Remote Plasma-enhanced Chemical Vapor Deposition Research Articles

Study of the influence of NH 3 flow rates on the structure and photoluminescence of silicon-nitride films with silicon nanoparticles

Silicon-nitride films with silicon nanoparticles have been prepared at 300 °C by remote plasma-enhanced chemical vapor deposition using mixtures of H 2, Ar and SiH 2Cl 2 and various NH 3 flow rates. The films were characterized by means of Rutherford backscattering spectrometry, Fourier-transform infrared spectroscopy, single wavelength ellipsometry, high-resolution transmission electronic microscopy, atomic force microscopy and photoluminescence measurements. It was found a chemical stability as well as an increase in the photoluminescence signal for those films with the greatest amount of NH 3. The increase in the photoluminescence signal is due to a quantum confinement effect produced by the nanoparticles, which were formed during the film's preparation process.

Carbon Nanotube Vias Fabricated by Remote Plasma-Enhanced Chemical Vapor Deposition

Multiwalled carbon nanotubes (CNTs) have been grown by remote plasma-enhanced chemical vapor deposition at temperatures as low as 400 °C. In via formation, the selective growth of CNT bundles in via holes at 430 °C and chemical mechanical polishing for planarization have been performed. The electrical evaluation of CNT single vias with various diameters reveals that the via resistance is inversely proportional to the via area. This result indicates that the CNTs are grown with uniform quality and density in the via holes with various diameters and stable contact formations are obtained. Moreover, the resistances of single vias are approximately equivalent to the via resistances estimated from the resistances of via chains, demonstrating the via-to-via uniformity of the CNT vias obtained by the remote plasma-enhanced chemical vapor deposition.

In situ spectroscopic ellipsometry growth studies on the Al-doped ZnO films deposited by remote plasma-enhanced metalorganic chemical vapor deposition

In situ spectroscopic ellipsometry (SE) was applied to study the pyramidlike and pillarlike growth of Al doped ZnO (AZO) films deposited by means of remote plasma-enhanced metalorganic chemical vapor deposition for transparent conductive oxide applications. Real time SE studies in the visible region allowed discerning between the two growth modes by addressing the time evolution of the bulk and surface roughness layer thickness. While the pillarlike mode is characterized by a constant growth rate, a slower rate in the initial stage (up to 150–200 nm film thickness), compared to the bulk, is observed for the growth of pyramidlike AZO films. The two modes differ also in terms of surface roughness development: a saturation behavior is observed for film thickness above 150–200 nm in the case of the pyramidlike films, while a slow linear increase with film thickness characterizes the pillarlike mode. By extending the SE analysis of the AZO films to the near infrared region, valuable information about the in grain properties could be extracted: excellent in grain mobility values, i.e., larger than 100 and 50 cm2/V s, are determined for the pyramidlike and pillarlike AZO layers, respectively. The comparison between the outcome of the in situ real time SE studies and the ex situ electrical and chemical characterization highlights the limitations in the electron transport occurring in both types of films and allows one to address routes toward further improvement in AZO conductivity.

Characterization of the Intrinsic Amorphous Silicon (a-Si:H) Layer Prepared by Remote-PECVD for Heterojunction Solar Cells: Effect of the Annealing Treatment on Multi-crystalline Si Wafer

The effect of hydrogenated amorphous silicon (a-Si:H) intrinsic layers, deposited on boron-doped multicrystalline silicon (mc-Si) wafers at various deposition temperatures, on heterojunction solar cells prepared using the radio-frequency remote PECVD method are investigated. The structural and optical properties of the a-Si:H films formed at various deposition temperatures that ranged from 50 to 400°C changed with increasing temperature. The effective carrier lifetimes of the mc-Si wafers with the a-Si:H films increased with increasing deposition temperature to a maximum of 250°C. Furthermore, the wafers passivated with the a-Si:H films deposited temperatures below 250°C, and the effective carrier lifetime drastically improved to about 2-5 times its as-deposited value and over the chemical passivation lifetime after annealing treatment at 350°C. It was found that a combination of a-Si:H film deposition and annealing treatment provides excellent bulk passivation. [DOI: 10.1380/ejssnt.2008.124]

Structural and optical properties of high density Si-ncs synthesized in SiN x:H by remote PECVD and annealing

