4H-SiC Homoepitaxial Films Research Articles

Multiple-Layer Triangular Defects in 4H-SiC Homoepitaxial Films Grown by Chemical Vapor Deposition

In this study, a special triangular defect (TD) was identified on 4H-SiC epitaxial wafers. The morphology and composition characteristics of these special TDs were revealed by Raman, atomic force microscope (AFM), and scanning electron microscope (SEM). Compared to ordinary triangular defects, this defect protruded from the epitaxial layer and exhibited a laminated shape. The study also discussed the effects of several factors, such as C/Si ratio and growth time, on the triangular defects. Through analysis of these results, we developed methods to suppress the triangular defects. This research provides new insights into the morphology, structure, and composition of this serious destructive defect and is helpful for improving the performance of SiC epitaxial wafers.

Achievement of Low Carrier Concentration of High-Uniformity SiC Films Grown by High Speed Wafer Rotation Vertical CVD Tool

N-type 4H-SiC homo-epitaxial films were grown by high speed wafer rotation vertical CVD tool, and effect of surface C/Si ratios on in-wafer uniformity and lower limit of carrier concentration of the SiC films on 150 mm diameter wafers was investigated. From analysis of in-wafer distribution by mapping of whole wafers, it was found that high in-wafer thickness uniformity was obtained for the films grown both at lower introduced C/Si ratio of about 1.35, which corresponds to surface C/Si ratio is lower than 1.0, and at higher introduced C/Si ratio of about 1.80, which corresponds to surface C/Si ratio is higher than 1.0. However, larger fluctuation of the carrier concentration at wafer edge was observed for the film grown at lower introduced C/Si ratio, compared with the film grown at higher introduced C/Si ratio. Lower fluctuation of the carrier concentration for the film grown at higher introduced C/Si ratio is thought to be due to lower sensitivity of carrier concentration on growth temperature, which is observed for the film grown at surface C/Si ratio higher than 1.0. Also, the film grown at higher introduced C/Si ratio showed longer carrier lifetime with higher uniformity, although the film grown at lower introduced C/Si ratio indicated shorter carrier lifetime with lower uniformity. The mean carrier concentration of the films grown at higher introduced C/Si ratio was reduced by two digits compared with those grown at lower introduced C/Si ratio, and low carrier concentration of 1.7 x 1014 cm-3 with high in-wafer uniformity for intentionally doped SiC film grown at higher introduced C/Si ratio was achieved. Based on the results mentioned above, fabrication of thick and low-doped epi layer on 150 mm diameter wafer with high in-wafer uniformity was demonstrated.

Improvement of Repeatability on N-Type 4H-SiC Epitaxial Growth by High Speed Wafer Rotation Vertical CVD Tool

N-type 4H-SiC homo-epitaxial films were grown on 150 mm diameter wafers by high speed wafer rotation vertical CVD tool, and effect of surface C/Si ratio on short-term and long-term repeatability of the SiC films was investigated. By tuning of growth condition, high uniform SiC film with in-wafer thickness uniformity of ±2.8 % (1.6 % σ/mean) and carrier concentration uniformity of ±3.1 % (1.9 % σ/mean) was successfully grown at higher introduced C/Si ratio of about 1.80, which corresponds to surface C/Si ratio higher than 1.0 on the whole wafer. This result was comparable to the film grown at lower introduced C/Si ratio of about 1.35, which corresponds to surface C/Si ratio lower than 1.0 on the whole wafer. On the other hand, the films on 13 wafers successively grown at higher introduced C/Si ratio indicated low fluctuation from 1.85 to 3.09 % (σ/mean), and the short-term repeatability of the in-wafer carrier concentration uniformity of the films grown at higher introduced C/Si ratio was improved compared with the films grown at lower introduced C/Si ratio. Additionally, in-wafer carrier concentration uniformity of the films on 171 wafers grown at higher introduced C/Si ratio showed 75 % quartile of 4.26 % (σ/mean), and this result was greatly superior to that of 8.21 % (σ/mean) for the films on 130 wafers grown at lower introduced C/Si ratio.

