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Pushing CMOS Beyond 7nm

August 29, 2017

Author: David Kanter

Leading semiconductor companies agree that FinFETs are the best high-performance transistors for the next couple of nodes and that copper will deliver the right mix of low resistance and reliability for interconnect and via layers. Most manufacturers also agree that scaling these technologies beyond the 7nm foundry node (equivalent to Intel’s 10nm node, which is expected later this year) will be difficult, if not impossible.

Semiconductor manufacturers are researching technologies to replace FinFETs and copper interconnects. The leading candidates for 5nm CMOS (equivalent to Intel’s 7nm node) and beyond are gate-all-around (GAA) transistors and copper interconnects with a more complex and robust barrier. This combination should enable further scaling with good performance. Both of these technologies require big changes to chip manufacturing flows, but they’re evolutionary extensions of the current approaches.

Whereas a FinFET wraps a gate around the transistor channel on three sides, a GAAFET surrounds the channel on all four, increasing the control of electron flow from source to drain. This tighter control should enable lower-voltage operation, albeit at higher manufacturing cost. Samsung has already committed to a variant of GAAFETs for its 5nm process, which is due to enter production in 2020. IBM’s research alliance also identified potential replacements for copper interconnects, using tantalum-nitride (TaN) barriers. It concluded that copper wiring with a new barrier would offer the best performance, beating out new metals that don’t need barriers.

These and other innovations will sustain scaling for the next five years, but not for all applications. The new transistors and wiring schemes are more expensive than their predecessors, further increasing the cost gap between cutting-edge and mainstream products. High-performance processors will be able to afford the greater performance, power efficiency, and density, but manufacturers must reduce costs to draw other customers.

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