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Atmospheric-pressure plasma-enhanced spatial atomic layer deposition (PE-spatial-ALD) of SiNx is demonstrated for the first time. Using bis(diethylamino)silane (BDEAS) and N2 plasma from a dielectric barrier discharge source, a process was developed at low deposition temperatures (≤ 250 °C). The effect of N2 plasma exposure time and overall cycle time on layer composition was investigated. In particular, the oxygen content was found to decrease with decreasing both above-mentioned parameters. As measured by depth profile X-ray photoelectron spectroscopy, 4.7 at.% was the lowest oxygen content obtained, whilst 13.7 at.% carbon was still present at a deposition temperature of 200 °C. At the same time, deposition rates up to 1.5 nm/min were obtained, approaching those of plasma enhanced chemical vapor deposition and thus opening new opportunities for high-throughput atomic-level processing of nitride materials.

An atmospheric-pressure plasma-enhanced spatial atomic layer deposition (PE-s-ALD) process for SiO2 using bisdiethylaminosilane (BDEAS, SiH2[NEt2]2) and O2 plasma is reported along with an investigation of its underlying growth mechanism. Within the temperature range of 100−250 °C, the process demonstrates self-limiting growth with a growth per cycle (GPC) between 0.12 and 0.14 nm and SiO2 films exhibiting material properties on par with those reported for low-pressure PEALD. Gas-phase infrared spectroscopy on the reactant exhaust gases and optical emission spectroscopy (OES) on the plasmaregion are used to identify the species that are involved in the ALD process. Based on the identified species, we propose a reaction mechanism where BDEAS molecules adsorb on −OH surface sites through the exchange of one of the amine ligands upon desorption of diethylamine (DEA). The remaining amine ligand is removed through combustion reactions activated by the O2 plasma species leading to the release of H2O, CO2, and CO in addition to products such as N2O, NO2, and CH-containing species. These volatile species can undergo further gas-phase reactions in the plasma as indicated by the observation of OH*, CN*, and NH* excited fragments in OES. Furthermore, the infrared analysis of the precursor exhaust gas indicated the release of CO2 during precursor adsorption. Moreover, this analysis has allowed the quantification of the precursor depletion yielding values between 10 and 50% depending on the processing parameters. Besides providing insights into the chemistry of atmospheric-pressure PE-s-ALD of SiO2, our results demonstrate that infrared spectroscopy performed on exhaust gases is a valuable approach to quantify relevant process parameters, which can ultimately help evaluate and improve process performance.

Area-selective atomic layer deposition (AS-ALD) holds great potential for advancing device manufacturing.1 Recently, outstanding progress on this topic has been made in terms of understanding and developing highly selective processes for various material systems; some of these processes have already been transferred into fabs.2 In this work we provide an overview of AS-ALD of silicon-based materials with high selectivity and high throughput, especially silicon oxide and nitride. While the selectivity is mostly governed by the method of choice and the underpinning chemistry, the aspect of high-throughput is ensured by using spatial ALD, which is, in our case, performed at atmospheric pressure. The processes presented here comprise three steps: selective inhibitor chemisorption, plasma-based spatial ALD and spatial back-etching. Particular focus is given to the choice of inhibitors as the most critical step in enabling high-selectivity. Here, density functional theory (DFT) calculations have been employed to unveil the chemistries governing the selectivity for the two different inhibitors within the same growth system. General guidelines on the inhibitor chemistries are derived by combining experimental and DFT results. Finally, process details and effect of plasma chemistries on different surfaces are discussed in an effort to expand the selectivity toolbox to other silicon-based materials. [1] A. Mameli, et al., “Area-Selective Atomic Layer Deposition of SiO2 using acetylacetone as a chemoselective inhibitor in an ABC-type cycle”, ACS Nano, 11, 9303, 2017. [2] H.-P. Chen, , et al., “Fully Self-Aligned Via Integration for Interconnect Scaling Beyond 3nm Node”, IEDM 2021, paper 22-1. Figure 1

In the past decade, atmospheric-pressure spatial atomic layer deposition (AP-SALD) has gained momentum as a fast deposition technique in thin-film manufacturing [1]. The key benefits of conventional ALD, such as superior control of layer thickness, conformality and homogeneity, in addition to the high throughput enabled by the spatial separation of the half-reactions and the more cost-effective processing at atmospheric pressure, make AP-SALD an interesting option for industrial large-area applications. Finally, the use of atmospheric pressure plasmas as co-reactants enables to rapidly deposit high-quality, dense films at relatively low temperatures [2]. Despite its industrial potential, the further advancement of atmospheric-pressure plasma-enhanced spatial ALD processing still lacks a detailed understanding of the underlying plasma physics and chemistry. Here, effective ALD metrology techniques are of prime importance to obtain more detailed insights into the nature of the process with the aim to improve process performance and thus to open up new industrial application fields. However, due to the very nature of the spatial concept, monitoring AP-SALD processes is rather challenging: especially in the case of close-proximity systems the substrate is typically at ~100 μm distances from the gas injection head. In this work, we employed optical emission spectroscopy (OES) and infrared spectroscopy on effluent plasma gases as diagnostics tools to study the basic chemistry of the AP-SALD process of Al2O3 films grown from Al(CH3)3 and Ar-O2 plasma in a rotary lab-scale reactor (see Fig. 1 and ref. 1). We identified the main reaction products and studied their behavior as a function of the exposure time to the precursor to verify the ALD layer-by-layer growth characteristics. The results show that using spatial separation of the ALD half-reactions and atmospheric pressure plasma as the reactant gives rise to a complex underlying chemistry (see Fig. 2). Infrared absorbance spectra show CO, CO2, H2O and CH4 as the main ALD reaction by-products originating from 1) combustion-like reactions of the methylated surface with oxygen plasma radicals and ozone, and 2) a concurrent latent thermal component related to the substrate. Moreover, CH2O and CH3OH are identified as ALD reaction by-products either formed at the surface or in the plasma by electron-induced dissociation. The investigated trends in CO2, CO and CH4 formed as a function of the exposure time confirm a self-limiting ALD behavior. Finally, the OES results corroborate that, as soon as the plasma-enhanced SALD process takes place, emission from OH and CH arises while excited oxygen species are being consumed. -------------------------------------------------------------------------------------------------------------------------------------------------------------------- References P. Poodt, A. Lankhorst, F. Roozeboom, C. Spee, D. Maas and A. Vermeer, ‘High-speed atomic layer deposition of aluminum oxide layers for solar cell passivation’, Adv. Mater., 22, 3564 - 3567 (2010). M.A. Mione, I. Katsouras, Y. Creyghton, W. van Boekel, J. Maas, G. Gelinck, F. Roozeboom, and A. Illiberi, ‘Atmospheric Pressure Plasma Enhanced Spatial ALD of ZrO2 for Low-Temperature, Large-Area Applications’, ECS Journal of Solid State Science and Technology, 6 (12) N243-N249 (2017), and refererences therein. -------------------------------------------------------------------------------------------------------------------------------------------------------------------- Figure 1

Atomic layer deposition (ALD), a gas-phase thin film deposition technique based on repeated, self-terminating gas-solid reactions, has become the method of choice in semiconductor manufacturing and many other technological areas for depositing thin conformal inorganic material layers for various applications. ALD has been discovered and developed independently, at least twice, under different names: atomic layer epitaxy (ALE) and molecular layering. ALE, dating back to 1974 in Finland, has been commonly known as the origin of ALD, while work done since the 1960s in the Soviet Union under the name "molecular layering" (and sometimes other names) has remained much less known. The virtual project on the history of ALD (VPHA) is a volunteer-based effort with open participation, set up to make the early days of ALD more transparent. In VPHA, started in July 2013, the target is to list, read and comment on all early ALD academic and patent literature up to 1986. VPHA has resulted in two essays and several presentations at international conferences. This paper, based on a poster presentation at the 16th International Conference on Atomic Layer Deposition in Dublin, Ireland, 2016, presents a recommended reading list of early ALD publications, created collectively by the VPHA participants through voting. The list contains 22 publications from Finland, Japan, Soviet Union, United Kingdom, and United States. Up to now, a balanced overview regarding the early history of ALD has been missing; the current list is an attempt to remedy this deficiency.

