Vladimir Volynets

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...

Experimental study of spatial nonuniformities in 100MHz capacitively coupled plasma using optical probe

Plasma spatial nonuniformities in the 100MHz rf driven capacitively coupled reactor used for reactive ion etching of 300mm substrates were experimentally studied using a linear scanning optical emission spectroscopy probe. Radial profiles of plasma emission intensity were measured both in argon and fluorocarbon-containing gas mixtures in the pressure interval of 10–80mTorr and the rf power range of 500–1250W. It was demonstrated that the plasma emission profiles strongly depend on the working gas composition and pressure. The profiles have a bell-like shape at pressures about 10mTorr for all gases. As the pressure increases, the profile shape becomes more complex with the central and peripheral peaks, and the amplitudes of the peaks strongly depend on the working gas composition. It is suggested that the emission profiles show plasma spatial nonuniformities that can influence the etching rate profiles obtained with such systems. According to the existing theoretical models, the most probable reasons for t...

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.

Spatial variation of plasma parameters and ion acceleration in an inductive plasma system

Plasma parameters of inductively coupled plasma system with an annular plasma source have been studied experimentally. At low pressures (about 1mTorr), electron temperature inside the plasma source is rather high (8–13eV) and is much greater than in the diffusion (main) chamber (4–5eV). The plasma potential inside the source is also much higher than in the main chamber. There is a rapid drop of the electron temperature and plasma potential at the boundary between the plasma source and the main chamber. The drop of the plasma potential at the boundary (about 20V) means the existence of a strong axial electric field, which retards the electrons inside the plasma source and accelerates the ions from the source into the main chamber. Measurements of ion energy distributions in the main chamber volume reveal the existence of ions with kinetic energies about 15eV.

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.

Insights to scaling remote plasma sources sustained in NF3 mixtures

Remote plasma sources (RPSs) are being developed for low damage materials processing during semiconductor fabrication. Plasmas sustained in NF3 are often used as a source of F atoms. NF3 containing gas mixtures such as NF3/O2 and NF3/H2 provide additional opportunities to produce and control desirable reactive species such as F and NO. In this paper, results from computational investigations of RPS sustained in capacitively coupled plasmas are discussed using zero-dimensional global and two-dimensional reactor scale models. A comprehensive reaction mechanism for plasmas sustained in Ar/NF3/O2 was developed using electron impact cross sections for NF2 and NF calculated by ab initio molecular R-matrix methods. For validation of the reaction mechanism, results from the simulations were compared with optical emission spectroscopy measurements of radical densities. Dissociative attachment and dissociative excitation of NFx are the major sources of F radicals. The exothermicity from these Franck–Condon dissocia...

Ponderomotive effects in an electromagnetic accelerator

An inductive coupled plasma (ICP) source of a new type for dry etching lias been developed. It is driven by a planar inductive coil, which is placed at the top of the channel formed by two coaxial dielectric cylinders. At low pressure, the radial component of the radiofrequency (RF) magnetic field causes a ponderomotive force acting on the electrons directed towards the bottom of the channel. Charge separation gives rise to an ambipolar electric field, which retards electrons and accelerates ions. The source represents an electrodeless electromagnetic accelerator (KMA) and can create an axially directed flux of ions. EMA has been modeled as an axisymmetric ICP discharge in argon gas based on experimental data of the plasma density and electron temperature profile. The magnetic field and RF current densities obtained have been used for calculation of the Lorentz force acting on the electrons and ambipolar plasma potential. Simulations of electron trajectories show that electrons are trapped in the EMA channel and make a number of oscillations before leaving the channel. The ponderomotive potential produces acceleration of the ions in the channel up to 13 -16 eV.

Downstream etching of silicon nitride using continuous-wave and pulsed remote plasma sources sustained in Ar/NF3/O2 mixtures

Remote plasma sources (RPSs) are being investigated to produce fluxes of radicals for low damage material processing. In this computational investigation, the properties of a RPS etching system are discussed where an Ar/NF3/O2 gas mixture is flowed through an inductively coupled plasma source into a downstream chamber containing a silicon nitride coated wafer. The plasma is largely confined in the RPS due to the highly attaching NFx (x = 1–3) and an isolating showerhead although a weak ion-ion plasma maintained by [NO+] ≈ [F−] leaks into the downstream chamber. The etching of silicon nitride proceeds through iterative removal of Si and N subsites by isotropic thermal neutrals. When the fluxes to the wafer are rich in fluorine radicals, the etch rate is limited by the availability of NO molecules and N atoms which remove N subsites. As power deposition increases with continuous-wave excitation, the etch rate increases almost linearly with the increasing fluxes of NO and N atoms, as production of NO through...