Thermal Chemical Vapor Deposition Reactor Research Articles

Order-of-Magnitude Increase in Carbon Nanotube Yield Based on Modeling Transient Diffusion and Outgassing of Water From Reactor Walls

Abstract While reactor wall preconditioning was previously shown to influence the yield in chemical vapor deposition (CVD), especially for the growth of carbon nanotubes (CNTs), it was limited to studying accumulating carbonaceous deposits over a number of runs. However, the effects of temperature and duration as the reactor walls are exposed to hot humidity for extended periods between growth runs were not previously studied systematically. Here, we combine experimental measurements with a mathematical model to elucidate how the thermochemical history of reactor walls impacts growth yield, especially knowing that only a specific range of humidity promotes growth. Importantly, we demonstrate a one-order-of-magnitude higher CNT yield by increasing the interim, i.e., the time between runs. We explain the results based on previously unexplored process sensitivity to trace amounts of oxygen-containing species in the reactor. In particular, we model the effect of small amounts of water vapor being desorbed from reactor walls during growth. Our results reveal the outgassing dynamics and show the underlying mechanism of generating growth-promoting molecules. By installing a humidity sensor in our custom-designed multizone rapid thermal CVD reactor, we are able to uniquely correlate the amount of moisture within the reactor to real-time measurements of growth kinetics, as well as ex situ characterization of CNT alignment and atomic defects. Our findings enable a scientifically grounded approach toward both boosting growth yield and improving its consistency by reducing run-to-run variations. Accordingly, engineered dynamics recipes with added preprocessing steps can be envisioned to leverage this phenomenon for improving manufacturing process scalability and robustness.

Fabrication of silicon PIN diode with SiGe junction for soft x-ray detector using low-temperature technology

In this paper, a low-temperature technology was introduced for the fabrication of PIN photodiode. A double dielectric oxide layers were prepared by nitric acid oxidation and PECVD, respectively. The selective epitaxial growth of SiGe thin layers, which were in-situ doped in a reactive thermal chemical vapor deposition system, were applied for the preparation of PN junction and high-low junction. A SiNx passivation layer combined with a post-annealing was adopted to lower the reverse current. The temperature was controlled below 450 °C for the whole fabrication process. Finally, the reverse current of 0.7 nA was achieved at room temperature for our 5 mm-diameter PIN detector and the energy resolution of 240 eV was obtained at 5.9 keV, −60 °C. The results indicated that the low-temperature technology is suitable for the fabrication of high quality PIN detector, and the cost can be reduced effectively.

Reducing Variability in Chemical Vapor Deposition of Carbon Nanotubes Based on Gas Purification and Sample Support Redesign

Abstract The synthesis of vertically aligned carbon nanotubes (CNTs), also referred to as CNT forest, by chemical vapor deposition (CVD) is an intricate process that is sensitive to multiple factors other than control of temperature, pressure, and gas flows. In particular, growth is highly sensitive to factors like ambient humidity, as well as small quantities of oxygen-containing species and carbon deposits inside the reactor. These typically uncontrolled factors significantly affect growth reproducibility and hinders the fundamental study of process–structure–property relationship for these emerging materials. Accordingly, universally applicable design modifications and process steps toward improving growth consistency are sought after. In this study, we introduce two new modifications to our custom-designed multizone rapid thermal CVD reactor and demonstrate their impact on growth: (1) reconfiguring the inlet gas plumbing to add a gas purifier to the helium (He) line, and (2) designing a new support wafer for consistent loading of substrates. We use statistical analysis to test the effectiveness of these modifications in improving growth and reducing variability of both CNT forest height and density. Analysis of our experimental results and hypothesis testing show that combining the implementation of He purifier with the redesigned support wafer increases forest height and reduces the variability in height (17-folds), both at statistically significant and practically significant levels.

Vertically aligned carbon nanotubes-coated aluminium foil as flexible supercapacitor electrode for high power applications

