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In this study, electron-assisted photoresist (PR) etching is conducted using oxygen inductively coupled plasma at a pressure of 3 mTorr. During the PR etching, a low-energy electron beam is generated and is controlled by varying the acceleration voltage (0–40 V) on the grid to assist with the PR etching. When a low acceleration voltage (25 V), the etch rate increases, and the ion bombardment energy decreases with increasing electron beam energy. The electron energy probability function is measured to verify the relation between the etch rate and acceleration voltage with respect to the sheath thickness on the grid. Furthermore, low contribution of the [Formula: see text] radical to the etch rate increment is observed via optical emission spectroscopy measurements.

A hysteresis phenomenon observed in neon inductive discharge at low gas pressure is investigated in terms of the evolution of the electron energy distribution function (EEDF). Generally, the hysteresis phenomenon has been reported at high-pressure Ramsauer gas discharges. However, in neon plasma, we found that the hysteresis phenomenon occurs even at low gas pressure (5 mTorr). Furthermore, the hysteresis vanishes with an increase in the gas pressure (10 and 25 mTorr). To analyze this hysteresis, the EEDF is measured depending on the radio frequency power. The EEDF at 10 mTorr sustains the bi-Maxwellian distribution during an E–H transition. On the other hand, the EEDF at 5 mTorr changes dramatically between discharge modes. At 5 mTorr, the measured EEDF for the E mode has the Maxwellian distribution due to high collisional heating in the bulk plasma. The EEDF for the H mode has the bi-Maxwellian distribution because collisionless heating in the skin depth is dominant. This apparent evolution of the EEDF causes a nonlinear energy loss due to collisions during the discharge mode transition. Therefore, the plasma can maintain the H mode discharge with high ionization efficiency, even at a lower applied power, which results in the hysteresis.

The electron temperature Te is a key plasma parameter in both industrial plasma processes and fundamental laboratory research. A noninvasive method to measure Te in current and next-generation semiconductor plasma processes is urgently required for fine-tuning the processing result and virtual metrology based on the plasma monitoring. In this Letter, we propose a noninvasive method for obtaining Te in radio frequency capacitively coupled plasma (CCP) by measuring the floating potential and substrate potential. The Te obtained using this simple method was compared with the results measured by a floating Langmuir probe in both pure Ar and Ar/He mixture CCPs, and they showed good agreement.

Total energy loss per ion–electron pair lost ( e T) is investigated to optimize the plasma generation at various RF powers and gas pressures in an argon inductively coupled plasma (ICP). The ion densities and electron temperatures are measured to obtain e T at the plasma–sheath edge. At a fixed RF power, the obtained e T has a minimum at a certain electron temperature, and at this condition, an optimal plasma generation is achieved according to a global model. Since the electron temperature is a function of the gas pressure, at that certain gas pressure the energy loss in the plasma is minimized and plasma is generated most efficiently. Interestingly, the electron temperature at which e T becomes the minimum decreases as the RF power increases. This is explained by multistep ionization and the electron density dependence of the density of the excited states. Measured e T is compared with the calculated result from the global model that includes multistep ionization, and these are consistent with each other.

The effects of external discharge parameters (applied RF power, operating pressure, and gas flow rate) on ion flux uniformity are investigated in a dual inductively coupled plasma. The ion fluxes and electron temperatures are measured using a Langmuir probe floated by a DC blocking capacitor based on the floating harmonic method. The RF power applied to the top antenna focuses on the total ion flux control throughout the chamber, while the power introduced to the bottom antenna can control the ion flux uniformity in the diffusion chamber. At high pressures, the local electron heating in the vicinity of the bottom antennas results in local maximum ionization, thereby increasing the ion flux near the chamber wall. Furthermore, the ion flux uniformity also can be affected by the gas flow rate and pressure because they are associated with the gas residence time and the electron heating region. A physical understanding of the effects of external discharge parameters on plasma uniformity is useful for optimizing plasma processes.