Atmospheric-pressure Plasma-Enhanced spatial Atomic Layer Deposition (PE-s-ALD) is a high-throughput technique for synthesizing thin films at low temperatures for large area applications. The spatial separation of the ALD half-reactions and the use of an atmospheric pressure plasma as the reactant give rise to complex surface chemistry which is not yet well understood. Here, we employed gas-phase infrared spectroscopy and optical emission spectroscopy (OES) to study the underlying chemistry of the PE-s-ALD process of Al2O3 films grown at 80 C using Al(CH3)3 and an Ar-O2 plasma. We identified the reaction products and investigated their dependence on the exposure time of the substrate to the precursor. Infrared absorbance spectra show CO, CO2, H2O, and CH4 as the main ALD reaction byproducts originating from (i) combustion-like reactions of the methylated surface with O plasma radicals and O3 and (ii) a concurrent latent thermal ALD component due to produced and/or residual H2O molecules. In addition, CH2O and CH3OH were identified as reaction by-products either originating at the surface or formed in the plasma. The OES spectra provide a corroborative proof of the combustive nature of the PE-s-ALDreactions showing OH and CH emissions arising during the spatial ALD process while excited O species are being consumed.

The continuous driving force from the semiconductor industry for realizing smaller features and device structures with higher density and higher-aspect ratio poses increasing challenges in traditional etching techniques. Atomic layer etching (ALE) provides the opportunity to overcome the shortcomings of more conventional etching processes. Extensive research in this field has led to the development of two main classes: plasma ALE to achieve anisotropic etching and thermal ALE for the isotropic counterpart. Besides anisotropic etching, plasma can also be applied for achieving isotropic etch profiles. Yet, this process option has not been explored extensively. In this work, we demonstrate isotropic ALE of ZnO on a regular array of vertical nanowires, using the alternated doses of O2 plasma and acetylacetone (Hacac). A linear ZnO thickness decrease with increasing number of cycles was measured by in-situ spectroscopic ellipsometry, and saturation behavior was demonstrated for both Hacac and O2 plasma, at 250 oC. The etch rates per cycle were found to increase from 0.5 to 1.3 A/cycle with process temperature increasing from 100 to 250 oC. Transmission electron microscopy (TEM) studies conducted on ZnO-coated nanowires before and after ALE proved the isotropic character of the process. Moreover, the ALE process produced no surface damage as concluded from high resolution TEM inspection. In-situ infrared spectroscopy measurements were conducted to elucidate the mechanism underlying self-limited etching. Based on these measurements, a preliminary reaction mechanism is proposed, in which Zn(acac)2 is assumed to be the etching product and persisting acac-species on the ZnO surface provide the self-limiting character. Finally, a high etch selectivity over SiO2 and HfO2, and the possibility to extend the process to other oxides such as Al2O3 are also demonstrated. We believe that this plasma-based ALE process represents a valuable addition to the ALE toolbox and opens-up new possibilities for using plasma-processing to achieve isotropic etch profiles. Furthermore, similar approaches can be used to extend the process to other materials by tuning the plasma chemistry accordingly.

Area-selective atomic layer deposition (ALD) of ZnO was achieved on SiO2 seed layer patterns on H-terminated silicon substrates, using diethylzinc (DEZ) as the zinc precursor and H2O as the coreactant. The selectivity of the ALD process was studied using in situ spectroscopic ellipsometry and scanning electron microscopy, revealing improved selectivity for increasing deposition temperatures from 100 to 300 °C. The selectivity was also investigated using transmission electron microscopy and energy-dispersive X-ray spectroscopy. Density functional theory (DFT) calculations were performed to corroborate the experimental results obtained and to provide an atomic-level understanding of the underlying surface chemistry. A kinetically hindered proton transfer reaction from the H-terminated Si was conceived to underpin the selectivity exhibited by the ALD process. By combining the experimental and DFT results, we suggest that the trend in selectivity with temperature may be due to a strong DEZ or H2O physisorption on the H-terminated Si that hampers high selectivity at low deposition temperature. This work highlights the deposition temperature as an extra process parameter to improve the selectivity.

The combination of area-selective ALD intermitted with back-etching steps has recently attracted much interest because of its potential in achieving high selectivity. Compared to non-interrupted area-selective ALD this supercycle approach has proven to be very effective in reducing the defectivity on the non-growth areas and thickening the layers on the growth areas.1, 2 In this work we studied the case of selective SiO2 deposition on silicon substrate wafers (growth area) with large ZnO patterns (non-growth area). We will demonstrate the effectiveness of this complementary approach, i.e., deposition and etch-back corrections in a rotary atmospheric-pressure all-spatial processing (= ‘dep/etch’) reactor (Fig. 1) to maximize SiO2 selectivity while obtaining high deposition rates. For the selective spatial ALD part of the supercycle a three-step (‘ABC’-type) recipe was adopted,3 consisting of exposure to: A) inhibitor, B) silicon precursor (BDEAS) and C) O2 plasma. The periodic back-etch intermissions in the supercycle were carried out in the same integrated spatial process reactor by exposing the substrate to a CF4-O2-N2 plasma. The plasma source used for both O2-plasma and the back-etch was of the atmospheric-pressure Dielectric Barrier Discharge (DBD) type4. Figure 2 gives an illustration for a supercycle process with the substrate rotating at 20 rpm and using 3 repetitions of 40 ‘ABC’-cycles and 6 corrective back-etch cycles. During the each set of 40 ‘ABC’-cycles we could selectively grow sufficient (i.e., up to ~3.5 nm) SiO2 layer thickness on the growth area before the first nucleation of SiO2 became apparent on the ZnO non-growth areas. This way some selectivity is gradually lost with the number of ALD cycles increasing. As shown in Fig. 2 the selectivity loss can be repeatedly restored by a CF4-O2-N2 plasma back-etch with no silicon detected on the non-growth area by XPS. We demonstrated that with 3 repeated ‘dep/etch’ supercycles up to 10 nm thick SiO2 could be grown on the growth area. We will discuss how Low Energy Ion Spectroscopy (LEIS), with its extreme sensitivity to the top monolayer(s) of a thin film, can give more and reliable quantitative information on the process selectivity and the defectivity on the non-growth area in terms of surface coverage and derived thickness. In addition, scanning probe FTIR-AFM microscopy can give information about the defects and contaminants at the substrate surface. Furthermore, we extended the selective spatial ALD of SiO2 to other oxidic non-growth areas like Al2O3, IGZO, SnO2, Ta2O5 and ZrO2. 1. R. Vallat, et al., J. Vac. Sci. Technol. A, 35, 01B104 (2017). 2. S. K. Song, et al., Chem. Mater. 31, 4793-4804 (2019). 3. A. Mameli, et al., ACS Nano, 11, 9303-9311 (2017). 4. Y. Creyghton, P. Poodt, M. Simor, F. Roozeboom, US Patent Application 20170137939. Figure 1

Open-space nanomaterials are a widespread class of technologically important materials that are generally incompatible with analysis by atom probe tomography (APT) due to issues with specimen preparation, field evaporation and data reconstruction. The feasibility of encapsulating such non-compact matter in a matrix to enable APT measurements is investigated using nanoparticles as an example. Simulations of field evaporation of a void, and the resulting artifacts in ion trajectory, underpin the requirement that no voids remain after encapsulation. The approach is demonstrated by encapsulating Pt nanoparticles in an ZnO:Al matrix created by atomic layer deposition, a growth technique which offers very high surface coverage and conformality. APT measurements of the Pt nanoparticles are correlated with transmission electron microscopy images and numerical simulations in order to evaluate the accuracy of the APT reconstruction.

