Showing papers on "Plasma-enhanced chemical vapor deposition published in 2000"

Plasma deposition of optical films and coatings: A review

Abstract: Plasma enhanced chemical vapor deposition(PECVD) is being increasingly used for the fabrication of transparent dielectric optical films and coatings. This involves single-layer, multilayer, graded index, and nanocomposite optical thin filmsystems for applications such as optical filters, antireflective coatings, optical waveguides, and others. Beside their basic optical properties (refractive index, extinction coefficient, optical loss), these systems very frequently offer other desirable “functional” characteristics. These include hardness, scratch, abrasion, and erosion resistance, improved adhesion to various technologically important substrate materials such as polymers, hydrophobicity or hydrophilicity, long-term chemical, thermal, and environmental stability, gas and vapor impermeability, and others. In the present article, we critically review the advances in the development of plasma processes and plasmasystems for the synthesis of thin film high and low index optical materials, and in the control of plasma–surface interactions leading to desired film microstructures. We particularly underline those specificities of PECVD, which distinguish it from other conventional techniques for producing optical films (mainly physical vapor deposition), such as fabrication of graded index (inhomogeneous) layers, control of interfaces, high deposition rate at low temperature, enhanced mechanical and other functional characteristics, and industrial scaleup. Advances in this field are illustrated by selected examples of PECVD of antireflective coatings, rugate filters, integrated optical devices, and others.

Correlation between luminescence and structural properties of Si nanocrystals

Abstract: Strong room-temperature photoluminescence (PL) in the wavelength range 650–950 nm has been observed in high temperature annealed (1000–1300 °C) substoichiometric silicon oxide (SiOx) thin films prepared by plasma enhanced chemical vapor deposition. A marked redshift of the luminescence peak has been detected by increasing the Si concentration of the SiOx films, as well as the annealing temperature. The integrated intensity of the PL peaks spans along two orders of magnitude, and, as a general trend, increases with the annealing temperature up to 1250 °C. Transmission electron microscopy analyses have demonstrated that Si nanocrystals (nc), having a mean radius ranging between 0.7 and 2.1 nm, are present in the annealed samples. Each sample is characterized by a peculiar Si nc size distribution that can be fitted with a Gaussian curve; by increasing the Si content and/or the annealing temperature of the SiOx samples, the distributions become wider and their mean value increases. The strong correlation betw...

Field emission properties of carbon nanotubes

Abstract: We have investigated the field emission properties of nanotube thin films deposited by a plasma enhanced chemical vapor deposition process from 2% CH4 in H2 atmosphere Depending on the deposition of the metallic catalyst [Fe(NO3)3 in an ethanol solution or sputtered Ni] the nanotube films showed a nested or continuous dense distribution of tubes The films consisted of multiwalled nanotubes (MWNTs) with diameters ranging from 40 down to 5 nm, with a large fraction of the tubes having open ends The nanotube thin film emitters showed a turn-on field of less than 2 V μm−1 for an emission current of 1 nA An emission site density of 10 000 emitters per cm−2 is achieved at fields around 4 V μm−1 The emission spots, observed on a phosphorous screen, show various irregular structures, which we attribute to open ended tubes A combined measurement of the field emitted electron energy distribution (FEED) and the current-voltage characteristic allowed us to determine the work function at the field emission site

Synthesis of diamondlike carbon films with superlow friction and wear properties

Abstract: In this study, the authors introduce a new diamondlike carbon (DLC) film providing a friction coefficient of 0.001 and wear rates of 10{sup {minus}9} to 10{sup {minus}10} mm{sup 3}/N.m in inert-gas environments (e.g., dry nitrogen and argon). The film was grown on steel and sapphire substrates in a plasma enhanced chemical vapor deposition system that uses using a hydrogen-rich plasma. Employing a combination of surface and structure analytical techniques, they explored the structural chemistry of the resultant DLC films and correlated these findings with the friction and wear mechanisms of the films. The results of tribological tests under a 10-N load (creating initial peak Hertz pressures of 1 and 2.2 GPa on steel and sapphire test pairs, respectively) and at 0.2 to 0.5 m/s sliding velocities indicated that a close correlation exists between the friction and wear coefficients of DLC films and the source gas chemistry. Specifically, films grown in source gases with higher hydrogen-to-carbon ratios had the lowest fiction coefficients and the highest wear resistance. The lowest friction coefficient (0.001) was achieved with a film on sapphire substrates produced in a gas discharge plasma consisting of 25% methane and 75% hydrogen.

