Diagnostics of reactive RF plasmas (original) (raw)
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Review of Scientific Instruments, 1994
A "reference cell" for generating radio-frequency (rf) glow discharges in gases at a frequency of 13.56 MHz is described. The reference cell provides an experimental platform for comparing plasma measurements carried out in a common reactor geometry by different experimental groups, thereby enhancing the transfer of knowledge and insight gained in rf discharge studies. The results of performing ostensibly identical measurements on six of these cells in five different laboratories are analyzed and discussed. Measurements were made of plasma voltage and current characteristics for discharges in pure argon at specified values of applied voltages, gas pressures, and gas flow rates. Data are presented on relevant electrical quantities derived from Fourier analysis of the voltage and current wave forms. Amplitudes, phase shifts, self-bias voltages, and power dissipation were measured. Each of the cells was characterized in terms of its measured internal reactive components. Comparing results from different cells provides an indication of the degree of precision needed to define the electrical configuration and operating parameters in order to achieve identical performance at various laboratories. The results show, for example, that the external circuit, including the reactive components of the rf power source, can significantly influence the discharge. Results obtained in reference cells with identical rf power sources demonstrate that considerable progress has been made in developing a phenomenological understanding of the conditions needed to obtain reproducible discharge conditions in independent reference cells.
Contributions to Plasma Physics, 2005
Modern diagnostic methods are applied for investigation of spatial and temporal behaviour of selected reactive species in oxygen and fluorocarbon rf plasmas. Comprehensive investigations of the spatial distribution of atomic oxygen were done by means of two-photon absorption laser induced fluorescence spectroscopy. Exemplarily, axial and radial O-concentrations are shown for an asymmetric capacitively coupled rf plasma in pure oxygen. The time resolved threshold ionization mass spectrometry was applied for investigation of small fluorocarbon radicals. In pulsed CF4/H2 rf plasma the concentrations of the extracted radicals CF2, CF3, C2F5 as well as the intermediate product C2F4 in the plasma on and off phase are presented.
Applied Physics Letters, 1992
The relative concentration of atomic fluorine was measured in a radio frequency (rf) glow discharge and a modified electron cyclotron resonance microwave/r-f hybrid discharge in CF, using an actinometric technique. The dependence of fluorine concentration on rf and microwave power, pressure, flow, and excitation source are presented. Anomalous behavior with rf power at constant microwave power was observed when using the Ar 750nm line as the actinometric species.
Argon metastable densities in radio frequency Ar, Ar/O2 and Ar/CF4 electrical discharges
Journal of Applied Physics, 1997
The spatial distributions of excited states in radio frequency electrical gas discharges have been observed to be dynamic functions of gas mixture, pressure, and applied voltage. Recent measurements of two-dimensional profiles of excited states in the Gaseous Electronics Conference reference cell ͑GECRC͒ ͓McMillin and Zachariah, J. Appl. Phys. 77, 5538 ͑1995͒; 79, 77 ͑1996͔͒ have shown that the spatial distribution of the Ar(4s) density varies considerably with operating conditions. The peak density of Ar(4s) systematically shifted in position, as well as changed in magnitude, with variations in pressure, applied voltage, and gas mixture. In this article, we present results from a two-dimensional computer simulation of Ar, Ar/O 2 , and Ar/CF 4 discharges sustained in the GECRC with the intent of investigating the experimental trends. The simulations, performed with the Hybrid Plasma Equipment Model, agree well with experiments. They show that the shift in Ar(4s) densities is largely explained by the reduction in the electron mean free path, and local perturbations in the ambipolar electric field resulting from electrode structures. Additions of small amounts of O 2 and CF 4 decrease the Ar(4s) density due to quenching, and change its profile due to a transition to an electronegative plasma.
Spectrochimica Acta Part B: Atomic Spectroscopy, 1975
&&a&-Models of induction coupled plasma (ICP) discharges are developed for arrangements important in spectrochemical analysis. These models account for fhe spatial distribution of gas properties and major energy losses found in high temperature discharges. Realistic gas flows, and sample particle motion and decomposition are incorporated into the models. Computer simulations based on these models provide spatial temperature, gas velocity, sample concentration, and radiation distributions for a number of experimental ICP discharge configurations. The alteration of these distributions for various operskional parameters permits evaluation of some important factors in developing spectrochemical analysis with the ICP source. Recognized differences between theory and experiment are discussed.
Experimental and Theoretical Studies of a Pulsed Microwave Excited Ar/CF 4 Plasma
Plasma Chemistry and Plasma Processing - PLASMA CHEM PLASMA PROCESS, 1998
The present work deals with a pulsed microwave discharge in an Ar/CF4gas mixture under a low pressure (1–10 mbar). The discharge chamber developed has a cylindrical geometry with a coupling window alternatively made of quartz or alumina. The setup allows one to investigate the plasma–wall interactions (here etching of the quartz window) and the ignition process of the pulsed microwave plasma. Microwave pulses with a duration of 50–200 µs and repetition rate between 1 and 10 kHz are typical for the experiments. The space-time behavior of the fluorine number density in the discharge has been investigated experimentally by optical actinometry. The discharge kinetics is modeled using electron-transport parameters and rate coefficients derived from solutions of the Boltzmann equation. Together with the solution of the continuity and electron balance equations and the rate equations describing the production of CFx(x=2, 3, 4) radicals and F atoms, a good agreement between experimental and...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1996
The translational gas temperature was measured in 13.56 MHz radio-frequency ͑rf͒ discharges in CF 4 and CHF 3. Infrared absorption spectra of CF 4 and CF 2 were recorded using a tunable diode laser and the gas temperature was deduced from the linewidths of the absorption lines of these molecules. It is shown that linewidth measurements yield a simple and direct method to determine the gas temperature, with an accuracy up to ϳ10 K. The results obtained in CF 4 and CHF 3 plasmas indicate that the translational temperatures of all particles investigated in these plasmas are, at most, 50 K above the room temperature. The temperature increases with increasing gas pressure and rf power, but it is independent of the flow rate. This is attributed to an increased heating rate of the gas. Moreover, it was found that the temperature rise is significantly smaller in CHF 3 than in CF 4 , under the same plasma conditions. This can be attributed to a higher power dissipation by chemical conversion of the parent gas in a CHF 3 discharge, as compared with a CF 4 plasma.
