4H-SiC Boules Research Articles

Influence of the Size Distribution of the SiC Powder Source on the Shape of the Crystal Growth Interface during PVT Growth of 4H-SiC Boules

We compared the evolution of three different SiC sources during standard PVT growth runs. The evolution of the growing crystal and the morphological changes in the SiC source were visualized using in-situ X-ray visualization. Computer simulation was used to calculate the temperature field distributions. It is found that the densification and shrinkage of the SiC source material during the growth process can affect the growth conditions in such a way that the convexity of the growth interface is increased in an unfavorable manner. While unfavorable growth conditions can be related to thermal properties due to less favorable SiC powder evolution, predicting such behavior is a rather complex task that still relies on the support of experimental methods.

Undulated Step Structure on the (0001¯) Facet of Physical Vapor Transport-Grown 4H-SiC Crystals.

The step structure on the (000)C facet of 4H-SiC boules grown by the physical vapor transport growth method with different nitrogen doping concentrations was examined in various scales, using different types of microscopy, such as differential interference contrast optical microscopy (DICM) and atomic force microscopy (AFM). DICM observations unveiled characteristic macroscopic surface features of the facet dependent on the nitrogen doping concentration. AFM observations revealed the existence of step trains of half unit-cell height (0.5 nm) on the facet and found that their separation was undulated with a characteristic wavelength dependent on the nitrogen doping concentration; the higher the nitrogen concentration, the longer was the undulation wavelength of step separation. Based on these results, we discussed the origin and formation mechanism of the separation-undulated step structure observed on the (000)C facet of nitrogen-doped 4H-SiC boules.

Sublimation growth and property characterization of p-type 4H-SiC by Al[sbnd]B co-doping technique

Silicon carbide (SiC) is a wide bandgap semiconductor with promising application prospect in high-voltage power electronics devices. Herein, p-type 4H-SiC boules without foreign polytype inclusions were grown by physical vapor transport method using AlB co-doping technique. The concentrations of Al and B were measured to be 2.0 × 1019, 4.7 × 1017 cm−3, respectively. The small lattice distortion was verified by X-ray diffraction and quantum simulation methods. Furthermore, the polytype stabilization mechanism was clarified and electrical properties were investigated. This study shed light on growing p-type SiC for high-voltage power electronics devices.

Structural Characterization of the Growth Front of 4H-SiC Boules Grown Using the Physical Vapor Transport Growth Method

The defect structure at the growth front of 4H-SiC boules grown using the physical vapor transport (PVT) method has been investigated using high resolution x-ray diffraction and x-ray topography. The crystal parameters such as the c-lattice constant exhibited characteristic variations across the growth front, which appeared to be caused by variation in surface morphology of the as-grown surface of the boules rather than the defect structure underneath the surface. X-ray topography also revealed that basal plane dislocations are hardly nucleated at the growth front during PVT growth of 4H-SiC crystals.

Formation of basal plane stacking faults on the ([formula omitted]) facet of heavily nitrogen-doped 4H-SiC single crystals during physical vapor transport growth

The formation of stacking faults in heavily nitrogen-doped (mid-1019cm−3) 4H-SiC boules grown by the physical vapor transport (PVT) growth method was investigated by studying surface morphologies on the (0001¯) facet of the boules. Low-voltage scanning electron microscopy (LVSEM) observations detected stacking faults on the (0001¯) facet of heavily nitrogen-doped 4H-SiC crystals. LVSEM and atomic force microscopy (AFM) studies revealed that the stacking faults showed characteristic morphologies, which stemmed from the interaction between stacking faults and surface steps. These observations also revealed that heavy nitrogen doping resulted in the nucleation of a number of surface hillocks on the (0001¯) facet; the hillocks were never observed on the facet of conventionally doped (nitrogen concentration: mid-1018cm−3) 4H-SiC boules. Furthermore, the hillocks were nucleated only on the facet and never observed on the outer regions of the facet. Based on these results, the stacking fault formation mechanism in heavily nitrogen-doped 4H-SiC crystals is discussed.

