High-k Metal Oxide Research Articles

MEMS Capacitive Switch Fabrication using Photodefinable Metal Oxide Dielectrics

In this paper, design, fabrication and measurement of reliable low cost capacitive RF MEMS switches with a novel fabrication approach using direct photo-definable high-k metal oxides are presented. In this approach, a radiation sensitive metal- organic precursor is deposited via spin coating and converted to a high-k metal oxide via ultraviolet exposure. Measurements of the bridge-type switches have been done up to 40 GHz. These switches are reliable (> 340 million cycles) and exhibited low insertion loss (around 0.3 dB at 20 GHz) and better isolation (around 24 dB at 20 GHz) at frequencies below resonant frequency as compared to switches fabricated using a simple silicon nitride dielectric.

Germanium MOSFETs for Nanoelectronics

Ge is a promising channel material for nanoscale MOSFETs due to its high mobility, which translates into higher drive current and smaller gate delay. However, for Ge to become main-stream, surface passivation and heterogeneous integration of crystalline Ge layers on Si must be achieved. We have demonstrated growth of fully-relaxed smooth single crystal Ge layers on Si using a novel multi-step growth and hydrogen anneal process without any graded buffer SiGe layer. Surface passivation of Ge has been achieved with its native oxynitride and high-k metal oxides of Al, Zr and Hf. High mobility p-MOSFETs have been demonstrated in bulk Ge with these gate dielectrics and metal gates. However, due to its smaller bandgap Ge suffers from large leakage currents. We present novel, Si and Ge based heterostructure MOSFETs, which significantly reduce the leakage while retaining high mobility, making them suitable for scaling into the sub-20nm regime.

Probing Point Defects in Stacks of Ultrathin High-k Metal Oxides on Semiconductors by Electron Spin Resonance: The Si/HfO2 vs the Ge/HfO2 System

Combined electron spin resonance and electrical analysis of (100)Si/HfO2 and (100)Ge/HfO2 interfaces reveals dramatic differences in their interface defect properties. No interfacial Ge dangling bond type defects could be revealed. The observed paramagnetic defects do not correlate with the slow acceptor states dominating the Ge/insulator trap spectrum, and are resistant to passivation. The dangling bond type defects observed, upon hydrogen detachment, at the (100)Si/HfO2 interfaces are the trivalent Si defects common for Si/SiO2 interfaces, Pb0 and Pb1 centers. The density of the Pb0 is higher than in the (100)Si/SiO2 structures and is sensitive to the deposition process. However, the density can be significantly reduced by annealing of the Si/HfO2 structures in O-containing ambient, likely through re-establishing the Si/SiO2 interface. The density of fast interface states closely follows the variations in the Pb0 center density, suggesting it as the dominant contribution to the fast interface states.

Transient bicarrier response in high-k dielectrics and its impact on transient charge effects in high-k complementary metal oxide semiconductor devices

In this letter, transient charge trapping and detrapping characteristics in high-k n∕p metal oxide semiconductor field effect transistors (MOSFETs) were studied. Transient charge trapping was found to be an interface thickness-limited phenomenon. Additionally, transient trapping of electrons, rather than holes, was found to be dominant even in pMOSFETs. Transient charge recombination or bicarrier response within the high-k layer was the main reason for the dependence on input signal in high-k devices. Detrapping characteristics for nMOSEFTs and pMOSFETs were correlated to the transient hole and electron trappings, respectively.

PART II: CONDUCTION BAND-EDGE STATES ASSOCIATED WITH REMOVAL OF d-STATE DEGENERACIES BY THE STATIC JAHN-TELLER EFFECT

X-ray absorption spectroscopy (XAS) is used to study band edge electronic structure of high-k transition metal (TM) and trivalent lanthanide rare earth (RE) oxide dielectrics. The lowest conduction band d*-states in nano-crystalline TiO 2, ZrO 2 and HfO 2 are correlated with features in the O K 1 edge, and transitions from occupied Ti 2p, Zr 3p and Hf 4p states to empty Ti 3d-, Zr 4d-, and Hf 5d-states, respectively. Optical band gaps, E opt , and conduction band offset energy with respect to Si , E B , scale monotonically with d-state energies of the TM/RE atoms. The multiplicity of d-state features in the Ti L 2,3 spectrum of TiO 2, and the O K 1 derivative spectra for ZrO 2 and HfO 2 indicate a complete removal of d-state degeneracies resulting from a static Jahn-Teller effect. Similar degeneracy removals are shown for complex nano-crystalline TM/RE oxides such as Zr and Hf titanates, and La , Gd and Dy scandates. XAS and band edge spectra indicate an additional band edge defect state assigned Jahn-Teller distortions at internal grain boundaries. These defect states are electronically active act as bulk traps in metal oxide semiconductor (MOS) devices, contributing to asymmetries in tunneling and Frenkel-Poole transport with important consequences for performance and reliability in advanced Si devices.