Vertically Aligned Carbon Nanotubes (VACNTs)-coated flexible aluminium (Al) foil is studied as an electrode for supercapacitor applications. VACNTs are grown on Al foil inside thermal Chemical Vapor Deposition (CVD) reactor. 20 nm thick layer of Fe is used as a catalyst while Ar, H2 and C2H2 are used as precursor gases. The effect of growth temperature on the structure of CNTs is studied by varying the temperature of CVD reactor from 550 °C to 625 °C. Better alignment of VACNTs arrays on Al foil is recorded at 600 °C growth temperature in comparison to other processing temperatures. Cyclic voltammetry results shows that VACNTs-coated Al foil has a specific capacitance of ~ 3.01 F/g at a scan rate of 50 mV/s. The direct growth of VACNT array results in better contact with Al foil and thus low ESR values observed in impedance spectroscopy analysis. This leads to a fast charge–discharge cycle as well as a very high value of power density (187.79 kW/kg) suitable for high power applications. Moreover, wettability study shows that the fabricated VACNT electrode has a contact angle of more than 152° which signifies that it is a superhydrophobic surface and hence shows lower specific capacitance in comparison to reported values for VACNT array. Therefore, it is necessary to develop suitable post-processing strategies to make VACNTs hydrophilic to realize their full potential in supercapacitor applications.

Structural and chemical network studies of thermal chemical vapour deposited ZnO nanostructured thin films

In this work, we have investigated the role of process temperature on microstructural, structural, vibrational and phonon behaviour of Zinc Oxide Nanostructured (ZnO-NS) thin films deposited via thermal chemical vapour deposition reactor (TCVD) on Si substrate. The various spectroscopic methods such as Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) and Raman Spectroscopy were used to evaluate its morphology, structural, vibrational and phononic behaviour. We have observed that the change in process temperature considerably modifies the inherent material properties of ZnO-NS thin films. The AFM result revealed that the density distribution of agglomerated ZnO-nanograins increases with increasing process temperature from 650° C to 750° C. XRD result revealed that the average crystallites size of ZnO-NS thin films was decreased from 22.35 to 12.47 nm with increasing process temperature. The lattice strain and stress in ZnO-NS thin films decrease with increasing process temperature. The FTIR spectra revealed the decreasing intensity of ZnO stretch with increasing process temperature indicates a change in defect distribution of nanostructure at the higher temperature. The Zn-O–H bond shows asymmetry towards the lower wavenumber region can be attributed to the presence of another chemical compound with similar bonding strength overlap with each other. The Raman spectrum confirmed that the FWHM of E1(TO), E2(high), A1(LO) and E1(LO) phonon were increased whereas FWHM of A1(TO) and SO phonon decreased with increasing process temperature. The phonon lifetime of various phonons was calculated using energy-time uncertainty relation and found that the phonon lifetime of E1(TO), E2(high), A1(LO) and E1(LO) phonon decreased with increasing process temperature.

Multizone Rapid Thermal Processing to Overcome Challenges in Carbon Nanotube Manufacturing by Chemical Vapor Deposition

For the scalable production of commercial products based on vertically aligned carbon nanotubes (VACNTs), referred to as CNT forests, key manufacturing challenges must be overcome. In this work, we describe some of the main challenges currently facing CNT forest manufacturing, along with how we address these challenges with our custom-built rapid thermal processing chemical vapor deposition (CVD) reactor. First, the complexity of the multistep processes and reaction pathways involved in CNT growth by CVD limits the control on CNT population growth dynamics. Importantly, gas-phase decomposition of hydrocarbons, formation of catalyst nanoparticles, and catalytic growth of CNTs are typically coupled. Here, we demonstrated a decoupled recipe with independent control of each step. Second, significant run-to-run variations plague CNT growth by CVD. To improve growth consistency, we designed various measures to remove oxygen-containing molecules from the reactor, including air baking between runs, dynamic pumping down cycles, and low-pressure baking before growth. Third, real-time measurements during growth are needed for process monitoring. We implement in situ height kinetics via videography. The combination of approaches presented here has the potential to transform lab-scale CNT synthesis to robust manufacturing processes.

3D Graphene Fibers Grown by Thermal Chemical Vapor Deposition.

3D assembly of graphene sheets (GSs) is important for preserving the merits of the single-atomic-layered structure. Simultaneously, vertical growth of GSs has long been a challenge for thermal chemical vapor deposition (CVD). Here, vertical growth of the GSs is achieved in a thermal CVD reactor and a novel 3D graphene structure, 3D graphene fibers (3DGFs), is developed. The 3DGFs are prepared by carbonizing electrospun polyacrylonitrile fibers in NH3 and subsequently in situ growing the radially oriented GSs using thermal CVD. The GSs on the 3DGFs are densely arranged and interconnected with the edges fully exposed on the surface, resulting in high performances in multiple aspects such as electrical conductivity (3.4 × 104 -1.2 × 105 S m-1 ), electromagnetic shielding (60 932 dB cm2 g-1 ), and superhydrophobicity and superoleophilicity, which are far superior to the existing 3D graphene materials. With the extraordinary properties along with the easy scalability of the simple thermal CVD, the novel 3DGFs are highly promising for many applications such as high-strength and conducting composites, flexible conductors, electromagnetic shielding, energy storage, catalysis, and separation and purification. Furthermore, this strategy can be widely used to grow the vertical GSs on many other substrates by thermal CVD.

