Xue-Chun Li

Fluid simulation of the E-H mode transition in inductively coupled plasma

One self-consistent method combined with the electromagnetic theory and fluid model is developed to investigate the E-H mode transition of argon inductively coupled plasma (ICP) by adjusting the external electric parameters of the reactor. ICP dynamic characteristics of radial and axial space are also studied when E and H modes coexist. By regulating the radio-frequency current in the coil and voltage across the powered end of the coil and the ground, the E-H mode transition is observed, accompanied by the substantial variations in the electromagnetic field and plasma parameters (density, temperature, and deposited power). Besides, the evolution characteristics of ICP are examined when the discharge mechanism transforms from an E-mode dominated to an H-mode dominated.

Mode transition in CF4 + Ar inductively coupled plasma

The E to H mode transitions are studied by a hairpin probe and optical emission spectroscopy in inductively coupled CF4 + Ar plasmas. Electron density, optical emission intensity of Ar, and the voltage and current are measured during the E to H mode transitions. It is found that the electron density and plasma emission intensity increase continuously at low pressure during the E to H mode transition, while they jump up discontinuously at high pressure. Meanwhile, the transition threshold power and △P (the power interval between E and H mode) increase by increasing the pressure. When the ratio of CF4 increases, the E to H mode transition happens at higher applied power, and meanwhile, the △P also significantly increases. Besides, the effects of CF4 gas ratio on the plasma properties and the circuit electrical properties in both pure E and H modes were also investigated. The electron density and plasma emission intensity both decrease upon increasing the ratio of CF4 at the two modes, due to the stronger el...

Equivalent circuit effects on mode transitions in H2 inductively coupled plasmas

It is well known experimentally that the circuit matching network plays an important role in the mode transition behavior of inductively coupled plasmas. To date, however, there have been no reports of numerical models being used to study the role of the matching circuit in the transition process. In this paper, a new two-dimensional self-consistent fluid model that couples the components of an equivalent circuit module is developed to investigate the effects of the equivalent circuit on the mode transition characteristics of an inductively coupled, hydrogen plasma. The equivalent circuit consists of a current source, impedance matching network, reactor impedance, and plasma transferred impedance. The nonlinear coupling of the external circuit with the internal plasma is investigated by adjusting the matching capacitance at a fixed input current. The electron density and temperature as well as the electromagnetic fields all change suddenly, and the E to H mode transition occurs abruptly at a certain matching capacitance as the impedance matching of the external circuit is varied. We also analyze the fields and the plasma characteristics during the transition process, especially for the case of the capacitive E mode.

Modulations of the plasma uniformity by low frequency sources in a large-area dual frequency inductively coupled plasma based on fluid simulations

As the wafer size increases, dual frequency (DF) inductively coupled plasma (ICP) sources have been proposed as an effective method to achieve large-area uniform plasma processing. A two-dimensional (2D) self-consistent fluid model, combined with an electromagnetic module, has been employed to investigate the influence of the low frequency (LF) source on the plasma radial uniformity in an argon DF discharge. When the DF antenna current is fixed at 10 A, the bulk plasma density decreases significantly with the LF due to the less efficient heating, and the best radial uniformity is obtained at 3.39 MHz. As the LF decreases to 2.26 MHz, the plasma density is characterized by an edge-high profile, and meanwhile the maximum of the electron temperature appears below the outer two-turn coil. Moreover, the axial ion flux at 3.39 MHz is rather uniform in the center region except at the radial edge of the substrate, where a higher ion flux is observed. When the inner five-turn coil frequency is fixed at 2.26 MHz, t...

Fluid simulation of the bias effect in inductive/capacitive discharges

Computer simulations are performed for an argon inductively coupled plasma (ICP) with a capacitive radio-frequency bias power, to investigate the bias effect on the discharge mode transition and on the plasma characteristics at various ICP currents, bias voltages, and bias frequencies. When the bias frequency is fixed at 13.56 MHz and the ICP current is low, e.g., 6 A, the spatiotemporal averaged plasma density increases monotonically with bias voltage, and the bias effect is already prominent at a bias voltage of 90 V. The maximum of the ionization rate moves toward the bottom electrode, which indicates clearly the discharge mode transition in inductive/capacitive discharges. At higher ICP currents, i.e., 11 and 13 A, the plasma density decreases first and then increases with bias voltage, due to the competing mechanisms between the ion acceleration power dissipation and the capacitive power deposition. At 11 A, the bias effect is still important, but it is noticeable only at higher bias voltages. At 13 ...

