Low-temperature RPCVD of Si,SiGe alloy,and Si1−yCy films on Si substrates using trisilane (Silcore)

Si homo-epitaxial growth by low-temperature reduced pressure chemical vapor deposition (RPCVD) using trisilane (Si₃H₈) has been investigated. The CVD growth of Si films from trisilane and silane on Si substrates are compared at temperatures between 500 and 950 °C. It is demonstrated that trisilane efficiency increases versus silane's one as the surface temperature decreases. Si epilayers from trisilane, with low surface roughness, are achieved at 600 and 550 °C with a growth rate equal to 12.4 and 4.3 nm min⁻¹, respectively. It is also shown that Si_1−xGe_x layers can be deposited using trisilane chemistry.     

Growth of carbon nanotubes from waste blast furnace gases at atmospheric pressure

Carbon emissions from industrial sources are of major global concern, especially contributions from the steel manufacturing process which accounts for the majority of emissions. Typical blast furnace gases consist of CO₂ (20‐25%), CO (20‐25%), H₂ (3‐5%) and N₂ (40‐50%) and trace amounts of other gases. It is demonstrated that gas mixtures with these compositions can be used at atmospheric pressure to grow carbon nanotubes (CNTs) by chemical vapor deposition (CVD) on to steel substrates, which act as catalysts for CNT growth. Computational modelling was used to investigate the CNT growth conditions inside the CVD chamber. The results show that industrial waste pollutant gases can be used to manufacture materials with significant commercial value, in this case CNTs.     

Vapour phase growth of epitaxial silicon carbide layers

After a brief overview of different epitaxial layer growth techniques, the homoepitaxial chemical vapour deposition (CVD) of SiC with a focus on hot-wall CVD is reviewed. Step-controlled epitaxy and site competition epitaxy have been utilized to grow polytype stable layers more than 50 μm in thickness and of high purity and crystalline perfection for power devices. The influence of growth parameters including gas flow, C/Si ratio, growth temperature and pressure on growth rate and layer uniformity in thickness and doping are discussed. Background doping levels as low as 10¹⁴ cm⁻³ have been achieved as well as layers doped over a wide n-type (nitrogen) and p-type (aluminium) range.

Furthermore the status of numerical process simulation is mentioned and SiC substrate preparation is described. In order to get flat and damage free epi-ready surfaces, they are prepared by different methods and characterised by atomic force microscopy and by scanning electron microscope using channelling patterns. For the investigation of defects in SiC high purity CVD layers are grown. The improvement of the quality of bulk crystal substrates by micropipe healing and so-called dislocation stop layers can further decrease the defect density and thus increase the yield and performance of devices. Due to its high growth rate functionality and scope for the use of multi-wafer equipment hot-wall CVD has become a well-established method in SiC-technology and has therefore great industrial potential.     

Ordered arrays of epitaxial silicon nanowires produced by nanosphere lithography and chemical vapor deposition

Gold dot arrays on (1 1 1) Si substrates obtained through nanosphere lithography (NSL) combined with sputtering and annealing in Ar at 1000 °C are used to catalyze vapor liquid solid (VLS) epitaxial growth of silicon nanowires (Si NWs) using chemical vapor deposition (CVD) with SiH₄ in Ar. The NWs grow primarily epitaxially on the underlying (1 1 1) Si wafer following the four independent 〈1 1 1〉 directions. The diameter distribution of the wires reflects the diameter distribution of the catalyst gold dot arrays and is therefore predictable. The wire length depends on the size of the gold catalyst for the same CVD parameters. The wire position is foreseeable within the limits of the pattern geometrical quality, but one-to-one growth of NWs to gold dots is not always observed, probably due to (very locally) the remaining presence of silicon oxide. Overall, this inexpensive patterning method for obtaining high-quality crystalline VLS Si NWs by CVD fulfills the requirements of many device applications, where patterning control, quality and reproducibility of the nanostructures are crucial.     

