Growth Of SiC Epitaxial Layers Research Articles

Optimizing the chemical vapor deposition process of 4H–SiC epitaxial layer growth with machine-learning-assisted multiphysics simulations

This work addresses a novel technique for selecting the best process parameters for the 4H–SiC epitaxial layer in a horizontal hot-wall chemical vapor reactor using a transient multi-physical (thermal-fluid-chemical) simulation model and combined with a machine-learning model. An experiment was performed to validate the feasibility of the numerical model. Secondly, a single-factor analysis was conducted to investigate the effects of process parameters, including the deposition temperature, inlet-flow volume, rotational speed of the susceptor, and cavity pressure, on the quality of the 4H–SiC epitaxial layer. Finally, a machine learning algorithm, the ant colony optimization-back propagation neural network (ACO–BPNN), was employed to develop the input/output model and optimize process parameters for obtaining a high-quality epitaxial layer and reducing the optimization cycle and costs. Notably, the optimized process was validated by real experiments, where the error between calculation and experiment is 4.03 % for deposition rate and 0.49 % for coefficient of variation, respectively. The results highlight the model as reliable and lay the foundation for the CVD growth of the 4H–SiC epitaxial layer.

Preface

Analytical Review of the Reports Presented at the 15th International Conference on Films and Coatings (ICFC2021)

ChemInform Abstract: Theory and Practice of SiC Growth on Si and Its Applications to Wide‐Gap Semiconductor Films.

The recent advances in epitaxial SiC films' growth on Si are overviewed. The basic classical methods currently used for SiC films' growth are discussed and their advantages and disadvantages are explored. The basic idea and the theoretical background for a new method of the synthesis of epitaxial SiC films on Si are given. It will be shown that the new method is significantly different from the classical techniques of thin-film growth where the evaporation of the atoms onto the substrate surface is exploited. The new method is based on the substitution of some atoms in the silicon matrix by the carbon atoms to form the molecules of silicon carbide. It will be shown that the following process of SiC nucleation happens gradually without destroying the crystalline structure of the silicon matrix, and the orientation of a grown film is imposed by the original crystalline structure of the silicon matrix (not only by the substrate surface as in conventional methods of film growth). A comparison of the new method with other epitaxy techniques will be given.The new method of solid-phase epitaxy based on the substitution of atoms and on the creation of dilatation dipoles solves one of the major problems in heteroepitaxy. It provides the synthesis of low-defective unstrained epitaxial films with a large difference between the lattice parameters of the film and the substrate without using any additional buffer layers. This method has another unique feature distinguishing it from the classical techniques of SiC films' growth—it allows the growing of SiC films of hexagonal polytypes. A new kind of phase transformation in solids owing to the chemical transformation of one substance into another will be described theoretically and revealed experimentally. This type of phase transformation, and the mechanism of a broad class of heterogeneous chemical reactions between gas and solid phases, will be illustrated by an example of the growth of SiC epitaxial layers due to the chemical interaction of CO gas with the monocrystalline silicon matrix. The discovery of this mechanism yields a new kind of template: namely, substrates with buffer transition layers for wide-gap semiconductor growth on silicon. The properties of a variety of heteroepitaxial films of wide-gap semiconductors (SiC, AlN, GaN and AlGaN) grown on a SiC/Si substrate by solid-phase epitaxy will be reported. Grown films contain no cracks and have a quality sufficient to manufacture micro- and opto-electronic devices. Also, the new abilities in the synthesis of large (150 mm diameter) low-defective SiC films on Si substrates will be demonstrated.

Recent Developments in the High-Rate Growth of SiC Epitaxial Layers by the Chemical Vapor Deposition Method

Although the performance of existing SiC power devices is superior to that of Si power devices, SiC power devices are not in general use. This is because their production costs are so high that the devices have not been accepted in the power-electronics market. Because the costs of homoepitaxial growth processes involving chemical vapor deposition (CVD) make up the largest proportion of the total cost of producing SiC wafers, an improvement in the growth rate is highly desirable. In this review, I explain three factors that prevent epitaxial growth and show that homogeneous nucleation in the gas phase is the main factor that prevents high-rate growth. And then I introduce recent developments in the high-rate growth of SiC epitaxial layers by CVD. I focus on three topics that realize high-rate growth, namely partial pressure control method, halide method and high efficient gas supply method.

SiC Warm-Wall Planetary VPE Growth on Multiple 100-mm Diameter Wafers

Experimental results are presented for SiC epitaxial layer growth employing a large-area, up to 8x100-mm, warm-wall planetary SiC-VPE reactor. This high-throughput reactor has been optimized for the growth of uniform 0.01 to 80-micron thick, specular, device-quality SiC epitaxial layers with low background doping concentrations of <1x1014 cm-3 and intentional p- and n-type doping from ~1x1015 cm-3 to >1x1019 cm-3. Intrawafer layer thickness and n-type doping uniformity (σ/mean) of ~2% and ~8% have been achieved to date in the 8x100-mm configuration. The total range of the average intrawafer thickness and doping within a run are approximately ±1% and ±6% respectively.

