Plasma-enhanced Chemical Vapor Deposition Technique Research Articles

Structure of defects in silicon oxynitride films

Amorphous silicon oxynitride (a-SiNxOy) films were deposited at 300 °C using a plasma-enhanced chemical vapor deposition technique, which was carried out with variation in the nitrogen-flow-rate ratio (RN) and the oxygen-flow-rate ratio (RO) to control the nitrogen and oxygen contents, x and y, respectively. Changes in the structural properties and the characteristics of defects in the films were examined based on the electron spin resonance as well as infrared and optical absorption measurements. An increase in either RN or RO was found to decrease the deposition rate, the density of charged or neutral defects, and the randomness of the bonding network. Thus the incorporation of O or N atoms into Si nitride or Si oxide films, respectively, acts to improve the qualities of the insulating films. Furthermore, the nearest N and O atom neighboring to a Si site would be randomly bonded to the Si atom. Our results also showed that N-related dangling bonds, other than so-called K centers, are favorably created after annealing, but that the formation of Si–O bonds in the films makes the formation of such defects difficult.

Optical properties of silicon nanocrystallites in polycrystalline silicon films prepared at low temperature by plasma-enhanced chemical vapor deposition

Silicon crystallites produced by low-temperature plasma-enhanced chemical vapor deposition technique have been shown to have size-dependent photoluminescent and second harmonic generation responses. The crystalline volume fraction was estimated by Raman spectra and the grain sizes of crystallites were measured by X-ray diffraction. The structural chemical properties of poly-Si films were studied by means of Fourier-transform infrared spectroscopy and transmission spectrophotometry. The size- and shape-dependent second-harmonic generation (SHG) of poly-Si films is also studied. The resonant SHG spectra show the fine structure with peak position at approximately 3.26 eV which is attributed to the response from Si–SiO 2 interface (for aged films). The second resonant peak can be explained as the size-dependent SHG response from the bulk of nanocrystallites.

Structural and Optical Features of Nano-Crystalline Silicon Films Prepared by Pecvd and Rf Magnetron Sputter Techniques

ABSTRACTNano-crystalline Si films were prepared by plasma enhanced chemical vapor deposition (PECVD) and rf-magnetron sputter techniques at various deposition conditions, and the relations of the photoluminescence (PL) phenomena of the films with process variables are discussed. The phase of the films prepared at R.T. by PECVD techniques is somewhere between amorphous and crystalline states, consisting of nano-crystallites of size ranging from 3.2 to 5.3 nm. These films exhibit significant PL intensities near blue light region; the PL peaks shift from 510 to 460 nm with decreasing the reaction gas (SiH4) fraction from 4.7 to 2.0%. The films prepared at 500 °C by PECVD are composed of about 5 and 150 nm crystallites, exhibiting little PL phenomena. The PL intensity of the films prepared by sputter techniques was observed to increase with raising the sputter power and the post-deposition heat-treatment temperature.

Preparation and etching processing of planar thin film of Pr3+-doped fluorozirconate glass

Planar thin-films of a 60ZrF4 · 35BaF2 · 5PrF3 composition were successfully prepared from Zr(hfa)4, Ba(hfa)2(tg), Pr(fod)3 and NF3 by an electron cyclotron resonance plasma-enhanced chemical vapor deposition technique. The films obtained were colorless and amorphous. As etching processing of the prepared thin-film, dry etching was performed using Ar, CF4, SF6, Cl2 and Cl2-BCl3 gases. The Ar etching in which no reactive ion-etching is anticipated exhibited the fastest etching rate. Wet etching was also performed using a ZrOCl2-HCl etching solution. The etching rate was extremely fast compared with those of dry etching. In this etching, however, undesirable side-etching occurred. At the present stage, therefore, the most preferable etching processing is dry etching by an Ar gas.