Point Defects and Traps in Stacks of Ultrathin High-k Metal Oxides on Si Probed by Electron Spin Resonance: The Si/HfO2 System and N Incorporation

not Available.

Probing Point Defects in Stacks of Ultrathin High-k Metal Oxides on Semiconductors by Electron Spin Resonance: The Si/HfO2 vs the Ge/HfO2 System

not Available.

Enhanced Reliability and Performance of High-k MOSFET by Two-Step Annealing

The effect of high pressure (HP) H 2 /D 2 annealing and subsequent N 2 annealing, to enhance reliability, on hafnium-based high-k metal oxide semiconductor field effect transistor (MOSFET) has been studied. HP hydrogen annealing effectively passivates dangling bonds which in turn reduce the interface state density. Additional annealing in nitrogen ambient reduces threshold voltage shifts (ΔV th ) due to bias temperature instability and hot carrier injection. This improvement due to subsequent annealing might be related with the annihilation of hydrogen-related trapping sites from the high-k bulk. Since charge trapping is attributed mainly to dangling bonds at the interface and excess hydrogen species in the bulk of the high-k oxide, by optimizing annealing conditions, both reliability and performance of high-k MOSFETs are improved.

Conduction band-edge d-states in high-k dielectrics due to Jahn–Teller term splittings

X-ray absorption spectroscopy (XAS) is used to study conduction band edge electronic structure of high-k transition metal (TM) and trivalent lanthanide series rare earth (RE) oxide dielectrics. Empty TM/RE d-states are studied by intra-atomic transitions originating in core level spin-orbit split p-states, and conduction band states are studied in inter-atomic transitions which originate in the oxygen atom 1s core level state. In non-crystalline Zr and Hf silicate alloys, the local bonding symmetry, or crystal field splits these d-states into doubly and triply degenerate features. In nano-crystalline oxides, there are additional d-state splittings due to contributions of more distant neighbors that completely remove d-state degeneracies via the Jahn–Teller effect mechanism. This gives rise to highly localized band edge states that are electronically active in photoconductivity, internal photoemission, and act as bulk traps in metal oxide semiconductor (MOS) devices.

Engineering chemically abrupt high-k metal oxide∕silicon interfaces using an oxygen-gettering metal overlayer

High-k metal oxide gate dielectrics may be required to extend Moore’s law of semiconductor device density scaling into the future. However, growth of a thin SiO2-containing interface layer is almost unavoidable during the deposition of metal oxide films onto Si substrates. This limits the scaling benefits of incorporating high-k dielectrics in future transistors. A promising approach, in which oxygen-gettering metal overlayers are used to engineer the thickness of the SiO2-based interface layer between metal oxide and Si substrate after deposition of the metal oxide layer, is reported. Using a Ti overlayer with high solubility for oxygen on ZrO2 or HfO2 dielectrics, the effective removal of the low-k interface layer at 300K has been confirmed by electron microscopy and spectroscopy techniques. Significant enhancement of the gate capacitance density, while retaining low leakage current densities, has also been demonstrated for these interface-engineered high-k gate stacks.

Subnanometer Scaling of HfO[sub 2]/Metal Electrode Gate Stacks

The equivalent oxide thickness (EOT) of high-k n-channel metal oxide semiconductor (NMOS) transistors was scaled using 3 methods, reduction of the bottom interfacial layer (BIL) using interface engineering, thickness reduction of the dielectric, and use of metal gate electrodes to minimize top interfacial growth formation and polysilicon depletion. NMOS transistors fabricated using these methods demonstrate 0.72 nm EOT using the BIL with scaled /metal gates and 0.81 nm EOT using the BIL with scaled /metal gates. Charge pumping, mobility, and device performance results of these high-k NMOS transistors is discussed. © 2004 The Electrochemical Society. All rights reserved.

