Heat flux distribution on a substrate in capacitively coupled radio-frequency discharges

This letter investigates the heat flux distribution on a substrate in capacitively coupled radio-frequency argon glow discharges. The heat fluxes were determined from substrate temperature distributions measured by a high-sensitivity laser interferometer method with a LiNbO3 birefringent substrate. This method is based on monitoring the variation of refractive index with temperature. The distribution was obtained by sliding the 1-cm long LiNbO3 substrate between two semicircular glass substrates placed on a disk electrode, 12 cm in diameter. The gap length was fixed at 2 cm and gas pressure was 100 mTorr. For the substrate placed on the powered electrode, the heat flux increases radically from the glow center to the radial electrode edge from 40 to 58 mW/cm2. The heat flux toward the grounded electrode increases radically from 15 to 21 mW/cm2. The total measured heat flux to the electrode is in good agreement with electrical power consumption determined from voltage and current measurements. The radial electron density profile in the discharge chamber was measured using a Langmuir probe. The results show that the maximum electron density observed at the electrode edge coincides with the maximum heat flux