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.

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.

A planar high-density (∼10 12 cm −3 ) plasma, 22 cm in diameter and 9 cm in length, is produced by a 2.45 GHz microwave radiation of 500 W through small slot antennas in argon at 20-350 Pa without a magnetic field. Several types of azimuthal and radial standing wave mode pattern are observed in the optical emission from the plasma depending on the discharge conditions. The microwave field in the plasma measured by a movable antenna decreases exponentially in the axial direction from the quartz wall adjacent to the slot antennas, thus suggesting the propagation of surface waves in the r, θ directions. The measured azimuthal microwave field distributions and the optical emission pattern clearly show a mode transition of the standing surface wave from a TM 33 mode to a TM 62 mode when the pressure is decreased from 140 to 44 Pa at the constant power of 400 W. Here TM mn denotes the transverse magnetic mode of azimuthal mode number m and radial mode number n. A wave dispersion analysis based on a one-interface uniform-density model predicts these modes in a range of electron densities corresponding to those measured by a Langmuir probe in the experiment.

Two different modes of electron heating are found in microwave discharges: the bulk heating mode characterized with low electron density n e and high electron temperature T e (∼10 eV), and the surface heating mode with high n e and low T e (∼3 eV). The correlation between the heating mode and the electron energy distribution function (EEDF) is qualitatively interpreted in terms of non-local kinetic theory, taking account of the ambipolar potential well. A biased optical probe diagnostics of a surface wave plasma (SWP) reveals that the surface heating mode gives a bi-Maxwellian type EEDF, that is, a sum of two Maxwellian distributions of bulk temperature T b and tail temperature T t > T b . On the other hand, the EEDF of inductively coupled plasma (ICP) is close to a single-Maxwellian distribution with electron temperature higher than the bulk temperature T b of the SWP. Such differences in the EEDFs make the composition of the reactive species of the two plasmas different; namely, ion and radical measurements at the same electron density show that the ICP contains more F radicals and less CF 3 and CF 2 radicals in comparison with the SWP. In addition, a simplified model based on the bi-Maxwellian EEDF shows how the EEDF determines the ion and radical compositions, supporting the major experimental results. These observations and calculations suggest that plasma chemistry is controllable by tailoring the EEDF with proper adjustment of bulk heating and/or surface heating of electrons.