Microwave power coupling in a surface wave excited plasma

2016

Microwaves are frequently used to produce high density plasmas for industrial and laboratory applications, because they present several advantages when compared to radio-frequency discharges and discharges created using electrodes. Stable and reliable microwave plasma equipment based on magnetrons, and designed for automatic control of the operating parameters has already proved its efficiency in low temperature diamond deposition, exhaust gas abatement, thin-film deposition, etc. However, larger-scale processing with high density and uniform plasma is mandatory for surface treatments to get uniform etching or deposition rates. To meet these industrial requirements AuraWave, an ECR microwave plasma source operating in the 10-2–1 Pa pressure range, and Hi-Wave, a collisional plasma source for higher pressure gas processing (i.e. 1 – 100 Pa) have been designed. Furthermore, because each plasma source is powered by its own microwave solid-state generator, multiple sources operating in ...

Microwave sheath-Voltage combination Plasma (MVP) is a high density plasma source and can be used as a suitable plasma processing device (e.g., ionized physical vapor deposition). In the present report, the spatio-temporal behavior of an argon MVP sustained along a direct-current biased Ti rod is investigated. Two plasma modes are observed, one is an "oxidized state" (OS) at the early time of the microwave plasma and the other is "ionized sputter state" (ISS) at the later times. Transition of the plasma from OS to ISS, results a prominent change in the visible color of the plasma, resulting from a significant increase in the plasma density, as measured by a Langmuir probe. In the OS, plasma is dominated by Ar ions and the density is in amplitude order of 1011 cm-3. In the ISS, metal ions from the Ti rod contribute significantly to the ion composition and higher density plasma (1012 cm-3) is produced. Nearly uniform high density plasma along the length of the Ti rod is produced at very low input microwave powers (around 30 W). Optical emission spectroscopy measurements confirm the presence of sputtered Ti ions and Ti neutrals in the ISS.

The interaction of electromagnetic waves with matter is an important area of research from past several decades. Surface plasmon or Surface Plasma Wave (SPW) is a guided electromagnetic mode that propagates along the interface between a conductor and a dielectric. One may use the attenuated total reflection (ATR) geometry in which a metal film is deposited over on a glass prism to excite a SPW . The laser is launched through the glass onto the glass-metal interface with a wave number, whose component along the surface matches the wave number of the SPW at the metal-free space boundary. Plasma processing of materials is one of the major tools in micro electronics industry. The unique property of plasma to modify the surface is exploited in plasma- aided manufacturing processes viz. ion implantation, sputtering, etching etc. Microwave created plasmas have advantages of no contamination & surface damages to substrates and less power requirements as compared to a rf power system. Due to small penetration depth of microwaves, creation of large volume homogenous plasma is difficult. In past few years, efforts have been made to create large-volume microwave created plasmas employing slow -wave structures where the surface plasma wave (SPW) couples with the slow wave of the conductor - dielectric structure to give a slow surface plasma wave. This slow surface plasma wave can sustain a large volume plasma for material processing.

Journal of Microwave Power and Electromagnetic Energy, 2017

To meet industrial requirements for large-scale processing with high-density and uniform plasma, mandatory for surface treatments to get uniform etching and high deposition rates, we have conceived a new electron cyclotron resonance (ECR) coaxial microwave plasma source which can sustain stable plasmas from 10 ¡2 Pa to a few Pa, whatever the processing gas, the minimum sustaining microwave power being only a few watt. Furthermore, because the plasma source is powered by its own microwave solidstate generator, multiple ECR plasma sources operating in different conditions of gas type and microwave power can be distributed together in the same reactor. In this design, the solid-state microwave generator produces a forward wave with variable frequency from 2400 to 2500 MHz; this feature is used in an automatic adjustment loop which enables to lower the reflected power created occasionally by changes in the operating conditions. The advantages of the new technology are reported in connection with the plasma scaling-up requirements to distribute uniformly the electric field over large areas. Optical emission spectroscopy and Langmuir probe have been used for the measurement of plasma density, uniformity and electron temperature in argon, oxygen and nitrogen. The results are reported in as a function of the gas type, number of sources and their distribution inside the plasma reactor. The new plasma source enables the production of plasma densities >10 11 cm ¡3 in all tested gases-Ar, O 2 , N 2 , airat d D 85 mm.

