Examination of flatband and threshold voltage tuning of HfO2∕TiN field effect transistors by dielectric cap layers

Guha, Supratik; Paruchuri, Vamsi; Copel, M.; Narayanan, V.; Wang, Y. Y.; Batson, Philip E.; Bojarczuk, N. A.; Linder, B.; Doris, B.

doi:10.1063/1.2709642

Cited by 102 publications

(68 citation statements)

References 10 publications

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“…It has recently been reported that Hf-based high-k materials doped with rare earth elements can induce a dipole layer and modulate V fb in nMOS. Guha et al [22] Figure 5(b), when the thickness of the La 2 O 3 is small (from 0.11 to 0.27), V fb also shifts to a negative direction. It implies that the V fb shift with La incorporation is not induced by the fixed charges.…”

Section: Fb Modulation With Rare Earth Doping In Nmosmentioning

confidence: 99%

“…La substitution of Hf forms a negatively charged defect ( Hf La ) and a positively charged oxygen vacancy defect to ensure charge neutrality. When there are two kinds of defects in the interface between the high-k layer and Si, a dipole forms [22]. The interface dipole model has been investigated using rare earth doped Hf-based high-k nMOS [7,26,27].…”

Section: Fb Modulation With Rare Earth Doping In Nmosmentioning

confidence: 99%

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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: Fb Modulation With Rare Earth Doping In Nmosmentioning

confidence: 99%

Section: Fb Modulation With Rare Earth Doping In Nmosmentioning

confidence: 99%

Interface dipole engineering in metal gate/high-k stacks

et al. 2012

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“…An Ov model is also frequently invoked to explain the n-type flat band (FB) voltage shift in metal-oxide-semiconductor (MOS) structures [62,63]. The idea is that negatively charged interfacial substitution states tend to give rise to the formation of a positively charged Ov nearby or in the bulk in order to conserve the charge neutrality; and if the centroids of negative and positive charges do not coincide, a net dipole is created that modulates the system Fermi energy.…”

Section: Ov Formation Energies In Ta2o5 and Tio2mentioning

confidence: 99%

Identifying and Engineering the Electronic Properties of the Resistive Switching Interface

Hong

Zhang

Shi

2015

Journal of Elec Materi

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We study the electronic structures of TiO2/Ti4O7 and Ta2O5/TaO2 interfaces using the screened exchange (sX-LDA) functional. Both of these bilayer structures are useful infrastructures for high performance RRAMs. We find that the system Fermi energies of both interfaces are just above the conduction band edge of the corresponding stoichiometric oxides. According to the charge transition levels of the oxygen vacancies, the oxygen vacancies are stabilized at the -2 charged state in both Ta2O5 and TiO2. We propose to introduce interfacial dopants to shift the system Fermi energies downward so that the +2 charged oxygen vacancy can be stable, which is important for the controlled resistive switching under the electrical field. Several dipole models are presented to account for the ability of Fermi level shift due to the interfacial dopants. IntroductionMetal oxides have been widely used in the emerging nonvolatile memory technologies like the resistive random access memory (RRAM) [1,2] and the memristor [3][4][5]. Both of these devices are characterized by the reversible resistance switching (RS) which is commonly due to the growth and rupture of the conducting filaments (CFs) consisting of charged oxygen vacancies (Ov) [6][7][8]. Numerous reports have been published on metal oxides operating through this RS mechanism like TiO2 [9,10], Ta2O5 [11], SrTiO3 [12], NiO [13,14], and so on. Among various oxide candidates, TiO2 demonstrates both unipolar [9,10] and bipolar [15,16] RS. Transmission electron microscopy of the unipolar RS TiO2 has suggested that the CFs in unipolar switching are composed of Magneli phase Ti4O7 [10]. Recently, real time identification of the evolution of Ti4O7 CFs in TiO2 has been reported [17]. However, the problem of TiO2 is the co-existence of more than one stable substoichiometric Magneli phases which is unfavorable for long device endurance [18]. On the other hand, Ta2O5 keeps the longest endurance record among these oxides [11] and it operates in a bipolar manner. The long endurance of Ta2O5 based devices is partly attributed to only one stable substoichiometric phase, Ta, under 1000°C [18] despite of large amount of metastable substoichiometric phases such as TaO2. The in situ observation of CFs in Ta2O5 has recently been reported [19].One of the biggest challenges of these oxide based devices is the requirement for the electroforming process [20,21]. This could induce physical damages to the device due to oxygen gas release [22]. Besides, wide variance of device properties depends on the details of the electroforming which are yet to be understood. Therefore, it is essential to achieve electroforming free RS so as to eliminate the device variance for applicable computer circuits [20,21].

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“…An alternative way to control the band alignment (and the threshold voltage) would be to develop a gate stack where one can effectively modify the position of the Fermi level of the metal [6,7]. Experimental attempts of adjusting the Fermi level include doping the gate dielectrics stack, which includes an HfO 2 -based film and a thin layer of SiO 2 (which either spontaneously forms at the interface with the Si substrate or is intentionally grown), with metal ions.…”

Section: Introductionmentioning

confidence: 99%

“…In particular, group III metals have been suggested to modify the interfacial dipole. For example, La has been used for the n-type silicon field effect transistors (FETs) [6,[8][9][10][11] and Al for the p-type FETs [7,[12][13][14][15][16][17]. The doping can be achieved, for instance, via the ion diffusion from a thin metal oxide capping layer deposited on top of the HfO 2 -based dielectric.…”

Section: Introductionmentioning

confidence: 99%

Band alignment at the SiO2/HfO2interface: Group IIIA versus group IIIB metal dopants

Luo

Bersuker²,

Demkov

2011

Phys. Rev. B

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Abstract:Using density functional theory we examine the effect of Al and La incorporation on the electronic properties of the interface in the SiO 2 /HfO 2 high-k gate stacks recently introduced into the advanced modern field effect transistors. We show that La and Al doping have opposite effects on the band alignment at the SiO 2 /HfO 2 interface: while the Al ions, which substitute preferentially for Si in the SiO 2 layer, promote higher effective work function (EWF) values, the substitution of La for Hf decreases EWF. The analysis of the electronic structure of the doped interface suggests a simple relation between the electronegativity of the doping metal, screening properties of the interfacial layer and the band offset, which allows predicting qualitatively the effect of the high-k gate stack doping with a variety of metals on its EWF.

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Examination of flatband and threshold voltage tuning of HfO2∕TiN field effect transistors by dielectric cap layers

Cited by 102 publications

References 10 publications

Interface dipole engineering in metal gate/high-k stacks

Interface dipole engineering in metal gate/high-k stacks

Identifying and Engineering the Electronic Properties of the Resistive Switching Interface

Band alignment at the SiO2/HfO2interface: Group IIIA versus group IIIB metal dopants

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