SiC Epitaxial Growth Research Articles

Ion beam induced reaction of carbon films on Si(1 0 0)

The irradiation effects of 2 MeV He + and Ar + ions on the film structure of the C–Si system were investigated with RHEED and XPS. The formation of SiC phase and/or the growth of epitaxial SiC were possible by He + irradiation for the carbon films up to 0.7 nm in thickness, which was thinner than that by Ar + irradiation. The He + irradiation could not grow the turbostratic graphite which could be grown by Ar + irradiation. The mechanism of the formation and the epitaxial growth of SiC by ion irradiation was discussed from the view point of the energy transfer from the irradiated ions.

Liquid-phase epitaxy on 6H-SiC Acheson seed crystals in closed vessel

SiC epitaxial growth was carried out on 6H-SiC Acheson seed crystals in liquid phase using a closed carbon crucible. The growth was carried out in the temperature range of 1500–1700°C. The geometrical configurations of seed crystals inside the crucible were specific, such that epitaxial layer growth occurred simultaneously on both faces of the same seed crystal under the same growth conditions. Growth rates as high as 20–30 μm/h have been achieved. The growth rate and surface morphologies observed after the growth indicated that the temperature gradient on the seed crystal faces plays a dominant role for the growth mechanism of the epitaxial layers. The convection within the solvent caused by the temperature gradient enhances the mass transport to the growing layer faces enhancing the growth rate and also results in a better surface morphology of the epitaxial grown layers.

Fast SiC Epitaxial Growth in a Chimney CVD Reactor and HTCVD Crystal Growth Developments

The epitaxial growth of SiC is investigated in a CVD process based on a vertical hot-wall, or chimney, reactor geometry. Carried out at increased temperatures (1650 to 1850 degreesC) and concentr ...

Adsorption of group III atoms on SiC(111) surfaces

We investigate the adsorption of boron and aluminium on β-SiC(111) 3 × 3 R30° surfaces by means of first-principles structure calculations utilizing density functional theory in its local density approximation. We focus on potential surfactant effects of group III adsorbates concerning epitaxial growth of SiC. For both adatoms considered we find the same sites as favoured for adsorption on Si(111) surfaces: aluminium adsorbs on the T 4 site, whereas boron occupies the so-called S 5 site substituting a carbon atom. However, in contrast to the adsorption on Si(111) we find a second interface phase for the boron adsorption under carbon-rich conditions energetically favourable where boron substitutes for an Si atom. We discuss geometrical, energetic and electronic properties of the most favourable adsorbate models.

An apparatus for supersonic jet epitaxy of thin films

An ultrahigh vacuum chemical beam epitaxy growth system has been built using multiple supersonic jets as precursors. Supersonic jets provide very high flux to the growth front while maintaining low growth pressures (10−5 Torr). Activation barriers to chemisorption are overcome by using hyperthermal (1–10 eV) precursors for heteroepitaxial growth. Improvement in growth rates and higher degrees of structural orientation are obtained at lower temperatures. Wide band gap semiconductors (SiC, GaN, and AlN) are deposited on silicon substrates using neutral chemical precursors. Epitaxial growth of SiC on silicon has been obtained at the lowest temperatures reported to date using a supersonic jet of methylsilane.

Epitaxial Growth of SiC on Non-Typical Orientations and MOS Interfaces

ABSTRACTHigh-quality 4H-SiC has been epitaxially grown on (1120) substrates by chemical vapor deposition. The physical properties of epilayers and MOS interfaces on both (1120) and off-axis (0001) substrates are elucidated. An unintentionally doped 4H-SiC epilayer on (1120) shows a donor concentration of 1×1014 cm−3 with a total trap concentration as low as 3.8×1012 cm−3. Inversion-type planar MOSFETs fabricated on 4H-SiC (1120) exhibit a high channel mobility of 96 cm2/Vs. The channel mobility decreases according to the T−2.2 dependence above 200K, indicating reduced Coulomb scattering and/or electron trapping. The superior MOS interface on (1120) originates from the much lower interface state density near the conduction band edge.

