Atomic Layer Deposition Film Growth Research Articles

Influences of deposition conditions on atomic layer deposition films for enhanced performance in perovskite solar cells

Atomic layer deposition (ALD) is a key technology for fabricating functional layers in perovskite solar cells, as it can deposit pinhole-free films with atomic-level thickness and tunable composition on high-aspect-ratio surfaces. Various deposition conditions have significant effects on the growth, physical, and chemical properties of ALD films, which, in turn, critically influences the performance of associated devices. Here, we review the reaction mechanisms underlying ALD and summarize how variables, such as precursors, deposition temperatures, and substrates, impinge upon the quality of ALD films and the related devices. We emphasize the role of substrate in determining the nucleation and growth behavior of ALD films, which has been overlooked in previous reviews. Finally, we highlight the potential application of ALD in efficient perovskite solar cells in terms of carrier transport, encapsulated, and buffer layers, especially for tandem cells.

In situ x-ray photoelectron spectroscopy analysis of the atomic layer deposition of Al2O3 on SiO x /Si: Interface dipole and persistent surface groups

Atomic layer deposition (ALD) has become an essential technology in many areas. To better develop and use this technology, it is of the pivot to understand the surface chemistry during the ALD film growth. The growth of an ALD oxide film may also induce an electric dipole at the interface, which may be further tuned to modulate the flat band voltage for electronic device applications. To understand the associated surface chemistry and interface dipole formation process, we herein employ an in situ x-ray photoelectron spectroscopy technique to study the ALD growth of Al2O3, from trimethylaluminum and H2O, on the SiO x /Si surface. We find that an electric dipole is formed at the Al2O3/SiO x interface immediately after the first Al2O3 layer is deposited. We also observe persistent surface methyl groups in the H2O half-cycle during ALD, and the amount of the persistent methyls is particularly higher during the initial Al2O3 ALD growth, which suggests the formation of Si−CH3 on the surface. These findings can provide useful routes and insights toward interface engineering by ALD.

(Invited) Advances in Atomic Layer Processing of Hafnia-Zirconia Ferroelectrics

The limits of integrating ferroelectric materials on commercial semiconductor chips were demolished the moment ferroelectricity in hafnia and zirconia films was reported in 2011. This breakthrough moment in the history of ferroelectric materials was made possible by the fortuitous interplay between advances in atomic layer processing and the strong surface energy dependence of crystal phases in HfO2 and ZrO2. Aided by commercial investment in using both materials as high-k gate and DRAM dielectric materials, atomic layer deposition (ALD) processes are beginning to take full advantage of the completely solid-soluble hafnia-zirconia (Hf1-xZrxO2) ferroelectric system with new precursors and new insights obtained by systematically evaluating film growth conditions. The capability to precisely adjust the compositional profile and to alter oxidation conditions during atomic layer deposition film growth are giving an unprecedented level of control to engineer Hf1-xZrxO2 and doped HfO2 thin films for ferroelectric applications.The latest advances in atomic layer processing of Hf1-xZrxO2 and doped-HfO2 are presented where the dynamic interaction between composition and film growth conditions provide an engineering roadmap to adjust the physical and structural properties of the dielectric films. Metal precursors play a crucial role in the ensuing film properties. The adjustability of the electrical and structural properties of Hf1-xZrxO2 with ozone exposure during ALD film growth is discussed with respect to the important role oxygen and oxygen vacancies have in the overall phase stability of these novel ferroelectric materials, as well as C incorporation caused by ALD precursors. Just as atomic layer deposition has proven to be instrumental in the discovery and stabilization of the ferroelectric phase in HfO2-based thin films, atomic layer etching (ALE) of HfO2/ZrO2-based layers is now being used to preserve ferroelectricity while pushing the thickness dimension to new limits, yielding high performance films for ferroelectric tunnel junction applications. Further innovations in atomic layer processing will continue to be a harbinger of high performance ferroelectrics in the coming years based on the current status and future outlook for ferroelectric Hf1-xZrxO2 and other emerging ferroelectric materials.

A toolbox for easy entry low wavenumber in situ atomic layer deposition transmission FTIR spectroscopy studies.