Influence of the substrate gas-inlet gap on the growth rate, morphology and microstructure of zirconium carbide films grown by chemical vapour deposition

The influence of the gap between the gas inlet and the substrate in an in-house developed thermal chemical vapour deposition (CVD) reactor, on the growth rate, surface morphology, phase composition and microstructure of deposited ZrC films was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ZrC films were grown on high density graphite substrates at different substrate-inlet gaps, viz. 70mm, 90mm, 120mm, 145mm and 170mm, at substrate temperatures of 1200°C and 1400°C. The growth rate of ZrC films prepared at 1400°C was observed to be higher than at 1200°C., and was found to decrease with increase in substrate-inlet gap at both temperatures. The boundary layer thickness increased with an increase in substrate-inlet gap. The diffusion coefficients of the reactants were found to be 0.176cm2/s and 0.200cm2/s for the ZrC films deposited at 1200°C and 1400°C respectively. A model illustrating the diffusion of source materials through the boundary layer to the reacting surface was also given. The XRD results of ZrC films showed that at both 1200°C and 1400°C the (111) plane was the less preferred orientation, while (200) and (220) were the preferred planes. The degree of preferred orientation of ZrC films was found to decrease with increasing substrate-inlet gap. SEM results indicated that as the substrate-inlet gap increased from 70mm to 170mm for 1400°C, the films became more uniform with increased particle agglomeration. The cauliflower-like clusters of particles grew larger in size and covered the whole surface. By contrast, at 1200°C the surface crystallites had complex facets that decreased in size as the substrate-inlet gap increased from 70mm to 170mm.

Degradation of silicon wafers at high temperatures for epitaxial deposition

AbstractThe material quality degradation of silicon wafers by metal impurities, various crystal defects as well as light and thermally induced mechanisms is very important for the solar cell performance and has been investigated by various groups. In this paper, the material degradation during epitaxial deposition at high temperatures above 1100°C will be discussed. Annealing experiments in hydrogen atmosphere are done with the laboratory rapid thermal chemical vapor deposition reactor to mimic the thermal process conditions for epitaxial growth of silicon from the gas phase. A general investigation of crystallographic and electronic properties of n‐ and p‐type silicon wafers has been done between 950°C and 1150°C. A detailed sensitivity analysis of process parameters like cooling ramp, peak temperature, duration, and ambient gasses has been conducted. The degradation mechanism by metal impurities has been investigated by using silicon wafers with different diffusion barriers. Besides effective minority carrier lifetime, measurements by quasi steady state photo conductance, etch pit density, Raman spectroscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy measurements have been done. The presented results have been used to improve the deposition process of epitaxial thin‐film solar cells, the production of silicon foils with a thickness <80 μm, and the fabrication of epitaxial multi junction solar cells with silicon bottom cell.

Thermal Rounding Kinetics and Demonstration of Steep and Flat Facets Succession in Selective Si-Based Epitaxy

