Effects of External Cusp Magnetic Fields on Inductively Coupled Plasma Properties

Inductively Coupled Plasma (ICP) is a widely used low-temperature plasma source for various semiconductor processes such as etching, deposition, and cleaning. It offers the advantage of generating high-density plasma in the range of 10¹⁶ ~ 10¹⁸ m^-3. However, structural limitations such as electron diffusion losses and plasma density non-uniformity remain significant challenges. To address these issues, this study applies an external DC magnetic field to increase electron lifetime and control the plasma density distribution, thereby promoting the formation of a more uniform and stable plasma.

Magnetic fields can be applied through different methods, including simple permanent magnets, easily controllable Helmholtz coils, and cusp field known for their strong plasma confinement effects. Among these, the Cusp field offers unique structural advantages by creating magnetic boundary regions that suppress particle losses and enhance density uniformity. It is particularly effective under low-pressure conditions where electron losses are typically more severe.

In this study, a custom system incorporating a cusp field was constructed to quantitatively evaluate its effect. Plasma diagnostics were performed using a single Langmuir probe with RF compensation. The results confirmed that magnetic confinement effect associated with cusp field increases plasma density and improves spatial uniformity. These findings demonstrate that cusp field-assisted plasma control can effectively contribute to high-uniformity and high-precision semiconductor processing.