A detailed description of a flexible and portable atomic layer deposition (ALD) system is presented for conducting in situ Fourier transform infrared (FTIR) absorption spectroscopy studies during the evolution and growth of ALD films. The system is directly integrated with a commercial FTIR spectrometer (Bruker Vertex 80V) to avoid the necessity of an external optical path to the instrument, thereby mitigating complexity and optical losses. In this work, we use potassium bromide (KBr) with a 5nm layer of sputtered Si as a substrate due to higher infrared transmittance when compared to a single-side polished Si wafer. The FTIR absorption study is conducted at normal incidence in transmission mode using a deuterated L-alanine doped triglycine sulfate (DTGS) detector owing to its potential applicability for reliable measurements at wavenumbers below ∼700cm-1. We demonstrate this by measuring ex situ the transverse optical phonon of bulk Al2O3 centered at 680cm-1. The integrity and functionality of the system to track the nucleation stage are validated by conducting in situ FTIR absorption measurements of Al2O3 using tri-methyl aluminum (TMA) and H2O. The measured IR absorption spectra for the Al2O3 growth after each cycle of TMA and H2O show the formation and removal of CH3 (2800-3000cm-1) groups on the substrate surface and CH4 (3016 and 1306cm-1) molecules in the reactor, thus confirming the successful tracking of ligand exchange. Thus, this instrument, together with the choice of KBr as substrate, can enable straightforward ALD nucleation studies using a DTGS detector having sufficient signal without additional optical setup and modifications to off-the-shelf FTIR systems that allow low wavenumber experiments.

Machine learning-based analysis of the physio-chemical properties for the predictive thickness control of atomic layer deposition

Atomic layer deposition (ALD) is an outstanding thin film deposition technique based on the surface chemical reaction. As the conventional device fabrication method is reported to be ineffective under the 5nm process, ALD drew attention to its ability to control the film growth. To develop an efficient ALD process, controlling film thickness is one of the most important factors. The key requirement for the film thickness control is to understand their chemical reactivity upon adsorption on different substrate surfaces. However, the current research on viable ALD development have remained inefficient because of the expensive and time-consuming experiments. In this study, we aim to analyze and suggest a strategy for identifying the contribution of ALD process features on the device film thickness based on principal component analysis (PCA) method. First, the features of ALD experiment (Precursor properties, reactant type, substrate properties, operating conditions) are compiled to define the chemical dimension of ALD process. Then, the contributions of ALD experiment features on the thickness growth are analyzed by projecting ALD chemical dimension into the information space using PCA technique. As a result, we could identify highly sensitive features for ALD film growth and suggest the strategy for controlling film thickness. From providing the analysis for the film growth, we elucidate the importance of high dimension analysis of ALD process and improve the understanding on film growth control.

Intelligent Agents for the Optimization of Atomic Layer Deposition.

Atomic layer deposition (ALD) is a highly controllable thin film synthesis approach with applications in computing, energy, and separations. The flexibility of ALD means that it can access a massive chemical catalogue; however, this chemical and process diversity results in significant challenges in determining processing parameters that result in stable and uniform film growth with minimal precursor consumption. In situ measurements of the ALD growth per cycle (GPC) can accelerate process development but it still requires expert intuition and time-consuming trial and error to identify acceptable processing parameters. This procedure is made more difficult by the presence of experimental noise in the GPC values and the complexity of ALD surface chemistries. A need exists for efficient optimization approaches capable of autonomously determining processing conditions resulting in optimal ALD film growth. In this work, we present the development of three optimization strategies and compare their performance in optimizing four simulated ALD processes. Furthermore, the effect of noise in the GPC measurements on optimization convergence is studied.

Enhanced Interfacial Toughness of Thermoplastic-Epoxy Interfaces Using ALD Surface Treatments.

Interfacial fracture and delamination of polymer interfaces can play a critical role in a wide range of applications, including fiber-reinforced composites, flexible electronics, and encapsulation layers for photovoltaics. However, owing to the low surface energy of many thermoplastics, adhesion to dissimilar material surfaces remains a critical challenge. In this work, we demonstrate that surface treatments using atomic layer deposition (ALD) on poly(methyl methacrylate) (PMMA) and fluorinated ethylene propylene (FEP) lead to significant increases in surface energy, without affecting the bulk mechanical response of the thermoplastic. After ALD film growth, the interfacial toughness of the PMMA-epoxy and FEP-epoxy interfaces increased by factors of up to 7 and 60, respectively. These results demonstrate the ability of ALD to engineer the adhesive properties of chemically inert surfaces. However, in the present case, the interfacial toughness was observed to decrease significantly with an increase in humidity. This was attributed to the phenomenon of stress-corrosion cracking associated with the reaction between Al2O3 and water and might have a significant implication for the design of these tailored interfaces.

