Reducing Iron in Single Crystal Silicon Grown Using CZ Process

The metal iron, that is present in graphite hot zone components used in CZ silicon process, contaminates the crystal. To eliminate and reduce contamination, graphite components were coated with two protective layers including a first protective layer of silicon carbide and a second protective layer of silicon. The effectiveness of these coatings to prevent iron contamination was tested. At test temperature of 1100{degree sign}C and 900{degree sign}C, the Fe concentrations in the monitor wafer that was exposed to graphite sample with layers of silicon and silicon carbide coating was ten times lower. Several hot zone structural components were coated using this method and were used to grow single crystal silicon. The wafers from these crystals were tested for iron concentrations using standard SPV method and are found to be much lower when compared to wafers from crystals grown using only silicon carbide coated graphite components.

Source:IOPscience

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Characterization of Crystal Quality by Crystal Originated Particle Delineation and the Impact on the Silicon Wafer Surface

Characterization of Si wafers by delineation of crystal originated particles (COP) provides insight into size and radial distribution of crystal related defects. A good correlation of the COP densities with gate oxide integrity and flow pattern defect densities is observed. The density and size distribution of COP in Czochralski Si ingots can be modified by the pulling rate and the cooling conditions of the crystal and is further influenced by high doping concentrations. The COP densities are comparable on wafers with (100) Si and (111) Si orientation as well as on p‐ and n‐type wafers with moderate doping level. No COP are found on float zone (FZ) and on epitaxially grown wafers. Crystal defects are also delineated by chemomechanical polishing and can be detected on the wafer surface as light point defects (LPD). LPD densities, however, do not necessarily correlate with the corresponding COP densities after SC1 treatment and do not reflect the quality of the crystals because polishing delineates only part of the larger crystal defects to a size which is above the detection limits of commercially available scanning surface inspection systems. High temperature annealing results in reduction of defect sizes and partial dissolution of COP. Investigations of FZ and oxygen doped float zone indicate that oxygen is participating in the formation of COP.

Source:IOPscience

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Relationship between Basal Plane Dislocation and Local Basal Plane Bending in PVT-Grown 4H-SiC Crystals

Synchrotron monochromatic beam x-ray topography (SMBXT) shows black and white contrast of BPDs for Burgers vectors of opposite signs based on the principle of ray tracing. We have evaluated the ratio of black and white contrast of BPDs along both [1120] and [1100] directions across multiple 4-inch and 6-inch diameter 4H-SiC substrates. Results show the predominance of white contrast BPDs along both radial directions indicating that the basal planes on Si face are bent in a convex manner. Line scans of 0004 reflection using HRXRD was carried out which further confirmed the nature of basal plane bending in these wafers. Detailed analysis on the subsequent wafers across the crystal boule reveals the inheritance of basal plane bending behavior in these wafers. The radius of curvature in 6-inch wafers was found to be larger than the 4-inch wafers. Additional studies on the effect of low angle grain boundaries were also discussed.

Source:IOPscience

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Characterization of Crystal-Originated Particles in Silicon Nitride Doped, CZ-Grown Silicon Wafers

Grown-in crystal-originated particles (COPs) on the surface of silicon nitride-doped Czochralski (CZ)-grown silicon wafers were characterized using atomic force microscopy and scanning electron microscopy. These nanometer-scale COPs are categorized into kite-shaped, parallelepiped-plate and needle-shaped COPs, respectively, with unique features distinctively different from the octahedral voids commonly found in conventional CZ-grown silicon wafers. Based on the experimental data obtained, it is postulated that nitrogen dopants in the silicon crystals could influence the formation of these COPs with different morphologies and sizes. This may be supported by a simple analysis of the mapping distribution of COPs on the nitride-doped CZ-grown silicon wafer, which reveals that the densities of the smaller-size parallelepiped-plate and needle-shaped COPs are negligible at the center of the silicon wafer but increase to a significant proportion comparable to that of the kite-shaped COPs at the outer edges of the silicon wafer along the radial directions. These observations are thought to correlate well with the presence of nitrogen dopants and the radial concentrations of the excess free vacancy.

Source:IOPscience

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