Low-temperature Epitaxial Growth Research Articles

Morphology of Silicon Oxide Film on Silicon Wafer Surface during Its Removal Process in a Hydrogen Ambient

In order to develop the low-temperature silicon epitaxial growth process, the change in the surface morphology of the silicon dioxide film and the silicon surface is studied in a transient state, for the first time, at 1223 K at a pressure of 40–101 kPa in a hydrogen ambient. A very smooth and clear silicon substrate surface is achieved using a uniform silicon dioxide film formed using ozonated ultrapure water and a very low flow rate of hydrogen gas. The surface morphology of the silicon substrate finally becomes smooth and the pit formation is suppressed, although the surface shows a nonuniform island appearance during the removal of the silicon dioxide film. The microroughness of the silicon substrate surface is improved by heating in a hydrogen ambient and by the silicon epitaxial film growth after complete removal of the ozone oxide film.

Fundamental properties of ECR plasma CVD and hydrogen-induced low temperature Si epitaxy

The etching properties of Si(100) and (111) substrates by H2 and Ar plasmas excited by the ECR technique were investigated. The Si(100) substrate is more easily etched than the Si(111) substrate. This is explained by the difference of the bonding formation of surface Si atoms. The Si film structure deposited on a glass substrate was characterized to be an amorphous/polycrystalline bilayer structure. A 30–40-nm thick amorphous Si layer first grew, followed by a (110) preferentially oriented poly Si layer. Low temperature epitaxial growth properties of Si films obtained using the ECR plasma CVD technique were investigated. The crystallinity of Si films deposited on a Si(100) substrate was influenced by the H2 flow rate. The mechanism of epitaxial growth is explained by the selective etching model of the amorphous region at temperatures below 300°C.

Low temperature epitaxial growth of Si and Si1−yCy films by hot wire cell method

The Hot Wire (HW) Cell method was applied to grow epitaxial Si films at a substrate temperature of 200°C. C2H2 gas was added to this system and C containing epitaxial Si films were also obtained. After annealing the films at 600–700°C, the vibration mode at 607 cm−1, which indicated the presence of the C atoms located at the Si substitutional sites, was observed in Fourier transform infrared absorption and Raman scattering spectroscopy. The X-ray diffraction peak of the annealed films shifted to a greater extent compared to the substrate, which indicated the decrease in the lattice constant of the epitaxial layer. The carbon composition was controlled by changing the partial pressure of the C2H2 gas and we successfully obtained 0.8 at.% substitutional carbon composition.

Low-temperature Si epitaxial growth on oxide patterned wafers by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition

Low-temperature electron cyclotron resonance hydrogen plasma cleaning was developed for low-temperature epitaxial growth of Si by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition on oxide-patterned wafers. Defect-free undoped Si epitaxial layers could be obtained by optimizing the hydrogen ion flux and cleaning time, however, in the case of boron-doped Si epitaxial growth, Si epilayers had defect zones away from the bird’s beak along the window edges and a defect-free zone at the center of the window. Cross section transmission electron microscopy and energy dispersive spectroscopy results suggest that the defect zone formation is closely related with local oxygen contamination. Possible origins of the local oxygen contamination are discussed.

Structural and Magnetic Properties of Spinel Ferrite Epitaxial Films Pulsed-Laser-Deposited at Low Temperature

Thin films of NiZn- and MnZn-ferrites have been epitaxially grown on sapphire substrates at low temperatures by pulsed laser deposition (PLD). The structural and magnetic properties of the deposited films were investigated in detail. All films crystallized in the spinel phase even when deposited at room temperature and low oxygen pressures of 1 ×10-4 Torr to 1 ×10-6 Torr. X-ray diffraction analysis and atomic force microscopy showed that the spinel ferrite thin films grown at low temperatures below 200°C have high structural and morphological qualities, comparable to those of films grown at higher temperatures. The saturation magnetization of the room-temperature grown films was much lower than that of the bulk for NiZn-ferrite, while, for MnZn-ferrite, was 80% (270 emu/cm3) of that of the bulk. These results make PLD a prime candidate technique for low-temperature epitaxial growth of ferrite thin films.

Low-temperature epitaxial growth of Si by electron cyclotron resonance chemical vapor deposition

We report on a study of low-temperature epitaxy at 325°C on Si(100), (111), (311), and (011) by electron cyclotron resonance chemical vapor deposition (ECR-CVD) with a growth rate of 10–12 nm/min. Epitaxial films grown on Si(100) exhibit a well-defined and smooth interface and a well-ordered lattice structure up to a layer thickness of more than 300 nm. Beyond a critical thickness of approximately 500 nm we observe a slow transition from the crystalline to the amorphous state by the formation of isolated conically shaped amorphous regions. At a thickness of 1.6 μm only 10–15% of the surface consist of these amorphous cones. The critical epitaxial thickness h epi depends on the crystallographic orientation of the substrate decreasing in the sequence h epi(100)≫ h epi(311)> h epi(111)> h epi(011).

