Metal gate technology for nanoscale transistors—material selection and process integration issues

Abstract

Reduction of the gate length and gate dielectric thickness in complementary metal oxide semiconductor (CMOS) transistors for higher performance and circuit density aggravates problems such as poly-silicon (poly-Si) gate depletion, high gate resistance, and dopant penetration from doped poly-Si gate. To alleviate these problems in nanoscale transistors, there is immense interest in the replacement of the conventional poly-Si gate material with metal gate materials. A metal gate material not only eliminates the gate depletion and dopant penetration problems but also greatly reduces the gate sheet resistance. In this paper, we discuss the material requirements for metal gate CMOS technology and the challenges involved in the integration of metal gate electrodes in a nanoscale transistor. Issues addressed include the choice of metal gate materials for conventional bulk and advanced transistor structures, the physics of the metal–dielectric interface, and the process integration of these materials in a CMOS process.