Hot-wall Low-pressure Chemical Vapor Research Articles

Hot-wall low pressure chemical vapor deposition growth and characterization of AlN thin films

Hot-wall low pressure chemical vapor deposition (LPCVD) of highly crystalline epitaxial thin-film AlN grown on silicon (111) substrates is reported for the first time. Deposition was carried out in a modified commercial LPCVD at 1000°C and 2torr. Preflow time for the aluminum precursor, trimethylaluminum, was varied to nucleate Al, and the resulting variation in X-ray diffraction (XRD) crystalline AlN peaks is presented. With a 30s dichlorosilane (SiH2Cl2) pretreatment at 700°C and the optimal TMAl preflow time, the FWHM of the resulting film was 1116 arcsec for the AlN (002) 2θ-ω peak, and the AlN (002) peak had an omega rocking curve FWHM of 1.6°. This AlN film was shown to be epitaxially aligned to the Si (111) substrate.

Thermal Hysteresis of MEMS Packaged Capacitive Pressure Sensor (CPS) Based 3C-SiC

Presented herein are the effects of thermal hysteresis analyses of the MEMS packaged capacitive pressure sensor (CPS). The MEMS CPS was employed on Si-on-3C-SiC wafer that was performed using the hot wall low-pressure chemical vapour deposition (LPCVD) reactors at the Queensland Micro and Nanotechnology Center (QMNC), Griffith University and fabricated using the bulk-micromachining process. The MEMS CPS was operated at an extreme temperature up to 500°C and high external pressure at 5.0 MPa. The thermal hysteresis phenomenon that causes the deflection, strain and stress on the 3C-SiC diaphragm spontaneously influence the MEMS CPS performances. The differences of temperature, hysteresis, and repeatability test were presented to demonstrate the functionality of the MEMS packaged CPS. As expected, the output hysteresis has a low hysteresis (less than 0.05%) which has the hardness greater than the traditional silicon. By utilizing this low hysteresis, it was revealed that the MEMS packaged CPS has high repeatability and stability of the sensor.

The effect of nitrogen doping on the elastic modulus and hardness of 3C-SiC thin films deposited using methyltrichlorosilane

For thin-film sensor applications, the mechanical properties, such as the hardness and elastic modulus, of the sensing material are important in addition to its electrical properties. The mechanical properties of the material need to be known at the design stage of the sensor because these properties are influenced by doping. The effect of in situ nitrogen doping on the mechanical properties of 3C-SiC (111) thin films are presented in this paper. These films are deposited at a pressure of 2.5 mbar and a temperature of 1040 °C on thermally oxidized Si (100) substrates from methyltrichlorosilane and ammonia using a resistively heated vertical hot-wall low-pressure chemical vapour deposition reactor. The effect of in situ nitrogen (0, 9 and 17 atomic per cent of nitrogen) doping on the mechanical properties of the material is investigated using nanoindentation. The x-ray diffraction patterns of 3C-SiC thin films show a decrease in the crystallanity and the intensity of the peak (111), with an increase in the dopant concentration from 0 to 17 atomic percent (%). AFM investigations show a decrease in the roughness and an increase in grain size of the 3C-SiC thin films with an increase in the nitrogen concentration. Nanoindentation measurements revealed that the elastic modulus and hardness of nitrogen doped 3C-SiC thin films decreased from 353 ± 5 to 178 ± 3 GPa and from 35 ± 1.4 to 22 ± 0.6 GPa, respectively, with an increase in the nitrogen doping concentration. This study shows that the mechanical properties of films strongly depend on the grain size, which is influenced by the effects of nitrogen doping. The elastic modulus and hardness are found to be 178 GPa and 22 GPa, respectively, for 3C-SiC thin films doped with 17 atomic % of nitrogen concentration, making it suitable as a sensing material for sensor applications.

