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Semion Multi Sensor

Semion Multi Sensor

Establishing The Uniformity of Your Key Process Drivers

The Semion Multi Sensor retarding field energy analyser (RFEA) measures the uniformity of ion energies hitting a surface using a number of plasma measurement sensors.

This cutting edge retarding field energy analyser (RFEA) also measures the uniformity of ion flux, negative ions and bias voltage at any position inside a plasma chamber.

The Semion Multi Sensor retarding field energy analyser (RFEA) allows users to change their plasma input parameters such as power, pressure, frequencies and chemistries in real time to find their optimum ion energy distribution and ion flux uniformity for their application.



Features

Substrate Bias Compatible | High RF Bias Resistant |
Easily Installed | High Temperature Resistant


Applications

Process Parameters Correlation with Process Outcome | Process Uniformity |
Process Development | Equipment Design




 

Overview

Ion Energy / Ion Flux Across 450mm WaferThe Semion Multi Sensor Retarding Field Energy Analyser (RFEA) measures the ion energy uniformity, ion flux uniformity, negative ion uniformity and Vdc at the substrate position inside a plasma chamber. The Semion Multi Sensor is primarily used for researching wafer uniformity in industrial plasma applications but it also finds applications in research. Users in the semiconductor community are concerned with the uniformity of ion interactions with the substrate and this holds true for coatings, etching, plasma sputtering, PECVD and ion beam applications. With ever increasing substrate sizes plasma uniformity becomes increasingly critical. The Semion Multi Sensor retarding field energy analyser (RFEA) helps save time to confirm plasma uniformity models, develop new uniform plasma processes and experiments that use plasma, design of larger plasma tools and plasma research.

The Semion Multi Sensor Retarding Potential Analyser (RPA) consists of 19" rack mounted electronics unit, vacuum feed-through, sensor holder with up to 13 Button Probe sensors which are replaceable. The sensor holder, complete with the Button Probe sensors, can be located at any position inside a plasma reactor, even on a biased electrode. Connecting to the electronics unit with a laptop or a PC allows the user to analyse the plasma interactions using the Semion intelligent software suite. The Semion Multi Sensor ion energy analyser comes with a number of holder options ranging from 100mm to 450mm depending on the users application. Applications which require uniformity measurements normally need a larger sensor holder. These holders can accommodate up to 13 sensors depending on its size.

The Semion Multi Sensor ion energy analyser empowers users to adjust their plasma input parameters in real time i.e pressure, power, chemistry and frequency to find the optimum ion energy uniformity and ion flux uniformity for their application at multiple sites across the measuring location. The system also measures temperature uniformity, bias voltage (Vdc) and the energy uniformity and flux uniformity of negative ions. The Semion Multi Sensor Retarding Potential Analyser (RPA) can be used for wafer uniformity and helps users in plasma manufacturing with troubleshooting, chamber matching, process monitoring, fault detection, processes development, preventative maintenance in an offline environment. The Semion System can help reduce downtime and offline substrate analysis.

Plasma Parameters Measured

  • Ion Energy Distribution (Up to 13 Locations)
  • Ion Flux (Up to 13 Locations)
  • Negative Ion (Up to 13 Locations)*
  • Vdc (Average)
  • Edge Profiling (Close to Edge Sensors)

Measurement Functionality

Time Averaged Measurements
This provides an average over time of the ion energy distribution arriving at the substrate position

Time Resolved Measurements
This allows the user to synchronise the ion energy distribution measurements with an external synchronisation signal. The user can then obtain detailed information on the ion energy distribution as a function of time or phase through the synchronisation pulse period*. Typically the pulse period would be on a timescale of milliseconds to microseconds. *For pulsed plasmas with Semion mounted on a grounded or floating electrode

Time Trend Measurements
This allows the user to obtain information on the variation of the ion energy distribution as time progresses through a particular process. This feature does not require external synchronisation and the timescales involved can be in range of seconds to hours.

Further Product Information

Semion Ion Energy Analyser Electronics and Software

Electronics UnitThe user-friendly high energy electronics and software takes accurate and reliable data to provide industry leading ion energy distribution and ion flux measurements. Using intelligent analysis, the optimal plasma parameter measurements are performed easily and repeatedly.

