Ion assisted thin film growth in dual microwave/radio frequency plasmas

Many recent publications on low pressure plasma processing have underlined the important role of plasma-surface interactions. In the present contribution we discuss a frequently overlooked variable, the plasma excitation frequency, by critically reviewing its effect on processes in the plasma bulk, and on low energy ion bombardment at the substrate surface. We refer extensively to our own recent work on the application of ''dual frequency'' plasma, which comprises a large area microwave discharge with accompanying RF power applied to the substrate. In this way, one can quite independently control the bulk plasma processes (eg. active species creation) on the one hand, and the ion flux and ion energy on the other hand. We illustrate this with plasma diagnostic results (optical emission spectroscopy, electrostatic probe measurements), and correlate them with characteristics of plasma deposited silicon- and carbon-compound films (a-Si:H, P-SiO2, P-SiN, PP HMDSO, a-C:H). The present status of large area industrial application is also briefly addressed. (orig.)