Highly Reversible Water Oxidation at Ordered Nanoporous Iridium Electrodes Based on an Original Atomic Layer Deposition.

Nanoporous iridium electrodes are prepared and electrochemically investigated towards the water oxidation (oxygen evolution) reaction. The preparation is based on ‘anodic’ aluminum oxide templates, which provide straight, cylindrical nanopores. Their walls are coated using atomic layer deposition (ALD) with a newly developed reaction which results in a metallic iridium layer. The ALD film growth is quantified by spectroscopic ellipsometry and X‐ray reflectometry. The morphology and composition of the electrodes are characterized by scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and X‐ray diffraction. Their catalytic activity is quantified for various pore geometries by cyclic voltammetry, steady‐state electrolysis, and electrochemical impedance spectroscopy. With an optimal pore length of L≈17–20 μm, we achieve current densities of J=0.28 mA cm−2 at pH 5 and J=2.4 mA cm−2 at pH 1. This platform is particularly competitive for achieving moderate current densities at very low overpotentials, that is, for a high degree of reversibility in energy storage.

Three-dimensionally stacked Al2O3/graphene oxide for gas barrier applications

We investigated the growth behavior of Al2O3 using atomic layer deposition (ALD) on the surface of chemical vapor deposition (CVD)-grown graphene and graphene oxide (GO). While selective ALD growth was observed on CVD-grown graphene along defective sites, smooth and continuous films were grown on GO without selective growth. Linear growth of Al2O3 on GO was observed without a nucleation region or growth selectivity. This result indicates that the ALD film growth is more suitable for GO because of the abundant and homogeneously distributed reactive sites over its basal plane. By taking advantage of GO as an ideal substrate for the ALD growth of metal oxides, highly aligned, multiple-stacked, three-dimensional Al2O3/GO structures were fabricated, which showed much better effective gas barrier characteristics (1.73 × 10−4 g/m2day) than that exhibited by pristine single Al2O3 thin films of the same thickness.

Insights Towards Mitigated Mn Dissolution through Structure-Sensitive Al2O3 Film Nucleation on LiMn2O4 By Atomic Layer Deposition

Dissolution of transition metal (TM) cations into organic electrolytes is a significant impediment to capacity retention in various lithium ion battery electrode materials. Interfaces engineered via substitutional doping and protective coatings, however, have been demonstrated to be effective techniques to reduce TM dissolution, preventing counterelectrode crossover1–3. In this work, we present an integrated theoretical and experimental approach to gain a molecular level understanding towards the functionality of protective thin films. As a model system, we consider Al2O3 film growth by atomic layer deposition (ALD) on spinel LiMn2O4 (LMO), a cathode material exhibiting the well-documented capacity fade mechanism of Mn dissolution. Using first principles DFT+U calculations in concert with in situ experimental characterization, the mechanisms for Al2O3 ALD film growth by trimethylaluminum (TMA) and H2O half-reactions are evaluated. Using thermodynamically stable low-index surface truncations, as well as stepped defect features4, we identify facile pathways for full demethylation of the TMA precursor on the LMO surface. Trends from microbalance experiments indicate sub-monolayer film coverage for ~10 ALD cycles, wherein film growth is initially slow, but gradually increases until the limit of a fully formed Al2O3 film is reached. DFT calculations suggest that sluggish film growth at the onset is predicated by site blocking from decomposed CH3 groups. An electronic structure descriptor is presented to demonstrate evidence that, in early ALD pulses, Al2O3 preferentially nucleates at sites on LMO that are most susceptible to Mn dissolution. The chemical nature of these relevant defect sites will be discussed further in the context of Mn dissolution through charge disproportionation, with enhanced stability by selective nucleation of the protective films. The unique mechanisms for ALD on LMO lead to modest enhancements in electrochemical performance for only ~1-2 ALD cycles, whereas cycling capabilities reduce with further TMA/H2O pulses in the limit of a fully formed coating on the substrate. This research was supported as part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

Selective Ru ALD as a Catalyst for Sub-Seven-Nanometer Bottom-Up Metal Interconnects

