You can get a good (but not perfect) estimate of the stress by measuring
the height of the center of the wafer compared to its edges (the wafer
bow).  You can use the Stoney formula, in an excellent book by Milton
Ohring http://www.mat.stevens-tech.edu/faculty/ohring.html (the first
book in his list) to compute the stress from the bow, the wafer and
films' moduli, the thicknesses of the wafer and film, and the diameter
of the wafer.  Be sure to include all stress layers, front and back.
Effects will add at the usual stress levels.
-Steven


Patrick Ping-Chi Lu wrote:

>Hi,
>
>After releasing the substrate for my devices, which are made using SOI
>wafers, the sacrificial oxide layer wants to expand to its "natural size"
>since it was previously held under compressive stress (came that way from
>the vendor). I am trying to quantify the amount of compressive stress in my
>SOI wafers. I also want to know the amount that the oxide layer will expand
>when released. Does anyone have good tips as to where I can find this
>information, such as journal articles or websites? Any help would be greatly
>appreciated!
>
>Thank you!
>Patrick Lu
>
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