Papers by Keyword: MOCVD

Abstract: Rapid progress in the growth of 4H-SiC epitaxial layers allow device scientists/engineers to tighten the specifications of doping and thickness uniformities of SiC epitaxial films. Further, reducing the cost of SiC epitaxial layers is a continuing goal. A compelling approach is to choose a multi-wafer warm-wall epi reactor which has been shown to have very high wafer throughput. The precursors decompose upon heating by passing over hot reactor components, however, the precursor molecules crack before reaching the substrate and can form parasitic SiC coatings. Such coatings change the emissivity of reactor parts, changing their temperatures. The allowed vapor pressure in the gas phase is also a function of the chemical composition of these deposits. Consequently, the effective Si/C ratio at the wafer varies the nitrogen incorporation efficiency on the SiC epitaxial wafer. In this paper, we have reported an approach on how to minimize the effect of changing Si/C ratio on absolute layer doping and thickness over the full campaign. We analyzed the data, identified the pattern, and have used it to make predictions or decisions to keep the deviation within control limits. The nitrogen incorporation was analyzed as a function of cumulative coating on the reactor parts. The derived models were used to make the decisions for predictive doping by adjusting the flow rates of nitrogen precursors during upcoming campaigns at specific cumulative thickness of reactor parts coating. The same approach was also used for the adjustment of growth time to obtain the targeted epi layer thickness as a function of cumulative coating. Consequently, the predictive doping control resulted in the improvement of doping Cpk from 0.37 to >1.67 and the predictive thickness control resulted in the improvement of thickness Cpk from 0.75 to 1.61. This implies that the process is six sigma qualified and expected overall nonconformance was 0.001% for doping. Moreover, the average 200 source contrast projected 5×5 mm² chip yield using a Lasertec system 88-HIT and the machine learning based PLDLZ recipe was >94% by considering the Particle, Bump, Micropipe, ComplexSF, Polytype Inclusion, Particle Inclusion, and ScratchTrace as device killer defects. The average BPDs were <25 on 150mm wafers using a 1µm thick buffer layer. Initial results on 200 mm wafers are also presented.

Abstract: This work explores the application of gallium nitride (GaN)-based solid-state devices for high-power, high-frequency, and high-temperature technologies. It presents an in-depth study of GaN on semi-insulating SiC substrates. The study demonstrates, through bow range investigation, optical microscopy, and X-ray diffraction (XRD), that by adapting growth parameters from those used for Si substrates to those suitable for SiC substrates, it is possible to achieve high-quality crystalline MOCVD growth both under on-axis and 4°off-axis substrate orientations.

Abstract: Indium gallium nitride / gallium nitride (InGaN/GaN) heterostructures were grown by using metal organic vapor deposition technique with four different growth temperatures (740 °C, 760 °C, 780 °C, and 800 °C). The structural properties and crystalline quality were investigated using high resolution X-ray diffraction (HRXRD) technique. XRD ω-2θ scan mode at GaN (002) diffraction plane was performed to assess the film’s quality. Through the simulation fitting, the indium composition and the thickness of the thin films were obtained. From the observation, an increase in the growth temperature resulted in higher intensity and smaller full-width at half maximum value of the InGaN (002) diffraction peak, which indicated improvement to the crystalline quality of the InGaN/GaN heterostructure. Moreover, the indium composition of the InGaN epilayer was found to decrease with an increase of the growth temperature due to the thermal decomposition of In-N bond and its re-evaporation from the growing surfaces.

Abstract: Tantalum carbide (TaC) coating, produced in an ultrahigh temperature chemical vapor deposition (CVD) process, exhibited high thermal and chemical stabilities, low emissivity, and high purity. Low emissivity of 0.3~0.43 was measured on TaC coating at 1000°C and compared with the one of SiC coating. As revealed in both simulation and experiment, the low emissivity of TaC coatings not only improves temperature uniformity in the SiC PVT process, but also reduces power consumption in both SiC crystal growth and GaN epitaxial deposition. The results provide important guidance to process tuning when switching from a conventional graphite or SiC-coated component to its TaC-coated counterpart.

Abstract: Abstract. In an effort to successfully fabricate InGaN-based for green emitting devices on patterned sapphire substrate, the indium composition in In_xGa_1-xN/GaN multi-quantum well structure is crucial because lower indium composition will shift the wavelength towards ultraviolet region. In this study, 5 micrometre of undoped GaN epilayer was deposited as a buffer layer prior to the growth structure. 6 pairs of InGaN/GaN multi-quantum well structure grown by metal organic chemical vapour deposition (MOCVD). In this research, the indium to gallium composition ratio was 9:1. The crystal and optical properties of the samples were characterized using field effect atomic force microscopy, high resolution x-ray diffraction, and photoluminescence spectroscopy.

