Hi,Aslam

I experimented with TMAH etching last year. The same problem appeared at that
time.

As the silicon wafer was etched, more pyramidal hillocks were found on the
surface. They not only affect the roughness of the etched surface, but also
prevent the following etching. The etching seems to be negligible when hillocks
become more and more.

The available solutions are to increase the etching temperature, add some strong
oxidizers and lower the solution concentration of TMAH water. In addition,
please note that first, the solution has to be stirred magnetically during the
etching; secondly, TMAH solution tends to volatile.

At last I think too long etching time is not suitable for TMAH solution. Maybe
you alternate another kind of etchants.

Good luck

Zhu Xiaorui
China,People's Republic

            zhuxiaorui
            zhuxiaorui@public.cta.cq.cn