Dear Dr Zeng,
in case you really want to have precise alignment,
there is no other way around than to make an extra
mask and etch the silicon by KOH (TMAH) to fin out the
locatino of the <111> planes. The mask is quite
trivial but it is an extra step.
The other option such as getting precisely made wafers
is fine except the final alignment precision is also
affected by yout litho tool.
Pavel
SiMEMS

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