Dual Frequency Capacitive Plasma Research Articles

Dual frequency capacitive plasmas in Fe and Ni sputter applications: correlation of discharge properties on thin film properties

Dual frequency capacitively coupled plasmas (CCPs) are widely used in (large area) etching and plasma enhanced chemical vapor deposition processes. However, applications in physical vapor deposition (PVD) are still sparse due to the well-established dc magnetron cathode discharges. Nevertheless, there exist critical applications such as ferromagnetic or ceramic thin film deposition which are difficult to handle even for dc magnetron systems. For these materials systems dual frequency CCPs pose a good alternative, because for insulators charging can be avoided and for ferromagnetic materials the target thickness becomes independent of the magnetron configuration at comparable deposition rates.In this work we investigate two separate subjects. First, in dual frequency capacitive discharges a complex coupling of the applied excitation frequencies can be observed, which from a plasma parameter point of view limits the separability of ion flux (usually controlled by frequencies >60 MHz) and ion bombarding energy (usually controlled by frequency <15 MHz) onto the sputter target. By performing deposition experiments it was found that by following simple tuning guidelines a very good degree of separability is achievable. Additionally, the deposition homogeneity is not affected.Second, we correlate the growth conditions with crystalline and magnetic properties as well as the degree of O content for Fe and Ni films. Therefore, we applied different signals as a substrate bias to influence thin film growth. It was found that the crystalline and magnetic properties can be influenced for both Fe and Ni films but is more pronounced for Ni.

Direct measurement of spatial electron density oscillations in a dual frequency capacitive plasma

The spatio-temporal electron density oscillation in a narrow gap dual frequency (27.12 and 1.937 MHz) capacitive discharge has been measured for the first time by using a floating microwave hairpin resonance probe. By measuring the probe’s resonance frequency in a space and phase-resolved manner, we observe significant oscillation in electron density at both drive frequencies throughout the region between the parallel plate electrodes. The observed phenomenon is attributed to the influence of presheath electric fields of the opposing electrodes in alternate fashion.

Fluorine negative ion density measurement in a dual frequency capacitive plasma etch reactor by cavity ring-down spectroscopy

F − negative ions were detected by direct observation of the weak photodetachment absorption continuum below 364.5nm by cavity ring-down spectroscopy. The negative ions were generated in a modified industrial dielectric plasma etch reactor, with 2+27MHz dual frequency capacitive excitation in Ar∕CF4∕O2 and Ar∕C4F8∕O2 gas mixtures. The F− signal was superimposed on an unidentified absorption continuum, which was diminished by O2 addition. The F− densities were in the range of (0.5–3)×1011cm−3, and were not significantly different for single (27MHz) or dual (2+27MHz) frequency excitation, not confirming recent modeling predictions.

Ion energy distribution control in single and dual frequency capacitive plasma sources

Particle-in-cell/Monte Carlo simulations are used to study the possibility of ion energy distribution function (IEDF) control on the powered electrode in asymmetric single and double frequency capacitive discharges in argon. The possibility of IEDF control is demonstrated. It is shown that the IEDF shape and spread on the cathode can be controlled by the driven voltage in a single frequency discharge and by the low frequency voltage in a dual frequency capacitive discharge. It is shown that the IEDF shape on the powered electrode can be controlled by the driven frequency in single frequency capacitively coupled plasmas. It is shown that the density of plasma decreases, and the sheath width, the plasma potential and the self-bias voltage increase, with growth of the low frequency voltage in the dual frequency capacitive discharge.

A simple model of an asymmetric capacitive plasma with dual frequency

Recently, simulations have been carried out to investigate a dual frequency capacitive plasma in a system consisting of a pair of coaxial cylindrical electrodes. Considering the same asymmetric configuration, it is shown here that a sharp plasma–boundary model may be used to capture the essential dynamical features of the simulations.