Sensor Holder

The retarding field energy analyser (RFEA) holder is available in various sizes (150mm, 200mm, 300mm, 450mm and Custom Shapes). It sits on a grounded or biased electrode and is used to hold the replaceable Button Probe Sensors. It is available a number of materials including aluminium, anodised aluminium & stainless steel (custom materials are available).

Holder Options

Replaceable Button Probe

Button ProbesThe Semion Button Probe is a compact Retarding Field Energy Analyser (RFEA) which is designed to support continuous Semion system operation. When the probe is coated or etched away after a long period of exposure to reactive or insulating plasmas, the sensing element (Button Probe) can easily be replaced. 

Installation

The Semion Ion Energy Analyser is simple to install and requires no adjustments to your plasma chamber. It is a portable system and can be used across a number of different chambers.

Measuring Parameters

Ion Energy Range 2000 eV - Vdc
Ion Current 1 mA DC max
Ion Flux Ranges* Low: 0.001 - 3 | Std: 0.01 - 50 | High: 0.1 - 700 (A/m²)
IEDF Resolution ± 1 eV nominal

*Choice dependent on plasma density

Probe Bias Conditions

Max RF Bias Voltage 1 kV peak-to-peak
Max DC Bias Voltage -1940 V
Bias Frequency Range (Time Averaged Measurements) 100 kHz to 80 MHz
Bias Frequency Range (Time Resolved Measurements) 0 Hz to 100 kHz
Time Resolution* 100 µs

*For pulsed plasmas with Semion mounted on grounded or floating electrode

RFEA Probe

Number of Sensors 1 to 13
Probe Configuration 4-grid
Button Probe Diameter 33 mm
Holder Diameter 150 mm, 200 mm, 300 mm, 450 mm and custom shapes
Holder Thickness 5 mm
Max Operating Temperature 200º C
Mounting RFEA probe holder mounted on electrode
Probe Enclosure and Holder Material Aluminium, anodized aluminium, stainless steel* and ceramic (Al2O3)*
RFEA Probe Cable Length 650 mm standard (custom available)

*on request

Feed-Through Assembly

Flange Type CF40 (custom available)

Control Unit Electronics

Grid Voltage Range -2 kV to +2 kV
Current Range 100 pA to 2.4 mA
Connectivity USB 2.0

Application Software

Operating System Windows 2000 / XP / Vista / Windows 7 / Windows 8

Operating Parameters

Pressure (Pascal) <0.1 Pa to 40 Pa*
Pressure (Torr) 0 to 300 mTorr*
Density Ranges(for Ar at 3 eV) Low: 1.2 x 1012 to 7.4 x 1015 | Std: 2.0 x 1013 to 1.2 x 1017 | High: 2.7 x 1014 to 1.6 x 1018 (m-3)
Gas Reactivity Inert to highly reactive

*dependent on ion mean free path

The Semion Multi Sensor used in Plasma Etching applications

Ion flux and ion distribution function measurements in synchronously pulsed inductively coupled plasmas

Abstract

Pulsed inductively coupled plasmas (ICPs) have recently attracted considerable interest in the field of integrated circuit fabrication. This is because pulsing provides more flexibility for tuning an etch process by bringing in new reactor control parameters: the pulsing frequency, the duty cycle of the pulses, and the phase between the ICP pulses and the bias pulses. Recent experiments have shown that the duty cycle has a strong influence on plasma chemistry. In this study, the authors look at the impact of the duty cycle on the time variations of the ion flux and on the time-averaged ion distribution function measured at the wafer surface in an ICP-processing chamber subject to pulse modulation of source excitation and bias at 1kHz, in several plasma chemistries.

SE02: Ion flux and ion distribution function measurements in synchronously pulsed inductively coupled plasmas

Ion velocity distribution measurement through high-aspect ratio holes using the Semion system

Abstract

Plasma etching and filling of high aspect-ratio (AR) structures is becoming more difficult at each new semiconductor technology node for several reasons. Ion bombardment of the sidewalls of the feature (due to the angular distribution of ion energies) complicates etching profile control. Also, ion loss on the sidewall reduces ion flux to the bottom of the feature. Ions are directed to the substrate with an angular spread due to the ion thermal velocity at the sheath edge. The thermal velocity causes ions to have a velocity component parallel to the substrate surface while the sheath electric field accelerates the ion toward the substrate in the perpendicular direction. As a result, the ion arrives at the surface at off-normal incidence.

