Dear all,

I was performing TMAH etching of silicon on one of my
devices that has Al on it.I was following the process
given in "An Improved TMAH si-etching solution without
attacking exposed Aluminum",Guizhen Yan
et,al,Proceedings of the IEEE Micro Electro Mechanical
Systems (MEMS), 2000, p 562-567.


This paper explains that with the addition of adequate
amounts of silicon(1.6%) and Ammonium peroxy
disulphate(APODS)[0.5%] in 5%TMAH solution can give
good protection on Al and good surface smoothness.

After i performed the process given in the paper,i
could get good protection from Al.But after sometime
the surface roughness increased drastically and
resulted in slow etch rate of silicon.I presume that
this roughness is due to depletion of APODS in the
solution for which extra APODS is needed to be added
to make up for the lost amount of APODS in the
solution.

This paper did not explain about addition of some
quantity of APODS to be added at regular intervals of
time.

If someone is familiar of the TMAH process,please
guide me in this aspect.

I would appreciate your help.

Thanks
Kris

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