Control of plasma parameters using grid voltage biasing and inert gas mixing in inductively coupled plasma

Abstract

Electron temperature can be controlled from 2.5 eV to 0.5 eV in 1 mTorr using grid bias voltage. Electron temperature is higher in lower pressure, when the electron temperature is high and not controlled. Electron density increases by about 3 times by decreasing the source gas pressure from 20mTorr to 1mTorr, and by about 2 times by He mixing in the temperature controlled region(diffusion region), while the electron density decreased in the source region. This electron density increase is mainly due to the increase of the high energy electron population, and the measured electron energy distribution functions clearly show this. The electron temperature is a strong function of substrate bias voltage in the grid system. The main control parameter determining the electron temperature is the potential difference between grid-biased voltage and the plasma potential in the temperature controlled region ($Δ_ΦII,g$). When substrate bias voltage is negative, plasma parameters do not vary with substrate bias voltage due to constant $Δ_ΦII,g$. Under the grid, the electron temperature, as well as electron density, is a strong function of a mixing ratio. The electron temperature decreases with a mixing ratio of molecular gases ($O_2$ and $CF_4$), and the large inelastic cross section of molecular gas is the reason for the decrease in the electron temperature. When the length of sheath around the grid wires is comparable to the space between the grid wires, only 10% mixing of $CF_4$ decreases the electron temperature to 0.8 eV in 10 mTorr Ar/$CF_4$ plasma. We set a grid in a chamber to obtain low electron temperature inductively coupled plasma. The electron temperature is less than 1 eV at 15 mTorr. We carry out silicon dioxide etching in the grid system to investigate the etching characteristics in low electron temperature. Compared to the etching characteristics without the grid, the etching characteristics become very different after setting the grid. The low dis...