Atomic Layer Deposition Chamber Research Articles

Exploring TMA and H2O Flow Rate Effects on Al2O3 Thin Film Deposition by Thermal ALD: Insights from Zero-Dimensional Modeling

This study investigates the impact of vapour-phase precursor flow rates—specifically those of trimethylaluminum (TMA) and deionized water (H2O)—on the deposition of aluminum oxide (Al2O3) thin films through atomic layer deposition (ALD). It explores how these flow rates influence film growth kinetics and surface reactions, which are critical components of the ALD process. The research combines experimental techniques with a zero-dimensional theoretical model, designed specifically to simulate the deposition dynamics. This model integrates factors such as surface reactions and gas partial pressures within the ALD chamber. Experimentally, Al2O3 films were deposited at varied TMA and H2O flow rates, with system conductance guiding these rates across different temperature settings. Film properties were rigorously assessed using optical reflectance methods and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The experimental findings revealed a pronounced correlation between precursor flow rates and film growth. Specifically, at 150 °C, film thickness reached saturation at a TMA flow rate of 60 sccm, while at 200 °C, thickness peaked and then declined with increasing TMA flow above this rate. Notably, higher temperatures generally resulted in thinner films due to increased desorption rates, whereas higher water flow rates consistently produced thicker films, emphasizing the critical role of water vapour in facilitating surface reactions. This integrative approach not only deepens the understanding of deposition mechanics, particularly highlighting how variations in precursor flow rates distinctly affect the process, but also significantly advances operational parameters for ALD. These insights are invaluable for enhancing the application of ALD technologies across diverse sectors, including microelectronics, photovoltaics, and biomedical coatings, effectively bridging the gap between theoretical predictions and empirical results.

Room temperature atomic layer deposition of zinc titanium oxide using sequential adsorption of dimethyl zinc and tetrakis(dimethylamino)titanium

Complex oxide films of TiO2 and ZnO are deposited by RT atomic layer deposition (ALD) with a sequential adsorption process. In this ALD, a Zn precursor of dimethyl zinc (DMZ) and a Ti precursor of tetrakis(dimethylamino)titanium (TDMAT) are used. In the sequential adsorption step, the DMZ saturation on the surface is followed by partial adsorption of TDMAT. It is assumed that the TDMAT molecule is adsorbed on the DMZ uncovered area. The mixed layer of DMZ and TDMAT is formed in the adsorption step, followed by being oxidized with the plasma-excited humidified Ar. All the ALD processes are performed at RT without any sample heating in the ALD chamber. The growth per cycle of the balanced Zn and Ti oxide deposition is recorded at 0.086 nm/cycle. The mixing ratio of Zn and Ti is controlled by the TDMAT exposure in the adsorption step. In this study, the reaction model and the related rate equations to calculate the mixing concentration ratio are proposed based on the in situ observation of the surface reaction by IR absorption spectroscopy.

Conformal coating of macroscopic nanoparticle compacts with ZnO via atomic layer deposition

Conformal atomic layer deposition (ALD) inside macroscopic nanoporous solids with aspect ratios greater than 103 can require ALD reactant exposures on the order of 103 Torr-s or greater. For some ALD chemistries, such large exposures raise the concern of non-self-limiting deposition. In the case of ZnO ALD from diethylzinc (DEZ) and H2O, exposures in the 10–103 Torr-s range have resulted in metallic Zn deposition at typical temperatures used for ZnO ALD on wafers (e.g., ∼180 °C). This Zn deposition can be suppressed by lowering the deposition temperature, but this slows H2O desorption and, thus, can necessitate impractically long purge times. In this work, we use static-dose ALD with DEZ and H2O exposures >104 Torr-s to deposit ZnO inside Al2O3 nanoparticle compacts (NPCs) with 50.5 ± 0.3% porosity, 100 nm NP diameter, 1.55 ± 0.05 mm thickness, and an aspect ratio of 7800 ± 200 (based on the half-thickness), and we explore a novel approach to the deposition temperature, T: T is cycled between 160 °C (for H2O purges) and 120 °C (for all other steps). For comparison, we also deposit ZnO with T held constant at 120 or 160 °C. Whereas the T = 160 °C process results in Zn metal deposition and nonuniform infiltration, the temperature-cycled process yields apparently self-limiting ZnO deposition at a growth per cycle (GPC) of ∼2.1 Å/cyc, forming an electrically conductive ZnO network that is uniform throughout the thickness of the NPC, with the exception of some ZnO depletion near the NPC surfaces, possibly due to the (unoptimized) long DEZ purge time. The T = 120 °C process produces similar results, although the GPC is slightly elevated, indicating diminished removal of H2O and/or OH during purges. We employ scanning electron microscopy with energy-dispersive x-ray spectroscopy, x-ray diffractometry, electrical resistivity measurements, and ALD chamber pressure analysis in our comparison of the three ALD processes.