Today, Li-ion batteries are key devices in energy storage, with a wide set of applications ranging from mW to kW, such as portable electronics devices, electric vehicles and grid-storage. Typically, high energy density anodes such as Si or Li, combined with Ni- or Li-rich cathodes 1,2 are necessary to obtain the targeted gravimetric energy density (>350 Wh/kg). However, several high-potential redox-chemistries can lead to serious safety and degradation issues during charge-discharge cycling due to oxidative and reductive instabilities 3, that often occur at the electrode-electrolyte interfaces 4. Therefore, for every Li-ion battery chemistry the optimization of these interfaces with chemo-mechanically stable and Li-ion conductive passivation layers is essential in mitigating the non-compatibility of the individual cell components. These interface stabilizing layers can be incorporated either in-situ by using electrolyte additives or ex-situ by chemical and physical methods. One popular option here is offered by atomic layer deposition (ALD) which is today’s technology of choice to achieve films with superior quality and 3D-conformality with atomic-scale thickness precision. However, conventional vacuum-based temporal ALD is not compatible with industrial high-throughput roll-to-roll battery electrode production. Here, the technique of large-area atmospheric-pressure spatial-ALD (s-ALD) as pioneered by TNO-Holst Centre over a decade ago can offer prime solutions for various applications including thin-film batteries 5. This technique opens up a wide range of cost-effective applications based on materials like metal oxides, nitrides, sulfides, oxysulfides as well as hybrid organic-inorganic material combinations. In this presentation, we will discuss the growth of several s-ALD films made from Al2O3, TiO2, and ZnO which have been specifically optimized for dendritic Li-growth suppression, interface stabilization, and cathode degradation protection. Next, we will discuss some recent results on the up-scalable s-ALD growth of thin LiPON electrolyte films with a high Li-ion conductivity of >10-7 S/cm, low electronic conductivity of -12 S/cm, and high stability against anodic Li-metal during cycling. This electrolyte is also essential in the development of protective layers in liquid and polymer electrolyte-based Li-ion batteries, and in thin-film solid-state batteries with ultra-thin electrolyte layers and planar and 3D topologies. REFERENCES S. Myung et al., ACS Energy Lett. 2, 196–223 (2017). G. Assat and J. M. Tarascon, Nat Energy 3, 373–386 (2018). H. Ryu et al., Chem. Mater. 3 (30), 1155-1163 (2018). D. Aurbach et al., Solid State Ionics 148, 405–416 (2002). P. Poodt et al., J. Vac. Sci. and Technol. A 30, 010802 (2012).

Welcome to G01: Atomic Layer Deposition Applications 16! Take a moment to listen to welcome remarks from the lead organizer, Fred Roozeboom.

Area-selective ALD interleaved with etch-back steps in a supercycle fashion has recently been reported as very effective in achieving high selectivity. Such supercycles can result in lower defectivity on the non-growth area and thicker layers on the growth area, as compared to solely area-selective ALD.1, 2 Here, we use low energy ion scattering (LEIS) to probe the selectivity of the first supercycle, consisting of plasma-enhanced selective spatial-ALD of SiO2 and conventional CF4-based reactive ion etching (RIE). Given its extreme sensitivity to the top monolayer(s) of a thin film, LEIS can reliably quantify the selectivity/defectivity on the non-growth areas in terms of surface coverage and derived thickness. A three-step approach was used for the area-selective spatial ALD of SiO2,3 which consisted of inhibitor, silicon precursor (BDEAS), and O2 plasma exposures. The process selectivity as a function of the number of cycles was probed using LEIS to monitor the SiO2 surface coverage on the non-growth area. After 20 spatial ALD cycles, no silicon was detected on the non-growth area (detection limit 2 % SiO2 surface coverage), implying excellent process selectivity. Increasing the number of ALD cycles resulted in a gradual loss of selectivity. Interestingly after 110 ALD cycles, the SiO2 coverage was 86%, indicating a not yet closed layer. At the same time, a SiO2 thickness of 11 nm was measured on the growth area, using spectroscopic ellipsometry. As the last step of the super-cycle, a 3 seconds RIE was sufficient to bring the SiO2 coverage back to zero on the non-growth area, while an 8 nm thick SiO2 layer was left on the growth area. The data presented in this work demonstrate the effectiveness of combining area-selective spatial ALD + etch-back corrections to achieve extreme SiO2 selectivity while retaining high deposition rates. Finally, we have extended the plasma-enhanced area-selective spatial ALD of SiO2 to other oxides and metals non-growth areas. REFERENCES 1. R. Vallat et al., JVSTA, 35, 01B104 (2017). 2. S. K. Song et al., Chem. Mater. 31 4793-4804 (2019). 3. A. Mameli et al., ACS Nano, 11, 9303-9311 (2017). Figure 1

Zinc oxysulfide (ZnOS) is synthesized at atmospheric pressure in a laboratory-scale spatial atomic layer deposition setup by sequentially exposing the substrate to diethyl zinc and an H2O/H2S mixture, separated by a nitrogen gas curtain. The co-injection of H2O and H2S vapors in the same deposition zone enables an accurate control of the S/(O + S) ratio, the morphology, and the optoelectronic properties of the films. Next, the ZnOS deposition process is transferred to an industrial roll-to-roll spatial-ALD setup. ZnOS is applied as a buffer layer in flexible Cu(In,Ga)Se2 solar cells, instead of the commonly used CdS, achieving a best efficiency of typically 13% in small area cells (0.57 cm2) and 9.2% in flexible mini-modules (270 cm2). These results show the viability of atmospheric spatial-ALD as a new technique for roll-to-roll manufacturing of flexible photovoltaics modules based on a Cu(In,Ga)Se2 absorber.

In this manuscript, the authors investigate the growth of indium zinc oxide, indium zinc oxide (InZnO, IZO) as a channel material for thin-film transistors. IZO is grown at atmospheric pressure and a high deposition rate using spatial atomic layer deposition (S-ALD). By varying the ratio of diethylzinc and trimethylindium vapor, the In/(In + Zn) ratio of the film can be accurately tuned in the entire range from zinc oxide to indium oxide. Thin film transistors with an In to Zn ratio of 2:1 show high field-effect mobility—exceeding 30 cm2/V s—and excellent stability. The authors demonstrate large scale integration in the form of 19-stage ring oscillators operating at 110 kHz. These electrical characteristics, in combination with the intrinsic advantages of atomic layer deposition, demonstrate the great potential of S-ALD for future display production.

The maximum conductivity achievable in Al-doped ZnO thin films prepared by atomic layer deposition (ALD) is limited by the low doping efficiency of Al. To better understand the limiting factors for the doping efficiency, the three-dimensional distribution of Al atoms in the ZnO host material matrix has been examined on the atomic scale using a combination of high-resolution transmission electron microscopy (TEM) and atom probe tomography (APT). Although the Al distribution in ZnO films prepared by so-called "ALD supercycles" is often presented as atomically flat δ-doped layers, in reality a broadening of the Al-dopant layers is observed with a full-width-half-maximum of ∼2 nm. In addition, an enrichment of the Al at grain boundaries is observed. The low doping efficiency for local Al densities > ∼1 nm-3 can be ascribed to the Al solubility limit in ZnO and to the suppression of the ionization of Al dopants from adjacent Al donors.

Area-selective atomic layer deposition (AS-ALD) allows nanostructures of arbitrary composition and lateral shape to be built with atomic precision on pre-selected substrate locations. Most current approaches for AS-ALD are based on local inhibition (e.g. with self-assembled monolayers) or activation. However, for some applications of AS-ALD (e.g. in self-aligned fabrication) it is relevant to be able to exploit differences in chemical behavior of a pre-patterned substrate. For this reason, investigating inherent differences in nucleation on diverse substrates is of crucial importance for developing future AS-ALD processes. In this paper we are focussing on substrates of silicon and silicon-based dielectric materials (SiC, Si0 2 and SiNx) used in electronics.