The correlation of RF impedance with Ar plasma parameters was analyzed in semiconductor etch equipment using inductively coupled plasma. Since the impedance measured by a VI probe installed behind the RF bias matcher had information for plasma and structural parts of chamber simultaneously, the impedance was corrected by excluding transmission line and peripheral parts of the bias substrate. The corrected impedance was compared with plasma parameters, such as plasma density and electron temperature. The coefficient of determination between the corrected plasma resistance and the theoretical formula of the resistance for bulk plasma was over 0.9 unlike the resistance measured by the VI probe. It is expected that the corrected RF impedance can assist in monitoring the status of plasma and maintaining the quality of the etch process in semiconductor mass production lines.

To observe the evolution of electron temperature and electron density when varying gas mixing ratio and pressure, the measurement of electron energy probability functions (EEPFs) and a kinetic simulation are performed in an O2/Ar inductively coupled plasma. When O2 gas is diluted to pure Ar plasma, the electron density significantly drops regardless of gas pressures and the reduction of electron density increases with gas pressure. This sudden drop of plasma density is due to various inelastic collisions between electrons and O2 molecules. However, the trend of electron temperature variation with respect to the ratio of O2 and Ar is opposite at low and high pressures. At low pressure (5 mTorr), the electron temperature decreases with the addition of O2 up to a 10% O2 ratio. With further addition of O2, the electron temperature increases gradually. On the other hand, at high pressures (25 and 80 mTorr), the electron temperature rises with addition of O2 up to a 10%–20% O2 ratio and then falls gradually with further addition of O2. Simulations show a similar variation of EEPFs to the EEPFs from experiments. In addition, we measured the EEPFs along axial positions and the variation of electron temperature with respect to the ratio of O2 and Ar is opposite at low and high pressures, regardless of spatial positions. This result indicates that the opposite trend of electron temperature variation is mainly affected by the gas mixing ratio and gas pressure.

Electron energy distribution functions (EEDFs) are measured with varying radio-frequency (RF) power in an oxygen inductive discharge. At a pressure of 10 mTorr, the EEDF has a Maxwellian distribution, and the low-energy (1–5 eV) electron temperature, T e , low, monotonically decreases with RF power. However, at a pressure of 100 mTorr, T e , low increases at low RF power (80–150 W) and decreases at high RF power (150–300 W), and the EEDF has a Druyvesteyn-like distribution. These changes in T e , low are attributed to electron attachment and detachment reactions, which are the main creation and loss reactions of negative ions. To investigate this relationship between T e , low and collisional reactions, the reaction coefficients of several reactions are calculated, and the electronegativity ( α) is measured with varying RF power. The EEDF is modified by electron attachment and detachment reactions, which lead to a change in T e , low; this modification of EEDF is supported by calculated reaction coefficients and measured α.

We developed a hybrid plasma source combined with an inductively coupled plasma (ICP) antenna and a capacitively coupled plasma (CCP) electrode. The ICP antenna and the CCP electrode are connected to a single RF power generator in parallel and a variable capacitor Cv is connected to the ICP antenna in series. The currents flowing through each source and the CCP electrode voltage are measured for analysis of the electrical characteristics, and the ion densities are measured while adjusting the capacitance of the Cv. Interestingly, when a series LC resonance occurs between the inductance of the ICP antenna and the capacitance of the Cv, different trends are observed depending on the discharge mode. In capacitive mode (E-mode), the ion density is minimized and is controlled by the CCP current. On the other hand, in inductive mode (H-mode), the ion density is maximized and is affected by the ICP current. The change of the ion density can be explained by the balance between the total power absorption and power dissipation. It is also in good qualitative agreement with the calculated plasma density from the power balance equation. By adjusting the Cv, linear control of the ion density can be achieved. To evaluate the proposed source in terms of O atom generation, the number density ratio of O atom nO to Ar nAr is obtained by using the optical emission spectroscopy actinometry method. These results show that nO/nAr is controlled. Our source can be applied to plasma processing, in which ion density and O atom generation controls are important factors.

Changing the RF bias is widely used to control the ion energy in inductively coupled plasma (ICP). Here, the plasma densities were measured using the floating harmonic method at various ICP powers and RF bias power frequencies. It is observed that there is an RF bias power (PB,min) that minimizes the plasma density. With increasing ICP power, PB,min is increased. When the frequency is changed from 12.5 MHz to 2 MHz, PB,min is decreased. To understand this phenomenon, the relative variation of the plasma density (δn) with the RF bias power is considered based on a power balance equation. PB,min is determined by δn, and δn changes based on the self-bias voltage caused by the RF bias power. Because the self-bias voltages change depending on the ICP power and frequency of the RF bias power, PB,min is shifted by altering the ICP power and the RF bias power frequency. The results are in good agreement with the experimental results.

