Recent development of large-diameter (>30 cm) high-density (>10 11 cm −3 ) microwave plasma production at low pressures (<20 mTorr) without an external DC magnetic field is reviewed in view of application to the next generation ULSI devices and flat panel displays. Understanding the discharge physics-excitation, propagation and absorption of the surface wave in a flat plasma geometry under overdense conditions (ω p ω)-is indispensable for controlling the plasma. Experimental evidence of discrete surface-wave modes is clearly found in optical emission and microwave field measurements. The analysis of the full-wave electromagnetic dispersion successfully identified the observed eigenmodes. Stability analysis of the wave-plasma interaction resulted in a stability criterion predicting hysteresis loops in the power-density dependence, which were found in the experiment. A possibility of collisionless absorption of surface waves, i.e. mode conversion to electron plasma waves at the resonant layer, is discussed with the recent experimental results taken into account. From the plasma technology point of view, examples of surface-wave plasma tools (some of them commercially available) are introduced and the significance of the antenna structure is emphasized. Finally, the advantages of the surface-wave plasma source in comparison with other high-density sources are summarized.

In this paper, we describe a novel and simple technique for measuring electron density using a plasma absorption probe (PAP). PAP enables us to measure the local absolute electron density even when the probe surface is soiled with processing plasmas. The technique relies on the resonant absorption of surface waves (SWs) excited in a “cavity” at the probe head. The PAP consists of a small antenna connected with a coaxial cable and is enclosed in a tube (dielectric constant ε) inserted in a plasma (electron plasma frequency ωp). A network analyzer feeds a rf signal to the antenna and displays the frequency dependence of the power absorption. A series of resonant absorptions are observed at frequencies slightly above the SW resonance frequency, ωSW = ωp/(1+ε)1/2, which allows us to determine the electron density. The measured electron densities are in good agreement with the data obtained by the plasma oscillation method.

A large-diameter (50 cm) high-density (>10 11 cm −3 ) plasma is produced in a few mTorr argon by inductive RF discharge using a conventional external antenna or a plasma-immersed internal antenna. A power transfer efficiency, i.e., the ratio of net power deposited into plasma to total power into the matching circuits, is measured as a function of the electron density based on a test antenna method. The measured density dependence of the power efficiency is well described by an equivalent circuit where both inductive and capacitive couplings are included with stochastic power deposition process taken into account. The internal antenna, for the conditions studied, has higher power efficiency than the external antenna and enables a stable discharge at low pressures without density jump. The density jump observed in the external antenna discharge is attributed to the mode transition between a capacitive discharge and an inductive discharge. A mechanism of the density jump is successfully explained in terms of the density dependence of the power transfer efficiency.

The resonance frequencies of electromagnetic surface modes propagating along a plane dielectric-plasma interface are computed, taking into account the finite area of the latter. The analysis results in simple analytical formulae for estimating the plasma density at which a given mode can be expected to occur for given geometry and wave frequency. Comparison with measurements in large-area circular plasmas is made.

Anomalous side wall etching, called 'notching' in gate poly-Si etching, is suppressed in a pulsed-power chlorine inductively coupled plasma (ICP). To understand the mechanism, comprehensive time-resolved measurements were performed on such key parameters as chlorine negative ion (Cl − ) density, electron density, electron temperature T e and plasma potential. Comparison of these data with argon afterglows reveals a rapid electron cooling and a remarkable electron density drop which are caused by electron dissociative attachment forming abundant Cl − negative ions. The measurements of RF bias and plasma potential suggest a new mechanism of notch-free etching. Namely, the substrate potential V s in the positive RF phase instantaneously exceeds the plasma potential V p in the afterglow by a considerable amount, e(V s − V p ) κT e . Then electrons are accelerated through a sheath and neutralize positive charges on the gate oxide layer. Finally, the poly-Si etching process utilizing abundant Cl − is examined, focusing on the bias-frequency-dependence.

This article reports a new type of sensitive plasma absorption probe (PAP), which is characterized with a thin wire antenna directly exposed to plasma. In the sensitive PAP, the power reflection coefficient resonantly decreases at a certain frequency due to absorption of a surface wave, which is excited along a sheath formed around the antenna. The electron density is derived from the measured absorption frequency in comparison to a wave dispersion relation: the dispersion is calculated under assumptions that the sheath width is twice the Debye length and that wavelength is twice the antenna length. This sensitive PAP also enables measurements of very low electron densities (∼108 cm−3) and very high pressures (∼10 Torr), in comparison to a conventional standard PAP. In addition, both electron temperature and electron density can be measured using a pair of sensitive PAPs of different antenna radii.

A large-planar (22 cm diam.) high-density ( ∼2×1012 cm-3) plasma is produced in argon gas at 140 Pa by 2.45 GHz–1 kW discharges, using a microwave launcher of small slot antennas. The two-dimensional distributions of optical emission intensities as well as microwave field intensities are measured near the plasma surface irradiated with microwaves. Both the optical emission and the microwave field clearly show stationary patterns of azimuthal mode m=3 and radial mode n=3 at higher pressures (140 Pa), while a mode change to m=6 and n=2 is observed at lower pressures (44 Pa). These patterns are attributed to the excitation and absorption of standing surface waves near the cutoff layer.

A compact new type of microwave resonator probe called curling probe is proposed for electron density measurements in reactive plasmas, where a spiral slot is excited by a monopole antenna. The resonance characteristic of the curling probe is simulated by the finite-difference time-domain (FDTD) method. The frequency dependence of power reflection coefficient and the electromagnetic field structures revealed two types of resonance at the same density: the high-frequency volume wave resonance along a spiral slot and the low-frequency surface wave resonance in an aperture of the probe. The analytical formulae of resonance frequencies as a function of electron density are derived.