Cyclotron Resonance Plasma-enhanced Chemical Vapor Research Articles

Crystalline structures of the PbTiO 3 films prepared using the ECR PECVD method

The electron cyclotron resonance plasma-enhanced chemical vapor deposition method is used to prepare ferroelectric PbTiO 3 films. Single-phase perovskite PbTiO 3 films are successfully fabricated on Pt/Ti/SiO 2/Si and Pt/SiO 2/Si substrates at temperatures of 390–530 °C using metal-organic (MO) sources. When the deposition temperature is sufficiently high (above 500 °C), lead titanate film has a stoichiometric composition independently of the MO source supply ratio. Whereas the deposition temperature is low (below 450 °C), the composition and, in turn, the structure are depended on the source supply ratio. With adequate MO source ratio, stoichiometric perovskite PbTiO 3 film can be obtained at a temperature as low as 390 °C. The variations of preferred orientation, degree of c-axis orientation and film morphology with process temperature, MO source supply ratio and substrate are also examined.

Electrical properties of silicon nitride films grown on a SiGe layer by distributed electron cyclotron resonance plasma-enhanced chemical vapor deposition

Silicon nitride films have been deposited on relaxed Si 0.83Ge 0.17 films using distributed electron resonance plasma-enhanced chemical vapor deposition without intentional substrate heating. The electrical properties of metal–insulator–semiconductor structures have been investigated. The electrical properties are strong functions of the post-processing treatment. The hysteresis of C–V curves can be reduced significantly after 30 min post-metallization annealing at 450 °C in forming gas. The flat-band voltage is then very low, thereby indicating that positive charges retained in the silicon nitride films are compensated for by negative charges located at the interface with the SiGe alloy. Conduction properties have also been analyzed from I–V measurements. A critical field of ≈2 MV cm −1 and a high resistivity of ≈2×10 15 Ω cm have been obtained. For higher electric fields, the leakage current is governed by a Poole–Frenkel conduction mechanism.

Amorphous and Microcrystalline Silicon Deposited by Low-Power Electron-Cyclotron Resonance Plasma-Enhanced Chemical-Vapor Deposition

The structural and optoelectronic properties of intrinsic amorphous silicon (a-Si:H) and microcrystalline silicon ( µc-Si:H) deposited using electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) with a microwave power of 150 W were studied as a function of the ECR source-to-substrate distance, d ss, process pressure, hydrogen dilution and substrate temperature. Hydrogen was used as the excitation gas and silane was injected into the main chamber. Deposition rates show a maximum as a function of the deposition pressure. For d ss=6 cm this maximum occurs between 5 and 10 mTorr. ECR-deposited a-Si:H films show a high Tauc bandgap (∼1.9 eV), low dark conductivity (∼10-11 Ω-1 cm-1), relatively high Urbach energy (≥55 meV) and high defect density (≥5×1015 cm-3) compared with a-Si:H grown by RF glow discharge. Hydrogen evolution and infrared spectroscopy reveal the presence of voids and/or columnar structure. The transition from amorphous to microcrystalline silicon occurs under conditions of high hydrogen dilution, low deposition pressure, and low d ss. The higher the hydrogen dilution, the lower the substrate temperature needed to achieve µc-Si:H. Raman spectra of the µc-Si:H suggest small grain size ( ∼4 nm) and crystalline fraction (∼60%). A growth model is proposed that includes silane excitation both by the ECR electrons and by the excited hydrogen species.