Si1-xGex(SiGe) alloys are integrated in more and more complex structures, and their applications are numerous. Initially, epitaxy process was applied for SiGe channels in 32nm technologies and beyond [1]. In the 20nm technology generation, SiGe epitaxial growths are used for raised source/drain (RSD) in Fully Depleted Silicon-On-Insulator (FD-SOI) p-Metal Oxide Semiconductors (p-MOS). However, since the scaling of the transistors’ dimensions is reaching physical, material, and technological limitations [2], new challenges in Si-based technologies have to be defined. Up to now, one of the most promising studies overcoming major device issues such as parasitic capacitance [3], is the morphology’s control of SiGe epitaxial growths. This is the reason why the morphological behavior of epitaxial SiGe is of great interest for performance improvements. In SiGe epitaxies, surface morphology depends on different parameters such as deposited thickness, Ge content... But, one of the most important parameters for the morphological change is the thermal budget brought to the film during or after epitaxial growth. The consequence of a thermal budget on an epitaxial layer is the modification of the morphology to reduce the surface energy leading to thermal rounding. Finally, the transistors’ dimensions being very small, the morphology is even more affected and sensitive to any process conditions (temperature, pressure), and extensive studies on SiGe morphology are needed. For this work, patterned 300mm Si(001) bulk wafers are used as substrates. All the layers were selectively grown in a Rapid Thermal Chemical Vapor Deposition reactor using dichlorosilane, germane, and HCl chemistry at low pressure and relatively low temperature. The purge and unloading steps were adjusted to freeze the as-deposited morphology. This way, the observed morphology is the closest as possible to the one during the deposition. The first part consists of a quantitative study of the thermal rounding’s kinetics in Si1-xGex (x=0.25) epitaxies. To do so, as-deposited SiGe layers are annealed at different thermal budgets. Then, the morphology evolution during annealing is studied as a function of temperature and time. The results of post annealed SiGe epitaxies are reported in Fig.1. It is observed that an annealing temperature increase of 25°C (from 650°C to 725°C) considerably impacts the morphology which evolves progressively passing through different steps. First, the edges begin to round and retract. In this step, the as-grown facets and their corresponding overgrowths fade away completely. Then, the thermal rounding gives rise to a formation of rounded ridges all around the pattern. Finally, the corner ridges approach towards each other until they collapse to form a single large dome. The rounding kinetics is quantified by measuring the displaced volume of matter. In the final paper, an extensive study will be given in which the effect of H2pressure on the kinetics will be presented. It will be shown that the pressure has a real influence on the rounding effect due to an increase of the hydrogen coverage slowing the Si diffusion at the surface. In many MOS applications, the SiGe epitaxy has to be capped typically with a Si (or SiGe) layer to maintain good performances. In this second part, the morphology behavior of such caps is studied. Si and SiGe layers of different thicknesses, growth rates and Ge contents were grown on a rounded SiGe layer, prepared as explained in the first part. It is shown that both Si and SiGe behave differently. The SiGe cap decreases the surface undulation amplitudes more efficiently than Si. Indeed, in large patterns, the 16 nm thick SiGe cap surface is smoother (RRMS=3.57nm) than the surface of Si cap (RRMS=7.37nm) (see Fig.2). In small patterns, a regular faceted morphology is observed for thick SiGe cap which is not the case for Si cap, showing once again that SiGe cap is more efficient (Fig.3). On the other hand, for thin Si and SiGe caps, the top surface presents domes with a succession of flat and steep facets. Those facets are <113> facets for the steep ones, and <11h> with h being 9 or even more, for flat facets (Fig.4). To summarize, firstly, the thermal rounding has been quantified and shown to be very sensitive to moderate thermal budgets (e.g.700°C). Secondly, Si and SiGe caps deposited on such a rounded surface have been compared. It has been reported that thin caps present successive terraces rather than regular faceted morphology. Keywords: SiGe, Si, Epitaxy, Rounding, Capping. [1] Weber,O Symp. VLSI Techno Dig Tech Pap, 2004, p. 42. [2] Haron,N. IEEE, 2008; pp 98–103. [3] Cheng,K. Symp. VLSI Tech., 2009, pp 212-213. Figure 1

Morphometric and topographic study of foramen ovale

The influence of the gap between the gas inlet and the substrate in an in-house developed thermal chemical vapour deposition (CVD) reactor, on the growth rate, surface morphology, phase composition and microstructure of deposited ZrC films was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ZrC films were grown on high density graphite substrates at different substrate-inlet gaps, viz. 70 mm, 90 mm, 120 mm, 145 mm and 170 mm, at substrate temperatures of 1200 °C and 1400 °C. The growth rate of ZrC films prepared at 1400 °C was observed to be higher than at 1200 °C., and was found to decrease with increase in substrate-inlet gap at both temperatures. The boundary layer thickness increased with an increase in substrate-inlet gap. The diffusion coefficients of the reactants were found to be 0.176 cm2/s and 0.200 cm2/s for the ZrC films deposited at 1200 °C and 1400 °C respectively. A model illustrating the diffusion of source materials through the boundary layer to the reacting surface was also given. The XRD results of ZrC films showed that at both 1200 °C and 1400 °C the (111) plane was the less preferred orientation, while (200) and (220) were the preferred planes. The degree of preferred orientation of ZrC films was found to decrease with increasing substrate-inlet gap. SEM results indicated that as the substrate-inlet gap increased from 70 mm to 170 mm for 1400 °C, the films became more uniform with increased particle agglomeration. The cauliflower-like clusters of particles grew larger in size and covered the whole surface. By contrast, at 1200 °C the surface crystallites had complex facets that decreased in size as the substrate-inlet gap increased from 70 mm to 170 mm.

