Silicon sample impurities, comparison

Table II. Comparison of Three Silicon Samples Impurities in ppm Weight...

The analysis of semiconductor materials is illustrated in Tables II and III. Table II shows comparison of the Impurity content of a series of silicon samples. These materials are received as chunks (in the case of starting materials) or slices from a crystal. They are cut to the appropriate size and etched for cleaning with high purity acid. The figure Illustrates high sensitivity analysis of three polycry stall ine silicon samples with the -20 material showing natch higher aluminum content than the others. SSMS performs well in this type of comparative analysis. 

NAA is a quantitative method. Quantification can be performed by comparison to standards or by computation from basic principles (parametric analysis). A certified reference material specifically for trace impurities in silicon is not currently available. Since neutron and y rays are penetrating radiations (free from absorption problems, such as those found in X-ray fluorescence), matrix matching between the sample and the comparator standard is not critical. Biological trace impurities standards (e.g., the National Institute of Standards and Technology Standard Rference Material, SRM 1572 Citrus Leaves) can be used as reference materials. For the parametric analysis many instrumental fiictors, such as the neutron flux density and the efficiency of the detector, must be well known. The activation equation can be used to determine concentrations ... 

Burson and Kenner determined the purity of trichlorosilane and silicon tetrachloride with the SF-96 column. DC-LSX-3-0295 tri-fluoropropyl silicone gum was found to be the best for analysing samples of the methylchlorosilanes. Figure 57 shows a chromatogram of a sample of methyltrichlorosilane containing as impurities 0.02% silicon tetrachloride, 0.03% methyldichlorosilane, 0.04% trimethyl-chlorosilane, 0.12% dimethyldichlorosilane, and 0.07% 1,1,3,3,-tetra-chloro-1,3-dimethyldisiloxane. The concentrations of these impurities were determined by comparison of peak areas with standards prepared by adding known amounts of these impurities to methyltrichlorosilane of 99.99% purity. 

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