Inductively Coupled Plasma Source Research Articles

Inductively coupled plasmas: Optimizing the inductive-coupling efficiency for large-area source design

An inductively coupled plasma (ICP) source enabling high-density plasma generation was developed for large area processing. Technological difficulties related to the scaling up of the coil antenna, dielectric vacuum window, and gas distribution have been addressed. The proposed solution consists in using a magnetic core to concentrate the magnetic field produced by the antenna. Both are placed within the plasma chamber, and the gas injection is done through the magnetic pole. A 75×72-cm2 plasma source has been designed based on this solution. First, the electrical operation and coil geometries were optimized. The results show that the use of a low excitation frequency (2MHz) increases the electrical efficiency of the magnetic core, enabling a higher plasma-density generation than at the classical radio frequency of 13.56MHz. The antenna configuration providing the better uniformity is composed of three loops connected in parallel. Some tuning inductances in series with each loop were added to balance the rf power, i.e., the plasma density over the reactor area. Deviation from plasma uniformities better than 12% over 60×60cm2 were achieved. Preliminary SiO2 etching experiments with CF4 gas show that the etching uniformity deviation reaches 7% over 60×60cm2 with etching rates larger than 150nm∕min. These results are very promising and open the way to the successful scale-up of ICP sources to large areas.

Development of a Dual Inductively Coupled Plasma Source for Direct and Remote Plasma Generation in a Reactor

A dual inductively coupled plasma (ICP) system consists of a remote ICP reactor with small volume and a main ICP reactor with a substrate. Two ICP antennas were connected in parallel and a variable capacitor (Cvar) was installed in series at the end of the main ICP antenna. By adjusting the capacitance of the variable capacitor, the plasma densities in the remote region and the main region are controlled. For the remote region, the plasma was considerably changed such that it had high density and the electron temperature was higher than that in the main region because of its small volume. As such, reactive species in the remote region appeared to be effectively generated. The dual ICP system was applied to Si etching. It was observed that Si etch rate increased by 20% as the plasma density in the remote region increased, even though the plasma density in the main region decreased. This might be understood by considering the role of the remote ICP as a radical generator.

Similarity analysis for the high-pressure inductively coupled plasma source

It is well known that the optimal operating parameters of an inductively coupled plasma (ICP) torch strongly depend upon its dimensions. To understand this relationship better, we derive a dimensionless form of the equations governing the behaviour of high-pressure ICPs. The requirement of similarity then naturally leads to expressions for the operating parameters as a function of the plasma radius. In addition to the well-known scaling law for frequency, surprising results appear for the dependence of the mass flow rate, dissipated power and operating pressure upon the plasma radius. While the obtained laws do not appear to be in good agreement with empirical results in the literature, their correctness is supported by detailed numerical calculations of ICP sources of varying diameters. The approximations of local thermodynamic equilibrium and negligible radiative losses restrict the validity of our results and can be responsible for the disagreement with empirical data. The derived scaling laws are useful for the design of new plasma torches and may provide explanations for the unsteadiness observed in certain existing ICP sources.

Reduction of the electrostatic coupling in a large-area internal inductively coupled plasma source using a multicusp magnetic field

A large area (1020mm×830mm) inductively coupled plasma (ICP) source has been developed using an internal-type linear antenna with permanent magnets forming a multicusp magnetic field. The large rf antenna voltages, which cause the electrostatic coupling between the antenna and the plasma in a large area internal-type linear-antenna ICP source, were decreased significantly by applying the magnetic field near and parallel to the antenna. Through the application of the magnetic field, an approximately 20% higher plasma density, with a value of close to 1.0×1011cm−3 at a rf power of 2000W, and about three times higher photoresist etch rates were observed, while maintaining the plasma nonuniformity at less than 9%.

ZnO synthesis by high vacuum plasma-assisted chemical vapor deposition using dimethylzinc and atomic oxygen

Zinc oxide thin films were produced by high vacuum plasma-assisted chemical vapor deposition (HVP-CVD) from dimethylzinc (DMZn) and atomic oxygen. HVP-CVD is differentiated from conventional remote plasma-enhanced CVD in that the operating pressures of the inductively coupled plasma (ICP) source and the deposition chamber are decoupled. Both DMZn and atomic oxygen effuse into the deposition chamber under near collisionless conditions. The deposition rate was measured as a function of DMZn and atomic oxygen flux on glass and silicon substrates. Optical emission spectroscopy and quadrupole mass spectrometry (QMS) were used to provide real time analysis of the ICP source and the deposition chamber. The deposition rate was found to be first order in DMZn pressure and zero order in atomic oxygen density. All films demonstrated excellent transparency and were preferentially orientated along the c-axis. The deposition chemistry occurs exclusively through surface-mediated reactions, since the collisionless transport environment eliminates gas-phase chemistry. QMS analysis revealed that DMZn was almost completely consumed, and desorption of unreacted methyl radicals was greatly accelerated in the presence of atomic oxygen. Negligible zinc was detected in the gas phase, suggesting that Zn was efficiently consumed on the substrate and walls of the reactor.

