Temporal evolution of plasma potential in a large-area pulsed dual-frequency inductively coupled discharge

Lee

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

2014

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Using a Langmuir probe, time resolved measurements of plasma parameters were carried out in a discharge produced by a pulsed dual frequency inductively coupled plasma source. The discharge was sustained in an argon gas environment at a pressure of 10 mTorr. The low frequency (P2 MHz) was pulsed at 1 kHz and a duty ratio of 50%, while high frequency (P13.56 MHz) was maintained in the CW mode. All measurements were carried out at the center of the discharge and 20 mm above the substrate. The results show that, at a particular condition (P2 MHz = 200 W and P13.56 MHz = 600 W), plasma density increases with time and stabilizes at up to ∼200 μs after the initiation of P2 MHz pulse at a plasma density of (2 × 1017 m−3) for the remaining duration of pulse “on.” This stabilization time for plasma density increases with increasing P2 MHz and becomes ∼300 μs when P2 MHz is 600 W; however, the growth rate of plasma density is almost independent of P2 MHz. Interestingly, the plasma density sharply increases as the pulse is switched off and reaches a peak value in ∼10 μs, then decreases for the remaining pulse “off-time.” This phenomenon is thought to be due to the sheath modulation during the transition from “pulse on” to “pulse off” and partly due to RF noise during the transition period. The magnitude of peak plasma density in off time increases with increasing P2 MHz. The plasma potential and electron temperature decrease as the pulse develops and shows similar behavior to that of the plasma density when the pulse is switched off.

“…A similar increasing trend was also observed in the plasma potential during the pulse off-time for the time-resolved plasma potential measurement using an emissive probe. 30 …”

Section: Resultsmentioning

confidence: 99%

Plasma dynamics in a discharge produced by a pulsed dual frequency inductively coupled plasma source

Lee

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

2014

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“…It has been found that the floating potential measured by emissive probe is in good agreement with Langmuir probe measurements as explained elsewhere. 22 095101…”

Section: Experimental Arrangementmentioning

confidence: 99%

Transient plasma potential in pulsed dual frequency inductively coupled plasmas and effect of substrate biasing

2016

AIP Advances

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An electron emitting probe in saturated floating potential mode has been used to investigate the temporal evolution of plasma potential and the effect of substrate RF biasing on it for pulsed dual frequency (2 MHz/13.56 MHz) inductively coupled plasma (ICP) source. The low frequency power (P2MHz) has been pulsed at 1 KHz and a duty ratio of 50%, while high frequency power (P13.56MHz) has been used in continuous mode. The substrate has been biased with a separate bias power at (P12.56MHz) Argon has been used as a discharge gas. During the ICP power pulsing, three distinct regions in a typical plasma potential profile, have been identified as ‘initial overshoot’, pulse ‘on-phase’ and pulse ‘off-phase’. It has been found out that the RF biasing of the substrate significantly modulates the temporal evolution of the plasma potential. During the initial overshoot, plasma potential decreases with increasing RF biasing of the substrate, however it increases with increasing substrate biasing for pulse ‘on-phase’ and ‘off-phase’. An interesting structure in plasma potential profile has also been observed when the substrate bias is applied and its evolution depends upon the magnitude of bias power. The reason of the evolution of this structure may be the ambipolar diffusion of electron and its dependence on bias power.

“…56 MHz pulsing have been demonstrated. [31][32][33] In Argon discharge, pulsing 2 MHz and different combination of 2/ 13.56 MHz power levels has shown significant modulation in the plasma potential during the pulse-off phase. 31 From an estimate of electron temperature from plasma potential and floating potential measured by floating emmisive probe, it was found that the effect of increasing 2 MHz power level is to lower the electron temperature; however, increasing 13.56 MHz power increases the electron temperature.…”

Section: Introductionmentioning

confidence: 99%

“…[31][32][33] In Argon discharge, pulsing 2 MHz and different combination of 2/ 13.56 MHz power levels has shown significant modulation in the plasma potential during the pulse-off phase. 31 From an estimate of electron temperature from plasma potential and floating potential measured by floating emmisive probe, it was found that the effect of increasing 2 MHz power level is to lower the electron temperature; however, increasing 13.56 MHz power increases the electron temperature. 31 Langmuir probe study under the same set-up and similar discharge conditions has predicted a slow rise in the electron density during the 2 MHz pulse-on phase in order to reach to a quasisteady state value.…”

Section: Introductionmentioning

confidence: 99%

Electron density modulation in a pulsed dual-frequency (2/13.56 MHz) dual-antenna inductively coupled plasma discharge

Sirse

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

et al. 2016

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The electron density, n e , modulation is measured experimentally using a resonance hairpin probe in a pulsed, dual-frequency (2/13.56 MHz), dual-antenna, inductively coupled plasma discharge produced in argon-C 4 F 8 (90-10) gas mixtures. The 2 MHz power is pulsed at a frequency of 1 kHz, whereas 13.56 MHz power is applied in continuous wave mode. The discharge is operated at a range of conditions covering 3-50 mTorr, 100-600 W 13.56 MHz power level, 300-600 W 2 MHz peak power level, and duty ratio of 10%-90%. The experimental results reveal that the quasisteady state n e is greatly affected by the 2 MHz power levels and slightly affected by 13.56 MHz power levels. It is observed that the electron density increases by a factor of 2-2.5 on increasing 2 MHz power level from 300 to 600 W, whereas n e increases by only $20% for 13.56 MHz power levels of 100-600 W. The rise time and decay time constant of n e monotonically decrease with an increase in either 2 or 13.56 MHz power level. This effect is stronger at low values of 2 MHz power level. For all the operating conditions, it is observed that the n e overshoots at the beginning of the onphase before relaxing to a quasisteady state value. The relative overshoot density (in percent) depends on 2 and 13.56 MHz power levels. On increasing gas pressure, the n e at first increases, reaching to a maximum value, and then decreases with a further increase in gas pressure. The decay time constant of n e increases monotonically with pressure, increasing rapidly up to 10 mTorr gas pressure and at a slower rate of rise to 50 mTorr. At a fixed 2/13.56 MHz power level and 10 mTorr gas pressure, the quasisteady state n e shows maximum for 30%-40% duty ratio and decreases with a further increase in duty ratio.