Growth of 3C–SiC on 150-mm Si(100) substrates by alternating supply epitaxy at 1000 °C

To lower deposition temperature and reduce thermal mismatch induced stress, heteroepitaxial growth of single-crystalline 3C–SiC on 150 mm Si wafers was investigated at 1000 °C using alternating supply epitaxy. The growth was performed in a hot-wall low-pressure chemical vapor deposition reactor, with silane and acetylene being employed as precursors. To avoid contamination of Si substrate, the reactor was filled in with oxygen to grow silicon dioxide, and then this thin oxide layer was etched away by silane, followed by a carbonization step performed at 750 °C before the temperature was ramped up to 1000 °C to start the growth of SiC. Microstructure analyses demonstrated that single-crystalline 3C–SiC is epitaxially grown on Si substrate and the film quality is improved as thickness increases. The growth rate varied from 0.44 to 0.76 ± 0.02 nm/cycle by adjusting the supply volume of SiH 4 and C 2H 2. The thickness nonuniformity across wafer was controlled with ± 1%. For a prime grade 150 mm virgin Si(100) wafer, the bow increased from 2.1 to 3.1 μm after 960 nm SiC film was deposited. The SiC films are naturally n type conductivity as characterized by the hot-probe technique.

Characterization of the heteroepitaxial growth of 3C-SiC on Si during low pressure chemical vapor deposition

3C-SiC heteroepitaxial layers were grown on Si substrates using a horizontal, hot-wall low pressure chemical vapor deposition system. The crystal quality, surface morphology and thickness uniformity of the layers were characterized by X-ray diffraction, atomic force microcopy and Fourier transform infrared spectroscopy, respectively. Growth of the epitaxial layer was determined to follow a three-dimensional island mode initially and then switch to a step-flow mode as the growth time increases. Barrier epithelia, especially airway epithelial cells, are persistently exposed to micro-organisms and environmental factors. To protect the host from these microbial challenges, many immune strategies have evolved. The airway epithelium participates in the critical innate immune response through the secretion of immune effectors such as mucin, antimicrobial peptides (AMP), and reactive oxygen species (ROS) to entrap or kill invading microbes. In addition, airway epithelial cells can act as mediators connecting innate and adaptive immunity by producing various cytokines and chemokines. Here, we present an overview of the role of mucosal immunity in airway epithelium, emphasizing the framework of bacterial and viral infections along with regulatory mechanisms of immune effectors in human cells and selected animal models. We also describe pathophysiological roles for immune effectors in human airway disease.

Island-growth of SiCGe films on SiC

SiCGe ternary alloys have been grown on SiC by hot-wall low-pressure chemical vapour deposition. It has been found that the samples exhibit an island configuration, and the island growth of SiCGe epilayer depends on the processing parameters such as the growth temperature. When the growth temperature is comparatively low, the epilayer has two types of islands: one is spherical island; another is cascading triangular island. With the increase of the growth temperature, the islands change from spherical to cascading triangular mode. The size and density of the islands depend on the growth duration and GeH4 flow-rate. A longer growth time and a larger GeH4 flow-rate can increase the size and density of the island in the initial stage of the epitaxy. In our case, The optimal growth for a high density of uniform islands occurred at a growth temperature of 1100°C for 1-minute growth, with 10 SCCM GeH4, resulting in a narrow size distribution (about 30nm diameter) and high density (about 3.5 × 1010 dots/cm2). The growth follows Stranski– Krastanov mode (2D to 3D mode), both of the islands and the 2D growth layer have face-centred cubic structure, and the critical thickness of the 2D growth layer is only 2.5 nm.