Scalable and highly tunable conductive oxide interfaces

Conducting oxide interfaces have attracted considerable attention, motivated by both fundamental science and potential for oxide electronic devices. An important gap for maturing such device technology is scalability and routes to control the electronic properties, which can narrow the device engineering space. Here, we demonstrate and explain the mechanisms of highly tunable conductive oxide interfaces. We synthesized amorphous–crystalline Al2O3/SrTiO3 interfaces using the scalable and industry-compatible atomic layer deposition (ALD) technique. An NH3 plasma pretreatment is employed in the ALD chamber, and its duration is used as a tuning parameter for the electrical properties, where a span of three orders of magnitude in the sheet resistance is observed at room temperature. For the most conductive sample, our results are comparable to the highest carrier density values reported for all-crystalline oxide interfaces prepared with state-of-the-art epitaxial growth techniques, such as pulsed laser deposition. We pinpoint the origin of conductivity to oxygen vacancies caused by the SrTiO3 reduction by the NH3 plasma pretreatment. These results present a simple, scalable, and industry-compatible route for realizing conductive oxide interfaces, with a broad parameter space, offering a versatile and flexible toolkit for oxide device engineering.

Wake-up free ferroelectric hafnia-zirconia capacitors fabricated via vacuum-maintaining atomic layer deposition

Ferroelectric hafnium-zirconium oxide (HZO) is an excellent candidate for low-power non-volatile memory applications due to its demonstrated ferroelectricity at the nanoscale and compatibility with silicon-based technologies. The interface of HZO in contact with its electrode, typically TiN in a metal–ferroelectric–metal (MFM) capacitor configuration, is of particular interest because factors, such as volume confinement, impurity concentration, interfacial layers, thermal expansion mismatch, and defect trapping, are believed to play a crucial role in the ferroelectric performance of HZO-based devices. Processing variables, such as precursor type, oxygen source, dose duration, and deposition temperature, are known to strongly affect the quality of the oxide–metal interface. However, not many studies have focused on the effect of breaking or maintaining vacuum during MFM deposition. In this study, sequential, no-atmosphere processing (SNAP) is employed to avoid atmospheric exposure, where electrode TiN and ferroelectric HZO are deposited sequentially in the atomic layer deposition chamber without breaking vacuum. The effect of breaking vacuum during the sequential deposition steps is elucidated by fabricating and characterizing MFM capacitors with and without intentional vacuum breaks prior to the deposition of the HZO and top TiN. Using x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS), we reveal that breaking vacuum after bottom TiN electrode deposition leads to interfacial oxidation and increased carbon contamination, which preferentially stabilizes the non-ferroelectric tetragonal phase and lead to diminished remanent polarization. Avoiding carbon impurities and interfacial TiOx at the HZO and TiN interface using SNAP leads to heightened remanent polarization, reduced leakage current density, and elimination of the wake-up effect. Our work highlights the effect of vacuum breaking on the processing-structure-properties of HZO-based capacitors, revealing that maintaining vacuum can significantly improve ferroelectric properties.

Scaling-Up of Thin-Film Photoelectrodes for Solar Water Splitting Based on Atomic Layer Deposition.