Repeatability of Epitaxial Growth of n-Type 4H-SiC Films by High Speed Wafer Rotation Vertical CVD Tool

N-type 4H-SiC homo-epitaxial films were grown by high speed wafer rotation vertical CVD tool, and both short term repeatability and long term repeatability of epitaxial growth were investigated. In the short term repeatability investigated by 6 epitaxial wafers chosen from successively grown 12 epitaxial wafers using same recipe, it was found that total variation of thickness and carrier concentration for all measurement points of 6 wafers is 1.44 and 4.64 % respectively, which indicates excellent repeatability as well as high uniform thickness and carrier concentration. In the long term repeatability investigated by a very large number of growth experiments, probability achieving target uniformity of thickness and carrier concentration of the SiC films was increased up to 1.32 times by optimizing gas nozzle structure in gas inlet compared with in the case of conventional gas nozzles. Moreover, adjustment range of C/Si ratio necessary to achieve target uniformity of thickness and carrier concentration of the films was considerably reduced to 22 % by optimized gas nozzles.

Continuous Growth of Buffer/Drift Epitaxial Stack Based on 4H-SiC by Quick Change of N<sub>2 </sub>Flow Rate under High Growth Rate Condition

N-type 4H-SiC homo-epitaxial films were grown under high growth rate condition by high speed wafer rotation vertical CVD tool, and dependence on N2 flow rate for in-wafer distribution of thickness and carrier concentration was investigated. By adjusting only the N2 flow rate from 0.33 to 130 sccm, average carrier concentration of the SiC film was controlled within a range from 3 x 1015 to 1 x 1018 cm-3, while maintaining good in-wafer uniformity less than ±7.0%. Average growth rate higher than 54 μm/h and in-wafer uniformity less than ±3.1% were maintained and no dependence for thickness distribution on N2 flow rate was observed. Buffer/drift epitaxial stack using quick change of N2 flow rate was fabricated, and the crystalline quality and steepness of N concentration at buffer/drift interface were also investigated. The epitaxial stack showed lower defect density compared with single drift layer and showed steep interface between buffer layer and drift layer.

Impacts of surface C/Si ratio on in-wafer uniformity and defect density of 4H-SiC homo-epitaxial films grown by high-speed wafer rotation vertical CVD

Surface C/Si ratio was demonstrated as a useful indicator for the control of in-wafer distribution of thickness and carrier concentration in 4H-SiC homo-epitaxial films on large-diameter wafers. Close investigation of the dependence of growth rate and carrier concentration on the radial distance from the center of the 150 mm wafer revealed that the actual C/Si ratio just above the wafer: surface C/Si ratio, is quite different to the introduced C/Si ratio. In-wafer distribution of thickness and carrier concentration in the epitaxial films can be explained by the surface C/Si ratio, which suggests that the surface C/Si ratio could be a useful indicator for the precise control of uniform growth on large-diameter wafers. It is also found that two types of SiC films, one with extremely low defect density and the other with low pit density, both with highly uniform growth rate and carrier concentration, could be grown by controlling of the surface C/Si ratio on the whole wafers.

Reduction of Surface and PL Defects on n-Type 4H-SiC Epitaxial Films Grown Using a High Speed Wafer Rotation Vertical CVD Tool

4H-SiC homo-epitaxial films were grown using a high speed wafer rotation vertical CVD tool, and effects of wafer rotation speed during initial temperature ramping before epitaxial growth were investigated. Also, the effects of conditions during growth of the highly doped buffer layer on both surface and PL defect densities were investigated. It was found that the wafer rotation speed during the temperature ramping has a large influence on the surface defect density of the films. Especially, triangles generated from small pits were considerably reduced in the samples grown at a higher wafer rotation speed during the temperature ramping. The phenomena could be explained as a result of suppressed interfacial reaction between down-falls (DFs) and the wafer surface. Additionally, it was found that the density of basal plane dislocations (BPDs) on a drift layer is remarkably reduced by adjusting the C/Si ratio during growth of the buffer layer grown prior to the drift layer. By applying higher wafer rotation speed during the temperature ramping and optimizing the C/Si ratio for the growth of the buffer layer, a total defect density of 0.75 cm-2 on the film, which includes DFs, triangles, DF-triangles, stacking faults (SFs) and BPDs, was achieved.

