Zeng

We do a lot of Boron diffusion here at the University of Cincinnati. I have had
such problems while doing boron diffusion. The reason the cracks appear is due
to the formation of some sort of boro silicate galss. The ring are formed, but
most cases the rings reduces after an oxidation process The rings dont effect
the charecteristics. We had problems with preserving the field oxide, removing
the boron skin when the diffusion is done at high temperature above 1000 C. The
problems were solved by checking the leaks in sytems. If there is some H2 or
water vapor leak in the system enhances the diffusion of boron in oxide and
silicon. Oxidation of the BN wafer were also done for only 15 mins. While doing
the diffusion a certain percentage of oxygen with nitrogen is also used. if you
have any questions please feel to contact me at pramadas@uceng.uc.edu or call
at (513)-556-4795 and ask for Padmaja.

good luck.