Atomic layer deposition (ALD) is an established method to prepare protective layers for Si-based photoelectrodes for photoelectrochemical (PEC) water splitting. Although ALD has been widely used in microelectronics and photovoltaics, it remains a great challenge to design simple and effective ALD systems to deposit large and uniform protective films for Si-based photoelectrodes with industrial sizes. This paper describes the design and realization of a simple ALD chamber configuration for photoelectrodes with large sizes, in which the influence of a gas redistributor over the gas flow and heat transfer during film growth was revealed by computational fluid dynamics simulations and experimental investigations. A simple circular baffle-type redistributor was proposed to establish a uniform gas flow field throughout the ALD reactor, resulting in a uniform temperature profile. With this simple baffle redistributor, the large-area Al2O3 monitor film (46 nm thickness) reached a good nonuniformity (Nu %) of 0.88% over a large area of 256 cm2. This design enables the fabrication of large-scale photocathodes from standard industrial-grade 166 mm Si(100) wafers (276 cm2) by depositing 50 nm TiO2 protective films with Nu % less than 5%. The obtained photocathode achieves a saturation current of 6.45 A with a hydrogen production rate of 43.2 mL/min under outdoor illumination. This work elucidates how flow pattern and heat transfer may influence the deposition of protective layers over large photoelectrodes, providing guidance for future industrial applications of PEC water splitting.

Atomic layer deposition of lithium metaphosphate from H3PO4 and P4O10 facilitated via direct liquid injection: Experiment and theory

We report the use of H3PO4 as a reactant in atomic layer deposition (ALD) of lithium metaphosphate. The ALD growth cycle starts by injection of the lithium tetramethyl heptadionate (LiTMHD) precursor followed by injection of the H3PO4 reactant. Both the reactant and the precursor are injected into the ALD chamber via direct liquid injection, which allows us to achieve ALD without plasma or high temperatures. The liquid H3PO4 solution, injected 10 s after the precursor, evaporates and decomposes into the gaseous mixture of H3PO4, P4O10, and H2O. The H3PO4 and P4O10 molecules finally react with the LiTMHD molecules adsorbed at the sample substrate, which results in the film growth. The obtained films are amorphous, and the x-ray photoelectron spectroscopy measurements reveal the LiPO3 composition. The growth process exhibits the features of the ALD, namely, the saturation of the growth rate with cycle duration and the maximum growth rate when the number of the injected precursor/reactant molecules reaches a critical value. We show theoretically that the growth rate is governed by the gas-phase equilibrium between H3PO4 and P4O10, both of which are reactive but to different degrees. Depending on the temperature and other conditions, we obtain a reactive gas adjustable at will between pure H3PO4 and pure P4O10. Our theory explains essential features of the observed ALD growth. It determines which of the two reactants (H3PO4 or P4O10) causes the growth and which of them provides a faster growth.

Structural, Optical, and Electronic Properties of Cu-Doped TiNxOy Grown by Ammonothermal Atomic Layer Deposition.

Copper-doped titanium oxynitride (TiNxOy) thin films were grown by atomic layer deposition (ALD) using the TiCl4 precursor, NH3, and O2 at 420 °C. Forming gas was used to reduce the background oxygen concentration and to transfer the copper atoms in an ALD chamber prior to the growth initiation of Cu-doped TiNxOy. Such forming gas-mediated Cu-doping of TiNxOy films had a pronounced effect on their resistivity, which dropped from 484 ± 8 to 202 ± 4 μΩ cm, and also on the resistance temperature coefficient (TCR), which decreased from 1000 to 150 ppm °C-1. We explored physical mechanisms causing this reduction by performing comparative analysis of atomic force microscopy, X-ray photoemission spectroscopy, X-ray diffraction, optical spectra, low-temperature transport, and Hall measurement data for the samples grown with and without forming gas doping. The difference in the oxygen concentration between the films did not exceed 6%. Copper segregated to the TiNxOy surface where its concentration reached 0.72%, but its penetration depth was less than 10 nm. Pronounced effects of the copper doping by forming gas included the TiNxOy film crystallite average size decrease from 57-59 to 32-34 nm, considerably finer surface granularity, electron concentration increase from 2.2(3) × 1022 to 3.5(1) × 1022 cm-3, and the electron mobility improvement from 0.56(4) to 0.92(2) cm2 V-1 s-1. The DC resistivity versus temperature R(T) measurements from 4.2 to 300 K showed a Cu-induced phase transition from a disordered to semimetallic state. The resistivity of Cu-doped TiNxOy films decreased with the temperature increase at low temperatures and reached the minimum near T = 50 K revealing signatures of the quantum interference effects similar to 2D Cu thin films, and then, semimetallic behavior was observed at higher temperatures. In TiNxOy films grown without forming gas, the resistivity decreased with the temperature increase as R(T) = - 1.88T0.6 + 604 μΩ cm with no semimetallic behavior observed. The medium range resistivity and low TCR of Cu-doped TiNxOy make this material an attractive choice for improved matching resistors in RF analog circuits and Si complementary metal-oxide-semiconductor integrated circuits.

