Horizontal Hot-wall Chemical Vapor Deposition Research Articles

Impact of Doping on Cross-Sectional Stress Assessment of 3C-SiC/Si Heteroepitaxy.

In this paper, we used micro-Raman spectroscopy in cross-section to investigate the effect of different doping on the distribution of stress in the silicon substrate and the grown 3C-SiC film. The 3C-SiC films with a thickness up to 10 μm were grown on Si (100) substrates in a horizontal hot-wall chemical vapor deposition (CVD) reactor. To quantify the influence of doping on the stress distribution, samples were non-intentionally doped (NID, dopant incorporation below 1016 cm-3), strongly n-type doped ([N] > 1019 cm-3), or strongly p-type doped ([Al] > 1019 cm-3). Sample NID was also grown on Si (111). In silicon (100), we observed that the stress at the interface is always compressive. In 3C-SiC, instead, we observed that the stress at the interface is always tensile and remains so in the first 4 µm. In the remaining 6 µm, the type of stress varies according to the doping. In particular, for 10 μm thick samples, the presence of an n-doped layer at the interface maximizes the stress in the silicon (~700 MPa) and in the 3C-SiC film (~250 MPa). In the presence of films grown on Si(111), 3C-SiC shows a compressive stress at the interface and then immediately becomes tensile following an oscillating trend with an average value of 412 MPa.

Characterization of epitaxial layers grown on 4H-SiC (0 0 0 −1) substrates

SiC is an excellent semiconductor material that can be used in power semiconductor devices. It has the advantages of high thermal conductivity, stable chemical properties, and high critical breakdown field strength. The active region of a SiC device is usually in the SiC epitaxial layer, so the growth of high-quality SiC epitaxial layers is extremely valuable. In this paper, we investigate the epitaxial growth of SiC on n-type 4° off-axis SiC (0 0 0–1) substrates. We used a horizontal hot-wall chemical vapor deposition apparatus for rapid epitaxy on SiC substrates, using C2H4, and SiHCl3 as precursors and H2 as carrier gas, respectively, and growing at 1350 °C,1400 °C,1450 °C,1500 °C, 1550 °C, 1600 °C for half an hour to get epitaxial layer. The effect of growth temperature on the surface morphology of SiC (0 0 0 –1) epitaxial layer was analyzed and epitaxial layers is characterized by optical microscope, scanning electron microscope, atomic force microscope and Raman scattering instrument, and the growth rate of epitaxial layer was obtained. It is found that the higher growth temperature is helpful to obtain the epitaxial layer with smooth surface and higher content of 4H-SiC under certain pressure, C/Si molar ratio, and following rate of precursor and carrier gas.

Effect of Nitrogen and Aluminum Doping on 3C-SiC Heteroepitaxial Layers Grown on 4° Off-Axis Si (100).

This work provides a comprehensive investigation of nitrogen and aluminum doping and its consequences for the physical properties of 3C-SiC. Free-standing 3C-SiC heteroepitaxial layers, intentionally doped with nitrogen or aluminum, were grown on Si (100) substrate with different 4° off-axis in a horizontal hot-wall chemical vapor deposition (CVD) reactor. The Si substrate was melted inside the CVD chamber, followed by the growth process. Micro-Raman, photoluminescence (PL) and stacking fault evaluation through molten KOH etching were performed on different doped samples. Then, the role of the doping and of the cut angle on the quality, density and length distribution of the stacking faults was studied, in order to estimate the influence of N and Al incorporation on the morphological and optical properties of the material. In particular, for both types of doping, it was observed that as the dopant concentration increased, the average length of the stacking faults (SFs) increased and their density decreased.

Study of a new type nominal “washboard-like” triangular defects in 4H-SiC 4° off-axis (0 0 0 1) Si-face homoepitaxial layers

In this work, 4H-SiC epilayers were performed on 4°off-axis Si-face substrates by horizontal hot wall chemical vapor deposition (HWCVD). A new type nominal “washboard-like” triangular defects without particulate located at their apex were observed. The microstructure and formation mechanism were investigated by micro-Raman spectroscopy, electron backscatter diffraction (EBSD) and cross-section transmission electron microscopy (TEM). Characterization results indicate that the triangular defects observed have a 3C-SiC nature. In addition, the phenomenon that a serious of other triangular defects of which the vertices arranged in a row neatly with the new type nominal “washboard-like” triangular defect was observed. Based on these observations and analysis, a model of the formation mechanism of the triangular defect had been proposed. In this model, the 3C-SiC crystal formed by 2D nucleation of adatoms on the terraces is mainly triggered by the scratch in the substrate.