Carbon doping effect on strain relaxation during Si1−x−yGexCy epitaxial growth on Si(1 0 0) at 500 °C

On strain relaxation during Si1−x−yGexCy epitaxial growth on Si(1 0 0) using an ultraclean hot-wall low-pressure chemical vapour deposition system at 500 °C, the carbon doping effect has been investigated. The depth profile of the strain in Si1−x−yGexCy films is measured by x-ray diffraction and Raman scattering spectroscopy combined with a wet etching technique. It is confirmed that the strain relaxation of Si1−xGex films (x = 0.45) occurs uniformly at every depth from the surface to the heterointerface. On the other hand, strain relaxation occurs partially in the surface part of Si1−x−yGexCy films (x = 0.45, y = 0.016), although the bottom part near the heterointerface is still strained.

Effect of grain boundary on electrical characteristics in B- and P-doped polycrystalline Si1−x−yGexCy film deposited by ultraclean LPCVD

The effect of grain boundary on electrical characteristics in B- and P-doped polycrystalline (poly) Si 1− x − y Ge x C y films was investigated. Poly-Si 1− x − y Ge x C y films were deposited on thermally oxidized Si(100) at 500–650 °C in a SiH 4 –GeH 4 –SiH 3 CH 3 –H 2 gas mixture by an ultraclean hot-wall low-pressure chemical vapor deposition. B and P were doped into the films by ion implantation and diffusion by heat-treatment. The electrical properties are characterized by grain size, width of disordered region near grain boundaries, carrier trap density and the amount of impurity segregation at grain boundaries. In the B-doped poly-Si 1− x − y Ge x C y films heat-treated at 900 °C, the increase of carrier concentration n poly and the decrease of resistivity ρ poly with Ge addition are caused by the narrowing of the width of disordered regions, i.e., crystallization of disordered regions induced by Ge atoms. The decrease of n poly and the increase of ρ poly with C addition are explained by the suppression of crystallization of disordered region due to C atom segregation at grain boundaries. In the P-doped poly-Si 1− x − y Ge x C y films, it is found that n poly and ρ poly are influenced by P atom segregation at grain boundaries due to lowering solid solubility of P in grain by the existence of Ge.

Carbon effect on strain compensation in Si 1− x − yGe xC y films epitaxially grown on Si(100)

Carbon effect on strain compensation in Si 1− x − y Ge x C y films epitaxially grown on Si(100) at 500 °C has been investigated using an ultraclean hot-wall low-pressure chemical vapor deposition. The introduction of C into thin strained Si 1− x Ge x films reduces the average lattice constant. On the other hand, results of the Raman scattering measurement show that C incorporation scarcely affects on local strain of Si–Si, Si–Ge and Ge–Ge bonds. The critical thickness at which the Raman shift peak begins to be decreased tends to become larger for the higher C fraction. It is considered that the C introduction effectively increases the critical thickness by relieving the overall strain.

High hole mobility in p-strained Si grown on relaxed SiC virtual substrate by low-pressure chemical vapor deposition

Abstract The strained Si layer has been grown on the relaxed 3C–SiC virtual substrate by a hot-wall low-pressure chemical vapor deposition (LPCVD) system. The relaxed SiC virtual substrate was grown on Si(1 1 1) substrate by LPCVD and the crystal quality of the layer is characterized by X-ray diffraction and Fourier transform infrared absorption spectroscopy. It is apparent to find three regions in the Auger electron spectroscopy depth profile graph of the sample, which refer to the cap Si layer, the relaxed 3C–SiC virtual substrate and the Si(1 1 1) substrate, respectively. The bonding states of the relaxed 3C–SiC virtual substrate in the sample are analyzed by X-ray photoelectron spectroscopy. The Raman spectra of the sample indicate the cap Si layer is strained. A high hole Hall mobility value of 889 cm 2 /V s (300 K) is obtained in the strained Si layer, which is due to the in-plane compressive biaxial strain in this layer.

