Hi Changhong Ke
regd. ur querry "Anisotropic etchant of silicon"
most popular Si anisotropic etchant is KOH...but major disadvantage with
KOH is protection of Aluminium (which is generally used for mtz).
i.e why currently most of the people using another Si anisotropic etchant
called TMAH ( tetra methyl ammonium hydroxide) which is not attacking
Aluminium (u can assume, due to very very very  low etch rate of Al).
i do not know the effect of KOH on Tungsten , generally Cr/Au u can use
as masking material in KOH...
in my openion u can perform simple experiment  by dipping ur tungsten
sample in KOH .
Si etch rate is 0.7um/min with 44wt% KOH @70 deg centigrate

with regards
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 Devendra Kr. Maurya
 Scientific Officer
Microelectronics Centre
Advanced Tech. Centre
Dept.of Electronics& ECE
I.I.T Kharagpur- 721302,INDIA
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Phone: 91-3222-281479(O)
Fax  : 91-3222-755303
EMail: dkm@ece.iitkgp.ernet.in
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