Homoepitaxial Growth Of 4H-SiC Research Articles

Study and reduction of the surface pits in 4H-SiC epitaxial wafer

Pit defects in SiC epitaxial materials is a new issue which shows an influence on different type of SiC devices such as SBD and MOS. The surface pits generated a leakage current and caused the occurrence of a local electric field crowding in the SBD. While the original and mechanism of the surface pits is still not clear. In the paper, the original and reduction of surface pits during 4H-SiC homoepitaxial growth by a warm wall planetary reactor have been investigated. The C/Si ratio and Cl/Si ratio have great effects on the surface pits. Lower C/Si ratio and higher Cl/Si ratio will form a Si-rich environment on the wafer surface during growth, which is crucial for reduction of the surface pits in 4H-SiC epitaxial wafer. With the optimized parameters, high quality epi-wafer with lower pit defects density has been obtained.

Analysis of relaxation time for nitrogen-containing species to enter steps on misoriented (0001) surfaces during homoepitaxial growth of 4H-SiC

Reported experimental results on homoepitaxially grown nitrogen-doped 4H-SiC on (038) and misoriented (0001) substrates under carbon-rich conditions in a SiH4–C3H8–N2–H2 system were analyzed according to surface diffusion theory dealing with step kinetics. On misoriented (0001) surfaces at 1723–1873 K, the relaxation time for a silicon adatom to enter a step was negligibly small. This finding, however, was not the case with the relaxation time for nitrogen-containing species (τ k N). The ratio of τ k N to the residence time of the nitrogen-containing species on the surfaces was estimated to be 0.1–0.2 at 1723–1823 K and 0.04 at 1873 K.

Influence of the facet trace region in 4H-SiC substrate on the glide and propagation behaviors of basal plane dislocations in 4H-SiC homoepitaxial layers

The influence of the facet trace region in the 4H-SiC substrate on the glide and propagation behaviors of basal plane dislocations (BPDs) in a 4H-SiC homoepitaxial layer was investigated using x-ray topography, high-resolution x-ray diffraction, and micro-Raman scattering spectroscopy. The facet trace region in the substrate, which has a higher nitrogen doping concentration than the other regions in the substrate, is of great interest since it could influence the glide and propagation behaviors of BPDs during 4H-SiC homoepitaxial growth through enhanced nitrogen doping concentration in the region. It was found that the epitaxial layer grown on the facet trace region in the substrate significantly suppressed glide motion of BPDs and exhibited a reduced conversion probability of BPDs to threading edge dislocations during the homoepitaxial growth process. Based on these results, the mechanisms that the epilayer grown on a substrate region with a slightly higher nitrogen concentration showed significantly different glide and propagation behaviors of BPDs are discussed.

Analysis of surface diffusion of carbon- and nitrogen-containing molecules during homoepitaxial growth of 4H-SiC (0001) under silicon-rich conditions

Reported experimental results on homoepitaxial 4H-SiC grown by chemical vapor deposition on 1°- and 4°-off (0001) surfaces under silicon-rich conditions in a SiH4−C3H8−N2−H2 system are quantitatively analyzed according to surface diffusion theory dealing with step dynamics. The surface-diffusion lengths of carbon- and nitrogen-containing molecules are, respectively, estimated to be λ C = 25 nm and λ N ≥ λ C at 1773 K. This magnitude relationship agrees with the reported assumption made for the variation in nitrogen concentration on (000) facets of 4H-SiC grown by physical vapor transport.

Wafer Scale On-Axis Homoepitaxial Growth of 4H-SiC(0001) for High-Power Devices: Influence of Different Gas Phase Chemistries and Growth Rate Limitations

On-axis homoepitaxy of 4H-SiC has the advantage of producing epilayers that are free of basal plane dislocations. Such layers can be highly beneficial for SiC-based high-power bipolar electronic de...

On-axis Si-face 4H-SiC epitaxial growth with enhanced polytype stability by controlling micro-steps during the H2 etching process

In situ H2 etching and homoepitaxial growth of 4H-SiC were performed on on-axis Si-face substrates using low-pressure chemical vapor deposition. We investigated the effect of various etching temperatures and durations on the surface of the on-axis substrates and used optimized etching characteristics to enhance the polytype stability of the epitaxial layer. It was found that the micro-steps at the etched surface of the on-axis substrates play a vital role in enhancing the stability of the 4H-SiC polytype. Homoepitaxial 4H-SiC with up to 99% stability was successfully grown with spread-out micro-steps without step-bunching during the etching process.

