The Semion 800 is a precision plasma measurement instrument used in a large number of plasma laboratory applications. The Semion 800 is the key instrument used by scientists to measure the ion energy and flux arriving at a surface in a plasma process chamber.
The Semion 800 can be placed on a biased or grounded surface. Among the key parameters measured are Ion Energy, Ion Flux, Electron Energy, Plasma Potential and Floating Potential. The Semion 800 provides plasma parameter measurement in DC, RF, Microwave, Continuous and Pulsed plasma. The Semion 800 is the most advanced and trusted, fully automated retarding field energy analyser on the market.
The Semion 800 helps the user to understand plasma surface interactions, such as deposition mechanisms, etch mechanisms and energy transfer mechanisms, due to plasma ions impacting on the surface. It is an essential plasma process diagnostic to understand the correlation between plasma inputs and the plasma state. The Semion 800 helps to reduce process development, source development and tool development time, as well as the time to market for new plasma products. Pulsed plasmas are used to tailor the electron or ion energy and the Semion 800 is an integral part of such a process development.
Semion Ion Energy Analyser Electronics and Software
The user-friendly 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.
Button Probe Holder
The holder is available in various sizes (70mm, 100mm & 300mm). 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).
Replaceable Button Probe
The Semion Button Probe™ is a compact Retarding Field Energy Analyser (RFEA) which is designed to support continuous Semion system operation. It assists with the maintenance of the Semion Ion Energy Analyser system where the RFEA probe materials are coated or etched away during exposure to a plasma process. The probes are supplied in a range of materials, surface finishes, and transmission grades to meet the requirements of a wide range of applications in etch, PECVD, magnetron sputtering, HiPIMS, and other aggressive plasma processes.
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.
Introduction
Plasma processes are used extensively in modern industry to remove and deposit layers. Substrates exposed to the plasma are bombarded by reactive species including energetic ions. Energetic ion bombardment plays a crucial role in most types of plasma processing. As substrates become larger, and feature sizes smaller, there is an increasing demand for ion flux and ion energy measurement to aid process development.
Direct measurement of the ion energy distribution (IED) and total ion flux can be performed using our advanced retarding field energy analyzer (RFEA) technology, Semion 800™ system. 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 800™ system incorporates a miniature design to avoid the need for differential pumping. Operating pressures of up to 300 mTorr can be achieved in Argon discharges. The Semion 800™ 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 1kV peak-to-peak maximum. High temperature cabling connects the RFEA to the external data acquisition unit through a vacuum feed-through, which is mounted at the reactor wall, and enables the senor to operate to 200o Celcius. Replaceable Button Probe™ sensing elements is convenient feature for the user especially when operating in deposition systems. The standard system uses three grids, there is also a four grid option where the fourth grid is configured to prevent secondary electron emission from the collector plate.
Theory of Operation
Figure 1(a) shows a schematic of the Semion 800™ 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 analyzer. 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 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 GUI 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 1(b).
The analyzer (including G0, G1, G2, 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 (not relative to ground). The SemionTM 800 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 450 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.
Figure 1: (a) Schematic of the Semion 800™ RFEA structure and (b) grid potential configuration.
Typical Results
A typical Semion 800™ system installation is shown in figure 2. The RFEA was mounted at the biased substrate holder in an Lam Research capacitively coupled plasma reactor. The substrate holder was driven with 13.56MHz rf power to ignite the discharge. The working gas was pure Argon at a pressure of 10 mTorr. IEDs were measured for a range of rf power levels applied to the substrate holder.
Figure 2: Semion 800™ installation in an Lam Research CCP reactor.
A typical current-voltage characteristic and IED are shown in figure 3. The rf power was set at 50W and the argon gas pressure was 10 mTorr. The well know bi-modal saddle shaped IED structure associated with sinusoidal biasing is clearly visible.
Figure 3: Current-Voltage characteristic (dashed) and IED measured at 50W and 10 mTorr.
Figure 4 shows how the ion energy distribution varies as a function of rf power applied to the substrate holder while the pressure is maintained at 10 mTorr throughout.
Retarding Field Energy Analyser Ion Current Calibration and Transmission.
K Denieffe1, CMO 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
Online at stacks.iop.org/JPhysD/44/075205
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.
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 Hopkins1,2
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
Online at stacks.iop.org/PSST/18/025018
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.
Comparison of Plasma Parameters Determined with a Langmuir Probe and with a Retarding Field Energy Analyzer
D Gahan1, B Dolinaj2 and M B Hopkins1,2
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
Online at stacks.iop.org/PSST/17/035026
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.
Retarding Field Analyzer for Ion Energy Distribution Measurements at a Radio-Frequency Biased Electrode
D. Gahan,1,a B. Dolinaj,2 and M. B. Hopkins1
1National Centre for Plasma Science and Technology, Dublin City University, Glasnevin, Dublin 9, Ireland
2Impedans 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
The Electrical Asymmetry Effect in Capacitively Coupled Radio-Frequency Discharges
U Czarnetzki1, J Schulze1,2, E Sch¨ungel1 and Z Donk´o2
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
Online at stacks.iop.org/PSST/20/024010
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 modeling results.
Semion 800 - Retarding Field Energy Analyzer (