Hafnium-Based Gate Dielectric Materials

Abstract

In this chapter, we focus on hafnium-based gate dielectrics. HfO 2 is regarded as the most promising material for the high-k gate dielectrics owing to its large dielectric constant and large band-gap energy. In the first part of this chapter, these characteristics are addressed in a comparison with SiO 2 and other high-k materials. Thermal stability is a major issue for the application of high-k materials to MOSFETs in LSIs. Although HfO 2 satisfies this requirement, severer process conditions may cause problems even with this material. Suppression of these issues is also addressed in the second part of this chapter. In order to enhance the characteristics of HfO 2 , transformation of the monoclinic phase to the tetragonal and the cubic phases with larger dielectric constant has been pursued recently. We mention the issue in the last part of this chapter. Introductory Remarks and Brief Outline of the ChapterSince the proposal of the materials in the early 2000s [1-3], hafnium-based gate dielectrics have been regarded as the most promising materials for the application to large scale integrations (LSIs). In 2007, Intel announced the start of manufacturing of 45 nm-node LSIs with high-k/metal gate stack, with the remark that the world's first high-k material in commercial production was hafnium-based [4].There are several characteristics that the high-k materials should meet for the application to metal oxide semiconductor field effect transistors (MOSFETs) in LSIs. First, we clarify the properties so that readers can understand their A. Nishiyama

Selected Success Stories from Twenty Years of High-k Gate Dielectric Research

“…14 is perhaps the best that can be achieved for the interface between covalent Ge and (covalent but also slightly ionic) GeO2 and may remain higher than what obtains for the covalent Si/SiO2 interface (a mid-gap value of below 5X10 10 cm -2 V -1 ). If GeO2 had only electronic polarization, its value of dielectric constant would have been close to that of SiO2, which is 3.9; the extra k is due to ionic polarization (37). To reiterate what has been commented already on the IL (intermediate layer) of the high-k gate stack, it has to a transition layer bridging the covalent channel with the highly ionic high-k layer (higher the value of k -higher is the ionicity or the ionic character (38).…”

Plasma-Enhanced Atomic Layer Deposition of HfO2 with Substrate Biasing: Thin Films for High-Reflective Mirrors

“…Hafnium dioxide (HfO 2 ) is a widely studied dielectric material due to its application in integrated circuits and optics for its high dielectric constant, high refractive index, and low optical losses in the UV spectral range down to 266 nm wavelength. − Hafnia thin films are typically used as a high refractive index material in interference coatings, especially for high-power laser applications. , HfO 2 thin films for optics are deposited mostly by physical vapor deposition (PVD) ,− and chemical vapor deposition (CVD) ,, techniques. Atomic layer deposition (ALD) has gained importance due to the ability to coat wide-area surfaces with excellent uniformity and grow conformal coatings on high aspect ratio nanostructured substrates. − This technology is a subclass of the CVD technique where gas-phase precursors are sequentially introduced into the deposition chamber.…”