Abstract
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.
Highlights
Plasma processing plays a major role in various applications such semiconductor manufacturing, display panels solar cells etc.[1,2,3] As the number of transistors in a single chip is increasing by a factor of ∼ 2 in a year and device size is continuously shrinking, that results in increasing fabrication cost
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 present study investigates the temporal evolution of plasma potential and the effect of substrate biasing on it, in the pulsed discharges produced by a dual-frequency/dual-antenna ICP source by using an emissive probe
Summary
Plasma processing plays a major role in various applications such semiconductor manufacturing, display panels solar cells etc.[1,2,3] As the number of transistors in a single chip is increasing by a factor of ∼ 2 in a year and device size is continuously shrinking, that results in increasing fabrication cost. Yeom study is few tens of volts and assuming temperature of emitting electron ∼ 0.3 eV,[31] it can be fairly said that plasma potential measurements are under-estimated by an amount of kTe/e Another source of error comes from using the emissive probe in RF plasmas. Wang et al.[24] showed that, depending upon the load resistor, the impedance across which the probe current is measured, the floating potential may follow the average plasma potential, it could vary with RF voltage This technique is very useful in measuring the plasma potential in pulsed plasmas and provides accurate and quick qualitative information about the temporal evolution of plasma potential. The present study investigates the temporal evolution of plasma potential and the effect of substrate biasing on it, in the pulsed discharges produced by a dual-frequency/dual-antenna ICP source by using an emissive probe. The plasma potential has been measured using a Tektronix voltage probe TPP0201 (input impedance of 10 MΩ, oscilloscope impedance)
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