Silicon nanocrystals (Si-ncs) embedded in silicon nitride are of great interest for micro and optoelectronic devices such as non-volatile memories and solar cells. Indeed, Si 3N 4 is a “high- k” dielectric and can replace SiO 2 in Si-ncs memories, increasing their performances. On the other hand, Si-ncs embedded in Si 3N 4 antireflection layer of solar cells can be used as luminescent converters to enhance photovoltaic conversion in the blue region of the spectrum. Controlling Si-ncs characteristics (density, size, surface passivation, etc.) is necessary to the optimisation of both electrical and optical properties of the layers. In this work, we synthesized SiN x :H 50 nm thick layers by ECR-PECVD using NH 3 and SiH 4 gases. Si-ncs are obtained thanks to a Si atom excess in the matrix, controlled by the gas flow ratio. The samples were annealed under Ar flow, first in a RTA furnace at 1000 °C during 1 min for particles nucleation, and then in a classic furnace, from 700 °C to 1100 °C, in order to investigate the Si nanostructure evolution. We studied the structural characteristics of Si-ncs population by energy-filtered transmission electron microscopy (EF-TEM). The layers composition was determined by Rutherford back scattering spectroscopy (RBS) and elastic recoil detection analysis (ERDA). Their optical properties were studied by photoluminescence spectroscopy (PL). Results clearly show that structural and optical characteristics of these systems can be controlled by deposition parameters and annealing.

Electronic band gap of Si/SiO2 quantum wells: Comparison of ab initio calculations and photoluminescence measurements

We investigate the influence of layer thicknesses and interface modifications on the fundamental electronic gap of Si/SiO2 multilayers by a combined ab initio calculation and photoluminescence (PL) analysis. For the band gap calculations different Si/SiO2 interface models are studied. Experimentally investigated multiple quantum wells are prepared by remote plasma-enhanced chemical vapor deposition and rapid thermal annealing. The well-width dependence of the band gap obtained from PL measurements is much weaker than found in previous studies. This sublinear variation is in accordance with simulated electronic band gaps for hydrogen-free Si/SiO2 interfaces. The presence of hydrogen at the interfaces enforces the confinement effect for the band gap. Materials involved: nanocrystalline silicon, amorphous silica, β-cristobalite silica, and Si/SiO2 interface.

Preparation and characterization of thin organosilicon films deposited on SPR chip

The paper reports on the preparation and characterization of organosilicon thin polymer films deposited on glass slides coated with 5 nm adhesion layer of titanium and 50 nm of gold. The polymer was obtained by the decomposition of 1,1,3,3-tetramethyldisiloxane precursor (TMDSO) premixed with oxygen induced in a N 2 plasma afterglow using remote plasma-enhanced chemical vapor deposition (PECVD) technique. The film thickness was controlled by laser interferometry and was 9 nm. The chemical stability of the gold substrate coated with the organosilicon polymer film (p-TMDSO) was studied in different acidic and basic solutions (pH 1–14). While the gold/polymer interface showed a high stability in acidic media, the film was almost completely removed in basic solutions. The resulting surfaces were characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), water contact angle measurements, cyclic voltammetry, and surface plasmon resonance (SPR).

Evolution of the electrical and structural properties during the growth of Al doped ZnO films by remote plasma-enhanced metalorganic chemical vapor deposition

Al-doped zinc oxide (AZO) films were deposited by means of remote plasma-enhanced metalorganic chemical vapor deposition from oxygen/diethylzinc/trimethylaluminum mixtures. The electrical, structural (crystallinity and morphology), and chemical properties of the deposited films were investigated using Hall, four point probe, x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), electron recoil detection (ERD), Rutherford backscattering (RBS), and time of flight secondary ion mass spectrometry (TOF-SIMS), respectively. We found that the working pressure plays an important role in controlling the sheet resistance Rs and roughness development during film growth. At 1.5 mbar the AZO films are highly conductive (Rs<6 Ω∕□ for a film thickness above 1200 nm) and very rough (>4% of the film thickness), however, they are characterized by a large sheet resistance gradient with increasing film thickness. By decreasing the pressure from 1.5 to 0.38 mbar, the gradient is significantly reduced and the films become smoother, but the sheet resistance increases (Rs≈100 Ω∕□ for a film thickness of 1000 nm). The sheet resistance gradient and the surface roughness development correlate with the grain size evolution, as determined from the AFM and SEM analyses, indicating the transition from pyramid-like at 1.5 mbar to pillar-like growth mode at 0.38 mbar. The change in plasma chemistry/growth precursors caused by the variation in pressure leads to different concentration and activation efficiency of Al dopant in the zinc oxide films. On the basis of the experimental evidence, a valid route for further improving the conductivity of the AZO film is found, i.e., increasing the grain size at the initial stage of film growth.

