Sang-Hun Seo

On the heating mode transition in high-frequency inductively coupled argon discharge

In high-frequency inductively coupled argon discharges with a planar-type coil the phenomena of discharge mode transition (E–H mode transition) are investigated. Experimental observation is done at the low pressure of 10 mTorr and the high frequency of 19 MHz over a range of rf power, 40–525 W. First of all, the discharge mode transition is observed through a change of luminous intensity. This transition is found to occur at the relatively high power of about 280 W compared with the mode transition in a 6.5 MHz discharge. Also, some distinctive features are compared to low-frequency discharges during this transition. In particular, during the E–H mode transition the apparent changes of plasma potential are observed and the sudden variation of plasma potential is proposed as an important factor that indicates the change of power coupling. The features of the discharge mode transition in high-frequency discharge are discussed by considering the power coupling at each mode by measurements of the electron ene...

The deposition of SiOF film with low dielectric constant in a helicon plasma source

SiOF films deposited by a helicon wave plasma chemical vapor deposition method has been characterized using Fourier transform infrared spectroscopy and ellipsometry. High density plasma of ≳1012 cm−3 can be obtained on a substrate at low pressure (<10 mTorr) with rf power ≳400 W with a helicon plasma source. A gas mixture of SiF4, O2, and Ar was used to deposit SiOF films on 5 in. Si(100) wafers not intentionally heated. Optical emission spectroscopy was used to study the relation between the relative densities of the radicals and the deposition mechanism. It was found that the addition of Ar gas to the SiF4/O2 mixture greatly increased the F concentration in the SiOF film. Discharge conditions such as gas composition, sheath potential, and the relative densities of the radicals affect the properties of the film. The dielectric constant of the SiOF film deposited using the helicon plasma source was 3.1, a value lower than that of the oxide film by other methods.

Electron energy distribution function and plasma potential in a planar inductive argon discharge without electrostatic screen

Studies on electron heating are done during the power coupling change in the discharge mode transition (E–H mode transition) in a planar inductive argon discharge without electrostatic screen (Faraday shield). The electron energy distribution function (EEDF) evolution is measured by the alternating current superposition method with a radio frequency (rf) compensated Langmuir probe. The trend of its integrals, electron density and effective electron temperature, and especially the plasma potential against rf power are presented. It is demonstrated that the plasma potential is governed primarily by the high-energy electron tail in a plasma with bi-Maxwellian EEDF. The interdependence of the EEDF and the plasma potential is discussed. The experimental results show that the plasma potential against rf power reflects a change in the relative contribution of capacitive power coupling to electron heating.

Review of heating mechanism in inductively coupled plasma

Abstract Electron heating is fundamental and essential to sustain plasma in an inductively coupled plasma as well as other plasmas. Ohmic heating randomized by collisions, especially electron–neutral collisions, is dominant at high pressure (ν en ≫ω). Stochastic heating (collisionless heating) is caused by collisions with inhomogeneous fields in inductive mode or moving sheath in the capacitive mode of inductively coupled plasma (ICP). These electron-heating mechanisms in ICP are classified in this paper and recent experimental and theoretical results focusing on the electron energy distribution function (EEDF) and rf fields in the collisionless regime are presented. We suggest that further issues need to be resolved to better understand the main heating process in low-pressure ICP operation.

Measurements of electron energy distribution functions and electron transport in the downstream region of an unbalanced dc magnetron discharge

In this study, electron energy distribution functions (EEDFs) are measured using a Langmuir probe in conjunction with the ac superposition method in the downstream region of a planar and unbalanced magnetron argon discharge and the effects of an anode sheath boundary on the discharge characteristics are investigated. The potential of the anode sheath can be controlled by applying a dc voltage to the substrate, and the nonlinear behaviour of the plasma potential with respect to the dc substrate voltage causes the distinctive evolution of the potential of the anode sheath. It is found that when the potential of the anode sheath reaches a specific value, which is related to the threshold energies of argon for the inelastic collisions, an outstanding EEDF transition from a bi-Maxwellian distribution to a single Maxwellian distribution occurs. We introduce the concept of the total electron bounce frequency as an indicator of how the electron collisions such as the electron–electron collision and the inelastic collisions affect the EEDF features as the potential of the anode sheath changes. This result provides the decisive clue to explaining the appearance of the bi-Maxwellian distribution in magnetron discharges. The results of the spatially resolved measurements of EEDF and plasma characteristics are also presented. From these results, we will discuss the electron transport in the downstream region in detail.

