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The incessant downscaling of building blocks for memory and logic in computer chips requires energy-efficient devices. Thermoelectric-based temperature sensing, cooling as well as energy harvesting could be useful methods to reach reliable device performance with stable operating temperatures. For these applications, complementary metal–oxide–semiconductor (CMOS)-compatible and application ready thin films are needed and have to be optimized. In this work, we investigate the power factor of different phosphorous-doped silicon germanium (SiGe) films fabricated in a 300 mm CMOS-compatible cleanroom. For the thermoelectric characterization, we used a custom-built setup to determine the Seebeck coefficient and sheet resistance. For sample preparation, we used low pressure chemical vapor deposition with in situ doping and subsequent rapid thermal annealing on 300 mm wafers. Thin film properties, such as film thickness (12–250 nm), elemental composition, crystallinity, and microstructure, are studied via spectroscopic ellipsometry, x-ray photoelectron spectroscopy, x-ray diffraction, atomic force microscopy, and TEM. The SiGe-based thin films vary in the ratio of Si to Ge to P and doping concentrations. A power factor of 0.52 mW/m K2 could be reached by doping variation. Our results show that SiGe is a very attractive CMOS-compatible material on the 300 mm wafer level and is immediately ready for production of thermoelectric embedded applications. [ABSTRACT FROM AUTHOR]

The hafnium oxide material class is characterized by the coexistence of several polymorphs between which phase transitions are induced by means of composition and external electric fields. Pyroelectric materials, which convert heat into electrical energy, exhibit the largest response at such morphotropic or field-induced phase transitions. The hafnium oxide material system is of special interest for pyroelectric applications since it allows for scalable and semiconductor-compatible fabrication. Here, we report large pyroelectric coefficients at the morphotropic transition from the ferroelectric orthorhombic to the centrosymmetric tetragonal phase. The electric field-induced transition between these two phases in doped HfO2 is found to yield large pyroelectric coefficients of up to −142 µCm−2 K−1, a value that is 20 times larger compared to AlN. [ABSTRACT FROM AUTHOR]

In this Letter, we report the percentage of the ferroelectric phase in a 10-nm-thick Hf0.5Zr0.5O2 (HZO) film deposited in a metal-insulator-metal stack by atomic layer deposition. The ferroelectric behavior was confirmed by polarization measurements and piezoresponse force microscopy. Ferroelectric behavior in this material has been attributed most likely to the formation of the polar non-centrosymmetric orthorhombic phase [Müller et al., Appl. Phys. Lett. 99, 102903 (2011)], which is difficult to distinguish from the tetragonal phase in x-ray diffraction due to peak overlap. Using a model for each of the crystal phases of hafnia-zirconia, the phase percentages were estimated using a Rietveld refinement method applied to grazing incidence x-ray diffraction data and a linear combination fit analysis procedure [McBriarty et al., Phys. Status Solidi 257, 1900285 (2020)] applied to grazing incidence extended x-ray absorption fine structure data. Using these methods, it was found that the tetragonal (P42/nmc) phase is the most prevalent at 48–60% followed by the polar non-centrosymmetric orthorhombic (Pca21) phase at 35%–40% with the remainder consisting of the monoclinic (P21/c) phase. Understanding the details of the effect of the phase structure on the electrical properties of these materials is extremely important for device engineering of HZO for logic and emerging nonvolatile memory applications. [ABSTRACT FROM AUTHOR]

Metal-Insulator-Metal capacitors, with ZrO2/Al2O3/ZrO2 (ZAZ)-nanolaminate thin-films as a dielectric layer, exhibit reduced leakage currents compared to corresponding capacitors based on pure ZrO2 while maintaining a sufficiently high dielectric constant for the DRAM application. This work is a comparative study demonstrating how the incorporation of a small amount of Al is responsible for the suppression of crystallization during deposition. Extensive electrical characterization leads to the identification of a defect band which conductive atomic force microscopy shows to be formed along crystallite grain boundaries, extending through the entire ZrO2-film. The incorporation of a sub-layer of Al2O3 prevents these grain boundaries resulting in an effective reduction of leakage currents, despite the film being in the nanocrystalline phase, necessary for it to exhibit the required high dielectric constant. A transport model based on phonon assisted trap to trap tunneling is proposed. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the influence of electrode roughness on the leakage current in TiN/high-κ ZrO2/TiN (TZT) thin-film capacitors which are used in dynamic random access memory cells. Based on a microscopic transport model, which is expanded to incorporate electrode roughness, we assess the ultimate scaling potential of TZT capacitors in terms of equivalent oxide thickness, film smoothness, thickness fluctuations, defect density and distribution, and conduction band offset (CBO). The model is based on three-dimensional, fully self-consistent, kinetic Monte Carlo transport simulations. Tunneling transport in the bandgap of the dielectric is treated, which includes defect-assisted transport mechanisms. Electrode roughness is described in the framework of fractal geometry. While the short-range roughness of the electrodes is found not to influence significantly the leakage current, thickness fluctuations of the dielectric have a major impact. For thinner dielectric films they cause a transformation of the dominant transport mechanism from Poole-Frenkel conduction to trap-assisted tunneling. Consequently, the sensitivity of the leakage current on electrode roughness drastically increases on downscaling. Based on the simulations, optimization of the CBO is suggested as the most viable strategy to extend the scalability of TZT capacitors over the next chip generations. [ABSTRACT FROM AUTHOR]