Development of Multiwafer Warm‐Wall Planetary VPE Reactors for SiC Device Production

AbstractThe development of SiC vapor phase epitaxial (VPE) growth for advanced SiC device production is reviewed with an emphasis on multiwafer reactors. Initially SiC epitaxial growth was performed in small homemade reactors on tiny, several millimeter on a side SiC crystals. While interest in SiC has its origins in the late 1950s, along side the elemental semiconductors Si and Ge, its technological development has been delayed by the extreme temperatures (∼1600 °C) required to grow SiC epitaxial layers, the late development of suitable substrates, and the various polytypes that can form. In large part these challenges have now been overcome. The most recent SiC epitaxial layer growth results, including those from the highest reported throughput, 8 × 100 mm, warm‐wall planetary SiC‐VPE reactor, are presented in detail. The growth of device‐quality SiC epitaxial layers with low background doping concentrations <1 × 1014 cm–3, and intentional p‐ and n‐type doping from ∼1 × 1015 cm–3 to >1 × 1019 cm—3 will be described. These layers have intrawafer thickness and n‐type doping uniformity (σ/mean) of ∼2 % and ∼8 %. The total range of the average intrawafer thickness and doping within a run are approximately ±1 % and ±6 %, respectively. Long term run‐to‐run variations (σ/mean) while under process control are currently ∼3 % for thickness and ∼5 % for doping. Multiwafer SiC epitaxial layer throughput has been increased by over a factor of twenty in just the past seven years while achieving these desirable layer characteristics. This new epitaxial capability is enabling the economical production of advanced SiC devices for the marketplace.

Surface studies of SiC epitaxial layers grown by chemical vapor deposition

We have systematically carried out investigations on the growth of SiC epitaxial layers by varying C/Si ratio over the range of 0.5, 1.0, 3.0, 6.0, and 9.0 in the gas phase. The studies by an optical Nomarski microscope and an atomic force microscope revealed the growth of hillocks and nano-tube like structures for particular deposition conditions on the C-face ( 0 0 0 1 ¯ ) and Si-face (0 0 0 1) 4H-SiC substrates. Indeed, at extreme conditions, the triangular shape hillocks formation was found on the C-face 4H-SiC substrates whereas on the Si-face 4H-SiC substrates, the cone or dome shape structures exhibited were black in color. Several carrot-like type structures, pits, etc., were also observed on the surface of the epilayers, which affect the quality of the layers and reduce the device efficiency. At optimized conditions, the surface looked like featureless with low roughness. In addition to C/Si ratios, N 2 dopant into SiC epitaxial layers have also been studied.

Growth of SiC epitaxial layers on porous surfaces of varying porosity

The presence of micropipes and dislocations in SiC wafers used as substrates for SiC epitaxial growth may cause formation of lattice defects in the epi layers. In previous research, optical and electrical characterization of epitaxial layers grown on porous substrates consistently indicated an improvement in the material quality over conventional substrates. Both the mechanism(s) for this improvement as well as the optimum porous composition to maximize material quality is a topic of intense interest. To provide insight into the optimum porous layer composition two 2 in. 4H–SiC(0 0 0 1) 8° off-axis SiC substrates were processed to form 1 cm regions (stripes) across each substrate, with each stripe having been subjected to different anodization conditions. For both samples the last stripe was left unanodized to serve as a control sample. CVD growth was then conducted to produce a 3–4 μm thick n-type epitaxial layer. Raman spectroscopy, C– V, X-ray diffraction and topography, and photoluminescence spectroscopy were conducted on the stripes to determine the difference in epi character as a function of porous composition.

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.

Morphology and polytype disturbances in sublimation growth of SiC epitaxial layers

Epitaxial layers of 6H and 4H-SiC have been grown with high growth rate by sublimation epitaxy on SiC substrates with different surface orientation. Polytype disturbances, i.e. regions within the layer where the polytype differs from that of the underlying substrate, may be observed at domain boundaries, defects and along the edges of the samples. The formation of polytype disturbances is more pronounced as the off-axis angle of the substrate decreases. For on-axis substrates, due to a dislocation controlled growth mechanism, many nucleation centers are formed thus creating several domains with polycrystalline growth along the boundaries. This results in a severe roughening of the layer surfaces. With increasing substrate off-orientation, the morphology improves and the appearance of polytype disturbances is diminished or prevented. For thick layers obtained with high growth rates, the surfaces of the layers grown on vicinal substrates are specular with some defects which are formed from obstacles. The growth proceeds via step-flow growth mechanism. A polytype change at the edge, where the growth steps start, may occur indicating a change in the growth mechanism from step-flow growth to 2D nucleation. 3C-SiC can become the dominant polytype in the epitaxial layer grown on 6H- or 4H-SiC substrates. The polytype disturbance at the edge is considerably reduced or has completely disappeared if the layer thickness does not exceed 300–400 μm as obtained with moderate growth rate of 100–200 μm/h.

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.

Study of silicon carbide epitaxial growth kinetics in the SiC-C system

The results of the study of SiC epitaxial layer growth kinetics in the system SiC-C are reported. The effects of temperature, pressure and heterogeneous reactions during the epitaxial layer formation have been studied in vacuum and at different partial pressures of argon in the system. An analysis of the experimental results was made on the basis of the theory of mass transfer by diffusion, taking into consideration the surface reactions. The dependence of the total supersaturation on the velocity of the epitaxial layer growth has been proposed. It has been established that above a certain pressures of argon in the system, and depending on the temperature of growth, the process is controlled primarily by mass transfer by diffusion, while at lower pressures the heterogeneous surface processes influence the kinetics of growth.