Designs for minimizing resistive substrate effects on wafer metallization

Two design concepts for reducing spatial variations in the thickness of electrodeposited thin copper films on 300-mm (∼ 11.8-in.) wafers are explored by numerical simulation. One design employs a strategically positioned current shield and the other employs a ring-disk anode with the ability to control the ring-disk potential difference. Both designs are intended to modify the potential field in the electrolyte to compensate for significant potential variations in the resistive substrate. The influence of the ratio of the initial seed-layer thickness to the electrolyte conductivity is shown to be an important parameter in determining the design of the electrochemical cell. The two cell designs are also considered within the context of practical limitations.