bluuebunny/crossref_metadata_2025 huggingface dataset:
Adsorption and Corrosion Inhibition Behaviour of Some N-{n-[1-R-5-(quinoxalin-6-yl)-4,5-Dihydropyrazol-3-Yl]Phenyl}Methanesulfonamides on Mild Steel in 1 M HCl (n = 2, 3, 4; R = propanoyl, methylsulfonyl): Experimental and Theoretical Studies
Authors: Olasunkanmi Lukman Olawale , Ebenso Eno E
Published: February 2020

Mild steel (MS) is a material of choice for diverse structural and industrial applications owing to its excellent mechanical strength and relatively low cost [1]. Certain requisite industrial activities involve the use of acidic solutions that constitute strong corrosive environment for MS.  Therefore, corrosion of MS causes great economic loss and present huge safety threats to the concerned industries. Addition of corrosion inhibitors to aggressive solution has been identified as an economical and practical means of controlling metal corrosion. The existing data have shown that organic compounds containing O, N, S, and P heteroatoms, and pi-electron or aromatic systems often exhibit good anticorrosion properties [2,3]. Quinoxaline derivatives possess these features and their corrosion inhibition properties have been reported. These compounds form parts of many essential biological and pharmaceutical compounds and fit into the class of environmentally benign inhibitors [3].

In the present study, adsorption and corrosion inhibition properties of six quinoxaline derivatives namely, N-{n-[1-R-5-(quinoxalin-6-yl)-4,5-dihydropyrazol-3-yl]phenyl}methanesulfonamides: R = propanoyl & n = 2,  3, 4 for MS-2-PQPP, MS-3-PQPP, and MS-4-PQPP respectively; and R = methylsulfonyl &  n = 2,  3, 4 for MS-2-PQPMS, MS-3-PQPMS and MS-4-PQPMS were investigated on MS in 1 M HCl solution. The techniques employed in the study include potentiodynamic polarization and electrochemical impedance spectroscopy. Quantum chemical calculations and molecular dynamic simulations studies were used to support experimental results.

All the studied compounds were found to exhibit appreciable inhibition efficiency and they are all mixed type inhibitors. The compounds inhibit MS corrosion by adsorbing on the steel surface and geometrically blocking the active sites for the corrosion reaction. Both MS-3-PQPP and MS-3-PQPMS showed higher inhibition performances, which suggests that the interplay of electronic and steric effects of the carbonyl/methylsulfonyl substituents ensures higher inhibition performance when n = 3 (meta-substitution). The adsorption of the studied compounds obeyed the Langmuir adsorption isotherm model. Theoretical quantum chemical calculations and molecular dynamic simulations corroborate experimental results.

References

(1)        De la Fuente, D.; Diaz, I.; Simancas, J.; Chico, B.; Morcillo, M. Corros. Sci.
2011, 53, 604.

(2)        Mashuga, M.E.; Olasunkanmi, L.O.; Adekunle, A.S.; Yesudass, S.; Kabanda, M.M.; Ebenso, E.E. Materials
2015, 8, 3607.

(3)        Olasunkanmi, L.O.; Obot, I.B.; Kabanda, M.M.; Ebenso, E.E. J. Phys. Chem. C
2015, 119, 16004.

Figure 1
(Invited) Trench-Gated MOSFET Instability Caused by High Temperature Reverse-Bias Stress
Authors: Hao Jifa
Published: February 2020

The trench-gated MOSFET is widely used in power management applications because of its ultra-low on resistance [1]. Studies of trench-gate MOSFET reliability and degradation of blocking voltage and leakage current as well as edge termination effects are becoming increasingly important as the device dimensions shrink and its applications are diversified. The HTRB (high temperature reverse-bias) and HAST (highly accelerated temperature & humidity stress test) are often used in reliability assessment of planar discrete power MOSFETs [2] and are currently used in trench-gated MOSFET. The both HTRB stress and HAST stress apply a reverse bias voltage on the drain side with the source and gate grounded at elevated temperature in a MOSFET device. However, the HAST stress is at 85% HR relative humidity under pressure condition. The possible failure modes for HTRB and HAST stress are IDSS (drain to source) leakage current increase or shift, breakdown voltage shift or degradation, and Vth (threshold voltage) shift or instability. The failure mechanism under various failures is complex. They depend on not only device design and process, but also package process and its materials such as mold compound, as well as interaction between device and package.

In this paper, we discuss the instability of n-channel trench-gated MOSFET under HTRB and HAST reliability stresses. The devices are packaged by using state-of-the-art “low pitch” wafer-level-chip-scale package (WLCSP) without the use of mold compound or leads frame. We have observed that the HTRB and HAST stress increases gate oxide interface trap density. However humid HAST stress is observed to further introduce mobile positive charge in the gate oxide of the trench-gated MOSFET. This positive charge is argued to comprise protons (H+s) [3]. The proton is generated through electric-field assisted interaction and hole injection into the gate oxide at the bottom of the trench. The mobility of these protons is observed to cause gate-voltage induced modulation in the threshold voltage and leakage current of the trench-gated MOSFET.

In order to determine the mechanism by which H+s are introduced in the oxide, SEM inspection of the n-channel trench-gated MOSFET deprocessed to passivation showed the presence of passivation cracks in the device’s edge termination which cause moisture penetrated in the device during the HAST stress.

