M. Tuominen

Growth of 6H and 4H—SiC by sublimation epitaxy

The epitaxial sublimation growth process of SiC has been investigated. Layers with specular surfaces and growth rates up to 2 mm/h have been obtained. No step bunching is observed by optical microscopy even on very thick layers which indicates a stable step growth mechanism. Under certain growth conditions the morphology degrades. The morphological stability is investigated and discussed in relation to the growth kinetics. Impurities in the epitaxial layers are investigated by secondary ion mass spectroscopy and low-temperature photoluminescence. The carrier concentration is measured by capacitance–voltage measurements. The structural quality of the grown material is improved compared to the substrate as shown by X-ray diffraction measurements.

Crystalline imperfections in 4H SiC grown with a seeded Lely method

Abstract Commercially available 4H SiC wafers have been studied concerning their crystal quality. A variety of structure sensitive techniques has been utilized to reveal specific macro-defects in the material. Microscopy examination combined with preferential chemical etching have imaged dislocation networks, micropipes, basal plane defects and cracks. Synchrotron X-ray topographs have shown defect-associated strain and lattice misorientation arising in the vicinity of some micropipes. High resolution X-ray diffractometry and Bragg angle topography were used to provide evidence of existing domains and their misorientation. The results obtained are discussed in the context of defect origin and formation mechanisms. A comparison with 6H SiC is made to derive possible similarities of defect appearance in both polytypes.

Preferential etching of SiC crystals

Abstract Preferential etching of 6H and 4H SiC in molten KOH is studied at different temperatures as to the etching rate and defect appearance. The effect of etching time on micropipe related etch-pit size is revealed. Optimal etching conditions are suggested in order to gain information on defect type and distribution.

Growth-related structural defects in seeded sublimation-grown SiC

Abstract Structural defects in 4H and 6H SiC wafers have been studied by means of synchrotron X-ray topography and optical microscopy. The effect of seed crystal attachment, orientation, growth face shape, reloading and continued growth are discussed. A comparison between 4H and 6H material is made also. The results relate the origin of different defects to the mentioned growth conditions.

Defect origin and development in sublimation grown SiC boules

SiC boules were grown by the modified Lely method. Macro-defects in the boules and wafers cut from them were studied by means of optical microscopy and chemical etching. The influence of the quality, the surface orientation and attachment of the seed crystal on secondary evaporation, domain and micropipe formation was studied. The results obtained are discussed in terms of defect development at different stages of the crystal growth and under different growth conditions.

Seeded sublimation growth of 6H and 4H-SiC crystals

Abstract Growth of 6H and 4H-SiC crystals via sublimation technique has been studied in a temperature range of 2300–2450°C. The growth rate strongly depends on temperature distribution, growth pressure, and source to seed distance. The influence of the seed quality on the polytype stability and defect occurrence has been studied. 6H–SiC crystals up to 35 mm in diameter and 20 mm in length have been grown with low micropipe density, 50 cm −2 . Micropipe free areas up to 1 cm 2 have been obtained under optimized growth conditions. The analysis of the results obtained with 4H–SiC growth has shown that this polytype has more narrow window of growth parameters which requires more strict control especially at the initial stage of growth. The seed quality plays an important role for the stability of the polytype and for defect control in the growing crystal.

SiC – a semiconductor for high-power, high-temperature and high-frequency devices

SiC has in comparison with Si superior basic properties for applications in high-power, high-frequency and high-temperature electronics. The potential applications of SiC were known decades ago, but the poor quality of the material produced at that time has delayed the device development. However, during the last years the crystal growth process of SiC has been improved considerably. We will present some important properties of SiC, describe the two most common growth processes and discuss fundamental materials problems that remain to be solved. A further aspect, which we will discuss, is the polytypism of SiC, which may allow us to obtain generic knowledge of, for instance, defects in semiconductors.

Defect analysis in Lely-grown 6H SiC

Abstract Two Lely-grown 6H polytype SiC platelets were investigated in terms of their crystalline quality and defect characteristics. Synchrotron X-ray topography, along with optical microscopy and high-resolution X-ray diffractometry were used as characterization techniques. In the first platelet a distored area where the nucleation has started was observed. It consists of micropipes and a complex network of the Frank-Read dislocation loops. Their Burgers vectors were completely determined by X-ray topographic analysis. Outside the distorted area the only large defects observed were dislocations with a low density (in the order of 10 2 cm −2 ) and few stacking faults. The quality of this platelet has improved during the growth. The second platelet was found to be of an excellent crystalline quality. It does not contain micropipes or stacking faults and its dislocation density is very low (about 30 cm −2 ). The rocking curve widths (FWHM) of both samples were very narrow (from 5.8″ to 8.3″). Possible relationships between the observed defects and their formation mechanisms in the growth processes are discussed.

Wafer warpage, crystal bending and interface properties of 4H-SiC epi-wafers

Abstract The relationship between the warpage of 4H-SiC CVD grown epi-wafers with crystal bending and substrate properties is investigated. The wafer surface preparation before and after epitaxy is found to affect both long range properties such as the wafer flatness and to some extent local properties such as the epi-substrate interface. Structural characterisation is carried out using X-ray diffraction techniques and KOH etching.

Nature and occurrence of defects in 6H-SiC Lely crystals

Synchrotron white beam topography has been applied to study defects in 6H-SiC platelets grown by the Lely method. In addition, high resolution X-ray diffraction, chemical etching, capacitance-voltage and photoluminescence measurements were carried out to confirm and complement the topography results. The occurrence of structural defects such as various misorientations, dislocations, stacking faults and precipitates are classified into grown-in and post-growth defects. The results are related to the assumed growth process of the differently shaped platelets.