The capacitance behavior of metal insulator metal (MIM) structures with Zr1-xAlxO2 dielectrics and TiN metal electrodes is analyzed. The capacitance nonlinearity, the dielectric relaxation, and the loss phenomena are found to depend strongly on the Al content, the dielectric thickness, and the amorphous/crystalline phase of the dielectric layer. Two different kinds of phenomena—crystallization-related and interface-related, are considered to explain the observed results, especially the polarity asymmetry in the dielectric behavior. It is found that crystallization of the films enhances the effects of dielectric relaxation and loss, most likely due to charge trapping at grain boundaries. Further on, reactions between the oxidizing ambient (ozone) and the bottom electrode during high-k deposition result in structural changes (formation of TiOx interfacial layer) and thus in generation of defects which cause a different electrical behavior of the two TiN/Zr1-xAlxO2 interfaces at the top and the bottom electrode and a polarity asymmetry of the capacitance performance. [ABSTRACT FROM AUTHOR]

Lithium titanate (Li4Ti5O12) (LTO) has several promising properties with regard to energy storage. The most important is its low volume expansion during lithium (de-) intercalation enabling the material for complex three-dimensional battery anode designs. To employ this property at a small scale, e.g., for micro batteries (<100 nm active layer thickness), a highly conformal deposition process like atomic layer deposition (ALD) is needed. However, the ALD of lithium containing layers is quite ambitious. Particularly, thermally activated deposition of lithium containing layers with water as a coreactant is challenging due to the high reactivity and hygroscopic nature of many lithium compounds, e.g., lithium hydroxide. That is why a novel ALD process regime has been developed, which allows the deposition of highly conformal and single phase LTO layers with excellent step coverage and composition. The process uses two metalorganic precursors: one acting as lithium and another as a titanium source. In contrast to usual ALD processes, these two precursors are subsequently applied. The reactive pulse with water is applied after the two metal precursor pulses. In this work, this novel ALD process sequence has been introduced and successfully demonstrated on 200 mm wafers using standard industrial ALD equipment. The layers are transformed to single phase Li4Ti5O12 by rapid thermal processing as proven by crystal phase analysis. Elemental composition has been analyzed by time of flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy (XPS). Results show that the amounts of contaminants like carbon and chlorine are below the detection limits of XPS. Also, a uniform element distribution and stoichiometry in good agreement with theoretical expectations for lithium titanate could be shown. [ABSTRACT FROM AUTHOR]

Capacitors based on 10 nm antiferroelectric silicon-doped hafnium oxide (Si:HfO2) thin films are investigated in terms of energy storage efficiency, cycling endurance, and reliability. Atomic layer deposition (ALD) on an area-enhanced substrate with large-scale arrays of deep-trench structures is used to significantly increase the energy density, yielding a value of 450 μJ/cm2 and an energy storage efficiency of 67% at a voltage of 3 V. High breakdown fields are obtained, and the reliability measurement indicates that more than 90% of the devices survive three years when subjected to an operating voltage of 3 V. The film stoichiometry is optimized in terms of energy storage properties to achieve an antiferroelectric-like hysteresis loop with low fatigue during electric field cycling and uniform electrical characteristics throughout the 300 mm wafer. Si:HfO2 is a promising material for novel integrated energy storage applications, as it combines CMOS compatible manufacturing, high scalability, and conformal deposition using ALD. [ABSTRACT FROM AUTHOR]

ZrO2-based metal-insulator-metal capacitors are used in various volatile and nonvolatile memory devices as well as for buffer capacitors or radio frequency applications. Thus, process optimization and material tuning by doping is necessary to selectively optimize the electrical performance. The most common process for dielectric fabrication is atomic layer deposition which guarantees high conformity in three dimensional structures and excellent composition control. In this paper, the C-V and J-V characteristics of ZrO2 metal-insulator-metal capacitors with TiN electrodes are analyzed in dependence on the O3 pulse time revealing the optimum atomic layer deposition process conditions. Moreover, a detailed study of the leakage current mechanisms in undoped ZrO2 compared to SiO2- or Al2O3-doped ZrO2 is enclosed. Thereby, the discovered dependencies on interfaces, doping, layer thickness, and crystalline phase's enable the detailed understanding and evaluation of the most suitable material stack for dynamic random access memory devices below the 20 nm generation. [ABSTRACT FROM AUTHOR]

