Experimental Studies On Uniformity Of Large Area Very High Frequency Capacitive Coupled Plasma

Very high frequency (VHF) capacitively coupled plasma (CCP) source can produce high plasma density, low ion energy, so it have been widely used to the thin film deposition and etching process in the semiconductor manufacturing. In very high frequency capacitively coupled plasma, with the increase of frequency, wavelength is equivalent to size of the plasma discharge plate, and electromagnetic effect is the main reason for the large area plasma uniformity. The electromagnetic effect which affects the spatial distribution of plasma discharge mainly includes:the standing wave effect, the skin effect, the edge effect and the plasma discharge to the sidewall. Experiment via the emission spectrum (OES) measures the spatial distribution of the very high frequency plasma. Through the experimental data, in this experiment system, in the situation of low power, low pressure, the discharge intensity in edge of plate is higher than in center of the plate. The nonuniformity of the spatial distribution of the main is casued by the edge effect and the plasma to discharge to sidewall. The edge effect is caused by the plate edges enhanced the electric field, resulting in plasma discharge enhancement; the plasma to discharge to sidewall is due to the plasma chamber grounded, and plasma discharges to grounded side wall. Through joining in the insulation board on the inside of sidewall, experiment makes the edge of the plasma discharge intensity a certain weakened. According to the analysis of experimental data, plasma to discharge to sidewall grounded is the main reason of the nonuniformity of plasma spatial distribution. And the main reason of plasma discharge strong in edge of the plate is the impedance of plasma discharge circuit. There are two discharge circuits in the plasma, one is the discharge plate grounded circuit, and the other is the sidewall grounded circuit. In the plasma discharge, because of the sidewall grounded circuit impedance is small, in the competition of the discharge to two grounded circuits, the side wall grounded have more advantage than the plate grounded, resulting the discharge intensity in the edge is relatively high. Joining in the insulation board inside sidewall, the impedance of the ground circuit is equivalent to an increase, thus increasing the plasma discharge of plate ground circuit, thus weakened the plasma discharge intensity in the edge. Changing the discharge circuit, the method of further by reducing discharge plate ground circuit impedance to weaken the strength of the plasma discharge in edge. Experiment by increasing the grounded discharge circuit of the capacitive reactance and impedance, concluded that in this experimental system, plasma discharge circuit of capacitive reactance the spatial distribution of the plasma is the main function for the spatial distribution of the plasma the spatial distribution of the plasma, and the discharge circuit impedance has a little influence on the spatial distribution of the plasma. We can be concluded that, in the very high frequency plasma discharge plasma the discharge circuit is the main reason of the spatial distribution of plasma, changing the impedance of the discharge circuit can make the spatial distribution of the plasma uniform.