bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermally Activated Gas-Phase Chemical Reactions in a Single-Wafer Wet Clean Process
Authors: Kawaguchi Mark N , Zhu Ji , Fischer Christian , Man Xia , Bandarapu Bhaskar , Kon Stanley 
Published: February 2020

A conventional high-dose ion-implanted photoresist strip and clean process flow consists of using a dry remote plasma ashing tool to remove the crust layer and underlying photoresist formed during the implant, followed by sulfuric-peroxide mixture (SPM) and ammonium hydroxide-hydrogen peroxide (SC1) chemistries applied on a wet clean tool to remove the remaining bulk photoresist and implant residues. However, film loss control and residue removal are increasingly difficult to maintain for sub-10 nm devices with conventional approaches. We investigate an alternative sequence that replaces the remote plasma strip with a thermally activated, atmospheric gas-phase oxidation process and replaces the SPM chemistry with a de-ionized water/ozone (DIO3) wet clean. The alternative sequence is entirely processed in a modified single-wafer wet clean chamber. For the oxidation process, a dry O3/O2 gas mixture decomposes and reacts directly with the ion-implanted photoresist wafer that is heated above 300°C from the backside. 9,000 Å/min strip rates are measured on 193 nm photoresist, and 650 Å/min are measured for the implanted crust removal. Based on both X-ray photoelectron spectroscopy (XPS) analysis of the reacted surface as well as the composition of the gas phase products by residual gas analysis (RGA), the crust layer and bulk photoresist are removed by oxidation mechanisms similar to remote oxygen plasma strip processes. Above 350°C, it is found that O2 gas itself reacts with the photoresist but to a lesser extent than the O3/O2 mixture. Reactivity to silicon is lower than a typical remote oxygen plasma based on ~1 Å silicon loss measured on blanket films. This in-situ thermally activated oxidation reaction allows for subsequent wet processing without any queue time delay. The integrated process completely removes 5E15-1E16 at/cm2 high-dose implanted 193 nm photoresist with no residue on patterned substrates.
Fig 1: In-situ thermally activated oxidation reaction in a single-wafer wet clean chamber process sequence consisting of (a) a dry ozone-oxygen gas environment, (b) ozone-oxygen decomposition and reaction on a heated wafer surface, (c) ozonated de-ionized water rinse in an N2 environment, (d) ammonium hydroxide-hydrogen peroxide clean in an N2 environment, and (e) a de-ionized water rinse and spin dry.

Figure 1
(Invited) Materials Selectivity in Atomic Layer Etching of SiO2, Si, and Si3N4 Using Plasma Process Sequences
Authors: Oehrlein Gottlieb S. 
Published: February 2020

Using steady-state Ar plasma in conjunction with periodic injection of a defined number of C4F8 molecules and synchronized plasma-based Ar+ ion bombardment enables controlled removal of SiO2 layers with a thickness in the Angstrom-range.1 The physical sputter rate of SiO2 vanishes for Ar+ ion bombardment with a maximum ion energy of 20 eV and lower, whereas for a fluoroccarbon-coated SiO2 surface, chemical modifications of the SiO2 surface are induced by low energy ion bombardment and SiO2 etching is initiated. In this work we examined SiO2:Si and SiO2:Si3N4 etching selectivity and the roles of maximum ion energy, etching step length (ESL), FC surface coverage, and fluorocarbon precursor selection in controlling these. By optimization of ALE process parameters, e.g. low ion energies, ESL, and FC film deposition per cycle, highly selective SiO2 to Si3N4 etching can be achieved for conditions where FC selectively accumulates on Si3N4 surfaces.2 Surface oxidation of Si takes place during the Ar+ ion bombardment step, and makes it more difficult to achieve abrupt and highly selective removal of thin SiO2 layers from Si. Mechanism of the observed ALE behaviors will be discussed using real-time and post-plasma surface analysis data.

