Experimental Study on Heat Flux from an Argon RF Plasma Using Laser Interferometry Method

The plasma heat flow to a birefringent substrate (LiNbO3) in an argon rf discharge has been investigated with the help of a laser interferometry method. This method is based on monitoring the variation of natural birefringence with temperature by the interferometry. The evaluation of the temperature curve shows that heat flux from the plasma towards the substrate depends on which electrode the substrate is put on. While the value is about 8% of the applied power in the case of the substrate on the powered electrode, the heat flux decreases to less than 1% in the case of on the grounded electrode. Ion fluxes have been obtained from the measured values of plasma potential, electron density and electron temperature. In the case of low pressure the ion flux approximately agrees with the value of the heat flux. However it decreases with an increase in pressure, and is almost 35% of the heat flux at 200 mTorr. Gas temperature in the plasma has been measured using a thermocouple in order to investigate the influence of gas pressure on the heat flux by neutral particles. The result shows that the gas temperature increases by raising the gas pressure.