Formation of high-quality silicon dioxide films by electron cyclotron resonance plasma oxidation and plasma-enhanced chemical vapour deposition

High-quality silicon dioxide films have been deposited by plasma-enhanced chemical vapour deposition and plasma oxidation using a single magnet electron cyclotron resonance plasma generator with both oxygen and nitrous oxide as the oxygen source, Langmuir probe measurements were used to characterise both molecular oxygen and nitrous oxide discharges. Low electron temperatures, resulting in low sheath potential drops, coupled with the shape of the field lines results in low sputtering from the chamber walls between the source region and substrate. The resulting buildup of an insulating layer of oxide on the chamber walls results in a very clean process. In situ thermal desorption and ellipsometry measurements coupled with X-ray photoelectron spectroscopy have allowed us to characterise the quality of the silicon surface prior to deposition and just after initiation of the plasma. Plasma oxidation dominates over chemical vapour deposition during the early stages of oxide film growth using either oxygen or nitrous oxide as the oxygen source gas. Extensive ex-situ spectroscopic ellipsometry (SE) indicates that the bulk properties of the films arc comparable to those of high-temperature thermal oxides. There is no interface layer measurable by SE for any of the films produced by plasma oxidation or chemical vapour deposition with silane using either molecular oxygen or nitrous oxide as the oxygen source gas even though the latter results in approximately a monolayer of nitrogen at the Si/SiO 2 interface. Chemical analysis by the total reflected X-ray fluorescence technique and by vapour-phase deposition coupled with graphite furnace atomic absorption spectroscopy found no impurities in the films made with silane and molecular oxygen. The high quality of the Si/SiO 2 interface made with these two gases was confirmed by capacitance-voltage measurements on Al-gate capacitors. After a 1 min anneal at 950°C interface state densities below 3×10 10 eV −1 cm −2 were obtained.

Fourier-transform design and electron cyclotron resonance plasma-enhanced deposition of lossy graded-index optical coatings

A Fourier-transform synthesis technique is applied to the design of inhomogeneous refractive-index optical thin films with dispersion of refractive index and absorption taken into account. Using measured properties of SiO(x) N(y), we have designed a broadband reflector and two three-line filters with high reflectance. One of the three-line filters was manufactured by electron cyclotron resonance plasma-enhanced chemical vapor deposition from a mixture of SiH(4), N(2), O(2), and Ar. Good agreement between design and measured performance proves the feasibility of applying the Fourier-transform technique to the design of reflection filters even in the case of highly dispersive, absorbing material, if its optical properties are well characterized.

The deposition of aluminum nitride on silicon by plasma-enhanced metal-organic chemical vapour deposition

Aluminium nitride (AlN) films were deposited by electron cyclotron resonance plasma-enhanced chemical vapour deposition using trimethylaluminum (TMA) as precurser at temperatures from 25 to 600 °C and at different concentrations of TMA. Adhesive layers with a thickness ranging from 100 to 200 nm and a refractive index of 1.65–2.0 are obtained. By Auger electron spectroscopy, reflectum high energy electron diffraction and ellipsometric measurements at 632 nm we found in all layers a high oxygen concentrations only slightly dependent on the deposition conditions. A quadrupole mass spectrometer was used to investigate the composition of the gas phase. The gas spectra did not indicate partial pressures of oxygen and water. Sputtering effects and plasma chemical etching of the microwave window made of quartz glass seem to be the source for the incorporated oxygen.

C-axis orientation of AlN films prepared by ECR PECVD

AlN films were deposited on silicon substrates at low temperatures (300–500 °C) by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) using trimethylaluminum, N 2 and H 2 gases. The degree of c-axis orientation, crystallinity, functional groups and chemical composition of the films were investigated for various deposition conditions. The degree of c-axis orientation depends on the substrate surface condition and it improves with increasing substrate temperature as well as with increasing microwave power. A c-axis oriented ( σ = 4.3°) AlN film was prepared at 500°C. The importance of the system design which allows the precursor to be dissociated efficiently by the ECR plasma is discussed.

Composition Control of Lead Zirconate Titanate Thin Films in Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition System

Lead zirconate titanate (PZT) thin films were fabricated on Pt/Ti/SiO2/Si substrates by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD). Lead β-diketonate ( Pb(DPM)2, zirconium t-butoxide ( Zr(OC4H9)4) and titanium i-propoxide ( Ti(OC3H7)4) were used as metalorganic (MO) precursors. Perovskite single-phase PZT films were obtained at temperatures below 500° C when the Pb/(Zr+Ti) concentration ratio was close to 1. The cation concentrations in the PZT films were successfully controlled by adjusting the flow rate of each MO source. The variation in composition and structure with the process temperature and the MO source flow rates was discussed.

