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Silicon-filled trenches for bipolar device isolation can be mo reliably and simply capped beneath crossing metal conductors by forming the cap with tetraethoxysilane (TEOS) oxide.
English (United States)
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Trench Cap Formation
Silicon-filled trenches for bipolar device isolation can be mo reliably and
simply capped beneath crossing metal conductors by forming the cap with
tetraethoxysilane (TEOS) oxide.
After a trench is lined with a silicon dioxide/nitride composite and filled with
either epitaxial silicon or polysilicon, the subsequent planarization leaves the
silicon slightly below the wafer surface. The trench silicon is further slightly
recessed up to a half micron depending on trench width. Oxide by the TEOS
process is added to the trench silicon and any excess is removed down to the
nitride layer on the device surface.
The formed trench cap does not have a closing seam due to its smaller
thickness relative to half the trench width. Subseque annealing at 900oC in
steam densifies the TEOS and grows oxide beneath it. The oxide can be grown
to the necessary thickness without inherent stress that accompanies other
processes Trench sides are protected from further oxidation by a nitride layer in
the previously formed side wall so that this cap can be used where device
structures butt the trench.