Computationally efficient modeling of wafer temperatures in a low-pressure chemical vapor deposition furnace

A new thermal model is developed to predict wafer temperatures within a hot-wall low pressure chemical vapor deposition furnace based on the furnace wall temperatures as measured by thermocouples. Based on an energy balance of the furnace system, this model is a transformed linear model which captures the nonlinear relationship between the furnace wall temperature distribution and the wafer temperature distribution. The model can be solved with a direct algorithm instead of iterative algorithms which are used in all existing thermal models. Since the direct algorithm is noniterative, there is no convergence problem, nor local minima problem, related to nonlinear optimization. In addition, the direct algorithm greatly reduces the computation effort. Configuration factors are calculated by a finite area to finite area method. This avoids numerical integration methods which are much more difficult to implement and require more computation. The simplicity of the model form and the fast algorithm make the model useful for real-time updating and control. Model predictions show excellent agreement with experimental data.

Work function of impurity-doped polycrystalline Si1−x−yGexCy film deposited by ultraclean low-pressure CVD

Work function of in situ heavily P- or B-doped poly-Si1−x−yGexCy films were investigated. The poly-Si1−x−yGexCy films were deposited on thermally oxidized Si(100) at 550°C using an ultraclean hot-wall low-pressure chemical vapor deposition system in a SiH4–GeH4–SiH3CH3–dopnat (PH3 or B2H6) gas mixture, and the gate-to-substrate work function difference was estimated from flat-band voltage determined by high-frequency capacitance–voltage measurement. With increasing Ge and C fractions, the work function of B-doped poly-Si1−x−yGexCy film decreases, although that of P-doped poly-Si1−x−yGexCy scarcely changes. X-ray diffraction results show that the lattice constant increases with the C fraction, in other words, C is incorporated at interstitial site in the film at least at 550°C. It is suggested that the change in the work function of doped poly-Si1−x−yGexCy is universally explained by the change in the lattice constant as function of the Ge and C fractions.

Si epitaxial growth on SiH3CH3 reacted Ge(1 0 0) and intermixing between Si and Ge during heat treatment

Epitaxial growth of Si on SiH3CH3 reacted Ge(100) using ultraclean hot-wall low-pressure chemical vapor deposition (LPCVD), and the intermixing between Si and Ge during heat treatment has been investigated. By SiH3CH3 reaction at 450°C, Si and C atomic layers are self-limitedly formed on Ge(100), and the number of C atoms decreases with increasing heat treatment temperature in the range of 500–700°C. After such treatment, Si epitaxial growth on the 6×1013cm−2 C existing Ge(100) is achieved at 500°C. To clarify the interface abruptness, dependence of Ge3d intensity on the depth are obtained by repetition of X-ray photoelectron spectroscopy (XPS) measurements and wet etching. It is found that the intermixing between Si and Ge during Si epitaxial growth and heat treatment after its growth is suppressed by the existence of C atoms at the heterointerface.

Effect of Deposition Parameters on the Characteristics of Low-Pressure Chemical Vapor Deposited SiGe Films Grown from Si2 H 6 and GeH4

The growth rate, composition, and crystallinity of SiGe layers deposited in a hot-wall low-pressure chemical vapor deposition system, using disilane and germane as source gases, have been analyzed as functions of the deposition parameters, i.e., temperature, precursors, and carrier gas partial pressures. SiGe films with Ge fraction in the 0 to 0.38 range were deposited at temperatures of between 450 and 600°C. The growth rate increases with the partial pressure of the precursors and with the Ge content of the film, except for depositions made with high precursor partial pressure and low Ge fraction. The Ge content of the films increases with the germane fraction in the gas and the partial pressure of the precursors following a nonlinear dependence. The growth process has been analyzed assuming that the controlling reactions are the dissociation of the precursors at the SiGe surface, which are limited by the existence of free sites on the surface, originated by hydrogen desorption from it. The dissociation rate constants of disilane and germane depend on the surface composition and on the respective precursor partial pressure. Films with a Ge fraction lower than 0.5 deposited at temperatures below 500°C are amorphous, but films grown at higher temperatures or with higher Ge fraction are polycrystalline. © 2001 The Electrochemical Society. All rights reserved.

