Criteria of radio-frequency ring-shaped hollow cathode discharge using H2 and Ar gases for plasma processing

Abstract

In order to achieve high-density capacitively coupled plasma, a radio-frequency (RF) ring-shaped hollow cathode discharge has been developed as a candidate for processing plasma sources. The plasma density in the hollow cathode discharge reaches a high magnitude of 1010–1011 cm−3. The RF ring-shaped hollow cathode discharge depends on the pressure and mass of the working gas. Criteria required for producing a RF ring-shaped hollow cathode discharge have been investigated for various gas pressures using H2 and Ar gases for high-density plasma production. The results reveal that the criteria for the occurrence of the hollow cathode effect are that the trench width should be approximately equal to the sum of the electron-neutral mean free paths and twice the sheath thickness of the RF powered electrode.

Capacitive radio frequency discharges with a single ring-shaped narrow trench of various depths to enhance the plasma density and lateral uniformity

“…The results have revealed that the trench width must be approximately equal to the sum of the electron-neutral mean free path and twice the sheath thickness of the powered electrode in order to realize the desired effect of the trench on the plasma density. 43 This criterion is conceptually similar to those for the classical hollow cathode effect (HCE) based on similarity parameters. In previous works, however, the influence of the trench depth on plasma parameters was not understood.…”

“…The electron temperature and density as well as the plasma potential are obtained radially resolved from measurements of the current-voltage characteristics of a tiny cylindrical tungsten probe according to Langmuir probe theory 7,52,53 at various trench depths. The probe system is compensated with an L-C parallel circuit 12,26,[30][31][32][33][42][43][44] (choke) in order to avoid any parasitic effects of rf plasma potential oscillations on the probe current-voltage characteristics. At the gas pressure of 53.2 Pa, the electron-neutral mean free path is smaller than the dimensions of the probe and the electron saturation current detected by the probe must be revised.…”

“…Grooved electrodes have also been found to have an active influence on the collection of dust particles as well as their trapping behavior and movement in such plasmas. 52 In our previous works, 32,[42][43][44] ring-shaped hollow electrodes with various trench shapes were developed to produce a high-density capacitive plasma and densities of 10 11 cm À3 were realized in argon gas. The results have revealed that the trench width must be approximately equal to the sum of the electron-neutral mean free path and twice the sheath thickness of the powered electrode in order to realize the desired effect of the trench on the plasma density.…”

“…In order to enhance the plasma density and improve its lateral uniformity at the conventional frequency of 13.56 MHz, the use of structured electrodes has been proposed based on different trench shapes. 12,17,[39][40][41][42][43][44][45][46][47][48][49][50] A grooved target has been used in dc magnetrons to realize high discharge currents at very low pressures of a) Email: ohtsuy@cc.saga-u.ac.jp 1070-664X/2016/23(3)/033510/7/$30.00…”

The use of hollow cathodes in deposition processes: A critical review

“…Since in the hollow cathode, electrons are not as easily lost to ground as in the case of the planar magnetron, it is not completely clear how the magnetic field increases ionization. However, the use of magnetic fields has been reported to increase the plasma density and, correspondingly, the plasma current [195][196][197][198][199][200][201][202][203][204].…”