Conventional Atomic Layer Deposition (ALD) is also a cycled process, with the extra benefit of the half-reactions being self-limiting, thus enabling layer-by-layer growth. A major obstacle holding ALD from large-scale, high-throughput manufacturing has been the very low deposition rate. This was overcome only recently by introducing the spatial atmospheric-pressure version 1]. Today, spatial ALD is used commercially by the solar industry, and soon other application domains will follow. Shallow and deep plasma etching with nanoscale accuracy is also increasingly based on alternating half-cycles of a directional etch and an isotropic deposition of a passivating polymer layer (usually fluorocarbon or oxyfluoride). Also here the process rates are slow, and to speed up atomic precision etching we conceived a spatially-divided concept as well [2,3]. The process is converted from time- into spatially separated by inserting inert gas-bearing ‘curtains’ of heights down to ~100 μm that confine the reactive gases to individual injection slots in a gas injector head. By moving substrates back and forth under the head one accomplishes the alternate etch/ passivation cycles without idle times needed for switching pressure or purging. The pressure settings range from low-pressure for etching to (sub)atmospheric for passivation, and can be optimized for each separate process zone thus maximizing the total etch rate. A further improvement towards an all-spatial etch approach is in the passivation cycle where the conventional polymer passivation layer is replaced by a spatial atmospheric-pressure ALD-grown oxide passivation layer; see Fig. 1). We have conducted both thermal ALD of Al2O3 at 200 oC and plasma-enhanced SiO2 ALD at 50 oC in pre-etched high aspect ratio trenches (65 nm width and 9 μm depth) in a rotary spatial atmospheric-pressure reactor, and showed - with non-optimized processing and equipment - step conformality values of ³ 80 % for the Al2O3 and 70 % for the SiO2 which is sufficient for most passivations. We conducted a preliminary etch/ALD oxide passivation/etch cycle on a Si-sample with a trench-patterned hard SiO2 mask on top. The sample was processed in two separate (non-connected) reactor chambers, each chamber being supplied with a surface Dielectric Barrier Discharge (DBD) micro-plasma source. The following process cycle was carried out: 1) a 1 min. plasma etch step using SF6/O2 on a biased, non-moving Si-substrate in the low-pressure chamber at room temperature, 2) the thermal deposition of an Al2O3 passivation of only 5 monolayers (5 rotations) in the rotary spatial atmospheric pressure ALD reactor described as above, 3) an identical 1 min. plasma etch step in the low-pressure chamber. The cross-sectional etch profile thus obtained (Fig. 2) showed two typical scallops on the trench sidewall, revealing that both directional and lateral etch had been accomplished in a mixed anisotropic/ isotropic regime where as little as 5 monolayers of Al2O3 passivation were sufficient to preserve the shape of the scallop carved out in the first cycle. Another remarkable observation was the flat etch front of the trench bottom. This may be indicative for the robustness of ALD-grown Al2O3 passivation, and desired in atomically smooth precision etching. In continuous etching trench bottoms are often micro-trenched due to ion scattering from the trench sidewalls which results in faster etching of the side corners. We note that these results have been obtained with non-optimized processing and equipment, so we are confident that further optimization will give more improvements and insights. The process variables are manifold: gas concentration, pressure in the etch and passivation chambers, plasma power, substrate voltage biasing, room temperature processing, plasma source-to-substrate distance, passivation with other spatial ALD oxides like SiO2. We conclude by stating that this all-spatial concept, called ALD-enabled RIE, may find industrial use in cost-effective back-end- and front-end-of-line processing, especially in patterning of structures that require minimum interface, line edge and fin sidewall roughness (i.e., atomic-scale fidelity with selective removal of atoms and retention of sharp corners). Besides in CMOS scaling this concept may also become an important option for fast etching of silicon (or III/V) in die dicing, TSV and MEMS processing. References 1. P. Poodt, D.C. Cameron, E. Dickey, S.M. George, V. Kuznetsov, G.N. Parsons, F. Roozeboom, G. Sundaram, and A. Vermeer, J. Vac. Sc. Technol. A, 30, 010802-1 (2012). F. Roozeboom, A.M. Lankhorst, P.W.G. Poodt, N.B. Koster, G.J.J. Winands, and A.J.P.M. Vermeer, Apparatus and method for reactive ion etching, Patent application WO 2011/105908, 1 Sept. 2011; US 20130118895 A1, May 16, 2013. F. Roozeboom, F. van den Bruele, Y. Creyghton, P. Poodt, and W.M.M. Kessels, ECS Journal of Solid State Science and Technology, 4 (6) N5067 (2015). http://jss.ecsdl.org/content/4/6/N5067.full.pdf Figure 1

Current trends in semiconductor device manufacturing impose extremely stringent requirements on nanoscale processing techniques, both in terms of accurately controlling material properties and in terms of precisely controlling nanometer dimensions. To take nanostructuring by dry etching to the next level, there is a fast growing interest in so-called atomic layer etching processes, which are considered the etching counterpart of atomic layer deposition processes. In this article, past research efforts are reviewed and the key defining characteristics of atomic layer etching are identified, such as cyclic step-wise processing, self-limiting surface chemistry, and repeated removal of atomic layers (not necessarily a full monolayer) of the material. Subsequently, further parallels are drawn with the more mature and mainstream technology of atomic layer deposition from which lessons and concepts are extracted that can be beneficial for advancing the field of atomic layer etching.

Area-selective atomic layer deposition (ALD) is rapidly gaining interest because of its potential application in self-aligned fabrication schemes for next-generation nanoelectronics. Here, we introduce an approach for area-selective ALD that relies on the use of chemoselective inhibitor molecules in a three-step (ABC-type) ALD cycle. A process for area-selective ALD of SiO2 was developed comprising acetylacetone inhibitor (step A), bis(diethylamino)silane precursor (step B), and O2 plasma reactant (step C) pulses. Our results show that this process allows for selective deposition of SiO2 on GeO2, SiNx, SiO2, and WO3, in the presence of Al2O3, TiO2, and HfO2 surfaces. In situ Fourier transform infrared spectroscopy experiments and density functional theory calculations underline that the selectivity of the approach stems from the chemoselective adsorption of the inhibitor. The selectivity between different oxide starting surfaces and the compatibility with plasma-assisted or ozone-based ALD are distinct features of this approach. Furthermore, the approach offers the opportunity of tuning the substrate-selectivity by proper selection of inhibitor molecules.

To date, conventional thermal atomic layer deposition (ALD) has been the method of choice to deposit high-quality Pt thin films grown typically from (MeCp)PtMe3 vapor and O2 gas at 300 °C. Plasma-assisted ALD of Pt using O2 plasma can offer several advantages over thermal ALD, such as faster nucleation and deposition at lower temperatures. In this work, it is demonstrated that plasma-assisted ALD at 300 °C also allows for the deposition of highly conformal Pt films in trenches with high aspect ratio ranging from 3 to 34. Scanning electron microscopy inspection revealed that the conformality of the deposited Pt films was 100% in trenches with aspect ratio (AR) up to 34. These results were corroborated by high-precision layer thickness measurements by transmission electron microscopy for trenches with an aspect ratio of 22. The role of the surface recombination of O-radicals and the contribution of thermal ALD reactions is discussed.