Al2O3 growth optimisation using aluminium dimethylisopropoxide as precursor as a function of reaction conditions and reacting gases

Aluminum oxide films were grown in a hot-wall low-pressure metal organic chemical vapor deposition (MOCVD) system using aluminum dimethylisopropoxide as precursor. Experimental reaction conditions and the reacting gas (O 2 , H 2 O, N 2 O) have been systematically varied with the aim to decrease the deposition temperature and obtain transparent, dense and carbon-free films. Changes in the gas phase composition were studied by FT-IR spectroscopy using an in-line cell. The reactor temperature ranged from 230°C to 380°C. The microstructure of the films was investigated by X-ray Diffraction, while the surface chemical composition was studied by X-ray Photoelectron. Atomic Force Microscopy was employed to analyze the surface morphology of the films as a function of reaction conditions and reacting gases. The best performances have been obtained using dry oxygen at 1000 Pa and oxygen mixed with water vapor at 100 Pa. High growth rates such as 140 nm min -1 have been obtained at 270 °C in the latter case. Different reaction mechanisms have been proposed in the two cases.

Phosphorus Doping in Si1-x-yGexCy Epitaxial Growth by Low-Pressure Chemical Vapor Deposition Using a SiH4–GeH4–CH3SiH3–PH3–H2 Gas System

Phosphorus doping in Si1-x-yGexCy (0≦x≦0.78, 0≦y≦0.016) epitaxial growth on Si(100) at 550°C by ultraclean hot-wall low-pressure chemical vapor deposition using a SiH4–GeH4–CH3SiH3–PH3–H2 gas system is investigated. The relationship among the Ge, the C fraction, the P concentration (CP), the deposition rate, and the deposition conditions in the P-doped Si1-x-yGexCy epitaxial growth under the surface reaction-limited regime is experimentally obtained, and is explained by the modified Langmuir-type adsorption and reaction scheme. The relationships among the carrier concentration, the CP, and the resistivity in the P-doped Si1-x-yGexCy for various Ge and C fractions are also presented. The carrier concentration of the P-doped Si1-x-yGexCy with low Ge and C fractions (x≦0.48 and y≦0.0046) is nearly equal to CP below approximately 2×1020 cm-3. With increasing Ge and C fractions, the film has electrically inactive P atoms independent of CP. The existence of C (y≧0.0048) in the film reduces the Hall mobility.

Doping and electrical characteristics of in-situ heavily B-doped Si 1− x− yGe xC y films epitaxially grown using ultraclean LPCVD

Doping and electrical characteristics of in-situ heavily B-doped Si 1− x− y Ge x C y (0.22< x<0.6, 0< y<0.02) films epitaxially grown on Si(100) were investigated. The epitaxial growth was carried out at 550°C in a SiH 4–GeH 4–CH 3SiH 3–B 2H 6–H 2 gas mixture using an ultraclean hot-wall low-pressure chemical vapor deposition (LPCVD) system. It was found that the deposition rate increased with increasing GeH 4 partial pressure, and only at high GeH 4 partial pressure did it decrease with increasing B 2H 6 as well as CH 3SiH 3 partial pressures. With the B 2H 6 addition, the Ge and C fractions scarcely changed and the B concentration ( C B) increased proportionally. The C fraction increased proportionally with increasing CH 3SiH 3 partial pressures. These results can be explained by the modified Langmuir-type adsorption and reaction scheme. In B-doped Si 1− x− y Ge x C y with y=0.0054 or below, the carrier concentration was nearly equal to C B up to approximately 2×10 20 cm −3 and was saturated at approximately 5×10 20 cm −3, regardless of the Ge fraction. The B-doped Si 1− x− y Ge x C y with high Ge and C fractions contained some electrically inactive B even at the lower C B region. Resistivity measurements show that the existence of C in the film enhances alloy scattering. The discrepancy between the observed lattice constant and the calculated value at the higher Ge and C fraction suggests that the B and C atoms exist at the interstitial site more preferentially.