Furthermore, the experimental and simulation results lead us to conclude that in this study we are observing negative bias temperature instability (NBTI) in a parasitic p-MOSFET structure arising at the bottom of the trench in an n-channel trench-gated MOSFET during HTRB stress [4]. The NBTI is enhanced by the presence of moisture in the oxide.

References:

[1]: J. Zeng et al ISPSD 2002, pp. 147-150.

[2]: JEDEC, IESD22-A108D, November (2010).

[3]: J. Hao, M. Rioux, S. Suliman, O. Awadelkarim, Microelectronics Reliability, 54(2014) 374-380.

[4]: J.Hao, M. Rioux, and O. Awadelkarim, IIRW 2011, pp129-131.

Figure 1
Numerical Investigation on Atomic Migration Effect on Thermal Conductivity of Al/Cu Interface Structures in Electronic Interconnection Packaging
Authors: Zhang Liqiang , Ge Daohan
Published: February 2020

At present, MEMS and micro/nano electronic packaging technology have an exhaustive range of applications in the field of mass-produced commercial products, such as cell phones, computer, automobiles, and pedometers, which cause a strong demand for the reliability of heat transfer in nano or micro scales. Wire bonding process has been widely used in the MEMS or devices packaging approach to create high aspect interconnection structures [1], hence, the thermal analysis, thermal design, and thermal management become more and more important for microelectronic system or microelectronic devices. The interfacial structures of dissimilar materials are suffering the high stress gradients due to the thermal and stiffness mismatches of the different materials [2, 3]. The interface structures of dissimilar materials are very prone to crack initiations under the heat flow effect. The heat transfer across the interface is a critical consideration for the thermal design in the IC or devices manufacturing.

Here we reveal the relationship between the atomic migration and thermal conductivity of Al/Cu interface in nanoscale heat transfer by using non-equilibrium molecular dynamics method.

To create the Al/Cu interface, the modified Embedded-atom method (EAM) for alloy is used to describe the interatomic interactions between Cu/Cu, and Al/Cu interface.

The results show that the interfacial diffusion is enhanced with the increase of the temperature from 400K-600K. The thermal conductivity of the Al/Cu interface, first increases, and then decreases.  When the temperature is over 600K, it reaches the recrystallization temperature of Al. which makes to Al atoms recrystallization. The recrystallization of Al atoms may reduce the heat transfer efficiency of the Al/Cu diffusion region. That is to say, it reduces the thermal conductivity of Al/Cu interface when the temperature is over 600K. This means that we can enhance the interfacial heat transfer efficiency of Al/Cu interface and the cooling efficiency of IC by heat treatment in advance on interface structures. This investigation is helpful for understanding the interfacial heat transfer mechanism of the interface structures in the IC, which is helpful for the design of the interface in micro/nano manufacturing and benefit for the estimate the reliability of the IC manufacturing.

Figure 1
(Invited) Non-Volatile Resistive Memory: Technology Capable of Revolutionary Compromises
Authors: Navarro Gabriele , Vianello Elisa , Sousa Véronique , Molas Gabriel , Nowak Etienne , De Salvo Barbara , Perniola Luca
Published: February 2020

LETI, a French research center, has developed during the past 20 years a strong expertise on Non-Volatile Memory Devices, covering Flash evolutive solutions (Si-Ncs, TANOS, FinFLASH, 3D, Splitgate) and disruptive technologies (Phase-Change PCM, Oxide-based RAM OxRAM, Conductive-Bridge RAM CBRAM, Magnetic STT-MRAM). Main LETI expertise concerns material science, memory module integration, physico-chemical analyses, device electrical characterization, physical modeling and simulation up to circuit design, to exploit at best the memory performances of each of the aforementioned technologies.

Few key examples in the domain of the OxRAM, CBRAM and PCRAM will be provided in order to target the high temperature data retention specifications of emebedded memory market.

Some tradeoffs appears in each of the aforementioned technologies, like stability against temperature stress versus crystallization speed in PCRAM; or stability against temperature versus forming or programming voltages in CBRAM (in particular chalcogenide based CBRAM with respect to oxide based CBRAM).

In order to develop an optimized memory stack and accelerate the adoption of these new technologies, LETI offers a so-called Memory Advanced Demonstrator (MAD) that is today based on 130 nm ground rules with 4 copper metal lines. The memory module that can consist of PCM, or OxRAM, or CBRAM or MRAM technology is fabricated in the BEOL before pad level. This versatile test vehicle offers the possibility to have on the same silicon test structures spanning from simple resistors (1R), resistors with its selector transistor (1T1R), memory arrays (1kb cuts) up to complex designs allowed by the routing placed on the 4 metal levels. Such complex design may come from client designers using DK plus memory add-on provided by LETI.

All such structures are essential for a deep analysis of the memory functionality: from bulk material (with its interfaces) screening, obtained by the 1R and 1T1R; passing through statistical analysis of extrinsic bits, obtained by memory arrays; up to first validation of complex functions obtained by specific designs.

