Intrinsic Origin of Electron Mobility Reduction in High-k MOSFETs - From Remote Phonon to Bottom Interface Dipole Scattering

Ota, Hiroyuki; Hirano, Akito; Watanabe, Yoshihiro; Yasuda, Naoki; Iwamoto, Kunihiko; Akiyama, Katsuya; Okada, Kenji; Migita, Shinji; Nabatame, Toshihide; Toriumi, Akira

doi:10.1109/iedm.2007.4418864

Cited by 35 publications

(19 citation statements)

References 5 publications

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“…Although a great deal of progress has been made across the community, electron mobility values for HKMG stacks typically fall below the trend for conventional SiO(N)/Poly-Si stacks. The degradation is attributed to intrinsic properties of high-κ, such as soft optical phonons [ 62 ], fixed charges [ 63 , 64 , 65 ], surface roughness [ 19 , 64 ], and interface dipoles [ 66 ]. Figure 10 (a) illustrates impacts of a SiO 2 /HfO 2 /TiN stack on electron mobilities at different effective fields (E eff ).…”

Section: Interfacial Layer Scavenging Approachmentioning

confidence: 99%

“…It has been reported by many researchers that introduction of high-κ dielectrics brings about additional degradation in each E eff regime. In the low E eff regime, fixed charges in the high-κ layer or interface dipoles localized at the IL/high-κ interface cause remote Coulomb scattering (RCS) [ 63 , 64 , 65 , 66 ]. In the middle E eff regime, Fischetti et al predicted that soft optical phonons in high-κ layers can couple with carrier electrons, resulting in remote phonon scattering (RPS) [ 62 ].…”

Section: Interfacial Layer Scavenging Approachmentioning

confidence: 99%

“…The experimental data for remote IL scavenging delineate a straight tradeoff line, which is slightly steeper and shifted downwards from the prediction based on the RPS theory. The deviation is attributable to the additional RCS from the fixed charges [ 65 ] and/or interface dipoles [ 66 ] at the SiO 2 /HfO 2 interface. It is interesting to note that the trend line for the La-induced dipole is identical to that of the intrinsic IL scaling, indicating no additional RCS.…”

Section: Interfacial Layer Scavenging Approachmentioning

confidence: 99%

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Ultimate Scaling of High-κ Gate Dielectrics: Higher-κ or Interfacial Layer Scavenging?

2012

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Current status and challenges of aggressive equivalent-oxide-thickness (EOT) scaling of high-κ gate dielectrics via higher-κ (>20) materials and interfacial layer (IL) scavenging techniques are reviewed. La-based higher-κ materials show aggressive EOT scaling (0.5–0.8 nm), but with effective workfunction (EWF) values suitable only for n-type field-effect-transistor (FET). Further exploration for p-type FET-compatible higher-κ materials is needed. Meanwhile, IL scavenging is a promising approach to extend Hf-based high-κ dielectrics to future nodes. Remote IL scavenging techniques enable EOT scaling below 0.5 nm. Mobility-EOT trends in the literature suggest that short-channel performance improvement is attainable with aggressive EOT scaling via IL scavenging or La-silicate formation. However, extreme IL scaling (e.g., zero-IL) is accompanied by loss of EWF control and with severe penalty in reliability. Therefore, highly precise IL thickness control in an ultra-thin IL regime (<0.5 nm) will be the key technology to satisfy both performance and reliability requirements for future CMOS devices.

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Section: Interfacial Layer Scavenging Approachmentioning

confidence: 99%

Section: Interfacial Layer Scavenging Approachmentioning

confidence: 99%

Section: Interfacial Layer Scavenging Approachmentioning

confidence: 99%

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Ultimate Scaling of High-κ Gate Dielectrics: Higher-κ or Interfacial Layer Scavenging?

2012

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“…The impact of interface dipoles on channel mobility has been pointed out in several papers, e.g., high- k /Si and high- k/ III-V-channel MOSFETs [ 53 , 54 , 55 ]. Actually, electron mobility of direct-contact HfO 2 /Si MOSFET is smaller than that of HfO 2 /SiO 2 /Si stack MOSFET, as shown in Figure 8 (a).…”

Section: Mosfet Characteristics and Channel Mobilitymentioning

confidence: 99%

Study of Direct-Contact HfO2/Si Interfaces

Miyata

2012

Materials

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Controlling monolayer Si oxide at the HfO2/Si interface is a challenging issue in scaling the equivalent oxide thickness of HfO2/Si gate stack structures. A concept that the author proposes to control the Si oxide interface by using ultra-high vacuum electron-beam HfO2 deposition is described in this review paper, which enables the so-called direct-contact HfO2/Si structures to be prepared. The electrical characteristics of the HfO2/Si metal-oxide-semiconductor capacitors are reviewed, which suggest a sufficiently low interface state density for the operation of metal-oxide-semiconductor field-effect-transistors (MOSFETs) but reveal the formation of an unexpected strong interface dipole. Kelvin probe measurements of the HfO2/Si structures provide obvious evidence for the formation of dipoles at the HfO2/Si interfaces. The author proposes that one-monolayer Si-O bonds at the HfO2/Si interface naturally lead to a large potential difference, mainly due to the large dielectric constant of the HfO2. Dipole scattering is demonstrated to not be a major concern in the channel mobility of MOSFETs.

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“…Although this technique is very effective in scaling EOT, the thinner SiO 2 results in undesirable leakage 19 and mobility degradation 2,16,20,21 .…”

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confidence: 99%