Integrating bottom-up area-selective building-blocks in microelectronics has a disruptive potential because of the unique capability of engineering new structures and architectures. Atomic layer deposition (ALD) is an enabling technology, yet understanding the surfaces and their modification is crucial to leverage area-selective ALD (AS-ALD) in this field. The understanding of general selectivity mechanisms and the compatibility of plasma surface modifications with existing materials and processes, both at research and production scale, will greatly facilitate AS-ALD integration in microelectronics. The use of self-assembled monolayers to inhibit the nucleation and growth of ALD films is still scarcely compatible with nanofabrication because of defectivity and downscaling limitations. Alternatively, in this Research Article, we demonstrate a straightforward H2 plasma surface modification process capable of inhibiting Ru ALD nucleation on an amorphous carbon surface while still allowing instantaneous nucleation and linear growth on Si-containing materials. Furthermore, we demonstrate how AS-ALD enables previously inaccessible routes, such as bottom-up electroless metal deposition in a dual damascene etch-damage free low-k replacement scheme. Specifically, our approach offers a general strategy for scalable ultrafine 3D nanostructures without the burden of subtractive metal patterning and high cost chemical mechanical planarization processes.

Epitaxial Atomic Layer Deposition of Sn-Doped Indium Oxide

Coherently strained, epitaxial Sn-doped In2O3 (ITO) thin films were fabricated at temperatures as low as 250 °C using atomic layer deposition (ALD) on (001)-, (011)-, and (111)-oriented single-crystal Y-stabilized ZrO2 (YSZ) substrates. Resultant films possess cube-on-cube epitaxial relationships with the underlying YSZ substrates and are smooth, highly conductive, and optically transparent. This epitaxial ALD approach is favorable compared to many conventional growth techniques as it is a large-scale synthesis method that does not necessitate the use of high temperatures or ultrahigh vacuum. These films may prove valuable as a conductive growth template in areas where high-quality crystalline thin film substrates are important, such as solar energy materials, light-emitting diodes, or wide bandgap semiconductors. Furthermore, we discuss the applicability of this ALD system as an excellent model system for the study of ALD surface chemistry, nucleation, and film growth.

(Invited) Non-Covalent Functionalization of Epitaxial Graphene for Atomic Layer Deposition of Dielectric Oxides

The successful integration of graphene with dielectric materials is an important step in the development of high-performance graphene-based nanoelectronics. For optimal performance, dielectric layers on graphene need to be ultrathin, conformal, and the growth process needs to be well-controlled and reproducible. In practice, atomic layer deposition (ALD) – a thin film growth process that utilizes self-limiting surface reactions for digital thin film thickness control – is an industrially relevant route to grow dielectric films and nanostructures for electronic applications. However, the chemical inertness and hydrophobicity of graphene typically cause direct ALD processes to yield films of poor quality (defected, non-uniform, and poorly adhered), thereby limiting the ultimate device performance. The key to successful integration of graphene and ALD film growth resides, therefore, in the ability to tailor the graphene surface in such a way that it is amenable to ALD chemistries, but in a manner that does not perturb the properties of the graphene itself. Here, we utilize non-covalently functionalized monolayers to seed uniform film growth by ALD as well as to facilitate directed growth of dielectric nanostructures, such as nanowire arrays. We specifically highlight the use of synchrotron characterization, including X-ray surface scattering and grazing-incidence small-angle scattering, to assess the influence that the functional layers have on thin film, interfacial, and nanoscale structure.

Focus on software and semiconductor equipment

Focus on software and semiconductor equipment

Atomic Layer Deposition of AlF3 Using Trimethylaluminum and Hydrogen Fluoride

The atomic layer deposition (ALD) of AlF3 was demonstrated using trimethylaluminum (TMA) and hydrogen fluoride (HF). The HF source was HF-pyridine. In situ quartz crystal microbalance (QCM), quadrupole mass spectrometer (QMS), and Fourier transform infrared (FTIR) spectroscopy measurements were used to study AlF3 ALD. The AlF3 ALD film growth was examined at temperatures from 75 to 300 °C. Both the TMA and HF reactions displayed self-limiting behavior. The maximum mass gain per cycle (MGPC) of 44 ng/(cm2 cycle) for AlF3 ALD occurred at 100 °C. The MGPC values decreased at higher temperatures. The MGPC values were negative at T > 250 °C when TMA and HF were able to etch the AlF3 films. Film thicknesses were also determined using ex situ X-ray reflectivity (XRR) and spectroscopic ellipsometry (SE) measurements. The AlF3 ALD growth rate determined by the ex situ analysis was 1.43 A/cycle at 100 °C. These ex situ measurements were in excellent agreement with the in situ QCM measurements. FTIR analysis monitor...

