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Optical lithography is key to enabling the technologies we use daily, driving increased performance while maintaining affordability. This is largely due to the ability of optical lithography to transfer trillions of mask features to wafers at defect densities approaching virtually zero in high-volume manufacturing (HVM). The talk will begin with a comprehensive overview of how state-of-the art cell architecture choices affect pitch scaling. For instance, there is a widely-held misconception that novel cell architectures such as transistor stacking deliver cell size scaling without the need for (interconnect) pitch scaling. However, since the number of terminals or interconnects increases with the number of gates, transistor stacking still requires continued pitch scaling. The talk will then focus on the four major challenges state-of-the-art patterning has to meet and recent progress made in these areas: (i) ability to print tight-pitch features, (ii) ability to accurately align tight-pitch features, (iii) ability to deal with pattern variations induced by photon and resist stochastics, and (iv) ability to enable flexible design rules. While EUV lithography with NA 0.33 can now routinely print sub 30 nm pitch patterns and EUV high-NA micro exposure tools print sub 20 nm pitch patterns, variations in the critical dimensions (CD) caused by photon and resist stochastics require not only continued innovation in photoresist design but also complementary lithographic approaches. One example for a powerful complementary lithography technique is directed self-assembly (DSA). DSA produces dense, periodic features with low defect numbers and with pattern uniformity not readily achieved by optical lithography alone. DSA offers a fundamental advantage over optical lithography since the line and space CDs are chemically encoded into each molecule with unprecedented accuracy. We will report on recent progress made for a process flow based on DSA that rectifies complex, multi-pitch and multi-CD EUV patterns and the focused, decade-long material and process flow development required to achieve HVM-grade materials, low integrated defects and compatibility with standard design rules. The talk will conclude with an appeal and challenge to academia and research consortia alike to vigorously pursue material and patterning innovation that complements optical lithography. Novel complementary patterning approaches such as DSA, if properly resourced and developed, will ensure that Moore’s Law scaling will continue in the foreseeable future.
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