Physics of Plasmas, 1999

Significant improvements in the performance of microwave sources have been achieved in recent years by the introduction of the appropriate amount of plasma into tubes designed to accommodate plasma. Plasma filling has been credited with increasing the electron beam current, bandwidth, efficiency and reducing or eliminating the need for guiding magnetic fields in microwave sources. Neutralization of the e-beam space charge by a plasma enhances the current capability and beam propagation, and the generation of hybrid waves in plasma-filled sources increases the electric field on axis and improves the coupling and efficiency. Control of the plasma density in these microwave sources is often required to avoid instabilities and variations in the output power level and pulse length. Recent experimental and theoretical advances in this field, and the benefits and limitations of plasma filling of several different types of microwave sources, will be discussed.

Plasma Processes and Polymers, 2009

Atmospheric plasma processes become more and more popular in recent times. A new integrated atmospheric plasma source is presented which consists of a microwave resonator combined with a solid-state power oscillator. This allows for a very compact and efficient design of a microwave plasma source without external microwave power supply and matching units. Hydrophobic polymers have to be activated to ensure an effective painting or glueing. The performance of this new plasma source has been investigated with respect to surface activation depending on axial and radial distance to the substrate, process time, process gas, and flow velocity. Several polymeric materials have been compared. Polyethylene, polyamide, polystyrene, polypropylene, polycarbonate, and polytetrafluorineethylene show good activation results. This tool can be used especially for bulky goods and/or mass products, when a vacuum process is not possible or too expensive.

Electrical Engineering in Japan, 2005

A three-dimensional simulation code with the finite difference time domain (FDTD) method combined with the electron fluid model has been developed for the microwave excited surface wave plasma in the RDL-SWP device. This code permits the three-dimensional numerical analysis of the spatial distributions of electric field, power absorption, electron density, and electron temperature. At a low gas pressure (about 10 mTorr), the numerical results were compared with the experimental measurements that show the validity of this 3D simulation code. A simplified analysis assuming that the electron density is spatially uniform has also been studied and its applicability is evaluated by the comparison of the 3D simulation and the analytical solutions. The surface wave eigenmodes are determined by the electron density, and it is found that the structure of the device strongly influences the spatial distribution of the electric fields of surface waves in a low-density area (n e < 3.0 × 10 11 cm-3). A method to irradiate by microwave the whole surface area of the plasma is proposed. The method is found to be effective in obtaining a high uniformity distribution of electron density.

In the etching and deposition steps in the production of semiconductor chips, plasma processing is required for three main reasons. First, electrons are used to dissociate the input gas into atoms. Second, the etch rate is greatly enhanced by ion bombardment, which breaks the bonds in the first few monolayers of the surface, allowing the etchant atoms, usually Cl or F, to combine with substrate atoms to form volatile molecules. And third, most importantly, the electric field of the plasma sheath straightens the orbits of the bombarding ions so that the etching is anisotropic, allowing the creation of features approaching nanometer dimensions. The plasma sources used in the semiconductor industry were originally developed by trial and error, with little basic understanding of how they work. To achieve this understanding, many challenging physics problems had to be solved. This chapter is an introduction to the science of radiofrequency (RF) plasma sources, which are by far the most common. Sources operating at zero or other frequencies, such as 2.45 GHz microwaves, lie outside our scope. Most RF sources use the 13.56 MHz industrial standard frequency. Among these, there are three main types: (1) capacitively coupled plasmas or CCPs, also called reactive ion etchers (RIEs); (2) inductively coupled plasmas (ICPs), also called transformer coupled plasmas (TCPs); and (3) helicon wave sources, which are new and can be called HWSs.

