The effect of two ECR zones on dual frequency inductively coupled plasma using a gradient DC magnetic field

Abstract

The effect of a spatial gradient direct-current (DC) magnetic field on the evolution of the electron energy probability function was investigated in a dual frequency (DF) cylindrical inductively coupled plasma (ICP). The DF-ICP system was established using two independent one-turn antennas, with one placed in the upper part of the chamber powered by 13 MHz and the other in the lower part powered by 27.12 MHz. Different currents were applied to the upper and lower coils of the Helmholtz coil to form a gradient magnetic field, simultaneously satisfying the electron cyclotron resonance (ECR) condition at both 13 and 27.12 MHz frequencies. The significant increase in electron density and electron temperature observed under a gradient magnetic field can be attributed to the presence of two ECR heating zones within the chamber. Compared with uniform magnetic fields, which satisfy the ECR condition for only a single frequency in DF-ICP, the gradient magnetic field exhibited a more pronounced enhancement of electron density and electron temperature. This effect is primarily attributable to ECR heating and confinement of radial electron transport by a DC magnetic field. The effect of pressure on ECR heating was also investigated. As the pressure increased, frequent electron-neutral collisions disrupted the ECR process, leading to rapid weakening of the effect of the magnetic field, ultimately resulting in reduced electron density and electron temperature. These findings demonstrate that a gradient magnetic field can improve etching and sputtering in the processing of plasma materials at low pressure.