Atomic layer deposition (ALD) is renowned for its step coverage in porous substrates. Several emerging applications require a combination of this high step coverage with high throughput ALD, like spatial ALD. Often, high throughput ALD is performed at atmospheric pressure, and therefore, the effect of reactor pressure on the saturation dose is investigated. ALD inside porous substrates is governed by three key parameters: the reaction probability, the pore aspect ratio, and the precursor diffusion coefficient, of which the latter one contains the reactor pressure dependency. The effect of these parameters on the saturation dose is validated using Monte Carlo modeling, where the reactor pressure dependency is included through the mean free path. A reaction-limited and a diffusion-limited regime can be identified, and it is shown that for many realistic experimental conditions, even at low reactor pressures, the saturation dose is in the diffusion-limited regime. An expression for the pressure dependent saturation dose in the diffusion-limited regime is derived. For small pore diameters, the saturation dose is pressure independent, but for larger pores, higher saturation doses are required for atmospheric reactor pressures than for low reactor pressures. However, as high reactor pressures enable much higher precursor partial pressures than low reactor pressures, the resulting saturation times can be much shorter at atmospheric pressure than low pressure. Often, high surface area porous substrates will lead to supply limited conditions, and increased saturation times have to be taken into account. These results show that the atmospheric pressure ALD can be used for high throughput ALD inside porous substrates, as long as high precursor partial pressures and molar flows can be applied. This is experimentally demonstrated by a near 100% step coverage obtained by atmospheric spatial ALD of alumina in high aspect ratio pores.

Researchers present a novel method for area-selective atomic layer deposition (AS-ALD) large-area electronics. It is a direct-write ALD process of In 2O 3:H, a highly promising and relevant transparent conductive oxide (TCO) material which makes use of printing technology for surface activation. first the surface of H-terminated silicon materials is locally activated by a μ-plasma printer in air or O 2, and In 2O 3:H is deposited selectively on the activated areas. The selectivity stems from the fact that ALD In 2O 3:H leads to very long nucleation delays on H-terminated silicon materials.

High permittivity (high-k) materials have received considerable attention as alternatives to SiO2 for CMOS and low-power flexible electronics applications. In this study, we have grown high-quality ZrO2 by using atmospheric-pressure plasma-enhanced spatial ALD (PE-sALD), which, compared to temporal ALD, offers higher effective deposition rates and uses atmospheric-pressure plasma to activate surface reactions at lower temperatures. We used tetrakis(ethylmethylamino)zirconium (TEMAZ) as precursor and O2 plasma as co-reactant at temperatures between 150 and 250◦C. Deposition rates as high as 0.17 nm/cycle were achieved with N- and C- contents as low as 0.4% and 1.5%, respectively. Growth rate, film crystallinity and impurity contents in the films were found to improve with increasing deposition temperature. The measured relative permittivity lying between 18 and 28 with leakage currents in the order of 5 × 10−8 A/cm2 demonstrates that atmospheric PE-sALD is a powerful technique to deposit ultrathin, high-quality dielectrics for low-temperature, large-scale microelectronic applications.

Atomic layer deposition (ALD) using (MeCp)PtMe3 and O2 gas or O2 plasma is a well-established technique for the deposition of thin films of Pt, but the potential of ALD to deposit platinum oxide (PtOx) has not yet been systematically explored. This work demonstrates how PtOx can be deposited by plasma-assisted (PA)-ALD in a temperature window from room temperature (RT) to 300¿°C by controlling the O2 plasma and (MeCp)PtMe3 exposure. With increasing substrate temperature, the thermal stability of PtOx decreases and the reducing activity of the precursor ligands increases. Therefore, longer O2 plasma exposures and/or lower (MeCp)PtMe3 exposures are required to obtain PtOx at higher temperatures. Furthermore, it is established that, during the nucleation stage, PtOx ALD starts by the formation of islands that grow and coalesce during the initial ~40 cycles. Closed-layer thin films of PtOx with an O/Pt ratio of 2.5 can be deposited at 100¿°C with a minimal thickness of only ~2¿nm. It is also demonstrated that a conformality of ~90% can be reached for PtOx films in trenches with an aspect ratio of 9 when using optimized O2 plasma and precursor exposure times.

The industrial need for high-throughput and low-cost ZnO deposition processes has triggered the development of atmospheric vapor-phase deposition techniques which can be easily applied to continuous, in-line manufacturing. While atmospheric CVD is a mature technology, new processes for the growth of transparent conductive oxides on thermally sensitive materials or flexible substrates are being developed, such as atmospheric plasma-enhanced (PE)-CVD and atmospheric spatial atomic layer deposition (ALD). In this article, the challenges and recent results on the growth of ZnO under atmospheric pressure by CVD, PE-CVD, and spatial ALD are reviewed and the use of these films as transparent electrodes in thin film solar cells are presented.

Indium-doped zinc oxide (ZnO:In) has been grown by spatial atomic layer deposition at atmospheric pressure (spatial-ALD). Trimethyl indium (TMIn), diethyl zinc (DEZ) and deionized water have been used as In, Zn and O precursor, respectively. The metal content of the films is controlled in the range from In/[In+Zn] = 0 to 23% by co-injecting the vaporized metal precursors (i.e. DEZ and TMIn) in the deposition region and varying their flows. A high doping efficiency (up to 95%) is achieved, resulting in films with very high carrier density (6 1020 cm-3), low resistivity (3 mΩ cm) and high transparency in the visible range (> 85%). The morphology of the films changes from polycrystalline to amorphous with increasing indium content above 15%, while maintaining a low resistivity value (< 7 mΩ cm). Spatial-ALD combines a fine tuning of the composition, morphology and electrical properties of ZnO:In films with high deposition rates (> 0.1 nm/s). cop. 2014 The Electrochemical Society.

The atomic layer deposition (ALD) process of hydrogen-doped indium oxide (In

Area-selective atomic layer deposition (AS-ALD) has great potential in reducing cost by maskless device manufacturing of patterned layers. Still, in this new bottom-up approach the selectivities currently obtained for film growth on patterned growth areas vs. that on the non-growth areas are often very limited. Also the substrate throughput values for conventional low-pressure ALD is too low for industrial acceptance (1,2). In this work we present a process for AS-ALD of SiO2 using intermittent plasma etch-back steps to increase the selectivity above 10 nm film thickness (3). In addition, the deposition process itself is performed in a spatial ALD reactor at atmospheric pressure which allows for achieving high throughput (4). AS-ALD of SiO2 on a substrate with pre-patterned SiO2 and ZnO areas was demonstrated using a chemo-selective inhibitor that chemisorbs preferentially on the non-growth area (ZnO) while allowing the deposition of SiO2 on the growth area (SiO2). In order to maximize the process selectivity, a blanket fluorocarbon plasma etch-back step was interleaved after every 110 ALD cycles. This way, selective SiO2 deposition up to ~ 30 nm film thickness was demonstrated (Fig. 1). Furthermore, X-ray Photoelectron Spectroscopy was carried out to verify the selectivity of the process: no Si was detected (detection limit 0.3 at. %) on the non-growth area, demonstrating the high selectivity of the process. The process presented here combines selective inhibitor chemisorption, plasma-based spatial ALD with high deposition rates and plasma etch-back steps to correct for selectivity loss. This approach is compatible with roll-to-roll and sheet-to-sheet concepts and can therefore enable high-throughput AS-ALD on large-area and flexible substrates. ---------------------------------------------------------------------------------------------------------------------------------------------------------------- References 1. A. Mameli, M.J.M. Merkx, B. Karasulu, F. Roozeboom, W.M.M. Kessels and A.J.M. Mackus, ‘Area-Selective Atomic Layer Deposition of SiO2 using acetylacetone as a chemoselective inhibitor in an ABC-type cycle’, ACS Nano, 11, 9303-9311 (2017). 2. F. S. Minaye Hashemi, C. Prasittichai and S. F. Bent, ‘Self-Correcting Process for High Quality Patterning by Atomic Layer Deposition’, ACS Nano, 9, 8710-8717 (2015). 3. R. Vallat, R. Gassilloud, B. Eychenne and C. Vallée, ‘Selective deposition of Ta2O5 by adding plasma etching super-cycles in plasma-enhanced atomic layer deposition steps’, J. Vac. Sc. Technol. A, 35, 01B104 (2017). 4. P. Poodt, A. Lankhorst, F. Roozeboom, C. Spee, D. Maas and A. Vermeer, ‘High-speed atomic layer deposition of aluminum oxide layers for solar cell passivation’, Adv. Mater., 22, 3564-3567 (2010). ---------------------------------------------------------------------------------------------------------------------------------------------------------------- *Presenting author: F. Roozeboom (f.roozeboom@tue.nl ; fred.roozeboom@tno.nl) ---------------------------------------------------------------------------------------------------------------------------------------------------------------- Figure 1

