Gate dielectrics for advanced semiconductor devices: thermally-grown SiO2 - a very difficult act to follow

摘要

The end of an era has passed, and SiO2 is no longer the gate dielectric of choice for advanced Si devices. This is a direct result of aggressive scaling of the effective oxide thickness, EOT, to below 1.5 nm. 1.5 nm corresponds a physical thickness at which the direct tunneling leakage current for a 1 volt applied bias in excess of flat band exceeds to approximately 1 A-cm'2. This paper provides insights into the reasons why it has proven a formidable challenge to find an alternative dielectric that will significantly reduce the direct tunneling current leakage, whilst at the same time realizing all of the performance and reliability metrics targeted and required for advanced device scaling. Several distinct generations of alternative gate dielectrics are identified, and discussed. Finally, it is demonstrated that scaling of EOT can proceed to at least -0.7 to 0.8 nm in devices utilizing Zr or Hf Si oxynitride gate dielectrics.