The Mechanical Behavior of ALD‐Polymer Hybrid Films Under Tensile Strain

Atomic layer deposition (ALD) is increasingly becoming commonplace to deposit high density, conformal films, as novel deposition techniques allow improved deposition rates on various substrates. Diffusion and miscibility of ALD precursors with polymers are known to affect film nucleation. To assess the influence of polymeric underlayer on the growth and mechanical behavior of ALD films, we deposited aluminum oxide (Al2O3) and titanium dioxide (TiO2) films on three different polymers with known reactivity to the ALD precursors and compared them to films on polyethylene terephthalate (PET). We present the trends in nucleation and penetration of the ALD films on the various polymers as well as the in situ mechanical behavior under tensile strain. X‐ray photoelectron spectroscopy (XPS) revealed that Cytop, a fluorinated polymer and polyethyleneimine ethoxylated (PEIE) delay the nucleation of Al2O3 and TiO2 films. Time‐of‐flight mass spectrometry (ToFSIMS) shows the extent of diffusion of the ALD precursors into the polymer underlayer, delaying nucleation. Tensile tests show that while the crack onset strain remained unchanged despite the various polymer underlayers, the crack saturation density decreased for ALD films on PEIE and polyhydroxystyrene (PHOST). Films on Cytop showed no crack saturation limit until the nucleation delay was overcome indicating that judicious choice of the ALD film and polymer underlayer will allow tailoring of the length of the diffusion zone and crack saturation, but not the crack onset strain, which will be addressed in future studies.

Surface Selective Atomic Layer Deposition of Hafnium Oxide for Copper Diffusion Barrier Application Using Tetrakis(diethylamino)Hafnium and Ethanol

Atomic layer deposition (ALD) is a thin film deposition technique, in which substrate surface is exposed to reactants in cyclic manner separated by discrete purging steps. Thus one atomic layer of material is deposited per ALD cycle. This cycle is repeated until desired thickness is achieved. The bottom up nature of this deposition process facilitates excellent conformality, uniformity and thickness and composition tunability.Patterning of ALD films for various device applications is commonly performed by removing the specific part of the film or by selectively depositing films on specific areas of the surface. In the former method, patterning is done with the use of extra processing steps such as etching, lithography etc. The latter method involves the use of masking layers to prevent ALD on specific areas.1, 2 Maskless ALD, i.e., surface selective atomic layer deposition of thin films has recently garnered considerable interest due to its simplicity. This method of patterning ALD films is unique in that no surface mask is required. Materials nucleate on different surfaces to different extents. This difference in nucleation time is used to achieve selective atomic layer deposition (SALD). In our earlier studies on SALD of HfO2 and TiO2, we used water as the oxygen source.3, 4 In this study, ALD of HfO2 was carried out using tetrakis(diethylamino)hafnium and a primary alcohol (ethanol) in a custom built ALD reactor (Fig. 1). Unlike common ALD processes, here we used ethanol as the oxygen source. Ethanol reacts with the hydroxyl (-OH) groups on silicon surface and forms alkoxides that serve as a starting surface for the ALD film growth. Thus the film growth is obtained on the Si surface. Figure 2 shows the thickness tunability of the HfO2 ALD process on Si surface using ethanol as the oxygen source. HfO2 was found to grow at a rate of 0.05 nm/cycle, without any growth inhibition on the silicon surface. Linear dependence indicates self-limited growth of HfO2 thin film, typical to the ALD process. On the other hand, significant growth delay was observed on copper surface. The use of ethanol reduces surface copper oxide into metallic copper and reduces the number of potential ALD nucleation sites. Thus selective deposition of HfO2 was achieved on silicon surface over copper surface. Such selectivity depends on many ALD processing parameters and substrate pretreatment conditions. In this report, the effect of these parameters on the extent of selectivity will be discussed in detail along with copper diffusion barrier characteristics of such selectively deposited ultrathin (1-2 nm-thick) HfO2 layers. The growth rate on silicon side was measured using spectral ellipsometry. X-ray photoelectron spectroscopy was used to probe the presence of HfO2 on copper surface. Results of this study can be used to selectively deposit ultra-thin layers of HfO2 on silicon surface over copper surface for copper diffusion barrier applications. This work was supported in part by the National Science Foundation (CBET 1067424 and EEC 1062943). We also thank Dr. Gregory Jursich for many helpful discussions.

