Circuit designs are becoming denser and more complex in advanced semiconductor process technologies. The foundry process windows are becoming smaller and smaller which increases sensitivity to wafer surface defects. These defects should be detected early to resolve the root causes and eventually help to improve the yield. Wafer defects are still often inspected manually while the defect counts can reach into the millions. It takes a long time to analyze and review the results while the identification of the root causes may be less accurate and buried in noise. In this paper, UMC advance research teams, in collaboration with the Cadence DFM team, utilized the Pegasus Computational Pattern Analytics (CPA) software to develop an enhanced inspection flow. This flow includes defect data preprocessing, classification, filtering, and reduction of huge data volumes to create visible and easy to review results. By finding more accurate root causes, we could reduce process develop time and finally improve wafer yields.
KEYWORDS: Chemical mechanical planarization, Copper, Metals, Systems modeling, Data modeling, Oxides, Calibration, Performance modeling, Back end of line, Process modeling
As we move to more advanced nodes, the number of Chemical Mechanical Polishing (CMP) steps in semiconductor processing is increasing rapidly. CMP is known to suffer from pattern dependent variation such as dishing, erosion, recess, etc., all of which can cause performance and yield issues. One such yield issue seen in back end of line (BEOL) Cu interconnect CMP processes is pooling. Pooling exists when there is uncleared bulk Cu and/or barrier residue remaining after final CMP step, leading to shorts between neighboring interconnect lines. To detect potential pooling locations on a given design, for a given CMP process, predictive CMP models are needed. Such models can also aid in CMP process and chip design optimizations. In this paper we discuss how a pattern dependent CMP effect that we call the “local neighborhood effect” causes large recesses that can lead to pooling in Cu interconnect CMP processes. We also discuss modeling this effect as part of an advanced predictive CMP modeling system and show how the resulting modeling system accurately predicts Cu pooling on several 14 nm designs.
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