|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.|
|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.
|The lowest concentration given in the table (look for it) is 5 · 1010 cm–3 ; it corresponds to 1 ppt or 10–12.|
|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.
|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?
|Here is a link
with precise defininitioons of geometricla parameters: |
6.1.2 Silicon Crystal Growth
The Science and Art of Si Crystal Growth
© H. Föll (Electronic Materials - Script)