Synergetic effects in a discharge produced by a dual frequency–dual antenna large-area ICP source

Abstract

Using an RF-compensated Langmuir probe, plasma parameters have been investigated in a discharge produced by a dual frequency–dual antenna: the next generation of large-area inductively coupled plasma (ICP) sources. The ICP source was made of two concentric spiral copper coils embedded into each other. The inner and outer coils were energized by RF frequencies of 2 and 13.56 MHz, respectively.The discharge was operated at an average pressure of 10 mTorr in an argon gas environment. The probe was positioned at a fixed location of 70 mm from the source and 160 mm from the centre of the ICP source to measure the plasma parameters. However, for discharge uniformity measurements, the probe position was varied from the centre of the discharge to 200 mm towards the edge.It was found that the ion density distribution over the wafer varies with RF power ratio (P2MHz/P13.56MHz). For a fixed power at 13.56 MHz (P13.56MHz), the plasma density increases very slowly with P2MHz, when P2MHz   400 W. The electron temperature and plasma potential measurements show decreasing trends with increasing P2MHz at constant P13.56MHz. The ion density measurements over the substrate show that good discharge uniformity (∼4%) can be achieved by adjusting the RF power ratio (P2MHz/P13.56MHz).