Investigation of Aluminum Incorporation in 4H-SiC Epitaxial Layers

In the present contribution, the trends in voluntary incorporation of aluminum in 4H-SiC homoepitaxial films are investigated. The films were grown on Si-and C-face 4H-SiC 8°off substrates by chemical vapor deposition (CVD) in a horizontal, hot wall CVD reactor. Secondary Ion Mass Spectrometry (SIMS) and capacitance-voltage (C-V) measurements were used to determine the Al incorporation in the samples. The influence of Trimethylaluminum (TMA) flow rate, growth temperature, growth pressure and C/Si ratio on the dopant incorporation was studied.

In situ monitoring of stacking fault formation and its carrier lifetime mediation in p-type 4H-SiC

Using the fine control of an electron beam (e-beam) in scanning electron microscopy with the capabilities of both electrical and optical imaging, the stacking fault (SF) formation together with its tuning of carrier lifetime was in situ monitored and investigated in p-type 4H-SiC homoepitaxial films. The SFs were formed through engineering basal plane dislocations with the energy supplied by the e-beam. The e-beam intensity required for the SF formation in the p-type films was ∼100 times higher than that in the n-type ones. The SFs reduced the minority-carrier lifetime in the p-type films, which was opposite to that observed in the n-type case. The reason for the peculiar SF behavior in the p-type 4H-SiC is discussed with the cathodoluminescence results.

Direct imaging and optical activities of stacking faults in 4H-SiC homoepitaxial films

Both Shockley- and Frank-type stacking faults (SFs) in 4H-SiC were directly observed by scanning electron microscopy (SEM) and their optical activities were investigated by cathodoluminescence technique. The Shockley-type SFs identified by transmission electron microscopy show strong luminescence at wavelength of 471 nm while the Frank-type ones emit the luminescence at 482 nm. Both types of SFs present bright contrast in in-lens SEM images while no obvious contrast in out-lens images. The positions of the SFs observed by SEM correlate well with those detected in cathodoluminescence images. The bright SF contrast in SEM is discussed.

Surface defects and accompanying imperfections in 4H–SiC: Optical, structural and electrical characterization

The optical, structural and electrical properties of the killer defects termed down-fall particles and their accompanying imperfections in 4H–SiC homoepitaxial films were studied using electron microscopy techniques. Down-fall particles are polycrystalline 3C–SiC several tens of microns in size. They show unexpected dark contrast at their band edge (525 nm) using cathodoluminescence (CL). Down-fall particles have different effects on epitaxial growth. Most of them (common ones) are accompanied by stacking faults (SFs) which luminesce at 471 nm, while some promote the occurrence of 3C inclusions nearby. Transmission electron microscopy has revealed that the displacement vector of the accompanying SF is in the {0 0 0 1} basal plane, whereas the interface between the 3C inclusion and 4H matrix is composed of Shockley-type and Frank-type partials. The effects of down-fall particles on epitaxial growth as well as their dark contrast in the CL images are discussed. The differences between the common and special particles and the correlation with the electrical properties of the device are also discussed. The detailed structure–property analysis in this study thus provides a fundamental understanding of defect formation and development during the homo- or hetero-epitaxial growth of various materials.

Electrical activities of stacking faults and partial dislocations in 4H-SiC homoepitaxial films

The electrical activities of stacking faults (SFs) and partial dislocations in 4H-SiC homoepitaxial films were investigated by using the electron-beam-induced current (EBIC) technique. The basal plane dislocation was dissociated into Si ( g) 30 ∘ and C ( g) 30 ∘ partials under electron-beam irradiation, with a SF formed in between. The SF shows bright contrast at RT and dark contrast at 50 K in EBIC images. The reasons were discussed according to the quantum-well state of SF. C ( g) 30 ∘ partial is always more electrically active than Si ( g) 30 ∘ partial at each specific accelerating voltage. The EBIC contrasts of those two partials were discussed with the number of recombination centers.