Nitride film growth morphology using remote plasma enhanced chemical vapor deposition

Gallium nitride and indium nitride films have been grown by remote plasma enhanced chemical vapor deposition (RPECVD) at temperatures between 570 and 650 °C for GaN and between 350 and 570 °C for InN on different substrates. For GaN vast improvements in film morphology and quality have resulted from reductions in background impurities when compared to previous reports. Epitaxial material can now be grown at 650 °C under optimized growth conditions. Columnar growth still occurs for growth on some substrates, however film coalescence is observed when using appropriate buffer layers and epitaxial growth can also be observed. High resolution SEM images show examples of this. The root-mean-square surface roughness of epitaxial samples, as measured using atomic force microscopy, shows values of as little as 10 Angstroms. While X-ray diffraction shows that these surfaces are not amorphous but have a strong (0001) preferred axis with FWHM limited by instrumental effects to (2θ) 0.085 degrees. The improvement in film quality has allowed heavily doped n-type films to be grown with an electron mobility of 160 cm2/V·s for a carrier concentration of ∼ 1x1019 cm–3 at 650 °C. Moss-Burstein shifted absorption data confirms the high doping level. For InN film growth by RPECVD, columnar growth is commonly observed in the temperature region of interest for films grown directly on sapphire, however film coalescence and epitaxial films are also observed for this material. X-ray diffraction indicates very sharp (0002) peaks with FWHM of (2θ) 0.07 degrees. High resolution SEM images show examples of film morphology at different growth temperatures. Electron backscattered diffraction images indicate a wurtzite structure even for InN films with strong deviations from the accepted lattice parameters. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Passivation Effects of 100 nm In0.4AlAs/In0.35GaAs Metamorphic High-Electron-Mobility Transistors with a Silicon Nitride Layer by Remote Plasma-Enhanced Chemical Vapor Deposition

In0.4AlAs/In0.35GaAs metamorphic high-electron-mobility transistors (MHEMTs) have been successfully fabricated. In order to reduce the surface effects on the barrier layer, Si3N4 layer passivation by remote plasma-enhanced chemical vapor deposition (PECVD) is utilized, which might suppress the surface trap density in side-recessed region and reduce the parasitic resistance. The device simulation was performed to derive the effects of surface trap in the side-recessed region. As the surface trap density decreases, ID.max increases because of the stabilization of the surface states in the side-recessed region. This result indicates that the increases of gm.max and ID.max are related with both the reduction of parasitic resistance and the gate-sinking effect. The fabricated 100 nm MHEMTs with the passivated of Si3N4 layer exhibited excellent characteristics such as a maximum extrinsic gm.max of 740 mS/mm and a cut off frequency ( fT) of 210 GHz.

Effect of Plasma Gases on Insulating Properties of Low-Temperature-Deposited SiOCH Films Prepared by Remote Plasma-Enhanced Chemical Vapor Deposition

Carbon-doped silicon oxide (SiOCH) films were deposited by plasma-enhanced chemical vapor deposition (PECVD) using tetraethoxysilane (TEOS) at low temperatures (27–53 °C). The structural and insulating properties of the films deposited with Ar or N2 plasma were investigated. In the deposition with low plasma density and low substrate temperature, both plasmas produced films with high hydrocarbon (CHn) content. The films prepared using Ar plasma showed a low leakage current of 7×10-10 A/cm2 at 1 MV/cm due to the incorporation of CHn groups, while the films with high CHn content prepared using N2 plasma showed poor insulating properties. The deposition using N2 plasma formed films with a defective structure, resulting in a higher etch rate than that of the films deposited with Ar plasma. The deposition with the low-density plasma of inert Ar gas is suitable for the low-temperature deposition of SiOCH films with high resistivity.