We investigated the profiles of electron and ion densities dependence on the gas pressure in the inductively coupled plasma with a passive resonant antenna. The inner powered antenna and the passive resonant antenna are independently installed on the top of the chamber, and a power of 13.56 MHz is applied to the powered antenna. A significant change in the plasma density profile is observed when the capacitance of the passive resonant antenna is adjusted from non-resonance to resonance. At a high pressure of 50 mTorr, the point of maximum electron density and temperature shift from near the powered antenna to near the passive resonant antenna. However, at a low pressure of 1 mTorr, the profile of the electron density and temperature hardly change, and the maximum electron density at resonance increases about 1.4 times (at 150 W) to 4 times (at 50 W) higher than at non-resonance. The controllability of the electron density profile, which depends on the gas pressure, can be understood by the electron kinetics effect, and the increase in the electron density can be explained by the increase in power transfer efficiency calculated from the circuit model. The electron density profile at bulk is compared to the ion density distribution at the wafer-level, and the results are discussed with the relevant physical mechanisms.

A hysteresis loop has been observed during the E–H mode transition in an inductively coupled plasma at high pressures. The cause of the hysteresis has been reported as a nonlinearity of the transferred and dissipated powers due to capacitive coupling, multi-step ionization, the change in the electron energy probability function (EEPF), and so on [M. M. Turner and M. A. Lieberman, Plasma Sources Sci. Technol. 8(2), 313–324 (1999) and H. C. Lee and C. W. Chung, Sci. Rep. 5, 15254 (2015)]. However, when a coil current reduction is considered, the previous interpretation of hysteresis cannot explain the observations in the intermediate pressure region, where the coil current reduction occurs, but hysteresis is not observed. In this work, the E–H mode transition and its hysteresis are discussed in three pressure regions, the low, intermediate, and high pressure regions, whether or not the coil current and the hysteresis are observed. The power transfer efficiency, transferred power, EEPF, and total energy loss are obtained at 10, 100, and 300 mTorr. Hysteresis is only observed at 300 mTorr, and the coil current reduces at 100 and 300 mTorr during the E–H mode transition. The mechanism of hysteresis is explained in a power balance diagram that includes the transferred power and the dissipated power by considering the power transfer efficiency in the E and H modes. In addition, the conditions of hysteresis and coil current reduction are revealed and classified in this work.

When dual frequency ω α , ω β voltages with small amplitudes are biased toward a floating Langmuir probe, intermodulation currents of i ω β ± ω α , i ω β ± 2 ω α are generated due to the nonlinearity of the sheath near the probe tip. Electron temperatures and plasma densities can be obtained from the intermodulation currents using the sideband method. If the probe has a capacitive load such as a contaminated probe tip, harmonic and intermodulation voltages of the probe bias can be applied to the sheath. The sideband method can be modified using a harmonic balance technique that analyzes the nonlinear circuit. The intermodulation currents from the modified sideband were compared with the measured intermodulation currents. The electron temperatures and plasma densities obtained from the intermodulation currents are in close agreement with those of the electron energy probability functions in argon inductively coupled plasmas.

The E to H transition is investigated in 2 MHz, 13.56 MHz, and dual frequency (2 MHz + 13.56 MHz) inductively coupled plasmas (ICPs). At argon gas pressures of 1 mTorr and 10 mTorr, the E to H transition power of 2 MHz ICP is the lowest and the transition power of 13.56 MHz ICP is the highest. However, at pressures of 25 mTorr and 50 mTorr, the transition power of 13.56 MHz ICP decreases and the transition power of 2 MHz ICP significantly increases. Interestingly, despite these changes, the E to H transition in the dual frequency operation occurs at the power between the 2 MHz and the 13.56 MHz transition power. The measurement shows that the plasma density in dual frequency operation is from about 1.1 to 11.7 times higher than that in single frequency operation, but this is changed with the pressure. For quantitative analysis, a global model including the capacitive coupling and the inductive coupling in the solenoidal ICP was developed and the E to H transition powers were calculated. It turns out that the results at various pressures and frequencies agree well with the experimental measurements and the relevant physical mechanism is also presented.