Effect of TMG Addition on the Epitaxial Growth of 3C-SiC on Si(100) and Si(111) Using Hexamethyldisilane

ABSTRACTEpitaxial and crack-free 3C-SiC film was successfully grown on Si(100)/(111) by a one step process without separate nucleation or carbonization steps at a low temperature of 1200°C by MOVPE. The growth was achieved by using hexamethyldisilane (HMDS) with the addition of a small amount of trimethylgallium (TMG) (0.5 sccm) with dilute hydrogen (12% H2 + Ar) as a carrier gas. Without the addition of TMG during growth, epitaxial growth of SiC on Si was only possible at temperatures above 1300°C following a nucleation step at 1200∼1250°C. After growth, all the films were analyzed by using cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Nomarski differential interference microscopy (NDIM). It was observed by XPS that the SiC film contained only a small amount of Ga, which means the Ga component of TMG does not much accumulate in SiC, in spite of a relatively high ratio of TMG/HMDS. To investigate the effect of TMG flow rate, various amounts of TMG (0.5 - 5sccm) were added during SiC deposition. Below 0.5 sccm of TMG flow rate, the SiC film showed epitaxial growth, observed by TEM and XRD. However, with an increasing flow rate of TMG above 1 sccm, the XRD peak of 3C-SiC becomes smaller and slightly shifted. At 5 sccm, the film was polycrystalline possibly implying that the SiC lattice is being strained gradually with TMG addition. It is also observed by AFM that, at the initial stages of growth, nucleation is much facilitated with the addition of TMG. The deposition rate with the addition of TMG at 1200°C is about 650 nm/hr, which is much faster than the rate without TMG addition (480 nm/hr). Thus, it is believed that TMG addition has a positive effect on the nucleation and HMDS decomposition during deposition. Also, with the addition of a small amount of Ar+10%HCl during growth, one-step deposition was possible helped by stress release due to void formation at the SiC/Si interface.

Optimization of the carbonized buffer layer for the growth of high quality single crystal SiC on Si

ABSTRACTCarbonized buffer layers were formed on Si (100) nominally oriented substrates with propane diluted in palladium purified hydrogen in a cold wall vertical reactor. Subsequent SiC layers were grown using silane and propane at atmospheric pressure. The growth temperature was ranging from 1150°C to 1350°C. The layers obtained were characterized by LT photoluminescence, IR reflectivity, X-ray diffraction, micro-Raman on cleaved edges, AFM imaging, and optical microscopy. Drastic influence on the layer surface morphology was evidenced depending on the transition step between the carbonization and the SiC epitaxial growth. As a result, we have developed a carbonization process leading to very high quality 3CSiC films grown at 1250°C.

A New Sublimation Etching for Reproducible Growth of Epitaxial Layers of SiC on SiC Substrate in a CVD Reactor

ABSTRACTWe have developed a new and simple method to etch SiC at relatively low temperature with very high rates. This method is particularly useful for cleaning the susceptor after growth. By employing this etching method to clean the susceptor prior to every growth run, we have greatly improved the reproducibility of SiC epitaxial growth and increased the lifetime of the susceptor. The method can also be used to etch SiC wafers at a very fast rate as an alternative to mechanical polishing. An etch rate of over 100μm/hr was obtained at 1600°C using this new method. The surfaces of the etched wafers were examined by atomic force microscope (AFM). Results of epitaxial growth using new etching method are presented.

