Dear all,

I did several experiments with TMAH etching, but I found that, the ER
of TMAH was variable, even on the same wafer.  For example, I was
trying to etch through a 370um thick silicon wafer in 25%TMAH at 85
degree(fresh solution, and typical etch rate is around
30microns/hour).  After 14hours' etching, part of the wafer had been
etched through, but half of them were not.  It happened several times.

Could someone tell me why?

I used wet thermal oxide as mask(1.5 micron thick) and  I am sure that
the exposed oxide had been completely removed after RIE.  Also, the
wafer was prime wafer.

Thanks very much.

Duan