SiC Epitaxial Growth Research Articles

Patterned substrate with inverted silicon pyramids for 3C–SiC epitaxial growth: A comparison with conventional (001) Si substrate

Abstract

Investigation of Basal Plane Dislocation Reduction/Elimination by Molten KOH-NaOH Eutectic Etching Method

An optimized molten KOH-NaOH eutectic etching method is developed to reveal defects in highly n-doped SiC substrates and to pre-treat the substrate prior to epitaxial growth. Different from the conventional KOH etching method, by way of eutectic method, the basal plane dislocation (BPD) conversion in the subsequent epitaxial growth is independent of the etch pit size pre-generated on the substrate. Even with a short period (~3 minutes) of pretreatment which does not generate any visible etch pits or degradation of surface morphology on the substrate, an epilayer with low BPD density -2 is still achieved. This simple and non-destructive method shows high potential to be practically employed as one of the basic pretreatment steps to the substrates in SiC epitaxial growth in order to achieve very low or free BPD density.

Behavior of Particles in the Growth Reactor and their Effect on Silicon Carbide Epitaxial Growth

Formation of particles and their effect on SiC epitaxial growth in the CVD reactor is investigated. Particle induced defects in the epilayer at different gas decomposition conditions are discussed. A higher number of pits with larger diameters are observed in the epilayer for conditions where gases decompose later in the gas injector tube (i.e. nearer to the substrate). On the other hand, the number and size of these pits reduce for the condition where gas decomposes earlier in the tube. To investigate the effect of particles during the growth, various particles with different size, shape and compositions are intentionally placed on the substrate surface before epitaxial films are grown. Samples are mapped and compared at similar locations in the pre-growth, post growth and post-etch (by molten KOH) conditions. It is found that the nature of particle induced defects depends primarily on size and shape of particles.

Study of the Lateral Growth by VLS Mechanism Using Al-Based Melts on Patterned SiС Substrate

In this work we report on SiC epitaxial growth by vapour-liquid-solid (VLS) mechanism on on-axis 4H-SiC(0001) substrates which were previously patterned to form mesa structures. The liquid phase was set to Al70Si30. At 1100°C, it led to very high homoepitaxial lateral growth (140 µm/h) with pronounced spiral growth and in plane anisotropy of growth rate. Upon temperature increase to 1200 °C, this spiral growth was suppressed and the lateral growth was further increased up to 180 µm/h. The in-plane versus out-of-plane anisotropy of growth rate was found to be as high as 60 at this temperature and 46 at 1100°C.

Basal Plane Dislocation Mitigation in SiC Epitaxial Growth by Nondestructive Substrate Treatment

An optimized molten KOH–NaOH–MgO eutectic mixture is used to pretreat the 8° off-axis 4H-SiC substrate prior to chemical vapor deposition epitaxial growth. Superior to the conventional pure KOH etching method, by way of the eutectic method, the conversion of basal plane dislocation (BPD) to threading edge dislocation in the subsequent epitaxial growth is independent of the etch pit size pregenerated on the substrate. Even with a very mild treatment using the eutectic mixture, which does not generate discriminable etch pits on the substrate, an epilayer with low BPD density <22 cm–2 (<0.1% of BPDs on the substrate) is still achieved, and further, there is no degradation of morphology on the entire sample surface. All of the BPD conversions occur at the initial stage of epitaxial growth.

Uniformity Improvement of Planetary Epitaxial Growth Processes through Analysis of Intentionally Stalled SiC Wafers

A method to improve the uniformity of epitaxial wafers grown in planetary rotation reactors through analysis of intentionally stalled wafer measurements is described. A set of basis functions that are completely uniform when rotated in the reactor environment are described and used to construct a nearest uniformity producing profile (NUPP). The methodology for use of stalled wafer profiles and comparison to the NUUP allows easy identification of the changes in process parameters necessary for more uniform epitaxial growth. Although described here as applied to SiC epitaxial growth, this method is applicable to all planetary rotation reactors which are utilized for SiC and III-V semiconductor epitaxial growth.

Growth characteristics of chloride‐based SiC epitaxial growth

AbstractIn this study some aspects of the chloride‐based CVD growth process have been investigated by using both the approach to add HCl to the standard precursors and by using the single molecule precursor methyltrichlorosilane (MTS). The efficiency of the process for different precursors, the growth rate stability and the effect that the C/Si and Cl/Si ratios have on the growth are studied. It is found that MTS is the most efficient precursor and that the growth becomes carbon limited at C/Si &lt; 1. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

SiC Epitaxial Growth on Multiple 100-mm Wafers and its Application to Power-Switching Devices

The development of SiC bulk and epitaxial materials is reviewed with an emphasis on epitaxial growth using high-throughput, multi-wafer, vapor phase epitaxial (VPE) warm-wall planetary reactors. It will be shown how the recent emergence of low-cost high-quality 100-mm diameter epitaxial SiC wafers is enabling the economical production of advanced wide-bandgap Power–Switching devices.