Deposition of hard carbon coatings using combined inductively and capacitively coupled plasma sources

A combined inductively coupled plasma (ICP) and capacitively coupled plasma (CCP) source has been presented. Diamond-like carbon (DLC) films can be prepared on BK7 glass substrates using only the CCP source. An efficient cooling of the substrates is very important to obtain DLC films when the ICP source is also supplied. The refractive index n and the thickness of the DLC films on BK7 glass substrates were determined from transmission spectra by a computer program. Without CCP power the deposits on scratched Si samples at the pressures of 0.1–1 mbar in a CH 4/H 2/Ar gas mixture are microcrystalline or nanocrystalline diamonds. The morphology of the diamond films changes to pyramidal-like on scratched and ball-like crystals on unscratched Si samples when a CCP power is applied to use as a bias voltage source. The effect of the ratio of CCP to ICP power on the structure and morphology of diamond films has been investigated. Ball- and pyramidal-like crystals size and sp 3 content increase with increasing ratio of CCP to ICP power.

Comparison of planar inductively coupled plasma etching of GaAs in BCl 3, BCl 3/Ar, and BCl 3/Ne

The characteristics of GaAs etched using planar inductively coupled plasmas (ICP) of BCl 3, BCl 3/Ar and BCl 3/Ne are reported. The etch rates generally increased with ICP source power and reactive ion etching (RIE) chuck power, while decreasing with increase of pressure. Anisotropic etched features were achieved through sidewall passivation, with a selectivity of GaAs etch rate to a photoresist of ∼3:1. BCl 3/Ar plasmas provided a factor of two times higher etch rate than BCl 3/Ne. Etched surface morphology was generally smooth (RMS roughness<2 nm) RMS roughness was 37.5 nm). XPS showed that the etched GaAs surface was chemically clean and residue-free.

Etching of As- and P-based III–V semiconductors in a planar inductively coupled BCl3/Ar plasma

A parametric study of the etch characteristics of Ga-based (GaAs, GaSb, and AlGaAs) and In-based (InGaP, InP, InAs, and InGaAsP) compound semiconductors in BCl3/Ar planar inductively coupled plasmas (ICPs) was performed. The Ga-based materials etched at significantly higher rates, as expected from the higher volatilities of the As, Ga, and Al trichloride, etch products relative to InCl3. The ratio of BCl3 to Ar proved critical in determining the anisotropy of the etching for GaAs and AlGaAs, through its effect on sidewall passivation. The etched features in In-based materials tended to have sloped sidewalls and much rougher surfaces than for GaAs and AlGaAs. The etched surfaces of both AlGaAs and GaAs have comparable root-mean-square (RMS) roughness and similar stoichiometry to their unetched control samples, while the surfaces of In-based materials are degraded by the etching. The practical effect of the Ar addition is found to be the ability to operate the ICP source over a broader range of pressures and to still maintain acceptable etch rates.

Planar Inductively Coupled BCl3 Plasma Etching of III-V Semiconductors

Both Ga-based (GaAs, AlGaAs) and In-based (InGaP, InP, InAs, and InGaAsP) compound semiconductors were etched in a planar inductively coupled plasma (ICP) reactor in pure The Ga-based materials etched at significantly higher rates, as expected from the higher volatilities of their trichloride etch products relative to In contrast to the more common cylindrical geometry ICP sources, the dc self-bias which controls ion energy is not strongly dependent on source power up to ∼400 W while etch rates increase rapidly over this power range. The source tunes easily even at very low powers (<100 W) but operates inefficiently above ∼10 mTorr, with a marked decrease in both emission intensity from the discharge and in resulting etch rates of the compound semiconductors. The etched surfaces of both AlGaAs and GaAs have comparable root-mean-square roughness and similar stoichiometry to the unetched control samples, while the surfaces of In-based materials are degraded by the etching. © 2004 The Electrochemical Society. All rights reserved.

Smooth and vertical-sidewall InP etching using Cl2/N2 inductively coupled plasma

Inductively coupled plasma (ICP) operated in the reactive-ion etching mode is used for mesa etching of InP using Cl2/N2 chemistry with a Ni metal mask. Etch rates of approximately 140 nm/min with very smooth and vertical sidewalls are obtained at a dc bias of 120 V. The effects of temperature, gas flow, chamber pressure, ICP source power, and substrate bias power on etch rate are studied; sidewall profile and surface morphology will be discussed.