Comparative Study of Tungsten Films Grown By Atomic Layer Deposition with Newly Synthesized Metalorganic and Halide Precursor

For continuous scaling down of semiconductor devices, metal deposition has been developed as a plug filling process for interlayer connecting. Tungsten (W) has a wide range of industrial applications since it has a relatively good electrical conductivity and a high electromigration durability due to its high melting point of 3380 °C. [1] Among various techniques, atomic layer deposition (ALD) has been investigated to find the most feasible way to grow uniform, dense, conformal, and conductive W thin film to thicknesses of a few nanometers in more complicated structures, since its growth mechanism is entirely based on self-limited surface reaction. [2] To date, several W precursors have been employed. Among them, the halide precursors have been widely used as precursors for metal deposition since it can fabricate a high-purity film compared to metal organic precursors. Tungsten hexafluoride (WF6) is the most widely reported halide-based precursor to date due to its simple structure and high reactivity. [3] However, the toxic by-product (HF) can provoke the interfacial Si consumptions and corrosion of devices. In this respect, in halide-based precursors, fluorine (F)-free tungsten precursors have recently received attention, but study on development of F-free tungsten precursor is still in its infancy. In contrast, the organic precursor is free from the formation of corrosive by-product. However, the carbon species derived from the organic ligand of the precursor can deteriorate film properties and device performance. [4] For this reason, studies for pure tungsten metal deposition with organic precursors have not been reported. Eventually, since the halide and organic precursors have their own strengths and weaknesses, there has been considerable controversy over the choice of precursors between the two groups.In this work, we fundamentally investigated the growth characteristics, chemical composition, crystallinity of W films on SiO2 substrate using two newly synthesized precursors (tungsten pentachloride (WCl5) and ethylcyclopentadienyltungsten(Ⅴ) tricarbonyl hydride (HEtCpW(CO)3)). Ar/H2 plasma as the reactant was generated between the showerhead and the substrate during the reactant exposure by capacitively coupled plasma (CCP) with a radiofrequency (RF) of 13.56 MHz at 200 W. We used Commercial showerhead type ALD chamber which has 8-inch wafer capacity, and the precursors were contained in individual stainless-steel bubblers and evaporated at 135 and 55 °C, respectively, to obtain a sufficient vapor pressure. The delivery lines were heated to a temperature approximately 10–15 °C higher than that of the bubbler to prevent the condensation of the precursor. The microstructure of W film were analyzed using Grazing-incidence X-ray diffraction (GIXRD), the film density of W film was analyzed via X-ray reflectivity (XRR), and the resistivity was electrically measured via Four point probe (FPP) with semiconductor analyzer. Growth characteristics and film properties were significantly affected by ligands of precursors. In addition, the electrical properties, including resistivity depending on the ALD cycles, and conformality at trench were evaluated for potential application. These results provide fundamental and useful information, with respect to the selection of the suitable precursor, for practical implementation of device fabrication.

Link between Gas Phase Reaction Chemistry and the Electronic Conductivity of Atomic Layer Deposited Titanium Oxide Thin Films.

In situ monitoring of gas phase composition reveals the link between the changing gas phase chemistry during atomic layer deposition (ALD) half-cycle reactions and the electronic conductivity of ALD-TiO2 thin films. Dimethylamine ((CH3)2NH, DMA) is probed as the main product of both the TDMAT and water vapor half-reactions during the TDMAT/H2O ALD process. In-plane electronic transport characterization of the ALD grown films demonstrates that the presence of DMA, a reducing agent, in the ALD chamber throughout each half-cycle is correlated with both an increase in the films' electronic conductivity, and observation of titanium in the 3+ oxidation state by ex situ X-ray photoelectron spectroscopy analysis of the films. DMA annealing of as-grown TiO2 films in the ALD chamber produces a similar effect on their electronic characteristics, indicating the importance of DMA-induced oxygen deficiency of ALD-TiO2 in dictating the electronic conductivity of as-grown films.