Laser-scanned p-i-n photodiode (LSP) for image detection

Amorphous and microcrystalline glass/ZnO:Al/p(a-Si:H)/i(a-Si:H)/n(a-Si 1 - x C x :H)/Al imagers with different n-layer resistivities were produced by plasma-enhanced chemical vapor deposition technique (PE-CVD). The transducer is a simple, large area p-i-n photodiode; an image projected onto the sensing element leads to spatially confined depletion regions that can be readout by scanning the photodiode with a low-power modulated laser beam. The essence of the scheme is the analog readout and the absence of semiconductor arrays or electrode potential manipulations to transfer the information coming from the transducer. The effect of the image intensity on the sensor output characteristics (sensitivity, linearity, blooming, resolution, and signal-to-noise ratio) are analyzed for different material composition. The results show that the responsivity and the spatial resolution are limited by the conductivity of the doped layers. An enhancement of one order of magnitude in the image intensity and on the spatial resolution is achieved with a responsivity of 0.2 mW/cm 2 by decreasing the n-layer conductivity by the same amount. In a 4 x 4 cm 2 laser-scanned photodiode (LSP) sensor, the resolution was less than 100 μm and the signal-to-noise (S/N) ratio was about 32 dB. A physical model supported by electrical simulation gives insight into the methodology used for image representation.

CONTROL OF THE SURFACE REACTIONS DURING THE LOW-TEMPERATURE GROWTH OF POLYCRYSTALLINE SILICON FILMS

Polycrystalline silicon (poly-Si) thin films were prepared by a remote microwave plasma-enhanced chemical vapor deposition technique at low temperatures using SiF4and H2 as reactive gases.It was found that the impact of the charged particles in the plasma on the growing surface significantly affects the surface reactions and the crystallinity of the resultant films.By applying the bias on the substrates to decelerate the particles,high-quality poly-Si films, with hydrogen content less than 0.9 at% and the FWHM of 520 cm-1 Raman peak as narrow as 4.4 cm-1,have been obtained at a low temperature of 360℃.

On the deposition mechanism of a-C:H films by plasma enhanced chemical vapor deposition

Amorphous hydrogenated carbon (a-C:H) films were deposited from a mixture of C 2H 2 and Ar, by a radio frequency direct current (r.f.-d.c.) plasma-enhanced chemical vapor deposition technique. The effect of process parameters on the deposition rate of the a-C:H films was systematically studied. It was found that the deposition rate increased initially and then decreased after passing a maximum with the increase of bias voltage and deposition pressure. The deposition rate increased gradually with increasing C 2H 2 content. However, a-C:H films could not be prepared at C 2H 2 contents lower than 10%. A simple phenomenological surface model, which takes into account the sputtering effect of a-C:H films by energetic Ar ion bombardment, is proposed on the basis of these results to describe the deposition mechanism of a-C:H films.

Optical properties of a Fabry–Pérot microcavity with Er-doped hydrogenated amorphous silicon active layer

Fabry–Pérot hydrogenated amorphous silicon (a-Si:H)/amorphous-SiOx:H microcavities with an erbium-doped a-Si:H active region are fabricated by a plasma-enhanced chemical-vapor deposition technique in a single technological cycle without exposure to air between the intermediate operations. A metalorganic compound is used to incorporate erbium in the active a-Si:H layer. Transmission, reflection, and photoluminescence spectra of the microcavities are measured. The experimental data are compared to theoretical calculations performed in terms of field amplitudes generated by stochastic excitation sources.

Plasma-enhanced chemical vapor deposition of PbTiO 3 thin films

Functional ceramic PbTiO 3 thin films have been prepared onto Si substrates by plasma-enhanced chemical vapor deposition (PECVD) technique at the substrate temperature of 170°C. Lead tetraethyl [Pb(C 2H 5) 4], titanium tetrachloride (TiCl 4), and oxygen (O 2) were used as precursors. The composition, structure and morphology of the thin films were investigated by means of X-ray fluorescence spectroscopy (X-FS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) methods.

Gas-sensing properties of PdO-modified SnO 2–Fe 2O 3 double-layer thin-film sensor prepared by PECVD technique

The SnO 2–Fe 2O 3 double-layer thin films have been fabricated onto silicon and ceramic substrates by using plasma-enhanced chemical vapour deposition (PECVD) technique. A small amount of PdO is coated over the surface of SnO 2 thin films to improve their gas-sensing properties to CO. The surface morphologies and the structures of the oxide thin films have been investigated by means of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) methods. Gas-sensing properties of the PdO-modified SnO 2–Fe 2O 3 double-layer thin film and its sensitive mechanism are discussed herein.

