Ion energy distributions for the identification of active species and processes in low pressure hollow cathode discharges

Abstract

Energy distributions of ions generated in hollow cathode low pressures dc discharges of different gases and gas mixtures containing Ar, H 2 , N 2 , O 2 or CH 4 are studied by quadrupole mass spectrometry. The ions are sampled through a small diaphragm in the grounded cathode. The measured distributions are mostly determined by the acceleration of ions in the sheath region between the negative glow and the cathode, displaying in general a narrow peak centred at energies close to the anode potential, but with specific features for the distinct ions. It is shown that information about ion production and sheath collision processes can be derived from the shapes of the different energy distributions. In some cases these distributions are used for the estimation of the relative abundance of ions with the same mass/charge ratio but different composition in complex gas mixtures.

Surprising importance of photo-assisted etching of silicon in chlorine-containing plasmas

“…For Ar þ energies of a few tens of eV, the symmetric charge exchange cross section is 3 Â 10 À15 cm 2 , [16][17][18] corresponding to mean free paths of 18 mm at 7 mTorr (the lowest pressure where the plasma can easily be sustained) and 2.5 mm at 50 mTorr and 80 C. At 50 mTorr; therefore, the ions would suffer collisions (86% probability) while traversing the space between the top grid and the sample, creating energetic neutrals and lower energy ions. The sample was biased (V C ) to repel ions without disturbing the plasma potential.…”

Sputtering of W and Al in D2/O2 plasma cleaning discharge

“…According to mass spectrum analysis the maximal values of the sputtering yields were observed when all O 2 entered plasma consumed to formation of D 2 O. An X range of 2-6 mol.% corresponded to the D 3 O + maximal ion concentration in D 2 /O 2 glow discharge [10,11]. Reduction of the sputtering yield with increasing of oxygen concentration may be related to selective sputtering of oxygen from the oxide surface [16,21].…”

“…In case of D 2 /O 2 discharge the plasma is a source of large variety of neutral and charged reactive species. In particular, it has been shown [10,11] also included in comparable or higher concentrations. As a rule, the concentrations of H + , O + , OH + ions are an order of magnitude lower than ones of protonated ions.…”

The use of hollow cathodes in deposition processes: A critical review

“…Several groups have reported the presence of Ar 2+ and the increased generation of such ions in the HCD state [160][161][162][163][164][165][166]. The importance of these ions is, firstly, that they are accelerated to higher energies by the cathode sheath, and secondly, when they strike the cathode, they generate approximately four times the number of electrons than singly-charged ions [67,72].…”