Session FT2: Inductively Coupled Plasmas I

Control of ion energy distributions in inductively coupled ratio-frequency plasmas with a biased electrode

We measured the ion energy distribution (IED) and plasma density as a function of the voltage phase shift $\varphi $ between the source and bias electrode in inductively coupled argon plasma driven at 13.56 MHz by using a retarding field energy analyzer and a commercial Langmuir probe, respectively. Our results demonstrate that under some certain discharge conditions, as the phase shift $\varphi $ increases from 0 to 2$\pi $, the plasma potential slightly decreases with $\varphi $, while the IED exhibits drastic changes in both the IED width and the energy of bimodal distribution. To be specific, as $\varphi $ increases from 0 to $\pi $, the IED width increases and the bimodal distribution shifts to high energy region. However the IED width almost keeps constant and the bimodal distribution shifts to low energy region, when $\varphi $ increases from $\pi $ to 2$\pi $.   

Gas composition influence on ion energy distribution functions in an industrial ICP reactor with biased cathode.

An industrial ICP reactor consisting of a top planar coil and RF biased lower electrode has been characterized using a hairpin resonator probe and gridded ion energy analyzer to measure electron density in the bulk plasma and ion energy distribution function (IEDF) at the surface of the biased cathode. Argon and oxygen were run at constant total flow with 20mTorr downstream pressure control with varying flow ratios between the two gases ranging from 0{\%} to 100{\%} oxygen content. ICP and bias power were adjusted to maintain constant electron density and sheath bias over this mixing matrix at four different setpoints reflecting high density / high bias, high density / low bias, low density / high bias, and low density / low bias. Although the fundamental parameters governing RF sheath behavior were held constant, several trends in ion energy distribution are observed with respect to gas composition (aside from the obvious influence of ion mass) that show considerable variation in measured IEDF particularly that can be attributed to ion collisions in the sheath as well as gas heating variation due to gas composition.   

Studies on the radical species in inductively coupled Ar/CH4 plasma using improved single Langmuir probe diagnostic methods and fluid simulation

An inductively coupled plasma source driven by 13.56MHz was prepared for the deposition of a-C:H thin film. Properties of the plasma source are investigated by fluid simulation including Navier-Stokes equation and home-made tuned single Langmuir probe. Signal attenuation ratios of the Langmuir probe at first and second harmonic frequency were 49dB and 46dB respectively. Numerical methods including fitting, digital smoothing, digital filter with window function were used to calculate the electron energy distribution accurately. Dependencies of plasma parameters on process were well agreed with simulation results. It was found that RF power, inlet pressure and composition ratio significantly affect to the electron density, temperature and energy distribution. Electron density and plasma potential profile were changed along the input power and gas pressure. Below the input power density of 0.1W/cm3, higher plasma potential was observed at higher pressure. However, over the 0.1W/cm3, lower plasma potential was observed along the higher pressure. This result was occurred owing to the change of electron energy distribution. And from the simulation results, the specific chemical reaction channel, not CxHy but CHx, affect to the radical density profile.   

An electromagnetic approach to a small-scale microwave ICP-plasmajet

Microwave-driven plasmas-jets offer attractive properties for various technical applications. They are usually operated in a capacitive mode, known as E-Mode. Experimental experience however show a number of disadvantages for capacitive coupling such as high boundary sheath voltage and thus high electrical losses. Therefore in large scale plasmas inductive coupling, known as H-mode, is attractive. Recently \textit{Porteanu et al.}[1] proposed a small scale plasma-jet operated as an inductive discharge. The key characteristic of the proposed plasma-jet is the implementation of an LC-resonance-circuit into a cavity resonator. In this work the proposed plasma-jet is examined theoretically. A global model for the electromagnetic fields and energy balance is presented. Consequent mathematical analysis of the electromagnetic fields leads to a description based on a sum of different modes. It is found that the modes of zero and first order can be identified with inductive and capacitive coupling. In a second step the matching network and its frequency depended characteristic are taken into account. Finally an investigation of stable working points and possible hysteresis effects is done. \newline [1]H. E. Porteanu et al. \textit{Plasma Sources Sci.Technol.}\textbf{22}, 035016(2013)   

Control of electron energy distribution by the power balance of the combined inductively and capacitively coupled RF plasmas

The control of electron energy probability function (EEPF) is important to control discharge characteristics in materials processing. For example, O radical density increases by changing the EEPF in O$_{\mathrm{2}}$ plasma, which provides high etching efficiency [1]. The effect of the power balance between the capacitively coupled plasma (CCP) and the inductively coupled plasma (ICP) on the EEPF in Ar and O$_{\mathrm{2}}$ plasmas is investigated with a 1d3v (one-dimensional space and three-dimensional velocity domain) particle-in-cell (PIC) simulation for the combined inductively and capacitively coupled plasmas. The combined effects of the transverse electromagnetic and the longitudinal electrostatic fields are solved in PIC simulation at the same time. In a pressure range of a few mTorr, high energy electrons (\textgreater 5 eV) are heated by the capacitive power in the sheath while low energy electrons (\textless 5 eV) are heated by the inductive power in the bulk region. The EEPF has bi-Maxwellian distribution when the CCP power is dominant, but it changes to Maxwellian-like distribution with increasing inductive power. Finally, the EEPF changes to Druyvesteyn-like distribution when the inductive power is dominant. [1] H. C. Lee and C. W. Chung, Plasma Sources Sci. and Technol. \textbf{24}, 024001 (2015)   

Neutral and ion dynamics at the plasma-surface interface region in inductively coupled plasmas

Understanding the dynamics of the plasma-surface interface in low temperature, low pressure plasmas is critical for developing industrial processes. In this context atomic neutral species and ions both play an important role. Presented in this work is an experimental characterization of the plasma-surface interface region in plasmas produced in O$_{\mathrm{2}}$/Ar and H$_{\mathrm{2}}$/He, operated in capacitive and inductive modes in a gaseous electronics conference (GEC) reference cell. The industrially relevant pressure range of 1-10 Pa is investigated at varying powers and gas mixtures. The dissociation degree and mean electron energy are determined through comparing ratios of calculated excitation rates with those measured using phase resolved optical emission spectroscopy. Two excited states each for hydrogen and oxygen are compared with the rare gas admixture (either He or Ar) using the newly developed Energy Resolved Actinometry (ERA) technique. For the excitation dynamics both direct and dissociative electron impact excitation are accounted for. In addition, the ion energy distribution function at the surface has been measured using a retarding field energy analyzer.