Crystal growth of boron monophosphide using a B2H6-PH3-H2 system

Boron monosphide (BP) with (100) orientation can be epitaxially grown on Si substrates with (100) orientation by thermal decomposition of B₂H₆ and PH₃ in hydrogen. In a horizontal CVD system, the growth rate was studied as a function of gas phase composition and temperature. The growth rate is independent of the PH₃ partial pressure in the region where the PH₃ is in excess. For low values of the B₂H₆ partial pressure the growth rate is proportional to the B₂H₆ partial pressure (a linear region) with an activation energy of 1.8 eV, and for high values of the B₂H₆ partial pressure the growth rate becomes constant (a saturation region) with an acivation energy of 3.0 eV. A simple adsorption-reaction model can be proposed to explain the experimental growth kinetics. The conductivity of the as-grown layer is determined by the PH₃ partial pressure. n-type BP can be obtained for high values of the PH₃ partial pressure and p-type BP for low values. Si doping during the growth and phosphorus anti-site donors are two possibilities to explain the results.     

Low-temperature growth of epitaxial (1 0 0) silicon based on silane and disilane in a 300 mm UHV/CVD cold-wall reactor

Epitaxial (1 0 0) silicon layers were grown at temperatures ranging from 500 to 800 °C in a commercial cold-wall type UHV/CVD reactor at pressures less than 7×10⁻⁵ Torr. The substrates were 300 mm SIMOX SOI wafers and spectroscopic ellipsometry was used to assess growth rates and deposition uniformities. High-resolution atomic force microscopy (AFM) was employed to verify the atomic terrace configuration that resulted from epitaxial step-flow growth. Deposition from disilane exhibited a nearly perfect reaction limit for low temperatures and high precursor flow rates (partial pressures) with measured activation energies of ≈2.0 eV, while a linear dependence of growth rate on precursor gas flow was found for the massflow-controlled regime. A similar behavior was observed in the case of silane with substantially reduced deposition rates in the massflow-limited regime and nearly a factor of 2 reduced growth rates deep in the reaction limited regime. High growth rates of up to 50 μm/h and non-uniformities as low as 1σ=1.45% were obtained in the massflow-limited deposition regime. Silicon layers as thin as 0.6 nm (4.5 atomic layers ) were deposited continuously as determined using a unique wet chemical etching technique as well as cross-sectional high-resolution transmission electron microscopy (HRTEM). In contrast, epitaxial silicon deposited in RPCVD at 10 Torr using disilane within the same temperature range showed imperfect reaction limitation. While activation energies similar to that of UHV/CVD were found, no partial pressure limitation could be observed. Furthermore, layers deposited using disilane in RPCVD exhibited a large number of defects that appeared to form randomly during growth. We attribute this effect to gas phase reactions that create precursor fragments and radicals—an effect that is negligible in UHV/CVD.     

Computational study on transamination of alkylamides with NH3 during metalorganic chemical vapor deposition of tantalum nitride

DFT calculations were employed to investigate transamination during metalorganic chemical vapor deposition (MOCVD) of transition metal nitrides films, such as titanium nitride (TiN) and tantalum nitride (TaN). The calculated energetics and rate constants for the ligand exchange of tert-butylimidotris(dimethylamido) tantalum (TBTDMT) with NH₃ demonstrated that NH₃ addition to form the ammonia adduct, TBTDMT·NH₃, proton transfer and dissociation of dimethylamine to afford net transamination of the dimethylamido ligand are facile even at low temperature (∼300 °C). The transamination of the tert-butylimido ligand, however, was relatively slow at those temperatures but became facile at temperatures appropriate for CVD growth (∼600 °C). Rapid transamination is consistent with lower temperature for growth of TaN by MOCVD in the presence of NH₃, efficient removal of carbon-containing ligands, and incorporation of higher levels of nitrogen in the resulting films.     