Heavily nitrogen-doped 4H-SiC homoepitaxial films grown on porous SiC substrates

Heavily nitrogen-doped 4H-SiC homoepitaxial films were grown on normal p-type and porous 4H-SiC (PSC) substrates. The nitrogen doping concentration and resistivity of the epitaxial films, measured by Hall measurement, were about 10 20–10 21 cm −3 and 0.002–0.006 Ω cm, respectively. From X-ray analysis, it was observed that the crystallinity of the epilayer grown on porous 4H-SiC substrates is better than that grown on p-type 4H-SiC substrates. In spite of the heavy doping, the full-width at half-maximum (FWHM) value of the epitaxial film, which was grown on the porous substrate, was about 13 arcsec, proving its excellent crystal quality. In contrast, the heavily nitrogen-doped epilayer, which was grown on the normal substrate, had a FWHM value of 16.9 arcsec. High-voltage transmission electron microscope (HVTEM) and scanning electron microscope (SEM) observations made clear that the enhancement of the crystallinity was caused by stress relaxation near pore boundary and defect terminations in the porous layer.

Origin of Surface Morphological Defects in 4H-SiC Homoepitaxial Films

Plan-view transmission electron microscopy (TEM) was applied to investigate the origin of surface defects in 4H-SiC homoepitaxial films. Their origin existed at the substrate/epi-film interface. Hence, almost the entire thickness of the epi-film was removed by plasma etching leaving a very thin film. Then, the etched epi-crystal was thinned from the substrate side so that we could observe the crystallographic imperfections at the substrate/epi-film interface in plan-view TEM. Morphological features of the epi-film surface remained unchanged after the plasma etching process. Hence, one-to-one correspondence between surface defects and crystallographic imperfections was confirmed by comparing optical micrographs and TEM images. Crystallographic imperfections associated with “carrot defects” were observed. They were composed of stacking faults on the (0001) plane and partial dislocations bounding them. These imperfections originated from foreign particles at the interface. From X-ray energy-dispersive spectrometry (XEDS), it was confirmed that particles contained zirconium (Zr). Selected area diffraction patterns showed that the particles were crystalline.

Source of Surface Morphological Defects Formed on 4H–SiC Homoepitaxial Films

Plan-view transmission electron microscopy (TEM) was carried out to investigate the source of morphological defects formed on the surface of 4H–SiC homoepitaxial films. The source at the substrate/epifilm interface consisted of an inclusion and partial dislocations emerging from it. Selected-area diffraction pattern analysis, energy dispersive X-ray spectroscopy and micro-Raman spectroscopy revealed that the chemical composition of the inclusion was ZrO2. From the comparison between TEM images and calculated images, it was suggested that the partial dislocations were sheared Frank dislocations with the Burgers vector of the (1/12)<4403> type.

Crystallographic Defects under Surface Morphological Defects of 4H-SiC Homoepitaxial Films

Crystallographic Defects under Surface Morphological Defects of 4H-SiC Homoepitaxial Films

Characterization of 4H-SiC Homoepitaxial Films on Porous 4H-SiC from Bis(trimethylsilyl)methane Precursor

4H-SiC homoepitaxial films were grown on 8° off-axis porous 4H-SiC (0001) faces in the temperature range of by chemical vapor deposition from bis(trimethylsilyl)methane (BTMSM) precursor. The activation energy for growth was 5.6 kcal/mol, indicating that the film growth is dominated by the diffusion-limited mechanism. Triangular stacking faults were incorporated in the SiC thin film grown at low temperature of 1280°C due to the formation of 3C-SiC polytype. Moreover, super-screw dislocations appeared seriously in the SiC film grown below 1320°C. Clean and featureless morphology was observed in the SiC film grown below 25 standard cubic centimeters per minute (sccm) carrier gas flow rate of BTMSM at 1380°C while 3C-SiC polytype with double positioning boundaries grew at 30 sccm flow rate of BTMSM. The dislocation density of the epi layer was strongly influenced by the growth temperature and flow rate of BTMSM. Double axis crystal X-ray diffraction and optical microscopy analysis revealed that the dislocation density decreased at the higher growth temperature and lower flow rate of BTMSM. The full width at half maximum of the rocking curve of the film grown at optimized condition was 7.6 arcsec and the sharp free exciton and Al bound exciton lines appear in the epi layer, which indicates that the 4H-SiC film was of very high quality. © 2003 The Electrochemical Society. All rights reserved.