Structural and Optical Characterizations of ZnO Films Grown by Reactive Electron Beam Evaporation

Low temperature epitaxial growth of ZnO films is achieved on Si(001) substrates by reactive electron beam evaporation. Growth temperature is varied from 125° C to 420° C and the optimum temperature is found between 200° C and 300° C. X-ray diffraction shows that the ZnO films are highly c-axis oriented and the line width of (002) diffraction peak is significantly smaller than that measured from the ZnO films deposited by magnetron sputtering. The combined photoluminescence and photoluminescence excitation (PLE) spectroscopic measurements demonstrate the sharp band-absorption edge and exciton absorption in the ZnO films. PLE has also revealed that the absorption characteristic near the band edge is remarkably improved with the increase of oxygen content in the ZnO films, although x-ray diffraction analysis shows that the crystalline structure of ZnO films grown under different oxygen pressures remains unchanged.

Si1−xGex selective epitaxial growth for ultra-high-speed self-aligned HBTs

Si1−xGex low temperature selective epitaxial growth was investigated by using a UHV/CVD system with high pressure H2 pre-cleaning of the substrate and SiGe HBTs were fabricated. The selective epitaxial growth was achieved by using different incubation times for Si(100) substrate and mask layers. Device performances show the good crystallinity of selectively grown Si1−xGex layer: an extremely high current gain of 45 000 and a high cutoff frequency of 154 GHz were achieved in the HBT with a maximum Ge content of 25%. Furthermore, the comparison of AC performance between self-aligned and non-self-aligned transistors demonstrates the advantage of the self-aligned structure formed by the Si1−xGex low-temperature selective epitaxial growth.

Low-temperature epitaxial growth of SrO on hydrogen-passivated Si (1 0 0) surface

Epitaxial growth of SrO films on hydrogen-passivated Si (1 0 0) surfaces has been demonstrated. The hydrogen-passivated Si, whose surface dangling bonds are saturated with hydrogen atoms, is chemically inactive, especially against oxidation. The alternate supply of Sr and O 2 gas during growth has made it possible to grow good epitaxial SrO films at low temperatures. The orientation relationships between epitaxial SrO and Si are found to be (1 0 0) SrO || (1 0 0) Si and [0 0 1] SrO || [0 0 1] Si.

Structural evolution of GaN during initial stage MOCVD growth

The structural evolution of GaN films during the initial growth process of metalorganic chemical vapor deposition (MOCVD) - low temperature nucleation layer growth, annealing, and high temperature epitaxial growth - was investigated in a synchrotron x-ray scattering experiment. The nucleation layer grown at 560°C that was predominantly cubic GaN consisted of tensile-strained aligned domains and relaxed misaligned domains. The hexagonal GaN, transformed from the cubic GaN during annealing to 1100 °C, showed disordered stacking. The atomic layer spacing decreased as the fraction of the hexagonal domains increased. Subsequent growth of epitaxial GaN at 1100 °C resulted in the formation of ordered hexagonal GaN domains with rather broad mosaicity.

Low-temperature molecular beam epitaxial growth of GaAs and (Ga,Mn)As

GaAs and (Ga,Mn)As were grown by low-temperature (LT) MBE. In this paper we report the growth condition dependence of properties of LT GaAs and (Ga,Mn)As. Transient reflectivity measurements showed that the carrier lifetime in LT GaAs can be modified by changing the V/III ratio. The Curie temperature of (Ga,Mn)As, determined by magneto-transport measurements, was also shown to be a function of V/III ratio.

Low temperature epitaxial growth of ZnO layer by plasma-assisted epitaxy

Plasma-assisted epitaxial growth of ZnO layers were achieved on C- and R-plane sapphire substrates in oxygen plasma excited by radio frequency power at 13.56 MHz with evaporation of pure elemental Zn. The ZnO layers were grown at 300–400°C with high growth rate around 1.7 μm/h. Surface cleaning of sapphire substrates using Ar-plasma was crucial for good quality ZnO growth. Photoluminescence spectra at 10 K were dominated by band-edge emission due to bound excitons without deep level emission in green-light region. The intensity of band-edge emission was strongly dependent on applied radio frequency power to excite Ar- and O 2-plasma for sapphire surface cleaning and ZnO growth, respectively, and was about 50 times larger on the layer grown in oxygen plasma than that grown in non-excited oxygen gas. The ZnO layer grown on R-plane sapphire was epitaxially grown above 300°C in oxygen plasma, however, on C-plane sapphire the ZnO layer was easily polycrystallized for thick films even at 400°C. Growth mode and surface morphology of ZnO layers were drastically changed with the substrate orientation.