High rate growth of microcrystalline silicon at low temperatures

Abstract: A high rate growth method of microcrystalline silicon at low temperatures has been developed using plasma enhanced chemical vapor deposition (PECVD). It has been found that energetic positive ion and atomic hydrogen impingement on to a growing surface have important affects and that atomic hydrogen density needs to increase correspondingly to the increasing growth rate, while keeping ion bombardment less. Based on this guide line, a novel control of plasma is demonstrated using a high deposition pressure of 2–4 Torr combined with a depletion condition of source gas (SiH 4 ) at a high RF power (a high-pressure-depletion method) and consequently a growth rate of 1.5 nm/s has been achieved using a conventional radio frequency plasma enhanced chemical vapor deposition at 13.56 MHz. Use of a very high frequency plasma at 60 MHz further increases the growth rate up to 5 nm/s and good crystallinity is maintained up to 3.8 nm/s at 250°C. Atomic hydrogen-mediated growth of crystalline silicon at low temperatures is discussed.

Low temperature, high quality silicon dioxide thin films deposited using tetramethylsilane (TMS) for stress control and coverage applications

Abstract: Silicon dioxide thin film have been deposited at temperatures from 25° C. to 250° C. by plasma enhanced chemical vapor deposition (PECVD) using tetramethylsilane (TMS) as the silicon containing precursor. At these temperatures, the PETMS oxide films have been found to exhibit adjustable stress and adjustable conformality. Post deposition annealing in forming gas at or below the deposition temperatures has been shown to be very effective in improving the PETMS oxide properties while preserving the low temperature aspect of the PETMS oxides.

Stability of low-temperature amorphous silicon thin film transistors formed on glass and transparent plastic substrates

Abstract: This article describes the formation of amorphous silicon thin film transistors (TFTs) on glass and flexible transparent plastic substrates using rf plasma enhanced chemical vapor deposition and a maximum processing temperature of 110 °C. Silane diluted with hydrogen was used for the preparation of the amorphous silicon, and SiH4/NH3/N2 or SiH4/NH3/N2/H2 mixtures were used for the deposition of the silicon nitride gate dielectric. The amorphous silicon nitride layers were characterized by transmission infrared spectroscopy and current-voltage measurements; the plastic substrates were 10 mil thick (0.25 mm) polyethylene terephthalate sheets. Transistors formed using the same process on glass and plastic showed linear mobilities ranging from 0.1 to 0.5 cm2/V s with ION/IOFF ratios⩾107. To characterize the stability of the transistors on glass, n- and p-channel transconductances were measured before and after bias stressing. Devices formed at 110 °C show evidence of charge trapping near the a-Si/SiNx interfa...

Quantum confinement and recombination dynamics in silicon nanocrystals embedded in Si/SiO2 superlattices

Abstract: In this study the structural and optical properties of nanocrystalline Si/SiO2 superlattices have been investigated and discussed. Ordered planar arrays of silicon nanocrystals (Si-nc) have been formed by thermal annealing of ten period amorphous Si/SiO2 superlattices prepared by plasma enhanced chemical vapor deposition. Thermal processing of the superlattices results in well separated (by about 5 nm of SiO2) nanocrystalline Si layers, when the annealing temperature does not exceed 1200 °C. The photoluminescence (PL) properties of these layers have been studied in details. The PL peaks wavelength has been found to depend on the laser pump power; this intriguing dependence, consisting in a marked blueshift for increasing power, has been explained in terms of the longer lifetime characterizing larger Si-nc. It is also observed that these decay lifetimes exhibit a single exponential behavior over more than two orders of magnitude, in clear contrast with the typical, nonsingle exponential trends observed for...