Composition and conduction properties of silicon nitrides deposited by plasma-enhanced ultra-high-vacuum chemical vapour deposition

Abstract A Some fundamental properties of silicon nitride deposition by electron cyclotron resonance plasma-enhanced chemical vapour deposition have been studied. Silane and nitrogen were used to deposit the layers used for the study. The deposition temperature was maintained above 500°C in order to ensure that the hydrogen content of the film was marginally small, which was confirmed by X-ray photoelectron spectroscopy measurement. It was observed that, in order to deposit stoichiometric Si3N4 films, the flux of the volatile component nitrogen must be increased until the [N2]/[SiH4] ratio is well above 25. The leakage currents in both silicon-rich and stoichiometric films were investigated. The measured refractive index of the films was used to highlight the role of various species during the deposition of the films.

Comparison of diamond-like carbon film deposition by electron cyclotron resonance with benzene and methane

A comparative study of the deposition of diamond-like carbon films using methane or benzene in a microwave electron cyclotron resonance plasma-enhanced chemical vapor deposition system has been performed. Process variables studied were reactor pressure, applied radio frequency substrate bias, and microwave power. The plasma stream was characterized using optical emission spectroscopy and mass spectrometry. Film properties studied included optical energy gap, total hydrogen content, integrated C-H stretch absorption, index of refraction, and Raman spectra. The use of a high C/H ratio reactant such as benzene was found to be advantageous over methane in that higher deposition rates were possible and the resultant films exhibit diamond-like properties without the application of large substrate biases. Another result of this investigation was further confirmation that hard carbon films contain a significant quantity of nonbonded hydrogen [A. Grill and V. Patel, Appl. Phys. Lett. 60 (17), 2089 (1992)].

Low temperature deposition of silicon nitride films by distributed electron cyclotron resonance plasma-enhanced chemical vapor deposition

Silicon nitride thin films have been deposited via distributed electron cyclotron resonance plasma-enhanced chemical vapor deposition, without intentional substrate heating, using SiH4 and N2 gas mixtures. The effects of N2/SiH4 gas flow (1.5–19) and microwave power (800–1500 W) on deposition rate, refractive index, composition, chemical bonds, and etch rate were studied by ellipsometry, MeV ion beam analysis techniques, and Fourier transform infrared spectroscopy. All parameters examined indicate that a highly diluted SiH4 gas phase and a microwave power of 1500 W help to prepare quasistoichiometric films with a high density (2.9 g/cm3) and a refractive index of 1.98. The effects of film density and film stoichiometry (N/Si) on refractive index are discussed through the Lorentz–Lorenz relation. The first electric results show that, under the optimized deposition parameters, a critical field of 2.3 MV/cm and an interface state density of 5×1010 eV−1 cm−2 can be achieved.

Effects of deposition temperature on the electrical properties of electron cyclotron resonance plasma-enhanced chemical vapor deposition Ta2O5 film and the formation of interfacial SiO2

High-quality Ta2O5 thin films for high-density memory devices were prepared at low temperatures by electron cyclotron resonance plasma-enhanced chemical vapor depostion (ECR-PECVD) without postannealing treatment. The effects of deposition temperature on the microstructure, composition, and electrical properties of the dielectric films were studied. The increase in deposition temperature from 145 °C to 205 °C improved the stoichiometry of the Ta2O5 thin films. As a consequence, EBD increased from 3.3 MV/cm to 4.4 MV/cm, and ∊Ta2O5, increased from 14 to 25. Interfacial SiO2 layer was observed by cross-sectional TEM, and its effects on the electrical properties of the overall dielectric film were also studied. The incubation period in which interfacial SiO2 grows was discussed with regard to reactivity between oxygen and Si substrate.

