Plasma deposition of hydrogenated amorphous silicon: Studies of the growth surface

This review focusses on the plasma-surface interactions and surface processes involved in a-Si: H thin film growth. We restrict our discussion of growth fluxes to a summary, and do not address plasma kinetics. In recent years, powerful in situ experiments have been carried out on the growing film surface, which reveal the adsorption, penetration, reaction, and elimination of precursor species, as well as the atomic-scale morphology and composition of the growth zone. Good data sets are available both for PACVD and reactive magnetron sputter deposition. These form an interesting comparison, since the former process is dominated by the hydrogen-rich radical SiH₃ at low energy, and the latter by energetic atomic Si and H. We review the key experiments and conclusions, underlining those aspects which are well established and those which remain qualitative; and we discuss the transition from amorphous to fine-grained polycrystalline film growth at high hydrogen pressures in terms of the surface mechanisms. This field is now entering a scientific stage where a detailed theory of low-temperature, plasma-assisted growth can be developed.     

Cavity ring-down spectroscopy of CH and CD radicals in a diamond thin film chemical vapor deposition reactor

A mixture of H₂ and CH₄ is passed over a hot-wire tungsten filament in a diamond thin film chemical vapor deposition reactor. The resulting CH radicals are measured in absorption using cavity ring-down spectroscopy (CRDS). The concentration of the CH radicals increases as the filament is approached. The rotational temperature measurements indicate a large temperature discontinuity between the filament and the CH in the gas phase. The pathways for CH production were investigated by replacing H₂ by D₂ in the feed gas mixture, which resulted in the exclusive production of CD. From this observation it is concluded that rapid H/D isotope exchange dominates in the gas phase. Nonperiodic temporal oscillations in the CH concentration are observed when a rhenium filament is used in place of a tungsten filament. The oscillations are attributed to the nonperiodic changes in the amount of carbon at the filament surface. Received: 21 August 2000 / Accepted: 23 August 2000 / Published online: 23 May 2001     

Thick gold-film deposition by high-repetition visible pulsed-laser chemical vapor deposition

A highly conductive gold film, over 10 m-thick with well-controlled linewidth, has been successfully deposited from dimethyl-gold-acetylacetonate and its fluorinated derivative by pyrolytic CVD (Chemical Vapor Deposition) with a high-repetition, visible, pulsed laser. The thermal damage to the polyimide substrate has been substantially suppressed by reducing the thermal diffusion length within 0.2 m in pulsed-laser-induced transient heating, in contrast to the cw laser-CVD scheme. Reproducible and low contact resistance as low as 0.5 between the written line and the existing gold line has been obtained. Sufficiently tough adhesion to polyimide has been observed for the deposit from dimethyl-gold-acetylacetonate. Reasonable agreement has been obtained between the observed deposition characteristics and analytical results for precursor supply rate and temperature increase during short-pulse irradiation.     

Bistable growth in laser chemical vapor deposition

This is the first report on the observation of a bistability in laser-CVD. The effect is demonstrated for silicon deposition from silane by means of Ar⁺-laser radiation.     

Film growth and mechanism of LICVD of chromium films from Cr(CO)6 at 248 nm

The probe-beam transmission method was used to study the chemical vapor deposition of chromium films due to photodecomposition of Cr(CO)₆ by pulsed excimer laser radiation at 248 nm in a reversed-substrate configuration, where the film forms on the quartz entrance window of the deposition cell. The dependence of the deposition rate and the film formation time on the laser pulse intensity and repetition rate as well as on the Ar buffer gas pressure was determined for different stages of the deposition process. The experiments were performed at room temperature, on a deposition area of about 0.15 cm², with laser fluences up to 100mJ cm^–2, pulse repetition rates between 5 and 80 pps and buffer gas pressures between 10 and 700 mbar. The results are discussed within the framework of a simple model for LICVD. They reveal the dominant role of gas-phase photodissociation and diffusion in chromium film deposition under the conditions employed. Some results concerning the morphology and the depth distribution of Cr, O, and C in films deposited in the reversed-substrate configuration are also presented.     