VE02: Ion velocity distribution measurement through high-aspect ratio holes using the Semion system

The Semion Multi Sensor used in HiPIMS Plasma applications

Plasma diagnostics of low-pressure high-power impulse magnetron sputtering assisted by electron cyclotron wave resonance plasma

Abstract

The study focused on the plasma measurement of parameters to explore the assistance of the electron cyclotron wave resonance (ECWR) on the evolution of HiPIMS discharge, where it has several benefits.

SE04/LP08: Plasma diagnostics of low pressure HiPIMS assisted by ECWR plasma

Semion retarding field energy analyzer used to investigate reactive HiPIMS + MF sputtering of TiO₂ crystalline thin films

Abstract

High-power impulse magnetron sputtering (HiPIMS) systems have been previously studied with mid-frequency (MF) plasma excitation, utilizing the “off” period to enhance the deposition rate, decrease the working pressure, and improve HiPIMS plasma generation. Our latest application note looks at the time-resolved ion velocity distribution function (IVDF) in a high-power pulse plasma in three modes of excitation: pure HiPIMS, medium-frequency pulsed bipolar (MF 350 kHz) and hybrid pulsed HiPIMS + MF.

SE05: Semion retarding field energy analyzer used to investigate reactive HiPIMS + MF sputtering of TiO₂ crystalline thin films

Semion Retarding Field Energy Analyser (RFEA) used in a study to form Ti–Cu thin films with regard to controlling the copper release

Abstract

Serious complications in orthopaedic surgery include aseptic loosening and infection of artificial implants. A number of studies have looked at ways to reduce these complications, and copper has been found to be one of the most promising metal ions for deposition applications because of its lower toxicity and higher cytocompatibility. Various studies have shown that sufficient (about 5 mmol/l) copper release over at least several days is needed to inhibit and then kill all bacteria. This study aimed to prepare Ti–Cu film with strong initial antimicrobial and cytotoxic effect, followed by long-lasting but moderate copper release using HiPIMS-based systems.

SE06: Semion Retarding Field Energy Analyser (RFEA) used in a study to form Ti–Cu thin films with regard to controlling the copper release

Semion used in a study of the effect of mid-frequency discharge assistance on dual-high power impulse magnetron sputtering

Abstract

This study introduces a hybrid-dual-HiPIMS system based on the simultaneous combination of dual-HiPIMS and MF discharges. The main body of the study is the time-resolved diagnostics taken using a Semion System during the deposition of Ti–Cu films, revealing the degree of assistance made by the MF discharge.

SE07: Semion used in a study of the effect of mid-frequency discharge assistance on dual-high power impulse magnetron sputtering

The Semion Multi Sensor used in Ion Beam Plasma applications
Coming soon
The Semion Multi Sensor used in PECVD applications

Ion energy distributions in bipolar pulsed DC discharges of methane measured at the biased cathode

Abstract

Ion processes at the growing surface of a depositing film are of huge importance in the achievement of special surface properties. The study of plasma processes at the sheath level complements the characterisation performed by other methods, and it provides a better assessment of the influence of deposition variables on material properties. Compact models of retarding field energy analysers (RFEA) are becoming popular instruments for measuring ion currents due to their rapid installation, high sensitivity to small currents and because no auxiliary pump is needed.
In this paper, the authors study the ion energy distributions (IED) of CH4 plasmas measured with a compact RFEA Semion system from Impedans Ltd placed at the biased electrode, which acts as cathode and coincides with the substrate location for DLC deposition.

SE01: Ion energy distributions in bipolar pulsed DC discharges of methane measured at the biased cathode

The Semion Multi Sensor used in Space Plasma applications
Coming soon
The Semion Multi Sensor used in Plasma Sputtering applications

Ion energy distribution measurements in RF and pulsed DC plasma discharges

Abstract

The energy and flux of bombarding ions play a vital role in the etching and deposition of layers on the substrate surface. Asymmetric radio-frequency (RF) capacitively coupled plasma (CCP) reactors are commonly used for plasma etching. Monitoring of the flux and energy of ions arriving at the substrate in these reactors is essential for process optimization and the control of films’ microstructure. This study used a commercial retarding field energy analyser (RFEA), the Semion System from Impedans Ltd, to measure the ion energy distribution functions (IEDFs) of impacting ions at the powered electrode in a 13.56MHz driven, capacitively coupled, parallel plate discharge operated at low pressure.