Investigation of GaAs Dry Etching in a Planar Inductively Coupled BCl3 Plasma

We investigated dry etching of GaAs in a planar inductively coupled plasma (ICP) reactor with gas chemistry. The process parameters included planar ICP source power, chamber pressure, reactive ion etching (RIE) chuck power, and gas flow rate. The ICP source power was varied from 0 to 500 W. Chamber pressure was changed from 5 to 20 mTorr. RIE chuck power was controlled from 0 to 150 W. The gas flow rate was varied from 10 to 40 sccm. We found that a process condition at 20 sccm 300 W ICP, 100 W RIE, and 7.5 mTorr chamber pressure gave an excellent etch result. The etched GaAs feature showed extremely smooth surface vertical sidewall, relatively fast etch rate (>3000 Å/min) and good selectivity to a photoresist (>3:1). X-ray photoelectron spectroscopy study on the surface of processed GaAs proved a very clean surface of the material after dry etching. We also noticed that our planar ICP source was successfully ignited both with and without RIE chuck power, which was generally not the case with a typical cylindrical ICP source, where assistance of RIE chuck power was required for turning on a plasma and maintaining it. These results indicate that the planar ICP source could be a very versatile tool for advanced dry etching of damage-sensitive compound semiconductors. © 2004 The Electrochemical Society. All rights reserved.

Gas-Phase Reactions of Transition-Metal Ions with Hexafluorobenzene: Room-Temperature Kinetics and Periodicities in Reactivity

An inductively coupled plasma (ICP) selected-ion flow tube tandem mass spectrometer has been employed in a systematic survey of room-temperature reactions of C6F6 with 29 transition-metal ions. The atomic ions were produced at ca. 5500 K in an ICP source and were allowed to decay radiatively and to thermalize by collisions with Ar and He atoms prior to reaction, although for some atomic ions, this quenching may be incomplete. Rate coefficients and product distributions were measured for the reactions of first-row atomic ions from Sc+ to Zn+, of second-row atomic ions from Y+ to Cd+ (excluding Tc+), and of third-row atomic ions from La+ to Hg+. Marked differences were observed for reactivities of early and late transition metal cations with regard to both the reaction efficiency and the type of reaction pathway. Remarkable multiple (up to four) fluorine atom abstraction, proceeding close to the collision rate, dominated the chemistry observed with early transition metal cations while simple association of up to two molecules of C6F6 to the metal cation dominated the chemistry of late transition metal cations. Correlations were found between the electronic configuration of the metal cation and the nature of the reaction path and the reaction efficiency. Only the early third-row Hf+, Ta+, and W+ transition-metal ions exhibited some C−C and C−F bond-dissociation channels leading to ring cleavage.

Low-Temperature Growth of Thermal Quality SiO[sub 2] Thin Films in High-Density He/O[sub 2] Plasma Generated by RF Driven ICP Source

We report on the growth of thermal quality SiO 2 thin films by a high-density plasma process employing an inductively coupled plasma (ICP) source driven by radio-frequency (rf) power. A high SiO 2 growth rate, with a thickness of 100 A after 10 min, was obtained at a substrate temperature of 360°C in a He/O 2 (3%) plasma. The observed low-temperature growth and electrical properties of the metal-oxide-semiconductor capacitors suggest that the high plasma density and energy and low plasma potential are effective in providing a dense microstructure with low defect concentration and good Si/SiO 2 interfacial characteristics.

Role of inert gas additive on dry etch patterning of InGaP in planar inductively coupled BCl 3 plasmas

The dry etch characteristics of InGaP in BCl 3 planar inductively coupled plasmas (ICP) with additions of Ar or Ne were determined. The inert gas additive provided enhanced etch rates relative to pure BCl 3 and Ne addition in particular produced much higher etch rates at low ratios of BCl 3 in the mixture. The etched features tended to have sloped sidewalls and much rougher surfaces than for GaAs and AlGaAs etched under the same conditions. The practical effect of the Ar or Ne addition was the ability to operate the ICP source over a somewhat broader range of pressures and still maintain practical etch rates. The use of room temperature BCl 3-based etching in a planar ICP appears feasible for base and emitter mesa applications in InGaP/GaAs heterojunction bipolar transistors.

Theoretical investigation of the evolution of electron energy distribution functions in inductively coupled discharges

The inductively coupled plasma (ICP) device is one of the high-density plasma sources being used for the present integrated circuit etching process on an ultra-large scale. Here, we develop a Fokker–Planck code for the ICP source, and evaluate an electron energy diffusion coefficient based on the solution of the wave equations for an ICP reactor. The electron energy distribution function (EEDF) dependence on various external parameters, such as wave frequency, gas pressure and magnetic field, is investigated using the Fokker–Planck code. The effects of changing external parameters on ICP heating characteristics are also discussed. It is shown that the heating of low-energy electrons is enhanced with increasing system collisionality, which is defined as the ratio of collision frequency to effective wave frequency.

