Control of Electron Induced Secondary Electron Emission for Plasma Uniformity Improvement in dual-Frequency CCP system

High-energy ballistic electrons (HEBE) generated from secondary electron emission play a crucial role in low-pressure radio frequency plasmas, particularly in dual-frequency capacitively coupled plasma (DF-CCP) systems. While previous studies have observed the presence of HEBE and the importance of secondary electron emission coefficients, research on utilizing this phenomenon for plasma uniformity improvement has been limited. This study presents a novel method to control HEBE effects through high-frequency modulation of the top electrode in a DF-CCP system. HEBE generated during ion-induced secondary electron emission occurs when high-energy ions impinge in large quantities during the negative phase of the low-frequency cycle. These high-energy electrons rapidly reach the opposing electrode, inducing electron-induced secondary electron emission or exhibiting bouncing characteristics. By systematically varying the frequency and voltage of the high-frequency signal on the top electrode, this work demonstrates that the spatiotemporal characteristics of HEBE can be controlled. Such control leads to improved plasma density uniformity, which is crucial for various plasma processing applications.