Effects of nitric-oxide-plasma treatment on the electrical properties of tetraethylorthosilicate-deposited silicon dioxides on strained-Si1−xGex layers

Gate-quality ultrathin silicon dioxide films on strained-Si0.74Ge0.26 layers have been deposited by microwave plasma-enhanced chemical vapor deposition technique using tetraethylorthosilicate. Effect of nitric-oxide (NO)-plasma treatment on the electrical properties of the deposited oxides have been studied using a metal–insulator–semiconductor structure. A significant improvement in the interface trap level density (Dit) and charge trapping behavior under Fowler–Nordheim constant current stressing is observed for NO-plasma treated deposited oxide films.

Reflectivity modeling of Si-based amorphous superlattices

The structural properties of superlattices composed by hydrogenated amorphous silicon/silicon carbide (a-Si:H/a- Si1−xCx:H) and silicon/germanium (a-Si:H/a-Ge:H), deposited by the plasma-enhanced chemical vapor deposition (PECVD) technique, were analyzed by means of small-angle X-ray diffraction. The relevant structural parameters, such as the multilayer period, the individual layer thickness, the width of the interface and the optical constants, were determined by modeling the experimental reflectivity. The model was based on the dynamical diffraction theory, including material mixing at the interface, interface roughness and random variation of component thickness. In addition, the effect of the direct beam and background on the measured intensities were considered.

Investigation of radiation damage in N doped a-SiC : H films annealed by pulsed electron beam

Nitrogen-doped amorphous silicon carbide films were grown by a plasma-enhanced chemical vapour deposition (PE CVD) technique. For irradiation experiments we used electron beams with a kinetic energy 160 and 200 keV, a pulse duration of 300 ns, and a beam current of 150 A cm −2. A simulation of the RBS spectra was used to calculate the concentration of carbon, silicon and nitrogen. The amount of incorporated hydrogen detected by the ERD analysis was about 20 at%. For the level of radiation damage and activation of dopants electrical characterization of SiC films was used when diode structures were formed on prepared SiC/Si samples. It was found that with increased kinetic energy of pulses the resistivity of the amorphous SiC films substantially reduced and the radiation damage increased.

Optical properties of large band gap Se- and S-doped amorphous hydrogenated silicon

Selenium- and sulfur-doped amorphous hydrogenated silicon films were prepared by the conventional plasma-enhanced chemical vapor deposition (PECVD) technique. Both Se- and S-doped films have band gaps that range from 1.7 to 2.0 eV, as a function of doping concentration. The photoresponse of the films was determined by illuminating with white light of 100 mW/cm 2 intensity. The intensity variation of photoconductivity (PC) showed monomolecular recombination mechanism for a-Si:H films doped with Se (for H 2Se/SiH 4⩽10 −1%) and S (for H 2S/SiH 4⩽10 −2%) and bimolecular for other dopings. The persistent photoconductivity (PPC) measurements at room temperature showed that PPC increased with increasing irradiation time. PPC for Se-doped a-Si:H for a concentration of 10 −3 at.% was of the same order as for 2.7×10 −2 at.% S-doped sample. Photodegradation results indicate that a-Si,Se:H system would be more stable than the a-Si,S:H system as the compensation of the photodegradation due to PPC is larger in the case of Se-doped films.

Thermal stability and breakdown strength of carbon-doped SiO2:F films prepared by plasma-enhanced chemical vapor deposition method

Carbon-doped SiO2:F films were deposited by changing the CH4 flow rate, [CH4], using a plasma-enhanced chemical vapor deposition technique from SiH4/O2/CF4/CH4 mixtures. The thermal stability for the films deposited with a fixed temperature of 300 °C was investigated through the changes in the dielectric constant (εS), IR spectra and stress with annealing temperature, TA, from 400 to 800 °C. The breakdown strength for films as-deposited were also measured. The addition of carbon to SiO2:F films resulted in the films with low εS (up to 3.0) and high water resistivity. Addition of high [CH4] in the films resulted in stable εS for TA=500 °C or less. The CH4 addition initially decreased the breakdown strength but then increases again. Under the application of sum rule to the analysis of the vibrational absorption, it was suggested that the decrease in εS with [CH4] results from the decrease in the effective dynamic charge of Si–O dipoles along with the direct contribution of Si–F bonds incorporated to SiO2. The decrease in Si–F and Si–O peak frequencies based on the analysis of the charge transfer model suggested an increase in the Si–F and Si–O bond length, in addition to a decrease in the Si–O–Si bond angle.

