Equivalent electric circuit model of accurate ion energy control with tailored waveform biasing

Abstract

For atomic scale plasma processing involving precise, (an)isotropic and selective etching and deposition, it is required to precisely control the energy of the plasma ions. Tailored waveforms have been employed to bias the substrate table to accurately control this ion energy. Recent research has shown that switched-mode power converters can be used to generate this kind of waveform, with the benefit of increased energy efficiency and flexibility compared to the traditionally used linear amplifiers. In this article, an improved equivalent electric circuit model of the plasma reactor is proposed to allow simulation and bias waveform optimization. The equivalent circuit is analysed for different process phases, including the charge, discharge and post-discharge phase. The proposed model is suitable for electric circuit simulation and can be used for predicting the electric waveforms and ion energy distribution. Plasma parameters are required as input for the model, thus an empirical parameter identification method based on the electric measurements of the bias voltage and output current waveforms is introduced. Since these electrical measurements do not interact with the plasma process, the proposed parameter identification method is nonintrusive. Experiments have been carried out, which demonstrate that the proposed model and parameter identification method provide the expected accuracy.

Accurate Ion Energy Control in Plasma Processing by Switched-Mode Power Converter

“…The ion energy can be controlled by biasing the voltage potential of the plasma reactor table with the power converter. For a typical dielectric wafer, the tailored waveform biasing is found promising for atomic scale processing [2]- [6], since it can offer a narrow IED under variant operating conditions [7].…”

“…In the previous research, a twostep resonant charge method is proposed to suppress the resonance based on an oversimplified equivalent electric circuit (EEC) model of the plasma reactor, which could lead to inaccuracy of the ion energy control. In this paper, a complete EEC model, which initially proposed in [7], is introduced. The functions of each part of the tailored waveform are explained in details.…”

“…For an initially neutral plasma near a surface, the electrons get lost in the surface and the ion density becomes larger in the region near the surface. As a result, the surface is negatively charged, forming an electric field which attracts ions and repels electrons [7].…”

“…In a plasma reactor, the bulk plasma forms three separate plasma sheaths with the substrate, the exposed part of the table (as depicted by the gridded area in Fig. 1), and the grounded reactor wall, respectively [7]. In this section, an EEC model of the plasma reactor is introduced as shown in Fig.…”

“…The time duration of T 0 ∼ T 3 and T 5 ∼ T 8 are very short but exaggerated here for better visualization. be found in [7] but is skipped here since it is not the major focus of this paper.…”