I.I. Khlebnikov

100 mm 4HN-SiC Wafers with Zero Micropipe Density

Recent advances in PVT c-axis growth process have shown a path for eliminating micropipes in 4HN-SiC, leading to the demonstration of zero micropipe density 100 mm 4HN-SiC wafers. Combined techniques of KOH etching and cross-polarizer inspections were used to confirm the absence of micropipes. Crystal growth studies for 3-inch material with similar processes have demonstrated a 1c screw dislocation median density of 175 cm-2, compared to typical densities of 2x103 to 4x103 cm-2 in current production wafers. These values were obtained through optical scanning analyzer methods and verified by x-ray topography.

Growth of micropipe-free single crystal silicon carbide (SiC) ingots via physical vapor transport (PVT)

The move towards commercialization of SiC based devices places increasing demands on the quality of the substrate material. While the industry has steadily decreased the micropipe (MP) levels in commercial SiC substrates over the past years, the achievement of wafers that are entirely free of MPs marks an important milestone in commercialization of SiC based devices. We present the results of a study for controlling the nucleation and propagation of MP defects in SiC ingots grown via PVT. Our studies confirm that during bulk growth of SiC, foreign polytype nucleation such as 3C-polytype occurs at the initial stages of growth (nucleation period) and/or during subsequent growth in the presence of facets. Results in this investigation suggest that polytype instability during crystal growth adversely impacts the MP density. Based on this key concept, growth conditions for nucleation and growth stages were optimized. These conditions were subsequently implemented in an innovative PVT growth environment to achieve a growth technique with highly effective polytype control. Under continuously modulated growth conditions, MPs induced by seed material and/or formed during the growth were eliminated. 2-inch and 3-inch diameter MP-free (zero MP density) conducting 4H-SiC ingots were obtained.

Defect Status in SiC Manufacturing

Availability of high-quality, large diameter SiC wafers in quantity has bolstered the commercial application of and interest in both SiC- and nitride-based device technologies. Successful development of SiC devices requires low defect densities, which have been achieved only through significant advances in substrate and epitaxial layer quality. Cree has established viable materials technologies to attain these qualities on production wafers and further developments are imminent. Zero micropipe (ZMP) 100 mm 4HN-SiC substrates are commercially available and 1c dislocations densities were reduced to values as low as 175 cm-2. On these low defect substrates we have achieved repeatable production of thick epitaxial layers with defect densities of less than 1 cm-2 and as low as 0.2 cm-2. These accomplishments rely on precise monitoring of both material and manufacturing induced defects. Selective etch techniques and an optical surface analyzer is used to inspect these defects on our wafers. Results were verified by optical microscopy and x-ray topography.

Dislocations as a source of micropipe development in the growth of silicon carbide

Micropipes are the primary macroscopic defects in silicon carbide single crystals. It is shown that a stable hollow core of dislocation can act as an initial site of micropipe development. The specific strain energy necessary to estimate the thermodynamic stability of a hollow dislocation core is expressed in terms of the macroscopic parameters of the material Young’s modulus and of the Gruneisen constant.Micropipes are the primary macroscopic defects in silicon carbide single crystals. It is shown that a stable hollow core of dislocation can act as an initial site of micropipe development. The specific strain energy necessary to estimate the thermodynamic stability of a hollow dislocation core is expressed in terms of the macroscopic parameters of the material Young’s modulus and of the Gruneisen constant.

A Method for Defect Delineation in Silicon Carbide Using Potassium Hydroxide Vapor

Defect evaluation of silicon carbide (SiC) wafers can be accomplished by potassium hydroxide (KOH) etching. The method described in this work employs etching by KOH in a vapor phase rather than in a liquid phase and this method allows reliable etching of both Si- and C-faces and furthermore it allows the delineation of defects on alternate orientation planes of SiC. Polished SiC wafers were etched in the temperature range from 700 to 1000°C at atmospheric air pressure. Etch pits were observed on (0001), (0001), (1120) and (1100) planes. The shape of the pits was found to be in accordance with the crystallographic symmetry. Activation energies for (0001) and (1120) planes were found to be ~17 kcal/mol and ~20 kcal/mol, respectively. It was demonstrated that the method of KOH vapor etching of SiC is simple for implementation having possibilities to reveal most of the important crystal defects.

