Low-pressure Chemical Vapor Deposition Reactor Research Articles

Simulation and optimization of polysilicon thin film deposition in a 3000 mm tubular LPCVD reactor

The high photoelectric conversion efficiency of tunnel oxide passivating contacts (TOPCon) photovoltaic (PV) cells and their process compatibility are increasingly recognized by the industry, making it of growing importance to develop deposition process technologies for high-capacity polysilicon thin films. Currently, the size of LPCVD reactors for preparing polysilicon thin films in the industry is getting enlarged, which directly leads to the degradation of axial uniformity of polysilicon thin films. In this paper, a coupled multi-physics field model is established to simulate the polysilicon thin-film Low Pressure Chemical Vapor Deposition (LPCVD) process based on COMSOL Multiphysics platform, and the validity of the model is verified by comparing experimental data with simulation results. By investigating the flow field, thermal field, chemical reaction field and surface reaction field, the effects of the process parameters such as chamber temperature and pressure are investigated, as well as characteristics of the polysilicon thin films deposition. The results show that the uniformity of thin films decreases with increasing temperature and pressure, and the deposition rate of thin films increases as temperature and pressure increase. With the help of optimized the process parameters, the deposition rate of polysilicon thin films was increased by 13.0% and the uniformity of thin films was controlled above 96%. The uniformity of the films can be further improved to 96.7% by optimizing the temperature zone parameters and adopting the wafers placement strategy.

Synthesis, characterization, and thermal properties of a 2-isopropyl-aminopyridine adduct of cobalt(II) chloride and its potential as a CVD precursor for cobalt-based films

• The detailed study on synthesis, characterization, and thermal properties of an alkyl-aminopyridine adduct of cobalt(II) chloride. • By adding alkyl-aminopyridine to cobalt(II) chloride, the obtained compound exhibits high stability, sufficient volatility, and suitable thermal stability, which is benefit for industrial application. • A promising CVD precursor for preparation of cobalt-based films. In this study, a 2-isopropyl-aminopyridine adduct of cobalt(II) chloride [Co(2- i PrNH-C 5 H 4 N) 2 Cl 2 ] was synthesized and used as a precursor for preparing cobalt-based films through chemical vapor deposition (CVD). This compound was synthesized through a simple coordination reaction and characterized through 1 H NMR, elemental analysis, and single-crystal diffraction. The thermal properties (including volatility, vapor pressure, and thermal stability) of the compound were investigated through thermogravimetric analysis (TGA) to determine its feasibility for use in CVD. Moreover, a film deposition experiment was conducted in a low-pressure CVD reactor system, and a Co 3 O 4 film was obtained. This result verified the reported compound’s applicability as a CVD precursor for fabricating cobalt-based films.

N-type doping of low-pressure chemical vapor deposition grown β-Ga2O3 thin films using solid-source germanium

We report on the growth and characterization of Ge-doped β-Ga2O3 thin films using a solid germanium source. β-Ga2O3 thin films were grown using a low-pressure chemical vapor deposition reactor with either an oxygen or a gallium delivery tube. Films were grown on 6° offcut sapphire and (010) β-Ga2O3 substrates with growth rates between 0.5 and 22 μm/h. By controlling the germanium vapor pressure, a wide range of Hall carrier concentrations between 1017 and 1019 cm−3 were achieved. Low-temperature Hall data revealed a difference in donor incorporation depending on the reactor configuration. At low growth rates, germanium occupied a single donor energy level between 8 and 10 meV. At higher growth rates, germanium doping predominantly results in a deeper donor energy level at 85 meV. This work shows the effect of reactor design and growth regime on the kinetics of impurity incorporation. Studying donor incorporation in β-Ga2O3 is important for the design of high-power electronic devices.