F-atom kinetics in SF6/Ar inductively coupled plasmas

The F-atom kinetics in SF6 and SF6/Ar inductively coupled plasmas(ICPs) were investigated using a global model. This report particularly focuses on the effects of ICP power and Ar fraction on F-atom density and its main production and loss mechanisms. The results are presented for a relatively wide pressure range of 1–100 mTorr. Very different behaviors were observed for Ar fractions in the low- and high-pressure limits, which can be attributed to different electron kinetics. In addition, the authors found that increasing the Ar fraction in the SF6/Ar plasma has almost the same effects on the F-atom kinetics as increasing the power in the SF6plasma. This is because a high electron density occurs in both cases. Moreover, it was confirmed that, for both sample types, a cycle of F atoms formed in the bulk plasma. The source of these is F2 molecules that are first formed on the chamber wall and then emitted. Finally, the simulations of F-atom kinetics are validated by quantitatively comparing the calculated electron and F-atom densities with identical experimental discharge conditions.

Electric transport coefficients in highly epitaxial LaBaCo2O5 + δ films with “p-to-n” transition induced by oxygen deficiency

Electric transport coefficients such as carrier type, density, and mobility are the important physical parameters in designing functional devices. In this work, we report the study on the electric transport coefficients of the highly epitaxial LaBaCo2O5 + δ (LBCO) films, which were discussed as a function of electric conductivity for the first time and compared with the results calculated by the theory for mixed conduction. The mobility in the LBCO films was determined to be ∼0.85 and ∼40 cm2/V s for holes and electrons, respectively, and the density of p-type carriers strongly depends on the oxygen deficiency. Solid evidence is presented to demonstrate that the oxygen deficiency cannot make LBCO materials changed from p- to n-type. The n-type conduction observed in experiment is a counterfeit phenomenon caused by the deficiency in Hall measurement, rather than a realistic transition induced by oxygen deficiency. In addition, the temperature-dependent conductivity was discussed using the differential coef...

Discontinuity of mode transition and hysteresis in hydrogen inductively coupled plasma via a fluid model

A new type of two-dimensional self-consistent fluid model that couples an equivalent circuit module is used to investigate the mode transition characteristics and hysteresis in hydrogen inductively coupled plasmas at different pressures, by varying the series capacitance of the matching box. The variations of the electron density, temperature, and the circuit electrical properties are presented. As cycling the matching capacitance, at high pressure both the discontinuity and hysteresis appear for the plasma parameters and the transferred impedances of both the inductive and capacitive discharge components, while at low pressure only the discontinuity is seen. The simulations predict that the sheath plays a determinative role on the presence of discontinuity and hysteresis at high pressure, by influencing the inductive coupling efficiency of applied power. Moreover, the values of the plasma transferred impedances at different pressures are compared, and the larger plasma inductance at low pressure due to less collision frequency, as analyzed, is the reason why the hysteresis is not seen at low pressure, even with a wider sheath. Besides, the behaviors of the coil voltage and current parameters during the mode transitions are investigated. They both increase (decrease) at the E to H (H to E) mode transition, indicating an improved (worsened) inductive power coupling efficiency.

Experimental study of hybrid capacitively/inductively coupled discharges

Summary form only given. Inductively coupled plasma (ICP) has been widely used in semiconductor industry, due to its perfect characteristics of reduced ion damage, independently controllable ion energy and high density plasmas.1, 2 In the actual industrial processes such as etching process, to control ion energy and plasma density, two independent RF power sources are conventionally applied to ICP, i.e., the power source through the coil and the bias source applied to a substrate electrode. And, the RF bias discharge is the same as capacitively coupled plasma (CCP).