SE03: Ion energy distribution measurements in RF and pulsed DC plasma discharges

The Semion Multi Sensor used in Dusty Plasma applications
Coming soon

Theory of Operation: Semion System
Retarding Potential Analyser | Retarding Field Energy Analyser

Introduction

Direct measurement of the ion energy distribution (IED) and total ion flux can be performed with the Semion System, using our advanced retarding field energy analyser (RFEA) technology. The RFEA is constructed from process compatible materials and the sensor’s miniature size allows it to be mounted on the substrate or any other surface inside the reactor. RFEAs have been used for decades to measure IEDs in plasma discharges with limited success. Most designs require mounting on a grounded surface to avoid complications with substrate biasing. Early designs were typically bulky and differential pumping was required for the device to operate even at the low pressures encountered in many plasma processes. The Semion System incorporates a miniature design to avoid the need for differential pumping. Operating pressures of up to 300mTorr can be achieved in Argon discharges. The Semion System also uses high impedance low-pass filters to allow the RFEA to float at the substrate bias potential. The system supports bias frequencies in the range 1kHz to 100MHz and bias potentials up to 3kV peak-to-peak maximum. High temperature cabling connects the RFEA to the external data acquisition unit through a vacuum feedthrough, which is mounted at the reactor wall and enables the sensor to operate to 250°C. Button probe sensing elements are easily replaceable, which is a convenient feature for the user especially when operating in processes using aggressive etching chemistry sets.

In-situ layout of the Semion System in a typical plasma chamber setup

Figure 1: In-situ layout of the Semion Sensor System in a typical plasma chamber setup

Theory of Operation

Figure 2 shows a schematic of the Semion RFEA design. Ions enter the RFEA through an array of sampling apertures exposed to the plasma (only one aperture is depicted for simplicity). A grid G0, covers the internal side of the apertures and reduces the open area ‘seen’ by the plasma to a scale less the Debye length to prevent plasma entering the analyser. A second grid G1, in a plane parallel to G0, is biased with a negative potential relative to G0 to repel any electrons that may enter the device. A third grid G2, is biased with a positive potential sweep, creating a potential barrier for the positive ions. A fourth grid G3, creates a negative potential barrier that prevents electrons from escaping and ensures that they are also collected. A collector plate C, oriented in the same plane as the grids, collects the current of ions which cross the potential barrier set by G2. The data acquisition unit records the ion current at each potential applied to G2 and the graphical user interface displays the resultant current-voltage characteristic. The IED is also displayed - obtained by differentiation of the current-voltage characteristic. The potential configuration is depicted in figure 2.

 

Figure 2: Schematic of the Semion RFEA structure and grid potential configuration

The analyser (including G0, G1, G2, G3 and C), floats at the AC/RF component of the substrate bias potential. This is achieved by means of high impedance low-pass filters. These high impedance filters prevent disturbance of the applied bias signal and provide sufficient attenuation at the output to protect the measurement electronics. The RFEA chassis also floats at the DC bias component of the powered electrode potential. The required DC electric fields between adjacent grids are produced by setting the grid potentials relative to each other (not relative to ground). The Semion feedthrough interface provides a filtered connection to the RFEA chassis to enable a direct measurement of the acceptance angle of a sampling orifice is approximately 45º allowing detection of ions arriving at the surface within this angle. The calculated IED is the energy distribution of the ions perpendicular to the electrode surface.

Typical Results

A typical Semion system installation is shown in figure 3. The RFEA was mounted at the biased substrate holder in a plasma etch reactor. The plasma is sustained by the 2.45GHz source. The substrate holder is biased with 2MHz RF power to control the energy of the ions impacting the substrate. The working gas was pure Argon at a pressure of 10mTorr. IEDs were measured for a range of RF power levels applied to the substrate holder.

Typical Semion Sensor Holder Installation

Figure 3: Semion Sensor Holder Installation

A typical current-voltage characteristic and IED are shown in figure 4. The RF power was set at 50W and the argon gas pressure was 10mTorr. The bi-modal saddle shaped IED structure associated with sinusoidal biasing is clearly visible.