150 mm 4H-SiC Epitaxial Layer Growth in a Warm-Wall Planetary Reactor

Homo-epitaxial growth of 4H-SiC on 4o off-axis 150 mm diameter substrates has been performed in a commercial warm-wall multi-wafer planetary reactor. Based on our well developed 100 mm 4H-SiC epitaxial growth process, which can achieve excellent thickness and doping uniformities (δ/mean) of <1% and <5%, respectively, the growth process and hardware were further fine-tuned and improved for 150 mm 4H-SiC homoepitaxy. After the improvement, the 6 to7 μm thick epilayer uniformity has reached 1.1% with a 5mm edge exclusion while the doping uniformity has improved to 16.5% (<10%) with an edge exclusion of 5 mm (10mm), respectively. Surface roughness of the as-grown 150 mm 4H-SiC epitaxial layer has an RMS value of 0.12 nm scanned by AFM on 20×20 μm2 areas. Homo-epitaxial growth on C-face 150 mm 4H-SiC substrates has also been carried out. Other than the doping concentration and uniformity, the other results are very close to the epi-growth on Si-face.

Investigation of giant step bunching in 4H-SiC homoepitaxial growth: Proposal of cluster effect model

We have investigated the H2 etching and growth conditions causing giant step bunching (GSB) in 4H-SiC homoepitaxial growth on 8° off-axis substrates by a chemical vapor deposition method and found that GSB does not occur during H2 etching under a wide range of experimental conditions, whereas GSB occurs during epitaxial growth at extremely low or high C/Si ratios, i.e., an excessive supply of SiH4 or C3H8. To explain these results, we have proposed a model taking into account the effect of Si or C cluster formation called “the cluster effect” model. We have shown that the cluster effect model can explain well our experimental result of GSB occurrence or nonoccurrence during etching and homoepitaxial growth of 4H-SiC.

Comparative Study of 4H-SiC Epitaxial Layers Grown on 4° Off-Axis Si- and C-Face Substrates Using Bistrimethylsilylmethane Precursor

In situ H2 etching and homoepitaxial growth of 4H-SiC have been carried out on 4° off-axis Si-face and C-face substrates by low-pressure chemical vapor deposition. We systematically analyzed H2 etching characteristics and epitaxial growth of 4H-SiC substrates on two different polarities using an organosilicon source material, bistrimethylsilylmethane (C7H20Si2). The effects of the growth conditions, such as growth temperature and source flow rate on the surface morphology, crystallinity, polytype conversion, defect generation, and structural imperfection of the epilayers on different polar surfaces, were investigated. High-quality epitaxial layers were successfully grown at low temperature range of 1320–1440°C on the Si-face and 1500°C on the C-face. A low source flow rate of 5–10 sccm was also preferred to grow defect-free epilayers.

Study of Surface Morphology, Impurity Incorporation and Defect Generation during Homoepitaxial Growth of 4H-SiC Using Dichlorosilane

The growth of 4° off-axis 4H-SiC epilayers by chemical vapor deposition is studied using dichlorosilane as the Si precursor in a chimney reactor. The unintentional and intentional nitrogen doping at various C/Si ratios and N2 flow rates are investigated. The C/Si ratio has a significant influence on the growth rate, surface morphology, conversion of basal plane dislocations (BPDs), and generation of other defects (e.g., in-growth stacking faults and morphological defects). Addition of N2 has no obvious influence on growth rate and BPD conversion. It is preferable to grow high quality n+ epilayers at a C/Si ratio in the range of 1.3–1.8 along with the addition of a suitable amount of N2 in consideration of high growth rate, good surface morphology, and low defect density. In this case, the conversion ratio of BPDs to threading edge dislocations is greater than 99.8% regardless of N2 addition. Therefore >99.8% substrate BPDs can be buried in an n+ buffer layer, which is beneficial to SiC bipolar power devices. No special treatment prior to, during or after the epigrowth is necessary. The epilayers with doping concentration all the way from p− (∼1e15 cm−3) to semi-insulating, then to n+ (∼1e18 cm−3), can be achieved, giving a great range of flexibility in growth using dichlorosilane precursor. Further optimization of in-situ etching and growth conditions to eliminate step bunching has also been suggested.

