Theoretical study of hafnium oxide as a gate-material for CMOS devices

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" Theoretical study of hafnium oxide as a gate-material for CMOS devices "
Onise Sharia A. A. Demkov

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	54620
Doc. No	:	TL24574
Call number	:	‭3320448‬
Main Entry	:	Onise Sharia
Title & Author	:	Theoretical study of hafnium oxide as a gate-material for CMOS devices\ Onise Sharia
College	:	The University of Texas at Austin
Date	:	2008
Degree	:	Ph.D.
student score	:	2008
Page No	:	120
Abstract	:	The continual downscaling of the thickness of the SiO 2 layer in the complementary metal oxide semiconductor (CMOS) transistors has been one of the main driving forces behind the growth of the semiconductor industry for past 20-30 years. The gate dielectric works as a capacitor and therefore the reduction in thickness results in increase of capacitance and the speed of the device. However, this process has reached the limit when the further reduction of the SiO 2 thickness will result in a leakage current above the acceptable limit, especially for mobile devices. This problem can be resolved by replacing SiO2 with materials which have higher dielectric constants (high-k). The leading candidates to replace SiO 2 as a gate material are hafnium dioxide and hafnium silicate. However, several problems arise when using these materials in the device. One of them is to find p and n type gate metals to match with the valence and conduction band edges of silicon. This problem can be rooted in lack of our understanding of the band alignment and its controlling mechanisms between the materials in the gate stack. Theoretical simulations using density functional theory can be very useful to address such problems. In this dissertation present a theoretical study of the band alignment between HfO 2 and SiO 2 interface. We identify oxygen coordination as a governing factor for the band alignment. Next, we discuss effects of Al incorporation on the band alignment at the SiO2 /HfO2 interface. We find that one can tune the band alignment by controlling the concentration of Al atoms in the stack. We also perform a theoretical study of HfO2 /Metal interface in case of Rh. We identify Rh as a good candidate for a p-type gate metal due to its large work-function and the low oxidation energy. Finally, we report a study of the stability of oxygen vacancies across the gate stack. We model a gate stack composed of n-Si/SiO 2 /HO2 /Rh. We find that oxygen vacancies are easier to create in SiO2 than in HfO 2 . Also, vacancies in HfO2 modify the band alignment, while in SiO2 they have no effect.
Subject	:	Pure sciences; High-k; Hafnia; Silica; DFT; Ab-initio; CMOS; Gate dielectrics; Condensation; 0611:Condensation
Added Entry	:	A. A. Demkov
Added Entry	:	The University of Texas at Austin