Formation and Evaluation of Al2O3 Layer By Direct ALD on Epitaxial SiGe

In recent years, SiGe and Ge have drawn considerable attention as a high mobility channel material toward next-generation complementary metal-oxide-semiconductor (CMOS) circuits. In particular, by inducing strain into Ge using Ge/SiGe hetero-structure, highly enhanced mobility which greatly exceed the bulk mobility have been reported [1]. In order to obtain high mobility, it is necessary to generate larger strain. As one of the methods, strained SiGe on Ge-on-Si is expected. In addition, in order to realize a high mobility SiGe channel MOSFET, it is necessary to form the high-quality gate stacks and interfaces between a gate insulator film and a SiGe surface. In fact, the use of atomic layer deposition (ALD) or plasma oxidation has provided a high quality interface between Ge and the insulator film [2, 3]. However, unlike Si, wet cleaning of Ge or hydrofluoric acid treatment does not provide a high-quality hydrogen-terminated surface, and there is concern about surface oxidation and impurity adsorption. Therefore, we have attempted direct ALD on epitaxially grown Ge and reported that the Ge/Al2O3 interface properties are improved [4]. In the case of SiGe, a high-quality hydrogen-terminated surface cannot be obtained by wet cleaning or hydrofluoric acid treatment. For this reason, oxidation or impurity adsorption on the SiGe surface is feared. In this study, for the application to strained SiGe channel MOSFET, an Al2O3 film was formed using ALD on epitaxially grown SiGe as a gate stack structure on SiGe, and the interface structure was evaluated.Two types of samples were prepared by two methods. An n-type Ge (100) substrate was used in this study. The Ge substrate was chemically cleaned with NH4OH solution and followed by a HF dip and de-ionized water rinse. The wet-cleaned Ge substrate was loaded into an MBE chamber and subjected to thermal cleaning at 600 °C for 10 min. Subsequently, a 50 nm thick SiGe layer (called epi-SiGe hereafter) was hetero-epitaxially grown on the Ge substrate at 300 °C. The as-grown sample was subsequently transferred to the vacuum-connected ALD chamber and an Al2O3 film was deposited by ALD (Sample (A)). For comparison, after the epitaxial growth of the SiGe, the sample was once taken out from the chamber and exposed to the atmosphere for 5 min. The sample was then reloaded into the ALD chamber and an Al2O3 film was deposited (sample (B)). ALD of Al2O3 films was carried out for 20 cycles with precursors of TMA and H2O at a substrate temperature of 300 °C. Chemical bonding states were examined by x-ray photoelectron spectroscopy (XPS) using an ESCA-300 manufactured by Scienta Instruments AB.According to figs.1 (a) and (b), it was confirmed that the GeOx peak of the sample (A) transferred in a vacuum was significantly smaller than that of the sample (B) once exposed to the atmosphere. In particular, almost no Ge4+ peak [5] arising from Ge in GeO2 was observed, indicating that oxidation of Ge was suppressed by transport in vacuum. It is considered that the GeOx peak in the sample (A) is derived from the interface between Al2O3 and SiGe. According to figs.1 (c) and (d), no Si4+ component (binding energy range 102eV to 104eV) is found in the Si 2p 3/2 spectrum of the sample (A) transferred in a vacuum. In summary, XPS analyses reveal that formation of GeO2 and SiO2 by natural oxidation can be almost avoided by ALD on the epitaxial SiGe, and it is indicated that the Al2O3/SiGe interface created does not contain the interfacial GeO2 layer which is present for the sample exposed to the air before ALD. These results clearly indicate that the direct ALD on epitaxial SiGe is very promising way to highly improve the SiGe MOSFET performances.AcknowledgmentsThis work was partly supported by the MEXT Supported Program for the Strategic Research Foundation at Private Universities 2015–2019, a Grant-in-Aid for Scientific Research from MEXT and Interdisciplinary Research Center for Nano Science and Technology in Tokyo City University.

