Capacitively Coupled Radio Frequency Research Articles

Formation kinetics and control of dust particles in capacitively-coupled reactive plasmas

Formation kinetics and behavior of dust particles below about 10 nm in size, referred to as clusters, in silane capacitively-coupled RF plasmas are studied using double pulse discharge and photon-counting laser-light-scattering methods. Even under so-called device quality conditions, clusters of ∼1011 cm-3 high compared to a plasma ion density of ∼10-9 cm3 are found at t ∼ 50 ms after the discharge initiation. Clusters begin to be composed of two size groups at t ∼ 10 ms. The ones in the small size group have an almost constant average size of ∼0.5 nm during the discharge period, while the ones in the large size group grow at a rate of ∼4 nm/s. This result indicates that the large clusters are nucleated by the small ones containing 3–4 Si atoms.Various methods for suppressing cluster growth have also been studied using two in situ cluster detection methods. Since species contributing to the initial growth of clusters are principally produced in the radical production region around the plasma/sheath boundary near the rf electrode, the pulse discharge modulation which has the discharge-off period in one modulation cycle longer than the diffusion time of clusters through the radical production region is effective in reducing the growth of clusters. Thermophoretic force due to heating of the grounded electrode drives neutral clusters above a few nm in size toward the cool RF electrode which is at room temperature. Periodical pulse discharge modulation is much more effective in reducing the cluster density when it is combined with grounded electrode heating. Hydrogen dilution of a high H2/SiH4 concentration ratio above about 5 is useful for suppressing cluster growth especially in the radical production region near the RF electrode.

Negative ions and the role of metastable molecules in a capacitivelycoupled radiofrequency excited discharge in oxygen

Axial distributions of negative oxygen ions in an asymmetric,capacitively coupled oxygen radiofrequency discharge (of the gaseouselectronics conference reference cell type) are investigated. The O- ion densities are measured by detecting the electrons released afterphoto-detachment with a Langmuir probe.At small power and a pressure of approximately 10 Pa the axialdistributions of both the O- ions and the electrons are flat. Athigher power (characterized by voltage amplitudes in excess of 200 V) bothquantities exhibit maxima in the central region between the electrodes.These maxima are displaced with increasing pressure (>50 Pa) towards the driven electrode. The absolute concentration of O- isinsensitive to admixtures of argon up to 50%. This can be understood, ifone assumes that the dominant loss channel for the negative ions involvesmetastable O2(a 1Δg) molecules. This assumption isconfirmed by measurements taken with the discharge operating in a pulsedmode.

Ultraviolet cavity ring-down spectroscopy of free radicals in etching plasmas

Many reactive species of interest in technological plasmas absorb light in the UV spectral region (200–300 nm). Measurement of these weak absorbances (typically 10 −2–10 −4 for a single pass) allows us to determine their absolute concentration. Low-resolution absorption spectra of these systems have previously been obtained by broad-band absorption spectroscopy. Here we present spectra obtained using laser cavity ring-down spectroscopy, which has much higher spectral resolution, and potentially higher sensitivity. Spectra were obtained for CF, CF 2, AlF and SiF 2 radicals in capacitively-coupled radio-frequency plasmas in fluorocarbon gases. This technique offers the possibility of real-time (1 s) absolute concentration measurements during wafer processing.

Hybrid Modeling of a Capacitively Coupled Radio Frequency Glow Discharge in Argon: Combined Monte Carlo and Fluid Model

A hybrid model has been developed for a capacitively coupled rf glow discharge in argon, employed as a spectroscopic source in the field of analytical chemistry. The cell is a rather small cylinder with a very small rf-powered electrode (only 5 mm in diameter). The typical working conditions applied for analytical spectroscopy are a gas pressure of 6 Torr and incoming power of 10 W. The hybrid model consists of a Monte Carlo model for the electrons and a fluid model for the electrons and argon ions. The latter model also contains Poisson's equation, to obtain a self-consistent electric-field distribution. The input values for the model are the gas pressure, the discharge power, the cell geometry and the collision cross sections. The typical calculated results include the rf and dc bias voltage, the electrical current at the rf electrode, the potential distribution, the density of argon ions and electrons, the electron energy-distribution function and information about the collision processes of the electrons. These results are presented throughout the discharge cell and as a function of time in the rf cycle. Moreover, we have investigated how many rf cycles have to be followed with the Monte Carlo model before a periodic steady state is reached.