CO2 inductively coupled plasmas (ICPs) were generated using a radio frequency power of 13.56 MHz at 100 mTorr. Electron energy distribution functions (EEDFs) were measured using a single Langmuir probe, and various plasma parameters such as the electron density and electron temperature were obtained from the measured EEDFs. EEDFs with multislope structures are obtained. However, changes in the gas composition in the ICP were observed via optical emission spectroscopy. The electron density barely increases when a sudden change in the gas composition occurs. The E to H mode transition occurs at a stationary gas composition as the absorbed power increases. The EEDFs of CO2 plasma, CO plasma, and O2 plasma were calculated using BOLSIG+, which is a two term Boltzmann solver [G. Hagelaar and L. Pitchford, Plasma Sources Sci. Technol. 14(4), 722 (2005)]. The measured EEDF is closest to the EEDF of the CO plasma.

The E to H mode transition is one of the most interesting phenomena in inductively coupled plasmas, and there is substantial evidence to show that the mode transition occurs. During the E–H mode transition, in a certain discharge condition such as low driving frequencies and high pressures, a decrease in the antenna coil current has been observed. The decrease in the coil current during the E to H mode transition at high pressures is investigated in a cylindrical inductively coupled plasma. The condition for the decrease in the coil current is derived and is analyzed through the comparison of the slopes of dissipated power and transferred power against the electron density. In addition, it is found that the electron density jump appears simultaneously with the current decrease. In order for the coil current to decrease, the slope of the dissipated power to the plasma against the electron density must be smaller than that of the transferred power, and this can be satisfied when the contribution of multistep ionization is considered in the dissipated power.

In low gas pressure radio frequency (RF) capacitive discharges, high energy electrons, which are responsible for the ionization process, are generated near the RF sheath where the electric field oscillates. The energetic electrons heated from the sheath cannot reach the plasma bulk at high gas pressures or in molecular gases because of their short electron energy relaxation length. In this letter, however, it is shown that from the probe measurements of the electron energy distribution function (EEDF), the high energy electrons at the plasma bulk are observed in the local kinetics regime as the RF bias power increases in an inductively coupled plasma of high mixing ratio of SF6/(Ar + SF6). The generation of the high energy electrons and the EEDF modification could be understood by the enhanced bulk electric field in negative ion rich plasmas, and the EEDF modification presents a direct experimental evidence of the drift-ambipolar electron heating at the plasma bulk.

The spatial distribution of floating potential for charging distribution at the wafer-level is measured by using a wafer-type probe array, and the experiment is performed in an inductively coupled oxygen plasma. At low pressures, the floating potential distribution exhibits a convex shape. As the pressure increases, the profile gradually evolves into a concave shape, indicating more negative charge at the center, which is unusual for electropositive plasmas. A similar evolution is observed for positive ion flux under the same discharge conditions. It is noteworthy that the charging distribution at the wafer position in process plasmas at high pressures can be reversed due to negative ions compared to that in electropositive plasmas. In addition, the correlation between the floating potential and electronegativity is also presented. In order to investigate the effect of negative ions on floating potential distribution, a 2D fluid simulation with an electron-heating model is conducted, and the experimental results are in good agreement with those from the 2D fluid simulation.The spatial distribution of floating potential for charging distribution at the wafer-level is measured by using a wafer-type probe array, and the experiment is performed in an inductively coupled oxygen plasma. At low pressures, the floating potential distribution exhibits a convex shape. As the pressure increases, the profile gradually evolves into a concave shape, indicating more negative charge at the center, which is unusual for electropositive plasmas. A similar evolution is observed for positive ion flux under the same discharge conditions. It is noteworthy that the charging distribution at the wafer position in process plasmas at high pressures can be reversed due to negative ions compared to that in electropositive plasmas. In addition, the correlation between the floating potential and electronegativity is also presented. In order to investigate the effect of negative ions on floating potential distribution, a 2D fluid simulation with an electron-heating model is conducted, and the experimental ...