Plasma enhanced chemical vapor deposition of amorphous, polymorphous and microcrystalline silicon films

Abstract: The plasma processes and growth reactions involved in the deposition of amorphous, polymorphous and microcrystalline silicon thin films are reviewed. The reference being a-Si:H deposition through surface reactions of SiH 3 radicals, we study the growth of microcrystalline silicon films produced by the layer-by-layer and standard hydrogen dilution techniques. We show that subsurface reactions play a key role, particularly during the incubation phase where hydrogen is responsible for the formation of a porous layer in which nucleation takes place. The evolution of the film properties is related to the long range effects of hydrogen. Coming back to a-Si:H deposition, we further consider the deposition at low substrate temperature (<200°C) and pressure (<5 Pa) where the role of ions is dominant and at deposition rates where powder formation takes place. We propose that rather than a drawback, nanoparticle formation in silane plasmas might be considered as a potential for obtaining new silicon films. We address in particular the deposition of polymorphous silicon consisting of an a-Si:H matrix with silicon nanocrystallites produced in the gas phase. Despite their heterogeneity polymorphous silicon films have improved transport properties and stability with respect to a-Si:H.

Plasma-enhanced chemical vapor deposition of a metal nitride layer

Abstract: A refractory metal layer is deposited onto a substrate having high aspect ratio contracts or vias formed thereon. Next, a plasma-enhanced CVD refractory metal nitride layer is deposited on the refractory metal layer. Then, a metal layer is deposited over the metal nitride layer. The resulting metal layer is substantially void free and has reduced resistivity, and has greater effective line width. Plasma-enhanced chemical vapor deposition of the metal nitride layer comprises forming a plasma of a metal-containing compound, a nitrogen-containing gas, and a hydrogen-gas to deposit a metal nitride layer on a substrate. The metal nitride layer is preferably treated with nitrogen plasma to densify the metal nitride film. The process is preferably carried out in an integrated processing system that generally includes various chambers so that once the substrate is introduced into a vacuum environment, the metallization of the vias and contacts occurs without exposure to possible contaminants.

Synthesis of superlow-friction carbon films from highly hydrogenated methane plasmas☆

Abstract: In this study, we investigated the friction and wear performance of diamond-like carbon films (DLC) derived from increasingly hydrogenated methane plasmas. The films were deposited on steel substrates by a plasma-enhanced chemical vapor deposition process at room temperature and the tribological tests were performed in dry nitrogen. Tests results revealed a close correlation between the hydrogen in the source gas plasma and the friction and wear coefficients of the DLC films. Specifically, films grown in plasmas with higher hydrogen-to-carbon ratios had much lower friction coefficients and wear rates than did films derived from source gases with lower hydrogen-to-carbon ratios. The lowest friction coefficient (0.003) was achieved with a film derived from 25% methane, 75% hydrogen, while a relatively high coefficient of 0.015 was found for films derived from pure methane. Similar correlations were observed for wear rates. Films derived from hydrogen-rich plasmas had the least wear, while films derived from pure methane suffered the highest wear. We used a combination of surface analytical methods to characterize the structure and chemistry of the DLC films and worn surfaces.

Deposition of Si-DLC films with high hardness, low stress and high deposition rates

Abstract: In this work silicon-incorporated diamond-like carbon (Si-DLC) films were produced by plasma enhanced chemical vapor deposition (PECVD) from gaseous mixtures of CH4 and SiH4. A study of the influence of self-bias and gas composition on the mechanical and structural properties of the films was carried out. Results show that films deposited at high self-bias present high deposition rates, low stress and surprisingly high hardness. Increasing silane concentration in the gas phase leads to an enhancement of the observed effects. Compositional and structural characterization show that deposition at high bias leads to increased sp2 character and rather low silicon contents. Increasing the silane content in the plasma leads to an increase in the sp3 fraction of the films, and yields a further reduction of stress with almost no effect upon hardness. In this way, the possibility of producing films with high hardness (>20 GPa), low stress (∼0.5 GPa) and high deposition rates (>40 nm/min) has been demonstrated. This result is thought to be very important from the point of view of technological applications.