Epitaxial growth of SiC-heterostructures on α-SiC(0001) by solid-source MBE

Epitaxial growth of SiC on α-SiC(0001) has been performed by means of solid-source molecular beam epitaxy (MBE). Low temperature ( T<1200°C) deposition on on-axis SiC substrates always results in the growth of 3C-SiC, which is significantly improved by an alternating supply of Si and C. On vicinal substrates, a step flow growth mode has been realized at T down to 1050°C. In experiments performed at T>1200°C, with a step decrease of supersaturation, a step-flow growth mode and for the first time nucleation of both 4H- and 6H-SiC under C-rich conditions was obtained. Based on these results we have demonstrated the growth of a double-heterostructure by firstly growing a 3C-SiC film on 4H-SiC(0001) at low temperature and a subsequent growth of 4H-SiC at low supersaturation on a C-stabilized surface on top of this film. Moreover, we also propose a new model to explain quantitatively the occurrence of different growth features and polytypes under certain growth conditions.

Epitaxial growth of SiC in a single and a multi wafer vertical CVD system: a comparison.

First results about a new system suited for epitaxial growth on six 2’ SiC-wafers at a time are presented in comparison to typical results in a single wafer CVD system. As expected, the multi wafer system today shows a by one order of magnitude higher background impurity level (≤ 10 15 cm −3 compared to ≤ 10 14 cm −3). On the other hand, the doping homogeneity is already very encouraging. The total variation on a 2 inch wafer is less than ± 20% at about 1*10 16 cm −3. The surface of the epitaxial layers is very smooth with a typical growth step height of 0.5 nm (4H 8° off orientation). First measurements on Schottky diodes show low leakage current values indicating low point defect density in the epitaxial layers.

SiC epitaxial layer growth in a novel multi-wafer vapor-phase epitaxial (VPE) reactor

Experimental results are presented for SiC epitaxial layer growths employing a unique planetary SiC-VPE reactor. The high-throughput, multi-wafer (7×2″) reactor, was designed for atmospheric and reduced pressure operation at temperatures up to and exceeding 1600°C. Specular epitaxial layers have been grown in the reactor at growth rates ranging from 3–5 μm/h. The thickest layer grown to date is 42 μm thick. The layers exhibit minimum unintentional n-type doping of ∼1×10 15 cm −3, and room temperature mobilities of ∼1000 cm 2/V s. Intentional n-type doping from ∼5×10 15 cm −3 to >1×10 19 cm −3 has been achieved. Intrawafer layer thickness and doping uniformities (standard deviation/mean at 1×10 16 cm −3) are typically 4 and 7%, respectively, on 35 mm diameter substrates. Moderately doped, ∼4×10 17 cm −3, layers, exhibit ∼3% doping uniformity. Recently, 3% thickness and 10% doping uniformity (at 1×10 16 cm −3) has been demonstrated on 50 mm substrates. Within a run, wafer-to-wafer thickness deviation averages ∼9%. Doping variation, initially ranging as much as a factor of two from the highest to the lowest doped wafer, has been reduced to ∼13% at 1×10 16 cm −3, by reducing susceptor temperature nonuniformity and eliminating exposed susceptor graphite. Ongoing developments intended to further improve layer uniformity and run-to-run reproducibility, are also presented.

Mechanisms of homo- and heteroepitaxial growth of SiC on α-SiC(0001) by solid-source molecular beam epitaxy

Epitaxial growth of SiC on hexagonal (or α)-SiC(0001) has been performed by means of solid-source molecular beam epitaxy (MBE). The solid-source MBE growth conditions have been analyzed concerning the supersaturation and the excess phase formation of silicon and carbon. In general, our results demonstrate that control of the Si/C ratio and the supersaturation (S) is essential for the growth mode and the kind of polytype grown. Low temperature (T 1450K under near surface equilibrium conditions, different growth modes, and conditions stabilizing the growth of certain polytypes have been found. With a step decrease of S, a step-flow growth mode of both 4H-and 6H-SiC was obtained and, for the first time in case of epitaxial SiC growth, a homogeneous nucleation of α-SiC at more C-rich conditions has been realized. Conditions stabilizing the growth of certain polytypes have been estimated by thermodynamic calculations considering the influence of polytype structure on the supersaturation and the surface energy. Based on these results, we have demonstrated the growth of a double-heterostructure by firstly growing a 3C-SiC layer on 4H-SiC(0001) at low temperature and a subsequent growth of 4H-SiC under near surface equilibrium conditions on a C-stabilized surface on top of this layer.

