Poly Shield To Prevent Dendritic Growth
Original Publication Date: 2002-Jan-07
Included in the Prior Art Database: 2002-Jan-07
Brad Smith: AUTHOR [+1]
This invention is the use of dummy gate poly shapes to shield the edges of wells from ambient light, which could cause dendritic growth to occur. The shapes would need to be fairly wide and follow some portion of the well junction
Poly “Shield” To Prevent Dendritic Growth
Brad Smith & Ed Travis
This invention is the use of dummy gate poly shapes to shield the edges of wells from ambient light, which could cause dendritic growth to occur. The shapes would need to be fairly wide and follow some portion of the well junction.
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 electrolytic 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 control or eliminate them is critical.
Placing a poly shape over the well junction blocks a significant portion of the light, which in turn reduces the photocurrent generated. This significantly reduces the amount of dendritic growth. Not all of the junction needs to be covered. The purpose is to reduce, but not necessarily eliminate, the amount of light hitting the junction.
The same trick could be applied to large field areas of the well, thus reducing the photocurrent generated by the bottom well junction.