Electron drift velocity in N2O in strong electric fields determined from rf breakdown curves

We report measurements of the breakdown curves of an rf capacitive discharge in low pressure nitrous oxide. The electron drift velocity was determined from the locations of the turning point and of the minimum in the breakdown curves in the range E/p = 87–840 Vcm−1 Torr−1. We compare our results with values calculated from the published cross-sections in the range E/p = 1–5000 Vcm−1 Torr−1 and find good agreement

Low-pressure gas breakdown in dual-frequency RF electric fields in nitrogen

This paper reports the recorded breakdown curves for dual-frequency (27.12MHz/2MHz and 13.56MHz/50Hz) discharges in nitrogen. Applying the LF voltage shifts the RF breakdown curve to the region of higher voltages and gas pressures, which is associated with the increased loss of charged particles due to the drift in the LF field. At higher LF voltage amplitudes the LF field contributes to gas ionization, the breakdown voltage for the RF discharge decreases and approaches zero when a self-sustained discharge in the LF field ignites. Applying the RF voltage leads to the decrease in the breakdown LF voltage, possibly due to the decrease of electron losses because of the oscillations in the RF field

The Effect of Discharge Chamber Geometry on the Characteristics of Low-Pressure RF Capacitive Discharges

We report the measured extinction curves and current–voltage characteristics (CVCs) in several gases of RF capacitive discharges excited at 13.56 MHz in chambers of three different geometries: 1) parallel plates surrounded by a dielectric cylinder (“symmetric parallel plate”); 2) parallel plates surrounded by a metallic cylinder (“asymmetric confined”); and 3) parallel plates inside a much larger metallic chamber (“asymmetric unconfined”), similar to the gaseous electronics conference reference cell. The extinction curves and the CVCs show differences between the symmetric, asymmetric confined, and asymmetric unconfined chamber configurations. In particular, the discharges exist over a much broader range of RF voltages and gas pressures for the asymmetric unconfined chamber. For symmetric and asymmetric confined discharges, the extinction curves are close to each other in the regions near the minima and at lower pressure, but at higher pressure, the extinction curve of the asymmetric confined discharge runs at a lower voltage than the one for the discharge in a symmetric chamber. In the particular cases of an “asymmetric unconfined chamber” discharge or “asymmetric confined” one, the RF discharge experiences the transition from a “weak-current” mode to a “strong-current” one at lower RF voltages than is the case for a “symmetric parallel-plate” discharge

Electron drift velocity in SF6 in strong electric fields determined from rf breakdown curves

This paper presents measurements of the electron drift velocity Vdr in SF6 gas for high reduced electric fields (E/N = 330–5655 Td (1 Td = 10−17 Vcm2)). The drift velocities were obtained using the method of Lisovskiy and Yegorenkov (1998 J. Phys. D: Appl. Phys. 31 3349) based on the determination of the pressure and voltage of the turning points of rf capacitive discharge breakdown curves for a range of electrode spacings. The Vdr values thus obtained were in good agreement with those calculated from the cross-sections of Phelps and Van Brunt (1988 J. Appl. Phys. 64 4269) using the BOLSIG code. The validity of the Lisovskiy–Yegorenkov method is discussed and we show that it is applicable over the entire E/N range where rf discharge ignition at breakdown occurs for rf frequencies of 13.56MHz or above

Rf discharge dissociative mode in NF3 and SiH4

This paper shows that the rf capacitive discharge in NF3 and SiH4 can burn in three possible modes: weak-current α-mode, strong-current γ -mode and dissociative δ -mode. This new dissociative δ-mode is characterized by a high dissociation degree of gas molecules (actually up to 100% in NF3 and up to 70% in SiH4), higher resistivity and a large discharge current. On increasing rf voltage first we may observe a weak-current α-mode (at low NF3 pressure the α-mode is absent). At rather high rf voltage when a sufficiently large number of high energy electrons appear in the discharge, an intense dissociation of gas molecules via electron impact begins, and the discharge experiences a transition to the dissociative δ-mode. The dissociation products of NF3 and SiH4 molecules possess lower ionization potentials, and they form an easily ionized admixture to the main gas. At higher rf voltages when near-electrode sheaths are broken down, the discharge experiences a transition to the strong-current γ -mode

