Ion Transport to a Photoresist Trench in a Radio Frequency Sheath

We present a model which is used to study ion transport in capacitively coupled plasma (CCP) discharge driven by a radio-frequency (rf) source for an etching process. The model combines a collisional sheath model with a trench model. The sheath model can calculate the ion energy distributions (IEDs) and ion angular distributions (IADs) to specify the initial conditions of the ions incident into the trench domain (a simulation area near and in the trench). Then, considering the charging effect on the photoresist sidewalls and the rf-bias applied to the substrate, the electric potentials in the trench domain are computed by solving the Laplace equation. Finally, the trajectories, IEDs and IADs of ions impacting on the bottom of the trench are obtained using the trench model. Numerical results show that as the pressure increases, ions tend to strike the trench bottom with smaller impact energies and larger incident angles due to the collision processes, and the existence of the trench has distinct influences on the shape of the IEDs and IADs. In addition, as the bias amplitude increases, heights of both peaks decrease and the IEDs spread to a higher energy region.