The present study reports the impact of process conditions and post annealing treatment on the stress and physico-chemical properties in different types of plasma enhanced atomic layer deposited (PEALD) SiNx films. More specifically, the SiNx films deposited at 500 °C were annealed subsequently at 1000 °C in N2 ambient for different times ranging between 30 and 6750 s and were subjected to thickness, mass, refractive index, chemical bonds and structure, H content, N/Si stoichiometry, morphology, roughness, and uniformity monitoring. Depending on the deposition process conditions, we confirm the possibility to form, at 500 °C with PEALD, some very compressive SiN films with reduced hydrogen content by controlling the plasma conditions along the deposition process. More interestingly, these compressive films with low hydrogen concentration exhibit high thermo-mechanical stability compared to hydrogenated PEALD and plasma enhanced chemical vapor deposition silicon nitride from this study or reported in the literature, films which typically tend to become tensile with a similar annealing sequence. These results confirm the importance of the plasma power to engineer the as-deposited silicon nitride stress but also highlight the role of hydrogen in the thermal instability of these layers, a low H concentration being needed for a better mechanical stability.

In this study, we explored the key properties and functionalities of plasma enhanced atomic layer deposition (PEALD) SiNx films, synthesized using different deposition temperatures (500–550 °C) and plasma conditions (lower and higher), both on 300 mm blanket Si and on several integrated 3D topology substrates, at the thicknesses relevant for diverse nanoscale applications. Our study shows that with an increase of temperature (500–550 °C), a small reduction in HF wet etch rate (1.1–0.69 nm/min), and H content (9.6% vs 7.4%) was observed. When using higher plasmas, significant improvements in blanket properties were observed. The films were denser (2.95 g/cm3), exhibited lower H content (2.4%), showed better etch rates (0.39 and 0.44 nm/s for HF and CF4 based), and SiNx grew without any nucleation delay on alternative Si1−xGex channel surfaces. The vertical and lateral conformality was found to be similar and appears not to be impacted with the plasma conditions. Extensive steam oxidation barrier studies performed at the sidewalls of different aspect ratio lines showed the PEALD SiNx liner scaling potentiality down to 1 nm when deposited using higher plasma. In addition, the outer gate and inner spacer properties were found to be superior (with lower loses) for higher plasma films when subjected to several dry etch, strips, and H3PO4 chemistries. The outstanding conformality (90%–95% on aspect ratios ≤10:1) combined with excellent high end material properties in the ultrathin regimes (1–10 nm) corroborate the virtue of PEALD SiNx toward integration in scaled down and advanced nanoelectronics device manufacturing.