Observation of Crystalline Defects Causing pn Junction Reverse Leakage Current

A major crystalline defect which causes a pn junction reverse leakage current has been identified. A faintish stripe defect (FSD), the main cause of the leakage current, was observed in about 90% of the current leak points of our pn diodes. Double shell pits were observed at the edge of the FSD after molten KOH etching, indicating that the FSD is elongated on a basal plane and crosses the epilayer surface. The FSDs are sorted into several groups in terms of the shapes and arrangements of the etch pits. A cross-sectional TEM image of an FSD shows an eight-hold stacked structure, demonstrating that the defect contains a stacking fault. Etch pit observation after repetitive RIE of an epilayer revealed that FSDs originate both in threading dislocations in SiC substrates and from an SiC epitaxial growth process itself.

Epitaxial Growth of SiC on Silicon on Insulator Substrates with Ultrathin Top Si Layer by Hot-Mesh Chemical Vapor Deposition

The epitaxial growth of SiC on silicon-on-insulator (SOI) substrates with an ultrathin (<10 nm) top Si layer by hot-mesh chemical vapor deposition (CVD) was investigated. This method utilizes heated tungsten wires arranged in a mesh, which promotes the high decomposition efficiency of H2 gas. Using the hot-mesh CVD method, SiC epitaxial films were successfully grown on SOI substrates without voids being formed, which are formed readily in thin (<100 nm) top Si layers at temperatures above 800 °C. Some micropatterns for micro-electro-mechanical systems were fabricated on SiC on insulator (SiCOI) structure substrates by reactive ion etching and wet etching.

A Designed Experiment Approach to Improvement and Understanding of the SiC Epitaxial Growth Process

A series of designed experiments have been conducted over a period of years in a multiwafer, planetary rotation, epitaxial reactor to quantify the effects of various epitaxial growth process parameters on the resulting SiC epitaxial layers. This paper summarizes the results obtained through statistically designed experiments varying process parameters and their resultant effect on the layer thickness, carrier concentration and the variability of these parameters wafer-to-wafer, and within a wafer.

Surface carbonization of Si(1 0 0) by C 2H 2 and its effects on the subsequent SiC(1 0 0) epitaxial film growth

Surface carbonization of Si(1 0 0) using C 2H 2 as the carbon source was performed in a cold-wall-type chemical vapor deposition reactor at a low pressure of 5 Torr. The carbonization process as a function of C 2H 2 partial pressure and treatment time was investigated using X-ray photoemission spectroscopy. It was found that in comparison with a complete transformation to SiC surface on Si(1 1 1) by 8 min treatment of 5×10 −2 Torr C 2H 2 at 1343 K, the carbonization on Si(1 0 0) under the same condition forms excessive carbon, plausibly due to the larger C 2H 2 adsorption heat on Si(1 0 0) surface. Reducing C 2H 2 partial pressure to 1.8×10 −3 Torr and treatment time to 2 min was enough for Si(1 0 0) to form a saturated carbide layer of about 2.0 nm in thickness. Subsequent 3C–SiC(1 0 0) epitaxial film growth was found successful especially on a 10 s carbonization-treated surface that has the least amount of excessive carbon.

SiCOI structure fabricated by catalytic chemical vapor deposition

Epitaxial growth of SiC on SOI substrates using a hot-mesh chemical vapor deposition (CVD) technique was investigated. This technique utilizes a catalytic reaction involving hot tungsten wires arranged in a mesh structure. Using this hot-mesh CVD method, SiC epitaxial growth on SOI substrates with a thin top Si layer was realized without formation of voids, which form readily in the thin Si top layer at temperatures above 800 °C. The SiC film grown on an SOI structure exhibited a large gage factor (GF) of − 27, which is approximately the same as that (GF = − 31.8) of a SiC epitaxial film on Si(100) grown at 1360 °C using atmospheric pressure CVD.

