Hello,
        I have done some etching ( isotropic ) on Si with HNO3 (63%)&
HF(49.3%) mixture and using DI H20 as diluent. On certain occasions it was
observed that there were blackish-brown marks ( like charring ) on the
wafer. This wafer was P-type. Also if the etching was done using glacial
ascetic acid as diluent then on no ocassion were these brown marks
observed. Also these marks were not consistently observed even in the H2O
diluent recipe.
        I would appreciate if anybody could give me any references or
suggestions about the cause of this phenomenon. Classic recipe handbooks
like Ghandhi, Donovan & Burger etc. do not mention any such phenomenon.
        Note that even in the case of glacial ascetic acid as the diluent,
some places(where water droplets were retained)  were charred in the step
where etching was stopped by a dip in DI water.

Thanking you all in advance

Regards
Amit Shiwalkar

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Amit Shiwalkar                         Dept. Of Bio-Medical Engineering.
3,Vasant,                              IIT Bombay.
Carter Road,                           Powai, Bombay-400076
Khar,
Bombay(Mumbai)-400052
INDIA.


                     Email: amits@cc.iitb.ernet.in

" Reality Is a Figment of IMAGINATION "
                                ----------- Amit Shiwalkar

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