Data retention and low voltage operation of Al2O3/Hf0.5Zr0.5O2 based ferroelectric tunnel junctions

Ferroelectric random-access memories based on conventional perovskite materials are non-volatile but suffer from lack of CMOS compatibility, scalability limitation, and a destructive reading scheme. On the other hand, ferroelectric tunnel junctions based on CMOS compatible hafnium oxide are a promising candidate for future non-volatile memory technology due to their simple structure, scalability, low power consumption, high operation speed, and non-destructive read-out operation. Herein, we report an efficient strategy based on the interface-engineering approach to improve upon the tunneling electroresistance effect and data retention by depositing bilayer oxide heterostructure (Al2O3/Hf0.5Zr0.5O2) using atomic layer deposition (ALD) on Ge substrate which is treated in-situ ALD chamber with H2-plasma before film deposition. Integrating a thin ferroelectric layer i.e. Hf0.5Zr0.5O2 (8.4 nm) with a thin interface layer i.e. Al2O3 (1 nm) allowed us to reduce the operation (read and write) voltage to 1.4 V, and 4.3 V, respectively, while maintaining a good tunneling electroresistance or ON/OFF ratio above 10. Furthermore, an extrapolation to 1000 years at room temperature gives a residual ON/OFF ratio of 4.

High-purity core / shell structured nanoparticles synthesis using high-frequency plasma technology and atomic layer deposition

In this study, an equipment for synthesizing high purity core/shell nanoparticles was developed using high frequency plasma technology and atomic layer deposition method. The plasma chamber was designed so that the gas phase precursor could stabilize the flow in the plasma, and a holder capable of adjusting the rotation and the height of substrate was constructed to enable the uniform deposition of nanoparticle on the substrate surface regardless of the precursor species. ALD (atomic layer deposition) deposition technique was used for the shell coating of the deposited nanoparticles. MTL (main transfer line) equipment was constructed to move the substrate from the plasma chamber to the ALD chamber without external exposure. By constructing a pneumatic gate, the contamination of ALD chamber by the plasma process can be prevented and the vacuum state can be maintained. By means of the SEM and TEM analysis, the growth rate of the core-TiO2 thin film and the growth thickness of the shell-Al2O3 were controlled at a growth rate of 0.05 μm/s and 1 Ẳ/cycle, respectively. In addition, it was confirmed that the weight fraction and the particle size can be controlled through the X-ray diffraction analysis and the dynamic light scattering analysis.

Impact of in situ atomic layer deposition TiN/high-κ stack onto In0.53Ga0.47As MOSCAPs on 300 mm Si substrate

We investigated the impact of an in situ atomic-layer-deposition (ALD) TiN/high-κ dielectric onto In0.53Ga0.47As metal-oxide-semiconductor capacitors (MOSCAPs) on a 300-mm (001) Si substrate. We found that an in situ ALD TiN/ZrO2 MOSCAP shows an improved hysteresis (36% reduction) compared to ex situ ALD TiN/ZrO2 MOSCAP in a capacitance–voltage (CV) measurement at 1 MHz. X-ray photoelectron spectroscopy (XPS) shows the formation of the ZrOxNy composition for the ex situ process which is affected by the increased hysteresis in the CV characteristics. In addition, the flat-band voltage (VFB) has shifted the forward direction for the in situ process device which is evidence of the decreasing oxygen vacancy (VO) in the high-κ layer through the in situ process in an ALD chamber. In order to confirm the concentration change of the oxygen vacancy, the ΔVth degradation of the TiN/ZrO2 with an In0.53Ga0.47As MOSCAP under constant voltage stress (CVS) was carried out. It turns out that the in situ process has a lower ∆Vth (63 mV) than the ex situ process at 1000 s stress. Based on the results, interface traps in between the TiN metal gate and high-κ are other defect sources which need to be considered in order to improve future III–V MOSFETs.

Fabrication of Ge MOS with low interface trap density by ALD of Al2O3 on epitaxially grown Ge

Effects of initial surface conditions on interface characteristics of Al2O3/GeOx/Ge gate stacks are studied. As a clean surface condition prior to atomic layer deposition (ALD), a non-terminated Ge surface is realized by the insertion of an epitaxial Ge layer are grown on a Ge substrates in a MBE chamber which is directly connected to an ALD chamber. For these structures, the fixed charge density (Qf) and interface trap density (Dit) are evaluated from the C-V characteristics and conductance method. Qf reduction of about 17% and 90% are achieved by insertion of the epi-Ge layer and additional GeOx formation using plasma post-oxidation, respectively. A 90% reduction of Dit is also confirmed. These results indicate the importance of the initial Ge surface conditions before ALD and the Al2O3/GeOx/Ge gate stacks are very promising for high mobility Ge based CMOS applications.