Effects of Acetylene on Deposition Rate of Stainless Steels Using Thermal Chemical Vapor Deposition

A hot filament thermal chemical vapor deposition (CVD) reactor was used to deposit solid thin films on stainless steel 316 (SS 316) and stainless steel 201 (SS 201) substrates at different flow rates of acetylene (C2H2) gas. The variation of thin film deposition rate with the variation of gas flow rate has been investigated experimentally. During experiments are conducted under gas flow rate (1-5) lit/min gas flow rate, duration of deposition (10-60 min), pressure (0.2-1 bar), average surface roughness (0.3-1.05) µm and temperature 800 °C considered. Experimental results show that deposition rate on SS 316 and SS 201 increases with the increase in gas flow rate. The deposition rate also shows increasing trend with pressure and duration of deposition. Under the above mentioned experimental conditions deposition is found to be maximum of SS-316 compared to SS-201. In relation to roughness the maximum deposition is found at 0.5 microns but comparing the both materials -316 and-201 highest of deposition rate is obtained from SS-316.

Investigation of thin film deposition on stainless steel 304 substrates under different operating conditions

In recent times, friction and wear in relation to the deposited carbon films on the steel substrates are important issues for industrial applications. In this research study, solid thin films were deposited on the stainless steel 304 (SS 304) substrates under different operating conditions. In the experiments, natural gas (97.14% methane) was used as a precursor gas in a hot filament thermal chemical vapor deposition (CVD) reactor. Deposition rates on SS 304 substrates were investigated under gas flow rates 0.5 - 3.0 l/min, pressure 20 - 50 torr, gap between activation heater and substrate 3.0 - 6.0 mm and deposition duration 30 - 120 minutes. The obtained results show that there are significant effects of these parameters on the deposition rates on SS 304 within the observed range. Friction coefficient of SS 304 sliding against SS 314 was also investigated under normal loads 5 - 10 N and sliding velocities 0.5 - m/s before and after deposition. The experimental results reveal that in general, frictional values are lower after deposition than that of before deposition.

Qualification of a sublimation tool applied to the case of metalorganic chemical vapor deposition of In₂O₃ from In(tmhd)₃ as a solid precursor.

A solid delivery system consisting of a source canister, a gas management, and temperature controlled enclosure designed and manufactured by Air Liquide Electronics Systems was tested in the context of gas-phase delivery of the In(tmhd)3 solid precursor. The precursor stream was delivered to a thermal metalorganic chemical vapor deposition reactor to quantify deposition yield under various conditions of carrier gas flow and sublimation temperature. The data collected allowed the determination of characteristic parameters such as the maximum precursor flow rate (18.2 mg min(-1) in specified conditions) and the critical mass (defined as the minimum amount of precursor able to attain the maximum flow rate) found to be about 2.4 g, as well as an understanding of the influence of powder distribution inside the canister. Furthermore, this qualification enabled the determination of optimal delivery conditions which allowed for stable and reproducible precursor flow rates over long deposition times (equivalent to more than 47 h of experiment). The resulting In2O3 layers was compared with those elaborated via pulsed liquid injection obtained in the same chemical vapor deposition chamber and under the same deposition conditions.

Deposition rates on stainless steel substrates of different surface roughnesses under different operating conditions using thermal CVD

A series of experimental tests were carried out to observe the deposition rates on different stainless steel substrates of different surface roughnesses under different operating conditions using a hot filament thermal chemical vapour deposition (CVD) reactor. The test parameters include gas flow rate of methane, temperature of substrate and activation heaters, distance between activation heater and substrate, pressure and duration. There are significant effects of these parameters on deposition rate of different stainless steel materials. It was found that deposition rates strongly depend on different surface roughnesses of the stainless steel substrates under different tested conditions within the observed range. Tribological properties, especially friction and wear of these stainless steel materials sliding against SS 314 under different normal loads and sliding velocities are also investigated before and after deposition. The obtained results reveal that the values of friction and wear are lower after deposition than that of before deposition.