Epitaxial Growth of SiC in a Vertical Multi-Wafer CVD System: Already Suited as Production Process?

ABSTRACTResults about a new CVD system suited for epitaxial growth on six 2 inch SiC-wafers at a time are presented. Excellent gas flow stability is achieved for this new reactor type as shown by in- situ observations of the gas flow dynamics in the reactor chamber. These experimental results agree favorably with numerical process simulation results.The epitaxial layers grown in the multi-wafer system so far show a by an order of magnitude higher background impurity level (≤1015 cm−3) as reported previously for layers grown in single-wafer systems by the authors and other groups (≤ 1014 cm−3). On the other hand, the doping homogeneity achieved until today is very encouraging. The variation on a 2 inch wafer is less than ± 20% at about 1*1016 cm−3. The wafer to wafer variation of the average doping value both within a run and from run to run is within 15 %. The reproducibility and uniformity of the layer thickness is even better (total thickness variation ≤5% on a 2 inch wafer). The surface of the epitaxial layers is very smooth with a typical growth step height of 0.5 nm (4H, 8° off orientation). First measurements on Schottky diodes build on these layers show low leakage current values indicating low point defect density in the epitaxial layers.

Hexagonal and cubic SiC thin films on SiC deposited by solid source MBE

Abstract Epitaxial growth of SiC on SiC was realized between 900 and 1100 °C by means of solid-source molecular beam epitaxy. In general, our results show that the growth mode is strongly influenced on the surface stoichiometry. In case of Si-stabilized surfaces, showing 3-fold superstructures, films grow layer-by-layer via two-dimensional nucleation even at relatively low temperatures ( 925°C and R

Silicon Carbide Epitaxy in a Vertical CVD Reactor: Experimental Results and Numerical Process Simulation

In this paper an overview is given on the epitaxial growth of SiC in a vertical CVD reactor. Results concerning impurity incorporation and ways to achieve background doping levels as low as 1014 cm—3 are discussed. Precise control of the C/Si ratio in the gas phase, which is easily achieved in the described reactor, and the use of reduced pressure, lead to good control of dopant incorporation over more than three orders of magnitude, and smooth surface morphology at growth rates higher than 5 μm/h. Doping variations <±12% across 35 mm wafers can routinely be obtained. The quality of the epilayers is proven by electrical brakdown fields as high as 2×106 V/cm at NA — ND = 5×10—15 cm—3 achieved in both pn and Schottky diodes and an electron mobility higher than 700 cm2/Vs at 300 K (4H-SiC) estimated from the on-resistance of these test devices. Another important experimental boundary condition, the influence of the gas composition at the end of the epitaxial growth process on the surface properties of the epitaxial layer, is described. It will be shown that surfaces nearly resistant against oxidation can be generated in a hydrogen free atmosphere. As a second main topic of this paper, results of an elaborate numerical process simulation will be described including both fluid mechanical and chemical behavior. The influence of the main process parameters like total flow, chamber pressure, and rotation speed on the stability of the flow was investigated. The results achieved are compared with experimental observations showing excellent agreement. The experimental observation of an irradiant layer in the gas phase in front of the wafer under typical process conditions is explained with the help of the numerical model. The usefulness of this specific feature for the optimization of process conditions is discussed.