New types of periodic structures in laser-induced chemical vapor deposition

New types of periodic structures that occur in laser-induced chemical vapor deposition have been investigated, mainly for polycrystalline Si deposited on glass substrates covered with a thin amorphous Si layer. These periodic structures, which are believed to be a general phenomenon in pyrolytic laser-induced processing, limit the resolution obtainable in direct writing of patterns.On leave from Fudan University, Department of Electronic Engineering, Shanghai, People's Republic of China     

Film growth mechanism of photo-chemical vapor deposition

The photo-chemical vapor deposition (CVD) of SiO₂ and SiN _x were investigated using 185 nm light of a low pressure mercury lamp. The film thickness deposited on the substrate was the function of the distance from the substrate to the light source and its relation was investigated by changing the reaction pressure. From these investigations, the space migration length of the active species was estimated, which was, at the processing pressure of 400 Pa, 10–20 mm. This migration length was confirmed by a model calculation. The step coverage of the film was investigated by the use of a two-dimensional capillary cavity. It was shown that the thickness decayed exponentially with the depth in the cavity. The decay constant did not show temperature dependence. From this result, the surface migration of the active species produced by photo-CVD was reported. To confirm this migration we presented a substrate-size effect of photo-CVD, which became obvious when the substrate size became smaller than the space migration length of the active species. From these results, the film growth mechanism of photo-CVD was discussed.Main parts of this paper were presented at the Material Research Society Fall Meeting at Boston 1987     

Direct writing of gold lines by laser-induced chemical vapor deposition

Stripes of gold metal were deposited by focussing an Ar⁺ laser (514nm) onto glass substrates in a heated vacuum cell containing the evaporator and the precursor. MeAuPMe₃, Me₃AuPR₃ (R = Me,Et) were used as precursors. Using MeAuPMe₃ or Me₃AuPEt₃, deposits of high quality were obtained above 40° C and 60° C evaporator temperature, respectively. With Me₃AuPMe₃ the same deposits of gold stripes were possible near room temperature. The stripes were characterized by scanning profilometry, electrical resistivity, SEM and SAM measurements. In general, the stripe resistivity was between 1.5 and 7 times of the bulk metal.     

Doping properties of microcrystalline silicon prepared by mercury sensitized photochemical vapor deposition

Conductivity of photo-CVD microcrystalline silicon (c-Si:H) in wide range of dopant gas concentration (10^–53/SiH₄, B₂H₆/SiH₄<10^–2) is investigated. As compared with a-Si:H, the conductivity of the film is improved more than two orders of magnitude by microcrystallization for a wide range of dopant concentration at a deposition temperature of as low as 150°C. This indicates the suitability of photo-CVD for low temperature processing. A conductivity minimum is found at a doping ratio of about B₂H₆/SiH₄=1×10^–5.     

Effect of Al incorporation on the AlGaN growth by metalorganic chemical vapor deposition

The effect of Al incorporation on the AlGaN growth by metalorganic chemical vapor deposition is investigated. With the increase of trimethylalluminum (TMAl) flux, the crystal quality becomes worse, and the epilayer surface becomes rougher. An interesting phenomenon is that the growth rate of AlGaN decrease with increasing TMAl flux, which is opposite to the AlN growth rate dependence on the TMAl flux. All these effects are attributed to the different properties of Al atoms due to the higher bond strength of Al-N compared with Ga-N, which lead to lower surface mobility and stronger competitive ability of Al atoms during the growth. The enhancement of the surface mobility of Al is especially important for improving the quality of AlGaN.     