Investigation of the Surface Morphology and Stacking Fault Nucleation on the (000-1)C Facet of Heavily Nitrogen-Doped 4H-SiC Boules

The stacking fault formation during physical vapor transport growth of heavily nitrogen-doped (mid-1019 cm−3) 4H-SiC crystals was investigated. Low-voltage scanning electron microscopy (LVSEM) observations detected the stacking fault formation on the (000-1) facet of heavily nitrogen-doped 4H-SiC crystals. Stacking faults showed characteristic morphologies, and atomic force microscopy (AFM) studies revealed that these morphologies of stacking faults stemmed from the interaction between surface steps and stacking faults. Based on these results, the stacking fault formation mechanism in heavily nitrogen-doped 4H-SiC crystals is discussed.

Characterization of Lattice Plane Bending and Stress Distribution in Physical Vapor Transport-Grown 4H-SiC Crystals

Basal plane bending and stress distribution in physical vapor transport-grown n-type 4H-SiC crystals were investigated. High resolution X-ray diffraction measurements were performed on commercially available 3-inch-diameter 4H-SiC substrates and along the growth front surface of as-grown 1-inch-diameter 4H-SiC boules. The measurements revealed that structural parameters such as the c-lattice constant, basal plane tilting, and FWHM showed characteristic variations across the substrates and as-gown boules, indicating that the crystals had a non-uniform distribution of dislocations comprising domain structures. Residual stress measured by micro Raman spectroscopy showed a similar behavior, which was an oscillatory spatial variation. On the basis of these results, defect structures in the crystals are elucidated.

150 mm 4H-SiC Substrate with Low Defect Density

150 mm diameter 4H-SiC boules were grown by the physical vapor transport (PVT) method. Synchrotron white beam X-ray topography (SWBXT) was carried out to investigate the distribution of defects in axial slices cut from the boule. It was found that an increase of dislocations and micropipes was mainly induced by inclusions. After eliminating these inclusions, which were formed in the mid to late stage of the crystal growth, both the screw dislocation density and base plane dislocation density could be decreased down to a magnitude of 102 cm-2, which is comparable to that of high quality 100 mm diameter SiC substrates.

Surface morphology and step instability on the (0001̄)C facet of physical vapor transport-grown 4H–SiC single crystal boules

Surface morphologies on the (0001¯) C facet of 4H–SiC boules grown using the physical vapor transport method were examined in various scales (from millimeter to nanometer) using different types of microscopies such as differential interference contrast (DIC) optical microscopy and atomic force microscopy (AFM). DIC optical microscopic observation revealed that there are three distinct morphological regions at the growth front of the 4H–SiC boules: the facetted region, non-facetted region and intermediate region between them. The local inclination of the facet surface from the {0001} basal plane increases toward the edge of the facetted region and then decreases in the intermediate region. AFM observations revealed that characteristic step structures were established in these two regions and that nitrogen doping significantly influenced the stability of the step structures. Based on the results, the formation mechanism of surface morphologies on the (0001¯) C facet of 4H–SiC boules is discussed.

Double Shockley Stacking Fault Formation in Higher Doping Regions of PVT-Grown 4H-SiC Wafers