The key challenges in next-generation all-solid-state Li-ion battery technology are related to the energy and power densities required, fast charging constraints, battery lifetime, while keeping the cost low by high-volume manufacturing. Currently, EVs are based on Li-ion batteries that often utilize highly flammable and toxic components such as liquid organic electrolyte, thus imposing a potential threat in case of failure. There is high pressure on developing batteries that are safer, smaller, and cheaper. Here, we report on innovative materials and architectural approaches that have the potential to disrupt current Li-ion battery technology, especially by combining high-capacity with high charging/discharging rates. We aimed at improving 3D battery performance by using large area atmospheric pressure spatial atomic layer deposition (sALD) for further tuning the electrode and electrolyte layers at the nanometer-scale. Apart from enabling high charge/discharge rates, 3D electrode architectures pave the way for the use of high-capacity materials without long-term cycling challenges. We will show the potential of the intrinsically safe 3D all-solid-state batteries that can be extended to energy densities required for automotive (850 Wh/l and 375 Wh/kg at cell level). However, novel architectures demand newer processing techniques, especially for conformal layer stacks over 3D structures. In this regard, we will present the results on high-rate 3D Li-ion battery electrodes coated using our patented sALD technology, which enables charging times below 10 minutes. Next, we will discuss the first-ever sALD-based LiPON electrolyte material, deposited at least 10x faster than the current technologies using conventional ALD systems, and exhibiting high Li-ion conductivity > 10-7 S/cm and very low electronic conductivity (< 10-12 S/cm). The LiPON layers are pinhole-free and demonstrated to be cycled without shorts. Such electrolytes are also relevant for the development of protection layers in wet electrolyte-based lithium ion batteries, as well as for enabling thin-film planar and 3D solid-state batteries with ultrathin electrolyte layers (few 10’s of nanometers). Highlighted during the presentation will also be the attribute of the sALD technique to produce conformal and upscalable coatings that can be applied in roll-to-roll processing using metal foils to further enable the innovative and cost-effective 3D battery layers.

Atomic layer deposition offers the unique opportunity to control, at the atomic level, the 3D distribution of dopants in highly uniform and conformal thin films. Here, it is demonstrated that the maximum doping efficiency of Al in ZnO can be improved from ∼10% to almost 60% using dimethylaluminum isopropoxide (DMAI, Al(CH3)2(OiPr)) as an alternative Al precursor instead of the conventionally used trimethylaluminum (TMA, Al(CH3)3). Due to the steric hindrance of the isopropoxyl ligand of the precursor, the Al atoms can be deposited more widely dispersed, which enables higher active-dopant densities and hence a higher conductivity of the Al-doped films.

Strontium titanate, SrxTiyOz (STO), thin films with various cation stoichiometries were deposited by plasma-assisted atomic layer deposition (ALD) using cyclopentadienyl-based metal precursors and oxygen plasma as counter-reactant. [Sr]/([Sr] + [Ti]) compositions ranging from 0.46 to 0.57 were obtained by changing the (SrO)/(TiO2) ALD cycle ratios. As-deposited 15–30 nm thick SrxTiyOz films prepared at 350 °C on Pt-coated silicon substrates were amorphous. Post-annealing at 600/650 °C for 10 min under N2 gas resulted in a crystallization into the perovskite phase. Stoichiometric STO and Sr-rich STO films exhibited a certain degree of (111) texture while the Ti-rich STO films showed a lower degree of crystallization. Crystallized layers exhibited a smaller band gap Eg than amorphous ones, while within the stoichiometry series the value of Eg increased with increasing Sr-content. Within the stoichiometry series Pt/STO/Pt structures with Sr-rich STO films showed the lowest leakage current densities. At 1.0 V values of about 2 × 10−8 and 5 × 10−6 A cm−2 were obtained for the as-deposited and the annealed films, respectively. Highest capacitance density was obtained for 15 nm polycrystalline stoichiometric SrTiO3 films resulting in a capacitor equivalent thickness CET of about 0.7 nm. Pt/SrxTiyOz/Pt capacitors with the STO being in amorphous state exhibited a positive voltage nonlinearity factor α of about 400 ppm V−2, while the negative α-values for crystallized films showed a systematic variation with the stoichiometry, the degree of crystallization and the thickness of the STO layer. This demonstrates that a broad performance range of MIM capacitors is accessible by controlling the stoichiometry and the degree of crystallization of plasma-assisted ALD SrxTiyOz thin films.

The crystallization behavior of thin strontium titanate (SrTiO3, STO) films with ~15 nm thickness was studied by Transmission Electron Microscopy (TEM). Amorphous STO films with [Sr]/([Sr]+[Ti]) ratio ranging from 0.50 to 0.63 were deposited at 350°C by plasma-assisted ALD and subsequently treated by rapid thermal annealing in flowing N2 for crystallization. Different temperatures and annealing durations were employed to fully characterize the crystallization process. TEM analysis showed that transrotational crystals were formed and evidenced the influence of the STO composition and of the thermal budget applied on the grain size, crack and void formation. In particular, Sr-rich layers ([Sr]/([Sr]+[Ti] = 0.59) showed a finer crystalline structure which was imputed to a higher nucleation probability at the onset of the crystallization process. Crystallization into the perovskite structure was confirmed for all the film compositions studied. By tuning the STO composition and the thermal budget of the annealing step it was demonstrated that it is possible to control the microstructure of the crystallized film as a further step in optimizing the STO film properties.

The current industrial process of choice for Deep Reactive Ion Etching (DRIE) of 3D features, e.g. Through-Silicon Vias (TSVs), Microelectromechanical Systems (MEMS), etc., is the Bosch process, which uses alternative SF6 etch cycles and C4F8-based sidewall passivation cycles in a time-sequenced mode. An alternative, potentially faster and more accurate process is to have wafers pass under spatially-divided reaction zones, which are individually separated by so-called N2-gas bearings ‘curtains’ of heights down to 10–20 μm. In addition, the feature sidewalls can be protected by replacing the C4F8-based sidewall passivation cycles by cycles forming chemisorbed and highly uniform passivation layers of Al2O3 or SiO2 deposited by Atomic Layer Deposition (ALD), also in a spatially-divided mode. ALD is performed either in thermal mode, or plasma-assisted mode in order to achieve near room-temperature processing. For metal filling of 3D-etched TSVs, or for deposition of 2D metal conductor lines one can use Laser-Induced Forward Transfer (LIFT) of metals. LIFT is a maskless, ‘solvent’-free deposition method, utilizing different types of pulsed lasers to deposit thin material (e.g. Cu, Au, Al, Cr) layers with μm-range resolution from a transparent carrier (ribbon) onto a close-by acceptor substrate. It is a dry, single-step, room temperature process in air, suitable for different types of interconnect fabrication, e.g. TSV filling and redistribution layers (RDL), without the use of wet chemistry.

