Навчально-науковий інститут "Фізико-технічний факультет"

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Applying RF current harmonics for end-point detection during etching multi-layered substrates and cleaning discharge chambers with NF3 discharge
(www.elsevier.com/locate/vacuum, 2007-11) Lisovskiy, V.; Booth, Jean-Paul; Landry, K.; Douai, D.; Cassagne, V.; Yegorenkov, V.
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.
The Effect of Discharge Chamber Geometry on the Characteristics of Low-Pressure RF Capacitive Discharges
(IEEE TRANSACTIONS ON PLASMA SCIENCE, 2007-04) Lisovskiy, V.; Booth, Jean-Paul; Landry, K.; Douai, D.; Cassagne, V.; Yegorenkov, V.
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.
The effect of discharge chamber geometry on the ignition of low-pressure rf capacitive discharges
(PHYSICS OF PLASMAS, 2005-09) Lisovskiy, V.; Martins, S.; Landry, K.; Douai, D.; Booth, Jean-Paul; Cassagne, V.; Yegorenkov, V.
This paper reports measured and calculated breakdown curves in several gases of rf capacitive discharges excited at 13.56 MHz in chambers of three different geometries: parallel plates surrounded by a dielectric cylinder (“symmetric parallel plate”), parallel plates surrounded by a grounded metallic cylinder (“asymmetric parallel plate”), and parallel plates inside a much larger grounded metallic chamber (“large chamber”). The breakdown curves for the symmetric chamber have a multivalued section at low pressure. For the asymmetric chamber the breakdown curves are shifted to lower pressures and rf voltages, but the multivalued feature is still present. At higher pressures the breakdown voltages are much lower than for the symmetric geometry. For the large chamber geometry the multivalued behavior is not observed. The breakdown curves were also calculated using a numerical model based on fluid equations, giving results that are in satisfactory agreement with the measurements.
Electron drift velocity in argon, nitrogen, hydrogen, oxygen and ammonia in strong electric fields determined from rf breakdown curves
(JOURNAL OF PHYSICS D: APPLIED PHYSICS, 2006-02) Lisovskiy, V.; Booth, Jean-Paul; Landry, K.; Douai, D.; Cassagne, V.; Yegorenkov, V.
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.
Electron drift velocity in N2O in strong electric fields determined from rf breakdown curves
(JOURNAL OF PHYSICS D: APPLIED PHYSICS, 2006-04) Lisovskiy, V.; Booth, Jean-Paul; Landry, K.; Douai, D.; Cassagne, V.; Yegorenkov, V.
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.
Electron drift velocity in NH3 in strong electric fields determined from rf breakdown curves
(JOURNAL OF PHYSICS D: APPLIED PHYSICS, 2005-03) Lisovskiy, Valeriy; Martins, Sofia; Landry, Karine; Douai, David; Booth, Jean-Paul; Cassagne, Valerick
We report measurements of the breakdown curves of a radio-frequency capacitive discharge in low pressure ammonia. The electron drift velocity was determined from the location of turning points in the breakdown curves in the range of E/p = 42–713 Vcm−1 Torr−1. We compare our results to values calculated from the published cross-sections in the range E/p = 1–5000 Vcm−1 Torr−1 and find good agreement.
Electron drift velocity in SF6 in strong electric fields determined from rf breakdown curves
(JOURNAL OF PHYSICS D: APPLIED PHYSICS, 2010-09) Lisovskiy, V.; Yegorenkov, V.; Booth, Jean-Paul; Landry, K.; Douai, D.; Cassagne, V.
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.
Electron drift velocity in silane in strong electric fields determined from rf breakdown curves
(JOURNAL OF PHYSICS D: APPLIED PHYSICS, 2007-05) Lisovskiy, V.; Booth, Jean-Paul; Landry, K.; Douai, D.; Cassagne, V.; Yegorenkov, V.
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.
Extinction of RF capacitive low-pressure discharges
(EUROPHYSICS LETTERS, 2005-08) Lisovskiy, Valeriy; Booth, Jean-Paul; Martins, Sofia; Landry, Karine; Douai, David; Cassagne, Valerick
Breakdown and extinction curves have been measured for RF capacitive low-pressure discharges in nitrogen and hydrogen at a frequency of 13.56 MHz and discharge gaps between 6 and 25 mm. In particular, the low-pressure, high-voltage region of the extinction curves is reported for the first time. The shape of the extinction curves was found to be similar to that of the breakdown curves. At sufficiently large gaps (L > 10 mm) the RF extinction voltage was found to be multi-valued in the low-pressure region, as is observed for the breakdown voltage. In this region, extinction can occur when the voltage is increased because the width of the two sheaths occupies the whole discharge space.
