ICMCTF2002 Session TS-1: Principles of Pulsed Plasmas

Monday, April 22, 2002 1:30 PM in Room Sunset

Monday Afternoon

Start	Invited?	Item
1:30 PM	Invited	TS-1-1 Surface Science Aspects of Plasma Processing J.W. Coburn (University of California) The use of molecular gas glow discharges to accomplish etching, deposition or surface modification of materials has grown rapidly during the last 30 years or so and this growth is expected to continue. Energetic electrons in a glow discharge cause dissociation and ionization of the injected feed gas. The atoms/radicals and positive ions that are produced allow many very important chemical reactions with surfaces to occur at or near room temperature. In most cases, unacceptably high temperatures would be required if only the molecular feed gas were present. One of the most important factors determining the outcome of a plasma-surface interaction is the volatility of the reaction products. High vapor pressure reaction products (i.e., greater than about 10^-4 Torr) are required for most etching work whereas low vapor pressure reaction products usually result in deposition or surface modification. Not only do the atoms/radicals react efficiently with surfaces but also some very important synergistic phenomena, involving the combination of reactive neutral species and energetic positive ions, have been observed. The combination of a rf inductively coupled (or wave-generated) plasma with a capacitively coupled rf electrode holding the surface of interest, allows independent optimization of the ion flux and the ion energy. In many processes the ratio of the reactive atom/radical flux to the ion energy flux determines the consequences of the plasma-surface interaction. Examples of some interesting plasma-surface interactions will be presented, emphasizing plasma-assisted etching which often utilizes simultaneous etching and deposition.
2:10 PM		TS-1-3 Investigations of Process/Coating Relationships in Pulsed Magnetron Sputtering P.J. Kelly (University of Salford, United Kingdom); J.W. Bradley (UMIST, United Kingdom) Pulsed magnetron sputtering is a highly successful technique for the deposition of transparent dielectric materials. Operating in the mid-frequency range (20-350kHz), the periodic target voltage reversals suppress arcing and stabilise the reactive sputtering process. Asymmetric bipolar pulsed DC power supplies are commonly used to drive this process. For simplicity these supplies are normally assumed to display ‘square wave’ characteristics. However, as pulse frequencies are increased, particularly to in excess of 150kHz, target voltage waveforms increasingly depart from this idealised behaviour. Very significant voltage overshoots are observed in each direction during each half of the pulse cycle. Concurrent studies are now being carried out to investigate the interrelationships between target voltage waveform, the subsequent plasma characteristics, the flux and energies of ions incident at the substrate and their collective impact on film structure and properties. To ascertain these relationships, metallic and ceramic films have been deposited at various pulse frequencies and duty cycles; time averaged and time resolved Langmuir probe studies have been performed; and ion energy distribution functions have been obtained using an energy-resolved mass spectrometer. The films themselves have been characterised in terms of their structures and properties including hardness, critical load and, in the case of the ceramic films, refractive index. The results to date, presented here, are beginning to shed some light on the complex processes occurring during asymmetric bipolar pulsed sputtering.
2:30 PM		TS-1-4 Electrostatic Quadrupole Plasma Mass Spectrometer and Langmuir Probe Measurements of Mid-Frequency Pulsed DC Plasmas C. Muratore, J.J. Moore (Colorado School of Mines); J.A. Rees (Hiden Analytical Limited, United Kingdom) The positive effects of mid-frequency (5-100 kHz) pulsed DC magnetron plasmas on the structure and properties of metal oxide and other reactively sputtered thin films are well documented. However, the understanding of the mechanism(s) by which these film characteristics are modified by pulsing the plasma is still under development, especially for compounds such as titanium oxide, in which charge build-up on the cathode is a less important process factor. Time-resolved electrostatic quadrupole plasma mass spectrometer and Langmuir probe measurements are one means by which intrinsic pulsed plasma parameters such as ion and electron energy distributions at any point on the cathode voltage profile can be characterized. Such data will be correlated to reactively sputtered titanium oxide thin films characterized by atomic force microscopy, X-ray photoelectron spectroscopy, and other techniques.
2:50 PM		TS-1-5 Plasma Conditions in Ionized PVD by High-power Pulsed Magnetron Discharges J. Alami (Linköping University, Sweden); J.T. Gudmundsson (University of Iceland); A.P. Ehiasarian, W-D Münz (Sheffield Hallam University, United Kingdom); U. Helmersson (Linköping University, Sweden) Spatial and temporal plasma conditions of high-power pulsed magnetron discharge are reported. Plasma parameters including electron density, plasma potential, floating potential, ion saturation current as well as electron energy distribution function are determined. Electron densities of up to 10¹⁹ m^-3 are reached at a distance 10 cm from target for 100 µs pulses with pulse energy 6 J, and up to 10²⁰ m^-3 for 11 J. Repetition frequency is 50 Hz. Influence of magnetron power and chamber pressure on plasma parameters are studied using a Langmuir cylindrical probe and a flat probe, at different distances from the target center and radially for some chosen target-probe distances. Plasma parameters for a magnetron dc-plasma are also studied and results are compared to those of the high-power pulsed plasma. Observed film thickness distributions indicate that the flux of deposition material is strongly affected by the magnetic field distribution of the magnetron source.
3:10 PM		TS-1-6 Application of Fourier Transform Analysis to Pulsed Magnetron Sputtering Technology V. Bellido-Gonzalez (Gencoa Ltd, United Kingdom); J. O'Brien (University of Salford, United Kingdom); D. Monaghan (Gencoa Ltd, United Kingdom) Magnetron sputtering using pulsed technology has found many interesting applications. Some of the phenomenae involved in the delivery of power during the sputtering process are not well understood. In the present paper we have used Fourier Transform Analysis (FTA) in order to gain an understanding of the pulse sputtering process in magnetron sources. Fourier Transform Analysis allows us to decompose a particular function of the time in its natural frequencies. Therefore, when applied to a periodic wave, such as the target voltage during a pulse period, it is possible to represent that function as a series of frequencies at which the energy is delivered. In the current paper we have studied the changes in pulse conditions for three target materials C, Ti and Al. By decomposing the target waveform response to the pulse condition we were able to identify some of the mechanisms in which the sputtering process absorbs energy. Deposited films have been analysed to ascertain whether an optimum pulsing condition can be reached for each material using the FTA. Conversely, by knowing the physical processes which involve the absorption of energy we are able to propose a new generation of pulsed power supplies.