Selecting Alternative Metals for Advanced Interconnects

TL;DR

This paper reviews the challenges of interconnect scaling in advanced CMOS circuits and discusses the selection criteria and current research on alternative metals to copper for future interconnects.

Contribution

It provides a comprehensive overview of the fundamental criteria for benchmarking and selecting alternative interconnect metals, including materials nearing adoption and future research directions.

Findings

Identification of key criteria for metal selection

Review of current alternative materials in research and industry

Discussion of future directions for interconnect metals

Abstract

Interconnect resistance and reliability have emerged as critical factors limiting the performance of advanced CMOS circuits. With the slowdown of transistor scaling, interconnect scaling has become the primary driver of continued circuit miniaturization. The associated scaling challenges for interconnects are expected to further intensify in future CMOS technology nodes. As interconnect dimensions approach the 10 nm scale, the limitations of conventional Cu dual-damascene metallization are becoming increasingly difficult to overcome, spurring over a decade of focused research into alternative metallization schemes. The selection of alternative metals is a highly complex process, requiring consideration of multiple criteria, including resistivity at reduced dimensions, reliability, thermal performance, process technology readiness, and sustainability. This tutorial introduces the fundamental criteria for benchmarking and selecting alternative metals and reviews the current state of the art in this field. It covers materials nearing adoption in high-volume manufacturing, materials currently under active research, and potential future directions for fundamental study. While early alternatives to Cu metallization have recently been introduced in commercial CMOS devices, the search for the optimal interconnect metal remains ongoing.