Applications of vertical cavity surface emitting lasers for low-pressure chemical vapor deposition reactors

Vertical cavity surface emitting lasers (VCSELs) with a wavelength of 980 nm were applied to design a low-pressure chemical vapor deposition (LPCVD) reactor as a promising heat source of excellent irradiation uniformity, rapid power controllability, and extended spatial scalability.The average divergence angle of the laser beam emitted from a myriad of cells was estimated from a comparison of the VCSEL emission distribution obtained from ray-tracing calculation with experimental measurements using a power meter. This property was closely related to irradiation uniformity and spatial scalability.The experimental temperature distribution of silicon wafers exposed to high power VCSEL beams was used to verify the performance of commercial codes on three-dimensional simulation models including conduction, convection and thermal radiation. For LPCVD reactor design, this code was used to predict the optimal placement of the VCSEL module for uniform irradiation on 300 mm diameter wafers.The best-fit values of the factors for the Arrhenius equation describing the deposition process of polycrystalline silicon (poly-Si) thin-film using silane gas species were obtained from a comparison of deposition rates from numerical simulations with experimental observations available in the literature. Using these factors and the optical characteristics of the VCSEL and Si, the deposition process on the wafer with 300 mm in diameter was simulated under various operation conditions. Especially, instead of the uniform surface temperature condition, the heat flux distribution estimated from experimental irradiations on the wafer was used for the boundary condition at the bottom surface of the wafer in order to realize a practical deposition process.Simulation using the realistic heat flux boundary conditions showed that deposition rates in the wafer edge-region were significantly reduced due to the severe temperature drop in that region, compared to that using the ideal uniform temperature condition. In order to minimize this wafer exclusion area, the emission power of the VCSEL emitters affecting the wafer edge-region was adjusted to slightly increase, resulting in a more uniform distribution of the deposition rate.

Decoupling Strain and Composition Effects on Ge1-YSny Lattice Vibrations

Probing the behavior of vibrational modes in semiconductors is central to understand their basic structural, optical, and phononic properties. This is particularly true for the emerging GeSn and SiGeSn. This family of group-IV semiconductors is of growing interest for optoelectronic applications, notably due to the possibility of tuning the bandgap to cover a broad range from the short-wave infrared to the mid-infrared. An indirect to direct transition in GeSn alloys is expected for Sn incorporation higher than 9%, which can lead to the development of high efficiency light emission and detection devices. The growth of such alloys has however proven challenging due to the low solubility of Sn in Ge (≈1%). In addition, any residual strain means more tin incorporation is required to obtain a direct-bandgap [1]. The alloying process enables tuning the electronic and optoelectronic properties, but it also comes with enhanced lattice disorder thus affecting the lattice vibrational modes. Raman spectroscopy is commonly used to assess the role of composition y and strain ε in shaping the lattice vibrations. Curiously enough, previous works on GeSn mainly focused on analyzing the behavior of Ge-Ge mode. This is due to the broad use of 488 nm [2] or 532 nm [3], [4] excitation lines, which yield a very weak signal of the Ge-Sn mode. Alternatively, the use of a 633 nm excitation enables a clear detection of all Raman modes in GeSn layers independently of their composition. This is plausibly attributed to the fact that this wavelength might be close to resonance with the alloy’s E1 gap [5]. There are very few reports on the identification of the Ge-Sn mode [6], but quantitative analyses of the effects of composition and strain on this mode remain conspicuously missing in literature. With this perspective, this work presents a detailed study of Raman vibrational modes in Sn-rich (7-18 at.%) GeSn semiconductors. Samples were grown in a low-pressure chemical vapor deposition (LP-CVD) reactor using monogermane and tin-tetrachloride precursors. The samples consist of one or two GeSn layer(s) on a Ge virtual substrate (VS) on a Si wafer. Using X-ray diffraction (XRD), reciprocal space mappings were performed on all samples to retrieve the composition and the strain. Raman measurements have been carried out on an InVia Microscope from Renishaw with a 633 nm laser. While Voigt or Lorentzian functions are commonly used for fitting peaks, they cannot reproduce the asymmetric broadening typical to GeSn Raman peaks (Fig. 1). This asymmetry is due to alloying as substitutional Sn atoms break the translational symmetry and lead to a relaxation of the momentum selection rule [7]. To perform the fits, we are therefore using exponentially modified gaussian (EMG) functions, which can better reproduce the line shape of the Raman modes. A typical Raman spectrum appears in Fig. 1. Two-dimensional linear regressions are then performed to decouple the influence of strain and composition on the Raman shift of both modes. The resulting functions are illustrated in Fig. 2 and the coefficients appear in table 1. The planar fits accurately represent the distributions, as confirmed by the relatively small error on both a and b parameters (<10%) and the coefficients of determination near 0.99. Furthermore, the calculated Raman shift of the Ge-Ge mode in the limit of a pure and completely relaxed Ge layer is equal to the value obtained for bulk germanium, and the a and b parameters are comparable to those found in earlier studies for the Ge-Ge mode. Based on these detailed Raman studies, an exhaustive discussion of the influence of lattice strain and Sn content on GeSn vibrational modes will be presented. Acknowledgements The authors thank J. Bouchard for the technical support, and NSERC Canada (Discovery, SPG, and CRD Grants), Canada Research Chair, Canada Foundation for Innovation, Mitacs, FRQNT, Institut de l’énergie Trottier and MRIF Québec for support.

