Semion Single Publications

Characterization of an Asymmetric Parallel Plate Radio-Frequency Discharge Using a Retarding Field Energy Analyzer

D Gahan¹, S Daniels², C Hayden², D O’Sullivan¹ and M B Hopkins¹

1. Impedans Ltd, Unit 8 Woodford Court, Woodford Business Park, Santry, Dublin 17, Ireland
2. National Centre for Plasma Science and Technology, Dublin City University, Dublin 9, Ireland

Published 19 December 2011

Abstract

A retarding field energy analyzer is used to characterize an asymmetric, 13.56MHz driven, capacitively coupled, parallel plate discharge operated at low pressure. The characterisation is carried out in argon discharges at 10 and 20mTorr where the sheaths are assumed to be collisionless. The analyzer is set in the powered electrode where the impacting ion and electron energy distributions are measured for a range of discharge powers. A circuit model of the discharge is used to infer important electrical parameters from the measured energy distributions, including electrode excitation voltages, plasma potential and sheath potentials. Analytical models of the ion energy distribution in a radio-frequency sheath are used to determine plasma parameters such as sheath width, ion transit time, electron temperature and ion flux. A radio-frequency compensated Langmuir probe is used for comparison with the retarding field analyzer measurements.

View online at stacks.iop.org/PSST/21/015002


The Electrical Asymmetry Effect in Capacitively Coupled Radio-Frequency Discharges

U Czarnetzki¹, J Schulze¹², E Schüngel¹ and Z Donkó²

1 Institute for Plasma and Atomic Physics, Ruhr-University Bochum, 44780 Bochum, Germany
2 Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences,Budapest, Hungary

Published 1 April 2011

Abstract

We present an analytical model to describe capacitively coupled radio-frequency (CCRF) discharges and the electrical asymmetry effect (EAE) based on the non-linearity of the boundary sheaths. The model describes various discharge types, e.g. single and multi-frequency as well as geometrically symmetric and asymmetric discharges. It yields simple analytical expressions for important plasma parameters such as the dc self-bias, the uncompensated charge in both sheaths, the discharge current and the power dissipated to electrons. Based on the model results the EAE is understood. This effect allows control of the symmetry of CCRF discharges driven by multiple consecutive harmonics of a fundamental frequency electrically by tuning the individual phase shifts between the driving frequencies. This novel class of capacitive radio-frequency (RF) discharges has various advantages: (i) A variable dc self-bias can be generated as a function of the phase shifts between the driving frequencies. In this way, the symmetry of the sheaths in geometrically symmetric discharges can be broken and controlled for the first time. (ii) Almost ideal separate control of ion energy and flux at the electrodes can be realized in contrast to classical dual-frequency discharges driven by two substantially different frequencies. (iii) Non-linear self-excited plasma series resonance oscillations of the RF current can be switched on and off electrically even in geometrically symmetric discharges. Here, the basics of the EAE are introduced and its main applications are discussed based on experimental, simulation, and modelling results.

Online at stacks.iop.org/PSST/20/024010


Ion and Photon Surface Interaction during Remote Plasma ALD of Metal Oxides

H. B. Profijt, P. Kudlacek, M. C. M. van de Sanden, and W. M. M. Kessels

Published 25 February 2011

Abstract

The influence of ions and photons during remote plasma atomic layer deposition (ALD) of metal oxide thin films was investigated for different O2 gas pressures and plasma powers. The ions have kinetic energies of ≤35 eV and fluxes of ∼1012–1014 cm−2 s−1 toward the substrate surface: low enough to prevent substantial ion-induced film damage, but sufficiently large to potentially stimulate the ALD surface reactions. It is further demonstrated that 9.5 eV vacuum ultraviolet photons, present in the plasma, can degrade the electrical performance of electronic structures with ALD synthesized metal oxide films.

Online at Journal of the Electrochemical Society DOI: 10.1149/1.3552663


Retarding Field Energy Analyser Ion Current Calibration and Transmission

K Denieffe¹, C M O’Mahony¹, P D Maguire¹, D Gahan² and M B Hopkins²

1. N.I. Biomedical Engineering Centre, Nanotechnology Research Institute, University of Ulster,BT 37 0QB, Northern Ireland.
2. National Centre for Plasma Science and Technology, Dublin City University, Glasnevin, Dublin 9, Ireland.

Published 2 February 2011

Abstract

Accurate measurement of ion current density and ion energy distributions (IEDs) is often critical for plasma processes in both industrial and research settings. Retarding field energy analysers (RFEAs) have been used to measure IEDs because they are considered accurate, relatively simple and cost effective. However, their usage for critical measurement of ion current density is less common due to difficulties in estimating the proportion of incident ion current reaching the current collector through the RFEA retarding grids. In this paper an RFEA has been calibrated to measure ion current density from an ion beam at pressures ranging from 0.5 to 50.0mTorr. A unique method is presented where the currents generated at each of the retarding grids and the RFEA upper face are measured separately, allowing the reduction in ion current to be monitored and accounted for at each stage of ion transit to the collector. From these I–V measurements a physical model is described. Subsequently, a mathematical description is extracted which includes parameters to account for grid transmissions, upper face secondary electron emission and collisionality. Pressure-dependent calibration factors can be calculated from least mean square best fits of the collector current to the model allowing quantitative measurement of ion current density.