Conduction properties of amorphous Ta2O5 films prepared by plasma enhanced chemical vapour deposition

Electrical properties of amorphous tantalum oxide, obtained by low pressure (mTorr range) electron cyclotron resonance plasma-enhanced chemical vapour deposition from Ta(OC 2 H 5 ) 5 and O 2 , have been investigated in Al/Ta 2 O 5 /Si structures by current density-voltage and capacitance-voltage measurements. For as-deposited oxide layers, which exhibit high level of leakage currents and interface state densities, the conduction mechanism is clearly attributed to the Poole—Frenkel effect under moderate electric field. After annealing films in a nitrogen ambient below the recrystallisation temperature of Ta 2 O 5 , the conduction properties are greatly modified and lead to excellent dielectric characteristics in terms of capacitance response and leakage currents (∼10 −10 A cm −2 at 2.5 V).

Conduction properties of amorphous Ta2O5 films prepared by plasma enhanced chemical vapour deposition

Electrical properties of amorphous tantalum oxide, obtained by low pressure (mTorr range) electron cyclotron resonance plasma-enhanced chemical vapour deposition from Ta(OC 2 H 5 ) 5 and O 2 , have been investigated in Al/Ta 2 O 5 /Si structures by current density-voltage and capacitance-voltage measurements. For as-deposited oxide layers, which exhibit high level of leakage currents and interface state densities, the conduction mechanism is clearly attributed to the Poole—Frenkel effect under moderate electric field. After annealing films in a nitrogen ambient below the recrystallisation temperature of Ta 2 O 5 , the conduction properties are greatly modified and lead to excellent dielectric characteristics in terms of capacitance response and leakage currents (∼10 −10 A cm −2 at 2.5 V).

Electron Cyclotron Resonance Plasma‐Enhanced Metalorganic Chemical Vapor Deposition of Tantalum Oxide Thin Films on Silicon near Room Temperature

Films of tantalum oxide, ranging in thickness from 25 to 2000 nm, were successfully deposited on silicon by the electron cyclotron resonance plasma‐enhanced metalorganic chemical vapor deposition (ECR‐MOCVD) process at deposition rates of up to 33 nm/min. The films were produced by decomposition of tantalum pentaethoxide into tantalum oxide in an oxygen ECR microwave plasma. The films were amorphous (but fully dense) since the temperature of the substrate, which was unheated, was estimated to be 76–120°C. The growth of the tantalum oxide films was accompanied by the formation of an interlayer of silicon dioxide at the silicon interface. The tantalum oxide films were oxygen rich (relative to Ta2O5). The effective relative dielectric constant of these dual‐layer dielectrics ranged from ɛef= 8.5 to 24; this range was explained in terms of a bilayer consisting of a 13‐nm‐thick silicon dioxide layer of ɛsx= 4, and a tantalum oxide overgrowth of varying thickness having ɛtx∼ 25. A maximum breakdown strength of the films was 6.9 MV/cm and the leakage current at a field of 1 MV/cm was 3.0 × 10‐8. The breakdown properties were related to the presence of stray particles on the substrate; these properties are expected to improve considerably if the processing is carried out in a clean‐room environment. The silicon dioxide layer is believed to have grown by the diffusion of oxygen through the tantalum oxide overlayer despite the low substrate temperature.