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.

Growth of Large-Area Graphene Single Crystals in Confined Reaction Space with Diffusion-Driven Chemical Vapor Deposition

To synthesize large-area graphene single crystals, we specifically designed a low-pressure chemical vapor deposition (LPCVD) reactor with confined reaction space (L 22 mm × W 13 mm × H 50 μm). Within the confined reaction space, a uniform distribution of reactant concentrations, reduced substrate roughness, and the shift of growth kinetics toward a diffusion-limited regime can be achieved, favoring the preparation of large-area, high-quality graphene single crystals. The gas flow field and mass transport pattern of reactants in the LPCVD system simulated with a finite element method support the advantages of using this confined reaction room for graphene growth. Using this space-confined reactor together with the optimized synthesis parameters, we obtained monolayer, highly uniform, and defect-free graphene single crystals of up to ∼0.8 mm in diameter with the field-effect mobility of μEF ∼ 4800 cm2 V–1 s–1 at room temperature. In addition, structural design of the confined reaction space by adjusting the...

Si Surface Preparation for Heteroepitaxial Growth of SiC Using &lt;i&gt;In Situ&lt;/i&gt; Oxidation

To achieve high quality SiC growth on Si substrate, it is essential to get a smooth Si surface without forming SiC and graphitic islands during the surface cleaning and before the carbonisation process. In this paper, a novel in-situ surface cleaning method designed for the hetero-epitaxial growth of SiC on Si substrate is developed using a custom-made low-pressure chemical vapour deposition reactor. The results indicate that the combination of ramping in oxygen and subsequent flowing of SiH4 avoids the contamination of Si, enables the oxide layer to be removed smoothly, and subsequently creates a smooth Si surface with regular atomic steps. SiC grown on off-axis Si has better crystallinity and significantly smaller roughness than that grown on on-axis Si.

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.

Three-step growth of metamorphic GaAs on Si(001) by low-pressure metal organic chemical vapor deposition

In this study, metamorphic growth of GaAs on Si(001) substrate was investigated via three-step growth in a low-pressure metal organic chemical vapor deposition reactor. Three-step growth was achieved by simply inserting an intermediate temperature GaAs layer between the low temperature GaAs nucleation layer and the high temperature GaAs epilayer. Compared with conventional two-step growth, three-step growth could further reduce surface roughness and etch pit density. By combining three-step growth with thermal-cycle annealing, the authors have grown a 1.8-μm-thick GaAs epilayer with root mean square roughness of only 1.8 and 0.73 nm in 10 × 10 μm2 and 2 × 2 μm2 scanning areas, respectively. The threading dislocation density of the 1.8-μm-thick GaAs epilayer was as low as 1.1 × 107 cm−2, as calculated directly from the double crystal x-ray diffraction ω-scan full width at half maximum of the GaAs diffraction peak. The corresponding etch pit density was only 3 × 106 cm−2.

3C-SiC on Si Hetero-Epitaxial Growth for Electronic and Biomedical Applications

The growth of cubic silicon carbide on silicon, namely 3C-SiC/Si, has been extensively studied at the University of South Florida over the past decade and numerous electronic and biomedical applications explored using this material system. The key step to 3C-SiC devices is the growth of high-quality epitaxial layers of 3C-SiC. In order to improve the manufacturability of future 3CSiC devices, a simplified 3C-SiC growth process on 50 and 100 mm Si (100) substrates has been developed in a low-pressure horizontal hot-wall chemical vapor deposition (CVD) reactor. A simplified growth process consists of a single thermal ramp to the growth temperature followed by the 3C-SiC growth. The 3C-SiC epitaxial layers were characterized via optical microscopy, secondary electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and secondary ion mass spectrometry (SIMS). Examples of biomedical devices realized with this material system are also introduced, including neural probes and in-vitro recording devices, as well as myoglobin and glucose biosensors.

