Publishing Venue
Motorola
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Abstract
This invention is an electrical test structure capable of detecting the presence of a dendritic growth at a via or metal level. Dendritic growth during Cu polish has been a chronic problem, and can only be detected optically. This structure is a metal comb that is normally open, but that can be shorted when a dendrite grows out from an nwell tie. It allows class probe to catch the problem. Many variations in the nwell design could be drawn, so the phenomenon of dendritic growth can be studied.
Electrical Test Structure to Detect Dendrite Growth
Brad Smith
ABSTRACT
This invention is an electrical test structure capable of
detecting the presence of a dendritic growth at a via or metal level. Dendritic growth during Cu polish has
been a chronic problem, and can only be detected optically. This structure is a metal comb that is
normally open, but that can be shorted when a dendrite grows out from an nwell
tie. It allows class probe to
catch the problem. Many variations
in the nwell design could be drawn, so the phenomenon of dendritic growth can
be studied.
BODY
Dendritic growth can occur during metal polish, particularly
with Cu. Light hitting a large p-n
junction like a well junction creates photocurrent, which can then be conducted
through an electrlytic solution (like those used during polish and/or
scrub). This current causes the
displacement of metal ions from the anode to the cathode, depleting the anode
and forming dendritic growths on the cathode. These can cause both yield and reliability problems so the
ability to detect them is crucial.
This test structure places a structure that is susceptible
to dendritic growth – such as a minimum-area shape of metal or via attached to
a large nwell – between a metal comb.
The comb is normally open, so any leakage between the sides of the comb
can be attributed to dendrites growing out fromt the shape in question and
shorting the combs. Any number of
layouts of the metal shape between the combs and/or the nwell can be d...