MAD offers also a benchmark opportunity between different technologies with the same test vehicle in order to extract benefits and drawback from each of them.
(Invited) Floating Gate Type SOI-FinFET Flash Memories with Different Channel Shapes and Interpoly Dielectric Materials
Authors: Liu Yongxun , Nabatame Toshihide , Matsukawa Takashi , Endo Kazuhiko , O'uchi Shinichi , Mizubayashi Wataru , Morita Yukinori , Migita Shinji , Ota Hiroyuki , Chikyow Toyohiro , Masahara Meishoku
Published: February 2020

It is well known that the high-k interpoly dielectric (IPD) layer is important for further scaling down of floating gate (FG) type flash memory to improve the gate coupling ratio [1, 2]. Therefore, the high-k Al2O3 layer has already been used as a blocking layer in the charge trapping (CT) type planar and bulk FinFET flash memories [3-5]. However, the high-k Al2O3 has not been used as an IPD layer in the FG type SOI-FinFET flash memories, to our knowledge. In this work, we introduce the high-k Al2O3 into the FG type triangular-fin (TF) and rectangular-fin (RF) channel SOI-FinFET flash memories, and investigate the effects of fin shape and IPD layer material on the electrical characteristics of the fabricated FG type SOI-FinFET flash memories. In the device fabrication, we used (100) and (110) oriented SOI wafers to fabricate TF and RF channels by using the orientation dependent wet etching [6]. A 30-nm-thick n+ poly-Si layer was used as the FG material. Figure 1 shows the cross-sectional STEM images of the fabricated FG-type SOI-FinFET flash memories with different channel shapes and different IPD layers. Figure 2 shows the P/E characteristics of the fabricated 3 kinds of SOI-FinFET flash memories at the same P/E condition. It is clear that a higher P/E speed, a larger memory window and a lower-voltage operation are achieved in the TF-ONA device as compared to the TF-ONO and RF-ONA ones. This result indicates that a high-k Al2O3 layer is very useful for enhancing memory window due to the improved gate coupling, and the TF channel is very suitable for the low-voltage operation thanks to the high-k of Al2O3 and the electric field enhancement at the sharp foot edges of a TF.

[1] B. Govoreanu et al., IEDM 2006, p. 479. [2] H.-T. Lue et al., IEDM 2011, p. 203. [3] C. H. Lee et al., IEDM 2003, p. 613. [4] S.-K. Sung et al., VLSI 2006, p.106. [5] B. J. Tang et al., IEDM 2011, p. 219. [6] Y. X. Liu et al., VLSI 2010, p.101.

Figure 1
Control of the Surface Chemistry of Magnetron-Deposited Silicon Nitride Etched with Various Wet Treatments
Authors: Brunet Marine , Gouget-Laemmel Anne-Chantal , Aureau Damien , Guillemot Francois , Etcheberry Arnaud , Ozanam François
Published: February 2020

Silicon nitride is a common material in the microelectronic industry, thanks to its dielectric, chemical and mechanical properties. However, when exposed to atmosphere, the silicon nitride layer tends to oxidize. This work presents several efficient ways to remove this native oxide layer while controlling the resulting surface chemistry. Achieving such a control may provide a reliable starting point for further surface functionalization by organic molecules.

The silicon nitride thin films are deposited by magnetron sputtering. The silicon nitride stoichiometry can be tuned by varying the gas fluxes (Ar, N2) during deposition.  Three wet treatments are studied and optimized: hydrofluoric acid (HF), ammonium fluoride (NH4F) and potassium hydroxide (KOH). The treatment efficiency is controlled by X-ray Photoelectron Spectroscopy measurements (XPS). The surface chemistry is investigated by combining Attenuated Total Reflection InfraRed (ATR-IR) and XPS measurements.

All of the three chemical treatments yield the removal of the native oxide, albeit at different rates. HF solution is an efficient and fast etching treatment of silicon nitride. On the resulting surface, fluorine is detected by XPS, suggesting the presence of Si-F bonds. No Si-H bonds are detected on the etched surface by ATR-IR, in agreement with the literature results.

NH4F solution is as efficient as HF in etching the silicon nitride surface, although much slower. This also leads to Si-F bonds, but in a lesser amount than after a HF treatment. KOH can also etch the native oxide of the silicon nitride layer. In this case, the resulting surface contains more oxygen than with the two previous solutions, a likely fingerprint of the presence of surface Si-OH species. Interestingly, the etching rate of the bulk silicon nitride appears much reduced upon etching with KOH as compared to HF.

The formation of Si-H bonds can be forced thanks to a H2plasma treatment performed after the wet native oxide stripping. As shown in the figure, a broad SiH stretching vibration builds up in the infrared spectra upon submitting the silicon nitride film to such a plasma treatment at room temperature. The detailed analysis of XPS signals of samples submitted to various treatment durations shows that the initial surface Si-F bonds are not broken by the plasma, but that the silicon nitride film is progressively etched during the treatment. The film roughens during its dry etching, accounting for the large increase of the SiH signal. 

An important parameter we also investigated is the silicon-nitrogen ratio. The chemistry of the etched surface is highly dependent on this ratio. As shown in the figure, with a silicon-rich silicon nitride layer, a HF treatment leads to the formation of some Si-H bonds on surface.

