FRAGMENTATION IN MAGNETICALLY ENHANCED REACTIVE ION ETCHING - A LIF AND OES STUDY IN A CF4 DISCHARGE

The fragmentation of a CF4 13.56 MHz plasma is studied by laser-induced fluorescence (LIF) and optical emission spectroscopy (OES) in a commercially available magnetron - used for reactive ion etching - with a modified magnetic field configuration. It is shown that the degree of fragmentation in the plasma and hence the etch results can be strongly affected by a variation of the magnetic field B up to 8 mT (80 Gauss) at typical low pressure etching conditions. The relative concentrations of CF2 radicals in the electronical and vibrational ground state as indicated by LIF increased by a factor of approximately 3 when B was varied from 0 to 8 mT. Essentially the same increase was observed for actinometrically normalized emission (AOES) intensities of atomic fluorine - suggesting a similar behaviour of ground state F - and in the etch rates of poly silicon. CF2* and F* emission intensities were found to deviate strongly from that of the CF2 and F ground state densities. This indicates a strong change in the electronic plasma properties when a B field is introduced to the plasma.