Due to the influence of facet, the dopant concentration is higher than that other region inside the boule during PVT grown 4H-SiC. A [0001] facet can be observed on top of the boule. The facet region is visible as an oval region of darker contrast indicating a higher doping concentration in c-plane wafers sliced from N-doped 4H-SiC boules. With the help of synchrotron white beam X-ray topography techniques, we have carried out detailed studies on the facet regions in 4H-SiC wafers from different boules. We observed the double Shockley stacking faults piling up insider the facet after the wafer has been subject to chemical mechanical polishing followed by high temperature heat treatment. The partials bonding the stacking faults are along the Peierls valley which is along <11-20> for 4H-SiC. The contrast of double Shockley stacking faults, which are formed by the gliding of two leading partial dislocations on adjacent basal planes, is found only inside the facet region. Our study indicates that the presence of scratch or the other surface source and a higher concentration of N doping within the facet gives rise to the double Shockley faults formation. Moreover, within the facet, the lower minority carrier lifetimes compare to the rest area of the wafer characterized by lifetime mapping measurements also indicates a high density of stacking faults.Due to the facet effect, the dopant concentration is higher than that other region inside the boule during PVT grown 4H-SiC. A [0001] facet can be observed on top of the boule. The facet region is visible as an oval region of darker contrast indicating a higher doping concentration in c-plane wafers sliced from N-doped 4H-SiC boules. With the help of synchrotron white beam X-ray topography techniques, we have carried out detailed studies on the facet regions in 4H-SiC wafers from different boules. We observed the double Shockley stacking faults piling up inside the facet after the wafer has been subject to chemical mechanical polishing followed by the high temperature heat treatment. The partials bonding the stacking faults are lying inside the Peierls valley which is along <11-20> for 4H-SiC. The contrast of double Shockley stacking faults, which are formed by the gliding of two leading partial dislocations on adjacent basal planes, is found only inside the facet region. Our study indicates that the presence of scratch or the other surface source and a higher concentration of N doping within the facet gives rise to the double Shockley faults formation. Moreover, within the facet, the lower minority carrier lifetimes compare to the rest area of the wafer characterized by lifetime mapping measurements also indicates a high density of stacking faults.

Observation of the Surface Morphology on the (0001)C Facet of 4H-SiC Boules

The surface morphology on the (000-1)C facet of 4H-SiC boules grown by the physical vapor transport method was examined in various scales (from millimeter to nanometer) using different types of microscopies such as differential interference contrast (DIC) optical microscopy and atomic force microscopy (AFM). The DIC optical microscope observation revealed that there exist three distinct morphological regions at the growth front of the 4H-SiC boules; they are facetted, non-facetted, and the intermediate region between them. The local inclination of the facet surface from the (000-1) basal plane increases toward the facet edge and then decreases over the intermediate region. AFM observations revealed characteristic step structures in these two regions and also that they are significantly influenced by nitrogen-doping. Based on the results, the formation mechanism of the facet morphology on 4H-SiC boules is discussed.

High Quality 100 mm 4H-SiC Substrate

High-quality 100 mm 4H-SiC boules were grown using the physical vapor transport (PVT) method with optimized growth parameters. Micro-Raman spectroscopy measurement shows that the 4H-SiC polytype of the entire wafer is uniform. The micropipe density is measured to be less than 1cm-2. The 1c threading screw dislocation (TSD) density can be suppressed to the magnitude of 102 cm-2. After chemical mechanical polishing (CMP), it is found that the warp of the substrate is less than 10 μm, and the surface roughness (Ra) is as low as 0.063 nm.

Synchrotron X-Ray Topography Studies of the Propagation and Post-Growth Mutual Interaction of Threading Growth Dislocations with C-Component of Burgers Vector in PVT-Grown 4H-SiC

Synchrotron White Beam X-ray Topography (SWBXT) imaging of wafers cut parallel to the growth axis from 4H-SiC boules grown using Physical Vapor Transport has enabled visualization of the evolution of the defect microstructure. Here we present observations of the propagation and post-growth mutual interaction of threading growth dislocations with c-component of Burgers vector. Detailed contrast extinction studies reveal the presence of two types of such dislocations: pure c-axis screw dislocations and those with Burgers Vector n1c+n2a, where n1 is equal to 1 and n2 is equal to 1 or 2. In addition, observations of dislocation propagation show that some of the threading dislocations with c-component of Burgers adopt a curved, slightly helical morphology which can drive the dislocations from adjacent nucleation sites together enabling them to respond to the inter-dislocation forces and react. Since all of the dislocations exhibiting such helical configurations have significant screw component, and in view of the fact that such dislocations are typically not observed to glide, it is believed that such morphologies result in large part from the interaction of a non-equilibrium concentration of vacancies with the originally approximately straight dislocation cores during post-growth cooling. Such interactions can lead to complete or partial Burgers vector annihilation. Among the reactions observed are: (a) the reaction between opposite-sign threading screw dislocations with Burgers vectors c and –c wherein some segments annihilate leaving others in the form of trails of stranded loops comprising closed dislocation dipoles; (b) the reaction between threading dislocations with Burgers vectors of -c+a and c+a wherein the opposite c-components annihilate leaving behind the two a-components; (c) the similar reaction between threading dislocations with Burgers vectors of -c and c+a leaving behind the a-component.