Low temperature epitaxial growth of CeO 2(110) layers on Si(100) using electron beam assisted evaporation

With the aims of lowering growth temperature and improvement of crystalline quality, the effect of electron-beam assistance is studied in the epitaxial growth of CeO 2(110) layers on Si(100) substrates by electron-beam evaporation in an ultrahigh vacuum. From experiments of evaporation at positive substrate bias, it is clarified that electron incidence onto the growing surface is effective in the facilitation of the epitaxial growth. Newly developed electron-beam assisted evaporation proves to have much greater effects in both the growth temperature lowering and the crystalline quality improvement. The epitaxial growth facilitation effect depends on incident electron energy. Optimum electron energy is determined to be around 360 eV, wherein the epitaxial temperature is lowered to 710 °C, i.e. temperature lowering of more than 100 °C compared with the conventional growth method.

Sructural evolution of GaN during initial stage MOCVD growth

AbstractThe structural evolution of GaN films during the initial growth process of metalorganic chemical vapor deposition (MOCVD) - low temperature nucleation layer growth, annealing, and high temperature epitaxial growth - was investigated in a synchrotron x-ray scattering experiment. The nucleation layer grown at 560°C that was predominantly cubic GaN consisted of tensile-strained aligned domains and relaxed misaligned domains. The hexagonal GaN, transformed from the cubic GaN during annealing to 1100°C, showed disordered stacking. The atomic layer spacing decreased as the fraction of the hexagonal domains increased. Subsequent growth of epitaxial GaN at 1100°C resulted in the formation of ordered hexagonal GaN domains with rather broad mosaicity.

Conducting (Si-Doped) Aluminum Nitride Epitaxial Films Grown by Molecular Beam Epitaxy

ABSTRACTAs a member of the III-V nitride semiconductor family, AlN, which has a direct energygap of 6.2eV, has received much attention as a promising material for many applications. However, despite the promising attributes of AlN for various semiconductor devices, research on AlN has been limited and n-type conducting AlN has not been reported. The objective of this research was to understand the factors impacting the conductivity of AlN and to control the conductivity of this material through intentional doping. Prior to the intentional doping study, growth of undoped AlN epilayers was investigated. Through careful selection of substrate preparation methods and growth parameters, relatively low-temperature molecular beam epitaxial growth of AlN films was established which resulted in insulating material. Intentional Si doping during epilayer growth was found to result in conducting films under specific growth conditions. Above a growth temperature of 900°C, AlN films were insulating, however, below a growth temperature of 900°C, the AlN films were conducting. The magnitude of the conductivity and the growth temperature range over which conducting AlN films could be grown were strongly influenced by the presence of a Ga flux during growth. For instance, conducting, Si-doped, AlN films were grown at a growth temperature of 940°C in the presence of a Ga flux while the films were insulating when grown in the absence of a Ga flux at this particular growth temperature. Also, by appropriate selection of the growth parameters, epilayers with n-type conductivity values as large as 0.2 Ω−1 cm−1 for AlN and 17 Ω−1cm−1 for Al0.75Ga0.25N were grown in this work for the first time.

Low temperature epitaxial growth of Si on Si(111) by gas-source MBE with heat-pulse annealing

Low temperature epitaxial growth technique of Si on Si(111) for gas-source molecular beam epitaxy (GS-MBE) has been performed. It consists of low temperature growth followed by heat-pulse annealing to improve crystallinity and surface roughness of the films. Surface morphology investigated with tapping-mode atomic force microscopy (TM-AFM) is dependent on annealing temperature, annealing time, growth temperature and film thickness. An annealing temperature of 850°C is sufficient to flatten a three-dimensional surface grown at 500°C. Ordered terraces having straight step edge can be obtained by setting these parameters properly. Once terraces reach a certain width, further annealing has little influence on the terrace width. Heat-pulse annealing is effective for both improving the film crystallinity and ordering the terraces.