Very high epitaxial growth rate of SiC using MTS as chloride-based precursor

We present results on chloride-based homoepitaxial growth of 4H-SiC in a hot wall CVD reactor. The addition of chlorinated species to the gas mixture prevents silicon nucleation in the gas phase, thus allowing higher input flows of the precursors resulting in much higher growth rate than that of standard SiC epitaxial growth using only silane, SiH 4, and ethylene, C 2H 4, as precursors. We have achieved growth rates higher than 100 μm/h, as compared to 5 μm/h for the standard case. The chlorinated precursor used is methyltrichlorosilane (MTS), CH 3SiCl 3, but since MTS contains both silicon and carbon, with the C/Si ratio 1, we have also added silane or ethylene to optimise the C/Si ratio in order to improve the morphology of the epitaxial layers. We present studies on how the growth rate depends on both the flow of MTS and C/Si ratio. The morphology of the grown epitaxial layer has been investigated using Nomarski microscope and atomic force microscope showing extremely smooth surface and low epi-defect density. The net doping has been determined using capacitance-voltage measurements. Low temperature photoluminescence and high-resolution X-ray diffraction confirm the high quality of the grown epilayers.

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 &lt;1x1014 cm-3 and intentional p- and n-type doping from ~1x1015 cm-3 to &gt;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.

High Purity SiC Epitaxial Growth by Chemical Vapor Deposition Using CH&lt;sub&gt;3&lt;/sub&gt;SiH&lt;sub&gt;3&lt;/sub&gt; and C&lt;sub&gt;3&lt;/sub&gt;H&lt;sub&gt;8&lt;/sub&gt; Sources

The epitaxial growth of SiC by a hot-wall CVD system using monomethylsilane (CH3SiH3) as a precursor is described. In the case of CH3SiH3 source only, an undoped homoepitaxial layer showed an n-type conduction around 1016-1017cm-3 on the Si face. To improve the quality of epilayers, the simultaneous supply of CH3SiH3 and C3H8 was carried out. The pit density of grown layers was reduced from 105 to 103cm-2, and a donor concentration as low as 1.6×1014cm-3 was achieved. An attempt to increase of the growth rate was also investigated.

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 &lt;1 × 1014 cm–3, and intentional p‐ and n‐type doping from ∼1 × 1015 cm–3 to &gt;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.

4H SiC Epitaxial Growth with Chlorine Addition

AbstractThe growth rate of a 4H‐SiC epitaxial layer has been increased by a factor of 19 (up to 112 μm h–1) with respect to the standard process, with the introduction of HCl in the deposition chamber. The epitaxial layers grown with the addition of HCl has been characterized by electrical, optical, and structural characterization methods. The effects of various deposition parameters on the epitaxial growth process have been described, and an explanation of this behavior in terms of the diffusion coefficient on the surface, Ds, and the ratio between the characteristic times, τD:τG, has been provided. The diodes, manufactured on the epitaxial layer grown with the addition of HCl at 1600 °C, have electrical characteristics comparable with the standard epitaxial process. This process is very promising for high‐power devices with a breakdown voltage of 10 kV.

Growth and Doping Modeling of SiC‐CVD in a Horizontal Hot‐Wall Reactor

AbstractModeling and simulation of the SiC epitaxial growth, and doping in a horizontal hot‐wall reactor from common precursors (SiH4; C3H8 diluted in H2 for growth; N2 and Al(CH3)3 for n‐type and p‐type doping) are presented. The growth and doping features of SiC thin layers on both Si‐terminated and C‐terminated surfaces are analyzed as a function of various inlet source gas conditions, i.e., various C/Si ratios. The role of the actual surface mass fluxes of both Si‐containing and C‐containing species and their ratio is analyzed and compared to the inlet experimental parameters. It is demonstrated that the doping level resulting from lattice site competition effects can be quantified by the actual C/Si ratio calculated above the growing surface. Moreover, the surface morphology of the epitaxial layer is explained on the basis of the mass fluxes at the growing surface.

Epitaxial growth of 4H–SiC at low temperatures using CH 3Cl carbon gas precursor: Growth rate, surface morphology, and influence of gas phase nucleation

This paper explores homoepitaxial growth of 4H–SiC on 8° and 2° off-axis 4H–SiC(0 0 0 1) substrates at temperatures below 1300 °C, which is more than 200 °C lower than in conventional state-of-the-art SiC epitaxial growth. In this work, the growth at reduced temperatures is enabled by using halo-carbon growth precursor chloromethane. The growth rate is strongly influenced by Si cluster nucleation in the gas phase. In addition, the condensation of silicon vapor results in decrease of the silicon-to-carbon (Si/C) ratio above the growth surface. The epilayer morphology becomes strongly dependent on the Si/C ratio when the growth temperature ( T g) is reduced. For growth on low-angle (2°) vicinal substrates, topographic defect generation is increasingly difficult to control at lower T g values. However, low to moderate values of T g in combination with a beneficial influence of chlorine-containing products of halo-carbon decomposition largely overcome the step-bunching problem of epitaxial growth on low-angle vicinal substrates.