Tim Styrnoll

The multipole resonance probe: characterization of a prototype

The multipole resonance probe (MRP) was recently proposed as an economical and industry compatible plasma diagnostic device (Lapke et al 2008 Appl. Phys. Lett. 93 051502). This communication reports the experimental characterization of a first MRP prototype in an inductively coupled argon/nitrogen plasma at 10?Pa. The behavior of the device follows the predictions of both an analytical model and a numerical simulation. The obtained electron densities are in excellent agreement with the results of Langmuir probe measurements.

On the electrical asymmetry effect in large area multiple frequency capacitively coupled plasmas

Recently, many publications have dealt with the electrical asymmetry effect in capacitively coupled radio frequency-discharges. The idea of this concept is the possibility of controlling the self-bias voltage by tuning the relative phase of harmonics in relation to the fundamental wave. In this work, we apply the electrical asymmetry effect on a large-area multiple frequency capacitively coupled plasma used for reactive sputtering by varying the relative phase of the 13.56 and 27.12 MHz excitation. The resulting voltage waveforms at the electrode are recorded using a high-voltage probe. The shape of the waveform is then analysed by Fourier analysis to study the influence of higher harmonics excited at the non-linearity of the plasma boundary sheath. To investigate the influence of the relative phase on the plasma itself, radially resolved multipole resonance probe measurements are performed.

The Multipole Resonance Probe: Progression and Evaluation of a Process Compatible Plasma Sensor

A robust and sensitive plasma sensor, the multipole resonance probe (MRP), and its process compatibility are presented and discussed in this paper. Based on its innovative concept and simple model describing the system “probe-plasma”, three steps of development are introduced. 3D electromagnetic field simulations are applied as an indispensable tool for an economical and efficient investigation and optimization of different sensor layouts. Independent of the chosen sensor design, a developed pulse-based measurement device yields an economical signal generation and evaluation. Electron density profiles, determined with the MRP and the pulse-based system utilized in a capacitive coupled plasma, confirm and demonstrate the simulation results and the measurement concept, respectively.

Characterization of low-pressure microwave and radio frequency discharges in oxygen applying optical emission spectroscopy and multipole resonance probe

Optical emission spectroscopy (OES) and multipole resonance probe (MRP) are adopted to characterize low-pressure microwave (MW) and radio frequency (RF) discharges in oxygen. In this context, both discharges are usually applied for the deposition of permeation barrier SiOx films on plastic foils or the inner surface of plastic bottles. For technological reasons the MW excitation is modulated and a continuous wave (cw) RF bias is used. The RF voltage produces a stationary low-density plasma, whereas the high-density MW discharge is pulsed. For the optimization of deposition process and the quality of the deposited barrier films, plasma conditions are characterized using OES and MRP. To simplify the comparison of applied diagnostics, both MW and RF discharges are studied separately in cw mode. The OES and MRP diagnostic methods complement each other and provide reliable information about electron density and electron temperature. In the MW case, electron density amounts to ne = (1.25 ± 0.26) × 1017 m−3, and kTe to 1.93 ± 0.20 eV, in the RF case ne = (6.8 ± 1.8)×1015 m−3 and kTe = 2.6 ± 0.35 eV. The corresponding gas temperatures are 760±40 K and 440±20 K.

Study on electrostatic and electromagnetic probes operated in ceramic and metallic depositing plasmas

This paper discusses plasma probe diagnostics, namely the multipole resonance probe (MRP) and Langmuir probe (LP), operated in depositing plasmas. The aim of this work is to show that the combination of both probes provides stable and robust measurements and clear determination of plasma parameters for metallic and ceramic coating processes. The probes use different approaches to determine plasma parameters, e.g. electron density ne and electron temperature Te. The LP is a well-established plasma diagnostic, and its applicability in technological plasmas is well documented. The LP is a dc probe that performs a voltage sweep and analyses the measured current, which makes it insensitive against conductive metallic coating. However, once the LP is dielectrically coated with a ceramic film, its functionality is constricted. In contrast, the MRP was recently presented as a monitoring tool, which is insensitive to coating with dielectric ceramics. It is a new plasma diagnostic based on the concept of active plasma resonance spectroscopy, which uses the universal characteristic of all plasmas to resonate on or near the electron plasma frequency. The MRP emits a frequency sweep and the absorption of the signal, the |S11| parameter, is analysed. Since the MRP concept is based on electromagnetic waves, which are able to transmit dielectrics, it is insensitive to dielectric coatings. But once the MRP is metallized with a thin conductive film, no undisturbed RF-signal can be emitted into the plasma, which leads to falsified plasma parameter.In order to compare both systems, during metallic or dielectric coating, the probes are operated in a magnetron CCP, which is equipped with a titanium target. We present measurements in metallic and dielectric coating processes with both probes and elaborate advantages and problems of each probe operated in each coating environment.