Film Thickness Prediction of Poly-Silicon LPCVD Process with a Simplified Two-Step Surface Reaction Model

Poly-silicon deposition rate profiles on silicon wafers were evaluated along the axial direction and radial direction in a mass-production scale low-pressure chemical vapor deposition (MPS-LPCVD) reactor using SiH4. Numerical analysis was made by computational fluid dynamics (CFD) considering coupled chemical reactions at several temperatures around 873 K. We have performed elementary reaction simulation, which includes 19 chemical species and 33 reactions. Despite the complexity of the chemical reaction process of poly-silicon film deposition, we could conclude that Si deposition rate was mainly controlled by the surface reaction of SiH4 under LPCVD condition. The contributions of chemical species formed in the gas-phase could be ignored. Thus, we successfully simulated the experimental results with a simplified 2-step surface reaction model of SiH4. Predicted film thickness along the axial direction of the reactor agreed well with experimental results, and the 2-step reaction model proved to be a good tool for the numerical simulation of the poly-silicon deposition process in an MPS reactor.

Deposition of Au Thin Films and Nanoparticles by MOCVD

AbstractUsing metal‐organic (MO)CVD, gold films and arrays of gold nanoparticles are obtained from volatile organometallic dimethylgold(III) complexes with O, N, S donor ligands. As precursors, such compounds as (CH3)2Au(OAc), (CH3)2Au(piv), (CH3)2Au(OQ), (CH3)2Au(SQ), (CH3)2Au(thd), and (CH3)2Au(dtc) were used. Deposition processes are carried out within a low pressure (LP)CVD reactor with additional vacuum ultraviolet (VUV) stimulation, with and without a hydrogen reactant gas. The influence of precursor structure on the morphology of the deposited layers is demonstrated. The use of precursor (CH3)2Au(OQ) results in obtaining ultra‐thin continuous gold film ∼3 nm thick. It is established that with hydrogen reactant gas injected into the system, the amount of impurities in the film decreases. With the VUV stimulation, the gold content in the films amounts to almost 100%; in addition, the morphology of coatings is observed to change significantly. According to the X‐ray diffraction (XRD) phase analysis, gold crystallites in the films grow mainly in the [111] direction.

Demonstration of p-type 3C–SiC grown on 150 mm Si(1 0 0) substrates by atomic-layer epitaxy at 1000 °C

The potential for enhancement of Si-based devices by growth of SiC films on large-diameter Si wafers is hampered by the very high temperatures (close to the Si melting temperature) that are needed for growth and doping by the existing techniques. Here, we present a unique doping method for growth of Al-doped single-crystalline 3C–SiC epilayers on 150 mm Si(1 0 0) substrates by atomic-layer epitaxy at 1000 °C using a conventional low-pressure chemical vapor deposition reactor. Al atomic concentration in the range of 2.8×10 19 to 2.1×10 20 cm −3, proportional to the supply volume of trimethylaluminium, is experimentally demonstrated. A doping mechanism, based on the supply sequence of precursors and reactor pressure, is proposed.

Effect of annealing process on the surface roughness in multiple Al implanted 4H-SiC

A P-layer can be formed on a SiC wafer surface by using multiple Al ion implantations and post-implantation annealing in a low pressure CVD reactor. The Al depth profile was almost box shaped with a height of 1 × 1019cm−3 and a depth of 550 nm. Three different annealing processes were developed to protect the wafer surface. Variations in RMS roughness have been measured and compared with each other. The implanted SiC, annealed with a carbon cap, maintains a high-quality surface with an RMS roughness as low as 3.8 nm. Macrosteps and terraces were found in the SiC surface, which annealed by the other two processes (protect in Ar/protect with SiC capped wafer in Ar). The RMS roughness is 12.2 nm and 6.6 nm, respectively.

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.