Redox-based resistive switching cells (ReRAM) are intensively studied for next generation non-volatile memory due to simple device structure, low power consumption, and good endurance.[1] High density integration demands for technologies like three dimensional (3D) stacking and 4F 2 crossbar array architectures.[2] However, passive ReRAM arrays require the integration of bidirectional selector devices with high selectivity to suppress sneak-path currents.[3] A promising concept is based on threshold-type devices as obtained from NbO2, which typically show a negative differential resistance (NDR) characteristic.[4] This volatile resistance change can be utilized for the realization of a highly non-linear selector element. The presentation comprises two studies. The first one addresses the fabrication and nano-scale characterization of combined threshold and memory cells (TS-ReRAM) with a potential for future high-density 3D integration. The cells are built from a 10 nm thick amorphous Nb2O5 layer grown by atomic layer deposition (ALD) and integrated into Pt/Nb2O5/Ti/Pt nano-crossbar structures. After electroforming, the devices combine the functions of volatile threshold and non-volatile memresistive switching. The structural changes induced by the electroforming step are analyzed by means of electron nano-diffraction. The results confirm the formation of crystalline NbO2 within a small regime localized inside the Nb2O5-x based switching cell.[5] This finding supports the proposal of an Nb2O5-x/NbO2 filament being the central element of the TS-ReRAM cell. The second study aims upon a deeper understanding of the threshold switching (TS) phenomenon in NbO2-based TS-ReRAM devices. A widely accepted model for TS in NbO2 is based on a combination of Joule heating and an insulator to metal transition (IMT) at TIMT , NbO2 ≈ 1080 K.[6] This model, however, leads to fundamental contradictions like a too low discontinuity in the I-V characteristics. Recently it has been shown that an increase in temperature of about 200 K is sufficient to suppress the TS-effect.[7] Therefore we set-up a two-dimensional axial symmetric simulation of the TS-behavior of the Nb2O5-x / NbO2 based cells.[8] The continuum model includes a filamentary switching, divided into a threshold and a memristive switching region. The fully coupled heat transfer and continuity equation system is solved by Newton-Raphson iteration. The conduction mechanism for the threshold regime is based on a Poole Frenkel (PF) like barrier lowering and exponentially coupled to the electric field. The interplay of Joule heating and an increase of conducting charge carriers causes an electric field controlled thermal runaway process, which is interrupted by the resistance of the memory in low resistance state limiting further Joule heating. The proposed model reproduces the experimental results fairly well. [8] The understanding of the structural modifications associated with the electroforming and resistive switching process in NbO2/Nb2O5-x based TS-ReRAM cells makes the fabrication of such devices by means of the ALD technique feasible. In addition, our proposed two dimensional simulation based on an electric field triggered thermal runaway (FTTR) mechanism provides a deeper understanding of the switching limitations in the TS-ReRAM structures. Additionally, the realization of Boolean logic functionality using the TS-ReRAM devices has been demonstrated.[9] This work was supported in part by the Deutsche Forschungsgemeinschaft (SFB917), and by FP7 under grant ENHANCE-238409. References: [1] R. Waser, R. Dittmann, G. Staikov, and K. Szot, Adv. Mater., vol. 21, pp. 2632-2663, 2009. [2] E. Cha, J. Woo, D. Lee, S. Lee, J. Song, Y. Koo, J. Lee, C. G. Park, M. Y. Yang, K. Kamiya, K. Shiraishi, B. Magyari-Kope, Y. Nishi, H. Hwang, Electron Devices Meeting (IEDM), 2013 IEEE Int., p. 10.5.1, 2013. [3] G. Burr, R. Shenoy; K. Virwani; P. Narayanan; A. Padilla; B. Kurdi; H. Hwang, J. Vac. Sci. Technol. B 32, p. 040802, 2014. [4] A. L. Pergament, P. P. Boriskov, A. A. Velichko, and N. A. Kuldin, J. Phys. Chem. Sol., 71, p. 874, 2010. [5] N. Aslam, T. Blanquart, J. Niinistö, M. Ritala, M. Leskelä, S. H. Du, M. Bornhöfft, J. Mayer, R. Waser, S. Hoffmann-Eifert, under submission, 2016. [6] M. D. Pickett and R. S. Williams, Nanotechnology, vol. 23, pp. 215202, 2012. [7] S. Slesazeck, H. Maehne, H. Wylezich, A. Wachowiak, J. Radhakrishnan, and A. Ascoli, RSC Adv., 5, p. 102318, 2015. [8] C. Funck, S. Menzel, N. Aslam, H. Zhang, A. Hardtdegen, R. Waser, S. Hoffmann-Eifert, Adv. Electron. Mater., submitted, 2016. [9] A. Siemon, T. Breuer, N. Aslam, S. Ferch, W. Kim, J. van den Hurk, V. Rana, S. Hoffmann-Eifert, R. Waser, S. Menzel, E. Linn, Adv. Funct. Mater., 25, p. 6414, 2015.

Thin films of rare-earth (RE) oxides (Y2O3, PrOx, Gd2O3, and Dy2O3) were deposited. by atomic layer deposition from liquid heteroleptic RE((PrCp)-Pr-i)(2)(Pr-i-amd) precursors with either water or ozone as the oxygen source. Film thickness, crystallinity, morphology, and composition were studied. Saturation was achieved with Gd2O3 when O-3 was used as the oxygen source at 225 degrees C and with Y2O3 with both oxygen sources at as high temperature as 350 degrees C. The growth rates were 0.90-1.3 angstrom/cycle for these processes. PrOx was challenging to deposit with both oxygen sources but with long, 20 s purges after the water pulses uniform films could be deposited. However, saturation was not achieved. With Dy2O3, uniform films could be deposited and the Dy((PrCp)-Pr-i)(2)(Pr-t-amd)/O-3 process was close to saturation at 300 degrees C. The different oxygen sources had an effect on the crystallinity and impurity contents of the films in all the studied processes. Whether ozone water was better choice for oxygen source depended on the metal oxide material that was deposited.