Low-pressure gas breakdown in dual-frequency RF electric fields in nitrogen
(Europhysics Letters www.epl journal.org, 2007-10) Lisovskiy, V.; Booth, Jean-Paul; Landry, K.; Douai, D.; Cassagne, V.; Yegorenkov, V.
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.
Modes and the alpha-gamma transition in rf capacitive discharges in N2O at different rf frequencies
(PHYSICS OF PLASMAS, 2006-10) Lisovskiy, V.; Booth, Jean-Paul; Landry, K.; Douai, D.; Cassagne, V.; Yegorenkov, V.
This paper reports current-voltage characteristics and pressure-voltage transition curves from the weak-current a-mode to the strong-current g-mode for rf capacitive discharges in N2O at frequencies of 2 MHz, 13.56 MHz, and 27.12 MHz. At 2 MHz the rf discharge is mostly resistive whereas at 13.56 MHz and 27.12 MHz it is mostly capacitive. The weak-current a-mode was found to exist only above a certain minimum gas pressure for all frequencies studied [N. Yatsenko Sov. Phys. Tech. Phys. 26, 678 (19810] previously proposed that the a−g transition corresponds to breakdown of the sheaths. However, we show that this is the case only for sufficiently high gas pressures. At lower pressure there is a smooth transition from the weak-current a-mode to a strong-current g-mode, in which the sheaths produce fast electrons but the sheath has not undergone breakdown.
Modes of low-pressure dual-frequency (27/2 MHz) discharges in hydrogen
(PLASMA SOURCES SCIENCE AND TECHNOLOGY, 2008-03) Lisovskiy, V.; Booth, Jean-Paul; Landry, K.; Douai, D.; Cassagne, V.; Yegorenkov, V.
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.
Modes of rf capacitive discharge in low-pressure sulfur hexafluoride
(JOURNAL OF PHYSICS D: APPLIED PHYSICS, 2007-11) Lisovskiy, V.; Booth, Jean-Paul; Jolly, J.; Martins, S.; Landry, K.; Douai, D.; Cassagne, V.; Yegorenkov, V.
This paper presents the results of an experimental study of rf capacitive discharge in low-pressure SF6. The rf discharge in SF6 is shown to exist not only in weak-current (α-) and strong-current (γ -) modes but also in a dissociative δ-mode. This δ-mode is characterized by a high degree of SF6 dissociation, high plasma density, electron temperature and active discharge current, and it is intermediate between α- and γ -modes. The δ-mode appears due to a sharp increase in the dissociation rate of SF6 molecules via electron impact starting after a certain threshold value of rf voltage. At the same time the threshold ionization energy of SFx (x = 1–5) radicals formed is below the ionization potential of SF6 molecules. The double layer existing in the anode phase of the near-electrode sheath is shown to play an important role in sustaining the α- mode as well as the δ-mode but it is not a cause of the rf discharge transition from α- to δ-mode.
Rf discharge dissociative mode in NF3 and SiH4
(JOURNAL OF PHYSICS D: APPLIED PHYSICS, 2007-10) Lisovskiy, V.; Booth, Jean-Paul; Landry, K.; Douai, D.; Cassagne, V.; Yegorenkov, V.
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.
Similarity law for rf breakdown
(www.epl journal.org, 2008-04) Lisovskiy, V.; Booth, Jean-Paul; Landry, K.; Douai, D.; Cassagne, V.; Yegorenkov, V.
This paper demonstrates that the similarity law for the rf gas breakdown has the form Urf =F(p ·L, L/R, f ·L)(where Urf is the rf breakdown voltage, p is the gas pressure, L and R are the length and diameter of the discharge tube, respectively, f is the frequency of the rf electric field). It means that two rf breakdown curves registered for narrow inter-electrode gaps or in geometrically similar tubes and depicted in the Urf (p ·L) graph will coincide only when the condition f ·L = const is met. This similarity law follows from the rf gas breakdown equation and it is well supported by the results of measurements.
A technique for evaluating the RF voltage across the electrodes of a capacitively-coupled plasma reactor
(http://www.edpsciences.org/epjap, 2006-10) Lisovskiy, V.; Booth, Jean-Paul; Landry, K.; Douai, D.; Cassagne, V.; Yegorenkov, V.
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).