Growth-etching competitive mechanism governing the structure and chemical composition of plasma-deposited silicon-based materials

Abstract The plasma-enhanced chemical vapour deposition technique has been utilized to deposit silicon-carbon alloys from SiH4-CH4 and SiF4-CH4 glow discharges and silicon films from SiF4-H2-He mixtures. The silicon-based material deposition is shown to result from a competition between growth and etching reactions. Control of the two competitive channels is capable of determining the alloy composition and the amorphous-to-microcrystalline transition. Data from optical emission spectroscopy can provide a powerful tool for monitoring the channels governing the net material deposition rate.

Application of in situ ellipsometry in the fabrication of thin-film optical coatings on semiconductors

Thin-film interference filters, suitable for use on GaAs- and InP-based lasers, have been fabricated by use of the electron-cyclotron resonance plasma-enhanced chemical vapor deposition technique. Multilayer film structures composed of silicon oxynitride material have been deposited at low temperatures with an in situ rotating compensator ellipsometer for monitoring the index of refraction and thickness of the deposited layers. Individual layers with an index of refraction from 3.3 to 1.46 at 633 nm have been produced with a run-to-run reproducibility of 0.005 and a thickness control of 10 A. Several filter designs have been implemented, including high-reflection filters, one- and two-layer anitreflection filters, and narrow-band high-reflection filters. It is shown that an accurate measurement of the filter optical properties during deposition is possible and that controlled reflectance spectra can be obtained.

Comparison of low temperature growth of Si thin films on amorphous substrates by MBE and PECVD methods

ABSTRACTLow temperature growth of thin crystalline Si films on amorphous glass substrates by Molecular Beam Epitaxy (MBE) as well as by two different plasma enhanced chemical vapour deposition (PECVD) systems both using a DC plasma was carried out and the mictrostructural properties were analysed. In particular, the control over the texture along [220] orientation and the resulting columnar nature of the films were studied. The TEM cross section of Si films grown by MBE shows grains with an average width of 750 nm and a length of 3 microns. Using the low energy PECVD (LEPECVD) technique microcrystalline Si films were obtained with a growth rate of up to 35Å/sec. For high quality Si films with larger grains one may grow Si films by MBE whereas for Si films with passivated grain boundaries and for increased deposition rate, it is preferred to grow Si films by the newly developed methods of DC-PECVD.

Tungsten deposition by dual-frequency inductively coupled plasma-assisted CVD

A new inductive plasma reactor has been developed for coating complex, three-dimensional parts using the plasma-enhanced chemical vapour deposition (PECVD) technique. In order to control independently the temperature of the parts to be treated, induction heating has been adapted to an inductively coupled plasma CVD reactor. Design of low-pass and high-pass filters has been made in order to prevent interference of the two frequencies: 13.56 MHz for plasma generation and 150 kHz for heating. Ion-current densities have been measured over a large pressure range: large ionic current can be obtained at an optimum pressure of 13 Pa (100 mtorr). Preliminary deposition tests of tungsten from WF6/H2 have been made. It has been found that the H2/WF6 flow rate ratio is strongly related to the microstructure and crystal structure. Tungsten films have a columnar microstructure. Lack of contamination by fluorine was verified.

Substrate temperature: A critical parameter for the growth of microcrystalline silicon-carbon alloy thin films at low power

P-type microcrystalline silicon-carbon alloy thin films have been prepared at low power by employing radio-frequency plasma-enhanced chemical vapor deposition (rf-PECVD) technique; judicious choice of deposition parameters is necessary. Substrate temperature has been observed to be the most critical parameter, while high hydrogen dilution is necessary but not a sufficient condition for obtaining crystallinity in silicon-carbon alloy thin films. Best microcrystallinity at moderate power density (78 mW/cm2) has been obtained at a fairly low substrate temperature (180 °C). The highest conductivity of 5.7 Scm−1 of a boron-doped microcrystalline sample could be achieved. Incorporation of carbon in these films has been confirmed from x-ray photoelectron spectroscopic (XPS) studies. Carbon is, however, incorporated only in the amorphous phase while the crystallites are of silicon only as observed from Raman spectra.