Role of ions in electron cyclotron resonance plasma-enhanced chemical vapor deposition of silicon dioxide

Silicon dioxide films were deposited in an electron cyclotron resonance plasma onto substrates at temperatures ranging from 65 to 200 °C. In order to determine the effect of ions on the deposition, both ion flux and ion energy were investigated. The ratio of ion flux to deposition flux was found to be a significant parameter and this ‘‘flux ratio’’ was varied between 8 and 100. Mean ion energy was investigated at 10, 50, and 75 eV. The silicon dioxide films were characterized by measurement of wet etch rate, density, composition, and stress, and by infrared spectroscopy. It was found that above a flux ratio of about 20, high-quality SiO2 was deposited whether or not the substrate was thermally floating or at 65–200 °C, indicating that the flux ratio was dominant over the temperature. Use of radio-frequency bias to increase the mean ion energy to 50 eV or above was effective in producing high-quality SiO2 when the flux ratio was below 20, but not as effective as using a high flux ratio. Thus high ion flux and low ion energy were found to be useful in producing SiO2 at temperatures as low as 65 °C with properties close to that of thermal silicon dioxide. The role of ions in the deposition process was found to be densification, removal of –OH (or hydrogen) and alteration of Si–O bonding.

Passivation of GaAs surfaces and AlGaAs/GaAs heterojunction bipolar transistors using sulfide solutions and SiNx overlayer

Stable passivation of GaAs surfaces and AlGaAs/GaAs heterojunction bipolar transistors has been achieved using sulfide solutions and SiNx overlayers. The SiNx layers are deposited at ∼200 °C using electron cyclotron resonance plasma-enhanced chemical vapor deposition technique. The capacitance–voltage measurements indicate a substantial reduction in the density of electronic defects at the SiNx/S–GaAs interface as a result of annealing in N2 ambient. The base current of a 36×36 μm2 AlGaAs/GaAs heterojunction bipolar transistor is reduced by approximately two orders of magnitude in the low collector current regime by using sulfide treatment, SiNx deposition, and anneal. Both the Al/SiNx/S–GaAs capacitors and transistors are stable for several months with no noticeable degradation in their electrical characteristics.

Microstructure and Electrical Properties of Tantalum Oxide Thin Film Prepared by Electron Cyclotron Resonance Plasma-Enhanced Chemical Vapor Deposition

High-quality tantalum oxide thin film was prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) for high-density memory devices. The tantalum oxide film deposited at 205°C showed excellent electrical properties: E bd= 4.4 MV/cm, ε (Ta2O5)=25 and J< 1×10-9 A/cm2 at 2.5 V. The deposited film was annealed at various temperatures in an oxygen ambient. The microstructure and the composition of the annealed tantalum oxide film were examined and they were related to the electrical properties of the film. The growth of the interfacial silicon oxide layer was observed by using a high-resolution transmission electron microscope (TEM) and its effects on the electrical properties of the dielectric film were also studied. The electrical properties of the film could not be improved by annealing in an oxygen ambient at high temperatures due to the crystallization of the tantalum oxide film and the growth of the interfacial silicon oxide layer.

Optical properties of SiNx deposited by electron cyclotron resonance plasma-enhanced deposition

The properties of thin SiN_<i>x</i> films deposited by computer-controlled electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) from a mixture of SiH₄ and N₂ onto sapphire substrates were investigated by optical transmission spectroscopy in the wavelength range 200 to 2600 nm. The wavelength dependencies of the refractive index <i>n</i>, extinction coefficient <i>k</i>, absorption coefficient α, and the optical bandgap <i>E</i>_<i>g</i> of the films were studied. The optical properties of SiN_<i>x</i>, were found to be strongly dependent on the gas flow ratio during deposition. The optical band gap displays a blue shift with increase of nitrogen content in the layer with values ranging from 1.7 to 4.2 eV.

P-Type μc-SiC prepared by ECR PECVD using tetramethylsilane gas

We have prepared a p-type microcrystalline silicon carbon thin film by an electron cyclotron resonance plasma-enhanced chemical vapor deposition using a Si(CH 3) 4 + SiH 4 + B 2H 6 + H 2 gas mixture. The p-type μc-SiC had an optical band gap of around 2.4 eV, a dark conductivity of around 10 −2 S/cm and a C/Si ratio of around 0.02, which had almost similar values as the p-type μc-SiC prepared with a CH 4 + SiH 4 + B 2H 6 + H 2 gas mixture.