Experimental investigations of the plasma radial uniformity in single and dual frequency capacitively coupled argon discharges

Abstract

In the current work, the radial plasma density has been measured by utilizing a floating double probe in single and dual frequency capacitively coupled argon discharges operated in a cylindrical reactor, aiming at a better understanding of electromagnetic effects and exploring a method of improving the radial uniformity. The experimental results indicate that for single-frequency plasma sustained at low pressure, the plasma density radial profile exhibits a parabolic distribution at 90 MHz, whereas at 180 MHz, the profile evolves into a bimodal distribution, and both cases indicate poor uniformities. With increasing the pressure, the plasma radial uniformity becomes better for both driving frequency cases. By contrast, when discharges are excited by two frequencies (i.e., 90 + 180 MHz), the plasma radial profile is simultaneously influenced by both sources. It is found that by adjusting the low-frequency to high-frequency voltage amplitude ratio β, the radial profile of plasma density could be controlled and optimized for a wide pressure range. To gain a better plasma uniformity, it is necessary to consider the balance between the standing wave effect, which leads to a maximum plasma density at the reactor center, and the edge field effect, which is responsible for a maximum density near the radial electrode edge. This balance can be controlled either by selecting a proper gas pressure or by adjusting the ratio β.

Fundamental study towards a better understanding of low pressure radio-frequency plasmas for industrial applications

“…Due to continuous growth in both the driving frequency and the wafer size, plasma non-uniformities caused by the standing wave effect have become a major challenge in the material etching and film deposition processes. To optimize the plasma uniformity, several methods have been put forward, such as the use of specially shaped electrodes, [163][164][165][166][167] phase-shift control, [168][169][170] the use of the dual-frequency or multi-frequency source, [133,138,139,171,172] discharge symmetry control, [173,174] etc.…”

“…[168][169][170] This is the so-called "phase-shift control" method. Besides, the dual-frequency [138,139,171,172] or multi-frequency [133] source can be used as an alternative way to optimize the plasma uniformity. By using a two-dimensional plasma model, Bera et al [171] found that the plasma distribution can be effectively controlled by mixing VHF source powers at 60 MHz and 180 MHz.…”

“…[20,21] Over the past two decades, the electromagnetic effects in VHF CCPs have been investigated by a variety of approaches, such as analytical models, [120][121][122][123][124] numerical simulations, [117,[125][126][127][128][129][130][131][132][133][134] and experiments. [118,119,[135][136][137][138][139] Overall, the physical reason causing the plasma non-uniformities can be divided into four categories:…”

Enhancing the Contact between a-IGZO and Metal by Hydrogen Plasma Treatment for a High-Speed Varactor (>30 GHz)

“…Various doping methods have been studied with a-IGZO. − Argon plasma bombardment was used in self-aligned top-gated TFTs, and the fluorine plasma process exhibited stable electron doping in a-IGZO . However, since both plasma treatments etch a-IGZO, even a slight difference in plasma density may cause large nonuniformity in electrical properties and surface roughness. , Hydrogen doping in a-IGZO has been widely studied with various approaches: thermal annealing, plasma treatment, and diffusion from a hydrogen-rich layer. , Hydrogen passivates native defects in a-IGZO and increases the electron density; however, unstable bonding between hydrogen and a-IGZO elements, which results in temporal instability even at room temperature, is yet to be solved. − …”

Consequences of atomic layer etching on wafer scale uniformity in inductively coupled plasmas

“…The wafer scale uniformity of plasma etching processes is crit ically important to semiconductor fabrication [1]. Techniques to address the uniformity of plasma properties, and in par ticular the uniformity of reactant fluxes to etching surfaces, continue to be a high priority [2][3][4]. As feature sizes and film thicknesses shrink, conventional techniques to obtain uniform reactant fluxes and etch rates are being challenged to meet process demands.…”