Overlay Control
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Overlay control has always played an important role in semiconductor manufacturing, helping to monitor layer to layer alignment on multi-layer device structures. Misalignment of any kind can cause short circuits and connection failures, which in turn impact fab yield and profit margins.
Overlay control has become even more critical now because the combination of increasing pattern density and innovative techniques such as double patterning and 193nm immersion lithography creates a novel set of pattern-based yield challenges at the 45nm technology node and below. This combination causes error budgets to shrink below 30 percent of design rules, where existing overlay metrology solutions cannot meet total measurement uncertainty (TMU) requirements.
Overlay metrology solutions with both higher measurement accuracy/precision and process robustness are key factors when addressing increasingly tighter overlay budgets. Higher order overlay control and in-field metrology using smaller, micro-grating targets are becoming essential for successful production ramps and higher yields at 45nm and beyond.
One of the widely adopted overlay measurement tools worldwide is KLA-Tencor's ARCHER [1] overlay metrology platform.