Low Temperature 4H-SiC Epitaxial Growth on 4H-SiC ( 112 ¯ 0 ) and ( 11 ¯ 00 ) Faces by Organometallic Chemical Vapor Deposition

Silicon carbide thin films were grown on and 4H-SiC substrates by chemical vapor deposition using a single precursor material, bis(trimethylsilyl)methane at substrate temperatures ranging from 990 to 1400°C. The morphological evolution of the films as a function of the growth temperature was explained using a model based on the Ehrlich Schwoebel (ES) barrier. On the faces, high quality 4H-SiC homoepitaxial thin films were grown above 1200°C while amorphous SiC films were obtained below 1100°C. Very narrow X-ray rocking curves with a full width at half-maximum of 6.9 arc s were observed for the 4H epi layer grown on at 1200°C. On the faces, epitaxial 4H-SiC films were grown at temperature as low as 990°C, which is approximately 500°C lower than the conventional growth temperature. It is believed that sufficient decomposition of the source material, at such a low temperature and the atomic arrangement of the a face containing the 4H stacking sequence (ABCB…) make low temperature epitaxy possible. © 2002 The Electrochemical Society. All rights reserved.

Photoluminescence and transport studies of boron in 4H SiC

Two distinct boron-related centers are known in silicon carbide polytypes, one shallow (ionization energy ∼300 meV) and the other deep (∼650 meV). In this work, 4H SiC homoepitaxial films are intentionally doped with the shallow boron center by controlling the silicon to carbon source gas ratio during chemical vapor deposition, based on site competition epitaxy. The dominance of the shallow boron center for samples grown with a low Si/C ratio, favoring the incorporation of boron onto the silicon sublattice, is verified by the temperature dependent Hall effect, admittance spectroscopy and deep level transient spectroscopy. In these samples a peak near 3838 Å appears in the low temperature photoluminescence spectrum. Further experiments support the identification of this peak with the recombination of a four particle (bound exciton) complex associated with the neutral shallow boron acceptor as follows: (1) The intensity of the 3838 Å peak grows with added boron. (2) Momentum conserving phonon replicas are observed, with energies consistent with other four particle complexes in SiC. (3) With increasing temperature excited states are observed, as for the neutral aluminum and gallium acceptor four particle complexes. However, the intensity of the shallow boron spectrum is quenched at lower temperatures than the corresponding spectra for Al and Ga, and the lineshapes are strongly sample dependent. These results may be related to the unusual configurational and electronic structure of this center inferred from recent spin resonance experiments by other groups. When the Si/C ratio is high, the optical signatures of the deep boron center, nitrogen-boron donor-acceptor pairs and conduction band to neutral acceptor free-to-bound transitions, are observed in the photoluminescence. At T=2 K well resolved, detailed nitrogen-boron pair line spectra are observed in addition to the peak due to distant pairs. As the temperature is raised, the donor-acceptor pair spectrum decreases in intensity while the free-to-bound no-phonon peak appears. Extrapolation of the temperature dependence of the free-to-bound peak to T=0 K, after correction for the temperature dependence of the exciton energy gap, leads to the value EA(B)−EX=628±1 meV, where EA(B) is the ionization energy of the deep boron center and EX is the binding energy of the free exciton which, for 4H SiC, can only be estimated at this time.

Defects In 4H Silicon Carbide CVD Epilayers

AbstractThe characteristic defects of 4H-SiC homoepitaxial thin films grown on bulk substrates using chemical vapor deposition (CVD) are described based on transmission electron microscopy (TEM), atomic force microscopy (AFM) and surface decoration studies. Emphasis is placed on understanding the formation mechanism of surface triangular defects. Cross-sectional TEM observations revealed the existence of two variants of 3C-SiC inclusions in 4H epitaxial films. In the plan-view orientation, g4H = 3304 type reflections were found useful for distinguishing the two variants of 3C-SiC platelets that are present in the 4H epilayer. A decoration technique was employed to reveal the relationship between the 3C platelets and surface features, e.g., surface steps. A formation mechanism for surface triangular defects is proposed, which is partially confirmed by the etch pit patterns obtained on the epilayer surfaces after a molten KOH etch.