Comparison between wet HF etching and vapor HF etching for sacrificial oxide removal

Abstract: In this work the etching of different Si-oxide, Si-nitride and metal layers in HF:H2O 24.5:75.5, BHF:glycerol 2:1 and vapor HF is studied and compared. The vapor HF etching is done in a commercially available system for wafer cleaning, that was adapted according to custom specifications to enable stiction-free surface micro- machining. The etch rates as a function of etching method, time and temperature are determined. Moreover, the influence of internal and external parameters on the HF vapor etching process are analyzed before choosing the standard HF vapor etch technique used for comparing the etching behavior of the different films.

High hole mobility in Si0.17Ge0.83 channel metal–oxide–semiconductor field-effect transistors grown by plasma-enhanced chemical vapor deposition

Abstract: We report on effective hole mobility in SiGe-based metal–oxide–semiconductor (MOS) field-effect transistors grown by low-energy plasma-enhanced chemical vapor deposition The heterostructure layer stack consists of a strained Si017Ge083 alloy channel on a thick compositionally-graded Si052Ge048 buffer Structural assessment was done by high resolution x-ray diffraction Maximum effective hole mobilities of 760 and 4400 cm2/Vs have been measured at 300 and 77 K, respectively These values exceed the hole mobility in a conventional Si p-MOS device by a factor of 4 and reach the mobility data of conventional Si n-MOS transistors

Low-k Si-O-C-H composite films prepared by plasma-enhanced chemical vapor deposition using bis-trimethylsilylmethane precursor

Abstract: Low-k Si–O–C–H composite films were prepared using bis-trimethylsilylmethane as a precursor and oxygen in a rf plasma reactor. The growth rate of the Si–O–C–H composite film followed a second-order exponential decay function. This behavior could be explained by the formation of nanosized voids due to Si–CH3 and OH-related bonds included in the film. OH-related bonds were detected in films deposited at 30 °C, but could not be observed for the films deposited above 60 °C. In contrast, Si–CH3 bonds were also detected at 30 °C, but decreased monotonically up to 210 °C and were absent of higher temperatures. After postannealing the film deposited at 30 °C, the Si–CH3 bonds were unchanged, but the OH-related bonds were easily removed. This film showed a low dielectric constant of 2.44 and leakage current density of 4.4×10−7 A/cm2 at 1 MV/cm.

High-Rate Deposition of High-Quality, Thick Cubic Boron Nitride Films by Bias-Assisted DC Jet Plasma Chemical Vapor Deposition

Abstract: Cubic boron nitride thin films were deposited on (100) silicon substrates by DC jet plasma chemical vapor deposition in an Ar–N2–BF3–H2 gas system. Negative DC bias was applied on the substrate during deposition. Scanning electron microscopy, x-ray diffraction, infrared and Raman spectroscopy were carried out to characterize the samples. It was found that boron nitride films with cubic phase over 90% were synthesized under optimized conditions. A high deposition rate of about 0.3 µm/min and a film thickness over 3 µm were firstly achieved. Furthermore, the Raman measurements show clear TO and LO characteristic peaks of c-BN with a full width at half maximum of 28.8 and 19.7 cm-1, revealing a high quality of the deposited films.

Modelling of silicon hydride clustering in a low-pressure silane plasma

Abstract: A new silicon hydride clustering model was developed to study the nucleation of particles in a low-temperature silane plasma. The model contains neutral silanes, silylenes, silenes and silyl radicals as well as silyl and silylene anions. Reaction rates were estimated from available data. Simulations were carried out for typical discharge parameters in a capacitive plasma. It was shown that the main pathway leading to silicon hydride clustering was governed by anion-neutral reactions. SiH2 radical insertion was found to be important only in the initial stages of clustering, whereas electron-induced dissociations were seen to lead to dehydrogenation. Increased ion density (radiofrequency power density) leads to faster clustering due to increased formation of reactive radicals.