Influence of Triangle Structure Defect on the Carrier Lifetime of the 4H-SiC Ultra-Thick Epilayer**Supported by the National Key Research and Development Program of China under Grant No 2016YFB0400500.

Effect of triangle structure defects in a 180-μm-thick as-grown n-type 4H-SiC homoepitaxial layer on the carrier lifetime is quantitatively analyzed, which is grown by a horizontal hot-wall chemical vapor deposition reactor. By microwave photoconductivity decay lifetime measurements and photoluminescence measurements, the results show that the average carrier lifetime of as-grown epilayer across the whole wafer is 2.59 μs, while it is no more than 1.34 μs near a triangle defect (TD). The scanning transmission electron microscope results show that the triangle structure defects have originated from 3C-SiC polytype and various types of as-grown stacking faults. Compared with the as-grown stacking faults, the 3C-SiC polytype has a great impact on the lifetime. The reduction of TD is essential to increasing the carrier lifetime of the as-grown thick epilayer.

Effect of Low Pressure on Surface Roughness and Morphological Defects of 4H-SiC Epitaxial Layers.

In this work, 4H-SiC epilayers are performed on 4° off-axis substrates under low pressure condition by horizontal hot wall chemical vapor deposition (HWCVD) with a standard chemistry of silane-propane-hydrogen, which focuses on the effects of growth pressure on morphology, basal plane dislocations (BPDs) and crystalline quality. It is found that morphological defects reduce with the decreasing of growth pressure, since the surface diffusion length of absorbed adatoms increases under low growth pressure, which suppresses the nucleation of adatoms on terraces and the formation of morphological defects. However, as the surface diffusion length increases under low growth pressure, the difference of growth velocity at steps is enhanced, which leads to the extension of the steps’ width and the formation of step-bunching. Besides variation of surface diffusion length, the phenomenon described above can be correlated with different dominate modes for the minimization of surface energy at varied growth pressure. Because of the contrary influence of increased C/Si ratio and enhanced step-flow growth on the propagation of BPDs, the dislocation densities of BPDs and threading edge dislocations (TEDs) in epilayers grown at varied pressures remain basically unchanged. The crystalline quality is almost independent of growth pressure based on high resolution X-ray diffraction (HRXRD) measurements.

Smooth 4H-SiC Epilayers Grown with High Growth Rates with Silane/Propane Chemistry Using 4° Off-Cut Substrates

4H-SiC epilayers with very smooth surfaces were grown with high growth rates on 4° off-cut substrates using standard silane/propane chemistry. Specular surfaces with RMS values below 0.2 nm are presented for epilayers grown with growth rates up to 30 μm/h using horizontal hot-wall chemical vapor deposition, with up to 100 μm thickness. Optimization of in-situ etching conditions and C/Si ratio are presented.

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.

Growth of silicon carbide epitaxial layers on 150-mm-diameter wafers using a horizontal hot-wall chemical vapor deposition

Epitaxial layers on a 150-mm-diameter silicon carbide wafer have been grown using a horizontal hot-wall chemical vapor deposition system for three 150-mm-diameter wafers. We investigated the surface morphology and surface defects such as shallow pits and triangular defects of the grown epitaxial layers, as well as the thickness and carrier concentration uniformities. The shallow pit and triangular defect densities were 4.6cm−2 and 1.6cm−2, respectively, and the thickness and the carrier concentration uniformities were 3.9% and 47%, respectively. We focused on improving the carrier concentration distribution for practical use and concluded that the cause of the distribution was the distribution in the effective C/Si ratio in the direction of the gas flow.

The influence of growth conditions on carrier lifetime in 4H–SiC epilayers

4H–SiC homoepitaxial layers have been grown in a horizontal hot-wall CVD (chemical vapor deposition) reactor and the measured carrier lifetimes have been correlated to the CVD growth conditions. Two different generations of reactors were compared, resulting in measured carrier lifetimes in two different orders of magnitude, from a few hundreds of ns to a few µs. The variations in measured carrier lifetime were correlated to deep level concentrations of the Z1/2 center and the D1 center, seen by photoluminescence. Decreasing the growth temperature clearly prolonged the carrier lifetime and showed lower Z1/2 concentrations, whereas lowering the growth rate only showed a small improvement of the carrier lifetime and no obvious tendency in Z1/2 defect concentrations, indicating that Z1/2 is not the only defect limiting the carrier lifetime. Increasing the C/Si ratio resulted in decreasing Z1/2 concentrations, indicating the carbon vacancy nature of the defect. However, carrier lifetime measurements showed maximum values for a C/Si ratio of 1 but otherwise an increasing tendency for increasing C/Si ratios. The reactor giving higher carrier lifetimes, correspondingly also showed lower Z1/2 concentrations indicating the lifetime limiting property of Z1/2. Furthermore, the D1 defect intensity increased with growth temperature and decreased with increasing C/Si ratio, similar to the Z1/2 concentration.

