Hello all,

               I am facing problems with the release of cantilevers
(220X110X1) microns through bulkmicromachining(BMM). I am using a P (100)
wafer with wafer flat in <110> direction. My cantilevers are placed
perpendicular to the wafer flat. I am making a pit of 240 microns initially
and fabricate the cantilever stack on the other side. Final release of
cantilevers is through bulkmicromachining through those pits. Everything is
according to the plan except silicon remaining at the bottom of the
cantilevers . All the portions surrounding the cantilevers are through and
through (as per plan) but beneath the cantilever some portion of Si is
forming an acute angle starting from the base of the cantilever. i tried to
eliminate this Si by over etching but the Si forms an acute angle very sharp
which is breaking cantilevers. I guess the etch induced stresses at the
sharp corner is one of the reason for the breaking of cantilevers.
cantilever stack is made of Oxide /poly/nitride. It may happend that
cantilevers  may develop thermal stresses while deposition and becaome very
weak sothat they are not compatiable with over etching. I am excited to know
the etch profile and charecterstics of Bulk micromachining using TMAH. The
question is when i am allowing TMAH to attack only the portions where Si is
exposed, it is doing the same but it is not eating away the Si on the
cantilever. It may be etching the Si ( because the Si remaining is only 15
microns) but not completely as the sarrounding area. For free release of
cantilevers ther should be no Si present. Never the less the concentration
of TMAH is 10% and Temperature 90 o C. Please suggest me some solution
because in all 5 runs i had the same problem.

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Thanks and Regards
M. Naresh