Microsystems are increasingly being applied in harsh and/or inaccessible environments, but many markets expect the same level of functionality for long periods of time. Harsh environments cover areas that can be subjected to high temperature, (bio)-chemical and mechanical disturbances, electromagnetic noise, radiation, or high vacuum. In the field of actuators, the devices must maintain stringent accuracy specifications for displacement, force, and response times, among others. These new requirements present additional challenges in the compensation for or elimination of cross-sensitivities. Many state-of-the-art precision devices lose their precision and reliability when exposed to harsh environments. It is also important that advanced sensor and actuator systems maintain maximum autonomy such that the devices can operate independently with low maintenance. The next-generation microsystems will be deployed in remote and/or inaccessible and harsh environments that present many challenges to sensor design, materials, device functionality, and packaging. All of these aspects of integrated sensors and actuator microsystems require a multidisciplinary approach to overcome these challenges. The main areas of importance are in the fields of materials science, micro/nano-fabrication technology, device design, circuitry and systems, (first-level) packaging, and measurement strategy. This study examines the challenges presented by harsh environments and investigates the required approaches. Examples of successful devices are also given.Subject terms:Electrical and electronic engineering • Materials science Figures at a glanceDisplaying 1 of 11 figures | Figures indexFigure 1 Figure 1 Figure 2 Figure 2 Figure 3 Figure 3 Figure 4 Figure 4 Figure 5 Figure 5 Figure 6 Figure 6 Figure 7 Figure 7 Figure 8 Figure 8 Figure 9 Figure 9 Figure 10 Figure 10 Figure 11 Figure 11 Show moreIntroductionAbstract • Introduction • Processing and materials • Harsh environments • Testing and reliability • Conclusions • References • Acknowledgements • Author information The earliest known weights and measures systems date to approximately the 4th or 3rd millennium BC and was developed among the ancient peoples of Egypt, Mesopotamia, the Indus Valley, and perhaps Elam (Iran). Over the centuries, different weights and measures systems have emerged. Sensors were designed that could use these systems to measure and define a wide range of parameters. With the industrial revolution, the need for measurements increased greatly, and measurement devices were increasingly used in harsh environments. In the early days, sensors were quite simple and relied on the operator to control the machinery. With the advent of automation, it became increasingly necessary to use sophisticated sensors as components of a control system. These sensors were designed to simply control the machinery. In the automotive industry, this approach was used to improve performance. In recent years, an increasing need has arisen for sensors for environmental control, for example, regulation of the exhaust from automobiles or from the process industry. The source of the harshness might not always be the measurand itself, for example, in the case of measuring pressure at high temperature.

Spatial Atomic Layer Deposition is emerging as an industrial thin-film manufacturing technology [1]. The technique is becoming so popular since it combines all advantages of conventional ALD (ultimate control of layer thickness and conformality over 3D-topologies, superior film material properties) with far higher deposition rates and processing at atmospheric pressure by means of spatial separation of the reactive gases. The integration of non-thermal plasma in spatial ALD reactors is expected to widen the thermal ALD process window towards lower operation temperatures and to enable to growth of specific materials requiring radicals (O, N, H, OH, NH, etc.). To this end, novel plasma sources with exceptional dimensional and chemical stability are required which provide the flow geometries optimized for efficient radical transport. This paper reports on our preliminary efforts to provide and examine the required linear scalable plasma sources. The effectiveness of close-proximity direct and remote plasma sources [2] are demonstrated using the deposition of thin dielectric films of Al2O3 and ZrO2 at temperatures ranging from room temperature to 100 oC. Both direct and remote plasma sources of the so-called surface DBD-type (Dielectric Barrier Discharge) can be applied for spatial ALD using the usual metal precursors and O2/N2 plasma. The advantage of the remote plasma option is avoidance of electrical source-substrate interaction which is often the cause of layer or substrate damage as a result of filamentary plasma discharges impacting the substrate. P. Poodt, et al., J. Vac. Sc. Technol. A, 30 010802-1 (2012). Y. Creyghton et al., Patent publication WO2015199539, Dec. 30 (2015).

Compared to conventional NAND flash resistive switching metal-oxide cells show a number of advantages, like an increased endurance, lower energy consumption, and superior switching speed. Understanding the role of defects for the resistive switching phenomenon in metal oxides is crucial for their improvement and thereby also for their acceptance as a next generation data storage device. Strontium titanate (STO) is considered a model material due to its thoroughly investigated defect chemistry. This paper presents a comparative study of the switching kinetics for three different compositions [Sr]/([Sr]+[Ti]) of 0.57 (Sr-rich), 0.50 (stoichiometric STO), and 0.46 (Ti-rich STO). The STO films, deposited by atomic layer deposition, were integrated in Pt/STO/TiN nanocrossbars with a feature size of 100 nm. By analysis of the transient currents, the switching kinetics are investigated between 10 ns and 104 s for the SET and 10 ns and 100 s for the RESET. A clear influence of the composition on the degree of nonlinearity of the switching kinetics was observed. Applying an analytical model for the oxygen vacancy migration, we were able to explain the differences in the SET kinetics by composition-dependent changes in the thermal conductivity and by a lower activation energy for the Ti-rich sample. This might be utilized in design rules of future ReRAM devices.I. INTRODUCTION

Silver (Ag) thin-films have attracted interest for applications in sensing1, light management2, imaging beyond the diffraction limit3, interlayer in tri-layer transparent conductors (TCs)4 and even as possible replacement for Cu interconnects5. For tri-layer TCs, a narrow optimum exists between optical transparency and electrical conductivity6. The former decreases exponentially whereas the latter increases with thickness. The ability to precisely control both thickness and electrical percolation is crucial in tri-layer TCs, for which ultra-thin and uniform, yet conductive Ag layers are required over large areas. Here, Atomic Layer Deposition (ALD) can fulfill the requirements for precise thickness control and conformal step coverage over large area substrates. In this work we studied the deposition of Ag by spatial-ALD on molybdenum (Mo) layers serving as a growth model substrate. Mo-layers were specifically selected for testing the suitability of spatial-ALD to fabricate MoO3/Ag/MoO3 tri-layer TCs for organic-based solar cells. Since Mo-films are known to have high surface energy (3 Jm-2), Ag is expected to wet a Mo surface. However, the presence of native MoO3 on the surface is likely to reduce the surface energy resulting in poor wetting. Therefore, an H2/N2 plasma pre-treatment was introduced before Ag deposition in order to reduce the native MoO3 and promote coalescence. Ultrathin Ag films were deposited at 120 °C using Ag(fod)(PEt3) as the precursor and an H2/N2 plasma generated by a surface dielectric barrier discharge (SDBD) source as the co-reactant. Ag(fod)(PEt3) was evaporated into the deposition chamber using Ar as carrier gas flowing at 100 sccm, at the same temperature as that of the reactor. An H2/N2 co-reactant gas mixture was composed from 800 sccm H2 and 600 sccm N2. Silicon substrates with sputter-deposited Mo were used as a model substrate for Ag growth, and compared with the growth on bare silicon substrates. Top view and cross-sectional SEM images of the Ag layers show that a more compact and closed Ag layer was achieved on Mo upon introduction of the plasma pre-treatment (Fig. 1). Spectroscopic ellipsometry measurements demonstrate that the use of an H2/N2 plasma pre-treatment significantly enhances the wetting, and therefore, the coalescence of Ag owing to the high surface energy of the Mo-layers (Fig. 2). Furthermore, the better wetting and interfacial quality of the Ag deposited on plasma pre-treated Mo, compared to Ag on Si was probed by post-growth rapid thermal annealing experiments and XRD stress measurements. It was found that at 450 °C the Ag films de-wetted from Si, resulting in discontinuous films whereas the films deposited on plasma pre-treated Mo remained unchanged. Since both Ag films show similar stress content, the de-wetting most likely originates from interfacial properties rather than stress phenomena. We can therefore conclude that a plasma pre-treatment of Mo layers promotes the Ag wetting. This leads to earlier film coalescence compared to that of Ag films grown on Si, as demonstrated by both morphological and optical inspections of the Ag thin films. Thus, upon plasma pre-treatment ALD deposited MoO3 layers can act as wetting layers for subsequent Ag spatial-ALD in tri-layer TCs. This can open up alternative pathways for the fabrication of TCs using ALD. Figure 1

Insights into the temperature dependence of atomic layer deposition (ALD) of Pt using (methylcyclopentadienyl)trimethylplatinum, (MeCp)PtMe3, precursor and O2 are presented, based on a study of reaction products by time-resolved quadrupole mass spectrometry (QMS) measurements. Above 250°C, Pt ALD proceeds through unhindered O2 dissociation at the Pt surface, inducing complete and instantaneous combustion of the precursor ligands. Quantification of the QMS data revealed that at 300°C, approximately 20% of the C-atoms react during the precursor pulse, forming mainly CH4 (~18%) balanced by CO2 (~2%). The remaining 80% of the C-atoms are combusted during the O2 pulse. Time-resolved data indicated that the combustion reactions compete with the hydrogenation reactions for the available surface carbon. Combustion reactions were found to be dominant, provided that a sufficient amount of chemisorbed oxygen is available. When the temperature drops below 250°C, deposition becomes hindered by the presence of a carbonaceous surface layer of partially fragmented and dehydrogenated precursor ligands, formed during the precursor pulse. The carbonaceous layer limits dissociative chemisorption of O2 and hence combustion reactions (leading to CO2) whereas reduced surface reactivity also limits (de-)hydrogenation reactions (leading to CH4). Below 100°C, the carbonaceous layer fully prevents O2 dissociation and ALD of Pt cannot proceed.

