SiC Homoepitaxial Growth Research Articles

Reduction of epitaxial defects on 4°-off 4H[sbnd]SiC homo-epitaxial growth by optimizing in-situ etching process

The investigations of in-situ etching of 4HSiC epi-growth on 4° off-axis 100 mm diameter substrates under different conditions have been carried out in a commercial warm-wall multi-wafer planetary reactor. The surface morphologies of the as-etched substrates have been characterized by atomic force microscopy on 20 × 20 μm2. Based on the step height and roughness mean square, the best etching condition for 4HSiC 4° off-axis substrates was determined to be H2 + HCl at 1500 °C for 10 min. With the optimized in-situ etching process, high quality 4HSiC epitaxial layers with excellent surface morphology have been obtained, and the defect density is lowered to 0.45 cm−2 resulting in a projected 2 × 2 mm die yield of ∼98%.

Trade-Off between Parasitic Deposition and SiC Homoepitaxial Growth Rate Using Halogenated Si-Precursors

We discuss the use of halogenated Si-X precursors, compared to the traditional silane precursor, to increase the growth rate of thick, high quality SiC homoepitaxial layers by chemical vapor deposition for power electronics applications. These precursors reduce gas phase nucleation and parasitic deposition to increase the availability of reactive Si-species at the SiC growth front due to their less reactive nature compared to silane. While less reactive Si-X species are expected to provide lower activity of Si-species at the growth front, the reduced parasitic deposition and precursor depletion from the gas delivery system leads to an effective increase in overall growth rate. This trade-off is explored in the context of parasitic deposition-induced particulate formation that degrades SiC epilayer morphology, while introducing structural defects. It is difficult to effectively compare different precursors used by various researchers, as there is no standard set of reported epilayer crystal quality parameters that takes into account various precursor/epilayer related benefits/tradeoffs. We propose a set of reactor-independent metrics that may enable realistic comparison across the various Si-X precursor chemistries. Results at the authors’ laboratory indicate that tetrafluorosilane precursor shows great promise in breaking the growth-rate/parasitic deposition trade-offs inherent in SiC growth, critical for widespread commercial adoption of SiC technology.

Extended study of the step-bunching mechanism during the homoepitaxial growth of SiC

We discuss the possible source of surface instabilities (with specific reference to the step bunching phenomena) during the growth of cubic and hexagonal Silicon Carbide polytypes. For this analysis we use: results from super-lattice Kinetic Monte Carlo simulations, atomic force microscope surface analysis and literature data. We show that only hexagonal polytypes with misorientation cut toward the <11–20> direction suffer “intrinsically” the step bunching phenomena (i.e. it is present, independently on the growth conditions) whereas cubic polytypes and hexagonal ones with misorientation cut toward the <10–10> direction do not.

Extended Study of the Step-Bunching Mechanism during the Homoepitaxial Growth of SiC

We discuss the possible source of surface instabilities (with specific reference to the step bunching phenomena) during the growth of cubic and hexagonal Silicon Carbide polytypes. For this analysis we use: results from super-lattice Kinetic Monte Carlo simulations, atomic force microscope surface analysis and literature data. We show that only hexagonal polytypes with misorientation cut toward the &lt;11-20&gt; direction suffer “intrinsically” the step bunching phenomena (i.e. it are present, independently on the growth conditions) whereas cubic polytypes and hexagonal ones with misorientation cut toward the &lt;10-10&gt; direction do not.

Atomistic and Continuum Simulations of the Homo-Epitaxial Growth of SiC

Using joined super-lattice Kinetic Monte Carlo simulations, continuous modelling and recent experimental data on the homoepitaxial growth of 4H Silicon Carbide we study the transition between monocrystalline and polycrystalline growth in terms of misorientation cut, growth rate and temperature. We compare these optimally calibrated results both with previous continuous models and literature data. We demonstrate that this study was, indeed, necessary to correctly reformulate the phase diagram of the transition.

