bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of Ammonium Silicate Residue during Polysilazane (PSZ) Dry Etching in NF3/ H2O Gas Chemistry
Authors: Kim Hyun-Tae , Kim Min-Su , Lee Jong-Seok , Choi Geun-Min , Park Jin-Goo 
Published: February 2020

For 28nm NAND flash memory, the aspect ratio of shallow trench isolation (STI) becomes large, and it makes difficult to fill STI structure by conventional oxide film without void formation. Several gap-fill methods such as high density plasma (HDP) and thermal chemical vapor deposition (CVD) are widely accepted, but they are difficult to make gap fill without void because of gap-fill margin. Recently, STI fill has been tried with polysilazane (PSZ) based inorganic spin-on dielectric (SOD) film. PSZ oxide has its good gap-fill ability, low moisture content and high etching resistance. However, PSZ oxide would produce amine etch residue during the NF3 dry etching process because of NH3component in PSZ oxide. For preventing this resudue, it is very important to control process parameters affecting the chemical reaction because the etch rate, and the surface quality depend upon the process reaction. During the STI etching back process, other layer also exposed. So, selectivity between other oxide must be considered.
In this study, we have employed plasma dry etching of nitrogen trifluoride (NF3) and H2O mixtures. We studied the effect of the gas chemistry on the etching of oxides. The materials used for these experiments were thermally grown SiO2 (1000Å, 10000Å), PSZ oxide (500Å), TEOS (315Å) and ALD oxide (300Å). Samples of size 25 x 25 mm were cleaned first in diluted SC-1 [NH4OH(25%): H2O2(38%): DIW =1:2:50] at 60°C for 10 min. The etching mechanism of PSZ oxide was investigated in plasma activated NF3/H2O gas. This process generates ammonium hexafluorosilicate ((NH4)2SiF6) as a by-product. By-products were formed on the PSZ surface which was confirmed by observing N–H, NH4+ and SiF6
2-peak in ATR-FTIR spectrum. These peaks are representative of (NH4)2SiF6 powder composition. Etch rates of several SiO2 were reported as a function of H2O ratio, substrate temperature, and pressure. NF3/H2O mixtures were excited using pulsed RF plasma. The NF3 flow rate for all experiments was kept at 150 sccm. The temperatures were varied from 8 to18ºC, the chamber pressures from 7 to 9 Torr., the H2O flow rates from 1500 to 2500 sccm and process times from 20 to 100 sec. Helium was used as a carrier gas. After dry etching, an annealing process was performed. The reaction mechanism was proposed by analyzing the oxide layer surface. We used an ellipsometer to measure the oxide thickness for evaluation of the etch rate. Also, various analyzing tools such as SEM, contact angle analyzer, and FT-IR were used to characterize the surface contaminants. The optimized drying process provides the high selectivity without any residue formation.
(Invited) Photo-Assisted ALD: Process Development and Application Perspectives
Authors: Miikkulainen Ville , Väyrynen Katja , Kilpi Väinö , Han Zhongmei , Vehkamäki Marko , Mizohata Kenichiro , Räisänen Jyrki , Ritala Mikko 
Published: February 2020

Photons can be utilized to create new ALD chemistry or enhance existing ALD processes. Photo-enhancement provides many potential advantages such as lower deposition temperature, novel growth chemistries, selective area deposition, and improvement of film properties. Despite these attractive advantages, there are not many reports available on the topic, materials deposited being mostly oxides, e.g. ZnO, Al2O3 and Ta2O5.[1-3] The main challenges are the reactor design and the complexity of photochemistry in the heterogeneous system. The reactor must ensure intensive light of appropriate wavelength on the substrate while avoiding film growth on the optical components. On the other hand, optical properties of the adsorbed precursor, the substrate, and the film can all contribute to the deposition photochemistry.
We have been studying and developing photo-assisted ALD processes for oxide and metal thin films. A customized Picosun™ R-200 ALD reactor with two alternative UV sources has been employed. A single-source approach with metal alkoxides has proved itself an effective method for depositing Ti, Zr, Hf, Nb, and Ta oxides.[4] Area-selectivity of the photo-assisted Ta2O5 ALD was demonstrated by depositing a University of Helsinki emblem with two aluminum shadow masks (Fig.1). Resolution does not allow device level patterning but can be exploited to protect contact areas, for example. The photo-assisted ALD of metals is fundamentally different from the case of oxides in that the deposited material is optically absorbing and electrically conductive. Furthermore, the metal typically needs to be reduced during the ALD cycle. In this presentation, results on process development and the material properties of photo-assisted ALD of metal oxides, and Ru and Cu will be discussed, together with potential applications in sight. Focused ion beam patterning, wet etching and pre-patterned substrates can be used to demonstrate the capabilities of photo-ALD films.
The Semiconductor Research Corporation (SRC) and Finnish Centre of Excellence in Atomic Layer Deposition (ALDCoE) are acknowledged for funding. Picosun provided the customized reactor for the project.
References
[1] Yamada, A.; Sang, B.; Konagai, M. Appl. Surf. Sci.
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[2] Lee, Y.-H.; Kwak, J.-C.; Gang, B.-S.; Kim H.-C.; Choi, B.-H.; Jeong, B.-K.; Park, S.-H.; Lee, K.-H. J. Electrochem. Soc.
2004, 151, C52.
[3] Chalker, P. R.; Marshall, P. A.; Dawson, K.; Brunell, I. F.; Sutcliffe, C. J.; Potter, R. J. AIP Advances
2015, 5, 017115.
[4] Miikkulainen, V.; Väyrynen, K.; Kilpi, V.; Mizohata, K.; Räisänen, J; Ritala, M., manuscript.