Structural evolution of nanocrystalline silicon studied by high resolution transmission electron microscopy

Abstract In this work, nanocrystalline silicon (nc‐Si) embedded in amorphous silicon nitride (a‐SixNy) films have been characterized by High Resolution Transmission Electron Microscopy (HRTEM). The films have been grown by remote plasma enhanced chemical vapour deposition (RPECVD) onto silicon substrates using a mixture of SiCl4, NH3 and H2. Subsequently, the sample has been introduced to an annealed process. The nanocrystalline inclusions have been measured from the analysis of HRTEM images. The size of nc‐Si inclusions is modified due to the annealing process. The diameter of nc‐Si inclusions in as‐grown films vary from 1.3 to 3.1 nm. In annealed films, a high density of new clusters with reduction of 1 nm of those diameters is observed, as well as the coalescence phenomenon among some nc‐Si inclusions is observed too. Consequently, the diameters of annealed films nc‐Si inclusions range from 0.7 to 4 nm. The thin films show an excellent photoluminescence emission. The density per unit area and size of the nc‐Si inclusions are correlated with the PL emissions. The influence of the structural changes of the nc‐Si on the PL emissions is discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fluorine content of SiOF films as determined by IR spectroscopy and resonant nuclear reaction analysis

In this article, the authors compare the fluorine concentrations obtained from the strength of the infrared-absorption band due to Si–F bonds, with the absolute concentrations determined from F19(p,αγ)O16 resonant nuclear reaction analysis, for a series of fluorinated silicon oxide (SiOF) films prepared by remote plasma-enhanced chemical-vapor deposition with different flow rates of H2 in SiF4∕O2∕He mixtures. The authors use this comparison to calibrate the proportionality constant between the strength (integrated absorption) of the infrared-absorption band due to Si–F bonds and the concentration of these bonds in the films. The authors found that (under the Gentzel and Martin approach [Surf. Sci. 34, 33 (1973)]) this calibration requires the correction of the “fudge” factor, to a new value, γ=1.28, which is more consistent with the small correction to the local field expected for porous SiOF films. The authors also found that the changes in the refractive index and density of the films introduce less significant corrections in the quantification process of fluorine by the infrared method.

Visible photoluminescence from silicon nanoclusters embedded in silicon nitride films prepared by remote plasma-enhanced chemical vapor deposition

The photoluminescence (PL) of silicon nanoclusters embedded in silicon nitride films grown by remote plasma-enhanced chemical vapor deposition at 200 °C, using mixtures of SiCl 4/H 2/Ar/NH 3 is investigated. It was found that the color and the intensity of the PL of the as-grown samples depend on the H 2 flow rate, and there is an optimum flow for which a maximum luminescence is obtained. A strong improvement of the PL intensity and change in color was obtained with annealing treatments in the range of 500–1000 °C. The changes in the composition, structure and optical properties of the films, as a function of H 2 flow rate and thermal treatments, were studied by means of Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, ellipsometry and ultraviolet–visible transmission measurements. We conclude that the PL can be attributed to quantum confinement effect in silicon nanoclusters embedded in silicon nitride matrix, which is improved when a better passivation of the nanoclusters surface is obtained.

Structural and optical properties of Si/SiO 2 multi-quantum wells

Structural and optical properties of Si/SiO 2 multi-quantum wells (MQW) were investigated by means of Raman scattering and photoluminescence (PL) spectroscopy. The MQW structures were fabricated on a quartz substrate by remote plasma enhanced chemical vapour deposition (RPECVD) of alternating amorphous Si and SiO 2 layers. After layer deposition the samples were subjected to heat treatments, i.e. rapid thermal annealing (RTA) and furnace annealing. Distinct PL signatures of confined carriers evidenced formation of Si-nanocrystals (nc-Si) in annealed samples. Analyses of Raman spectra also show presence of nc-Si phase along with amorphous-Si (a-Si) phase in the samples. The strong influence of the annealing parameters on the formation of nc-Si phase suggests broad possibilities in engineering MQW with various optical properties. Interestingly, conversion of the a-Si phase to the nc-Si phase saturates after certain time of furnace annealing. On the other hand, thinner Si layers showed a disproportionately lower crystalline volume fraction. From the obtained results we could assume that an interface strain prevents full crystallization of the Si layers and that the strain is larger for thinner Si layers. The anomalous dependence of nc-Si Raman scattering peak position on deposited layer thickness observed in our experiments also supports the above assumption.