Abstract: Aluminium oxide was deposited on silicon, silicon carbide and epitaxial graphene grown on silicon carbide by atomic layer deposition using a standard MOCVD equipment. The morphology and the electrical properties of the aluminium oxide layers on both substrates were determined and compared to aluminium oxide layers deposited with a standard atomic layer deposition equipment. The high-k material fabricated with the developed MOCVD process show comparable or better properties compared to the standard atomic layer deposition process.

Abstract: The aim of this work is, using finite element analysis, to study the effects of thermal load and rotation speed on the structural integrity of a substrate holder module in an MOCVD reactor. Several loading conditions are considered, including thermal load and rotational speeds of 0-1500 rpm. In addition, the wafer bow and residual stress of GaN film grown on silicon or sapphire wafer are systematically studied. Simulation results indicate the variation of critical stress with rotation speed in all of the components is small. Given a similar heat source in the MOCVD reactor, temperature of the upper components such as susceptor, substrate holders, and wafers is higher in the case of sapphire wafer than that in the case of silicon wafer. The temperature gradient of upper components is greater for the silicon wafer case. A greater temperature gradient in the film-substrate system generates a greater wafer bow and residual stress in the grown thin film. Therefore, temperature uniformity is an important parameter for the epitaxial process. The sign of residual stress is different between a GaN film grown on a sapphire wafer and a silicon wafer (compressive for sapphire wafer and tensile for silicon wafer). For growing a GaN thin film, sapphire wafer is better than silicon wafer in terms of lessening cracking in film.

Abstract: Compared to anatase and rutile TiO₂, the brookite TiO₂ (b-TiO₂) is relatively seldom investigated, because it is difficult to be prepared. In order to explore a scientific and effective approach to prepare high quality b-TiO₂ crystalline films, the effects of deposition rate on the properties of b-TiO₂ films prepared on yttria-stabilized zirconia (YSZ) (110) substrates by metal organic chemical vapor deposition (MOCVD) were investigated in this study. The structural analyses indicated that the b-TiO₂ film prepared with the lowest deposition rate of 1.25 Å/min had the best single crystalline quality for which the epitaxial relationship between the film and substrate was determined as b-TiO₂(120) || YSZ(110) with an in-plane epitaxial relationship of b-TiO₂[001]|| YSZ[001] and b-TiO₂[20]||YSZ[10]. The RMS surface roughness of the obtained films decreased from 7.02 to 1.11 nm as the deposition rate decreased. The average transmittances of all the obtained b-TiO₂ films exceeded 90% in the visible range. The optical band gaps increased from 3.54 to 3.63 eV as the deposition rate decreased. Apparently, the deposition rate has a significant influence on the structural, morphological and optical properties. Therefore, it provides a practicable way to manipulate such properties of b-TiO₂ films for different applications in the field of transparent optoelectronic devices.

Abstract: New wide band gap semiconductors with tunable properties are desperately needed to meet the ever-increasing demands of photoelectric devices operating in the ultraviolet (UV) or even deep ultraviolet (DUV) region. In this study, the ternary aluminum indium oxide (Al_2xIn_2(1-x)O₃) films with different Al compositions of x [Al/(Al+In) atomic ratio] were successfully grown on the α-Al₂O₃ (0001) substrates at 650 °C by metal organic chemical vapor deposition (MOCVD). The influence of Al content on the structural, compositional, electrical and optical properties of the obtained films was investigated in detail. The structural transition from polycrystalline structure of bixbyite In₂O₃ to amorphous was observed as the Al content increased. The lowest resistivity of 1.52×10^-3 Ω·cm was obtained for the sample with x=0.2, along with the respective hall mobility and carrier concentration values of 12.87 cm²V^-1s^-1 and 2.27×10²⁰ cm^-3. The average visible transmittances of over 83% were demonstrated for all the samples. The calculated values of optical band gap for the films indicated continuous increase from 3.82 to 5.88 eV as the x value increased from 0.1 to 0.9. The Al_2xIn_2(1-x)O₃ films with tunable properties may be potentially employed in the fabrication of transparent optoelectronic devices, such as UV detectors, transparent TFTs and short wavelength light-emitting devices.

Abstract: To characterize the properties of the as-grown Al_xGa_1-xN material for producing high property Al_xGa_1-xN photocathode in ultraviolet (UV) detection, the Ar⁺ sputtering and X-ray photoelectric spectroscopy (XPS) scan are performed. XPS spectra indicates that although processed with chemical solutions, Al_xGa_1-xN still contains large amount of carbon and oxide on the surface, which can be completely removed by Ar⁺ sputtering within few minutes. Ga3d and Al2p curves show that there are other compounds of Ga and Al on the surface but both become very concentrated when sputtering continues. The proportion of Al increases and that of Ga decreases gradually from surface to AlN bulk, which testify the graded band gap profile of the Al_xGa_1-xN sample. There is always a very slight amount of oxygen in the AlN layer, which is regarded as native element during material growth. At the interface of AlN and sapphire, an abrupt transition appears which can influence the properties of the Al_xGa_1-xN photocathode when it works with the transmittance mode