容量結合型高周波プラズマ中の電子エネルギー分布関数とイオン衝撃2次電子の観測

容量結合型高周波プラズマ中の電子エネルギー分布関数とイオン衝撃2次電子の観測

A Novel Sustaining Mechanism in Capacitively Coupled Radio Frequency Plasma in Oxygen

A Novel Sustaining Mechanism in Capacitively Coupled Radio Frequency Plasma in Oxygen

容量結合型RF放電の絶縁破壊機構

容量結合型RF放電の絶縁破壊機構

容量結合型RF放電プラズマの軸方向電子密度分布

容量結合型RF放電プラズマの軸方向電子密度分布

Mechanical stability of DLC films on metallic substrates: Part I—Film structure and residual stress levels

Hydrogenated diamond-like carbon (DLC) films have been deposited onto aluminium, titanium and silicon substrates using a 13.56 MHz capacitively-coupled RF glow discharge in a methane atmosphere. All of the DLC films, which were prepared with a negative bias voltage in the range 40 V to 345 V and a gas pressure in the range 1 Pa to 40 Pa. showed strong sp★-CH, FTIR absorbance peaks at 2900 cm★ and a broad Raman peak at 1540 cm★. Deposition temperatures, which were measured using irreversible self-stick thermax, varied from 25°C to 182°C. Stress levels in the films were measured by monitoring the curvature changes of thin (125 μm) Ti foil after depositing thick (several μm) DLC films, using an AI bonding layer. This intrinsic (deposition) stress was compressive and varied from −0.3 GPa to −2.0 GPa. It increased initially with the energy of the bombarding ions, as implantation became more pronounced, reached a maximum and then decreased, as a consequence of thermally-activated structural relaxation. The experimental stress data agree well with predictions from a model proposed by Davis [C.A. Davis, A simple model for the formation of compressive stress in thin film by ion bombardment. Thin Solid Films. 226 (1993) 30–34].

Behavior of Electrons and Negative Ions in a Capacitively-Coupled Radio-Frequency NF 3/Ar Plasma

The behaviors of electrons and negative ions in a low-pressure (100 mTorr) capacitively-coupled radio-frequency (13.56 MHz) NF3/Ar plasma have been studied at a low-power level (2–10 W) using a laser photodetachment technique combined with a microwave cavity resonance method for determining electron density. The wavelength dependent photodetachment measurement indicated that F- is the predominant negative ion species in the plasma. The negative ion density was higher than the electron density by a factor of ∼50 at a NF3 mixing ratio r as low as 1% and the negative-ion/electron density ratio further increased with increasing r mainly because of the decrease in the electron density. The overall change in the negative ion density in the studied range of 1%<r<40% was relatively small (a factor of ∼2). For small r (<∼10%), the negative ion density increased with decreasing r; the change in the electron-attachment and ion-ion recombination rate constants with varying r was investigated to explain the phenomenon.

Preparation of Stable F-Doped SiO 2 Thin Films from Si(NCO) 4/SiF 4/O 2 Gas Mixtures Using a Conventional Capacitively Coupled RF Plasma Source

Stable F-doped SiO2 (SiOF) films have been deposited using a simple conventional capacitively coupled RF plasma-enhanced chemical vapor deposition method using H-free tetraisocyanatesilane (Si(NCO)4: TICS) diluted with oxygen, and tetrafluorosilane (SiF4) having Si–F bonds in itself. The SiO2 films deposited only with TICS have poor water resistivity, which originates in the inclusion of the SiNCO structure in the films. This property has been improved by mixing O2 with the source gases. Although F atoms at the top surface of films desorbed upon air exposure, SiOF films deposited with TICS, SiF4 and O2 exhibit excellent water resistivity. A film with F concentration of 6 at.% exhibited a dielectric constant of 3.3, a resistivity of 3.6×1015 Ωcm and a break-down electric field of 7.7 MV/cm. These values are comparable to or better than the reported values for films prepared using tetraethylorthosilicate. These results indicate that the TICS, SiF4 and O2 system can be used to deposit high quality SiOF films using a much simpler method than those requiring complex high density plasma sources.

Two-Dimensional Fluid Simulation of Capacitively Coupled RF Electronegative Plasmas

A two-dimensional self-consistent fluid simulation of capacitively coupled rf glow discharges of electronegative plasma with a cylindrically symmetric parallel plate electrode is presented. The model equations include continuity equations, a Poisson equation, and an electron energy balance equation. The two-dimensional distributions of charged particle densities, electric potential, electron temperature, and ionization rate are calculated. The effects of the applied rf voltage, the driver frequency, and the gas pressure on the discharge characteristics are investigated in detail.

Pressure heating of electrons in capacitively coupled rf discharges.

Collisionless heating in low-pressure capacitively coupled rf discharges is usually attributed to a stochastic interaction between electrons and the oscillating sheath. We show that this explanation is not complete---there is a powerful heating mechanism associated with pressure effects that arise during the expansion and contraction of sheaths.

Dual-mode radio frequency/microwave plasma deposition of amorphous silicon oxide thin films

A new dual-plasma (surface wave-coupled microwave and capacitively-coupled radio frequency) plasma enhanced chemical vapor deposition reactor for high growth rate deposition of amorphous insulating alloys has been developed. A high degree of flexibility for thin film material synthesis is expected, because the energy of the ion bombardment can be controlled independently of the microwave plasma chemistry. In situ spectroscopic ellipsometry is used for the optimization of the dual-mode plasma deposition of hydrogenated silicon oxides a-SiO x :H (with 0 ≦ x ≦ 2) providing monitoring of the index of refraction and deposition rate. A new procedure for the real-time calculation of both parameters is reproted. The growth rate of nearly stoichiometric oxides increases as a function of the oxygen flow rate with a maximum value of 33 Å s −1 using a 315 W microwave power.