Silicon carbide nanowires grown on 4H-SiC substrates by chemical vapor deposition

AbstractIn this work, SiC nanowires (NWs) were grown by chemical vapor deposition (CVD) on commercial 4H-SiC substrates. The growth was conducted in an inductively heated hot wall CVD reactor traditionally used for homoepitaxy of 4H-SiC, operating at 150 Torr with H2 as the carrier gas. The growth experiments utilized the precursor chemistry that previously enabled the so-called low-temperature homoepitaxial growth of SiC – SiCl4 as the silicon precursor and CH3Cl as the carbon precursor. Vapor-liquid-solid (VLS) growth mode was employed. Two metal catalysts Au and Ni were used for NW growth in a wide range of growth temperatures from below 10500C to above 13000C. It was established that high precursor flow rates favor the regular epitaxial growth (though disturbed by the presence of the islands of the metal catalyst) at temperatures above 12000C. Reduction of the precursor flow rates and the growth temperature caused formation of micro-needles and eventually NWs. NW diameters in the range from below 10 to 100 nm were observed using scanning electron microscopy. Only SiC phase with no presence of Si, even for the growth temperatures down to 10500C, was confirmed by X-ray diffraction.

Theoretical Monte Carlo Study of the Formation and Evolution of Defects in the Homoepitaxial Growth of SiC

A novel Monte Carlo kinetic model has been developed and implemented to predict growth rate regimes and defect formation for the homo-epitaxial growth of various SiC polytypes on different substrates. Using this model we have studied the generation of both point like and extended defects in terms of the growth rate and off-cut angle, finding qualitative agreement with both electrical and optical characterization and analytical results.

Advances in Multi- and Single-Wafer SiC Epitaxy for the Production and Development of Power Diodes

In this paper, we present results of epitaxial layer deposition for production needs using our hot-wall CVD multi-wafer system VP2000HW from Epigress with a capability of processing 7×3” or 6×100mm wafers per run in a new 100mm setup. Intra-wafer and wafer-to-wafer homogeneities of doping and thickness for full-loaded 6×100mm and 7×3” runs will be shown. Results on Schottky Barrier Diodes (SBD) processed in the multi-wafer system will be given. Furthermore, we show results for n- and p-type SiC homoepitaxial growth on 3”, 4° off-oriented substrates using a single-wafer hot-wall reactor VP508GFR from Epigress for the development of PiN-diodes with blocking voltages above 6.5 kV. Characteristics of n- and p-type epilayers and doping memory effects are discussed. 6.5 kV PiN-diodes were fabricated and electrically characterized. Results on reverse blocking behaviour, forward characteristics and drift stability will be presented.

Effect of HCl addition on gas-phase and surface reactions during homoepitaxial growth of SiC at low temperatures

A complex influence of HCl addition on gas-phase and surface reactions during the low-temperature halo-carbon homoepitaxial growth of 4H-SiC was investigated. The addition of HCl was employed to reduce the undesirable effects of homogeneous gas-phase nucleation leading to formation of silicon clusters in the gas phase. It was established that dissociation of silicon clusters by HCl is efficient even at untraditionally low homoepitaxial growth temperature below 1300 °C. The information about the spatial distribution of this dissociation process along the gas flow direction was obtained. It was established that the influence of HCl is more complicated than the simple model suggesting that the enhanced dissociation of silicon clusters in the gas phase leads to an additional supply of silicon species for the epitaxial growth. While the growth rate does significantly increase at least for some HCl flow rates, complex changes in the effective silicon-to-carbon ratio in the growth zone of the reactor indicate that the supply of carbon species may also be enhanced at least at low HCl flow rates. This fact supports the hypothesis that the gas-phase clusters may contain a significant amount of carbon in addition to silicon. Also, the magnitude of the growth rate enhancement was found to be less significant than what was expected from the apparent degree of the cluster dissociation. Evidence of a new mechanism for precursors’ depletion are provided. Pronounced changes in the pattern of the polycrystalline deposits at the upstream portion of the hot zone of the reactor were caused by the HCl addition. Premature dissociation of the gas-phase clusters and release of silicon may cause depletion of silicon by vigorous polycrystalline deposition. Depending on the kinetics of the process, the carbon species may also get depleted by the polycrystalline deposition mechanism. This mechanism partially reduces the benefits of the HCl addition unless its influence is minimized.