Effect of duty cycle on plasma parameters in the pulsed dc magnetron argon discharge

The time-resolved probe measurements of the plasma parameters and the electron energy distribution function are carried out in a unipolar pulsed dc magnetron argon discharge. The cathode target is driven by the 20kHz midfrequency unipolar dc pulses at three operating modes, such as constant voltage, constant power, and constant current with the duty cycles ranging from 10% to 90%. It is observed that as the duty cycle is reduced, the electron temperature averaged during the pulse-on period rapidly increases irrespective of the operating mode although the average electron density strongly depends on the operating mode. The comparison of the measured electron energy distribution functions shows that the electron heating during the pulse-on period becomes efficient in the pulse operation with short duty cycle, which is closely related to the deep penetration of the high-voltage sheath into the bulk during the pulse-on period.

Evolution of the electron energy distribution function in a planar inductive argon discharge

The evolution of the electron energy distribution function (EEDF) over a pressure range of 5–100 mTorr is investigated in a planar inductive argon discharge. It is found that the EEDF, which appears to be a bi-Maxwellian distribution with a two-temperature structure at low pressures, evolves into a Druyvesteyn-like distribution as the pressure increases. The electron energy diffusion coefficient, which describes electron heating, is calculated under the same discharge conditions using discharge parameters and numerical results show that the heating of low-energy electrons is enhanced as the pressure increases resulting in a transition of the EEDF to a Druyvesteyn distribution.

Experimental investigation of plasma dynamics in dc and short-pulse magnetron discharges

The spatiotemporal evolution of the electron energy distribution function (EEDF) and of plasma parameters such as the electron density, the electron temperature and the plasma and floating potentials has been investigated using spatially and temporally resolved single Langmuir probe measurements in dc and mid-frequency, short-pulse magnetron discharges with a repetition frequency of 10 kHz and a duty cycle of 10%. In the pulsed discharge of the short duty cycle, a peak electron temperature higher than 10 eV was observed near the cathode fall region during the early phase of the pulse-on, which is about three times higher than the steady-state value of the electron temperature in the dc discharge. The temporal evolution of the measured EEDFs showed the initial efficient electron heating during the early phase of the pulse-on and the subsequent relaxation of electron energy by the inelastic collisions and the diffusive loss. The high-energy electrons generated during the pulse-on phase diffused the downstream region toward the grounded substrate, resulting in a bi-Maxwellian EEDF consisting of the background low-energy electrons and the high-energy electrons. The results of the spatially and temporally resolved probe measurements will be presented and the enhanced efficiency of the electron heating in the short-pulse discharge will be explained on the basis of the global model of a pulsed discharge.

A Study on Low Dielectric Material Deposition Using a Helicon Plasma Source

Characteristics of SiOF films deposited by a helicon plasma source have been investigated using Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and ellipsometry. High density Ar plasma of >10 12 cm -3 was obtained on a substrate at low pressure ( 400 W using a helicon plasma source. The effect of the RF power, the magnetic field strength, and the pressure on the helicon wave for high density plasma has been studied. A gas mixture of SiF 4 , O 2 , and Ar was used to deposit SiOF film on 5 in. (100) Si wafers not intentionally heated. Optical emission spectroscopy was used to study the relation between the relative densities of the radicals and the deposition mechanism. The effects of the RF power, the gas composition, and the Ar addition to the SiF 4 /O 2 mixture on the plasma-phase composition and on the properties of the film, have been studied. Discharge conditions such as gas composition, sheath potential, and relative densities of the radicals affect the properties of the film. The dielectric constant of the SiOF film deposited using the helicon plasma source was 3.1, a value lower than that of the oxide films obtained using other methods.

Electron transport in the downstream region of planar unbalanced magnetron discharge

In this study, we will investigate the electron transport in the downstream region of a planar and unbalanced (type II) magnetron discharge. The effects of the anode sheath boundary and diverging magnetic field on the electron kinetics such as the electron loss mechanism at plasma-sheath boundary and the electron distribution function will be examined through the probe measurements. The spatially resolved probe measurements reveal the existence of an electron drift from the cathode fall region to the downstream region. It is found that this drift is caused by the axial gradient of magnetic field (the magnetic mirror force) and then derives an electron current to the grounded substrate on which the potential of the sheath is very low; so the current balance between the cathode and anode currents is kept. The experimental results show that the electron transport in the downstream region is not governed by the classical diffusion (mobility and diffusion dominated) but is dominated by the modified diffusion i...