Growth of nitrogen-doped SiC boules by halide chemical vapor deposition

A novel halide chemical vapor deposition process has been developed for growth of single crystal 6H and 4H SiC boules. This process takes advantage of the thermal stability of halogenated precursors and a unique reactor design to produce SiC crystals up to 75 mm in diameter at growth rates up to 250 mm/h. Growth rate was significantly improved by using CH 4 instead of C 3H 8 as the carbon source gas. Growth of the 6H and 4H polytypes was evaluated as a function of seed polytype, off-cut and surface polarity at a growth temperature of 2020 °C, which is well above typical epitaxy conditions and well below typical sublimation growth conditions. The effect of the substrate and nitrogen flow rate on nitrogen incorporation were characterized by secondary ion mass spectrometry. Radial uniformity of doping was assessed by mercury probe capacitance–voltage measurements. Bulk crystals with an average boron concentration of 1.5e15 atoms/cm 3 and nitrogen doping level above 1.0e19 atoms/cm 3 were readily achieved. High-resolution X-ray diffraction showed that growth of the 4H polytype requires growth on the carbon face of 4H seed crystals.

Polytype stability in seeded sublimation growth of 4H–SiC boules

Process conditions for stable single polytype growth of 4H–SiC boules via a seeded sublimation technique have been developed. Reproducible results can be obtained in a narrow temperature interval around 2350°C and on the C-face of 4H–SiC seeds. Evidence is presented that during the initial stage of growth, morphological instabilities may occur resulting in structural defects. A solution is proposed based on the experimental findings, i.e. the first regions of growth ought to be carried out at a low supersaturation (growth rate ∼100 μm/h) until a proper growth front has developed.

Identification of prismatic slip bands in 4H SiC boules grown by physical vapor transport

Transmission electron microscopy (TEM) and KOH etching have been used to study the dislocation structure of 4H SiC wafers grown by physical vapor transport. A new type of threading dislocation arrays was observed. Rows of etch pits corresponding to dislocation arrays were observed in vicinity of micropipes, misoriented grains and polytypic inclusions at the periphery of the boules and extended along the \( \) directions. Plan view conventional and high resolution TEM showed that the arrays consisted of dislocations threading along the c-axis with Burgers vectors having edge components of the a/3\( \) type. The Burgers vectors were parallel to the corresponding arrays. The dislocation arrays were interpreted as slip bands formed by dislocation glide in the prismatic slip system \( \)\(\{ \bar 1100\} \) of hexagonal SiC during post-growth cooling.

Stress and misoriented area formation under large silicon carbide boule growth

The presence of slightly misoriented (less than 1°) comparatively large areas in silicon carbide boules grown by the sublimation method is one of the types of defects which can limit the operation of devices based upon such material. 6H- and 4H-SiC boules were grown by the modified Lely method elaborated at the St.-Petersburg Electrotechnical University. Formation of stress and misoriented areas in SiC crystals has been investigated. Nondestructive techniques for such material characterization have been developed.

Stepped structure on the {0001} facet plane of α-SiC

The surface topography of the {0001} facet of as-grown 6H and 4H SiC boules was observed ex-situ by atomic force microscopy (AFM). Peculiar stepped structures of SiC{0001} to the growth face polarity and the polytype were detected. Height steps equal to the c-lattice parameter (1.5 nm) were observed to be dominant on the 6H-SiC(0001)Si surface. They were very regularly arranged, i.e. straight and almost equally spaced. On the other hand, meandering macrosteps of height more than 10 nm were observed on the 6H-SiC(000 1 )C and the 4H-SiC(000 1 )C surfaces. Based on the results, the mechanism of formation of these surface morphologies is discussed.