Phase stability and oxygen doping in the Cu-N-O system

A growth stability diagram for the CuNO system has been determined in the temperature range 250-500 °C for a thermally activated CVD process, based on copper (II) hexafluoroacetylacetonate (Cu(hfac)₂), NH₃ and H₂O. Without any addition of water only Cu₃N was obtained. Addition of water introduces oxygen into the Cu₃N structure to a maximum amount of 9 at% at a water/nitrogen molar ratio of 0.36 at 325 °C. Above this molar ratio Cu₂O starts to deposit, in addition to an oxygen doped Cu₃N phase. Only Cu₂O is deposited at large excess of water.     

Role of halogen in low-temperature growth of polycrystalline thin films by reactive thermal CVD

Low-temperature growth of polycrystalline silicon by reactive thermal CVD, in which a set of reactive gasses are selected to promote film growth and/or crystallization at low-temperatures in thermal CVD, was studied with disilane and halogens such as fluorine and chlorine. High quality polycrystalline Si films were grown on glass substrates in Si₂H₆–F₂ system at 450 °C, while polycrystalline films were hardly deposited when Si₂H₆–Cl₂ system was adapted in the similar condition. We examined the major factors that govern the crystal growth at low-temperature by comparing the experimental results from these two systems. We suggest that the chemical processes on the growing surface in which Si-network is formed while the terminators are eliminated play a significant role for nucleation and growth in the low-temperature deposition by reactive thermal CVD.     

Epitaxial growth of graphitic carbon on C-face SiC and Sapphire by chemical vapor deposition (CVD)

Epitaxial, graphitic carbon thin films were directly grown on C-face/(0 0 0 1¯) SiC and (0 0 0 1) sapphire by chemical vapor deposition (CVD), using propane as a carbon source and without any catalytic metal on the substrate surface. Raman spectroscopy shows the signature of multilayer graphene/graphite growth on both the SiC and sapphire. Raman 2D-peaks have Lorentzian lineshapes with FWHM of ∼60 cm⁻¹ and the ratio of the D-peak to G-peak intensity (I_D/I_G) linearly decreases (down to 0.06) as growth temperature is increased. The epitaxial relationship between film and substrates were determined by X-ray diffraction. On both substrates, graphitic layers are oriented parallel to the substrate, but exhibit significant rotational disorder about the surface normal, and predominantly rhombohedral stacking. Film thicknesses were determined to be a function of growth time, growth temperature, and propane flow rate.     

Metal organic vapour phase epitaxy of MgO films grown on c-plane Sapphire

Metal organic vapour phase epitaxy (MOVPE) has been used to epitaxially grow MgO films on c-plane sapphire substrates. Bismethylcyclopentadienyl magnesium (MCP₂Mg) and nitrous oxide (N₂O) were used as the magnesium and the oxygen source, respectively, with nitrogen (N₂) as the carrier gas. The dependence of the growth rate on the partial pressure of magnesium and on the growth temperature was investigated. The growth rate increases with the magnesium partial pressure. The morphological and structural properties of MgO films were investigated using atomic force microscopy and X-ray diffraction. The structural properties are strongly dependent on the growth temperature in the range 400–800 °C. (1 1 1)-oriented MgO layers are observed at growth temperatures above 600 °C whereas no diffraction peak is found at lower growth temperatures. The atomic force microscopy (AFM) images reveal a smooth surface morphology.     

Investigation of 3C-SiC growth on Si(111) by vapor–liquid–solid transport using a SiGe liquid phase

The crystal growth of 3C-SiC onto silicon substrate by Vapor–Liquid–Solid (VLS) transport, where a SiGe liquid phase is fed with propane, has been investigated. Three sample configurations were used. In a preliminary approach, the VLS growth of SiC was conducted directly onto Si substrate using a Ge film as liquid catalyst. It led to the growth of a thick continuous SiC polycrystalline layer which was floating over a SiGe alloy located between the silicon substrate and the topping SiC layer. In the second configuration, a thin seeding layer of 3C-SiC grown by chemical vapor deposition (CVD) was used and the VLS growth was localized using a SiO₂ mask. The liquid phase was a CVD deposited SiGe alloy. The growth of a few hundred nanometers thick 3C-SiC epitaxial layer was demonstrated but the process was apparently affected by the presence of the oxide which was dramatically etched at the end. In the last configuration, the silicon substrate was patterned down to 10 μm and a thin seeding layer of 3C-SiC was grown by CVD onto this patterned substrate. The liquid phase was again a CVD deposited SiGe alloy. In this last configuration, the presence of epitaxial SiC was evidenced but it grew as trapezoidal islands instead of an uniform layer.     

