Dougyong Sung

Experimental study of plasma non-uniformities and the effect of phase-shift control in a very high frequency capacitive discharge

Plasma spatial non-uniformities were studied experimentally in a very high frequency (100 MHz) capacitive triode-type reactor used for etching of 300 mm wafers. It has been shown that in the traditional mode of operation there is considerable plasma non-uniformity due to the electromagnetic effects, namely at a low power, the plasma density profile is determined by the standing-wave effect, while at a high power the skin effect dominates. The influence of phase-shift control on plasma uniformity was examined. Phase-shift control means applying to the top and the bottom electrodes very high frequency voltages with a controlled phase shift between them. The experiments were carried out in process (C4F8/O2/Ar) plasma in a wide range of pressures and powers. It has been shown that the phase-shift control can considerably improve the plasma uniformity under a wide range of experimental conditions.

Effect on plasma and etch-rate uniformity of controlled phase shift between rf voltages applied to powered electrodes in a triode capacitively coupled plasma reactor

The influence of the phase shift between rf voltages applied to the powered electrodes on plasma parameters and etch characteristics was studied in a very high-frequency (VHF) capacitively coupled plasma (CCP) triode reactor. rf voltages at 100MHz were simultaneously applied to the top and bottom electrodes having a controlled phase shift between them, which could be varied between 0° and 360°. Several plasma and process characteristics were measured as a function of the phase shift: (i) radial profiles of plasma-emission intensity, (ii) line-of-sight averaged plasma-emission intensity, and (iii) radial profiles of blanket SiO2 etching rate over a 300mm wafer. Radial profiles of plasma emission were obtained using the scanning optical probe. It has been shown that all the measured characteristics strongly depend on the phase shift: (i) plasma-emission intensity is minimal at phase shift equal to 0° and maximal at 180° for all radial positions, while the emission radial profile changes from bell-shaped dis...

Plasma uniformity and phase-controlled etching in a very high frequency capacitive discharge

The influence of controlled phase shift between very high frequency (100MHz) voltages applied to the powered electrodes on the plasma uniformity and etch rate was studied in a capacitive triode-type reactor. Radial profiles of plasma optical emission were measured as a function of the phase shift in process (C4F8∕O2∕Ar) plasma with the low frequency bias power both turned off and on. Radial profiles of KrF photoresist etch rate over a 300mm wafer were obtained in the same conditions (with the bias power turned on). Besides, plasma density at the wafer center and edge was measured versus the phase shift in pure Ar plasma. It occurred that all measured characteristics strongly depend on the phase shift and correlate with each other. It has been shown that the phase-shift control can considerably improve both the plasma and etch-rate uniformity in very high-frequency capacitive reactors.

Study of fluorocarbon plasma in 60 and 100MHz capacitively coupled discharges using mass spectrometry

The signals of positive ions and radicals formed in the fluorocarbon plasma of the capacitively coupled plasma reactor were measured using a quadrupole mass spectrometry and optical emission actinometry. The plasma was produced at 60 and 100MHz frequencies for the same reactor configuration and gas mixtures. Experiments were performed at 25mTorr with a SiO2 wafer on the grounded electrode. Mass spectra of ions were measured in C4F8∕O2∕Ar and C4F6∕O2∕Ar gas mixtures at 500–1500W generator powers. For 60 and 100MHz discharges production of fluorocarbon ions and radicals is discussed. It was found that the production of heavy species increases with frequency. The high mass signals such as C3F3+, C2F4+, C2F5+, C3F5+, C4F7+ decrease when CHF3 is added to the gas mixture. However, the signals of CFx+ (x=1,2,3) do not change significantly. These results are compared to the results of polymer film deposition on the wafer. It was suggested to control the polymerization film formation by adding small amount of CHF3...

Frequency and electrode shape effects on etch rate uniformity in a dual-frequency capacitive reactor

SiO2 was etched on 300 mm wafers in a dual-frequency capacitive plasma reactor to study etch rate nonuniformity as a function of driving frequency and power. It is shown that the etch rate profile shape varies significantly with the driving frequency. It also is shown that for different driving frequencies, the behavior of etch rate profile shape with the power is quite different, namely: (i) for lower frequency (27 MHz), the shape almost does not change with the power; (ii) for higher frequency (100 MHz), the shape considerably varies with the power. These results clearly indicate that the main reason for the etch rate nonuniformity in high-frequency capacitive reactors is the plasma nonuniformity caused by electromagnetic (standing wave and skin) effects. Using a specially shaped top electrode rather than the traditional flat one is shown to considerably improve the etch rate uniformity.

Thermal adsorption-enhanced atomic layer etching of Si3N4

Atomic layer etching (ALE) is an alternative method for nanopatterning in which atomic layers of material are removed by sequential self-limiting surface reactions. In this study, the authors report a new cyclic process for atomic layer etching of Si3N4 films achieved by alternating exposure steps of CH3F gas adsorption and Ar+ bombardment. Self-limiting etching characteristics of the ALE process are demonstrated as a function of both CH3F etchant flow rate and CH3F exposure time. From comparative studies on the amount of Si3N4 etched using the ALE mode versus pure Ar+ ion sputtering, it is found that the ALE process operates with an ALE synergy factor of ∼67% and also removes Si3N4 with better uniformity due to cooperative interactions between the self-limited CH3F chemisorption and the Ar+ ion sputtering. Based on both the chemical bonding changes following the CH3F etchant exposure and reaction product analyses during the Ar+ plasma step, possible etch reaction steps for the ALE Si3N4 process are proposed.Atomic layer etching (ALE) is an alternative method for nanopatterning in which atomic layers of material are removed by sequential self-limiting surface reactions. In this study, the authors report a new cyclic process for atomic layer etching of Si3N4 films achieved by alternating exposure steps of CH3F gas adsorption and Ar+ bombardment. Self-limiting etching characteristics of the ALE process are demonstrated as a function of both CH3F etchant flow rate and CH3F exposure time. From comparative studies on the amount of Si3N4 etched using the ALE mode versus pure Ar+ ion sputtering, it is found that the ALE process operates with an ALE synergy factor of ∼67% and also removes Si3N4 with better uniformity due to cooperative interactions between the self-limited CH3F chemisorption and the Ar+ ion sputtering. Based on both the chemical bonding changes following the CH3F etchant exp...

High resolution electron energy loss spectroscopy study of Fomblin Z-tetraol thin filmsa)

High resolution electron energy loss spectroscopy has been used to obtain vibrational spectra of Fomblin Z-tetraol lubricant films on a commercial magnetic hard disk. The energy loss intensities of the ν(CF2) stretching mode are roughly independent of scattering angle up to angles of Δθ<14° indicating that they are excited by impact scattering. As a consequence there is little information that can be gleaned from the spectra about molecular orientation on the surface. A negative ion resonance enhances the energy loss cross section of the ν(CF2) stretching mode at the impact energy of EI=4eV. It is possible that this resonance is associated with the known sensitivity of fluorocarbons to electron induced dissociation. Annealing the disk sample to T=700K causes a dramatic decrease in the intensity of C–F stretching modes and an increase of the loss features due to C–H stretching. This indicates that the Fomblin Z-tetraol has decomposed and is exposing the a‐CHx overcoat on the magnetic media surface.