1 D. Metzler, R. Bruce, S. Engelmann, E. A. Joseph, and G. S. Oehrlein, J. Vac. Sci. Technol. A 32, 020603 (2014).

2 C. Li, D. Metzler, C. S. Lai, E. A. Hudson, and G. S. Oehrlein, J. Vac. Sci. Technol. A 34, 041307 (2016).
* I gratefully acknowledge the essential contributions and collaboration of Kang-Yi Lin, C. Li, D. Metzler, S. Engelmann, R. Bruce, E. Joseph , C. S. Lai, and E. A. Hudson on which this talk is based. Additionally, funding from Semiconductor Research Corporation (No. 2017-NM-2726), National Science Foundation (CBET-1134273), and US Department of Energy (DE-SC0001939) is thankfully acknowledged.
(Invited) Selective Atomic Layer Deposition of Cobalt for Back End of Line
Authors: Elko-Hansen Tyler D.-M. , Ekerdt John Gilbert 
Published: February 2020

This talk explores the area-selective atomic layer deposition (A-SALD) of cobalt on copper versus silicon dioxide and a porous low-k dielectric. Cobalt reduces copper electromigration as a capping layer on the copper metal line in back end of line applications. As device dimensions scale there is an increasing urgency to develop area-selective deposition methods that are selective for cobalt deposition on copper to eliminate the need for metal etching steps in metallization process schemes. The half reactions of bis(N-tert-butyl-N’-ethylpropionamidinato) cobalt(II) (CoAMD) and H2 are evaluated on Cu, SiO2, and a porous low-k (~2.6) dielectric. The first and second ALD half reactions of CoAMD on the respective substrates are evaluated by adsorbing the precursor on the substrates under ALD cycling conditions at 265 °C with and without H2 coreactant exposure. The adsorption studies indicate that CoAMD preferentially deposits most on Cu and least on the low-k surface. Further, CoAMD, like other amidinate precursors, readily dissociates on the Cu transition metal surface but the ultimate per-cycle coverage is self-limited by the slow desorption of amidinate ligands and fragments from the Cu surface. Co films deposited by ALD from CoAMD on Cu at 265 °C indicate that Co burrows into the lower energy Cu surface as the film grows in order to reduce the free surface energy. The Cu remains as a surfactant-like layer on the topmost Co surface up to film thicknesses of at least 16 nm. Moreover, considerable intermixing at the Co/Cu interface and Cu concentration several nm into the Co films is observed indicating high surface mobility of the two materials and Cu diffusion at polycrystalline Co grain boundaries. Finally, employing low-temperature ALD and selectively passivating the dielectric surfaces with OH targeting passivants, such as trimethylchorolosilane, leads to enhanced selectivity of CoAMD for deposition on Cu versus SiO2 and porous low-k surfaces. Depositing Co from CoAMD on Cu and the porous low-k surface at 165 °C after exposure to trimethylchlorosilane at 50 °C leads to a 30:1 preference for Co accumulation on Cu, a twelve times improvement compared to deposition on clean Cu or the low-k dielectric at 265 °C.
Exploring Electrochemical Energy Storage of SnO2, Sn3N4, and SnOxNy through Ald
Authors: Stewart David Murdock , Pearse Alex , Gregorczyk Keith , Rubloff Gary W 
Published: February 2020

As conversion electrodes in lithium ion batteries, Sn and SnO2 have been well studied in the literature, while the properties of Sn3N4 and SnOxNy have yet to be been explored in any detail. To study the differences in the electrochemical performance of SnO2, Sn3N4, and SnOxNy, an ALD process was developed which allows for a controlled N/O ratio. This process uses tetrakis(dimethylamido)tin (TDMAS) as a precursor with remote nitrogen plasma and H2O. As with many nitride ALD processes, obtaining Sn3N4 films with low O and C contamination is challenging due to the greater reactivity of Sn with O, and incorporation of precursor ligands. Optimized process parameters for the pulse times and substrate temperature were obtained for the nitride process, which were incorporated into the oxynitride process. SnOxNy films were grown by periodically pulsing water into the reactor after several cycles of the nitride process. By varying the number of nitride cycles between water pulses, the relative concentration of O and N in the film can be controlled between 0% N and 95% N.
The Li2O matrix formed on conversion of SnO2 is expected to be more chemically stable than the Li3N matrix formed from Sn3N4, but at the cost of lower ionic conductivity. Solid-state half cells were constructed using SnO2, Sn3N4, and SnOxNy thin films versus thermally evaporated Li with ALD LiPON as the electrolyte. The electrochemical properties of the anodes were tested by cyclic voltammetry and galvanostatic cycling. Only a single narrow conversion reaction was observed, regardless of film composition, but the voltage at which the reaction occurred shifted as a function of the N/O ratio. At voltages below 0.4 V vs Li/Li+ the half cells shorted, possibly due to mechanical breakdown of the LiPON layer from significant volume expansion of the anodes during the alloying reaction with Li. However, the stability of the cells was improved by varying the composition and thickness of the anodes. Galvanostatic intermittent titration and impedance spectroscopy were used to analyze the ionic conductivity of the anodes before and after the initial conversion reaction and as the N/O ratio was varied. The high energy storage capacity of SnOxNy electrodes, which can be deposited conformally by ALD, makes them attractive materials for applications in thin film, solid state devices, where the particle aggregation and delamination effects are limited by the physical constraints of the device.
Atomic Layer Deposition of NbC-Al2O3 Composite Films for Efficient Solar Selective Coatings
Authors: Avila Jason R , Peters Aaron , Mane Anil U. , Libera Joseph A. , Yanguas-Gil Angel , Farha Omar , Hupp Joseph T. , Elam Jeffrey W 
Published: February 2020