(Invited) Vapor Phase Surface Functionalization Using Atomic Layer Deposition (ALD) and Self Assembled Molecules (SAMs)

The growing adoption of Atomic Layer Deposition (ALD), as a means of producing highly uniform and conformal thin films, has paved the way for its use in an array of extremely important emerging technologies. Within this class of self-limiting deposition techniques, Self-Assembled Monolayer (SAMs) are gaining visibility as a means of functionalizing surfaces. The ability to use both SAMs and ALD together has enabled some unique applications, and presents an opportunity to study the intersection of these two thin film methods. In this work, an overview of SAMs and ALD deposition work will be presented, along with results of in-situ analysis of the growth of ALD films on the SAMs surfaces. Additionally, surface functionalization results using the hybrid ALD/SAMs combination will be explored along with prospective applications.

Synthesis, Structure, and Solution Reduction Reactions of Volatile and Thermally Stable Mid to Late First Row Transition Metal Complexes Containing Hydrazonate Ligands

Treatment of MCl2 (M = Ni, Co, Fe, Mn, Cr) with 2 equiv of the hydrazonate salts K(tBuNNCHCtBuO), K(tBuNNCHCiPrO), or K(tBuNNCMeCMeO) afforded the complexes M(tBuNNCHCtBuO)2 (M = Ni, 65%; Co, 80%; Fe, 83%; Mn, 68%; Cr, 64%), M(tBuNNCHCiPrO)2 (M = Ni, 63%; Co, 86%; Fe, 75%), and M(tBuNNCMeCMeO)2 (M = Ni, 34%; Co, 29%; Fe, 27%). Crystal structure determinations of Co(tBuNNCHCtBuO)2, M(tBuNNCHCiPrO)2 (M = Ni, Co), and M(tBuNNCMeCMeO)2 (M = Ni, Co, Fe) revealed monomeric complexes with tetrahedral geometries about the metal centers. To evaluate the potential of these new complexes as film growth precursors, preparative sublimations, thermogravimetric analyses, solid state decomposition studies, and solution reactions with reducing coreagents were carried out. M(tBuNNCHCtBuO)2 sublime between 120 and 135 °C at 0.05 Torr, whereas M(tBuNNCHCiPrO)2 and M(tBuNNCMeCMeO)2 sublime between 100 and 105 °C at the same pressure. All complexes afforded ≥96% recovery of sublimed material, with ≤3% of nonvolatile residues. The solid state decomposition temperatures were highest for M(tBuNNCHCiPrO)2 (273-308 °C), intermediate for M(tBuNNCHCtBuO)2 (241-278 °C), and lowest for M(tBuNNCMeCMeO)2 (235-250 °C). Treatment of Co(tBuNNCHCtBuO)2 in tetrahydrofuran with hydrazine, BH3(L) (L = NHMe2, SMe2, THF), pinacol borane, and LiAlH4 led to rapid formation of cobalt metal, while analogous reductions of Mn(tBuNNCHCtBuO)2 with BH3(THF), pinacol borane, and LiAlH4 appeared to afford manganese metal. The new complexes M(tBuNNCHCtBuO)2, M(tBuNNCHCiPrO)2, and M(tBuNNCMeCMeO)2 have very promising properties for use as precursors for the growth of the respective metals in atomic layer deposition film growth processes.

Study of Atomic Layer Deposition of ZnO on a Polar Oxide Substrate by In Situ Quartz Crystal Microbalance

ZnO thin films were grown using the atomic layer deposition (ALD) technique with diethyl zinc (DEZ) and deionized water as precursors. A viscous-flow atomic layer deposition reactor has been designed and constructed for the ZnO growth. An in-situ quartz crystal microbalance (QCM) has been interfaced with the reactor to monitor the ALD film growth. Using this ALD reactor we have grown ZnO films on oxidized Si(001) and on MgO(111) polar oxide substrates. QCM was used to monitor the film growth rate as function of precursor pulse time and temperature. In the ALD temperature window (130 to 170oC), the growth rate was found to be about 2.3 Aå/cycle. Ex-situ atomic force microscope (AFM) studies on ZnO thin films reveal surface roughness increases with number of ALD cycles.