One of the critical steps toward producing void-free and uniform bottom-up copper electroplating in high aspect-ratio (AR) through-silicon vias (TSVs) is the ability of the copper electrolyte to spontaneously flow through the entire depth of the via. This can be accomplished by reducing the concentration gradient of cupric ions from the via mouth to the via bottom by enhancing the wettability of the vias sidewalls. In this paper, we report on a new dry technique to enhance the hydrophilicity in high AR $({sim}{15})$ TSVs as one of the key solutions to face the mass transport limitation. low pressure chemical vapor deposition silicon nitride and atomic layer deposition titanium nitride of composition ${rm SiN}_{0.95}$ and ${rm TiN}_{1.1}$, respectively, are used as both barrier layers and wetting surfaces in these vias. Ammonia plasma immersion is used to treat silicon nitride. X-ray photoelectron spectroscopy shows both a partial oxidation and grafting of hydrophilic components. Alternatively, a rapid flood ultraviolet exposure step in order to photocatalytically activate the surface and induce a partially oxidized titanium nitride is used to create a highly wettable interface with a contact angle close to zero. These wettability enhancement steps were incorporated in a TSV process to produce 3-D cross-Kelvin structures using bottom-up copper electroplating. The vias lined with silicon nitride and titanium nitride exhibited a low average resistance of 25 ${rm m}Omega$ and 50 ${rm m}Omega$, respectively, making them very suitable for radio-frequency signal transmission. This all-dry technology to achieve superhydrophilic barrier layers- - can be employed in both high and low thermal budget processing, thus enabling via-last or via-first flowchart schemes for advanced 3-D interconnects.

Last decades great effort has been put in the development of 3D capacitors. These capacitors are used for RF decoupling and should therefore have a high capacitance density associated with a sufficient breakdown voltage. Increased capacitance densities have been achieved by exploring the use of the third dimension in silicon, e.g. pores and trenches and considering dielectric layers with a higher dielectric permittivity, so-called higher k dielectrics formed by alternative deposition techniques, e.g. Atomic Layer Deposition (ALD). Starting with the formation of wide pores using the ''Bosch'' process, we eventually developed high aspect ratio macropore arrays that have been used as the carrier substrate for the capacitors. These arrays have been filled by conventional LPCVD MOS layers with ONO-dielectrics and in situ doped polycrystalline silicon, initially as single layer stack, but also as a double stack capacitor (MOSOS/MIMIM). Further, higher k materials, such as Al"2O"3, Ta"2O"5, HfO"2 and even rare earth materials with nanoclusters have been considered in our attempt to achieve ultimate capacitance densities. Our current record capacitance density has been realized using a multiple capacitor structure with ALD electrodes and high k dielectric layers, the so-called MIMIMIM capacitor.

Remote plasma atomic layer deposition (ALD) of SrTiO3 films with different [Sr]/[Ti] ratios is reported, employing Star-Ti [(pentamethylcyclopentadienyl)trimethoxy-titanium, (CpMe5)Ti(OMe)(3)] and Hyper-Sr [bis(trisisopropylcyclopentadienyl)-strontium with 1,2-dimethoxyethane adduct, Sr((Pr3Cp)-Pr-i)(2)DME] precursors and O-2 plasma. The as-deposited films were amorphous, but crystallized after post-deposition anneal above 500 degrees C. For annealed SrTiO3 films with [Sr]/[Ti] = 1.3 and a thickness of 50 nm, a high dielectric constant k > 80 and low leakage current of similar to 10(-7) A/cm(2) at 1 V were obtained. It is demonstrated that changes in the composition and microstructure are apparent in the optical dielectric function of the SrTiO3 films, as obtained by spectroscopic ellipsometry. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3522768] All rights reserved.

Area-Selective Atomic Layer Deposition, AS-ALD, can be initiated by local area-activation1,2 or -deactivation.3 We studied the maskless growth of ZnO from diethyl zinc and water. The method is based on the different nucleation delays that arise from precursor adsorption on OH-terminated versus that on H-terminated Si-substrate. TEOS (tetraethyl orthosilicate) and H2O were used to deposit a SiO2 seed layer by EBID (e-beam-induced deposition) in a pattern of 500x500 nm2 dots on H-terminated a-Si:H substrate. After this local activation the substrate was coated with a ZnO film in a conventional ALD reactor using 80 cycles of diethyl zinc and water vapor. In situ spectroscopic ellipsometry (Fig. 1), SEM, cross-sectional TEM and energy dispersive X-ray spectroscopy (EDX) showed good areal selectivity with ZnO growth only occurring on the SiO2 dots. This observation was corroborated by Density functional theory calculations suggesting a kinetically hindered surface reaction between diethyl zinc and H-terminated Si. Atomic Layer Etching, ALE, was also tested on a ZnO case. Current ALE technology is emerging in both thermal, isotropic and plasma-based, anisotropic approaches.4 In this presentation we will demonstrate a plasma-assisted ALE-process driven by radicals, and therefore being isotropic. The ALE-process was tested at temperatures between 150 and 250 °C. We used alternating doses of acetylacetone (Hacac) and O2-plasma intermitted by Ar-purging. The ZnO-layer thickness as measured by spectroscopic ellipsometry decreased linearly with the number of cycles. In a synergy test, we proved that only the alternated dosing of Hacac and O2-plasma caused ZnO etching, whereas Hacac and O2-plasma alone did not (Fig. 2). Preliminary infrared studies suggest that Hacac forms volatile complexes by metal oxide surface chelation (e.g. Zn(acac)2), whereas the O2-plasma step removes non-reactive Hacac fragments to refresh the surface for the next etching cycle.5 TEM- and XPS-inspection indicated no damage of the ZnO surface, good preservation of the ZnO-stoichiometry throughout the etching process, and no distinct contamination. Furthermore, we demonstrated this ALE-process to be selective over SiO2. We believe that this novel plasma-assisted ALE-concept can be extended to several other materials. [1] A. J. M. Mackus et al., Nanoscale, 4, 4477 (2012). [2] R. Chen et al., Adv. Mater., 18, 1086 (2006). [3] A. Mameli et al., Chem. Mater. 29, 921 (2017). [4] D. R. Zywotko, et al., Chem. Mater. 29, 1183 (2017). [5] M. A. George, et al., J. Electrochem. Soc., 143, 3257 (1996). Figure 1

A method to avoid the stiction failure in nano-electro-opto-mechanical systems has been demonstrated by coating the system with an anti-stiction layer of Al2O3 grown by atomic layer deposition techniques. The device based on a double-membrane photonic crystal cavity can be reversibly operated from the pull-in back to its release status. This enables to electrically switch the wavelength of a mode over ~50 nm with a potential modulation frequency above 2 MHz. These results pave the way to reliable nano-mechanical sensors and optical switches.