Atomic layer deposition of hafnium oxide dielectrics on silicon and germanium substrates

Hafnium oxide films have been deposited at 250 °C on silicon and germanium substrates by atomic layer deposition (ALD), using tetrakis-ethylmethylamino hafnium (TEMAH) and water vapour as precursors in a modified Oxford Instruments PECVD system. Self-limiting monolayer growth has been verified, characterised by a growth rate of 0.082 nm/ cycle. Layer uniformity is approximately within ±1% of the mean value. MOS capacitors have been fabricated by evaporating aluminium electrodes. CV analysis has been used to determine the bulk and interface properties of the HfO 2, and their dependence on pre-clean schedule, deposition conditions and post-deposition annealing. The dielectric constant of the HfO 2 is typically 18. On silicon, best results are obtained when the HfO 2 is deposited on a chemically oxidised hydrophilic surface. On germanium, best results are obtained when the substrate is nitrided before HfO 2 deposition, using an in-situ nitrogen plasma treatment. © Springer Science+Business Media, LLC 2007.

Germanium MOS Capacitors with Hafnium Dioxide and Silicon Dioxide Dielectrics

Germanium (Ge) does not grow a suitable oxide for MOS devices. The Ge/dielectric interface is of prime importance to the operation of photo-detectors and scaled MOSTs. Therefore there is a requirement for deposited or bonded dielectric materials. MOS capacitors have been formed on germanium substrates with three different dielectric materials. Firstly, a thermally grown and bonded silicon dioxide (SiO2) layer, secondly, SiO2 deposited by atmospheric pressure CVD ‘silox’, and thirdly a hafnium oxide (HfO2) high-k dielectric deposited by atomic layer deposition (ALD). Ge wafers used were p-type 1 0 0 2 O cm. C–V measurements have been made on all three types of capacitors to assess the interface quality. ALD HfO2 and silox both display acceptable C–V characteristics. Threshold voltage and maximum and minimum capacitance values closely match expected values found through calculation. However, the bonded SiO2 has non-ideal C–V characteristics, revealing the presence of a high density of interface states. A H2/N2 post metal anneal has a detrimental effect on C–V characteristics of HfO2 and silox dielectrics, causing a shift in the threshold voltage and rise in the minimum capacitance value. In the case of hafnium dioxide, capacitor properties can be improved by performing a plasma nitridation of the Ge surface prior to dielectric deposition.

Comparative analysis of the DC performance of DG MOSFETs on highly-doped and near-intrinsic silicon layers

A comparison of dc characteristics of fully depleted double-gate (DG) MOSFETs with respect to low-power circuit applications and device scaling has been performed by two-dimensional device simulation. Three different DG MOSFET structures including a conventional N+ polysilicon gate device with highly doped Si layer, an asymmetrical P+/N+ polysilicon gate device with low doped Si layer and a midgap metal gate device with low doped Si layer have been analysed. It was found that DG MOSFET with mid-gap metal, gates yields the best dc parameters for given off-state drain leakage current and highest immunity to the variation of technology parameters (gate length, gate oxide thickness and Si layer thickness). It is also found that an asymmetrical P+/N+ polysilicon gate DG MOSFET design offers comparable dc characteristics, but better parameter immunity to technology tolerances than a conventional DG MOSFET. (C) 2004 Elsevier Ltd. All rights reserved.

CHARACTERIZATION OF SURFACE-PLASMONS ON METAL-OXIDE-SEMICONDUCTOR STRUCTURES

Using the Otto (prism-air gap-sample) configuration p-polarized light of wavelength 632.8 nm has been coupled with greater than 80% efficiency to surface plasmons on the aluminium electrode of silicon-silicon dioxide-aluminium structures. The results show that if the average power per unit area dissipated on the metal film exceeds approximately 1 mW mm-2, then the coupling gap and thus the characteristics of the surface plasmon resonance are noticeably altered. In modelling the optical response of such systems the inclusion of both a non-uniform air coupling gap and a thin cermet layer at the aluminium surface may be necessary.