Suitability of 4H-SiC Homoepitaxy for the Production and Development of Power Devices

ABSTRACTIn this paper, we present results of epitaxial layer deposition for production needs using our hot-wall CVD multi-wafer system VP2000HW from Epigress with a capability of processing 6×100mm wafers per run. Intra-wafer and wafer-to-wafer homogeneities of doping and thickness for full-loaded 6×100mm runs will be shown and compared to results of the former 7×3″ setup. The characteristic of the run-to-run reproducibility for the 6×100mm setup will be discussed. To demonstrate the suitability of the reactor for device production results on Schottky Barrier Diodes (SBD) processed in the multi-wafer system will be given. Furthermore, we show results for n- and p-type SiC homoepitaxial growth on 3″, 4° off-oriented substrates using a single-wafer hot-wall reactor VP508GFR from Epigress for the development of PiN-diodes with blocking voltages above 6.5 kV. Characteristics of n- and p-type epilayers and doping memory effects are discussed. 6.5 kV PiN-diodes were fabricated and electrically characterized. Results on reverse blocking behaviour, forward characteristics and drift stability will be presented.

Challenges in Large-Area Multi-Wafer SiC Epitaxy for Production Needs

The rapid market development for SiC-devices during the last years can be attributed particularly to the success in supplying high-quality SiC wafers and corresponding epitaxial layers. The device quality could be enhanced and the costs were reduced by enlarging the wafer size as well as by a significant progress in epitaxial growth of active layers by using multi-wafer CVD systems. In this paper we want to give an overview of CVD multi-wafer systems used for SiC growth in the past and today. We present recent results of SiC homoepitaxial growth using our multi-wafer hot-wall CVD system. This equipment exhibits a capacity of 5×3” wafers per run and can be upgraded to a 7×3” or 5×4” setup. By optimizing the process conditions epitaxial layers with excellent crystal quality, purity and homogeneity of doping and thickness have been grown. Issues like reproducibility, drift of parameters and system stability over several runs will be discussed.

Advances in 4H-SiC Homoepitaxy for Production and Development of Power Devices

AbstractIn this paper we present results of epitaxial layer deposition for production needs using our hot-wall CVD multi-wafer system. This equipment exhibits a capacity of 7x3” wafers per run and can be upgraded to a 6x4” setup. Characteristics of epilayers and reproducibility of the proc-esses are reported. Furthermore, we show recent results of p-type SiC homoepitaxial growth on 3” 4° off-oriented substrates using a single-wafer hot-wall CVD. The dependence of layer prop-erties on growth parameters, doping and thickness uniformity as well as doping memory effects are discussed. For the characterization of epitaxially grown pn-junctions first research grade pin-diodes were fabricated. The p-type emitters were either deposited in the same growth run to-gether with the n-type buffer and drift layers (continuous growth) or the n- and p-layers were grown in two different growth runs (separate growth).

Pressure Dependence of Aluminum Doping in SiC Vapor Phase Epitaxy

AbstractThe dependence of the aluminum incorporation on the total pressure in a hot wall vapor phase reactor for SiC homoepitaxial growth has been investigated. It was found that in the doping concentration range from 1·1017 cm−3 to 1·1019 cm−3 the incorporated aluminum concentration varies by the factor 3 to 4, when the reactor pressure is changed from 150 mbar to 250 mbar. Lower reactor pressure gives lower aluminum concentration. Periodically changing reactor pressure results in aluminum concentration periodically changing with depth in the epilayer. All results were measured electrically by capacitance-voltage measurements on nickel Schottky contacts. Additional experiments have been performed for n-type nitrogen doped SiC epilayers for comparison. The nitrogen doping concentration was found to be independent of the reactor pressure within the accuracy of the applied C-V measurements and the doping profile analysis method.