Applying RF current harmonics for end-point detection during etching multi-layered substrates and cleaning discharge chambers with NF3 discharge

The present paper reports the results of studying the characteristics of the etching process of multi-layered materials (Si3N4/SiO2/Si and SiO2/Si) and of cleaning technological chambers covered with silicon nitride films (Si3N4) in a NF3 RF capacitive discharge. The process of chamber cleaning was monitored with a mass spectrometer. The gas pressure, RF voltage amplitude, current–voltage phase shift, ohmic current as well as the second harmonic of the RF current were also recorded. The opportunity of using these parameters for end-point detection of etching and plasma cleaning is discussed. It is found that the second harmonic of the RF current may be successfully used for end-point detection of multi-layered materials etching and to monitor the cleaning process of technological chambers. The cleaning of chambers of complicated design may possess a double-stage pattern

Electron drift velocity in silane in strong electric fields determined from rf breakdown curves

We report measurements of the breakdown curves of an rf capacitive discharge in low pressure silane. The electron drift velocity was determined from the locations of the turning point and of the minimum in the breakdown curves in the range E/p = 145–1292 Vcm−1 Torr−1. We compare our results to values calculated from the published cross-sections in the range E/p = 1–2000 Vcm−1 Torr−1 and data calculated in other papers and find good agreement

Modes of low-pressure dual-frequency (27/2 MHz) discharges in hydrogen

This paper studies the modes of dual-frequency (high-frequency (HF)/low-frequency (LF)) low-pressure discharges. The dual-frequency discharges are shown to burn in one of three possible modes. At small LF voltages the first mode is observed, i.e. the HF discharge perturbed by the LF voltage. The second mode, i.e. the combined discharge, exists in the presence of intense ionization in the sheaths, when the LF voltage exceeds some critical value. The third mode (the LF discharge perturbed by an HF field) is observed when a small HF voltage is applied to the burning LF discharge. The range of parameters within which the first mode of the combined discharge may be extinguished by the LF voltage increase is shown to be limited by the HF discharge extinction curve from the low-pressure side as well as the lowest HF voltage for the transition of the discharge from the first mode to the second one

A technique for evaluating the RF voltage across the electrodes of a capacitively-coupled plasma reactor

We propose a new technique for evaluating the RF voltage across the electrodes of low-pressure capacitively-coupled plasma reactors when direct measurements are not possible. It is based on determining the coordinates of the turning point in the RF breakdown curve and using known values of the electron drift velocity for the gas. The results are in good agreement with those obtained by direct measurements at the driven electrode. Furthermore it allows RF breakdown curves to be determined for different frequencies, giving results that are physically reasonable (coincidence of right-hand branches) and in agreement with other published results. The technique for determining RF voltage we proposed is valid when there is no discharge plasma between electrodes (e.g., before gas breakdown), as well as for negligibly small discharge currents (before extinction of the weak-current discharge mode)

Electron drift velocity in argon, nitrogen, hydrogen, oxygen and ammonia in strong electric fields determined from rf breakdown curves

We report measurements of the breakdown curves for low-pressure rf capacitive discharges in nitrogen, hydrogen, argon, oxygen and ammonia. The electron drift velocity in these gases was deduced, as a function of reduced electric field, from the low-pressure turning points of the breakdown curves. The equation for rf breakdown proposed by Kihara (1952 Rev. Mod. Phys. 24 52) allows the position of both the turning point and the breakdown curve minimum to be calculated from the transport properties of each gas. Therefore we propose a new technique to determine the electron drift velocity from the position of the rf breakdown curve minima. We have determined the drift velocity in the range E/p = 52–1324 Vcm−1 Torr−1 for nitrogen, E/p = 33–720 Vcm−1 Torr−1 for argon, E/p = 32–713 Vcm−1 Torr−1 for ammonia, E/p = 32–550 Vcm−1 Torr−1 for hydrogen and E/p = 69–1673 Vcm−1 Torr−1 for oxygen