Current-voltage characteristic and IED

Figure 4 (a) Current-voltage characteristic (dashed) and IED measured at 50W and 10mTorr
(b) Ion energy distribution varies as a function of RF power applied to the substrate holder while the pressure is maintained at 10mTorr throughout

 

Download the Semion Sensor System Theory of Operation in PDF format
Theory of Operation: Semion System | Retarding Potential Analyser | Retarding Field Energy Analyser

Ion Energy Distribution Skew Control Using Phase-Locked Harmonic RF Bias Drive

D.J. Coumou, D.H. Clark, T. Kummerer, M. Hopkins, D. Sullivan, S. Shannon

20 June 2014

Abstract

The energy distribution of ions accelerated through a radio frequency sheath and incident on a plasma-facing material significantly influences material interaction with the plasma and can impact manufacturing at the nanoscale. Ion energy distributions are controlled through appropriate mixing of drive frequencies, which has been shown to control distribution width. This paper presents a modification to multifrequency drive for ion energy control by exploiting a digital frequency and phase controller that enables modification of the higher order moments of the distribution, specifically, controlling the skew of the distribution. By modulating the sheath with two frequencies where one frequency is the harmonic of the other and controlling the relative phase of these two waveforms incident on the plasma-facing surface, skew control is achieved. A simple empirical model is presented to describe this method, as well as experimental validation of the model and demonstration of skew control in a parallel plate capacitively coupled reactor.

Online at Plasma Science, IEEE Transactions on (Volume:42 , Issue: 7 ) DOI: 10.1109/TPS.2014.2326600


A spatially resolved retarding field energy analyzer design suitable for uniformity analysis across the surface of a semiconductor wafer

S. Sharma, D. Gahan, S. Kechkar, S. Daniels and M. B. Hopkins

17 April 2014

Abstract

A novel retarding field energy analyzer design capable of measuring the spatial uniformity of the ion energy and ion flux across the surface of a semiconductor wafer is presented. The design consists of 13 individual, compact-sized, analyzers, all of which are multiplexed and controlled by a single acquisition unit. The analyzers were tested to have less than 2% variability from unit to unit due to tight manufacturing tolerances. The main sensor assembly consists of a 300 mm disk to mimic a semiconductor wafer and the plasma sampling orifices of each sensor are flush with disk surface. This device is placed directly on top of the rf biased electrode, at the wafer location, in an industrial capacitively coupled plasma reactor without the need for any modification to the electrode structure. The ion energy distribution, average ion energy, and average ion flux were measured at the 13 locations over the surface of the powered electrode to determine the degree of spatial nonuniformity. The ion energy and ion flux are shown to vary by approximately 20% and 5%, respectively, across the surface of the electrode for the range of conditions investigated in this study.

Online at Rev. Sci. Instrum. 85, 043509 (2014)


Deposition of rutile (TiO2) with preferred orientation by assisted high power impulse magnetron sputtering

Vitezslav Stranak, Ann-Pierra Herrendorf, Harm Wulff, Steffen Drache, Martin Cada, Zdenek Hubicka, Milan Tichy, Rainer Hippler

21 February 2013

Abstract

The effect of energetic ion bombardment on TiO2 crystallographic phase formation was studied. Films were deposited using high-power impulse magnetron sputtering (HiPIMS) assisted by an electron cyclotron wave resonance (ECWR) plasma. The ECWR assistance allows a significant reduction of pressure down to 0.075 Pa during reactive HiPIMS deposition and subsequently enables control of the energy of the deposited species over a wide range. Films deposited at high ion energies and deposition rates form rutile with (101) a preferred orientation. With decreasing ion energy and deposition rates, rutile is formed with random crystallite orientation, and finally at low ion energies the anatase phase occurs. It is supposed that particles gain high energy during the HiPIMS pulse while the ECWR discharge is mostly responsible for substrate heating due to dissipated power. However, the energetic contribution of the ECWR discharge is not sufficient for annealing and phase transformation.

