Electrical Test Structure to Detect Dendrite Growth

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...