Dae-Jin Seong

Plasma frequency measurements for absolute plasma density by means of wave cutoff method

A method for precise measurements of absolute electron density in the plasma using plasma frequency is developed. A microwave perturbation of a frequency is introduced to plasma from a network analyzer and transmits in the plasma. The transmitting wave at a distance from a radiating antenna is monitored using a spectrum analyzer to scan the perturbing frequency. The transmitting wave rapidly decays by a cutoff at the plasma frequency, which gives the absolute electron density. The transmitting waves of some frequency including plasma frequency are characterized. The measured plasma frequency by this method is coincident with that obtained by the plasma oscillation method.

Gap length effect on electron energy distribution in capacitive radio frequency discharges

A study on the dependence of electron energy distribution function (EEDF) on discharge gap size in capacitive rf discharges was conducted. The evolution of the EEDF over a gap size range from 2.5to7cm in 65mTorr Ar discharges was investigated both experimentally and theoretically. The measured EEDFs exhibited typical bi-Maxwellian forms with low energy electron groups. A significant depletion in the low energy portion of the bi-Maxwellian was found with decreasing gap size. The results show that electron heating by bulk electric fields, which is the main heating process of the low-energy electrons, is greatly enhanced as the gap size decreases, resulting in the abrupt change of the EEDF. The calculated EEDFs based on nonlocal kinetic theory are in good agreement with the experiments.

Evolution of electron temperature in low pressure magnetized capacitive plasma

The evolution of electron temperature in a low pressure magnetized capacitive discharge was investigated under the collisionless electron heating regime. The results showed that while the electron temperature increases monotonously with the magnetic field in previous study [Turner et al., Phys. Rev. Lett. 76, 2069 (1996)], the electron temperature in our experiment exhibited nonmonotonic evolution behavior with the magnetic field. This nonmonotonic evolution of the electron temperature with the magnetic field was shown to be a combined effect of suppressing electron resonance heating and enhancing collisional heating while increasing the magnetic field.

Effect of substrate bias on deposition behaviour of charged silicon nanoparticles in ICP-CVD process

The effect of a substrate bias on the deposition behaviour of crystalline silicon films during inductively coupled plasma chemical vapour deposition (ICP-CVD) was analysed by consideration of non-classical crystallization, in which the building block is a nanoparticle rather than an individual atom or molecule. The coexistence of positively and negatively charged nanoparticles in the plasma and their role in Si film deposition are confirmed by applying bias voltages to the substrate, which is sufficiently small as not to affect the plasma potential. The sizes of positively and negatively charged nanoparticles captured on a carbon membrane and imaged using TEM are, respectively, 2.7–5.5 nm and 6–13 nm. The film deposited by positively charged nanoparticles has a typical columnar structure. In contrast, the film deposited by negatively charged nanoparticles has a structure like a powdery compact with the deposition rate about three times higher than that for positively charged nanoparticles. All the films exhibit crystallinity even though the substrate is at room temperature, which is attributed to the deposition of crystalline nanoparticles formed in the plasma. The film deposited by negatively charged nanoparticles has the highest crystalline fraction of 0.84.

Measurements of Electron Energy Probability Functions in inductively coupled plasma with laser Thomson scattering

Electron energy probability functions (EEPFs) having a fine resolution of electron energy were measured in low-pressure inductively coupled plasma with laser Thomson scattering method (LTS) at various plasma conditions (rf powers and gas pressures) and compared with the EEPFs measured by a single Langmuir probe (SLP) at the same experimental conditions. The result of LTS showed that the measured electron density normally increases with the rf power and the gas pressure, and the electron temperature decreased with the rf power and the gas pressure. This result have a good agreement not only with the previous reports qualitatively but also with our SLP measurement result quantitatively [15]. The reasons for the discrepancy between two methods in absolute value might be expected to these facts as following: the probe perturbation effect from the probe holder volume, RF noise, and not sufficient signal level of laser Thomson scattering.

Influence of N2 gas pressure on the chemical bonds of amorphous carbon nitride films

A study on the dependence of the microstructure of CNx films on N2 gas pressure was conducted in an RF magnetron sputtering system. A significant change in microstructure was observed as gas pressure decreased: the concentration of sp2 C=N and hydrogenated bonds decreased, while that of sp3 C–N and sp C≡N bonds increased. This implies that low pressure favours the synthesis of CNx films of good mechanical properties. A further investigation using a Langmuir probe and Monte Carlo collision simulations revealed that the energy of ions bombarding the film increased significantly with decreasing gas pressure. This can lead to changes in hydrogen content and chemical bonds in the growing CNx films.

Density measurement of particles in rf silane plasmas by the multipass laser extinction method

Measurement of the time evolution of the particle number density was investigated in rf silane plasmas by using the multipass laser extinction method. A He–Ne laser beam underwent multiple reflections on one horizontal plane of the plasma. The extinction signal increased in proportion to the beam pass numbers. A 1011cm−3 density of 8nm radius particles was measured at 10s in a 32mTorr and 50W discharge using nine passes. The primary particle density was obtained by comparing the measured particle sizes with the calculated sizes from the light extinction signals and the Brownian free molecule coagulation model.

On anomalous temporal evolution of gas pressure in inductively coupled plasma

The temporal measurement of gas pressure in inductive coupled plasma revealed that there is an interesting anomalous evolution of gas pressure in the early stage of plasma ignition and extinction: a sudden gas pressure change and its relaxation of which time scales are about a few seconds and a few tens of second, respectively, were observed after plasma ignition and extinction. This phenomenon can be understood as a combined result between the neutral heating effect induced by plasma and the pressure relaxation effect for new gas temperature. The temporal measurement of gas temperature by laser Rayleigh scattering and the time dependant calculations for the neutral heating and pressure relaxation are in good agreement with our experimental results. This result and physics behind are expected to provide a new operational perspective of the recent plasma processes of which time is very short, such as a plasma enhanced atomic layer deposition/etching, a soft etch for disposal of residual by-products on wafe...

Electron temperature measurements in plasmas with surface wave absorption and wave cutoff frequency

A method for the measurements of electron temperature in the plasma using cutoff frequency and surface wave absorption frequency is described. The cutoff frequency, which gives directly the plasma density, is obtained from the transmission spectrum measured between two antennas exposed to the plasma. The surface wave absorption frequency, which has the information of the sheath determined by the electron density and the electron temperature, is obtained from the reflection spectrum measured at radiating antenna. The electron temperature is derived from the dispersion equation of the surface wave with the electron density measured from cutoff frequency.

Measurement of electron density using reactance cutoff probe

This paper proposes a new measurement method of electron density using the reactance spectrum of the plasma in the cutoff probe system instead of the transmission spectrum. The highly accurate reactance spectrum of the plasma-cutoff probe system, as expected from previous circuit simulations [Kim et al., Appl. Phys. Lett. 99, 131502 (2011)], was measured using the full two-port error correction and automatic port extension methods of the network analyzer. The electron density can be obtained from the analysis of the measured reactance spectrum, based on circuit modeling. According to the circuit simulation results, the reactance cutoff probe can measure the electron density more precisely than the previous cutoff probe at low densities or at higher pressure. The obtained results for the electron density are presented and discussed for a wide range of experimental conditions, and this method is compared with previous methods (a cutoff probe using the transmission spectrum and a single Langmuir probe).