Effects of the focus ring on uniformity in capacitively coupled plasma etching reactors

In the fabrication of modern microelectronic devices, the uniformity of the wafer processing has been a critical problem in plasma etching. The non-uniformity is usually the most pronounced at the edge, due to different electrical properties at the wafer edge, resulting in sheath bending and ion trajectories distorting. In etching reactors, the wafer terminating structure, which is often called a focus ring, modifies the sheath structure around the edge of the wafer to enable uniform ion fluxes. However, the focus ring is a consumable component that is easily eroded by the plasma. It is expected that the ion energy bombarding the focus ring should be as small as possible. In this paper, the ion angle onto the wafer and the ion energy onto the focus ring with the variations of the wafer-focus ring gap, the focus ring height, and the dielectric constant of the focus ring are discussed by using a 2D3V particle-in-cell/ Monte Carlo collision model. Horizontal electric fields appear in opposite directions at the edge of the wafer and the inner edge of the focus ring. The ion angle onto the wafer edge can be improved by adjusting the material and geometry of the focus ring. In addition, lower ion energy at the focus ring can also be achieved by using a larger gap between the wafer and focus ring, or using a higher height/smaller dielectric constant of the focus ring. *This work was financially supported by the National Natural Science Foundation of China (NSFC) (Grant Nos. 11935005, 12105035), the Fundamental Research Funds for the Central Universities (No. DUT21TD104).