Figure 1
Impact of Business Trends on Advanced CMP Process Technology Development
Authors: Rhoades R.
Published: February 2020

The technology of chemical mechanical polishing (CMP) is directly influenced by business trends within the semiconductor industry. Companies that manufacture devices and integrated circuits can be grouped into three broad industry segments: leading edge, mainstream or established, and emerging technology. Development of new device architectures, new integration schemes, and ultimately new commercial products are often enabled by development of new and optimized CMP processes. This is illustrated with examples from three different CMP development projects: oxide CMP for advanced silicon substrates with inlaid features requiring sub-nanometer topography, Pt CMP for high temperature vias, and polymer CMP for an advanced packaging interposer design.
A Ring Type Residue Formation in Post Cu CMP Cleaning
Authors: Kim Hojoong , Liim Dong Hyun , Moon Jinok , Kim Jun-Yong , Hwang Hasub , Kim Taesung
Published: February 2020

A chemical mechanical planarization (CMP) of copper (Cu) damascene structure is prone to defect formation due to variety of chemical agents in slurry and chemical complex formation. In post CMP cleaning process, which should remove such defects, a mechanical scrubbing of wafer by porous and elastic brushes are eligibly used. Although, chemical effects are the main mechanism of defect detachment and dissolution during cleaning process, mechanical effects also play key role by transportation of chemical agent and discharge of reacted species.

The most relevant defect caused by mechanical effect is ring shaped scratch due to exceeding contact pressure. In this study, however, we focused on ring shaped residue after post Cu CMP cleaning which is not caused by direct solid contact. To investigate root cause, analysis are carried out such as chemical composition of residue, surface charge map on a wafer, kinematic analysis on brush and wafer motion, and fluid dynamic simulation on chemical motion. In conclusion, it is revealed that both chemical and mechanical effects are interacted to form ring shaped residue. Elimination of defects by chemical effect is suppressed by mechanical motion of brush and chemical fluid.

Figure 1
Advanced Process Control for Variability Control in Chemical Mechanical Polishing Process
Authors: Koli Dinesh R , Wan Hsiang Liang Rachel , Kim Hong Jin
Published: February 2020

With semiconductor technologies driving towards sub 14nm nodes, FIN based field effect transistors (FINFETs) have been the preferred design to meet device power and performance requirements. At the core of FINFET transistor design is gate last/replacement metal gate (RMG) integration scheme due to the advantages in thermal budgets. Chemical mechanical planarization has evolved from planarization technique to technology enabler for this integration scheme. Replacement metal scheme has its own share of challenges- the integration scheme is quite complex. Chemical mechanical planarization (CMP) plays a key role in enabling this integration with various CMP steps supporting dummy poly gate formation, poly removal and replacement metal gate formation. The final gate height of the replacement metal gate is one of the most important parameters controlling device resistance. Even a change of 1nm gate height can result in overall variation of 5ohms/sq resistance.  This requires CMP to control gate height as tightly as possible for every wafer. The two important factors contributing to the overall gate height variation are upstream processes and the metal gate CMP process itself. It is well known that CMP has its own variability in removal rate depending on consumable life resulting in unstable gate height. The gate height variation needs to be controlled within wafer and every wafer.  A dedicated metrology tool connected to the polishing tool has been employed for many years to measure wafer thickness parameters. This onboard metrology tool is used to measure every wafer and the data is used to develop automated process control to improve overall within wafer and wafer to wafer variation.  A two fold approach is used to achieve this. Integrated automated process control (iAPC) is initially used to control wafer to wafer variation and furthermore, zonal integration automated process control is used to improve within wafer uniformity. The basic concept is to use metrology data collected from each wafer and create a model to adjust polishing time to achieve desired final gate height target.  Using these two approaches, gate height control of less than 5nm has been demonstrated consistently. Both these approaches will be discussed in detail.
Immersion Metrology for CMP Pad Monitoring
Authors: Moore Terry , Arasanz Andres
Published: February 2020

Selectivity between materials being polished over the lifetime of the CMP consumable set will typically change. Changes in selectivity overtime are varied and complex, but one main contributor identified in this study using Sensofar immersion metrology, is the changing state of the polishing pad asperities overtime (aka Glazing).

  This study (of a damascene process) demonstrated;

    --> Successful monitoring of the same “wet” polishing pad while on the platen.

    --> Identification of multiple points in usage when glazing occurred

    --> Characterization of successful interventions to reverse the glazing effect

    --> Successful return to target selectivity

    --> Longer consumable lifetime

    --> Reduced manufacturing downtime (MTTR). 

Figure 1
Development of Cobalt Chemical Mechanical Planarization Slurries By Electrochemical/Surface Analytical Screening and Polishing Studies
Authors: Theivanayagam Murali Ganth , Wang Hongyu , Cohen Jamie , VanHanehem Matthew , Sabo Tim , DeNardi Stephan
Published: February 2020

As the technology nodes in integrated circuit (IC) fabrication continue to approach molecular dimensions, the defectivity and planarization provided by conventional chemical mechanical planarization (CMP) processes are no longer sufficient. Therefore, it is necessary to develop new chemistries and innovative screening techniques to solve difficult CMP challenges, including the use of new materials such as cobalt in advanced IC fabrication. For advanced nodes at 14 nm and below, cobalt is currently being implemented on top of Ta/TaN barrier layers and below the copper seeds for the first few metal lines, due to its better conformational coverage within high aspect ratio features and good adhesion to copper. In addition, replacing copper with cobalt in the trenches of interconnect lines for the first few metal layers in the BEOL has demonstrated lower resistivity at smaller dimensions, therefore cobalt interconnects are being considered for < 10 nm nodes for M1 and M2. All these new integration schemes require CMP to achieve planarity with requirements such as low dishing, defectivity, roughness, and tunable selectivity depending on the stack.