Online at Surface and Coatings Technology DOI: 10.1016/j.surfcoat.2013.02.012


Ion flux and ion distribution function measurements in synchronously pulsed inductively coupled plasmas

Melisa Brihoum, Gilles Cunge, Maxime Darnon, David Gahan, Olivier Joubert and Nicholas St. J. Braithwaite

Published 5 February 2013

Abstract

This paper reports on the time modulation of the ion flux and the time averaged ion energy distribution bombarding the substrate in pulsed ICP plasmas. For inert gas discharges in Helium and Argon the ion flux increases rapidly when the RF power is initiated and reaches a steady state value, similar to that seen in CW plasmas, within 50 µs. As a result the ion flux during the power ON-time in a discharge pulsed at 1 kHz is almost independent of the duty cycle. In contrast, for molecular electronegative discharges in Cl2/SiCl4, the ion flux during the ON-time reaches a steady state value that is strongly dependent on the duty cycle. The reason for this is that both the plasma chemistry and electronegativity depend on the duty cycle. It was found that the ion flux is more than an order of magnitude smaller during the ON-time of the pulsed plasma, with 10% duty cycle, than in the CW plasma. It was also found, that for a given rf bias power, the ion energy is much higher in pulsed plasmas than in CW plasmas. For this type of discharge, under the conditions discussed, the wafer is bombarded by a relatively low flux of very energetic ions, similar to low density capacitively coupled plasmas. Therefore, synchronous pulsing of the source and bias power in ICP plasmas allow an extension of the operating range of this type of discharge which is interesting for several applications.-----Online at Ion flux and ion distribution function measurements in synchronously pulsed inductively coupled plasmas

Online at scitation.aip.org/content/avs/journal/jvsta/31/2/10.1116/1.4790364


White Paper: Helping to address the issue of plasma uniformity in 450mm wafer processes

Prof Mike Hopkins

Published 17 October 2013

Abstract

In the recent decade large area plasma source have become extremely important in a wide range of applications. In flat panel displays, glass panels 2200mm x 2500mm need to be processed. Similarly, efficient manufacture of Si microcrystalline layers for solar applications are using similar larger area plasma sources. In semiconductor applications the most demanding uniformity requirements are in the area of plasma etch. Here dual, or multi frequency capacitively coupled (CCP) plasmas are needed with very high uniformity and process areas of 450mm.

Download

Click to downloadWP01: Helping to address the issue of plasma uniformity in 450mm wafer processes


Effect of mid-frequency discharge assistance on dual-high power impulse magnetron sputtering

Vitezslav Stranak, Steffen Drache, Robert Bogdanowicz, Harm Wulff, Ann-Pierra Herrendorf, Zdenek Hubicka, Martin Cada, Milan Tichy, Rainer Hippler

15 February 2012

Abstract

The present paper is focused on time-resolved diagnostics of the simultaneous combination of dual mid-frequency and dual-high power impulse magnetron sputtering discharges (so-called hybrid-dual-HiPIMS systems). Combined systems are operated with the following parameters – dual-high power impulse magnetron sputtering (fH = 100 Hz, duty cycle 1%) and dual mid-frequency discharge (fM = 94 kHz, duty cycle 30%) – running simultaneously with two magnetron guns. The magnetrons in dual configuration are electrically confined, i.e. electrodes are alternately operated as an anode–cathode (and vice versa) during the sputtering. The dual MF discharge causes a pre-ionization effect which is an important feature because of: (i) a significant reduction of the working pressure by more than one order of magnitude, (ii) an increase of electron and ion energy, and (iii) an increase of the deposition rate. It was found that the ion velocity distribution function (IVDF) during HiPIMS pulses reaches a maximum of about 15–20 eV whereby the dual MF discharge reaches about 0.5–1.5 eV. The time-resolved IVDF measurements revealed that ions with high energy generated at the cathode arrive at the substrate position about 25–30 μs after the HiPIMS pulse ignition. The effect of the hybrid system is illustrated on the deposition of Ti–Cu films. The crystallographic phase and properties of the deposited films are strongly influenced by the energy of incoming particles and by reduced pressure in the chamber.

Online at Surface and Coatings Technology: Volume 206, Issues 11–12, 15 February 2012, Pages 2801–2809


Characterization of an asymmetric parallel plate radio-frequency discharge using a retarding field energy analyser

D Gahan, S Daniels, C Hayden, D O'Sullivan, and M B Hopkins

Published 19 December 2011

Abstract

A retarding field energy analyzer is used to characterize an asymmetric, 13.56 MHz driven, capacitively coupled, parallel plate discharge operated at low pressure. The characterization is carried out in argon discharges at 10 and 20 mTorr 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.

Online at D Gahan et al 2012 Plasma Sources Sci. Technol. 21 015002

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