Coulomb collisions in materials processing plasmas

First, the method to calculate Coulomb collisions in materials processing plasmas is presented. Next, by use of the method, the effect of electron-electron (e^--e^-) collisions on the relaxation of electron energy distribution function (EEDF) is examined for a spatially uniform argon plasma. The EEDF is shown not to tend to the Maxwellian distribution without e^--e^- collisions because once high-energy electrons lose energy by inelastic collisions, they have no chance to recover their energy without e^--e^- collisions. When e^--e^- collisions are taken into consideration, the relaxation time of the EEDF at gas pressure 10 mTorr is 40, 20, and 10 μs for electron densities 10^l6, 10¹⁷, and 10¹⁸ m^{- 3} respectively. Lastly, the effect of e ^--e^- collisions on the EEDF is examined for a capacitively coupled plasma at gas pressure 25 mTorr. It is found that the effect is negligible even for the electron density 10¹⁷ m ^{- 3}.