A monitoring device is proposed to investigate the charge accumulation effects in a high-aspect-ratio trench structure. This monitoring device is made of an anodic aluminum oxide (AAO) template, which is a self-organized material with parallel pores, to demonstrate a high aspect ratio trench structure. A top electrode and bottom electrode were formed in the AAO contact structure for measuring electric potentials. These electrodes can be assumed to be electrically floating due to the very high input resistance of the measurement circuit. Therefore, the electric potentials resulting from the charge accumulation can be measured. In this paper, the fabrication process of the proposed device and experimental demonstrations are presented.

In cylindrical floating probe measurements, the plasma density and electron temperature are overestimated due to sheath expansion and oscillation. To reduce these sheath effects, a compensation method based on well-developed floating sheath theories is proposed and applied to the floating harmonic method. The iterative calculation of the Allen-Boyd-Reynolds equation can derive the floating sheath thickness, which can be used to calculate the effective ion collection area; in this way, an accurate ion density is obtained. The Child-Langmuir law is used to calculate the ion harmonic currents caused by sheath oscillation of the alternating-voltage-biased probe tip. Accurate plasma parameters can be obtained by subtracting these ion harmonic currents from the total measured harmonic currents. Herein, the measurement principles and compensation method are discussed in detail and an experimental demonstration is presented.

The edge-to-center density ratio is investigated in an inductively coupled plasma which has two discharge modes depending on the rf power: the E- and H-mode. The power dependence of the edge-to-center density ratio is obtained from the ion flux at the wall and the electron flux at the center. The transitions of the density ratio of edge-to-center are observed during the E-H mode transition at various pressures, which has different trends depending on the pressure. These can be understood by the changes in the plasma characteristics due to the heating mode transition and electron kinetics by pressures. The theoretical edge-to-center density ratio is similar to the measured ratio at low pressures where the electrons are in non-local kinetics. However, at high pressures where the electrons are in local kinetics, the theoretical edge-to-center density ratio has a large discrepancy with the measured value in the E-mode due to local heating of electrons near the antenna. The density ratio of edge-to-center meas...

A dual inductively coupled plasma (ICP) system in which a remote ICP (upper ICP) with small volume is attached to a main ICP (lower ICP) is developed. Two ICP antennas are connected in parallel and a variable capacitor Cvar is installed in series at the end of the main ICP antenna. By adjusting the capacitance of the variable capacitor, the plasma densities and the electron temperatures in the remote region and the main region are controlled. The electron energy distribution functions (EEDFs) and plasma potential from the EEDFs are measured along z axis. It is found that there is a potential dip in the midway of two ICP antennas and the potential dip is formed to keep two plasmas quasineutral. In two regions, the EEDFs in high energy range are almost same (nonlocal) but they are different in low energy range because low energy electrons cannot overcome the potential dip.

The two-dimensional temporal behavior of plasma was investigated at the wafer-level when applied power was turned on/off, which is one cycle of the pulsed plasma. For the measurement of transient plasma, the floating harmonic method and a post-processing method were used to obtain the ion flux and the electron temperature with a 1 ms time resolution. The results show that the transient behaviors of plasma such as antenna power absorption are observed in pulsed inductively coupled plasma. Antenna-shaped ion flux is observed when the power is turned on, and the radial profiles of the ion flux are followed by a diffusion solution when the power is turned off. Furthermore, the electron temperature shows pulsed plasma characteristics.

A floating type Langmuir probe was studied to measure the electron energy distribution function (EEDF) in plasmas. This method measures the current (I)-voltage (V) curve with rising and falling variations based on a floating potential by using charge-discharge characteristics of the series capacitor when a square-pulse voltage is applied. In addition, this method measures the EEDF by using the alternating current (ac) superposition method. The measured EEDFs were in good agreement with results from a conventional single Langmuir probe. This technique could be applied as a plasma diagnostic method in the capacitively coupled plasma where the plasma potential is extremely high or the processing plasma where the deposition gas is used.

Sulfur hexafluoride (SF6) gas or Ar/SF6 mixing gas is widely used in plasma processes. However, there are a little experimental studies with various external parameters such as gas pressure and mixing ratio. In this work, a study of the plasma parameters by changing the gas mixing ratio was done in an Ar/SF6 inductively coupled plasma from the measurement of the electron energy distribution function. At a low gas pressure, as the mixing ratio of SF6 gas increased at a fixed inductively coupled plasma (ICP) power, the electron density decreased and the electron temperature increased, while they were not changed drastically. At a high gas pressure, a remarkable increase in the electron temperature was observed with the decrease in the electron density. These variations are due to the electron loss reactions such as the electron attachment. It was also found that at a fixed ICP power, the negative ion creation with the diluted SF6 gas can change the discharge mode transition from an inductive mode to a capac...