Dependence of chemical composition and bonding of amorphous SiC on deposition temperature and the choice of substrate

Amorphous SiC has superior mechanical, chemical, electrical, and optical properties which are process dependent. In this study, the impact of deposition temperature and substrate choice on the chemical composition and bonding of deposited amorphous SiC is investigated, both 6 in. single-crystalline Si and oxide covered Si wafers were used as substrates. The deposition was performed in a standard low-pressure chemical vapour deposition reactor, methylsilane was used as the single precursor, and deposition temperature was set at 600 and 650 °C. XPS analyses were employed to investigate the chemical composition, Si/C ratio, and chemical bonding of deposited amorphous SiC. The results demonstrate that these properties varied with deposition temperature, and the impact of substrate on them became minor when deposition temperature was raised up from 600 °C to 650 °C. Nearly stoichiometric amorphous SiC with higher impurity concentration was deposited on crystalline Si substrate at 600 °C. Slightly carbon rich amorphous SiC films with much lower impurity concentration were prepared at 650 °C on both kinds of substrates. Tetrahedral Si–C bonds were found to be the dominant bonds in all deposited amorphous SiC. No contribution from Si–H/Si–Si but from sp 2 and sp 3 C–C/C–H bonds was identified.

Multifractal Spectra of INGaN/GaN Self-Assembled Quantum Dots Films

The surface shape and microstructure of semiconductor thin films, especially nanometer thin films, have important influence to construct physical characteristics, such as electricity, magnetic, and optics nature to the thin films. In this work, we use the multifractal spectra to study the surface morphology of InGaN/GaN self-assembled quantum dot films after the annealed process. Samples used in this study were grown on the (0001)-oriented sapphire (Al2O3) substrates in a vertical low-pressure metal-organic chemical vapor deposition reactor with a high-speed rotation disk. The fractal dimension and multifractal spectra can be used to describe the influence of different annealed conditions on surface characterization. Fractal analysis reveals that both the average surface roughness and root-mean-square roughness of nanostructure surfaces are decreased after the thermal annealing process. It can be seen that a smoother surface was obtained under an annealing temperature at 800°C, and it implies that the surface roughness of this case is minimum in all tests. The results of this paper also described a mathematical modeling method for the observation of the fractal and multifractal characteristics in a semiconductor nanostructure films.

Predictable Simple Reaction Model for Poly-Silicon LPCVD Process

Poly-silicon deposition rate profiles on silicon wafers in several temperatures around 873 K along axial direction in commercial low-pressure chemical vapor deposition (LPCVD) reactor were investigated by both experiments and numerical simulations considering coupled computational fluid dynamics (CFD) and chemical reactions. While the chemical reaction processes of poly-silicon film deposition is a complicated system with a huge number of elementary reactions, we could successfully simulate the experimental results with a simplified 2-step surface reaction model of SiH4. Simulated film deposition rate profiles along the axial direction of reactor were in good agreement with experimental results, and the 2-step reaction model was proved to be a good tool for the numerical simulation of poly-silicon deposition process in commercial reactor.

Design and Performance of an LPCVD Reactor for the Growth of 3C-Silicon Carbide

This paper discusses the design of a low pressure chemical vapor deposition (LPCVD) reactor and growth of β silicon carbide (3C-SiC) thin films on Si. The reactor’s hot-zone configuration radiatively couples the graphite heater (no physical contact) to Si substrates with realized temperatures . We implemented a four-stage growth procedure using silane and propane precursors and hydrogen as the carrier gas. Temperatures, pressures, and flows varied from , from , and from during growth, respectively. Growth of 3C-SiC was confirmed using X-ray diffraction (XRD) with the observation of a (200) peak located at 41.4°. Activation energies of 21.5 and were calculated for the kinetically and mass-transport-limited regimes for polycrystalline 3C-SiC growth. The polycrystalline 3C-SiC films with fewest defects and smallest XRD full width at half-maximum were deposited at with a growth rate of using flow rates of , , and of (conc. 1.16%). The composition of the films measured by X-ray photoelectron spectroscopy shows that the films are slightly carbon rich with oxygen as the main source of contamination. Voids were observed at the film–substrate interface for samples grown at high precursor concentrations.