Dislocation Content of Etch Pits in Hexagonal Silicon Carbide
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Dislocation Content of Etch Pits in Hexagonal Silicon Carbide Igor I. Khlebnikov, Mohsen B. Lari, Yuri I. Khlebnikov, Robert T. Bondokov, Ramakrishna Ayyagari, Peter Muzykov, Tangali S. Sudarshan University of South Carolina, College of Engineering and Information Technology, Columbia, SC 29208, U.S.A. T. Anderson and J. B. Whitlock Litton Airtron, Morris Plaines, NJ 07950, U.S.A.
ABSTRACT
6H- and 4H- SiC crystals grown on the Si-face were chemically etched on the as-grown (virgin) surface and the C-face (sliced side). The etching of both the surfaces revealed a strong relationship between a variety of etch pits and the morphological features of the grown boule surface. Several types of etched patterns were revealed. On the Si face, we observed small, medium, and large hexagonal shaped pits and a linear array of small etch pits. However, the C face contained only small pits and a linear array of small pits. We observed individual or group of dislocations that were connected from the Si face to the opposite C face of the wafer. Also, etch pit lines oriented along specific crystallographic directions were seen. Our experimental observations have provided a physical basis to explain the generation of defects in SiC. An analysis of our observations show that a correlation exists between the distribution of different size etch pits and the condition of the crystal growth process.
INTRODUCTION Based on the recently published literature, high dislocation density is characteristic of silicon carbide (SiC) crystal wafers grown by the seeded sublimation method (modified Lely). There are several powerful techniques to observe these defects, including transmission topography (Langue method), back reflection (Berg-Barrett), double-crystal topography, synchrotron white beam x-ray topography, and traditional molten KOH etching. Lebedev et al studied the dislocation structure of commercially available silicon carbide crystals [1]. Kuznetsov carried out the same investigation on the Lely samples [2]. Based on their results, the density of base dislocations for the Lely crystals were found to be two orders of magnitude lower than the modified Lely crystals (≤ 105 cm-2). According to the published literature, generation of dislocations in SiC crystals is mainly due to thermal stress introduced in the bulk during crystal growth. According to the results from calculations reported by Tairov et al and Müller et al [3, 4], it can be concluded that the generation of dislocations is due to increased thermo elastic stress introduced to the grown crystal during the cooling process.
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RESULTS AND DISCUSSION In order to investigate the distribution of dislocations on the silicon as well as the carbon face of SiC specimens, a gaseous selective etching process has been developed. Figure 1 shows
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20 µm
A- Silicon Face
B- Carbon Face
Figure 1: Micrographs of the faces of a 6H- SiC sample after selective etching. the micrographs of a specific area of the silicon and carbon faces (6H- sample) after the etching process. For the fi
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