Figure 1
Insights Towards Mitigated Mn Dissolution through Structure-Sensitive Al2O3 Film Nucleation on LiMn2O4 By Atomic Layer Deposition
Authors: Warburton Robert , Chen Lin , Voeroes Marton , Iddir Hakim , Chen Kan-Sheng , Liberia Joseph , Hersam Mark C. , Curtiss Larry A , Elam Jeffrey W , Greeley Jeff 
Published: February 2020

Dissolution of transition metal (TM) cations into organic electrolytes is a significant impediment to capacity retention in various lithium ion battery electrode materials. Interfaces engineered via substitutional doping and protective coatings, however, have been demonstrated to be effective techniques to reduce TM dissolution, preventing counterelectrode crossover1–3. In this work, we present an integrated theoretical and experimental approach to gain a molecular level understanding towards the functionality of protective thin films. As a model system, we consider Al2O3 film growth by atomic layer deposition (ALD) on spinel LiMn2O4 (LMO), a cathode material exhibiting the well-documented capacity fade mechanism of Mn dissolution. Using first principles DFT+U calculations in concert with in situ experimental characterization, the mechanisms for Al2O3 ALD film growth by trimethylaluminum (TMA) and H2O half-reactions are evaluated. Using thermodynamically stable low-index surface truncations, as well as stepped defect features4, we identify facile pathways for full demethylation of the TMA precursor on the LMO surface. Trends from microbalance experiments indicate sub-monolayer film coverage for ~10 ALD cycles, wherein film growth is initially slow, but gradually increases until the limit of a fully formed Al2O3 film is reached. DFT calculations suggest that sluggish film growth at the onset is predicated by site blocking from decomposed CH3 groups. An electronic structure descriptor is presented to demonstrate evidence that, in early ALD pulses, Al2O3 preferentially nucleates at sites on LMO that are most susceptible to Mn dissolution. The chemical nature of these relevant defect sites will be discussed further in the context of Mn dissolution through charge disproportionation, with enhanced stability by selective nucleation of the protective films. The unique mechanisms for ALD on LMO lead to modest enhancements in electrochemical performance for only ~1-2 ALD cycles, whereas cycling capabilities reduce with further TMA/H2O pulses in the limit of a fully formed coating on the substrate.
This research was supported as part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
Optimizing Process Parameters for Plasma Assisted Atomic Layer Deposition
Authors: Boris David R. , Wheeler Virginia D. , Anderson Virginia R , Nepal Neeraj , Rosenberg Samantha G , Kozen Alex C , Hite Jennifer K , Walton Scott G , Eddy Charles R. 
Published: February 2020