Si-nanostructures formation in amorphous silicon nitride SiN x:H deposited by remote PECVD

The formation of silicon nanoclusters embedded in amorphous silicon nitride (SiN x :H) can be of great interest for optoelectronic devices such as solar cells. Here amorphous SiN x :H layers have been deposited by remote microwave-assisted chemical vapor deposition at 300 °C substrate temperature and with different ammonia [NH 3]/silane [SiH 4] gas flow ratios ( R=0.5−5). Post-thermal annealing was carried out at 700 °C during 30 min to form the silicon nanoclusters. The composition of the layers was determined by Rutherford back scattering (RBS) and elastic recoil detection analysis (ERDA). Fourier transform infrared spectroscopy (FTIR) showed that the densities of Si H (2160 cm −1) and N H (3330 cm −1) molecules are reduced after thermal annealing for SiN:H films deposited at flow gas ratio R>1.5. Breaking the Si H bonding provide Si atoms in excess in the bulk of the layer, which can nucleate and form Si nanostructures. The analysis of the photoluminescence (PL) spectra for different stoichiometric layers showed a strong dependence of the peak characteristics (position, intensity, etc.) on the gas flow ratio. On the other hand, transmission electron microscopy (TEM) analysis proves the presence of silicon nanoclusters embedded in the films deposited at a gas flow ratio of R=2 and annealed at 700 °C (30 min).

The C2H2 gas effect on the growth behavior of remote plasma enhanced CVD SiC:H film

SiC:H films were produced in a remote plasma enhanced chemical vapor deposition (RPE-CVD) system. The HMDS was chosen as the primary source gas and was fixed at constant flow rate of 10 sccm. The C2H2 gas input amount was varied from 3 to 200 sccm for the study of carbon effect on the film stoichiometry and bonding properties. The deposition temperature of the substrate was fixed at 400∘C, and the plasma power was fixed at 300 W. Using auger electron spectroscopy, the depth profile of the film was investigated with C2H2 flow rate changes. The C2H2 played an important role in the transition between sp2 and sp3 carbon hybridization bonds, which affected the growth behavior and properties of the films.

Influence of substrate temperature on the properties of fluorinated silicon-nitride thin films deposited by IC-RPECVD

Fluorinated silicon-nitride films have been prepared from an Ar/SiF4/NH3 gas mixture by inductively coupled remote plasma-enhanced chemical vapor deposition (IC-RPECVD) at different substrate temperatures, ranging from 150 to 300°C. All of the resulting deposited silicon-nitride films were free of Si-H bonds, showed high dielectric breakdown fields (≥8 MV cm−1), and had root mean square (rms) surface roughness values below 3 A. The films’ refractive indices and the contents of O and F remain constant, but Si/N ratios drop from 5 to 2 and N-H bond concentrations decrease in the range (1.3–0.9) × 1022 cm−3 as the substrate temperature increases. The density of interface states (Dit) with c-Si was reduced from 2.4 × 1012 to 8 × 1011 eV−1 cm−2 at substrate temperatures ≥250°C.

Photoconductive Characteristics of Hydro-Oxygenated Amorphous Titanium Oxide Films Prepared by Remote Plasma-Enhanced Chemical Vapor Deposition

The photoconductive characteristics of amorphous titanium oxide films (a-TiOx:OH) prepared by remote plasma-enhanced (RPE) chemical vapor deposition, in inert Ar atmosphere with/without a small amount of oxygen, have been studied. In inert Ar atmosphere without oxygen, the residual decay of photocurrent (long decay time) is observed after removing UV irradiation. On the other hand, in inert Ar atmosphere with a small amount of oxygen, the photocurrent under UV irradiation is influenced strongly by an environmental gas with oxygen gas. The maximum of photocurrent (photosensitivity) is nearly inversely proportional to oxygen partial pressure, suggesting that the present films are useful for sensors of environmental oxygen gases. The decay of photocurrent, after removing UV irradiation, follows a stretched exponential function. The effective decay time τ is nearly inversely proportional to oxygen partial pressure. The results will be discussed in terms of the surface reaction of oxygen gas on the present films.

Apparent band-gap shift in InN films grown by remote-plasma-enhanced CVD

The properties of indium nitride grown at various temperatures on c-plane sapphire and glass substrates, using remote plasma-enhanced chemical vapour deposition, have been investigated. The optical absorption spectra show a broad range of apparent band-gap values from approximately 2.3–0.9 eV, depending on the growth temperature. The influence of growth temperature on crystallinity, level of impurity incorporation, stoichiometry, and lattice distortion are analysed. The possible causes of the apparent band-gap shift in indium nitride are discussed.