Solar selective films hold great promise for improving the efficiency of concentrated solar power (CSP) facilities. In this study, we used atomic layer deposition (ALD) to prepare solar selective films composed of metal-dielectric nanocomposites with tunable optical and electronic properties. We used niobium carbide (NbC) as the metallic component and Al2O3 as the dielectric component of the nanocomposite films, and these components were blended at the atomic scale by alternating between the NbC and Al2O3 ALD processes. In-situ quadrupole mass spectrometry and quartz crystal microbalance (QCM) measurements were performed to examine the growth of the NbC-AlO composite films as well as to establish the NbC ALD growth mechanism. These measurements revealed that the NbC inhibited the Al2O3 ALD, while the Al2O3 enhanced the NbC ALD. Next, NbC-AlO nanocomposite films wereprepared over the full range of 0-100% NbC in Al2O3 and the physical, optical and electrical properties were measured. We discovered that the band gap and electrical resistivity could be precisely tuned by controlling the composition, and that higher NbC contents yielded a lower band gap and a smaller resistivity. Based on the absorption spectra of the NbC-AlO composite films, we established that 10-20% NbC yield the highest selective absorption efficiencies due their high visible light absorption and low infrared absorption. However, the selective absorption properties of the NbC-AlO composite films were lost upon annealing to 400°C in air as a result of oxidation of the NbC. Our study demonstrates the efficacy for ALD preparing metal-dielectric nanocomposite films with tunable properties to achieve a high selective absorber efficiency. By applying this technique to more thermally robust metallic materials we hope to produce solar selective coatings suitable for deployment in CSP facilities.
Interface Studies of III-V Semiconductors and Oxides with an I
n-Situ Spectroscopic Ultra-High Vacuum (UHV) System Capable of Atomic Layer Deposition (ALD) and Atomic Layer Etch (ALEt)
Authors: Larrabee Thomas James , Prokes S. M. 
Published: February 2020

Preparation of gate dielectrics and high-quality interfaces by atomic layer deposition onto III-V and other sensitive substrates, which typically have multicomponent native oxides after air exposure, is a challenging problem that cannot be completely understood by ex-situ surface analysis techniques. Surface oxides can be detrimental or, in specific cases, even beneficial to device performance depending on how the interface affects the Fermi-level of the semiconductor.1,2 One such system is GaSb, which is a case study here for a high mobility p-type material. In this work, surfaces of GaSb <001> have been examined, with methods of oxide removal including H-atoms, Ar+ ions, and both, simultaneously tested as a function of temperature for determining the threshold of surface damage. The re-oxidation of the interface is examined after oxygen and water exposure, and after oxide films growth.
Description of the unique system designed and built at NRL for these type of studies will be presented.3 It combines a surface science UHV chamber; with X-ray photoelectron and Auger electron spectroscopies (XPS & AES), transmission or reflection-absorption thin-film FTIR spectroscopy, low-energy electron diffraction (LEED), reflection electron energy loss spectroscopy (REELS), and surface preparation, with a chamber-within-a-chamber design for performing ALD and ALEt at pressures from mTorr to Torr. Without exposure to ambient, the ALD system is pumped out and opened to the UHV environment for spectroscopy. A quantified, micro-dosing gas reagent delivery system is also implemented, so quantitative ALD reactant exposure may be correlated with actual surface reactions.4 Spectroscopic results and surface reconstruction patterns for GaSb interfaces acquired in above system will be presented.