Pressure and He mixing effects on plasma parameters in electron temperature control using a grid system are investigated. Electron temperature is higher in lower pressure, when the electron temperature is high and not controlled. Electron density can be increased by about three times by decreasing the source gas pressure from 20 to 1 mTorr, and by about two times by He mixing in the temperature controlled region (diffusion region), while the electron density is decreased in the source region. This electron density increase is mainly due to the increase of the high energy electron population, and the measured electron energy distribution functions clearly show this.

The electron energy distribution functions (EEDFs) are measured by a rf compensated Langmuir probe in a solenoidal inductive reactor at various frequencies and at 2 mTorr of argon. The frequency dependence of the electron energy distribution function is clearly observed. The energy diffusion coefficients against the applied frequencies are calculated from the nonlocal heating theory. It is found that the bounce resonance electrons determine the energy diffusion coefficient shape and the electron energy distribution function at the bounce resonance energy in the energy diffusion coefficient begins to flatten. The exact bounce resonance condition in solenoidal inductive discharge is presented. It is reported that the frequency dependence of the EEDFs is mainly due to the electron bounce resonance in a finite-size solenoidal inductive discharge.

Particle and power balance equations including stepwise ionizations are derived and solved in helium plasmas. In the balance equations, two metastable states (21S1 in singlet and 23S1 triplet) are considered and the followings are obtained. The plasma density linearly increases and the electron temperature is relatively in a constant value against the absorbed power. It is also found that the contribution to multi-step ionization with respect to the single-step ionization is in the range of 8%–23%, as the gas pressure increases from 10 mTorr to 100 mTorr. Compared to the results in the argon plasma, there is little variation in the collisional energy loss per electron-ion pair created (ec) with absorbed power and gas pressure due to the small collision cross section and higher inelastic collision threshold energy.

Radio frequency power with a low frequency of 4 MHz is delivered to a solenoidal inductively coupled plasma at a low pressure of 1 mTorr. The electron energy distribution functions (EEDFs) are measured by a rf compensated Langmuir probe at different rf powers. As the rf power increases, a Maxwellian EEDF evolves into a bi-Maxwellian EEDF with a low energy peak. This means that the electron heating in the plasma greatly changes. This EEDF transition can be understood by considering the rf magnetic field effect, which is strong at low frequency.

The number of antenna coil turns, N, that affects the plasma density is a significant factor to design an inductively coupled plasma source. The equivalent resistance and inductance of a transformer circuit seen at the antenna coil are known to increase with N. This can enhance the power transfer efficiency. However, there is an undesired capacitive coupling between the antenna coil and the plasma. The antenna voltage related to the capacitive coupling is known to be proportional to N. In this work, to investigate the effects of N, the plasma density and the antenna coil voltage are measured by a floating probe and high-voltage probes, respectively. A terminal capacitor is used to suppress the capacitive coupling. As a result, the effects of N are clearly observed on the plasma densities and the voltages of the antenna coil. The plasma density was found to dramatically increase with N while the capacitive coupling is suppressed. The antenna voltage was not increased with N, and it was investigated by the ...

The radio-frequency (RF) plasma diagnostics with an electrical probe facing a challenge, because the RF fluctuation oscillates the plasma potential and distorts the current-voltage (I-V) curve. As Langmuir probe is widely used in plasma diagnostics, many researchers have been studying the effect of RF fluctuation on probe and compensation methods. On the other hand, there have not been enough studies on the fluctuation effect on the floating harmonic method. Therefore, we investigated the impact of RF fluctuation on the floating harmonic method theoretically and experimentally. When the electrons are in ideal Maxwellian distribution, the floating potential is negatively shifted by the RF fluctuation, but the fluctuation does not distort I-V curve around the floating potential. However, in practical plasmas, the I-V curve and their harmonic components are distorted. This RF fluctuation effect becomes more significant in a low density plasma with a high impedance sheath. The second harmonic current decreases with the RF fluctuation while the first harmonic current is merely affected. Therefore, the electron temperatures measured with the floating harmonic method under low density plasma with uncompensated probe are overestimated than the results obtained with the compensated probe.