Under CMP conditions, however, cobalt can suffer from corrosion and static-etch issues, especially when in contact with copper (galvanic corrosion), due to the lower standard reduction potential of cobalt in aqueous solutions across a broad pH range. The corrosion issues must be solved in CMP slurries that deal with cobalt processes (both liner and bulk/plug) to successfully commercialize cobalt-based IC design for next generation semiconductor manufacturing. In this poster, we will discuss the results and learnings from corrosion inhibitor screening techniques such as electrochemical, static-etch, and quartz crystal microbalance (QCM) studies and their correlation with polishing results for developing cobalt slurry formulation platforms. Furthermore, fundamental understanding on the effects of pH and slurry components such as complexors/oxidizers/corrosion inhibitors on the corrosion and removal rate behavior of cobalt films will be discussed.
Role of Cerium Oxide Surface Chemistry in Adsorption of Polyacrylic Acid in CMP Slurries
Authors: Saraf Shashank , Mesbahi Ali , Harper James , Seal Sudipta
Published: February 2020

Chemical mechanical polishing (CMP) slurries formulated of cerium oxide nanoparticles (CNPs) and polyacrylic acid (PAA) are widely used in shallow trench isolation (STI) application. The critical parameter in slurry formulation is the amount of PAA which determines the extent of its adsorption on CNPs and the excess amount. The adsorption of PAA on CNPs results in a softer surface and prevents defects such as scratches on the wafer surface. The excess PAA selectively adsorbs on silicon nitride, slowing down its etching as compared to silicon dioxide.1 Therefore, the understanding of PAA adsorption on CNPs in a slurry formulation is critical to predict the CMP slurry characteristics.

In previous studies the adsorption of PAA on CNPs has been widely studied;2 however there is still a lack of understanding between adsorption behavior of PAA and the interfacial properties of CNPs. Here, we have systematically investigated the PAA adsorption on ceria slurries and correlating it to the CNPs interfacial properties. Three different commercial ceria slurries were obtained having similar hydrodynamic size, but different surface area as determined using BET. The catalytic properties of CNPs is assessed from the ratio of Ce3+/Ce4+  on its surface, determined using XPS.3 The surface functionalization of CNPs is evaluated from FTIR and NMR depicting three different types of organic moieties resulting in different zeta potentials. Lattice strain and grain size are another important parameter which signifies the internal energy of CNPs. These parameters were calculated using Williamson-Hall plots obtained from the XRD curve. The adsorption isotherm of PAA on CNPs is determined by measuring the carbon content in the supernatant separated from the CNPs using centrifugation. The carbon content is measured using TOC analyzer and the amount of PAA adsorbed on CNPs is calculated by mass balance equation.

1.             Ronay, M., Selective polishing with slurries containing polyelectrolytes. Google Patents: 2005.

2.             (a) Saraf, S.; Neal, C. J.; Das, S.; Barkam, S.; McCormack, R.; Seal, S., Understanding the Adsorption Interface of Polyelectrolyte Coating on Redox Active Nanoparticles Using Soft Particle Electrokinetics and Its Biological Activity. ACS applied materials & interfaces
2014,
6 (8), 5472-5482; (b) Kim, S.; So, J.-H.; Lee, D.-J.; Yang, S.-M., Adsorption behavior of anionic polyelectrolyte for chemical mechanical polishing (CMP). Journal of colloid and interface science
2008,
319 (1), 48-52.

3.             Pirmohamed, T.; Dowding, J. M.; Singh, S.; Wasserman, B.; Heckert, E.; Karakoti, A. S.; King, J. E.; Seal, S.; Self, W. T., Nanoceria exhibit redox state-dependent catalase mimetic activity. Chemical communications
2010,
46 (16), 2736-2738.
Mechanisms and Development of Ceria-Based, Fast Oxide Slurries
Authors: Urban Nathaniel D , Dickmann Dan , Her Bob , Santora Brian
Published: February 2020

Recent developments in vertical integration schemes such as 3D-NAND have introduced a significant need for fast oxide slurries. Balancing low defectivity and high planarization with extremely large bulk oxide removals is crucial. Ceria-based slurries with fine-tuned chemistries are well suited to meet these demands. Mechanisms for ceria-based slurries performance on oxide polish rates have been the subject of investigation for a number of years now. How these proposed mechanisms can drive the design and development of next generation CMP slurries will be discussed. Furthermore, stop on nitride (SON) remains a stringent requirement for various integration schemes. Mechanistic insight into SON additives and their role in ceria slurries will also be discussed.
(Invited) Magnetron Sputtering for Deposition of Photocatalyst Nanostructures on Transparent Conductive Oxides for Solar Applications
Authors: Kruth Angela
Published: February 2020

Photocatalysis has attracted an enormous amount of research interest, in especially with regard to applications such as solar hydrogen generation as well as pollutant degradation. Main research target is the development of corrosion-stable core candidate materials that are able to perform under the abundant visible light in the solar spectrum. Two main approaches are being employed, the development of visible light-sensitive semiconductors and  sensitisation of wide band-gap semiconductors. In materials synthesis, plasma-enhanced surface modification and layer deposition methods are based on the presence of non-equilibrium states of reactive species in a plasma environment. They are therefore able to overcome limitations of traditional catalyst synthesis methods, giving rise to new reaction pathways and resulting in unique properties of nanomaterials.