1L.B. Ruppalt et al., Appl. Phys. Lett.
101, 231601 (2012).

2V.M. Bermudez, J. Appl. Phys.
114, 024903 (2013).

3V.M. Bermudez, Rev. Sci. Instrum.
85, 114101 (2014).

4T.J. Larrabee, T.E. Mallouk, D.L. Allara, Rev. Sci. Instrum.
84, 014102 (2013).
Octahedral Pt-Ni Nanoparticles for Electrocatalytic ORR – New Insights Using in-Situ Scattering, Spectroscopy and Microscopy
Authors: Beermann Vera , Holtz Megan E , Gocyla Martin , Kühl Stefanie , Padgett Elliot , Erini Nina , Heggen Marc , Dunin-Borkowski Rafal E. , Muller David A. , Strasser Peter 
Published: February 2020

Shape-controlled octahedral Pt-Ni core shell nanoparticles have attracted much attention in recent years due to their promising oxygen reduction reaction (ORR) activities, presumably owing to their particular geometry and facet exposure. Yet much about their growth and degradation has remained insufficiently understood.
Here, we present some recent work where we learned more about the relations between particle synthesis, morphology, bulk structure, surface composition and their catalytic ORR activity and stability using, among others, in situ high-temperature TEM and in situ electrochemical TEM. We follow the particle morphology in real time during annealing protocols, and, using real time imaging, we track and observe changes in the catalyst structure and particle shape during different electrochemical treatments
Our study provides some interesting new insights in the real time behavior and degradation of shaped PtNi electrocatalysts, and may aid in out understanding of some of the parameters that will optimize the lifetime of the catalyst.
Insights into Platinum-Cobalt Electrochemical Dissolution from Platinum-Cobalt Alloy Polymer Electrolyte Fuel Cell Fuel Cell Cathode Catalysts Using Online ICP-MS
Authors: Kariuki Nancy , Papadias Dionissios D. , Myers Deborah J , Ahluwalia Rajesh 
Published: February 2020

The catalysts of choice in polymer electrolyte fuel cells (PEFCs) remain Pt-based nanoparticles on high-surface-area carbon support. One critical challenge facing commercialization of this fuel cell is the gradual decline in performance during operation, mainly caused by the loss of electrochemical surface area (ECA) of the Pt or Pt alloy nanoparticles at the cathode. In this respect, the understanding of the dominant mechanisms of the loss of ECA and loss of oxygen reduction activity, such as the electrochemical dissolution of Pt or the transition metal alloy component, is of vital importance. Several mechanisms for dissolution of platinum have been proposed including direct Pt dissolution and electrochemical oxidation of the Pt surface atoms followed by chemical dissolution of the resulting Pt surface oxide.
This presentation will outline the dissolution of PtCo under various operating conditions. Studies are performed to quantify the amount of dissolved Co and Pt during potentiodynamic conditions in an electrochemical flow cell system connected to an inductively-coupled plasma-mass spectrometer (ICP-MS) capable of detecting trace concentrations (<ppb) of dissolved elements in solution. The electrochemical data combined with the ICP-MS data are used to evaluate the influence of various factors such as potential, potentiodynamic profile parameters (e.g., scan rate, upper and lower potential limits), particle size, and support type on the dissolution processes in acidic electrolytes at room temperature.
Preliminary measurements showed that Pt dissolution occurs during both the positive-going and negative-going potential sweeps. When the potential was cycled from 0 to 1.0 VRHE, two distinct dissolution peaks were detected by the ICP-MS online analysis. The ratio of the amount of Pt dissolved during the two sweeps was found to be dependent on the sweep rate, potential hold times, and potential profile. Fundamental models will be developed to explain the mechanisms of degradation process under various potential conditions.
This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Fuel Cell Performance and Durability Consortium (FC-PAD). Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.
Unsupported Platinum-Metal Two-Dimensional Nanoframe Oxygen Reduction Electrocatalysts: Effect of Transition Metal Composition on Activity and Stability
Authors: Ying Yuanfang , Godinez-Salomon Fernando , Archer Randall , Rhodes Christopher 
Published: February 2020