Plasma assisted atomic layer deposition (PA-ALD) is a low temperature conformal layer-by-layer deposition technique that is based on a pair of self-terminating and self-limiting gas-surface half-reactions, in which at least one half-reaction involves species from a plasma. This approach generally offers the benefit of substantially reduced growth temperatures and greater flexibility in tailoring the gas phase chemistry to produce varying film characteristics. The flexibility and lower growth temperatures that plasmas provide come at the cost of a complex array of process variables that often require great care on the part of the user. In response to this challenge, this work focuses on the use of plasma diagnostics to inform the choice of process conditions for PA-ALD systems. In this work we employ optical emission spectroscopy and charged particle collectors to characterize a Fiji 200 (Ultratech/CNT) PA-ALD tool. In particular, we assess the total ion flux reaching the substrate surface and the relative fractions of atomic and molecular species generated in the plasma under a variety of pressures and gas input flow fractions in the context of PA-ALD of AlN and Ga2O3films. Changes in plasma parameters are then linked with changes in film characteristics. ________________________________ * This work supported by the Naval Research Laboratory Base Program
Interfaces Formed by ALD Metal Oxide Growth on Metal Layers
Authors: Aussen Stephan , Hardtdegen Alexander , Skaja Katharina , Hoffmann-Eifert Susanne 
Published: February 2020

Redox-based resistive switching random access memory (ReRAM) has the potential to fulfill the demands of future Green IT solutions for non-volatile memory circuits with high speed data access, high reliability, and low power consumption. A single valence-change-mechanism (VCM)-type switching cell is typically built from a transition metal oxide layer sandwiched between metal electrodes of different oxidation enthalpy. It is accepted in the scientific community that oxygen exchange and drift/diffusion processes play a major role in the resistive switching process. Thus, understanding oxidation/reduction reactions taking place already during the growth process is of utmost importance.
For future three-dimensional (3D) integrated arrays of ReRAM cells atomic layer deposition (ALD) will become the method of choice to grow ultra-thin, conformal, homogeneous and dense oxide films at a thermal budget below 450 °C. For todays’ two dimensional stacked crossbar arrays, the metal oxide films can be grown on nearly inert Pt electrodes, while the oxygen exchange layer built from a reactive metal is deposited on top of the metal oxide. However, in the 3D ReRAM arrays the metal oxide might need to be grown on the reactive metal as well.
In this study ultrathin ALD metal oxide layers are deposited on various metal electrodes by means of in-situ transfer from the sputtered metal into the ALD chamber. For the metal layers we utilized Pt, Hf, and Ta while for the metal oxides Al2O3, TiO2, and HfO2 were chosen. ALD metal oxide processes were performed by plasma assisted ALD in an Oxford FlexAlâ system.
Due to the passivation property of the dense ALD metal oxide layer the metal oxide / metal interfaces could be analyzed ex-situ if the vacuum break was kept short. Angle resolved X-ray photoemission spectroscopy studies combined with X-ray reflectivity analysis reveal a clear picture of the interface formation and the oxygen gradient formed at the interface already during growth. The influence of process parameters and stack sequences on this ‘built-in’ oxygen gradient at metal / ALD metal oxide interfaces will be covered in this presentation. Among others, the possibility for PtOx formation during remote oxygen plasma ALD processes will be discussed.
The Improvement of the Pattern Wiggling Profile by Photo Resist Treatment
Authors: Liu Pan-Pan , Zhang Cheng-Long , Zhang Hai-Yang 
Published: February 2020

Abstract

For advanced node such as 14nm technology and beyond, Patterning is one of the key challenges in the semiconductor industry. Advanced pattern transfer techniques such as negative tone development (NTD) technology are under investigation to enable the aggressive pitch requirements demanded. Even though, just as traditional positive tone development (PTD) technique, a pattern wiggling issue has arisen with the reduction of pattern dimension during dry etch process, which prevents the successful pattern transfer [1].
Two kinds of wiggling solutions have been proposed. One is the lithographic resolution such as changing the physical properties of the under-layer materials [2-4]. The other is the gases treatment in the tri-layer process such as H2plasma for spin-on carbon (SOC) hard-mask [5] and HBr and Ar plasma treatment for photoresist [6]. However, with the decrease of device size, a single method hardly eliminates wiggling and meets the pattern target. Besides, the requirements for Line Edge Roughness (LER)/Line Width Roughness (LWR); critical dimension uniformity (CDU); through pitch are extremely aggressive in advanced technology. Therefore, the characteristics of the dry etching process play an increasingly import role in defining the outcome of the pattern process.
In this paper, we will demonstrate the method of PR treatment (both PTD and NTD techniques) that improves LER/LWR for trench pattern in dry etch ICP etcher. Meanwhile, the difference of PR treatment methods between PTD and NTD is illuminated. What’s more, in PR treatment methods, other pattern behavers such as CD, CD uniformity, through pitch are concerned during improving LER/LWR process, and aim to get a good result of all aspects. At last, the role of various plasma etch parameters that influence the key patterning metrics of CD, resist selectivity and LER/LWR are studied.