Surface reaction of CH 3SiH 3 on Ge(100) and Si(100)

Surface reaction of CH 3SiH 3 on the Ge(100) and Si(100) surfaces was investigated in the low-temperature region of 400–500°C using ultraclean hot-wall low-pressure chemical vapor deposition (CVD) systems, where CH 3SiH 3 was supplied at a partial pressure of 18 Pa for 0–240 min. On Ge(100), the concentrations of Si and C deposited at 400°C and 450°C saturate to the value corresponding to the single atomic layer, but those at 500°C increase continuously with exposure time. Nevertheless, at all the temperatures studied, the concentration of deposited Si is nearly the same as that of deposited C. In the case of SiH 4 exposure at 450°C at partial pressures of 6 and 60 Pa, it was found that the Ge atoms segregate on the top surface at the early stage of Si deposition. By comparing these results, it is considered that the adsorption of CH 3SiH 3 suppresses the Ge segregation. On Si(100), the C deposition by CH 3SiH 3 has a similar tendency to that on Ge(100), but the initial deposition efficiency is lower than that on Ge(100). Moreover, the FTIR/RAS Si-hydride peak shifts to the lower wave numbers after CH 3SiH 3 exposure. These results suggest that CH 3SiH 3 is adsorbed without breaking the SiC bond on Ge(100) and Si(100) at 400–500°C.

Epitaxial growth of Si1−x−yGexCy film on Si(100) in a SiH4-GeH4-CH3SiH3 reaction

Epitaxial growth of Si1−x−yGexCy epitaxial films on Si(100) has been investigated at 550°C in a SiH4-GeH4-CH3SiH3-H2 gas mixture using an ultraclean hot-wall low pressure chemical vapor deposition (LPCVD) system. With increasing CH3SiH3 partial pressure, the deposition rate decreases depending on the Ge fraction, the C concentration increases linearly up to about 1021 cm−3, and the Ge fraction increases at a high CH3SiH3 partial pressure. These characteristics can be explained by the modified Langmuir-type formulation with the assumption that CH3SiH3 is adsorbed more preferably at the Si-Ge pair site, suppressing SiH4 and GeH4 adsorption. The electrical characteristics of the P-implanted Si1−x−yGexCy epitaxial film were evaluated and it was found that electrically inactive P increases at a C concentration over 3×1020 cm−3, which corresponds to the concentration where the lattice constant deviates from that calculated using Vegard's law.

Doping and electrical characteristics of in situ heavily B-doped Si 1− xGe x films epitaxially grown using ultraclean LPCVD

Doping and electrical characteristics of in situ heavily B-doped Si 1− x Ge x ( 0.15 < x < 0.80) films epitaxially grown on Si(110) were investigated. The epitaxial growth was carried out at 550 °C in a SiH 4-GeH 4-B 2H 6-H 2 gas mixture by using an ultraclean hot-wall low pressure chemical vapor deposition (LPCVD) system. With increasing B 2H 6 partial pressure, the deposition rate decreased only at the higher GeH 4 partial pressure, and the B concentration ( C B ) in the film increased proportionally up to 10 22 cm −3. The Ge fraction scarcely changed with the B 2H 6 addition. The carrier concentration was nearly equal to cb up to about 2 × 10 20 cm −3, and it tended to be saturated at around 5 × 10 20 cm −3 at C B < ~ 10 22 cm −3 . In other words, electrically inactive B increased with increasing C B above 2 × 10 20 cm −3. The resistivity decreased with increasing carrier concentration at c b <~ 10 22 cm −3 and was influenced by alloy scattering. Discrepancy of the lattice constants from Vegard's law was observed at higher cb in the order of 10 20 cm −3 and above, which corresponded with the saturation of the carrier concentration.