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.

A modified central difference method (MCDM) is proposed to obtain the electron energy distribution functions (EEDFs) in single Langmuir probes. Numerical calculation of the EEDF with MCDM is simple and has less noise. This method provides the second derivatives at a given point as the weighted average of second order central difference derivatives calculated at different voltage intervals, weighting each by the square of the interval. In this paper, the EEDFs obtained from MCDM are compared to those calculated via the averaged central difference method. It is found that MCDM effectively suppresses the noises in the EEDF, while the same number of points are used to calculate of the second derivative.

Variation of the floating potential in a Langmuir probe was investigated. When the dual frequencies ( ω1, ω2) were applied to the probe, the intermodulation frequencies, which are the linear combinations of two frequencies ( aω1±bω2), as well as the harmonic frequencies ( aω1,bω2), were induced by sheath nonlinearity. However, when two frequencies had a consecutive relationship ( ω2=2ω1), the DC components of the intermodulation frequencies ( aω1±bω2=0) were generated. This is known as the sheath rectification effect, which causes additional voltage to the floating potential at the probe. In our work, the induced voltage can be controlled by the phase difference between the two consecutive frequencies, and it was found to be in good agreement with the theoretical result, which is governed by the temperature of the high energy electrons.

Measurement of the plasma density is investigated to study plasma dynamics by adding reactive gas (O2) or rare gas (He) in Ar plasmas. When the O2 or He gas is added, plasma density is suddenly decreased, while the plasma density recovers slowly with gas off. It is found that the recovery time is strongly dependent on the gas flow rate, and it can be explained by effect of gas residence time. When the He gas is off in the Ar plasma, the plasma density is overshot compared to the case of the O2 gas pulsing due to enhanced ionizations by metastable atoms. Analysis and calculation for correlation between the plasma density dynamics and the gas pulsing are also presented in detail.

The floating harmonic method biases sinusoidal voltage to a probe sheath, and as its response, harmonic currents can be obtained. These currents can be used to determine the plasma parameters. However, different shapes of probes have different shapes of sheaths that can affect the diagnostic results. However, no research has been done on the sheath effect on the floating harmonic method. Therefore, we investigate the effect of the sheath during floating harmonic diagnostics by comparing cylindrical and planar probes. While the sinusoidal voltages were applied to a probe, because the sheath oscillated, the time variant ion current and their harmonic currents were added to the electron harmonic currents. In the floating harmonic method, the harmonic currents are composed of only the electron harmonic currents. Therefore, the ion harmonic currents affect the diagnostic results. In particular, the electron temperature obtained by the small probe tip was higher than that of the large probe tip. This effect was exacerbated when the ratio of the probe tip radius to the sheath length was smaller.

In a plasma discharge system, the power loss at powered line, matching network, and other transmission line can affect the discharge characteristics such as the power transfer efficiency, voltage and current at powered electrode, and plasma density. In this paper, we propose a method to reduce power loss by using a step down transformer mounted between the matching network and the powered electrode in a capacitively coupled argon plasma. This step down transformer decreases the power loss by reducing the current flowing through the matching network and transmission line. As a result, the power transfer efficiency was increased about 5%–10% by using a step down transformer. However, the plasma density was dramatically increased compared to no transformer. This can be understood by the increase in ohmic heating and the decrease in dc-self bias. By simply mounting a transformer, improvement of discharge efficiency can be achieved in capacitively coupled plasmas.

We measured electrical characteristics of transversely magnetized capacitively coupled plasma at low pressure (10 mTorr). From these measurements, we found that the power characteristics of the magnetized discharge were different from those of the unmagnetized discharge. As the magnetic field increases, a square dependence of power characteristic at high current changes to a linear dependence. This can be understood as a power dissipation mode transition by a magnetic field. A calculation from a simple sheath model agrees well with the experimental data.

