Evaluation of electrical linewidth determination using Cross-Bridge and Multi-Bridge test structures

The Multi-Bridge method is often used in the industry to measure electrical linewidths of interconnect lines because it requires less sensitive equipment than the standard Cross-Bridge method. The method assumes that the linewidth process bias is independent of design width, which is shown here to be only approximately correct. This can result in linewidth determinations that are significantly different from the values obtained by the Cross-Bridge method. This is observed most often at the narrower designed widths. A Composite method is described that minimizes these differences. The multi-bridge test structure can also be used to detect the linewidths at which chemical mechanical polishing (CMP) induces `dishing' effects in copper lines.