Growth of thin layers and coatings
Plasmas are often used in modern industries to apply layers or coatings. Such plasmas are generally driven either by radiofrequent fields (e.g. 13.56 MHz) or by microwave fields (e.g. 2.45 GHz). In EPG we mostly study microwave plasmas for deposition purposes. These plasmas are operated in low pressure (0.1-10 mbar) gases in order to achieve homogeneous plasma properties. The gas that is used depends on the required deposition layer type. For deposition of quartz (SiO2) a mixture of silicon tetrachloride (SiCl4) and oxygen is used while for the growth of amorphous silicon for solar cells a mixture of silane (SiH4) and hydrogen is used.
We mostly study the plasma properties that are needed for good deposition. Important parameters in the plasma are electron density, electron temperature, gas temperature, dissociation degree and densities of radical species. Such parameters are measured with a broad range of diagnostics like Thomson, Rayleigh and Raman scattering, Laser Induced Fluorescence, mass spectroscopy and more.
One of our set-ups designed to study microwave deposition plasmas is the coaxial plasma or plasmaline. In this set-up the plasma acts as the outer conductor of a coaxial cable. An example of this plasma can be seen in figure 1. As is shown here, at higher pressures this plasma is no longer homogeneous but filamentary instead. A high-speed movie of these filaments can be found in the video on the right.