LASER-INDUCED FLUORESCENCE AND EMISSION SPECTROSCOPIC STUDY OF MAGNETIC-FIELD EFFECTS IN A LOW-PRESSURE ETCH PLASMA

The influence of a magnetic volume field B on the chemical and physical properties of a 13.56-MHz CF4 plasma was studied by laser-induced fluorescence (LIF) and by optical emission spectroscopy (OES) at typical low-pressure etching conditions. The measurements were carried out in a commercial magnetron with a modified magnetic field configuration allowing a continuous variation of B up to a maximum field strength of 80 G. As indicated by LIF the densities of the CF2 radicals in the electronic and vibrational ground state increased by about a factor of 3 when the maximum B field was applied. No concentration gradients were detected by spatially resolved LIF. A similar increase as for CF2 was observed for actinometrically normalized F emission intensities. The ratios of CF2 LIF and CF2 OES signals are compared with the emission intensity behavior of argon, admixed to a small percentage, which suggest an increase of the electron induced production rates (electron densities) significantly stronger than that of the radical concentrations. This phenomenon is explained by simple considerations concerning B dependent production and losses of ions and radicals.