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Here are the specification for Si wafers from one of the worlds top companies, Wacker Siltronic, as they appear in the Internet in Nov. 2000. | |||
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Notice: Concentrations here are in
cm3. The conversion to parts per .. is simple: The atomic density of Si is 4.96 · 1022 cm–3 or about 5 · 1022 cm–3. 1 ppm thus corresponds to 5 · 1016 cm–3. |
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The lowest concentration given in the table (look for it) is 5 · 1010 cm–3; it corresponds to 1 ppt or 10–12. | |||
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Surface concentrations [S]
(given in cm–2) are converted to volume concentrations
[V] by [S] = [V] /a with a = lattice constant (= 0,5431 nm) or, more precise for single crystals, distance between the crystallographic planes. With a » 0,5 nm = 5· 10–8 cm, we have [V] = 5 · 1016 cm–3 = 1 ppm corresponds to S = 108 cm–2. |
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Many specifications relate to the
"flatness" of the wafers and the perfection of the surface; the
abbreviations used are LLS (sometimes also abbreviated LPDs): Localized Light Scattering Defect; this relates to a detection method of sub-µm size surface imperfections (resulting from bulk microdefects) SFQR: Site flatness quality requirements (??): Definitely a measure of flatness in a region comparable to the size of a single chip (The rest: Who knows? |
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Here is a link with precise
defininitioons of geometricla parameters: http://www.freiberger.com/english/products/geom_parameters.php |
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The Science and Art of Si Crystal Growth
© H. Föll (Electronic Materials - Script)
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