In order for sub-10 nm thin films of ZrO2 to have a dielectric constant larger than 30 they need to be crystalline. This is done by either depositing the layer at higher temperatures or by a postdeposition annealing step. Both methods induce high leakage currents in ZrO2 based dielectrics. In order to understand the leakage a thickness series of ultrathin ZrO2 and nanolaminate ZrO2/Al2O3/ZrO2 (ZAZ) films, deposited by atomic layer deposition, was investigated. After deposition these films were subjected to different rapid thermal annealing (RTA) processes. Grazing incidence x-ray diffraction and transmission electron microscopy yield that the crystallization of ZrO2 during deposition is dependent on film thickness and on the presence of an Al2O3 sublayer. Moreover, the incorporation of Al2O3 prevents crystallites from spanning across the entire film during RTA. C-V and I-V spectroscopies show that after a 650 °C RTA in N2 the capacitance equivalent oxide thickness of 10 nm ZAZ films is reduced to 1.0 nm while maintaining low leakage currents of 3.2×10-8 A/cm2 at 1 V. Conductive atomic force microscopy studies yield that currents are not associated with significant morphological features in amorphous layers. However, after crystallization, the currents at crystallite grain boundaries are increased in ZrO2 and ZAZ films. [ABSTRACT FROM AUTHOR]

We report on a simulation algorithm, based on kinetic Monte Carlo techniques, that allows us to investigate transport through high-permittivity dielectrics. In the example of TiN/ZrO2/TiN capacitor structures, using best-estimate physical parameters, we have identified the dominant transport mechanisms. Comparison with experimental data reveals the transport to be dominated by Poole–Frenkel emission from donorlike trap states at low fields and trap-assisted tunneling at high fields. [ABSTRACT FROM AUTHOR]

High-k dielectric layers (HfSixOy and ZrO2) with different film morphologies were investigated by tunneling atomic-force microscopy (TUNA). Different current distributions were observed for amorphous and nanocrystalline films by analyzing TUNA current maps. This even holds for crystalline layers where highly resolved atomic-force microscopy cannot detect any crystalline structures. However, TUNA enables the determination of morphology in terms of differences in current densities between nanocrystalline grains and their boundaries. The film morphologies were proven by high-resolution transmission electron microscopy. The investigations show TUNA as powerful current mapping tool for the characterization of morphology in thin high-k films on a nanoscale. [ABSTRACT FROM AUTHOR]

ZrO2 is of very high interest for various applications in semiconductor industry especially as high-k dielectric in metal-insulator-metal (MIM) capacitor devices. Further improvement of deposition processes, of material properties, and of integration schemes is essential in order to meet the strict requirements of future devices. In this paper, the authors describe a solution to solve one of the key challenges by reducing the process time of the bottle neck high-k atomic layer deposition (ALD). The authors extensively optimized the most common ALD process used for the ZrO2 deposition (TEMAZ/O3) resulting now in a doubled growth rate compared to the published growth rates of maximum 1 Å/cycle. Chemical reactions explaining the origin of the high growth rate are proposed by theoretical process modelling. At the same time, the outstanding electrical properties of ZrO2 thin films could be preserved. Finally, the integration of the ZrO2 process in MIM capacitor devices with TiN electrodes was evaluated. Thereby, the known effect of TiN bottom electrode oxidation by the O3 process was analyzed and significantly reduced by different integration approaches including wet chemical treatments and ALD process variations. The resulting MIM capacitors show low leakage current and high polarity symmetry. [ABSTRACT FROM AUTHOR]

Thin ZrO2 films are of high interest as high-k material in dynamic random access memory (DRAM), embedded dynamic random access memory, and resistive random access memory as well as for gate oxides. Actually, ZrO2 is predicted to be the key material in future DRAM generations below 20 nm. Profound knowledge of pure and doped ZrO2 thin films, especially of the structural properties, is essential in order to meet the requirements of future devices. This paper gives a detailed overview about the structural properties of ZrO2 films in dependence of various process parameters. The study of atomic layer deposition (ALD) growth mechanisms of ZrO2 on a TiN-substrate in comparison to a Si-substrate covered with native oxide exhibits significant differences. Furthermore, the structural properties crystallinity, surface roughness, and film stress are studied after the ALD deposition in dependence of the process parameters deposition temperature, layer thickness, and underlying substrate. Remarkable dependencies of the ZrO2 crystallization temperatures on the substrates are figured out. The structural properties after various annealing steps are monitored as well. The influence of doping by SiO2 and Al2O3 is studied, which is primarily used to keep the thin films amorphous during deposition. [ABSTRACT FROM AUTHOR]