This presentation reports on recent work on development of DC magnetron sputtering processes for deposition of TiO2 and WO3 semiconductor layers as well as RF magnetron deposition for synthesis of N-doped graphite electrodes on TCO. Electrode properties are characterised by means of XRD, TEM, UV/Vis, XPS, Raman spectroscopy and photoelectrochemical characterisation including IMVS/IMPS and IPCE measurements. Furthermore, plasma-enhanced deposition methods for surface enhancement of photocatalysts layers by nanoparticles and polymer-encapsulation are also discussed.
(Invited) Plasma-Liquid Interactions for Nanoparticle Synthesis, Functionalization and Biomedical Interactions
Authors: Bruggeman Peter J
Published: February 2020

Non-equilibrium atmospheric pressure plasmas interacting with liquids offer a unique source of highly reactive chemistry beneficial for many applications in biology, medicine and advanced materials manufacturing. Plasma-liquid interactions can involve synthesis of nanoparticles (NPs) and inactivation of pathogens. While the underlying mechanisms of these processes are poorly understood, the application potential is enormous.  

The presentation will highlight some examples of reaction pathways responsible for the synthesis of AgNPs at the plasma-liquid interface. This will include a detailed analysis of the reduction mechanism of Ag+, the initial step for the formation of NPs in solution, through various mechanisms proposed in literature including solvated electrons, UV photons and hydrogen atoms.

Plasmas are typically oxidizing and not reducing environments as they produce an abundant source of reactive oxygen species (ROS). We will present the possibility of using these ROS for the functionalization of NPs and in particular the generation of luminescent and hydrophobic water-soluble silicon quantum dots. In addition, we will discuss the importance of these ROS in the inactivation of pathogens in solutions. We will conclude with an overview of the challenges and opportunities ahead.
(Invited) Surface Science Aspects of Etching with Atomic Scale Fidelity
Authors: Lill Thorsten , Kanarik Keren J. , Tan Samantha S.H. , Shen Meihua , Pan Yang , Marks Jeffrey , Vahedi Vahid , Gottscho Richard A.
Published: February 2020

As the IC industry approaches devices with half pitches below 10 nm, etching requires atomic scale fidelity because the device dimensions and their allowed tolerances are of the same order of magnitude as the inter-atomic distances in the crystal lattice. Atomic Layer Etching is emerging as a solution and plasma assisted or directional ALE is being adopted in the manufacturing of integrated devices /1/.

Separation of the etching process into single unit processes allows to apply the large body of knowledge in surface science to improve fundamental understanding. In this talk we will focus on the fundamental processes at the wafer surfaces during etching of various materials with different ALE approaches. Strategies to obtain low physical and chemical surface damage will be presented.

1. K.J. Kanarik, T. Lill, E. Hudson, S. Tan, S. Sriraman, J. Marks, V. Vahedi, R.A. Gottscho; J. Vac. Sci. Technol. A 33, 020802 (2015)
Proton Inserted SiO2 Dielectrics for Nonvolatile Memory-Thin Film Transistor
Authors: Jang Jin Nyoung , Yun JangWon , Hong MunPyo
Published: February 2020

We demonstrated the nonvolatile memory functionality of both nano-crystalline silicon (nc-Si) and amorphous indium gallium zinc oxide (a-IGZO) field effect transistors (FETs) using mobile protons that are generated by very short time (within 5 minutes) hydrogen neutral beam (H-NB) treatment at room temperature (25 °C). Some researches try to hydrogen insertion process via long time (40 minutes) high-pressure hydrogen annealing (HPHA) at high temperature (400 °C) that also need several steps such as poly silicon deposition, HPHA process, and poly silicon etching process. However our hydrogen insertion process does not need any other additional process but only H-NB process during normal thin film transistor fabrication. Also the whole memory fabrication process kept under 50 °C (except SiO2 deposition process; 300 °C). These NVM-TFT(nc-Si and a-IGZO) and  devices exhibited reproducible hysteresis, reversible switching, and nonvolatile memory behaviors in comparison with those of the conventional FET devices. We also investigated neutral beam energy effect on non-volatile memory functionality with IGZO NVM-TFTs. The hysteresis widths of the IGZO NVM-TFTs exhibited strong linear dependency on the H-NB treatment energy. We expected this result from the energy dependent hydrogen surface density profile. The sandwiched hydrogen between insulators becomes mobile proton without annealing process. This H-NB dependent mobile proton density variation is meaningful because until now the only way to increase proton density was increasing ambient temperature or annealing time. The hydrogen neutral beam process between insulators to generate mobile proton is easily controlled by reflector bias. Our study will further provide a useful route of creating memory functionality and incorporating proton-based storage elements onto a probability of next generation flexible memorable electronics such as low power consumption flexible display panel.