Two heteroleptic titanium precursors were investigated for the atomic layer deposition (ALD) of titanium dioxide using ozone as the oxygen source. The precursors, titanium (N,N'-diisopropylacetamidinate)tris(isopropoxide) (Ti(O(i)Pr)3(N(i)Pr-Me-amd)) and titanium bis(dimethylamide)bis(isopropoxide) (Ti(NMe2)2(O(i)Pr)2), exhibit self-limiting growth behavior up to a maximum temperature of 325 °C. Ti(NMe2)2(O(i)Pr)2 displays an excellent growth rate of 0.9 Å/cycle at 325 °C while the growth rate of Ti(O(i)Pr)3(N(i)Pr-Me-amd) is 0.3 Å/cycle at the same temperature. In the temperature range of 275-325 °C, both precursors deposit titanium dioxide in the anatase phase. In the case of Ti(NMe2)2(O(i)Pr)2, high-temperature X-ray diffraction (HTXRD) studies reveal a thickness-dependent phase change from anatase to rutile at 875-975 °C. X-ray photoelectron spectroscopy (XPS) indicates that the films have high purity and are close to the stoichiometric composition. Reaction mechanisms taking place during the ALD process were studied in situ with quadrupole mass spectrometry (QMS) and quartz crystal microbalance (QCM).

The atomic layer deposition (ALD) process, an alternative to CVD, is universally appreciated for its unique advantages such as excellent repeatability, conformity, and thickness control at the atomic level. ALD precursor chemistry has mainly been based on homoleptic compounds such as, but not limited to, metal halides, alkylamides, and alkoxides, however these precursors have drawbacks such as possible halide contamination and low thermal stabilities in the case of the alkylamides and alkoxides. Consequently, heteroleptic precursors have been investigated as alternatives to the existing homoleptic counterparts, leading to the development of several advantageous processes. Nevertheless, there is no thematic review dedicated to the heteroleptic precursors and their properties, and it seems that no coherent strategy has been adopted for the development of heteroleptic precursors. This review gives a brief description of ALD and presents studies on the deposition of thin films of groups 4 and 5 metal oxides using ALD. A description of the general ALD properties of homoleptic precursors, in addition to a review on the thermal ALD of groups 4 and 5 metal oxides from heteroleptic precursors, is provided. Trends in the properties of heteroleptic ALD precursors, based on the literature review and recent experimental data, are discussed.

In this study the atomic layer deposition (ALD) of TiO2 and ZrO2 using two heteroleptic amido-guanidinate precursors, [Ti(NEtMe)(3)(guan-NEtMe)] and [Zr(NEtMe)(3)(guan-NEtMe)], together with water or ozone as oxygen sources, are investigated. All processes exhibit self-limiting growth at a deposition temperature of 275 degrees C. The zirconium precursor especially gives high growth rates (0.8/1.0 angstrom per cycle with H2O/O-3). The films are also relatively smooth, as determined by atomic force microscopy (AFM). The composition of the films is examined using X-ray photoelectron spectroscopy (XPS) and time of flight elastic recoil detection analysis (TOF-ERDA). When using ozone as the oxygen source the films present very high purity. The results are compared and discussed with respect to earlier studies on guanidinate, as well as homoleptic amido precursors.Full Paper: Atomic layer deposition of TiO2 and ZrO2 is performed using heteroleptic amido/guanidinate metal precursors, and ozone and water as oxygen sources. The results are compared to previous studies and the effect of the ligands on the precursor properties are discussed.

As the atomic layer deposition (ALD) method is based on sequential, self-limiting surface reactions the precursor chemistry is the key to a successful processing of conformal high quality thin films. ALD precursor chemistry has traditionally been based on homoleptic compounds such as, but not limited to, metal halides, alkylamides and alkoxides. However, these precursors sometimes have drawbacks such as possible halide contamination and low thermal stabilities. Consequently, heteroleptic precursors have been investigated as alternatives to the existing homoleptic counterparts, leading to the development of several advantageous processes. Here, examples of heteroleptic precursors for ALD processes of transition metals and their oxides are given. Special focus is given to oxides of the rare earths and groups 4 and 5. Trends in the properties of heteroleptic precursors are discussed. Several examples of our recent results are shown, including introduction of novel processes based on amidinate-cyclopentadienyl complexes for ALD of rare earth oxides.