Thin strain-relaxed SiGe grown by ultrahigh vacuum chemical vapor deposition

Large-scale preparation of thin strain-relaxed SiGe is achieved by combining ion implantation and ultrahigh vacuum chemical vapor deposition. The resulting materials were analyzed by double crystal X-ray diffraction, micro-Raman spectroscopy, and tapping mode atomic force microscope. Results revealed that 100-nm-thick Si_0.7Ge_0.3 layers with the diameter of 125 mm and full strain relaxation are successfully prepared by pre-modifying the Si substrates using 50 keV Ar⁺ ions. The strain relaxation is also disclosed to change with both ion species and energy. However, post-modification of SiGe by ion implantation will cause serious damage to the crystal structures, and result in the formation of poly-crystal SiGe.     

Atomic layer deposition of iridium(III) acetylacetonate on alumina, silica-alumina, and silica supports

The deposition of noble metal particles and films by atomic layer deposition (ALD) has recently gained interest in the fields of catalysis and microelectronics. However, there is little information on the mechanisms governing the reactions of noble metals with high surface area supports. In this work, iridium(III) acetylacetonate was deposited from gas phase onto alumina, silica-alumina, and silica supports to gain insight into the reaction mechanisms. According to elemental analysis and infrared spectroscopy, ligand exchange reaction between iridium acetylacetonate and surface OH groups took place on all substrate surfaces, but the iridium deposition on alumina and silica-alumina appeared to be hindered by sterical effects of the acetylacetonate ligands. Part of the iridium on silica was in metallic form. To reduce the content of iridium, reactive sites of the support surfaces were blocked with H-acetylacetonate (2,4-pentanedione). The blocking reduced the iridium content by more than 90% on alumina but by only 30-50% on silica-alumina. The attempted blocking had almost no effect on silica as expected. According to the results of this work, ALD can provide a feasible method for preparing iridium catalyst with reasonable iridium loadings.     

Plasma and surface modeling of the deposition of hydrogenated carbon films from low-pressure methane plasmas

The elementary mechanisms are described which determine the plasma and surface processes during the plasma-enhanced chemical vapour deposition of hydrogenated carbon films from methane. Corresponding model calculations are reviewed and critically discussed in comparison to experimental results. A realistic modeling requires the simultaneous and self-consistent treatment of plasma and surface effects. Several experimental data sets on plasma parameters and the growth and the composition of the films have been reproduced successfully. However, a broader experimental data base is needed for more critical tests of the models. The reliability of the modeling, in particular of the surface effects, is still limited due to the poor availability of elementary data.     

Growth of vertically aligned carbon-nanotube array on large area of quartz plates by chemical vapor deposition

A simple method has been developed for growth of well-aligned carbon nanotubes (CNTs) on nickel-film quartz plates by chemical vapor deposition (CVD) with organic ethylenediamine as a precursor. High-density carbon nanotubes were vertically aligned on a large area of the quartz plates. The height of the nanotube array could be controlled by varying the CVD time. High-resolution transmission electron microscopy analysis revealed that the multiwalled CNTs were composed of crystalline graphitic sheets with a bamboo structure. Received: 28 May 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002     

One-dimensional structures of Bi2O3 synthesized via metalorganic chemical vapor deposition process

We have demonstrated the synthesis of one-dimensional (1D) structures of bismuth oxide (Bi₂O₃) by a reaction of a trimethylbismuth (TMBi) and oxygen (O₂) mixture at 450 °C. Scanning electron microscopy showed that the product consisted of 1D materials with width or diameters less than 1 μm and lengths up to several tens of micrometers. The X-ray energy dispersive spectroscopy revealed that the materials contained elements of Bi and O. The results of X-ray diffraction and selected area electron diffraction pattern indicated that the obtained Bi₂O₃ were crystalline with monoclinic structure.     

Study on effects of substrate temperature on growth and structure of alignment carbon nanotubes in plasma-enhanced hot filament chemical vapor deposition system

Alignment carbon nanotubes (ACNTs) were synthesized on silicon substrate coated with Ni catalyst film and Ta buffer layer by plasma-enhanced hot filament chemical vapor deposition using CH₄, NH₃, and H₂ as the reaction gas, and they were investigated by scanning electron microscopy and transmission electron microscopy. It is found that the diameter of the bamboo-structured ACNTs is increased from 62 to 177 nm when the substrate temperature was changed from 626 to 756 °C. Their growth rate is enhanced by the substrate temperature in a range of 626-683 °C and it is reversely reduced with the substrate temperature after the substrate temperature is over 683 °C. Beginning with wetting phenomenon, the effects of the substrate temperature on the structure and growth rate of the ACNTs are analyzed.     

