What are the residual dopant striation and doping fluctuation in current Czochralski grown 200mm silicon wafers used for standard microelectronics circuits?
Any information and/or reference on amplitude as well as length scale of fluctuations is welcome. (NB: I am aware of FZ wafers or doping by transmutation, my question doesn't address these materials). Many thanks.
Dear Vincent,
spatial doping concentration variations in the crystalline silicon wafers are natural because the thermal random motions of the dopant atom in the silicon melt during crystallization. In addition there exist nonhomogeneous temperature distributions and temperature gradients basically in the axial pulling direction and also along the radial direction because of the heat radiation from the crystal and melt surface.
It is so, that there exists long term variation beside the statistical thermal variations of the doping density. The long term doping density variations causes striations when polishing silicon with slightly preferential etching solution. It is in form of nearly periodic rings.
You can your self measure the spatial doping density by the method of the spreading resistance. It is simple and straight forward. There also other measuring method such as the CV of the MOS capacitor arrays made on wafer.
I think the data which you need can be found in the paper at the Link: http://sun.anu.edu.au/files/publishedonlinenew.pdf
Best wishes
Dear Sir, we have found (confirming previous results of Murgai ... Fukuda ...) that the growth striations in 200mm Silicon (for PV application) can be clearly correlated to the interstitial oxygen concentration (usually to measure by FTIR Absorption microscopy). These fluctuation are more pronounced in undoped material than in doped one. This difference can also be observed by spreading resistance ... stress-induced birefringence, lifetime .... My best regards, Martin Herms.
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