Study of ion bombardment characteristics in high frequency plasmas

Modern industry and research widely use ions as part of the techniques in precise analytical instruments as well as in powerful processing tools for microfabrication, surface modification, and thin film deposition. The knowledge of ion energy distribution functions (IEDFs) and fluxes is necessary for the control of the processes and for the design of materials properties.

The main objectives of this work are to develop the methodology of IEDF measurements in different low-pressure plasma systems, and to apply it for the process diagnostics in a dual-mode microwave/radio frequency (MW/rf) plasma reactor and an ion beam assisted deposition (IBAD) reactor. The investigated conditions include those generally used for plasma enhanced chemical vapor deposition (PECVD) and surface treatment of polymers for improved adhesion.

Ion bombardment characteristics of continuous wave (cw) microwave (MW, 2.45 GHz), radio frequency (rf, 13.56 MHz) and dual-mode microwave/radio frequency plasmas were measured in the range of gas pressures from 20 to 200 mTorr. Special attention was paid to the characterization of two types of power modulated (pulsed) plasmas; these are a pulsed MW discharge and a dual-mode pulsed MW/cw-rf discharge. In the IBAD system, the IEDFs for argon, oxygen, and nitrogen at three different angles from the ion source axis were evaluated. We studied the evolution of the mean ion energy and ion flux as a function of the ion source drive current and the drive voltage.

In conclusion, the main contributions of the present work are the following: (i) a versatile multigrid ion energy analyzer has been developed and fully characterized; (ii) a methodology has been proposed and investigated which allows one to determine quantitatively the ion bombardment energies in complex discharges such as the MW/rf plasmas used for materials processing; and (iii) a close correlation between the IEDFs and the discharge parameters such as the sheath thickness, plasma density, and plasma and surface potentials has been demonstrated, thus making this approach a valuable tool for non-perturbing plasma diagnostics. (Abstract shortened by UMI.)