxwellian for the electron energies below 15-20 eV [10,16,32,33]. Secondly, for the low pressure plasmas, the steady-state condition depends mainly on the surface reaction kinetics, and not on the volume processes.…”

Two-dimensional fluid simulation of inductively coupled N2/NH3/SiH4 discharge

“…With increasing pressure, the electron density increases as the collision frequency between the electrons and neutrals increases. However, the spatial distribution of the electron density is further localized below the dielectric window because the diffusion length decreases, and non-local effects become insignificant [51,52]. Moreover, increasing the pressure decreased the electron temperature.…”