Metrology and Process Control Challenges for 10nm and 7nm Multi-Patterning Nodes
With the delay of EUV lithography extending beyond the 10nm and 7nm nodes chip makers must rely on complex multi-patterning technologies. Conventional patterning errors, such as overlay, CD, and films are becominge more challenging, and in addition these errors become convolved with one another in advanced multi-patterning. Variability is the enemy of patterning where non-lithography errors dominate. Precise process control both inside and outside the litho cell are critical for meeting patterning requirements. At R&D, measuring and controlling at every process step is essential. This, combined with an intelligent combination of feed forward and feed-back are required for pattern control. This presentation includes recent examples of how advanced fabs have incorporated innovative metrology and process control to reduce variability. For example, traditionally reducing overlay errors relied on improving lithography scanner performance. However, process induced overlay errors from outside the litho cell can be the dominant source of correctable error. Using high-resolution wafer geometry measurements, process steps that are major contributors to down-stream overlay can be identified and -corrected.
Ultimately, innovative wafer processing correction can be fed forward to the litho cell for further process control improvements. Another example of improved metrology and process control, in the litho cell, pertains to the precision limits of CD-SEM metrology. CD and profile uniformity requirements for advanced nodes have challenged CD-SEM metrology both in the case of scanner qualification and in-line monitor and control. Optical CD metrology has gained adoption due to superior precision, but has had challenges due to long time-to-results and robustness to process variation. New algorithms overcome both limitations providing superior accuracy and robustness to process variation enabling focus, dose, and CD metrology and process control with a single technology. At the same time, these new algorithms or measurements must improve cost of ownership of all the steps involved in patterning, and specifically litho. Other recent examples of improved metrology and process control will be discussed. Where every nanometer counts, process control inside and outside the litho cell is critical for success. Measuring and controlling at every step is essential, enabled by the intelligent combination of feed forward and feed-back.