The U10 undulator for the Pohang Light Source was measured with a pulsed wire measurement (PWM) method. By adjusting the aperture of the slotted optical switch (SOS) for PWM, the sensitivity of SOS output to the wire displacement improved significantly. A calibration table, which translates the output voltage to the displacement of wire, was obtained and the linearity of the PWM was enhanced using this table. The magnetic-field profile of the U10 undulator measured with the PWM method agrees well with that measured with Hall probe mapping. The effect of the wire dispersion on PWM is also discussed.

Electron energy distribution functions (EEDFs) at different radial positions are measured by a rf compensated Langmuir probe in a low-pressure solenoidal inductively coupled plasma. It is found that the measured EEDFs for trapped electrons with total energy e

Plasma parameters from the measured electron energy distribution are obtained with changing the chamber height at low pressure 2 mTorr. It is observed that electron density has a local peak at a certain chamber height while electron temperature decreases monotonously with increasing chamber height. The chamber height with the maximum electron density is shifted according to the bounce resonance condition when the driving frequency is changed. The electron kinetic model well agrees with the experiment. This shows that the electron density peak against the plasma size is due to the electron bounce resonance that has been theoretically discussed.

Electron energy probability functions (EEPFs) were measured in a low pressure argon inductive discharge. As radio frequency (RF) power increases, discharge mode is changed from E-mode (capacitively coupled) to H-mode (inductively coupled) and the EEPFs evolve from a bi-Maxwellian distribution to a Maxwellian distribution. It is found that the plasma densities at low RF powers (

The electrical probe diagnostics are very hard to be applied to atmospheric plasmas due to severe perturbation by the electrical probes. To overcome this, the probe for measuring electron temperature and ion current density is indirectly contacted with an atmospheric jet source. The plasma parameters are obtained by using floating harmonic analysis. The probe is mounted on the quartz tube that surrounds plasma. When a sinusoidal voltage is applied to a probe contacting on a quartz tube, the electrons near the sheath at dielectric tube are collected and the probe current has harmonic components due to probe sheath nonlinearity. From the relation of the harmonic currents and amplitude of the sheath voltage, the electron temperature near the wall can be obtained with collisional sheath model. The electron temperatures and ion current densities measured at the discharge region are in the ranges of 2.7–3.4 eV and 1.7–5.2 mA/cm2 at various flow rates and input powers.

Vibrational temperature (Tvib) of N2 gas and electron energy distribution function (EEDF) were measured in Ar/N2 mixture inductively coupled plasma (ICP). At a low gas pressure of 5 mTorr where the EEDF is bi-Maxwellian distribution, plasma density np and Tvib (from 7000 K to 5600 K) slightly decrease. However, remarkable decrease in np and Tvib is found with the dilution of N2 gas at a high gas pressure of 50 mTorr, where the EEDF is depleted Maxwellian distribution at a fixed ICP power of 150 W. When the ICP power increases from 150 W to 300 W at the gas pressure of 50 mTorr, the depleted tail on the EEDF is replenished, while np is little changed with the dilution of N2 gas. In this case, Tvib slightly decreases from 9500 K to 7600 K. These results indicate that the variation of Tvib is strongly correlated to the plasma parameters, such as the plasma density and EEDF.

The gap length effect on plasma parameters is investigated in a planar type inductively coupled plasma at various conditions. The spatial profiles of ion densities and the electron temperatures on the wafer level are measured with a 2D probe array based on the floating harmonic method. At low pressures, the spatial profiles of the plasma parameters rarely changed by various gap lengths, which indicates that nonlocal kinetics are dominant at low pressures. However, at relatively high pressures, the spatial profiles of the plasma parameter changed dramatically. These plasma distribution profile characteristics should be considered for plasma reactor design and processing setup, and can be explained by the diffusion of charged particles and the local kinetics.

A phase delay harmonic analysis method (PDHAM) with high-time resolution is proposed to measure the plasma parameters of the pulsed plasmas. The PDHAM, which is based on the floating harmonic method, applies the phase delayed voltages to a probe tip, and obtains each of the currents in the phase-domain at a given time. The time resolution of this method is 0.8 μs, and the total measurement is done within 2 s in the case of a pulsed plasma with a frequency of 1 kHz. The measurement result of the plasma parameters was compared with a conventional Langmuir probe using a boxcar mode, and shows good agreements. Because this PDHAM can measure the plasma parameters even in the processing discharges, it is expected to be usefully applied to plasma diagnostics for pulsed processing plasmas.