THE HOLLOW-CATHODE - A HIGH-PERFORMANCE TOOL FOR PLASMA-ACTIVATED DEPOSITION

The hollow cathode will be presented as a plasma source for reactive e vaporation processes. The hollow cathode generates an are discharge pl asma. This contains a high portion of directed electrons with an enhan ced mean energy, the so called low-voltage electron beam (LVEB). The m ean energy of the LVEB, in the range of 11 eV, results in a very effec tive ionization of the gas and vapor particles. Consequently, very hig h plasma densities can be achieved, which corresponds to high particle densities in high-rate deposition processes. Furthermore, a high self bias potential of about 16 V is obtained on insulating substrates. Fo r the coating of heat-sensitive substrates with high deposition rates a process with a low ratio between thermal load and deposition rate is necessary. The heat flux on plastic substrates has been measured at t he reactive Al evaporation process. The overall thermal load of about 4 W/cm(2) related to a deposition rate of 100 nm/s is low in compariso n to other processes. This makes the hollow cathode a favorable tool f or the plasma-activated high-rate deposition. The oxide layers deposit ed by this process show dense and glassy structures even at comparativ ely low condensation temperatures. This is caused by the high ion curr ent densities in the order of 30 mA/cm(2). The low ion energy determin ed by the self bias potential results in relatively low compressive st ress below 100 MPa. The low thermal load and the moderate intrinsic st ress of the layers makes the hollow cathode plasma-activated depositio n (HAD) process the method of choice for the deposition of oxides as a brasion resistant layers on plastic films and sheets. (C) 1998 Elsevie r Science S.A. All rights reserved.