Currently, oxygen reduction reaction (ORR) electrocatalysts used within proton-exchange membrane fuel cells (PEMFCs) are primarily platinum (Pt) and Pt-based alloys that are supported on high surface area carbon. At elevated voltages encountered during start-up/shut-down, the corrosion of the carbon support is accelerated which can significantly degrade the long-term stability of the catalyst. Recent work by our group has shown that unsupported (carbon-free) Pt-Ni two-dimensional (2D) nanoframes enable ORR electrocatalysts with significantly improved activity and stability compared with carbon-supported Pt and bimetallic Pt-metal alloy catalysts.1 The unique nanoframe structure consists of a hierarchical 2D framework composed of a highly catalytically active Pt-metal alloy phase with an interconnected solid and pore network that results in three-dimensional molecular accessibility. The effect of altering the transition metal was investigated as a route to further improve the ORR activity through control of the surface atomic and electronic structure of Pt. Unsupported Pt-metal (metal=Ni, Co) two-dimensional (2D) nanoframes were synthesized through controlled thermal treatments of Pt-decorated metal hydroxide/oxide nanosheets. The structure of the 2D nanoframes were determined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Analysis of XRD and SEM data supports that Co and Ni can be incorporated into Pt-metal 2D nanoframes. Electrochemical characterizing using a rotating disk electrode configuration shows that the Pt-M 2D nanoframes exhibit significantly higher activities compared with Pt/C. The ability to create metallic 2D structures with 3D molecular accessibility opens up new opportunities for the design of high activity and stability carbon-free catalyst nanoarchitectures for numerous electrocatalytic and catalytic applications.

References

Godínez-Salomón, F.; Mendoza-Cruz, R; Arellano-Jimenez, M. Jose-Yacaman, M.; Rhodes, C.P; (manuscript submitted).
Oxygen Reduction Reaction Activity of Platinum Thin Films with Different Densities
Authors: Ergul Busra , Begum Mahbuba , Kariuki Nancy , Myers Deborah J , Karabacak Tansel 
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFCs) have gained significant attention as alternative power sources, especially for automotive applications due to their high energy conversion efficiency, low operating temperature and being environmentally friendly compared to the other types of fuel cells. However, sluggish kinetics of oxygen reduction reaction (ORR) on the cathode requires a high loading of platinum (Pt), which increases the cost of the fuel cell. In addition, dissolution and agglomeration of Pt nanoparticles and oxidation of the carbon support are among the major factors that cause electrode degradation and performance loss. Therefore, extensive efforts are focused on developing high performance, durable, and low-cost electrocatalysts. Extended surfaces such as nanostructured thin films are good candidate for non-conventional catalysts due to their high surface area and having no need for a support material.
In this work, a new density-modulated platinum thin film (Pt-TF) design was fabricated by high pressure sputtering deposition (HIPS) and was investigated as potential electrocatalysts for the ORR in PEMFCs using cyclic voltammetry and rotating disk electrode techniques in aqueous perchloric acid electrolyte. Scanning electron microscopy and X-ray diffraction methods were used to study morphological and crystallographic properties of the density-modulated Pt-TF electrocatalysts. The Pt-TF catalyst was produced by changing working gas pressure from low to high values during film growth, which results in denser film bottoms and more porous tops. Low-density film top provides effective transportation of oxygen, which could enhance catalyst utilization and result in reduced Pt-loading and enhanced activity. Porous yet interconnected network of Pt atoms in the low-density Pt-TF surface can also eliminate the agglomeration and dissolution problems. In addition, high-density film bottom provides a strong adhesion to the substrate leading to enhanced physical and electrochemical stability of the Pt-TF. Stronger bonds along with self-protection against the acidic environment due to the dense-packing of Pt atoms at the interface with the substrate can hinder leaching of Pt and avoid the detachment of large regions of Pt-TF from the substrate as a whole. In addition, high-density layer can reduce contact resistance and enhance the electronic conductivity. This presentation will focus on electrochemically active surface area, area specific activity, and mass activity of density-modulated Pt-TFs during accelerated stability tests and compare them to conventional high-density Pt-TF and Pt/C electrocatalysts.