Graphitization of the Seeding Surface during the Heating Stage of SiC PVT Bulk Growth

A transient numerical simulation of the temperature field distri bu ion in a conventional resistively heated SiC PVT growth reactor revealed that the uni ntended seeding substrate sublimation typically exists during the furnace heat up stage. Conseque ntly, this would lead to the seeding surface graphitization due to nonstoichiometry of SiC evaporat ion. Suppression of the seeding surface graphitization requires significant reduction of the furnace heat up time. An optimal elevation of the argon partial pressure and seeding substrate tem p rature during the heat up stage would also promote repression of the seed graphitization. Introduction The elimination of silicon and carbon second phase inclusions (bulk defects) that may serve as new micropipe generation centers [1] is essential for high quality SiC bulk growth. While the silicon second phase formation at the growing surface of SiC was previously disc ussed and has been experimentally proven [2], the mechanisms of carbon second phase gener ation is not completely understood. One of the possible mechanisms being proposed here may result f rom unintended seeding substrate sublimation (thermal etching), which typically exists during the heating stage of SiC PVT bulk growth. Model description Transient numerical simulation of the temperature field distributi on during the initial (furnace heat up) stage and steady state phase of growth run i n a conventional resistively heated PVT reactor was performed using GAMBIT-1.3.1/FIDAP-8.6 software pa ckage. The numerical model incorporated the axi-symmetric geometry of the calculati on domain, time dependence of the heating power rise at the growth beginning and the temperature de pendent physical properties of the seeding substrate, SiC source material, argon/Si xCy vapor mixture and the materials used in the furnace design. Conduction in the solid elements of the calculation domai n and radiation along with conduction in the fluid (gaseous) regions represent the heat transfer mechanisms incorporated in the model, whereas the convective component of heat transfer was omitted [3, 4]. Results and Discussion According to the simulation results, the heating up rate of the sourc e material region significantly differs from that of the seeding substrate (see Fig. 1). Such a situation is primarily attributed to the large difference in the thermal conductivities of SiC source material λP and the seeding substrate λC (λC/λP>100 at 2500 K) [5, 6]. This difference determines the typical temperature rise dynamics of the source material and the grow in crystal shown in Fig. 2. As is clear from the plot, the furnace heat up stage continues ~3 hr afte r the heating power switch on. At the beginning of this stage 0 < t < tB the major part of the source material region is not heated up yet. In fact, the temperature inside the source material volume (point 3 in Fig.1) is significantly Materials Science Forum Online: 2003-09-15 ISSN: 1662-9752, Vols. 433-436, pp 99-102 doi:10.4028/www.scientific.net/MSF.433-436.99

SiC Epitaxial Growth on Carbon

The possibility of single crystal SiC expitaxial growth on freestanding amorphous carbon films (500–1000 A) as well as thin amorphous carbon layers deposited on mono-crystalline SiC seeds, by conventional physical vapor transport (PVT) technique, is demonstrated. Preliminary experiments indicate that under certain specific growth conditions, 3D SiC single crystals (100 – 600 A) of different polytypes can be grown on freestanding amorphous carbon layers, with more or less equal probability of formation for each polytype. On the other hand, under low axial temperature gradients (

Thick Oxide Layers on N and P SiC Wafers by a Depo-Conversion Technique

The electrical properties of thick oxide layers on n and p-type 6H-SiC obtained by a depo-conversion technique are presented. High frequency capacitance-voltage measurements on MOS capacitors with a {approximately} 3,000 {angstrom} thick oxide indicates an effective charge density comparable to that of MOS capacitors with thermal oxide. The breakdown field of the depo-converted oxide obtained using a ramp response technique indicates a good quality oxide with average values in excess of 6 MV/cm on p-type SiC and 9 MV/cm on n-type SiC. The oxide breakdown field was observed to decrease with increase in MOS capacitor diameter.

A Technique For Rapid Thick Film Sic Epitaxial Growth

In this paper we demonstrate the growth of thick SiC epitaxial layers (≥100 μm) of good structural quality at a high growth rate (>100 μm/hr) by controlling the vapor dynamics during conventional physical vapor transport (PVT) process. We propose that our PVT technique be used to ‘repair’ or ‘heal’ commercially available substrates dominated by micropipes, by ‘filling up’ the micropipes through crystal growth inside the micropipe. Extensive experiments performed on thick SiC epitaxial layers grown on Lely substrates indicate that the thick epitaxial layers are of single polytype of high structural quality, with a single peak X-ray rocking curve of less than 12 arcsecs FWHM.

Point and planar defect formation in SiC during PVT growth

The spontaneous nucleation of “negative” crystals from the solute of vacancies in SiC does not appear to be dominant due to the low super-saturation of vacancies. However, clustering of the vacancies is possible due to the energy gain in the system caused by coalescence of any two vacancies. The major reasons for point and planar defect formation in SiC are the liquid phase of free silicon and non-stoichiometry of the vapor.