The effects of a small transverse magnetic field upon a capacitively coupled RF discharge

A capacitively-coupled RF argon discharge at a pressure of 10 mTorr with a plate separation of 7.5 cm has been studied both experimentally and using a one-dimensional particle in cell simulation with Monte Carlo collisions. A magnetic field of 0 to 60 G is applied in the direction parallel to the capacitor plates. In the simulation it was found that as the magnetic field was increased such that the electron cyclotron orbit radius of the hot electrons became smaller than of the order of the discharge length, the electron heating in the bulk of the discharge increased. The dominant electron heating mechanism was observed to change from a stochastic sheath to a bulk ohmic electron heating mode, with a variation of field from a to 10 G. This was accompanied by a drop in the plasma density at small magnetic fields, which was also observed experimentally. At higher magnetic fields the plasma density was found to increase, A detailed discussion of the simulation results is presented drawing comparisons with the experimental results, with which there is good agreement, and a simple magnetohydrodynamic model for the bulk heating. >

Charged particle densities and kinetics in a radio-frequency SF6 plasma

Electron, negative ion, and positive ion densities in a capacitively-coupled radio-frequency (rf, 13.56 MHz) SF6 plasma have been investigated as functions of the pressure (30–700 mTorr) and rf power. The decay of the charged particle densities in the afterglow has also been studied to obtain information about their kinetics. The electron density was determined by using a microwave cavity resonance technique. Negative ions were detected by measuring the density of photodetached electrons produced by pulsed laser irradiation of the plasma. The positive ion density was obtained from Langmuir probe measurements. At a rf power of 0.13 W/cm2 and at low pressures (≲100 mTorr) the positive ion density, which is virtually equal to the negative ion density, is found to be larger than the electron density by a factor of a few hundred; the ion/electron density ratio increases with increasing pressure to reach a value of a few thousand at high pressures. Wavelength-dependent photodetachment measurements indicate that the dominant contribution to the photodetachment signal at 266 nm comes from F−, but F− is a minor negative-ion species with respect to the density; that is, the photodetachment efficiency for the dominant negative ion species (supposed to be SF−5) is low. The recombination rate constant for F− (supposedly with SF+5) is suggested to be an order of magnitude larger than that for the dominant ion species, the latter being estimated to be slightly smaller than 10−7 cm3 s−1.

Pressure dependences of electron energy distribution and power dissipation in symmetrical RF helium discharges

The electron energy distribution function (EEDF) is measured with a Langmuir probe in a symmetrically capacitively-coupled RF (13.56 MHz) helium discharge over a range of gas pressures from 0.1 to 1.0 Torr while keeping the discharge current constant at 100 mA. The bulk electrons are Maxwellian over this range, while the average electron energy decreases with increasing pressure, together with an increase in electron density. The power dissipation calculated from the EEDF and the discharge current-voltage relation agrees with that measured.

Optimization of a Dual-Mode RF / Microwave Plasma for Amorphous thin film Deposition

ABSTRACTA new dual-plasma (surface wave-coupled microwave and capacitively-coupled radiofrequency) PECVD reactor for high growth rate of Amorphous insulating alloys is being developped. A high flexibility for thin film materials synthesis is expected, because the energy of the ion bombardment can be monitored independently from the microwave plasma chemistry. In situ diagnostics (Optical EMission Spectroscopy and Spectroscopie Ellipsometry) are used for the optimization of the dual-Mode plasma deposition of hydrogenated Amorphous silicon a-Si:H and silicon oxides a-SiOx:H (with 0 ≤ × ≤ 2). The growth of stoichiometric oxide at 3.3 nm / s has been achieved.

Theory of the rf sheath in the regime between the ion and electron plasma frequencies

The collisionless space-charge sheath of a capacitivelyc oupled rf discharge is investigated in the frequency regime ωpi ≪ω≪ωpe . Assuming Boltzmann distributed electrons and starting from an existing charge exchange model of the presheath a self-consistent analysis is presented.

Detailed Study of Ion Bombardment in Rf Glow Discharge Deposition Systems: The Role of Helium Dilution

ABSTRACTWe present a detailed study of the variables (reactor geometry, gas pressure, rf power and silane dilution) which control the flux and energy of the ions impinging on the substrate in capacitively-coupled rf glow discharge systems. The ion flux and ion energy, measured with an electrostatic energy analyzer, were found to be largely dependent on the reactor geometry, which was quantified by the ratio of the area of the grounded surfaces Sg to the area of the rf electrode Sc. Special attention was paid to the effects of the dilution of silane in hydrogen, helium and argon. Helium and hydrogen dilution were found the most effective means to increase ion bombardment while argon dilution has little effect on the ion energy distribution. Furthermore, it is likely that ion bombardment at moderate energy (Eion &lt; 70 eV) does not induce any serious degradation of the electronic properties of a-Si:H films.