A plasma process for ultrafast deposition of SiGe graded buffer layers

Abstract: Low energy plasma enhanced chemical vapor deposition (LEPECVD) has been applied to the synthesis of Si-modulation doped field effect transistor structures, comprising a SiGe relaxed buffer layer and a modulation doped strained Si channel. A growth rate of at least 5 nm/s for the relaxed SiGe buffer layer is well above that obtainable by any other technique. Due to the low ion energies involved in LEPECVD, ion damage is absent, despite a huge plasma density. The structural quality of the LEPECVD grown SiGe buffer layers is comparable to that of state-of-the-art material. The electronic properties of the material were evaluated by growing modulation doped Si quantum wells on the buffer layers. We obtain a low temperature (2 K) Hall mobility of μH=2.5×104 cm2/Vs for the electrons in the Si channel at an electron sheet density of ns=8.6×1011 cm−2.

Pulsed-PECVD Films from Hexamethylcyclotrisiloxane for Use as Insulating Biomaterials

Abstract: Thin films produced by plasma-enhanced chemical vapor deposition (PECVD) have potential application as conformal coatings on implantable devices with complex topologies and small dimensions. Coatings on such devices need to be biocompatible, insulating, and flexible enough to minimize static forces on the surrounding tissue. In this study, we describe the use of pulsed-PECVD to deposit thin films from hexamethylcyclotrisiloxane (D3). Pulsed-PECVD is a method in which plasma excitation is modulated to favor deposition from neutral and radical species. Thin, conformal coatings were demonstrated on nonplanar substrates suitable for implantation, such as copper wires and neural probes. Coatings were resistant to prolonged immersion in warm saline solution, and wire coatings produced by pulsed-PECVD showed more flexibility than analogous coatings deposited by continuous-wave (CW) excitation. Using Fourier transform infrared spectroscopy, it was demonstrated that the mode of plasma excitation is important in de...

A new approach to SiO2 deposit using a N2-SiH4-N2O glow dielectric barrier-controlled discharge at atmospheric pressure

Abstract: The aim of this work is to study the properties of a silicon-based deposit realized with a glow dielectric barrier discharge at atmospheric pressure in a nitrogen, silane and nitrous oxide mixture. It is shown that a continuous thin film can be realized. The chemical composition of the thin layer has been determined by x-ray photoelectron spectroscopy and static secondary ion mass spectrometry. The characteristics of the deposit are correlated to those of the discharge. The first steps of a chemical pathway leading to the precursors of the deposit are proposed from the analysis of the optical emission spectrum of the discharge. It appears that, unlike the low-pressure PECVD in a N2O-SiH4 mixture, in an atmospheric-pressure glow discharge NO is the main oxidizing species, due to the action of the metastable nitrogen molecules.

A comparative study on inductively-coupled plasma high-density plasma, plasma-enhanced, and low pressure chemical vapor deposition silicon nitride films

Abstract: Silicon nitride films have been deposited using inductively-coupled plasma high-density plasma chemical vapor deposition (HDP CVD), plasma-enhanced chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD) methods. Characterization and comparison of the three films were performed using Fourier-transform infrared spectroscopy, secondary-ion mass spectroscopy, Rutherford backscattering spectrometry, and hydrogen forward-scattering spectrometry, in addition to wet-etch rate and stress measurement studies. It was found that silicon nitride films deposited using HDP CVD method have several advantages over the silicon nitride films that were deposited using the LPCVD and PECVD methods. The HDP CVD silicon nitride film can be deposited at much lower temperatures (⩽400 °C) than LPCVD silicon nitride, and has substantially less hydrogen (5.5 at. %) than the PECVD film. In addition, the PECVD film contains some oxygen in the film. The wet-etch rate of HDP CVD silicon nitride film is comp...

