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High-K materials and metal gates for CMOS applications

Accepted version
Peer-reviewed

Repository DOI


Type

Article

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Authors

Robertson, John 
Wallace, Robert M 

Abstract

The scaling of complementary metal oxide semiconductor (CMOS) transistors has led to the silicon dioxide layer used as a gate dielectric becoming so thin that the gate leakage current becomes too large. This led to the replacement of SiO2 by a physically thicker layer of a higher dielectric constant or ‘high-K’ oxide such as hafnium oxide. Intensive research was carried out to develop these oxides into high quality electronic materials. In addition, the incorporation of Ge in the CMOS transistor structure has been employed to enable higher carrier mobility and performance. This review covers both scientific and technological issues related to the high-K gate stack – the choice of oxides, their deposition, their structural and metallurgical behaviour, atomic diffusion, interface structure, their electronic structure, band offsets, electronic defects, charge trapping and conduction mechanisms, reliability, mobility degradation and oxygen scavenging to achieve the thinnest oxide thicknesses. The high K oxides were implemented in conjunction with a replacement of polycrystalline Si gate electrodes with metal gates. The strong metallurgical interactions between the gate electrodes and the HfO2 which resulted an unstable gate threshold voltage resulted in the use of the lower temperature ‘gate last’ process flow, in addition to the standard ‘gate first’ approach. Work function control by metal gate electrodes and by oxide dipole layers is discussed. The problems associated with high K oxides on Ge channels are also discussed.

Description

Keywords

High K oxide, Gate oxide, HfO2, Field effect transistor, CMOS

Journal Title

MATERIALS SCIENCE & ENGINEERING R-REPORTS

Conference Name

Journal ISSN

0927-796X
1879-212X

Volume Title

88

Publisher

Elsevier BV
Sponsorship
Engineering and Physical Sciences Research Council (EP/I014047/1)
RMW acknowledges an IBM Faculty award and JR acknowledges funding from EPSRC.