Figure 1
Perfect Separation of Hybrid Orientation Structure of CeO2(100) and (110) Regions Grown on SOI Substrates with Lithographically Formed Trenches
Authors: Inoue Tomoyasu , Shida Shigenari
Published: February 2020

Using magnetron sputtering with low energy electron beam irradiation, epitaxial growth of CeO2 layers on Si(100) substrates has been studied for the application to microelectronics. We have found that orientation selective epitaxial (OSE) growth of　 CeO2(100) and (110) layers on Si(100) is capable by controlling surface potential distribution. With the aim of application to hybrid orientation technology for higher speed CMOS devices, we are studying the hybrid orientation structure of the CeO2(100) and (110) regions on Si(100) substrates using electron beam-induced OSE growth by reactive magnetron sputtering. Two separate areas of growth are seen, with CeO2(100) layers found to grow in areas irradiated by electrons during the growth process, and the CeO2(110) layers growing in the areas without irradiation. The lateral orientation mapping by X-ray diffraction measurements reveal the existence of transition regions between these two orientation areas. The width of the transition region is found to　be considerably large and  decrease proportionally as the logarithm of the underlying Si substrate resistivity. To make a breakthrough in the limitation in reduction of the transition region width, we propose a new method of OSE growth on silicon on insulator (SOI) substrates with lithographically formed trenches. The trenches prevent spread of the potential distribution to the neighboring Si islands. We report the experimental results showing perfect isolation between OSE grown regions having different crystallographic orientations, optimizing the Si layer thickness of SOI and the cross-sectional geometry of the trenches.

Figure 1
Fabrication of PVDF- and NMP-Free Lithium Ion Electrodes By Electrophoretic Deposition
Authors: Uceda Marianna , Parsi Benehkohal Nima , Demopoulos George P.
Published: February 2020

Lithium-Ion batteries electrodes are fabricated by mixing the active (Li-ion host) and conductive material along with polyvinylidene fluoride (PVDF) and N-methyl-2-pyrrolidone (NMP) which are the binder and solvent respectively. The paste created is then doctor-bladed onto the current collector, convectively heated, and pressed. The problem with this method is that NMP is toxic and expensive and the binder has a limited solubility meaning replacing the solvent has proven difficult. Current attempts to eliminate the solvent have included finding a water soluble binder (such as Styrene Butadiene Rubber, SBR) or developing a new fabrication method. Among the new methods suggested is Electrophoretic Deposition (EPD). EPD is well suited to provide a low cost and green manufacturing technology for LIB battery electrodes thus contributing towards wider acceptance of electric vehicle transportation and renewable energy adoption. Thus EPD research can be very fertile ground in this domain. In particular, EPD systems that can produce thick electrode films using less hazardous solvents can be a major advancement. With this in mind our McGill HydroMET group has successfully used EPD recently to fabricate binder-free nanotitania/carbon anodes (Journal of The Electrochemical Society, 162, D3013-D3018 (2015)). The performance of the EPD-deposited electrodes was further improved via sintering, this was then compared to standard PVDF-based electrodes and shown to have higher capacity retention characteristics. These encouraging results prompted research into carbon-coated lithium titanate spinel (Li4Ti5O12, LTO) electrodes. After screening different solvents (e.g. water, isopropanol, and several aqueous/organic hybrids) an acetonitrile and water (90/10 vol% respectively) medium was selected which made a stable suspension for both the carbon coated LTO and the conductive carbon. To improve adhesion, SBR binder was added. EPD conditions were 60V for three 15-second stages which yielded a deposit thickness of ~20 μm. In this paper an overview of this work will be presented by emphasizing the selection of EPD medium, characterization of the film, and battery performance (evaluated via galvanostatic charging/discharging cycling tests). In addition post-EPD film processing (compression or sintering) are to be discussed as a means to improve the mechanical integrity of the film.
Reduced Graphene Oxide Hydrogel/Nickel Foam Electrodes, Fabricated By Electrophoretic Deposition for Supercapacitor Applications: Toward High Volumetric Capacitance
Authors: Dickerson James H. , Pham Viet Hung
Published: February 2020

Supercapacitors, a class of electrochemical energy storage devices with superior power densities and long cycling lifetimes, have attracted great attention for the last decade due to their widespread application in backup power supply systems, portable devices, power tools, and hybrid electric vehicles.  Graphene is considered as an ideal supercapacitor electrode material due to its large surface area, superior electrical conductivity, good chemical stability, and high mechanical strength.  The theoretical specific capacitance of graphene is as high as ~ 550 F/g.  The assembly of graphene sheets into three-dimensional interconnected porous microstructures, namely graphene hydrogels, has been considered the most effective approach to utilize these materials in supercapacitors that can achieve high specific capacitances.  However, graphene hydrogels typically consist of large amount of water, up to 99 wt. %, resulting in very low graphene packing density.  Therefore, the usual volumetric capacitance of graphene hydrogels is very poor, limiting their practical application.

In this study, we report a scalable method to prepare graphene hydrogels with high packing densities through the electrophoretic deposition of graphene oxide onto nickel foam, followed by an electrochemical reduction.  The obtained, electrochemically reduced graphene oxide hydrogels (ERGO) on nickel foam were hydraulic compressed (up to 156 MPa) to increase the packing density of ERGO from 0.0098 to 1.32 g/cm3.  In a two-electrode symmetric supercapacitor test using 6M KOH electrolyte, the compressed ERGO showed excellent performance with a volumetric specific capacitance up to 176.5 F/cm3 at a current density of 1 A g−1.  Further, ERGO exhibited favorable cycling stability with retentions in range of 79 - 90 % after 10,000 cycles, depending on packing density of ERGO.
From 1-D to 3-D Li Intercalation: Channel-to-Channel Li Migration Facilitated By Antisite Disorder
Authors: Kim Jae Chul , Seo Dong-Hwa , Ceder Gerbrand
Published: February 2020