Supervision and control of medical sterilization processes utilizing the Multipole Resonance Probe

An innovative and sensitive plasma probe suitable for the supervision and control of low-temperature plasma sterilization processes is presented in this contribution. For heat or chemical sensitive materials, plasmas are an indispensable tool regarding the sterilization of surgery instruments, for example. The presented Multipole Resonance Probe (MRP) allows for the simultaneous determination of plasma density, plasma temperature, and collision frequency by a simple and fast evaluation of its frequency response. Fed by an rf-signal, the MRP yields sensitive and local measurements for the determination of lowest fluctuations and for the application of a sensor network, respectively. With a minimal distance of 3 cm between two probes, the MRP can be deployed effectively as sensor network inside the plasma for the supervision of its stability and homogeneity. Based on 3D-electromagnetic field simulations the advantages of the MRP are discussed in detail. Compared to a Langmuir probe, measurements in a Double Inductive Coupled Plasma (DICP) show the suitability of the MRP inside an argon plasma.

A novel radio-frequency plasma probe for monitoring systems in dielectric deposition processes

This paper presents a novel industry compatible plasma probe for monitoring systems in dielectric deposition processes. The probe is based on the so called active plasma resonance spectroscopy and allows an extensive evaluation of different important plasma parameters, needed for the supervision and control of the plasma deposition process. Due to its assembly, the probe is insensitive against additional dielectric coating. Hence, the measurement performance is not affected. 3D-electromagnetic field simulations of the probe in a pseudo plasma deposition process, as well as the measurement with a prototype in a real deposition process show a good agreement with the expected behaviour and confirm the applicability of the probe as a monitoring tool for dielectric deposition processes.

The Planar Multipole Resonance Probe: Challenges and Prospects of a Planar Plasma Sensor

A novel compact plasma sensor applicable for the supervision and control of industrial plasma processes is presented in this contribution. Based on the multipole resonance probe (MRP), the new planar MRP (pMRP) is introduced as a powerful and economical monitoring tool, flush-mounted into the reactor wall. Hence, it can be used for an effective suppression of disturbances of the plasma process itself. Using 3D electromagnetic field simulations with CST Microwave Studio, the pMRP is investigated and challenges as well as prospects of the new sensor design are discussed in detail. Three different sensor versions are presented and compared with the resonance behavior of the MRP. Furthermore, limitations concerning position tolerances are shown and the suitability of the pMRP is proven. Measurements in a double inductive coupled plasma, with argon as process gas and varying excitation powers, demonstrate the suitability of the pMRP for monitoring purposes.

Implications of electron heating and non-uniformities in a VHF-CCP for sterilization of medical instruments

A capacitively coupled plasma driven at a frequency of 81.36 MHz from the VHF-band is investigated by means of optical emission spectroscopy (OES) and multipole resonance probe (MRP). The discharge is operated with hydrogen, yielding an electropositive discharge, as well as oxygen, yielding an electronegative discharge, and mixtures of both. Pressure is varied from Pa to Pa. Homogeneity of the discharge is investigated by CCD camera recordings as well as spatially resolved multipole resonance probe measurements. The results indicate the presence of electromagnetic edge effects as well as standing wave effects. Furthermore, a largely homogeneous discharge can be achieved with hydrogen as process gas at a pressure of –10 Pa. With increasing pressure as well as with increasing oxygen content, the discharge appears less homogeneously. The transition from an electropositive to an electronegative discharge leads to a change in electron heating mechanisms, with pronounced local maxima of electron density at the sheath edges. A comparison of OES and MRP results reveal a significant difference in electron density, which can be explained by a non-Maxwellian distribution function of electrons.

The multipole resonance probe: Evolution of a plasma sensor

A robust and sensitive plasma probe, the multipole resonance probe (MRP), and its importance for industrial purposes is presented and discussed in this paper. Based on its innovative concept and its simple model of the system ”probe-plasma”, a novel wall-mounted sensor is introduced. This sensor represents an optimized design of one sector of the MRPs assembly and is investigated within 3D-electromagnetic field simulations and compared to measurements of the MRP in an argon plasma. The resulting wall-mounted sensor can be designed for a desired application, which operates within a limited frequency range. The presented sensor covers a density range of approximately ne = 1016 m-3... 1017 m-3, which is sufficient for the considered process.