Experimental and Simulated Results of SiC Microwave Power MESFETs

A variety of RF and microwave electronic devices can be fabricated from SiC. These SiC-based devices have many properties that make them near ideal for high temperature, high frequency, high power, and radiation hard applications. Progress in SiC bulk and epitaxial layer growth has been rapid in recent years and corresponding progress has been achieved in device fabrication and contact technology. Both 6H- and 4H-SiC substrates are commercially available, and high quality epitaxial layers can be grown. Prototype SiC electronic devices with very good DC and RF performance have been demonstrated and devices such as diodes are commercially available, while RF and high frequency transistors are rapidly approaching the commercialization state. In particular, SiC transistors such as MESFETs (MEtal Semiconductor Field-Effect Transistors) and SITs (Static Induction Transistors) with excellent DC and RF performance have been demonstrated and these devices are being developed for microwave power amplifier and oscillator applications. One of the most promising devices for microwave power applications is the MESFET. In this work the performance of microwave SiC MESFETs is investigated with a simulator that contains a physically based device model. The simulator permits the operation of the device to be examined and optimum device structures to be determined. This, in turn, permits performance capability and limitations to be investigated. The results of the simulations are compared to experimental measurements where possible, and excellent agreement between the simulated and measured data are obtained.

Influence of growth conditions on the growth mode and layer structure in MBE-growth of SiC on SiC(0001)

Epitaxial growth of SiC on 6H-SiC(0001) was realized between 900 and 1100 °C by means of solid-source molecular beam epitaxy (MBE). In general, results show that the growth mode is strongly influenced by the surface stoichiometry. In case of Si-stabilized surface, showing 3-fold superstructures, films grow layer-by-layer via two-dimensional nucleation even at relative low temperatures (< 1000 °C). This may be a result of significant influence of exchange between Si and C suppressing island formation. In reflection high-energy electron diffraction (RHEED) investigations differences for the growth on 3C-SiC(100) and α-SiC(0001) were obtained. The grown film structure was found to be dependent on the deposition mode. Whereas in the case of continuous deposition the films consist of a mixture of the cubic and hexagonal polytypes, films grown by an alternating supply controlled in an atomic level using surface superstructures were dominantly of hexagonal SiC. Therefore, we assume that the stabilization of a certain superstructure (which corresponds to a certain surface energy) stabilizes the nucleation of one polytype.

An Overview of SiC Epitaxial Growth

SiC electronics research has been driven by the continued successful development of SiC technology for high-power and high-frequency semiconductor devices, and for service in high-temperature, corrosive, and high-radiation environments. The development of this technology has been accelerated by the introduction of commercially available SiC wafers, which have decreased in cost with time. The most recently demonstrated commercial SiC-based products include ultraviolet (uv)-flame sensors for terrestrial turbine engines and high-definition-television transmitter systems utilizing SiC-based transistors. Prototype microelectronic SiC devices include high-voltage Schottky rectifiers and power metal-oxide-semiconductor field-effect transistors, microwave and millimeter-wave devices, and high-temperature, radiation-resistant junction FETs (JFETs). These advancements in SiC-based device technology are attributable to both the successful development of commercially available, bulk SiC substrates and the recent advancements in SiC epitaxial layer growth technologies.

SiC Epitaxial Growth on Carbon

AbstractThe possibility of single crystal SiC expitaxial growth on freestanding amorphous carbon films (500–1000 Å) as well as thin amorphous carbon layers deposited on mono-crystalline SiC seeds, by conventional physical vapor transport (PVT) technique, is demonstrated. Preliminary experiments indicate that under certain specific growth conditions, 3D SiC single crystals (100 – 600 Å) of different polytypes can be grown on freestanding amorphous carbon layers, with more or less equal probability of formation for each polytype. On the other hand, under low axial temperature gradients (&lt; 30°C/cm), the SiC epitaxial growth on carbon is amorphous in nature. Also, experimental results that demonstrate two-dimensional single crystal SiC epitaxial growth on an amorphous carbon film deposited on mono-crystalline 6H-SiC wafer, is presented. Experiments performed in our laboratory indicate that monocrystalline SiC growth is possible on amorphous carbon layers upto 0.1 μm thickness.