The Growth of 3-Inch 4H-SiC Si-Face Epitaxial Wafer with Vicinal Off-Angle

We grew epitaxial layers on 3-inch epitaxial wafers with a vicinal off-angle, using a horizontal hot-wall chemical vapor deposition system that had a reactor capacity of 3 x 150 mm. Uniformity (σ/mean) of thickness and carrier concentration as small as 1.7% and 5.6%, respectively, were successfully obtained. We succeeded in decreasing triangular surface defects and polytype inclusions by increasing the growth temperature and lowering the C/Si ratio. In addition, I-V characteristics of Schottky barrier diodes on an epitaxial layer showed that a high blocking voltage of 960 V and a low leakage current of less than 1 x 10-6 A/cm2 were obtained with a yield of 78%.

Epitaxial Growth of 4H-SiC on 4° Off-Axis Substrate for Power Devices

Homo-epitaxial layers are successfully grown on Si-face 4° off-axis 4H-SiC substrates using the horizontal hot-wall chemical vapor deposition system. The smooth surface without morphological defects is obtained by the optimized in situ etching process and growth temperature. Schottky diodes fabricated on the epilayer present a typical I—V characteristic. This is the first report of Schottky diodes fabricated on 4° off-axis 4H-SiC substrates made in China.

Growth and Properties of SiC On-Axis Homoepitaxial Layers

Homoepitaxial growth has been performed on 3” Si-face on-axis 4H–SiC substrates using standard gas system in a horizontal Hot-wall chemical vapor deposition system. Substrate surface damages are found to act as preferential nucleation sites for 3C inclusions also, the surface morphology after in-situ etching is found to largely influence the polytype stability in the epilayer. Different in-situ etching conditions were studied where Si-rich conditions are found to be better. Growth parameters and starting growth conditions are refined to obtain stable polytype in the epilayer. High quality homoepitaxial layers with 100% 4H–SiC are obtained on 3” substrates. Different optical and structural techniques are used to characterize the layers and to understand the growth mechanisms. The layers are found to be of high quality and no epitaxial defects typically found on off-axis epitaxial layers are observed. A high surface roughness is observed in these layers, however higher growth rate significantly lowers the surface roughness without affecting the polytype stability in the epilayer.

Barium Titanate Thin Film Growth by Low-pressure Metalorganic Chemical Vapor Deposition

Barium titanate (BaTiO3) thin films were prepared from β-diketonate complexes as raw materials (on silicon substrates and into short quartz tubes) in the horizontal tubular hot-wall chemical vapor deposition reactor. The growth conditions, growth rate, and types of films grown were investigated. At high temperature (973 K), BaTiO3 could be prepared at concentrations equal to each of the metalorganic complexes, and its growth rate could be explained by summing the simple oxide growth rates because the growth rate of BaTiO3 is controlled by the mass transfer rate of the precursor. However, at low temperature (773 K), BaTiO3 could grow at a concentration of the Ti source that was richer than that of the Ba source because the growth rate of BaTiO3 is controlled by the rate of the chemical reaction and the Ti source reacts slower than the Ba source.

4H-SiC Bipolar Junction Transistors with Graded Base Doping Profile

This work reports 4H-SiC bipolar junction transistor (BJT) results based upon our first intentionally graded base BJT wafer with both base and emitter epi-layers continuously grown in the same reactor. The 4H-SiC BJTs were designed to improve the common emitter current gain through the built-in electrical fields originating from the grading of the base doping. Continuously-grown epi-layers are also believed to be the key to increasing carrier lifetime and high current gains. The 4H-SiC BJT wafer was grown in an Aixtron/Epigress VP508, a horizontal hot-wall chemical vapor deposition reactor using standard silane/propane chemistry and nitrogen and aluminum dopants. High performance 4H-SiC BJTs based on this initial non-optimized graded base doping have been demonstrated, including a 4H-SiC BJT with a DC current gain of ~33, specific on-resistance of 2.9 mcm2, and blocking voltage VCEO of over 1000 V.