In-situ phosphorous-doped SiGe layer on Si substrate by reactive thermal chemical vapor deposition at low temperature

We have studied in-situ phosphorus-doping characteristics in Ge-rich Si1−xGex (0.95≤x≤1) epitaxially grown on Si substrate by Reactive Thermal Chemical Vapor Deposition system at 350°C using GeF4 and Si2H6. The impact of PH3 in-situ doping on the growth kinetics, micro-structure and electric properties of Si1−xGex layers is investigated. The results indicate that the growth rate of Si1−xGex layers drops when the doping ratio (PH3/GeF4) is increased up to 750ppm. Correspondingly, the surface morphology as well as the crystal quality of Si1−xGex layers starts to deteriorate. The electrical measurements show that an excellent doping efficiency is achieved in the case of an acceptable surface morphology and crystalline quality. These results provide the promise for future n+/p diode fabrication by Reactive Thermal Chemical Vapor Deposition at low temperature.

Structural Tuning Using a Novel Membrane Reactor for Carbon Nanotube Synthesis

ABSTRACTCarbon nanotubes come in many varieties, with chemical, mechanical, and electrical properties depending on carbon nanotube (CNT) structural morphology. In order to provide a platform for CNT structural tuning, a membrane reactor was designed and constructed. This reactor provided more intimate gas-catalyst contact by decoupling the carbon feedstock gas from carrier gas in a chemical vapour deposition (CVD) environment using an asymmetric membrane and a macroporous membrane. Growth using this membrane reactor demonstrated normalized yield improvements of ∼300% and ∼1000% for the asymmetric and macroporous membrane cases, respectively, over standard CVD methods. To illustrate the possibility for control, growth variation with time was successfully demonstrated by growing vertically aligned multi-walled CNTs to heights of 0.71 mm, 1.36 mm, and 1.84 mm after growth for 15, 30, and 60 minutes in a commercial thermal CVD reactor. To demonstrate CNT diameter control via catalyst particle size, dip coating and spray coating methods were explored using ferrofluid and Fe(NO3)3 systems. CNT diameter was demonstrated to increase with increasing particle size, yielding CNT like growth with diameters ranging from 15 -150 nm. Demonstration of these dimensions of control coupled with the dramatic efficiency increases over growth in a commercialized CVD reactor establish this new reactor technology as a starting point for further research into CNT structural tuning.

Heteroepitaxial Growth of Ge-Rich SiGe Films on Si for Solar Cells

Germanium-rich silicon-germanium (Si1-xGex: 0.98≤x≤1) films were epitaxially grown on Si (001) substrate by reactive thermal chemical vapor deposition at low temperature. Si2H6 and GeF4 were used as source gases. The effect of gas flow ratio between Si2H6 and GeF4 was studied to optimize the film quality. The results indicated that Si1-xGex (x≥0.99) epilayer can be prepared directly on Si wafer at 350°C with a threading dislocation density of ~7×105/cm2 and surface RMS roughness of 1.0 nm. Hall-effect and conductivity measurements revealed that the epilayer was p-type conduction with the hall mobility of 767 cm2/Vs and the hole concentration of 6.08×1016/cm3. Those results indicated the Ge-rich Si1-xGex was an excellent candidate for bottom cells of multijunction solar cells.

Epitaxial growth of germanium-rich silicon–germanium films on Si(0 0 1) substrate by reactive thermal chemical vapor deposition

In this paper, a study on the growth kinetics of Ge-rich Si1−xGex films on Si substrate through a reactive thermal chemical vapor deposition (RTCVD) is conducted using Si2H6 and GeF4 as the source gases. The growth temperature is lower than 400°C. The influence of substrate temperature and gas pressure on the microstructure and crystallinity of Si1−xGex epilayer is investigated. By optimizing the growth parameters, high quality epitaxial Si1−xGex layer is fabricated at 350°C, with a threading dislocation density of ∼7×105/cm2 and surface RMS roughness of 1.44nm. The results suggest that the epitaxial Si1−xGex films by RTCVD are preferable materials for low-cost electronic devices.

Low-temperature epitaxial growth of high quality Si1−xGex (x ≥ 0.99) films on Si(001) wafer by reactive thermal chemical vapor deposition

Epitaxial growth of silicon-germanium (Si1−xGex: 0 ≤ x ≤ 1) thin films on Si(001) substrate at low temperature has been investigated using reactive thermal CVD. Si2H6 and GeF4 are used as source gases. The results indicate that Si1−xGex (x ≥ 0.99) epilayer can be prepared directly on Si wafer at 350 °C with the degree of strain relaxation up to 98.5%. Etching reaction between GeF4 and the growth surface plays an important role in both improving the crystal quality and suppressing the propagation of dislocations. High quality epitaxial Si1−xGex has been fabricated with a threading dislocation density of ∼7.0 × 105 cm−2 and RMS roughness of 1.44 nm.