It is generally recognized that the electron temperature Te either remains constant or decreases slightly with plasma power (plasma density). This trend can be simply verified using a single-step or multi-step fluid global model. In this work, however, we experimentally observed that Te evolved with plasma power in radio frequency (RF) inductively coupled plasmas. In this experiment, the measured electron energy distributions were nearly Maxwellian distribution. In the low RF power regime, Te decreased with increasing plasma power, while it increased with plasma power in the high RF power regime. This evolution of Te could be understood by considering the coupling effect between neutral gas heating and stepwise ionization. Measurement of gas temperature via laser Rayleigh scattering and calculation of Te using the kinetic model, considering both multi-step ionization and gas heating, were in good agreement with the measured value of Te. This result shows that Te is in a stronger dependence on the plasma power.
We propose a universal surface reaction model without any ad-hoc assumptions for fluorocarbon (FC) plasma oxide etching. A self-consistent numerical algorithm was developed to predict the deposition and etch yields simultaneously from our model considering the passivation layer and mixed layer. The internal model variables such as surface coverages showed consistent results under a wide range of FC plasma conditions. This model predicts the transition conditions between deposition and etch yield and the FC passivation layer thickness during the etching process. Finally, quantitative verification of the proposed model was performed through comparison to various FC plasma experimental data.
The electron bounce resonance was experimentally investigated in a low pressure planar inductively coupled plasma. The electron energy probability functions (EEPFs) were measured at different chamber heights and the energy diffusion coefficients were calculated by the kinetic model. It is found that the EEPFs begin to flatten at the first electron bounce resonance condition, and the plateau shifts to a higher electron energy as the chamber height increases. The plateau which indicates strong electron heating corresponds not only to the electron bounce resonance condition but also to the peaks of the first component of the energy diffusion coefficients. As a result, the plateau formation in the EEPFs is mainly due to the electron bounce resonance in a finite inductive discharge.
In plasma processing and application, the electron energy distribution function (EEDF) is of fundamental interest because the ion and radical densities related to physical and chemical reactions on the substrate are predominantly governed by the EEDF or electron temperature. In this paper, the effect of low frequency power on the EEDF is investigated when 2 MHz power is added to the plasma originally driven at 13.56 MHz. In a 13.56 MHz operation, the EEDF shows a Maxwellian-like distribution, and as the RF power increases, the electron density increases and the electron temperature decreases. However, when a small amount of 2 MHz power is applied to the 13.56 MHz discharge, the electron density slightly increases and the electron temperature significantly increases. In dual-frequency operation, EEDFs have a low slope of low-energy region and evolve into a Druyvesteyn-like distribution. It turns out that the dual-frequency operation can significantly change the electron temperature. This is consistent with the results calculated using the analytical electron heating model, and the relevant heating mechanism is also presented.
Crystalline silicon nanoparticles under nanometer scale have been garnering great interest in many different optoelectronic applications such as photovoltaic and light-emitting-diode devices. Formation, crystallization, and size control of silicon nanoparticles...
This work investigates the negative ion density via the floating harmonic method (FHM) in an oxygen inductively coupled plasma (ICP). When a small sinusoidal voltage is applied to the specific potentials of a planar Langmuir probe, harmonic currents will be generated by the sheath nonlinearity. Using harmonic current analysis, it is possible to obtain the positive ion currents, electron currents and electron temperatures within the plasma. One probe potential is set to floating and the other is kept in the range between the floating potential and the plasma potential. From the current ratios of positive ions to electrons, the electronegativity and modified pre-sheath potential can be deduced, thereby obtaining the negative ion density from the quasi-neutrality. The variations in the negative ion density and electronegativity distributions at various gas pressures and applied powers are compared with those of a two-dimensional fluid model incorporating electron heating kinetics and those found using a two-probe method in reference Chabert et al (1999 Plasma Source Sci. Technol. 8 561).
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