On-axis homoepitaxial growth on Si-face 4H–SiC substrates

Homoepitaxial growth has been performed on Si-face nominally on-axis 4H–SiC substrates using horizontal Hot-wall chemical vapor deposition system. Special attention was paid to the surface preparation before starting the growth. In-situ surface preparation, starting growth parameters and growth temperature are found to play a vital role to maintain the polytype stability in the epilayer. High quality epilayers with 100% 4H–SiC were obtained on full 2″ substrates. Different optical and structural techniques were used to characterize the material and to understand the growth mechanisms. It was found that the replication of the basal plane dislocation from the substrate into the epilayer can be completely eliminated. The on-axis grown epitaxial layers were of high quality and did not show surface morphological defects, typically seen in off-axis grown layers, but had a high surface roughness.

Improved SiC Epitaxial Material for Bipolar Applications

ABSTRACTEpitaxial growth on Si-face nominally on-axis 4H-SiC substrates has been performed using horizontal Hot-wall chemical vapor deposition system. The formation of 3C inclusions is one of the main problem with growth on on-axis Si-face substrates. In situ surface preparation, starting growth parameters and growth temperature are found to play a vital role in the epilayer polytype stability. High quality epilayers with 100% 4H-SiC were obtained on full 2″ substrates. Different optical and structural techniques were used to characterize the material and to understand the growth mechanisms. It was found that the replication of the basal plane dislocation from the substrate into the epilayer can be eliminated through growth on on-axis substrates. Also, no other kind of structural defects were found in the grown epilayers. These layers have also been processed for simple PiN structures to observe any bipolar degradation. More than 70% of the diodes showed no forward voltage drift during 30 min operation at 100 A/cm2.

Thin crystalline 3C-SiC layer growth through carbonization of differently oriented Si substrates

The growth of thin cubic silicon carbide (3C-SiC) buffer layers in an horizontal hot-wall chemical vapor deposition reactor, through the carbonization of differently oriented Si surfaces, is presented. A qualitative and quantitative study has been performed on statistical parameters related to voids due to the buffer layer growth on the different substrate orientations emphasizing shape, size, and density as a function of the substrate orientation. Variation in the void parameters can be attributed to the atomic packing density related to the substrate orientations, which were (100) Si, (111) Si, and (110) Si in this study. Scanning electron microscopy and transmission electron microscopy were performed to analyze the surface and the crystalline quality of the 3C-SiC films grown and, eventually, an empirical model for the carbonization of Si surfaces formulated. Large platens characterize the 3C-SiC films with shapes related to the orientations of the substrate. These platens derive from the two-dimensional growth of different SiC islands which enlarge during the process due to the continuous reaction between Si and C atoms. The interior part of platens was characterized by the presence of a pure crystalline material with the presence of small tilts affecting some grains in the 3C-SiC layer in order to relief the stress generated with the substrate.

Fast homoepitaxial growth of 4H-SiC with low basal-plane dislocation density and low trap concentration by hot-wall chemical vapor deposition

Fast homoepitaxial growth of 4H-SiC has been carried out on 8° off-axis (0 0 0 1) Si substrates by horizontal hot-wall chemical vapor deposition (CVD) at 1650 °C. Growth at low pressure, by which gas-phase Si condensation can be minimized, has made it possible to obtain mirror-like surface at high growth rate up to 50 μm/h. Epilayers grown on chemical mechanically polished (CMP) substrates show much better surface morphology than those on as-received substrates. The basal-plane dislocation (BPD) density can be decreased by fast epitaxy on CMP substrates, and the minimum BPD density obtained in this study is 22 cm −2. The concentration of Z 1/2 and EH 6/7 centers is in the low 10 12 cm −3 range even at high growth rate of 50 μm/h. In photoluminescence (PL), free exciton peaks are remarkably dominant, and impurity-related peaks and L 1 peak are hardly observed.

Growth and characterization of nitrogen-doped C-face 4H-SiC epilayers

In this paper, nitrogen-doped 4H-Silicon carbide (SiC) epilayers are grown on 4° off-axis 〈 0 0 0 1 ¯ 〉 C-face 4H-SiC substrates by horizontal hot-wall chemical vapor deposition. Surface morphology of the epilayers shows a strong dependence on N 2 flow, C/Si ratio and growth temperature. Surface defect densities are higher for samples grown under high C/Si ratio and high N 2 flow condition. Lightly doped epilayers with low defect densities have been achieved by growing under optimized conditions. Macrostep bunching is observed on epilayers grown under high N 2 flow condition. The degree of step bunching manifests a dependence on N 2 flow. Possible impurity-induced step-bunching mechanism is discussed to explain the results. Lightly doped C-face 4H-SiC epilayers exhibit a site-competition effect, while heavily doped epilayers do not. Schottky barrier diodes fabricated on C-face 4H-SiC epilayers are shown to be comparable to or outperform those on Si-face epilayers.