Ge incorporation inside 4H-SiC during homoepitaxial growth by chemical vapor deposition

In this work, we report on the addition of GeH4 gas during homoepitaxial growth of 4H-SiC by chemical vapor deposition. Ge introduction does not affect dramatically the surface morphology and defect density though it is accompanied by Ge droplet accumulation at the surface. The Ge incorporation level inside the 4H-SiC matrix, ranging from a few 1017 to a few 1018at.cm−3, was found to be mainly affected by the growth temperature and GeH4 flux. Other growth parameters, such as C/Si ratio, polarity or off-orientation, did not show any significant influence. The Ge incorporation inside SiC was determined to occur at Si sites. On the other hand, adding GeH4 led to an increase in the intentional n-type doping level by a factor of 2–5 depending on the C/Si ratio in the gas phase.

50 μm-Thick 100 mm 4H-SiC Epitaxial Layer Growth by Warm-Wall Planetary Reactor

Homo-epitaxial growth of 50 μm-thick 4H-SiC on 4° off-axis 100 mm substrates have been demostrated by using a commercial warm-wall multi-wafer planetary reactor (Aixtron 2800 G4). With optimized process, epitaxial layer with an average thickness of 48.146 μm and doping level of 8.39×1014/cm3are obtained. The thickness uniformity with an edge exclusion of 5 mm are 1.30% (σ/mean) and 2.17% (max-min/max+min), and the doping level uniformity are 4.66% (σ/mean) and 6.95% (max-min/max+min), respectively. Surface roughness of the as-grown 50 μm-thick epitaxial layer has an RMS value of 0.606 nm with one step bunching on the 20×20 μm2areas. This initial effort on thick 4H-SiC homoepitaxial growth indicates that this comercial multi-wafer planetary reactor has the potential for mass production of SiC epiwafers for 5000 V and above power devices.

Development of Homoepitaxial Growth Technique on 4H-SiC Vicinal Off Angled Substrate

We have investigated key factors for controlling the polytype and surface morphology of 4H-SiC homoepitaxial growth on less than 4ooff-axis substrates. In addition, we characterized the crystal quality and surface quality of the epitaxial layer of an entire 3-inch vicinal off angled substrate. The results suggested that the control of surface free energy, control of the vicinal off angle itself, and high temperature growth, is highly important in controlling the surface morphology and polytype stability of the epitaxial layer grown on a vicinal off angled substrate. We also obtained a high-quality epitaxial layer grown on a 3-inch vicinal off angle substrate, which was comparable to those on 4ooff-axis substrates.

Study on Grove model of the 4H-SiC homoepitaxial growth

In this paper, A Grove model on the homoepitaxial growth of 4H-SiC is presented, based on the structure and growth conditions of CVD system. According to the model analysis, the growth rate of 4H-SiC is quiet influenced by carrier gas flow rate and temperature, which is verified by experiments. Growth rate along the substrate has a bowl-shaped distribution, and the growth rate on the center is slightly lower than on the edge. As the carrier gas flow rate increases, the growth rate controlled by the transport changes into the reaction rate control, the growth rate first increases and then decreases. The position of highest temperature in the actor will be drifted with the carrier gas flow increasing. The reaction rate and the mass transport coefficient increase with the rise of growth temperature, which can cause the increase of growth rate. But the effect of temperature on reaction rate is much greater than on the mass transport. When the temperature rises excessively, the epitaxial growth will be determined by the mass transport. But the high reaction temperature results in forming some particles at the edge of reactor, which can reduce the growth rate, and the particles will have a chance to fall on the epitaxial layer, thus seriously affecting the quality of the epitaxial layer. All the above shows that the growth rate and thickness uniformity can effectively controlled by adjusting the flow rate of hydrogen, the rotational speed of the substrate and the growth temperature.