In this article, three novel cyclopentadienyl precursors are evaluated for the atomic layer deposition (ALD) of erbium oxide, with either ozone or water as the oxygen source. The erbium precursors evaluated are Er( i PrCp) 3 , Er(MeCp) 2 ( i Pr‐amd), and Er( n BuCp) 3 . The films are deposited on silicon within the temperature range 200–400°C. Self‐limiting growth is achieved with all three precursors, with both ozone and water. It is found that the water processes of all three precursors present significantly higher growth rates when compared to the ozone processes. An up to three‐fold increase in the growth rate is observed for the water processes of Er( i PrCp) 3 and Er(MeCp) 2 ( i Pr‐amd) (amd: amidinate) when compared to their ozone processes. The films are smooth and uniform, as determined by atomic force microscopy (AFM) (rms roughness < 3% of film thickness). The composition of the films is investigated by means of X‐ray photoelectron spectroscopy (XPS). It is found that the films contain small amounts of carbon as an impurity, especially in the case of ozone‐processed films. Using Er( n BuCp) 3 together with ozone as the oxygen source, a highly conformal Er 2 O 3 thin film is deposited on a 1:60 high‐aspect‐ratio substrate. This is the first report of the conformal growth of Er 2 O 3 thin films by ALD on a high‐aspect‐ratio structure.

[Zr(NEtMe)(2)(guan-NEtMe2)(2)], a recently developed compound, was investigated as a novel precursor for the atomic layer deposition (ALD) of ZrO2. With water as the oxygen source, the growth rate remained constant over a wide temperature range, whereas with ozone the growth rate increased steadily with deposition temperature. Both ALD processes were successfully developed: the characteristic self-limiting ALD growth mode was confirmed at 300 degrees C. The growth rates were exceptionally high, 0.9 and 1.15 angstrom/cycle with water and ozone, respectively. X-ray diffraction (XRD) indicated that the films were deposited in the high-permittivity cubic phase, even when grown at temperatures as low as 250 degrees C. Compositional analysis performed by means of X-ray photoelectron spectroscopy (XPS) demonstrated low carbon and nitrogen contamination (<2 at. % when deposited with ozone). The films presented low root-mean-square (rms) roughness, below 5% of the film thickness, as well as excellent step coverage and conformality on 30:1 aspect ratio trench structures. Dielectric characterization was performed on ZrO2 metal insulator metal (MIM) capacitors and demonstrated high permittivity and low leakage current, as well as good stability of the capacitance. The ALD reaction mechanism was studied in situ: adsorption of the precursor through reaction of the two guan-NEtMe2 ligands with the surface -OD groups was confirmed by the quartz crystal microbalance (QCM) and quadrupole mass spectrometric (QMS) results.

Metal-insulator-metal (MIM) capacitors were grown by atomic layer deposition using (BuN)-Bu-t = Nb(NEt2)(3) and ozone as niobium and oxygen precursors, respectively. Three different deposition temperatures were used and some of the films were postdeposition annealed. The permittivity values obtained reached a value of about 50 for the films crystallized after annealing at temperatures higher than 500 degrees C. However, the leakage current values for the crystalline films were higher than those in the case of amorphous films.

In this study, VOx films were grown by atomic layer deposition (ALD) using V(NEtMe)(4) as the vanadium precursor and either ozone or water as the oxygen source. V(NEtMe)(4) is liquid at room temperature and shows good evaporation properties. The growth was investigated at deposition temperatures from as low as 75 degrees C, up to 250 degrees C. When using water as the oxygen source, a region of constant growth rate (ca. 0.8 angstrom/cycle) was observed between 125 and 200 degrees C, with the ozone process the growth rate was significantly lower (0.31-0.34 angstrom/cycle). The effect of the process conditions and post-deposition annealing on the film structure was investigated. By varying the atmosphere under which the films were annealed, it was possible to preferably form either VO2 or V2O5. Atomic force microscopy revealed that the films were smooth (rms < 0.5 nm) and uniform. The composition and stoichiometry of the films were determined by X-ray photoelectron spectroscopy. Conformal deposition was achieved in demanding high aspect ratio structure.