Tetragonal tungsten oxide nanobelts synthesized by chemical vapor deposition

Tungsten trioxide (WO₃) nanobelts in tetragonal structure were grown on Si substrates by a hot-wall chemical vapor deposition (CVD) method without using catalysts. The products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence (PL) spectrum. The width of the nanobelts is in the range of 50–100 nm with width-to-thickness ratios of 5–10 and lengths of up to tens of micrometers. These nanobelts grew along the [0 0 1] direction and can be identified as the tetragonal WO₃ structures. Raman and PL measurements indicate the high quality of the nanobelts. The vapor–solid growth mechanism could be applicable in our experiment.     

Growth and properties of chemical-vapor-deposited Ti-P-O films grown under the CO2- and H2-existing conditions

Amorphous titanium phosphate (Ti-P-O) films are prepared by low-pressure chemical vapor deposition (CVD) using a mixture of titanium tetrachloride (TiCl₄) and trimethyl phosphite (P(O-CH₃)₃). Two systems are studied: one is the TiCl₄/P(O-CH₃)₃/CO₂ or the CO₂ system and the other is the TiCl₄/P(O-CH₃)₃/H₂ or the H₂ system. Growth and properties of the CVD Ti-P-O films are functions of deposition temperature and the CO₂ and H₂ inputs. The films have a higher growth rate and a lower Ti content at higher deposition temperature. A high CO₂ input favors for film growth, but a high H₂ flow rate is detrimental. Variations of growth rate and film composition with the CO₂ and H₂ inputs are rationalized by the proposed growth mechanisms. The changes in internal stress with deposition temperature and the CO₂ and H₂ inputs are mainly attributed to film thickness. The large difference in electrical resistivity of films of the two systems deposited at 500 °C can be related to the drift of defect protons on the oxygen sites under an electric field.     

MOVPE growth of InN films using 1,1-dimethylhydrazine as a nitrogen precursor

InN films have been successfully grown on sapphire substrates by MOVPE using trimethylindium (TMIn) and 1,1-dimethylhydrazine (DMHy) with N₂ carrier. DMHy is an advantageous precursor of N as it decomposes efficiently at relatively low temperature (T₅₀=420 °C) compatible with the InN growth. The reactor is specially designed so as to avoid parasitic reaction between TMIn and DMHy occurring at room temperature. The growth feature was studied by varying growth temperature, V/III ratio, TMIn flow and reactor pressure. The InN films were obtained at 500–570 °C and 60–200 Torr with a V/III ratio optimized to 100–200. The In droplets are seen on the grown surfaces, indicating an excess supply of TMIn. It is demonstrated that the InN films grows on the sapphire substrate in a single domain with an epitaxial relationship, [1 01¯ 0]_InN//[1 1 2¯ 0]_sapphire.     

Total pressure‐controlled PVT SiC growth for polytype stability during using 2D nucleation theory

A total pressure‐controlled physical vapor transport growth method that stabilizes SiC polytype is proposed. The supersaturation of carbon during SiC growth changed as a function of the growth time due to changes in the temperature difference between the surfaces of the source and the grown crystal. Supersaturation also varied as a function of the pressure inside the furnace. Therefore, modification of the pressure as a function of growth time allowed for constant supersaturation during growth. The supersaturation was calculated based on classical thermodynamic nucleation theory using data for heat and species of Si₂C and SiC₂ transfer in a furnace obtained from a global model. Based on this analysis, a method for polytype‐stabilized SiC growth was proposed that involves decreasing the pressure as a function of growth time. The 4H‐SiC prepared using this pressure‐controlled method was more stable than that of 4H‐SiC formed using the conventional constant‐pressure method.     