Experimental verification of the model by Klapper for 4H-SiC homoepitaxy on vicinal substrates

4H-SiC homoepitaxial layers free of basal plane dislocations (BPDs) are urgently needed to overcome the so-called bipolar degradation of high-voltage devices. BPDs being present in substrates are able to either propagate to the epilayer or convert to harmless threading edge dislocations (TEDs) in the epilayer. The model by Klapper predicts the conversion of BPDs to TEDs to be more efficient for growth on vicinal substrates with low off-cut angle. This paper aims to verify the model by Klapper by an extensive variation of epitaxial growth parameters and the substrates' off-cut. It is shown that the off-cut angle is the key parameter for growth of BPD-free epilayers. Furthermore, it is shown that the model also describes adequately the behavior of different types of TEDs, i.e., TED II and TED III dislocations, during epitaxial growth. Therefore, the model by Klapper is verified successfully for 4H-SiC homoepitaxial growth on vicinal substrates.

Reducing the Wafer Off Angle for 4H-SiC Homoepitaxy

We have investigated key factors for controlling the polytype and surface morphology of 4H-SiC homoepitaxial growth on less than 4o off-axis substrates. In addition, we characterized the crystal quality and surface quality of the epitaxial layer in whole 3-inch vicinal off angled substrate. The results suggested that the control of surface energy, control of the vicinal off angle itself, and high temperature growth, is highly important in controlling the surface morphology and polytype stability of the epitaxial layer grown on a vicinal off angled substrate. We also obtained a high-quality epitaxial layer grown on a 3-inch vicinal off angle substrate, which was comparable to those on 4o off-axis substrates. These results suggest that the wafer off angle for epitaxial growth can be reduced to less than 4 degrees.

4H-SiC Homoepitaxial Growth on Substrate with Vicinal Off-Angle Lower than 1°

We investigated homoepitaxial growth on 4H-SiC Si-face substrate with a vicinal off-angle lower than 1°. The control of the wafer off-angle to a precision of 0.1° is important to controlling the surface morphology of homoepitaxial growth on this substrate. Keeping the C/Si ratio low by controlling the SiH4 flow rate was effective in striking balance between surface morphology and polytype homogeneity. Homoepitaxial layers were successfully grown on whole, 2-inch Si-face vicinal off-angled substrate without large step bunching or polytype inclusions. The quality of the epitaxial layer was confirmed by I-V characteristics of Schottky barrier diodes fabricated on the epitaxial wafer.

On-Axis Homoepitaxial Growth of 4H-SiC PiN Structure for High Power Applications

We demonstrate on-axis homoepitaxial growth of 4H-SiC(0001) PiN structure on 3-inch wafers with 100% 4H polytype in the epilayer excluding the edges. The layers were grown with a thickness of 105 µm and controlled n-type doping of 4 x 1014 cm-3.The epilayers were completely free of basal plane dislocations, in-grown stacking faults and other epitaxial defects, as required for 10 kV high power bipolar devices. Some part of the wafer had a lifetime enhancement procedure to increase lifetime to above 2 s using carbon implantation. An additional step of epilayer polishing was adapted to reduce surface roughness and implantation damage.

In-Grown Stacking Faults in SiC-CVD Using Dichlorosilane and Propane as Precursors

In-grown stacking faults (IGSFs) were studied in 4H-SiC homoepitaxial growth from a SiH2Cl2-C3H8-H2 system. Most of the IGSFs, start from the epilayer/substrate interface, and exhibit photoluminescence emission peak at 2.58 eV (480 nm) indicating of 8H polytype. The growth parameters, including growth temperature, growth pressure, growth rate, hydrogen etching, et al., varied around the regular growth condition do not show a significant effect on the IGSF generation. Reactor furniture is identified to be a major reason of IGSF formation, especially when the insulation part of the furnace is not completely isolated from the growth zone. Dusting of insulation material is crucial in the formation of IGSFs. When using graphite felt as the insulation material, the IGSF density in the epilayer can be as high at ~104 cm-2. Improvement of the insulation material by using graphite foil reduces the density to 30-100 cm-2. Further reduction of IGSF density to less than 10 cm-2 is achieved by mild pretreatment of the substrate in molten KOH-NaOH eutectic.

Radial Variation of Measured Carrier Lifetimes in Epitaxial Layers Grown with Wafer Rotation

In this report we present homoepitaxial growth of 4H-SiC on the Si-face of nominally on-axis substrates with diameter up to 100 mm in a hot-wall chemical vapor deposition reactor. A comparatively low carrier lifetime has been observed in these layers. Also, local variations in carrier lifetime are different from standard off-cut epilayers. The properties of layers were studied with more focus on charge carrier lifetime and its correlation with starting growth conditions, in-homogeneous surface morphology and different growth mechanisms.