Low-temperature epitaxial growth of β-SiC by multiple-energy ion implantation

A cubic silicon carbide (\ensuremath{\beta}-SiC) buried layer was synthesized in Si(111) using a combination of multienergy carbon ion implantation at room temperature and post-thermal annealing. The crystal structure and the crystalline quality of the \ensuremath{\beta}-SiC layer was identified by x-ray diffraction in the \ensuremath{\theta}--2\ensuremath{\theta} mode and was examined by pole figure measurement of x-ray diffraction. Interestingly, by using the multienergy implantation technique, the \ensuremath{\beta}-SiC buried layer showed epitaxial growth at annealing temperatures as low as 400 \ifmmode^\circ\else\textdegree\fi{}C. At an annealing temperature of 800 \ifmmode^\circ\else\textdegree\fi{}C, the x-ray pole figures show that the \ensuremath{\beta}-SiC buried layer has a near-perfect epitaxial relationship with the silicon substrate.

Low-temperature epitaxial growth of Ge-rich Ge–Si–C alloys: Microstructure, Raman studies, and optical properties

Low-temperature (∼200 °C) molecular beam epitaxy of Ge-rich Ge1−x−ySiyCx alloys grown on Si(100) have been investigated by in situ reflection high-energy electron diffraction, ex situ x-ray diffraction, transmission electron microscopy, Raman scattering, and ellipsometry. The Si contents were either ∼20 or ∼40 at % and the C concentrations were nominally varied from zero up to ∼8 at %. Selected samples were annealed in an Ar ambient at 750 °C to evaluate the stability of the thin films. With increasing C concentration, the epitaxial growth mode changes from two-dimensional (2D) layer growth to 3D island growth. Under the growth conditions studied, the GeSiC films have a tendency to form planar defects, whose density increases with increasing C and Si concentrations. The x-ray diffraction data show that the lattice parameter decreases with increasing C concentration. It is estimated that a maximum of ∼2–3 at % C is substitutionally incorporated into these films. Raman spectra of the alloy films show that the effects of C on the strong Ge–Ge and Ge–Si local modes are far less than the effects due to Si. We are unable to observe any systematic change in the Ge–Ge mode, whereas the Ge–Si mode appears to shift to lower frequency with the small addition of C. Ge1−x−ySiyCx films formed by annealing Ge1−xCx films on Si are also discussed. Spectroscopic ellipsometry determinations of the film’s optical constants show that the primary effect of C is to reduce the strength of the E1 critical point feature.

Making nonmagnetic semiconductors ferromagnetic

REVIEW Semiconductor devices generally take advantage of the charge of electrons, whereas magnetic materials are used for recording information involving electron spin. To make use of both charge and spin of electrons in semiconductors, a high concentration of magnetic elements can be introduced in nonmagnetic III-V semiconductors currently in use for devices. Low solubility of magnetic elements was overcome by low-temperature nonequilibrium molecular beam epitaxial growth, and ferromagnetic (Ga,Mn)As was realized. Magnetotransport measurements revealed that the magnetic transition temperature can be as high as 110 kelvin. The origin of the ferromagnetic interaction is discussed. Multilayer heterostructures including resonant tunneling diodes (RTDs) have also successfully been fabricated. The magnetic coupling between two ferromagnetic (Ga,Mn)As films separated by a nonmagnetic layer indicated the critical role of the holes in the magnetic coupling. The magnetic coupling in all semiconductor ferromagnetic/nonmagnetic layered structures, together with the possibility of spin filtering in RTDs, shows the potential of the present material system for exploring new physics and for developing new functionality toward future electronics.

Low-temperature chemical-vapor deposition of 3C–SiC films on Si(1 0 0) using SiH 4–C 2H 4–HCl–H 2

The benefits of adding HCl on the low-temperature (1000°C) epitaxial growth of 3C–SiC on Si(1 0 0) were examined. At either silicon rich (C/Si<1) or carbon rich (C/Si>1) inlet gas ratios, the SiC film composition approached stoichiometry by adding HCl, but only at an inlet C/Si ratio of 1 was the composition of the SiC film approximate 1.0 with a Cl/Si input ratio of 50. The structure of the films improved with the addition of HCl, confirmed by both X-ray diffraction and TEM. For epitaxial films, the FWHM of X-ray diffraction rocking curves decreased to 0.37° or 1348 arcs with increasing Cl/Si to 50 at a C/Si ratio of 1. The film dislocation density was reduced from 1.1×10 10 cm −2 for a 2.0 μm thick film for a Cl/Si ratio of 0 to 4.27×10 9 cm −2 for a 0.75 μm thick film at a Cl/Si ratio of 50. The benefits of adding HCl are attributed to the suppression of pure silicon nucleation and the reduction in growth rate.