This chapter contains five sections related to advances in technology and characterization. The first section investigates influence of Ti top electrodes on the oxidation state of epi-taxially grown STO thin films and the corresponding resistive switching devices. The second section shows comparison of work diode- and CO2-laser heater versions. The third section reviews the influence of ALD processing and different top electrodes on the structural, morphological and electrical properties of ZrO2. The fourth section views the resistance switching characteristic of Nb2O5 thin films integrated into Pt/Nb2O5/Ti/Pt micro cross bar structures on Si/SiO2 substrates. The fifth section considers the investigations of CDW in Dy5Ir4Si10 at different temperatures using transmission electron microscopy (TEM) techniques including electron diffraction and dark-field imaging. Controlled Vocabulary Terms electron diffraction; switching; thin films; transmission electron microscopy

Atomic layer deposition (ALD) of Nb2O5 thin films was studied using three novel precursors, namely, (BuN)-Bu-t=Nb(NEt2)(3), (BuN)-Bu-t=Nb(NMeEt)(3), and (t)amylN=Nb((OBu)-Bu-t)(3). These precursors are liquid at room temperature, present good volatility, and are reactive toward both water and ozone as the oxygen sources. The deposition temperature was varied from 150 to 375 degrees C. ALD-type saturative growth modes were confirmed at 275 degrees C for (BuN)-Bu-t=Nb(NEt2)(3) and (BuN)-Bu-t=Nb(NMeEt)(3) together with both oxygen sources. Constant growth rate was observed between a temperature regions of 150 and 325 degrees C. By contrast, amylN=Nb((OBu)-Bu-t)(3) exhibited limited thermal stability and thus a saturative growth mode was not achieved. All films were amorphous in the as-deposited state and crystallized between 525-575 degrees C, regardless of the applied precursor and oxygen source. Time-of-flight elastic recoil detection analysis (TOF-ERDA) demonstrated the high purity of the films. Atomic force microscopy (AFM) revealed that the films were smooth and uniform. The films exhibited promising dielectric characteristics with permittivity values up to 60.

The atomic layer deposition of Ta2O5 thin films was studied using a novel imido-amido precursor (BuN)-Bu-t = Ta(NEt2)(3). This precursor is liquid at room temperature, possesses good volatility and is reactive toward both water and ozone as the oxygen sources. The deposition temperature was varied from 125 to 475 degrees C. Saturated film growth was confirmed at 325 degrees C for both water and ozone processes, and a region of constant growth rate was observed between 125 and 350 degrees C when using ozone as the oxygen source. All the films were amorphous in the as-deposited state and crystallized at around 700 degrees C into orthorhombic Ta2O5, regardless of the applied oxygen source. X-ray photoelectron spectroscopy demonstrated high purity of the films deposited at temperatures higher than 225 degrees C. Atomic force microscopy revealed that the films were smooth (rms < 0.3 nm) and uniform. The films exhibited permittivity values of similar to 25 and low leakage current.

Two novel heteroleptic titanium precursors for the atomic layer deposition (ALD) of TiO2 were investigated, namely, titanium (N,N'-diisopropylacetamidinate)tris(isopropoxide) (Ti((OPr)-Pr-i)(3)((NPr)-Pr-i-Me-amd)) and titanium bis(dimethylamide)bis(isopropoxide) (Ti(NMe2)(2)((OPr)-Pr-i)(2)). Water was used as the oxygen source. These two precursors are liquid at room temperature and present good volatility, thermal stability and reactivity. The self-limiting ALL)growth mode mode was confirmed at 325 degrees C for both precursors. The titanium (N,N'-diisopropylacetamidinate)tri(isopropoxide)/water process showed an ALD window at 300-350 degrees C, and titanium bis(dimethylamide)bis(isopropoxide) exhibited an interestingly high growth rate of 0.75 angstrom/cycle at 325 degrees C. The films were crystallized to the anatase phase in the as-deposited state. X-ray photoelectron spectroscopy analysis demonstrated that the films were pure and close to the stoichiometric composition. The refractive indexes and absorption coefficient of the films were measured by spectroscopic ellipsometry.

Nb2O5 films were grown by atomic layer deposition using (tert-butylimido)tris(diethylamido)niobium as the niobium source and ozone as the oxygen source. The effects of deposition and post-deposition annealing conditions, physical thickness as well as the phase composition on the dielectric properties of Nb2O5 thin films have been investigated. In addition, the optical properties of the films have been evaluated. It was found that by tuning the deposition parameters and post deposition treatments it was possible to obtain high k-values up to 120 with reasonably low leakage current.