Growth of hexagonal and cubic InN nanowires using MOCVD with different growth temperatures

We have performed a detailed investigation of the metal-organic chemical vapor deposition (MOCVD) growth and characterization of InN nanowires formed on Si(1 1 1) substrates under nitrogen rich conditions. The growth of InN nanowires has been demonstrated by using an ion beam sputtered (∼10 nm) Au seeding layer prior to the initiation of growth. We tried to vary the growth temperature and pressure in order to obtain an optimum growth condition for InN nanowires. The InN nanowires were grown on the Au+In solid solution droplets caused by annealing in a nitrogen ambient at 700 °C. By applying this technique, we have achieved the formation of InN nanowires that are relatively free of dislocations and stacking faults. Scanning electron microscopy (SEM) showed wires with diameters of 90–200 nm and lengths varying between 3 and 5 μm. Hexagonal and cubic structure is verified by high resolution X-ray diffraction (HR-XRD) spectrum. Raman measurements show that these wurtzite InN nanowires have sharp peaks E₂ (high) at 491 cm⁻¹ and A₁ (LO) at 591 cm⁻¹.     

MOVPE of AlN-free hexagonal GaN/cubic SiC/Si heterostructures for vertical devices

The heterostructures of GaN/SiC/Si were prepared without using AlN or AlGaN buffer layers (AlN buffers) in the metalorganic vapor phase epitaxy of GaN on SiC. GaN (0 0 0 1) with specular surface was obtained. The AlN buffers are usually used in the conventional growth of GaN on SiC due to the poor nucleation of GaN on SiC. Instead, the nucleation of GaN was controlled by varying the partial pressure of H₂ in the carrier gas, the mixture of H₂ and N₂, during the low-temperature (600 °C) growth of GaN (LT-GaN). After the LT-GaN, the high-temperature (1000 °C) growth of GaN was performed using pure H₂ as the carrier gas. The epitaxial film of cubic SiC (1 1 1) on a Si (1 1 1) substrate was used as the SiC template. Increasing the partial pressure of H₂ in the carrier gas decreased the coverage of SiC surface by LT-GaN. It is suggested that the hydrogen atoms adsorbed on the surface of SiC is preventing the nucleation of GaN.     

氧分压对化学气相沉积法合成ZnO纳米结构形貌的影响

本文利用化学气相沉积(CVD)法在镀有Au(10 nm)膜的单晶Si(100)上制备了ZnO薄膜,并研究了不同的氧分压对ZnO形貌的影响.借助扫描电镜(SEM)、X射线衍射仪(XRD)和透射电子显微镜(TEM)对样品的形貌、结晶质量和晶体生长取向进行了表征.结果表明:当O2分压较小的时候,O2只能与Zn团簇的某些界面发生反应并逐渐结晶生成层状的ZnO微米团簇.当 O2分压较大的时候,ZnO通过二次生长形成由微米柱阵列和表面无序纳米线构成的分层复合结构,并且表面纳米线的密度随着氧分压的增加而增加.高分辨透射电镜(HRTEM)和选取电子衍射(SAED)分析表明,单根纳米线是沿[001]方向生长的ZnO单晶.     

An overview of gallium nitride growth chemistry and its effect on reactor design: Application to a planetary radial-flow CVD system

In this paper, gallium nitride (GaN) growth chemistry is characterized by two competing reaction pathways. An overview of GaN gas-phase and surface-phase chemistry is used to generate a comprehensive model for epitaxial GaN growth from the commonly used precursors, trimethylgallium ((CH₃)₃Ga) and ammonia (NH₃). The role of reactor geometry in controlling the selectivity among the competing reaction pathways is explored in the context of a planetary radial-flow CVD system. Finally, application of a geometrically based uniformity criterion is presented for film uniformity optimization.