Development of a scanning probe microscopy integrated atomic layer deposition system for in situ successive monitoring of thin film growth

A dual chamber system integrated with atomic layer deposition (ALD) and atomic force microscopy (AFM) was developed for the successive monitoring of nanoparticles to thin film growth process. The samples were fabricated in the ALD chamber. A magnetic transmission rod enabled sample transferring between the ALD and the AFM test chambers without breaking the vacuum, avoiding possible surface morphology change when frequently varying the growth condition and oxidation under ambient condition. The sample transmission also avoids deposition and contamination on the AFM tip during the successive testing. The sample stage has machined a group of accurate location pinholes, ensuring the 10 μm2 measurement consistency. As a demonstration, the platinum thin films with different thickness were fabricated by varying ALD cycles. The surface morphology was monitored successively during the deposition. Under vacuum with controlled oxygen partial pressure, the aging and sintering phenomenon of particles has been studied in the AFM testing chamber after high temperature treatment. The integrated AFM/ALD instrument is potentially a powerful system for monitoring the thin film preparation and characterization.

Preventing carbon contamination of Ge (001) during atomic layer deposition with a barium-based Zintl layer

Carbon contamination of the clean Ge (001) 2 × 1 surface occurs during atomic layer deposition (ALD) of perovskite oxides and introduces impurities that can affect device performance. Zintl layers are formed by exposing a bare Ge (001) 2 × 1-reconstructed surface to 0.5-monolayers of elemental Ba, with the Ba atoms occupying the fourfold sites between Ge-dimer rows. The bare Ge (001) and Ba-Zintl layer surfaces feature a 2 × 1-reconstructed structure. Exposure of bare 2 × 1-reconstructed Ge (001) to 0.5 monolayers of elemental Sr leads to an 8 × 1- or 9 × 1-reconstructed Ge (001) surface. Bare Ge (001) and Ba-Zintl layer Ge (001), and 0.5-monolayer Sr-dosed Ge (001) surfaces were exposed to background molecules in the ALD chamber at 225 °C. Bare Ge (001) and Ba-Zintl layer Ge (001) were also exposed to barium bis(triisopropylcyclopentadienyl) at 225 °C and changes in the surface composition were monitored with x-ray photoelectron spectroscopy. The 2 × 1-reconstructed Ba-Zintl surface protects Ge (001) from carbon accumulation associated with ALD background molecules and cyclopentadienyl-based ligands originating from the ALD precursor. Surface structure is important in protecting Ge (001); the 8 × 1- or 9 × 1-reconstructed Ge (001) surface formed from 0.5-monolayers of Sr does not prevent carbon accumulation.

Enhanced nucleation and growth of HfO2 thin films grown by atomic layer deposition on graphene

Nucleation and growth characteristics of HfO2 thin films on graphene are investigated using atomic layer deposition (ALD). Substantial delay (∼70 ALD cycles) in the nucleation of HfO2 films is observed during HfO2 ALD on graphene, which causes large leakage current in Au/HfO2/graphene capacitors at low HfO2 ALD cycles (<200). The nucleation delay in HfO2 ALD decreases significantly to ∼10 ALD cycles with graphene surface treatment using trimethylaluminum (TMA) and H2O. Graphene surface treatment is performed in an ALD chamber prior to the deposition of HfO2 film using TMA and H2O at 150 °C (same as the HfO2 ALD process temperature). With the improvement in the nucleation of the HfO2 films, the leakage current decreases significantly by a factor of 102–105 (at 1 V) than that without surface treatment for a given number of HfO2 ALD cycles. A higher dielectric constant of HfO2 film is achieved using the surface treatment (k ∼14.5) than that without the surface treatment (k ∼5.6). The resistance of graphene increases substantially (ΔR/R0 ∼24%) after the growth of HfO2 films by ALD without surface treatment, indicating degradation of graphene properties. However, the electrical resistance of graphene changes negligibly (ΔR/R0 ∼0.5%) after the growth of HfO2 films with surface treatment, implying a conservation of the carrier mobility of graphene. This indicates the importance of surface treatment on graphene for HfO2 film growth by ALD. Therefore, the graphene surface treatment using TMA and H2O thus enables an achievement of enhanced nucleation and electrical properties of HfO2 films without degrading the mobility of graphene, thus providing promising opportunities in graphene electronics.