Formation of the ferroelectric domains in epitaxial PbTiO3 thin films grown by metalorganic chemical vapor deposition

3 thin films have been prepared by metalorganic chemical vapor deposition under reduced pressure. The formation of ferroelectric domains in films grown on SrTiO₃ and LaAlO₃ substrates was investigated by synchrotron radiation and Rutherford backscattering spectroscopy. Single-domain (3000-Å thick) and multi-domain (4500-Å thick) PbTiO₃ films were produced on SrTiO₃. For multi-domain PbTiO₃ film, the c-domain presented epitaxial structure with its c-axis perpendicular to the substrate surface, while a-domains aligned four-fold symmetrically with c-domains by 2.79^° off the c-axis of c-domains. In the film, the measured lattice constants (a, b and c) of the a- and c-domains were different from each other, indicating that the films suffered a modulated strain during domain formation. In contrast, both the a and c domains of films on LaAlO₃ were alternatively aligned on substrate with the a-axis of the a-domain and the c-axis of c-domains perpendicular to the substrate surface. Two-dimensional distribution of these domains is proposed and the formation of these kinds of domains is discussed. The surface morphology and phase transition process of single and multi domain PbTiO₃ film on SrTiO₃ were studied by atomic force microscope (AFM) and high temperature X-ray diffraction, respectively. Received: 15 August 1996/Accepted: 21 January 1997     

(001) textured PbTiO3 thin films grown on redopingn-Si by metalorganic chemical vapor deposition under reduced pressure

(001) textured PbTiO₃ thin films have been deposited on (001) redopingn-Si substrates by metalorgnic chemical vapor deposition (MOCVD) under reduced pressure, and the film ferroelectricity has been measured using the substrate as bottom electrode directly. Besides this investigation, a set of analysis including AFM surface morphology, SEM cross section morphology, electron-probe element analysis, XRD 0-20 scan and high temperature X-ray diffraction have been carried out to study the microstructure and phase transition process of the PbTiO₃ thin film.     

Polyethylene Oxide Films Polymerized by Radio Frequency Plasma-Enhanced Chemical Vapour Phase Deposition and Its Adsorption Behaviour of Platelet-Rich Plasma

We present polyethylene oxide (PEO) functional films polymerized by rf plasma-enhanced vapour chemical deposition (rf-PECVD) on p-Si (100) surface with precursor ethylene glycol dimethyl ether (EGDME) and diluted Ar in pulsed plasma mode. The influences of discharge parameters on the film properties and compounds are investigated. The film structure is analysed by Fourier transform infrared (FTIR) spectroscopy. The water contact angle measurement and atomic force microscope (AFM) are employed to examine the surface polarity and to detect surface morphology, respectively. It is concluded that the smaller duty cycle in pulsed plasma mode contributes to the rich C--O--C (EO) group on the surfaces. As an application, the adsorption behaviour of platelet-rich plasma on plasma polymerization films performed in-vitro is explored. The shapes of attached cells are studied in detail by an optic invert microscope, which clarifies that high-density C--O--C groups on surfaces are responsible for non-fouling adsorption behaviour of the PEO films.     

Deposition of thin rhodium films by plasma-enhanced chemical vapor deposition

Thin films of rhodium have been prepared starting from dicarbonyl-2.4-pentadionato-rhodium(I), Rh(CO)₂C₅H₇O₂, by plasma enhanced CVD. The dependence of the deposition rate and film properties on substrate temperature, partial pressure of the organometallic and on hydrogen has been studied. Metal contents of 100% and thin-film resistivities as low as 5 times the bulk resistivity of rhodium have been achieved.