Japanese Journal of Applied Physics, 2001

Surface wave plasmas (SWPs) of large area and high density are conventionally produced under a flat dielectric window for microwave irradiation through slot antennas. However, the SWPs often show discontinuous jumps in plasma density, and they tend to localize near the slots in the case of electronegative gas discharge. In this letter we report that such problems can be avoided by using a corrugated dielectric window with a periodicity of ∼ 10 mm pitch and 5 mm depth. Compared with the conventional flat plate, the corrugated plate gives a widely spreading uniform plasma with higher power efficiency and no density jump. Three-dimensional numerical simulations of microwave excitation under the experimental conditions clearly show a dramatic change in the wave propagation along the corrugated surface, supporting the experimental observations. Microwave discharge at a frequency of 2.45 GHz without a dc magnetic field enables generation of large-area high-density plasma, known as surface wave plasma (SWP), at low pressures. 1) The SWPs have already been applied to SiO 2 etching, metal etching, resist ashing and so forth. In the course of applying these materials processing techniques the need for improvement of SWP performance has been recognized. Firstly, an abrupt jump of the plasma density is often observed when the discharge power and/or pressure is changed, which influences the process window and stability. Such a density jump occurs due to resonant excitation of the discrete SW eigenmode at a certain plasma density, which depends on the wave dispersion and the slot antenna structure. 2-4) Secondly, the SWP is observed to localize around the slot antenna in oxygen high-pressure discharge for resist ashing 5) where negative ions make the ambipolar diffusion constant very small. These difficulties are due mainly to the use of slot antennas and to excitation of standing surface waves which are formed by propagation along the plasma-dielectric interface and reflection at the ends (chamber walls). The situation changes significantly if the dielectric surface is not flat but corrugated: partial reflection of the waves takes place sequentially in each groove during propagation along the corrugated surface. The effect of corrugated metal surfaces is well known in transmission lines and antennas for radio waves in free space. 6, 7) Recently, the authors applied this idea to plasma production, and showed in the previous paper 8) that corrugated metal surfaces enable production of high-density uniform plasma without using a dielectric plate. In this letter, we report the effect of a corrugated dielectric surface on plasma produces. Both the experiment and numerical simulation show that the corrugated surface produces uniformly distributed SWs on the dielectric plate, thus eliminating the plasma density jump and minimizing the plasma density nonuniformity. shows the 2.45 GHz microwave excitation system used in the present study: a rectangular waveguide, and a flat dielectric (quartz) plate 15 mm thick and 24 cm in diameter. We introduce a Cartesian coordinate: the z-axis is on the cylindrical vessel axis, the x-axis along the longitudinal waveguide, and the position z = 0 is on the flat dielectric plate. Surface wave plasmas are produced under the dielectric plate in an aluminum cylindrical plasma vessel 22 cm in diameter, using O 2 gas at typical flow rate of 50 sccm and pressure of 5 Pa. The electron density is measured using a plasma absorption probe of 6 mm diam. 9) Two-dimensional patterns of optical emission from the plasma are recorded by a conventional charge coupled device (CCD) camera. Further details are described in previous papers. As shown in , two slots are aligned in parallel at a distance of 96 mm. When the slot width is constant at 10 mm, strong plasma nonuniformity in the x direction was observed with oxygen discharge for the resist ashing process. In order to make the plasma uniform, the slot width is varied along the x axis in two steps, 15 mm and 11.5 mm, over the slot length of 170 mm. In the present study, we compare the discharge performance using the corrugated dielectric surface with that using the conventional flat dielectric surface. As shown in , the corrugated surface with a depth of 5 mm, a width of 5 mm and a pitch ρ = 7.5-30 mm is formed, simply by attaching many long bars (5 mm × 5 mm cross section) along the x axis to the flat quartz plate 15 mm thick and 24 cm in diameter.