New Experimental Device for Investigation of RF Discharge Plasma in Ar + I 2 Mixture
In this article we describe new experimental device which is currently in construction. In this device, the hollow cathode radiofrequency (RF) low pressure discharge in the mixture of Ar with I 2 vapors will be investigated by Langmuir probe. This work is loosely connected to the research of the oxygen-iodine laser at the Institute of Physics AS in Prague, where the RF discharge in mixtures containing iodine donors (molecules CH 3 I and CF 3 I) is currently investigated [Schmiedberger et al., 2008]. In this article the new experimental device and its current state of construction are described together with the necessary theory and future plans of the experiments. Theory Discharges can be divided into two groups: electropositive and electronegative discharges. Most of the discharges are electropositive, which means, that they consist of neutral particles, positive ions and electrons. Positive ions are mostly created in collisions of neutral particles with electrons in the process called electron impact ionization: A + e-→ A + + 2e-. Further ionization mechanisms are e.g. stepwise ionization, Penning ionization, thermal ionization, photoionization, etc. In electronegative discharges we have neutrals, positive ions, negative ions and electrons. Negative ions are usually created by so called electron attachment: A + e-→ A-. Gases which form electronegative discharges are for example halogens (F 2 , Cl 2 , I 2 vapor), halogen compounds (HI, SF 6) and some other gases (O 2 , H 2). These gases are very important for some branches of plasma processing like plasma etching (F 2 , SF 6) and plasma chemistry (O 2). Electronegative discharges are less stable than electropositive because a part of free electrons is consumed by electronegative particles and does not participate in further ionization. Electronegative plasmas have different structure than electropositive ones. They form layers: in the middle (usually in between the electrodes) there is electronegative plasma containing positive ions, which are electrically balanced by negative ions and electrons. This electronegative layer is surrounded by electropositive layer, where positive ion and electron densities are approximately equal and there are no negative ions. This layer then transforms to the sheath at walls or around the probesee figure 1 [Lieberman, 2005]. In our device we will deal with discharge in mixture of Ar with I 2. Iodine is halogen and therefore strongly electronegative. Negative iodine ions are mainly produced by electron dissociative attachment to iodine molecule: I 2 + e-→ I-+ I. Caution has to be asserted when interpreting the data from Langmuir probe measurements in electronegative discharges. The presence of negative ions changes the measured Langmuir probe I-V characteristics due to the smaller number of electrons and more complicated structure of these plasmas. There are several articles dealing with Langmuir probe measurements in electronegative plasma and ways how to obtain plasma parameters from the measured I-V characteristics applying various models. One of the first review articles about electronegative plasma is that of Boyd et al., [1959]. From further works we can cite Bryant et al. [2001], Braithwaite et al. [1988] and Amemiya et al. [1999]. Electronegative plasma theories are critically revisited in Franklin et al. [2001]. We expect that concentration of iodine will be very low, so the ratio of negative ion to electron concentration will be small (< 20%).
Characterization of SF6/Argon Plasmas for Microelectronics Applications
2002
This report documents measurements in inductively driven plasmas containing SF 6 / Argon gas mixtures. The data in this report is presented in a series of appendices with a minimum of interpretation. During the course of this work we investigated: the electron and negative ion density using microwave interferometry and laser photodetachment; the optical emission; plasma species using mass spectrometry, and the ion energy distributions at the surface of the rf biased electrode in several configurations. The goal of this work was to assemble a consistent set of data to understand the important chemical mechanisms in SF 6 based processing of materials and to validate models of the gas and surface processes. Project Overview The purpose of this report is to document measurements in inductively driven plasmas containing SF 6 / Argon gas mixtures. During the course of this work a number of measurements were performed to begin to assemble a consistent set of data to 1) understand the important physical and chemical mechanisms active in SF 6 based processing of microelectronic materials and 2) to generate a data set to validate models of the gas and surface processes, including feature evolution. While SF 6 has been used for many years in plasma processes, there is a significant lack of fundamental data of the type required to validate models. Results from the various measurements are presented in a series of appendices. The appendices include a brief description of the measurement technique and then the data. In many cases, there is a minimum of interpretation. Appendix 1 includes the results of optical emission measurements of SF 6 gas mixtures over a range of powers and pressures. Appendix 2 reviews data obtained using a mass spectrometer. A mass spectrometer was used to survey the ion and neutral species present in the plasma and in the case of ion species, measure the scaling with plasma condition. Appendix 3 is a preprint of a paper submitted to the Journal of Applied Physics on measurements of the electron and negative ion density in SF 6 / Ar gas mixtures. Appendix 4 is a preprint of a paper submitted to the Journal of Vacuum Science and Technology A on measurements of the ion energy at the surface of a rf biased electrode with surface features.