Development of an RF Plasma Source with Mirror Field for a Compact Neutron Generator

An RF plasma source has been designed and constructed for a compact neutron generator. The generation of neutrons is based on the D-D/D-T fusion reactions, producing 2.5/14.1MeV neutrons, respectively. The neutron yield of this device depends on the density of D or T monoatomic beams, which can be extracted from low-pressure high-density plasma sources, especially RF-driven plasma sources, such as an ICP (inductively coupled plasma) or a Helicon plasma source. In this presentation, the design of an ICP source with mirror field has been performed arranging targets in coaxial geometry. Plasma targets without any solid target as well as solid targets are arranged in this design for the comparison study and the effects of the mirror field on the plasma properties will be evaluated.

Ultra Shallow Incorporation of Nitrogen into Gate Dielectrics by Pulse Time Modulated Plasma

ABSTRACTIn order to obtain a controllability in the nitrogen depth profile in the oxy-nitride gate dielectrics which has been known to have a strong effect on MOS reliability, micro second ordered pulse was used for the inductive coupled plasma source in our pulse time modulated plasma. The radio frequency (RF) of source plasma and pulse frequency were 12.56 MHz and 10 kHz (100 micro second), respectively. Pulse duty ratio was varied from 20 to 100 %. 1.7nm thick thermal silicon dioxide films were subjected to the pulse time modulated plasma and analyzed by SIMS to see the depth profile of nitrogen. A new finding is that both the concentration and the peak position of nitrogen atoms in silicon dioxide films depend on the pulse duty ratio and plasma radiation time. NBTI lifetime was improved with decreased interface state density. We also used this technique to high-k material and investigated process characteristics of nitridation

Studies of a Reactive Sputter Ion Plating for Preparation of TiN Films Using a Facing Target Sputter and Immersed Inductive Coupled Plasma Source

A new type of sputter ion plating system with facing target sputter and immersed inductive coupled plasma (ICP) source was developed for hard coating of metals and various compound materials. The precise control of plasma conditions, such as ion bombardment energy and electron properties, was very important for high-quality film formation. The electron density (ne) of 1010–1012 cm-3 was obtained in the discharge region, and the electron temperature (Te) was in the range of 2.5–5.7 eV. The adhesive force of the TiN film prepared by this system on the stainless steel substrate was in the range of 20–50 N in the scratch test. The mechanical characteristics of TiN film such as adhesion and hardness almost completely depend on the ion energy incident onto the substrate, whereas the reactivity has a deep correlation with the density of RF plasma.

Measurements of atomic carbon density in processing plasmas by vacuum ultraviolet laser absorption spectroscopy

Measurements of the absolute C atom density in an inductively coupled plasma (ICP) source were carried out by using vacuum ultraviolet (VUV) laser absorption spectroscopy with the resonance lines of C atoms at wavelengths around 94.5 and 165.7 nm. A tunable VUV laser covering these wavelength ranges was generated by a two-photon resonance/four-wave mixing technique in Xe gas. No absorption at around 94.5 nm could be observed, but from the absorption spectra around 165.7 nm we successfully derived the absolute density of C atoms in the ICP source. The obtained values varied from 1×1010 to 1×1011 cm−3, depending on the source gas and operating conditions of the plasma source. The relatively small density values compared to other atomic species are attributed to the large loss rates, which mostly occur on the surface.

Generating high-efficiency neutral beams by using negative ions in an inductively coupled plasma source

To minimize radiation damage caused by charge buildup or ultraviolet and x-ray photons during etching, we developed a high-performance neutral-beam etching system. The neutral-beam source consists of an inductively coupled plasma (ICP) source and parallel top and bottom carbon plates. The bottom carbon plate has numerous apertures for extracting neutral beams from the plasma. When a direct current (dc) bias is applied to the top and bottom plates, the generated positive or negative ions are accelerated toward the bottom plate. Most of them are then efficiently converted into neutral atoms, either by neutralization in charge-transfer collisions with gas molecules during ion transport and with the aperture sidewalls in the bottom plate, or by recombination with low-energy electrons near the end of the bottom plate. We found that negative ions are more efficiently converted into neutral atoms than positive ions. The neutralization efficiency of negative ions was almost 100%, and the maximum neutral flux density was equivalent to 4.0 mA/cm2. A neutral beam can thus be efficiently produced from the ICP source and apertures in our new neutral-beam source.