View online at stacks.iop.org/JPhysD/44/075205


Retarding Field Analyzer for Ion Energy Distribution Measurement Through a Radio-Frequency or Pulsed Biased Sheath

David Gahan, Borislav Dolinaj, Chanel Hayden, Michael B. Hopkins

Published 16 June 2009

Abstract

A compact, floating retarding field energy analyzer for measurement of ion energy distributions impacting an electrode through a radio-frequency or pulsed bias sheath in a plasma discharge is presented. The analyzer is designed to sit on the electrode surface, in place of the substrate, and wide-band low pass filters allow it to float at the electrode potential. This avoids the need for modification of the electrode. The capabilities of the analyzer are demonstrated through ion energy distribution and electron energy distribution measurements at the electrode surface in an inductively coupled plasma reactor. For a sinusoidal radio-frequency driving signal applied to the electrode the analyzer is shown to resolve ions with different mass. When the radio-frequency power to the plasma pulsed the analyzer is used to resolve the ion energy distributions at different times in the pulse. The high energy tail of the electron energy distribution reaching the electrode surface is also measured. A comparison with a Langmuir probe shows exceptional agreement in the energy region where both devices overlap.

Online at Plasma Processes and Polymers DOI: 10.1002/ppap.200931607


Ion Energy Distributions at a Capacitively and Directly Coupled Electrode Immersed in a Plasma Generated by a Remote Source

C Hayden¹, D Gahan¹ and M B Hopkins¹²

1. National Centre for Plasma Science and Technology, Dublin City University, Glasnevin, Dublin 9,Ireland
2. Impedans Ltd, Invent Centre, Dublin City University, Glasnevin, Dublin 9, Ireland

Published 4 March 2009

Abstract

Ion energy distributions are investigated in an inductively coupled radio-frequency discharge at low pressures. A Langmuir probe is used to characterize the discharge and a retarding field energy analyzer measures the ion flux and energy distributions impacting a remote rf driven electrode. Comparisons are made between capacitive and direct coupling of the rf bias potential. The effects of ICP power, rf bias voltage (0–75V amplitude), bias frequency (0.5–20 MHz) and discharge pressure (0.2–1.2 Pa) are presented. Results are shown for Ar, O2 and Ar–He discharges. A double layer was observed during source characterization measurements in an O2 discharge; however, the focus of this paper is on the behavior of ions through capacitively and directly coupled plasma sheaths.

Online at stacks.iop.org/PSST/18/025018


Comparison of Plasma Parameters Determined with a Langmuir Probe and with a Retarding Field Energy Analyzer

D Gahan¹, B Dolinaj² and M B Hopkins¹²

1. National Centre for Plasma Science and Technology, Dublin City University, Glasnevin, Dublin 9,Ireland
2. Impedans Ltd., Invent Centre, Dublin City University, Glasnevin, Dublin 9, Ireland

Published 31 July 2008

Abstract

A comparison is made between plasma parameters measured with a retarding field energy analyzer (RFEA), mounted at a grounded electrode in an inductive discharge, and a Langmuir probe located in bulk plasma close to the analyzer. Good agreement between measured plasma parameters is obtained for argon gas pressure in the range 2–10mTorr. Parameters compared include time averaged plasma potential, the tail of the electron energy distribution function (EEDF), the electron temperature and the ion flux. This highlights the versatility of the RFEA for determining plasma parameters adjacent to the surface where probe measurements are not easily made. Combination of the probe and energy analyzer has enabled the measurement of the EEDF to a higher energy than otherwise possible.

Online at stacks.iop.org/PSST/17/035026


Retarding Field Analyzer for Ion Energy Distribution Measurements at a Radio-Frequency Biased Electrode

D Gahan¹, B Dolinaj², and M B Hopkins¹

1. National Centre for Plasma Science and Technology, Dublin City University, Glasnevin, Dublin 9, Ireland
2. Impedans Ltd., Invent Centre, Dublin City University, Glasnevin, Dublin 9, Ireland

Published 10 March 2008

Abstract

A retarding field energy analyzer designed to measure ion energy distributions impacting a radio-frequency biased electrode in a plasma discharge is examined. The analyzer is compact so that the need for differential pumping is avoided. The analyzer is designed to sit on the electrode surface, in place of the substrate, and the signal cables are fed out through the reactor side port. This prevents the need for modifications to the RF electrode—as is normally the case for analyzers built into such electrodes. The capabilities of the analyzer are demonstrated through experiments with various electrode bias conditions in an inductively coupled plasma reactor. The electrode is initially grounded and the measured distributions are validated with the Langmuir probe measurements of the plasma potential. Ion energy distributions are then given for various rf bias voltage levels, discharge pressures, rf bias frequencies—500 kHz to 30 MHz, and rf bias waveforms—sinusoidal, square, and dual frequency

View Online at scitation.aip.org/content/aip/journal/rsi/79/3/10.1063/1.2890100