Acknowledgement

REFERENCES

[1] Goji Wakamatsu, Kentaro Goto, Yoshi Hishiro, Taiichi Furukawa al., Advances in Resist Materials and Processing Technology XXIX, Proc. of SPIE Vol. 8325 83250T-1,(2012)
[2] Makoto, M., Mitsuaki, I., Takashi, K., Hisashi, H, and Seiji, F., Proc. SPIE7972,797226 (2011).
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[4] Someya, Y., Shinjo, T., Hashimoto, K., Nishimaki, H., Karasawa, R., Sakamoto, R., Matsumoto,T., Proceedings of the SPIE, vol.8325, 83250U (2012).

[5] M. Tadokoro, K. Yonekura, K. Yoshikawa, Y. Ono, T. Ishibashi,T. Hanawa, and N. Fujiwara, J. Vac. Sci. Technol. B 26 (1) Jan/Feb( 2008)
[6] E. Pargon, K. Menguelti, M. Martin, A. Bazin, O. Chaix-Pluchery, C. Sourd, S. Derrough, T. Lill, and O. Joubert, Journal of Applied Physics 105, 094902 (2009)
(Invited) Growth and Applications of Si1-xSnx Thin Films
Authors: Kurosawa Masashi , Nakatsuka Osamu , Zaima Shigeaki 
Published: February 2020

Integration of near-infrared light source/detector on Si chips has long been expected to achieve on-chip and/or chip-to-chip optical interconnectivity. However, the indirect band gap of group-IV semiconductor such as Si and Ge remains a challenge especially for photoemission. Although the direct band gap in Si is 3.1 eV above the indirect band gap and the solid solubility limit of Sn in Si is extremely low (0.1%), the Si1-xSnx alloys must have a direct band gap for a sufficiently high Sn content, as for Ge1-xSnx. From a device perspective, an experimental demonstration of the band gap is desired. However, the relevant optical property for Si1-xSnxhas to date not been obtained.
Under such a background, the present paper reports our recent progress in advanced low-temperature crystallizations for Si1-xSnx (x: 0–0.4) thin films on various substrates (insulators, Si, Ge, InP, etc.). Composition analyses indicate that approximately 20% of the Sn atoms are substituted into the polycrystalline (or epitaxial) thin films grown on an insulator (or Ge(001)) after annealing at 220 oC for 5 h. By using InP(001) substrates, the Sn content could raise up to about 40%. Comparison of the band gap with the calculated values and new applications, such as Si1-xSnx-source tunnel field effect transistors and thermoelectric generator, will be discussed.

Acknowledgments

This work was partially supported by Grants-in-Aid for Scientific Research (S) (Grant No. 26220605) and Young Scientists (A) (Grant No. 17H04919) from JSPS in Japan and PRESTO (Grant No. JPMJPR15R2) from JST in Japan.
(Invited) Ultrapure Homoepitaxial Diamond Films Grown by Chemical Vapor Deposition
Authors: Teraji Tokuyuki 
Published: February 2020

In this decade, studies on semiconducting diamond for the power device application have intensively been conducted in several research groups. A use of diamond crystals with low defect density is crucial for obtaining high blocking voltage. High crystalline quality and high purity of diamond crystals are also requested in the field of research on quantum information using diamond. Although a lot of effort was devoted to improve the quality of diamond films, dislocations still remain in the crystals with the number density higher than 104 cm-2. In this study, we propose advanced diamond growth condition that removes crystalline defects effectively during the growth process of homoepitaxial diamond films.
Homoepitaxial diamond films were deposited on Ib(100) substrates using the homebuilt microwave plasma-assisted chemical-vapor-deposition (MPCVD) apparatus [1]. In this study, effect of oxygen addition during diamond growth was investigated [2]. Typical growth condition was as follows; total gas pressure, microwave power, methane concentration (flow ratio of CH4 to the total gas flow), oxygen concentration (flow ratio of O2 to the total gas flow), and substrate temperature were 120‒140 Torr, 1.2‒1.4 kW, 4‒10%, 0‒2%, and 950‒1050 °C, respectively. Microwave power density estimated from the injected microwave power divided by the plasma volume was 110‒180 W cm-3.
By optimizing growth conditions with higher oxygen concentration of 2%, high-purity homoepitaxial (100) diamond layers, typical nitrogen concentration of which was less than 1 ppb, were successfully grown. Cathodoluminescence mapping and 3D Raman measurements indicated a number density of dislocations in the homoepitaxial layer is typically 104-105 cm-2. Tungsten carbide Schottky electrodes fabricated on the non-doped diamond showed high blocking voltage of 2.2 kV. This diamond films growth technique is promising for designing high-performance quantum information devices.
The author would like to thank Dr. T. Yamamoto, Dr. S. Koizumi, Dr. K. Watanabe, Dr. H. Umezawa, Dr. S. Onoda, Dr. O. Milikofu, Prof. F. Jelezko, and Prof. J. Isoya for helpful discussion and supporting characterization.
[1] T. Teraji, T. Yamamoto, K. Watanabe, Y. Koide, J. Isoya, S. Onoda, T. Ohshima, L. J. Rogers, F. Jelezko, P. Neumann, J. Wrachtrup, and S. Koizumi, phys. stat. sol. (a) 212, 2365(2015).
[2] T. Teraji, J. Appl. Phys. 118, 115304(2015).
(Invited) Metal Organic Frameworks for Thermoelectric Energy Conversion Applications
Authors: Talin Albert Alec 
Published: February 2020