Influences of surface treatment on In0.53Ga0.47As epitaxial layer grown on silicon substrate using trimethylaluminum

A development of high quality InxGa1−xAs epitaxial layers on Si substrates is essential for high-performance logic transistors due to the low fabrication cost and high compatibility with a conventional Si technology. We investigate the surface of In0.53Ga0.47As epitaxial layers grown by metal-organic chemical vapor deposition on a Si substrate (with InP/GaAs buffer layers) to obtain a high capacitance using high-k films (HfO2/Al2O3 bilayer). The high-k films were grown on In0.53Ga0.47As epitaxial layers by atomic layer deposition (ALD). The interface between the high-k bilayer and the In0.53Ga0.47As epitaxial layer was analyzed depending on a surface treatment of the In0.53Ga0.47As epitaxial layer, and the surface treatment of the In0.53Ga0.47As epitaxial layer using trimethylaluminum (TMA) enhanced the electrical performances of Pt/high-k film/In0.53Ga0.47As capacitors. The TMA was introduced on the In0.53Ga0.47As epitaxial layer in the ALD chamber, which reduced native oxides (such as gallium and arsenic oxides) of the In0.53Ga0.47As surface and minimized a formation of interfacial layers between the high-k film and In0.53Ga0.47As layer. A capacitance equivalent thickness (CET) of ~1.5nm was achieved with a low leakage current (~10−4A/cm2 at 1V). A CET as low as ~1.3nm and a capacitance >2.5μF/cm2 was attained by optimizing the high-k/In0.53Ga0.47As interface. The TMA treatment on the In0.53Ga0.47As epitaxial layer is compatible with the conventional Si technology and provides promising opportunities for the development of state-of-the-art field-effect transistor technology using InxGa1−xAs epitaxial layers.

Interfaces Formed by ALD Metal Oxide Growth on Metal Layers

Redox-based resistive switching random access memory (ReRAM) has the potential to fulfill the demands of future Green IT solutions for non-volatile memory circuits with high speed data access, high reliability, and low power consumption. A single valence-change-mechanism (VCM)-type switching cell is typically built from a transition metal oxide layer sandwiched between metal electrodes of different oxidation enthalpy. It is accepted in the scientific community that oxygen exchange and drift/diffusion processes play a major role in the resistive switching process. Thus, understanding oxidation/reduction reactions taking place already during the growth process is of utmost importance. For future three-dimensional (3D) integrated arrays of ReRAM cells atomic layer deposition (ALD) will become the method of choice to grow ultra-thin, conformal, homogeneous and dense oxide films at a thermal budget below 450 °C. For todays’ two dimensional stacked crossbar arrays, the metal oxide films can be grown on nearly inert Pt electrodes, while the oxygen exchange layer built from a reactive metal is deposited on top of the metal oxide. However, in the 3D ReRAM arrays the metal oxide might need to be grown on the reactive metal as well. In this study ultrathin ALD metal oxide layers are deposited on various metal electrodes by means of in-situ transfer from the sputtered metal into the ALD chamber. For the metal layers we utilized Pt, Hf, and Ta while for the metal oxides Al2O3, TiO2, and HfO2 were chosen. ALD metal oxide processes were performed by plasma assisted ALD in an Oxford FlexAlâ system. Due to the passivation property of the dense ALD metal oxide layer the metal oxide / metal interfaces could be analyzed ex-situ if the vacuum break was kept short. Angle resolved X-ray photoemission spectroscopy studies combined with X-ray reflectivity analysis reveal a clear picture of the interface formation and the oxygen gradient formed at the interface already during growth. The influence of process parameters and stack sequences on this ‘built-in’ oxygen gradient at metal / ALD metal oxide interfaces will be covered in this presentation. Among others, the possibility for PtOx formation during remote oxygen plasma ALD processes will be discussed.