Jin-Young Bang

A plasma diagnostic technique using a floating probe for the dielectric deposition process

Low-temperature RF discharges have been widely used in processing applications. Plasma diagnostics provide useful information about the plasma state which is important for processing results. In the deposition process, as the dielectric material is coated onto the probe surface, electrical diagnostic techniques using a dc current cannot be applied. Instead, an ac voltage is applicable for measuring plasma parameters. In this paper, electron temperatures and plasma densities were measured with an anodized aluminum probe using the floating-type harmonic method and the self-bias method. The Al2O3 layer on the probe surface and the sheath were modeled as a series connection of a capacitor and a resistor, respectively. The applied ac voltage was divided into the two parts depending on their impedances, and the voltage across the sheath was determined by the phase between the voltage and the current. According to experimental results, the conventional harmonic method, which uses the first and second harmonic current, was not valid to measure the electron temperature when the dielectric layer was thick. In contrast, the electron temperature measured by the self-bias method, which uses only the first harmonic current, was reliable regardless of the thickness of the dielectric layer.

A numerical method for determining highly precise electron energy distribution functions from Langmuir probe characteristics

Electron energy distribution functions (EEDFs) were determined from probe characteristics using a numerical ac superimposed method with a distortion correction of high derivative terms by varying amplitude of a sinusoidal perturbation voltage superimposed onto the dc sweep voltage, depending on the related electron energy. Low amplitude perturbation applied around the plasma potential represented the low energy peak of the EEDF exactly, and high amplitude perturbation applied around the floating potential was effective to suppress noise or distortion of the probe characteristic, which is fatal to the tail electron distribution. When a small random noise was imposed over the stabilized prove characteristic, the numerical differentiation method was not suitable to determine the EEDF, while the numerical ac superimposed method was able to obtain a highly precise EEDF.

Real-time observation of the capacitance variation in a surface dielectric layer in radio frequency discharge

The capacitance of an Al2O3 layer coated on a probe was measured in real-time in plasma using the harmonic method. The measured capacitance was influenced by the applied power and the exposure time to the plasma. Upon varying the power, the capacitance quickly changed and then slowly saturated. The change in the capacitance was partly understood to be due the temperature dependence of the dielectric constant. However, the rate of the capacitance change as a function of temperature was higher than that typically observed, and the quick response to varying power was too fast to be explained by the temperature variation. These results showed that other effects besides temperature should be considered to explain this phenomenon.

Characteristics of probe current harmonics based on various applied voltage waveforms in low temperature plasmas

The characteristics of probe currents induced by applying various probe voltage waveforms, such as sinusoidal, sawtooth, square, and triangular, were investigated at a floating potential. It was found that the measured probe currents have many harmonics depending on the voltage waveforms. This was mainly due to the nonlinearity of the sheath in the plasma and was analyzed using the fast Fourier transform and a circuit model. By applying a triangular voltage waveform to a probe, plasma parameters such as electron temperature and plasma density could be obtained and compared to those of a single Langmuir probe and a floating harmonic method.

Effect of helium on spatial plasma parameters in low pressure argon-helium plasma

Spatial distributions of the electron energy probability function were measured using a Langmuir probe in side-type argon-helium inductively coupled plasma. Collisional dominated electron heating and a concave shape of plasma density profile were observed at 10 mTorr pure argon. As the helium proportion increased, the electron heating and density profile changed to collisionless dominated heating and a convex shape respectively, and the same tendency was shown when the pressure decreased in the pure argon plasma. These changes were due to the decrease in the e-n collision frequency and the expansion of the electron power dissipation region.

Electromagnetically coupled resonators using toroidal ferrite core for wireless power transfer

Wireless power transfer technology via electromagnetic resonant coupling shows the probability of removing wires. Many researches have been published and have shown promising results. However, there were few efforts to lower resonance frequency. A low operating frequency in a system is a very important parameter because the lower operating frequency could reduce a system price. We lowered a self-resonant frequency until 500KHz by using a toroidal ferrite core and measured transmission parameter by a vector network analyzer. We achieved a transmission parameter of over 0.5 in a range of antenna diameter and improved the efficiency in the short range with rotating antenna angle.

Electron energy flux control using dual power in side-type inductively coupled plasma

Spatial distributions of plasma densities and plasma potentials were measured by the Langmuir probe in the plasma which has eight side sources driven by 400 kHz main power. At low pressure, the energy flux to the chamber from the remote plasma was controlled by 13.56 MHz auxiliary power applied around the center due to the variation of the potential distribution. The energy flux from the side sources toward the chamber led to the synergistic effect on the increase in the center density. The drastic increase in the center density and the decrease in the edge density resulted in the efficient power dissipation for ionization.

A new design of wireless power transfer system using hellical resonators applicapable to multi-channel power transmission

Wireless power transfer (WPT) technology via electromagnetic resonant coupling shows the probability of removing wires. Many researches have been published and have shown promising results. However, there were few studies to use a helical resonator for wireless power transfer, though it has great benefits of low resonant frequency and simple configuration. We present a new approach to design a wireless power transfer system using helical coil (transmitter) and LC resonant coil (receiver). The proposed system was optimized at self-resonant frequency of 3.4MHz and transmission parameters were measured by a vector network analyzer. We achieved that a minimum efficiency is about 40% when the transmitter-to-receiver distance is 1m. It was also shown that the transmit coil with helical resonator can be easily expanded to multi-channel wireless power transmitters.

Development of Ferrite-Enhanced Side-Type Inductively Coupled Plasma

A side-type inductively coupled plasma (ICP) reactor for large-area processing has been developed with the aid of ferromagnetic cores. A low-frequency operation with strong coupling to the plasma solved the problems occurring in conventional ICPs such as transmission line effect, capacitive coupling, low-power transfer efficiency, and inability to operate in a high-vacuum region. Using an auxiliary antenna, the additional electric field can be applied to the discharge center. The energy flux from the side sources toward the discharge center could be controlled by applying an additional electric field to the center using the auxiliary antenna on the quartz window. This result showed a drastic increase in the center density with a small amount of the auxiliary power and thus provided easy control of the spatial uniformity over 450 mm. An image of the ferrite ICP operated by single power is presented.

Probe diagnostics in the edge of kstar tokamak plasma using fast floating harmonic method

Summary form only given. Diagnostic of the edge region, called scrape-off layer (SOL) of tokamak plasma is of great interest because the research on the SOL plays an important role in understanding discharge characteristics between the plasma facing components and core region. For this reason, plasma diagnostics have been developed and adapted to the fusion plasma with high time resolution and small perturbation. Recently, Chung and co-worker [Lee et al, J. Appl. Phys. 101, 033305 (2007)] have developed a floating harmonic method that could measure plasma parameters, such as plasma density (or ion flux) and electron temperature without disturbing plasma, even in reactive plasmas which causes deposition on the probe. We have improved the floating harmonic method for more fast acquisition to utilize the diagnostic for tokamak plasmas. The ion flux and electron temperature were measured at far SOL region and compared with both interferometer and electron cyclotron emission (ECE) diagnostics. Our preliminary results show similar trend with that of interferometer and the ECE, which indicates that our method can be applied as a diagnostic for fusion plasma and the behavior of the edge plasma such as Edge Localized Mode (ELM) can be seen from the measurement.