Motivated by low cost, low toxicity, mechanical flexibility, and conformability over complex shapes, organic semiconductors are attractive as thermoelectric (TE) materials to replace the costly, brittle, and non-eco-friendly inorganic TEs for near ambient temperature applications. Metal organic frameworks (MOFs) are extended, crystalline compounds consisting of metal ions interconnected by organic ligands forming a crystalline, nanoporous structure, share many of the attractive features of all-organic polymers, including solution processability and low thermal conductivity. A potential advantage of MOFs and Guest@MOF materials for TE applications is their synthetic and structural versatility, which allows both the electronic and geometric structure to be tuned through the choice of metal, ligand, and guest molecules. These unique features could solve the long-standing challenge of finding stable, high ZT n-type organic semiconductors, as well as promote high charge mobility as a result of the long-range crystalline order inherent in MOFs. In addition, the low atomic density and long, bridge-like bonding characteristic implies that MOFs should exhibit low thermal conductivity, which is an attractive feature for thermoelectric energy conversion. In my presentation I will review the recent advances in the synthesis of MOF and Guest@MOF TEs and discuss how the Seebeck coefficient, electrical conductivity and the thermal conductivity could be tuned to further optimize their TE performance.
This work was supported by the Sandia Laboratory Directed Research and Development (LDRD) Program. Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
(Invited) Soft Mode Phase Transition and the Lattice Thermal Conductivity of PbTe-Based Materials
Authors: Savic Ivana 
Published: February 2020

Exploiting the fascinating properties of materials near soft mode phase transitions is an emerging concept in the quest to increase thermoelectric efficiency [1,2]. The underlying idea is that soft phonons lead to intrinsically low thermal conductivity, while possibly preserving electronic transport properties. Using first principles simulations, we show that driving PbTe near the transition from the rocksalt to a rhombohedral structure will significantly reduce its lattice thermal conductivity. We illustrate this concept by applying biaxial tensile (001) strain to both PbTe and its alloy with rocksalt PbSe, and also by alloying PbTe with rhombohedral GeTe [3]. Moreover, we investigate in detail how tuning the proximity to the soft optical mode phase transition via chemical composition affects the lattice thermal conductivity of (Pb,Ge)Te alloys [4]. We show that the anharmonic contribution to the lattice thermal conductivity is minimized at the phase transition due to the maximized acoustic-optical interaction. Furthermore, mass disorder shifts the conductivity minimum towards the composition at which the scattering due to mass disorder is maximized. The total lattice thermal conductivity and its anharmonic contribution vary continuously between the rocksalt and rhombohedral phases as expected for the second-order phase transition. Our results show that alloys with soft optical mode transitions are promising materials for achieving low thermal conductivity and possibly high thermoelectric efficiency.
[1] D. T. Morelli, V. Jovovic, and J. P. Heremans, Phys. Rev. Lett. 101, 035901 (2008).
[2] L.-D. Zhao et al, Nature 508, 373 (2014).
[3] R. M. Murphy, E. D. Murray, S. Fahy, and I. Savic, Phys. Rev. B 93, 104304 (2016).
[4] R. M. Murphy, E. D. Murray, S. Fahy, and I. Savic, Phys. Rev. B 95, 144302 (2017).