Suppression of oxygen vacancy formation in Hf-based high-k dielectrics by lanthanum incorporation

Umezawa, Naoto; Shiraishi, Kenji; Sugino, Shinya; Tachibana, Akitomo; Ohmori, Kenji; Kakushima, Kuniyuki; Iwai, Hiroshi; Chikyow, Toyohiro; Ohno, Takahisa; Nara, Yasuo; Yamada, Keiichi

doi:10.1063/1.2789392

Cited by 71 publications

(60 citation statements)

References 15 publications

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“…These dopants can also improve other MOSFET properties. Umezawa [36] reported that when La was incorporated into HfO 2 , the formation energy of a neutral oxygen vacancy in the vicinity of substitutional La in a Hf site was 0.7 eV larger than that in pure HfO 2 . This was indicative of reduced oxygen vacancy concentration.…”

Section: Dual-dipole Formation In Mos Stackmentioning

confidence: 99%

Interface dipole engineering in metal gate/high-k stacks

et al. 2012

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Although metal gate/high-k stacks are commonly used in metal-oxide-semiconductor field-effect-transistors (MOSFETs) in the 45 nm technology node and beyond, there are still many challenges to be solved. Among the various technologies to tackle these problems, interface dipole engineering (IDE) is an effective method to improve the performance, particularly, modulating the effective work function (EWF) of metal gates. Because of the different electronegativity of the various atoms in the interfacial layer, a dipole layer with an electric filed can be formed altering the band alignment in the MOS stack. This paper reviews the interface dipole formation induced by different elements, recent progresses in metal gate/high-k MOS stacks with IDE on EWF modulation, and mechanism of IDE. high-k dielectrics, metal gate, interface dipole, MOS stack, effective work function Citation:Huang A P, Zheng X H, Xiao Z S, et al. Interface dipole engineering in metal gate/high-k stacks. Chin Sci Bull, 2012, 57: 28722878, doi: 10.1007/s11434-012-5289-6As poly-Si/SiO 2 is replaced by metal gate/high-k stacks in the 45 nm MOS technological node and beyond, the interface becomes more complicated and there are still many challenges to be solved [1,2], such as the flatband voltage shift (V fb shift) [3]. Hence, the properties of the high-k layer must be reconsidered carefully. It has recently been reported that the interface dipole can induce potential difference across the interface and change the band alignment of the MOS stack, and this phenomenon can be exploited to modulate the V fb shift [4][5][6]. Elemental doping can also improve the performance of the high-k layer. Interface dipole engineering (IDE) by varying the dopants or inserting capping layers has attracted much attention in MOS technology. Not only can this technique control the V fb shift, but also the properties of the high-k dielectrics can be improved [7]. This paper reviews the formation of interface dipole, recent research progresses on IDE and effective work function (EWF) modulation, as well as mechanism of IDE in metal gate/high-k MOS stacks. Interface dipole formation in MOS stackTo control the threshold voltage (V th ), work function of a metal gate should be near the conduction band of Si (~4.3 eV) for nMOS and valence band (~5.2 eV) for pMOS. However, only very few metals can satisfy these requirements and furthermore, when a metal is in contact with the high-k layer, its Fermi-level will tend to be at the neutral level of the high-k layer. This phenomenon is called Fermi-level pinning (FLP) which causes EWF of the nMOS (pMOS) to be much greater (smaller) than the corresponding work function in vacuum [8]. The electron density in the metal gate can also influence the EWF [9]. Stacked metal layers used in the gate structure have been investigated. Misra et al. [10] reported that a metal gate stack using Ru-Ta alloys could yield a work function compatible with nMOS. Lin et al. [11] implanted N into a Mo gate that was

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Section: Dual-dipole Formation In Mos Stackmentioning

confidence: 99%

Interface dipole engineering in metal gate/high-k stacks

et al. 2012

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“…The highest peak l eff value was 230 cm 2 /V s at E eff of 0.2 MV/cm for the FETs incorporated with 1 nm-thick La 2 O 3 layer. As the incorporation of La atoms into HfO 2 is reported to reduce the formation of oxygen vacancies [13], the l eff improvement might be attributed to the reduction in the number of defects within the high-k in addition to the improvement of D it . Fig.…”

Section: Resultsmentioning

confidence: 98%

Effects of La2O3 incorporation in HfO2 gated nMOSFETs on low-frequency noise

Zade

Sato

Kakushima

et al. 2011

Microelectronics Reliability

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“…Since La impurities prefer the occupation of Hf lattice sites, 11 we have focused on In Fig. 1(a), schematic sketch of these defects is illustrated.…”

Section: Complex Lanthanum Defect Structuresmentioning

confidence: 99%

“…[7][8][9] In bulk HfO 2 , oxygen related defects are the predominant intrinsic defects. 1,3,[10][11][12][13] For technical reasons, often, additional impurity atoms are incorporated in the gate stack systems. For example, lanthanum impurities are used to adjust the effective work function 14,15 and to improve the overall reliability.…”

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confidence: 99%

Charge transition levels of oxygen, lanthanum, and fluorine related defect structures in bulk hafnium dioxide (HfO2): An ab initio investigation

Leitsmann¹,

Lazarevic²,

Nadimi

et al. 2015

Journal of Applied Physics

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Intrinsic defect structures and impurity atoms are one of the main sources of leakage current in metal-oxide-semiconductor devices. Using state of the art density functional theory, we have investigated oxygen, lanthanum, and fluorine related defect structures and possible combinations of them. In particular, we have calculated their charge transition levels in bulk m-HfO2. For this purpose, we have developed a new scaling scheme to account for the band gap underestimation within the density functional theory. The obtained results are able to explain the recent experimental observation of a reduction of the trap density near the silicon valence band edge after NF3 treatment and the associated reduction of the device degradation.

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Suppression of oxygen vacancy formation in Hf-based high-k dielectrics by lanthanum incorporation

Cited by 71 publications

References 15 publications

Interface dipole engineering in metal gate/high-k stacks

Interface dipole engineering in metal gate/high-k stacks

Effects of La2O3 incorporation in HfO2 gated nMOSFETs on low-frequency noise

Charge transition levels of oxygen, lanthanum, and fluorine related defect structures in bulk hafnium dioxide (HfO2): An ab initio investigation

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