Status of Large Diameter SiC Single Crystals

Large SiC single crystals, semi-insulating and n-type, up to 150mm in diameter are grown by II-VI Incorporated. In addition to the recent product launch of 150mm substrates, significant improvements have been made in crystal quality. The values of FWHM of x-ray rocking curves are typically 15-30 arc-seconds for 4H SI wafers and 11-25 arc-seconds for 4H n+ wafers. We have achieved 150 mm wafers free of stacking faults and micro pipes with total dislocation density of 2x103 cm-2, TSD density of ~3x102 cm-2, and BPD density of 2x102 cm-2. For semi-insulating wafers we have achieved resistivities in excess of 1E11Ω-cm.

Source:IOPscience

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Laser recovery of grinding-induced subsurface damage in the edge and notch of a single-crystal silicon wafer

The edges and notches of silicon wafers are usually machined by diamond grinding, and the grinding-induced subsurface damage causes wafer breakage and particle contamination problems. However, the edge and notch surfaces have large curvature and sharp corners, thus it is difficult to be finished by chemo-mechanical polishing. In this study, a nanosecond pulsed Nd:YAG laser was used to irradiate the edge and notch of a boron-doped single-crystal silicon wafer to recover the grinding-induced subsurface damage. The reflection loss and the change of laser fluence when irradiating a curved surface were considered, and the damage recovery behavior was investigated. The surface roughness, crystallinity, and hardness of the laser recovered region were measured by using white light interferometry, laser micro-Raman spectroscopy, and nanoindentation, respectively. The results showed that after laser irradiation the damaged region was recovered to a single-crystal structure with nanometric surface roughness, and the surface hardness was also improved. This study demonstrates that laser recovery is a promising post-grinding process for improving the surface integrity of the edge and notch of silicon wafers.

Source:IOPscience

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The Effect of the Crystal Grown‐in Defects on the Pause Tail Characteristics of Megabit Dynamic Random Access Memory Devices

The effect of the crystal grown‐in defects on the pause tail characteristics of megabit dynamic random access memory devices was investigated. By comparing the performance of the devices fabricated on epitaxial silicon wafers with those fabricated on polished Czochralski silicon wafers, it was found that the refresh time of the memory devices fabricated on a polished silicon wafer is strongly affected by the crystal grown‐in defects. Based upon the present results, the refresh time failure of the memory devices could be attributed to several types of crystal defects which include the D‐defects produced as a result of vacancy aggregation during crystal growth and those associated with oxygen precipitation.

Source:IOPscience

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Defects in Silicon Crystals and Their Impact on DRAM Device Characteristics

Polished p-wafers from vacancy-rich silicon crystals are used as substrates for many device applications and, in particular, for memory devices. Octahedral vacancy aggregates, the so-called crystal originated pits, are found in these wafers with sizes of 150 nm and densities of  To meet the design rule requirements of 0.13 μm and below, a reduction of defect size and density is required. The approaches to achieve silicon with nearly no intrinsic point defect aggregates are the growth of so-called perfect crystals, the growth of nitrogen-doped crystals with very fast cooling rates and subsequent high temperature wafer annealing, and epitaxy of wafers. In addition, new concepts like wafers with a thin refinement layer grown on a cost and bulk optimized substrate (so-called fLASH! wafers) will allow further cost reduction. © 2002 The Electrochemical Society. All rights reserved.

Source:IOPscience

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