Ab initio simulations of homoepitaxial SiC growth.

We present first-principle calculations on the initial stages of SiC homoepitaxial growth on the beta-SiC(111)-(sqrt[3]xsqrt[3]) surface. We show that the nonstoichiometric reconstruction plays a relevant role in favoring the attainment of high-quality films. The motivation is twofold: On one hand, we find that the reconstruction controls the kinetics of adatom incorporation; on the other hand, we observe that the energy gain upon surface stability can induce the reorganization of the deposited material into a crystalline structure, thus revealing that a surface-driven mechanism is able to stabilize defect-free layer deposition on Si-rich surfaces.

SiC Homoepitaxial Growth at Low Temperature by Vapor−Liquid−Solid Mechanism in Al−Si Melt

Homoepitaxial growth of SiC was successfully performed at a temperature as low as 1100 °C via a vapor−liquid−solid (VLS) mechanism where propane feeds an Al−Si droplet. This approach has several advantages compared to the conventional liquid-phase epitaxy (LPE) such as an easier mastering of the growth as no thermal gradient (vertical or radial) needs to be controlled. We observed however the formation at the surface of small crystals during the cooling. Some small nonwetted zones are also seen, but they occupy less than 1% of the sample area. Both defects were also present in LPE configuration.

Surface-induced stacking transition at SiC(0001)

We present the ab initio results for the energetics of several SiC surfaces having different underlying bulk polytypes, to investigate the role of surface effects in the mechanisms of stacking inversion in SiC. We considered the Si adatom $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ reconstruction for the cubic SiC(111) and the hexagonal SiC(0001) surfaces, taking into account the different subsurface bulk terminations compatible with the $4H$ and $6H$ polytypes, and allowing for two opposite stacking orientations of the topmost surface layer. Our investigation reveals that the energy differences among SiC polytypes are enhanced at the surface with respect to the bulk, and two-dimensional effects favor the formation of cubic SiC. We discuss the relevant role played by the surface energetics in the homoepitaxial growth of SiC.

Recent Achievements and Future Challenges in SiC Homoepitaxial Growth

Recent Achievements and Future Challenges in SiC Homoepitaxial Growth

Vapour–liquid–solid mechanism for the growth of SiC homoepitaxial layers by VPE

In order to reach fast growth regime, we have investigated the SiC homoepitaxial growth on off-axis 4H-SiC substrates from a vapour–liquid–solid (VLS) mechanism in a vertical cold wall CVD reactor. The experiments involved silane and propane diluted in hydrogen as feeding vapour phase and melted silicon as “liquid catalyst”. Growth rates up to 25 μm/h at 1500°C and 35 μm/h at 1600°C with a bunched step-terrace structure are demonstrated in such a system. The formation and stability of the VLS equilibrium is discussed with respect to the experimental parameters and a first approach of the mechanism is proposed.

Homoepitaxial growth and device characteristics of SiC on Si-face (0 0 0 1) 6H–SiC

Homoepitaxial growth of SiC on a Si-face (0 0 0 1) 6H-SiC substrate has been performed in a modified gas-source molecular beam epitaxy system with Si 2H 6 and C 2H 4 at temperatures ranging 1000–1450°C while keeping a constant Si/C ratio (0.7) in the gas phase. X-ray diffraction patterns, Raman scattering measurements, and low-temperature photoluminescence spectra showed single-crystalline SiC. Mesa-type SiC p–n junctions were obtained on these epitaxial layers, and their I– V characteristics are presented.

Gaseous Etching Effects on Homoepitaxial Growth of SiC on Hemispherical Substrates Using CVD

Gaseous Etching Effects on Homoepitaxial Growth of SiC on Hemispherical Substrates Using CVD