Antisite defects, disorder between Li and other cations, are often observed in Li storage compounds synthesized at elevated temperature. In battery materials that have distinct one-dimensional (1-D) Li diffusion channels, preventing antisite formation is considered a good way to obtain desirable electrochemical properties by avoiding channel blockage, which can significantly disrupt Li transport. Thus, it is of critical importance to understand how the antisite modulates the overall Li kinetics in cathode materials. In this work, we investigate lithium manganese borate (LiMnBO3) as a model system in which Li diffuses along the c-axis of its monoclinic lattice. Although it has high theoretical capacity of 222 mAh/g, antisite defects limit the achievable capacity to half of its theoretical value. Our approach to address this limitation is to partially substitute Mn with Fe, which not only leads to immediate improvement in electrochemical properties but also increases the antisite defect concentration. By using ab initio computation and analyzing experimental results, we find that different antisite configurations can affect Li intercalation in different ways and, counter to intuition, channel blockage by the antisite defects is not always detrimental in 1-D materials. At certain conditions, Li migration occurs by channel crossover to detour the channel-blocking defect, and the basic diffusion mechanism is modified from 1-D to 3-D conduction, thereby improving kinetics. This is a refreshing perspective on antisite issues in the 1-D materials. Our model may provide hints to understand and enhance the electrochemical performance of other 1-D materials that suffer from kinetic limitations due to antisite defect through engineering of defect chemistry.
Mechanism and Kinetics of Capacity Fade in Lithium Sulfur Batteries
Authors: Yan Jianhua , Li Bingyun , Liu Xingbo
Published: February 2020

Rechargeable Li-S batteries are receiving ever-increasing attention due to their high theoretical energy density and inexpensive raw sulfur materials. However, rapid capacity fade has been one of the main barriers to further improvements in Li-S batteries and is expected to remain so for the near future. It is generally thought that polysulfide species dissolution and shuttle, nonconductive Li­2S2/Li2S precipitation, and irreversible transformations of sulfur causes different degrees of the capacity fade. In an effort to analyze these degradation processes and elucidate the underlying mechanism of capacity fade, a comprehensive study of sulfur carbon nanotube composite electrodes in different amounts of electrolytes, is presented. Parameters obtained through electrochemical performance, EIS spectra and SEM figures are used to identify the primary cause of capacity fade. It was proved that the formation and accumulation of nonconductive Li2S2/Li2S films on the surface of sulfur electrode was the major reason for the rapid capacity fade in current liquid-type Li-S batteries.
(Invited) NMR Investigation of Ion Transport and Solvation in Electrolytes for Beyond Lithium Ion Applications
Authors: Greenbaum Steve , Gobet Mallory , Peng Jing , Munoz Stephen , Suo Liumin , Wang Chunsheng , Cresce Arthur v. , Russell Selena M , Borodin Oleg , Ho Janet , Xu Kang
Published: February 2020

Nuclear magnetic resonance (NMR) has been productively employed to investigate ion transport and solvation in standard carbonate-based Li ion battery electrolytes. Future electrochemical power sources require new electrolytes to adapt to disruptive changes in the basic working chemistry, such as moving from Li to Na. This work extends the application of some of the NMR tools developed by our lab and others to study the standard electrolytes to the new electrolytes. Using a combination of 23Na, 19F and natural abundance 17O NMR, and pulsed field gradient diffusion, we have examined NaPF6 solutions in binary solvent mixtures ethylene carbonate (EC) and ethylmethyl carbonate (EMC) for possible cation solvation preference as a function of EC/EMC ratio. Using similar methods, we also investigate the transport properties of newly discovered highly conductive ultra-concentrated aqueous solutions of LiTFSI.
(Energy Technology Division Supramaniam Srinivasan Young Investigator Award) Na-M-S-O Quaternary Cathode Materials for High Voltage Sodium Batteries
Authors: Dwibedi Debasmita , Barpanda Prabeer
Published: February 2020

Over the last decade, sodium-ion batteries are widely pursued as an alternative to Li-ion batteries.  Similar to the Li-ion batteries, the development of sodium batteries rely on discovery and optimization of efficient insertion materials. In this pursuit, polyanionic materials are put on anvil to unravel novel  compounds with descent electrochemical properties and thermal/ chemical stability.  Guided by the inductive effect principle, the redox potential of polyanionic cathodes can be tuned  by playing with the electronegativity of constituent anion units. Here, electronegative SO4-based materials can deliver the highest redox potential vis-a-vis other polyanionic materials. Based on this principle,  novel Na2Fe2(SO4)3 alluaudite cathode has been recently reported offering ~100 mAh/g capacity along with high rate kinetics and cycling reversibility [Nature Communications, 5, 4358, 2014]. It marks the highest Fe3+/Fe2+ redox potential (ca. 3.8 V vs. Na/Na+). We have pursued this high-voltage Na-M-S-O quaternary insertion material system employing low temperature solvothermal synthesis like (i) ionothermal method, (ii) spray drying route and (iii) Pechini synthesis. We will describe these new synthetic routes to obtain alluaudite high-voltage cathode material for sodium-ion batteries. Using these green synthesis routes, we have explored other 3d metal homologues in Na-M-S-O quaternary system. Using experimental and DFT calculations, we will summarise the structure and electrochemical performance of Na-M-S-O quaternary alluaudite cathode materials.