Semion Multi Publications

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


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


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


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


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

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

Prof Mike Hopkins

Published 17 October 2013


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.


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


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


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