Chris Carter and Joe Khachan
School Of Physics, University of Sydney
A helicon plasma processing source [1] utalising low pressure, high ion density, radial plasma uniformity, low plasma potential, ion energy control at the substrate and simplicity of machine design, has been investigated using an argon plasma. Experimental comparisons of ion density, radial uniformity and power coupling efficiency, amongst other factors, have been made between two common antenna types in helicon plasma processing devices. One antenna dominantly excites the m=0 azimuthal mode of a helicon wave, while the other antenna dominantly couples to the m=1 mode. For both cases we observe an argon ion density peak (1012 cm-3) at the substrate for a low applied magnetic field (10-40 G). The antenna that is observed to be better suited to plasma processing is measured to have a linear ion density to input power response (density mode jumps would prove difficult to handle in any automated control system), high central ion density, and good plasma uniformity over 16 cm. Additionally, an increase in ion density away from the source sets up a positive ion retarding potential ensuring that ions are not accelerated towards the substrate in the bulk plasma, which can only give better control over ion energy at the substrate. Work is currently being performed on depositing the III-V semiconductor aluminium nitride under optimal conditions for a nitrogen plasma.
[1] D. R. McKenzie, W. D. McFall, H. Smith, B. Higgins, R. W. Boswell, A. Durandet, B. W. James and I. S. Falconer, Nucl. Inst. and Meth. in Phys. Res. B, 106, 90 (1995).