Studies of a hollow cathode discharge using mass spectrometry and   electrostatic probe techniques
  Hollow cathode discharges (HCD) are capable of generating dense plasmas and have been used for development of high-rate, low-pressure, high-efficiency processing machines. The geometric feature of a HCD promotes oscillations of hot electrons inside the cathode, thereby enhancing ionization, ion bombardment of inner walls and other subsequent processes. At the same power the hollow cathode exhibits plasma density one to two orders of magnitude higher than that of conventional planar electrodes. The aim of the present studies was to obtain experimental observations about the main features of a dc hollow cathode discharge in order to evaluate its capability of generating compounds in the plasma medium, by reaction between sputtered species from the cathode and radicals from the gas discharge. Especial interest is focused on aluminum nitride (AlN) formation which is very desirable if a deposition of thin film of this material is concerned. Plasma properties were inferred from the current-voltage characteristics of a single Langmuir probe positioned at the inter-cathode space. Through mass spectrometry technique some species in the plasma gas phase could be monitored for various operating conditions of the discharge. This mass analysis together with the probe measurements gives guidance for optimization of AlN generation in the discharge consequently for deposition of thin films of this material. 
Homero Maciel, Gilberto Petraconi, Rodrigo Pessoa