A hybrid model is used to simulate the characteristics of a collisional sheath in a capacitively coupled plasma （CCP） driven by a dual frequency source including a RF and a pulsed current source applied to the same electrode. The hybrid model includes a fluid model used to simulate the characteristics of the collisional sheath, and a Monte-Carlo （MC） method to obtain both ion energy and ion angular distributions （IEDs and IADs） impinging on the substrate. The effects of the low frequency of the pulsed source and the gas pressure on the characteristics of the sheath, as well as the IEDs and IADs, are studied. The results show that the ratio of pulse/RF frequency and the gas pressure are crucial for the characteristics of the sheath and the IEDs. The IADs are significantly more sensitive to the gas pressure.
Local measurement of plasma radial uniformity was performed in a dual frequency capacitively coupled argon plasma （DF-CCP） reactor using an optical probe. The optical probe collects the light emission from a small separate volume in plasma, thus enabling to diagnose the plasma uniformity for different experimental parameters. Both the gas pressure and the low- frequency （LF） power have apparent effects on the radial uniformity of argon plasma. With the increase in either pressure or LF power, the emission profiles changed from a bell-shaped to a double-peak distribution. The influence of a fused-silica ring around the electrodes on the plasma uniformity was also studied using the optical probe. Possible reasons that result in nonuniform plasmas in our experiments are discussed.
This paper proposes a simple collisional-radiative model to characterise capacitively coupled argon plasmas driven by conventional radio frequency in combination with optical emission spectroscopy and Langmuir probe measurements. Two major processes are considered in this model, electron-impact excitation and the spontaneous radiative decay. The diffusion loss term, which is found to be important for the two metastable states （4s[3/2]2, 4s＇[1/2]0）, is also taken into account. Behaviours of representative metastable and radiative states are discussed. Two emission lines （located at 696.5 nm and 750.4 nm） are selected and intensities are measured to obtain populated densities of the corresponding radiative states in the argon plasma. The calculated results agree well with that measured by Langmuir probe, indicating that the current model combined with optical emission spectroscopy is a candidate tool for electron density and temperature measurement in radio frequency capacitively coupled discharges.
The characteristics of a collisional dual frequency （DF） sheath near an electrode with a cylindrical hole are studied by utilizing a two-dimensional model which includes time-dependent fluid equations coupled with the Poisson equation and an equivalent-circuit model, The effects of the gas pressure on the two-dimensional profiles of the potential, electric field, ion fluid velocity in a DF sheath are investigated. The simulation results show that the cylindrical hole on the electrode has a significant influence on the DF sheath structure, i.e., the sheath profile tends to wrap around the contour of the hole feature. Moreover, it is shown that the structure of the DF sheath is different from that of a single frequency （SF） sheath because the profile of the DF sheath is modulated by the combination of the high and low frequency sources. In addition the characteristics of the DF sheath are obviously affected by the collisional effects in the DF sheath.
Low pressure argon dual-frequency （DF） capacitively coupled plasma （CCP） is generated by using different frequency configurations, such as 13.56/2, 27/2, 41/2, and 60/2 MHz. Characteristics of the plasma are investigated by using a floating double electrical probe and optical emission spectroscopy （OES）. It is shown that in the DF-CCPs, the electron temperature Te decreases with the increase in exciting frequency, while the onset of 2 MHz induces a sudden increase in Te and the electron density increases basically with the increase in low frequency （LF） power. The intensity of 750.4 nm emission line increases with the LF power in the case of 13.56/2 MHz, while different tendencies of line intensity with the LF power appear for other configurations. The reason for this is also discussed.
Nitrogen dual-frequency capacitively coupled plasmas （DF-CCPs） with different fre- quency configurations, i.e., 60/2 MHz and 60/13.56 MHz, are investigated by means of opticM emission spectroscopy （OES） and a floating double probe. The excited nitrogen molecule ion N＋（B） is monitored by measuring the emission intensity of the （0,0） bandhead of the first neg- ative system （FNS） at 391.44 nm. It is shown that in the discharge with 60/13.56 MHz, the N＋ emission intensity decreases with the increase in pressure. In the discharge with 60/2 MHz, however, an abnormal enhancement of N＋ emission at higher pressure is observed when a higher power of 2 MHz is added. Variation in the ion density shows a similar dependence on the gas pressure. This indicates that in the discharge with 60/2 MHz there is a mode transition from the alpha to gamma type when a higher power of 2 MHz is added at high pressures. Combining the measurements using OES and double probe, the influence of low frequency on the discharge is investigated and the excitation route of the N＋（B） state in the discharge of 60/2 MHz is also discussed.