Contribution of ions to the growth of amorphous, polymorphous, and microcrystalline silicon thin films

Abstract: The growth of amorphous, microcrystalline, and polymorphous silicon has been investigated by studying the species contributing to the growth and resulting film structure. The surface reaction probability of the radicals and the contribution of ions to the growth have been determined. In a-Si:H deposition by hot wire chemical vapor deposition, the surface reaction probability (β=0.29) of the depositing radical is compatible with SiH3, whereas the surface reaction probability in microcrystalline silicon growth is higher (0.36⩽β⩽0.54). On the contrary, the deposition of amorphous silicon by plasma enhanced chemical vapor deposition indicates the contribution of more reactive radicals than SiH3. The deposition of polymorphous and microcrystalline silicon by plasma is dominated by ions, which can contribute up to 70% of the deposited film. This is attributed to efficient ionization of silane in charge exchange reactions with hydrogen ions. The surface reaction probability in the case of polymorphous silicon de...

Effect of higher-silane formation on electron temperature in a silane glow-discharge plasma

Abstract: Electron temperature measured by an optical-emission spectroscopy shows a strong substrate temperature dependence in a silane glow-discharge plasma The electron temperature increases with time after turning on the plasma at a low substrate temperature of 150 °C, while it stays constant at a high substrate temperature of 400 °C The electron temperature is drastically reduced when the source gas silane is diluted with hydrogen at low substrate temperatures These results suggest that the electron temperature in silane plasma is strongly affected by an electron-attachment process to higher-order silane molecules whose formation reactions show negative activation energies with gas temperature and are also suppressed by the presence of hydrogen molecules

Thin films deposition from hexamethyldisiloxane and hexamethyldisilazane under Dielectric-Barrier discharge (DBD) conditions

Abstract: Hexamethyldisiloxane (HMDSO) and hexamethyldisilazane (HMDSN) were used as organosilicon reagents for PE-CVD of thin films under filamentary barrier-discharge conditions at atmospheric pressure. Efficient discharges were obtained in the region of moderate frequencies (5 kHz). The following mixtures of organosilicon reagents with carrier gas and oxidants or ammonia were investigated: HMDSO+Ar, HMDSO+N2, HMDSO+O2+Ar, HMDSO+N2O+Ar, and HMDSN+NH3+N2. Under such conditions HMDSO was converted to produce thin films (10–1000 nm) of silicon oxide, generally containing admixtures of residual “organic” content (Si—CHn and Si—H groups). The films deposited from HMDSN+NH3+N2 contained silicon, nitrogen and oxygen.

Field emission from quasi-aligned SiCN nanorods

Abstract: We report on the preparation and field emission properties of quasi-aligned silicon carbon nitride (SiCN) nanorods. The SiCN nanorods are formed by using a two-stage growth method wherein the first stage involves formation of a buffer layer containing high density of nanocrystals by electron cyclotron resonance plasma enhanced chemical vapor deposition and the second stage involves using microwave plasma enhanced chemical vapor deposition for high growth rate along a preferred orientation. It should be noted that growth of the SiCN nanorods is self-mediated without the addition of any metal catalyst. Scanning electron microscopy shows that the SiCN nanorods are six-side-rod-shaped single crystals of about 1–1.5 μm in length and about 20–50 nm in diameter. Energy dispersive x-ray spectrometry shows that the nanorod contains about 26 at. % of Si, 50 at. % of C, and 24 at. % of N. Characteristic current–voltage measurements indicate a low turn-on field of 10 V/μm. Field emission current density in excess of ...

The physics of plasma-enhanced chemical vapour deposition for large-area coating: industrial application to flat panel displays and solar cells

Abstract: Designing plasma-enhanced chemical vapour deposition (PECVD) reactors to coat large-area glass plates (similar to1 m(2)) for flat panel display or solar cell manufacturing raises challenging issues in physics and chemistry as well as mechanical, thermal, and electrical engineering, and material science. In such reactive glow discharge plasma slabs, excited at RF frequency (from 13.56 MHz up to similar to 100 MHz), the thin-film deposition uniformity is determined by the gas flow distribution, as well as the RF voltage distribution along the electrodes, and by local plasma perturbations at the reactor boundaries. All these aspects can be approached by analytical and numerical modelling. Moreover, the film properties are largely determined by the plasma chemistry involving the neutral radicals contributing to film growth, the effect of ion bombardment, and the formation and trapping of dust triggered by homogeneous nucleation. This paper will review progress in this field, with particular emphasis on modelling developments.