A Selective Etching Process for Chemically Inert High-k Metal Oxides

ABSTRACTOnce annealed, high-k metal oxides such as HfO2 and Al2O3 can be extremely difficult to etch by wet chemical methods. Here we describe how ion bombardment at relatively low energy (a few hundred eV) can be used to make exposed regions of annealed HfO2 films etchable in aqueous HF-based solutions. HfO2 layers, 2–5 nm in thickness, were deposited by atomic layer chemical vapor deposition (ALCVD) on Si substrates, annealed at 700 °C, and subjected to selected-area ion bombardment supplied by an oxygen plasma in a reactive ion etching tool. Etch times (as indicated by time to “dewet“) were examined as a function of HfO2 thickness, the power and time of oxygen plasma treatments, post-oxygen-plasma anneals, and wet etch chemistry. Strategies for etching thicker films and additional data provided by electrochemical open circuit potential (OCP) measurements will also be discussed.

Thermodynamic Stability of High-K Dielectric Metal Oxides ZrO2 and HfO2 in Contact with Si and SiO2

AbstractWe present experimental results regarding the thermodynamic stability of the high-k dielectrics ZrO2 and HfO2 in contact with Si and SiO2. The HfO2/Si interface is found to be stable with respect to formation of silicides whereas the ZrO2/Si interface is not. The metal oxide/SiO2 interface is marginally unstable with respect to formation of silicates. Cross-sectional transmission electron micrographs expose formation of nodules, identified as silicides, across the polysilicon/ZrO2/Si interfaces but not for the interfaces with HfO2. For both ZrO2 and HfO2, the X-ray photoemission spectra illustrate formation of silicate-like compounds in the MO2/SiO2 interface.

Electrical Characteristics of High-k Metal Oxide/ SiO2 Stack Gate Dielectric Prepared by Reaction of Metal with SiO2

A unique process for the preparation of high permittivity metal oxide by direct thermal reaction of metal on is described. The samples prepared by this new process exhibit excellent electrical characteristics, including high capacitance, low leakage current, and low interface state density. In addition, the electrical characteristics of the metal/oxynitride stack are superior to that of a metal/oxide stack. The improvement of electrical characteristics of metal/oxynitride stack can be explained by less metal penetration through the oxynitride layer, which was confirmed by transmission electron microscopy and energy dispersive X-ray analysis. © 2001 The Electrochemical Society. All rights reserved.

Ultrathin high-K metal oxides on silicon: processing, characterization and integration issues

An overview of our recent work on ultrathin (<100 Å) films of metal oxides deposited on silicon for advanced gate dielectrics applications will be presented. Data on ultrathin Al 2O 3, ZrO 2, HfO 2, and Y 2O 3 will be shown to illustrate the complex processing, integration and device-related issues for high dielectric constant (‘high-K’) materials. Both physical and electrical properties, as well as the effects of pre- and post-deposition treatments will be discussed.

Transition from thermally grown gate dielectrics to deposited gate dielectrics for advanced silicon devices: A classification scheme based on bond ionicity

This article discusses the bonding chemistry of alternative high-k gate dielectrics that have been considered for advanced complementary metal–oxide–semiconductor devices. The replacement of SiO2 by alternative gate dielectrics requires a transition from a thermally deposited native oxide to a deposited gate dielectric. A classification scheme based on bond ionicity separates alternative gate dielectric materials into three groups that are differentiated by their amorphous morphology and electronic structure and properties. This scheme establishes trends between bond ionicity and (i) the average bonding coordination of the constituent atoms, (ii) the thermal stability against chemical phase separation and/or crystallization, and (iii) the dielectric constant. It also provides a framework for the evaluation of different criteria that have been proposed for optimization of alternative high-k metal and transition metal oxides, and their alloys with SiO2 and Al2O3. Based on technology targets for device and wafer performance and reliability, there is as yet no ideal replacement for SiO2 that increases capacitance while at the same time maintaining low levels of interfacial defects.

Luminescence and electrical conductivity of CsSnBr3 and related phases

X-ray absorption spectroscopy (XAS) is used to study conduction band edge electronic structure of high-k transition metal (TM) and trivalent lanthanide series rare earth (RE) oxide dielectrics. Empty TM/RE d-states are studied by intra-atomic transitions originating in core level spin-orbit split p-states, and conduction band states are studied in inter-atomic transitions which originate in the oxygen atom 1s core level state. In non-crystalline Zr and Hf silicate alloys, the local bonding symmetry, or crystal field splits these d-states into doubly and triply degenerate features. In nano-crystalline oxides, there are additional d-state splittings due to contributions of more distant neighbors that completely remove d-state degeneracies via the Jahn–Teller effect mechanism. This gives rise to highly localized band edge states that are electronically active in photoconductivity, internal photoemission, and act as bulk traps in metal oxide semiconductor (MOS) devices.