bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of a Lab-Scale Tribo-Electrochemical Approach for Chemical Mechanical Planarization
Authors: Afekare Dayo Akintan 
Published: February 2024

During chemical mechanical planarization (CMP), the electrochemical interactions between slurry additives and the polishing substrate metal films favor the formation of easily removable species that are then detached by mechanical abrasion effects of the CMP pad and nanoparticle abrasives in slurry. Yet, neither the mechanical nor chemical aspects alone dictate the CMP process; rather, it is the intertwined dependencies of tribology and electrochemistry that often control the polish performance. This highlights the importance of the functional synergies, otherwise known as tribo-electrochemistry, which has been largely under-explored in the CMP research community.
This work discusses the development of a novel small-scale tribo-electrochemical approach for metal CMP. It covers the tool design aspects, tribo-electrochemical measurements such as open circuit potentiometry (OCP) and polarization resistance, and relevance to CMP applications. The system is developed based on a small-scale CMP polisher coupled to a 3-electrode cell design circuit that is connected to a potentiostat. The design utilizes a common type of CMP metal film as the working electrode, with the accompanying pad and slurry consumables serving as baseline for method development. All other process conditions, including rotating speed, downforce, polish-hold duration, and pad conditioning process follow typical CMP standards.
The results show tribo-electrochemical responses to the presence of catalyst (C), oxidizer (O), inhibitor (I), and abrasive (A) in the experimental slurries. The data is of significant value in terms of the anodic & cathodic site functions on the CMP metal surface and in the context of material removal. In addition, notable sensitivity to pad texture, downforce, and temperature effects were observed, and removal rate measurements correlated with polarization resistance for varied levels of the O and I additives. In summary, the tribo-electrochemical aspects of CMP have been probed and an innovative analytical approach has been developed and demonstrated.
Morphological and Electrical Characterization of AlGaN/GaN Heterostructures Modified By Atomic Layer Etching
Authors: Miersch Christian , Wege Stephan , Heitmann Johannes , Beyer Franziska Christine 
Published: February 2024

Modern microelectronic components for high-power and high-frequency applications based on III-V compound semiconductors offer high break down voltage (GaN: 5 MV/cm and AlN: 15 MV/cm) at low specific on-resistance. However, it requires reliability and reproducibility of the production processes. Going to higher frequencies (5 GHz and beyond) and more integration in consumer electronics, smaller structure sizes are needed. This is going along with increasing demands on the manufacturing processes like dry etching. The main goal is to reach smaller and high controllable etching rates, going down to single atomic layers, low damage, and minimized surface roughness. Atomic layer etching (ALE) represents a key technology in order to achieve such requirements.
An ALE process consists of two independent steps forming a repeatable cycle with a specific etching amount per cycle (EPC). First a surface modification is done by a chemical precursor i.e., adsorbing or oxidizing the surface. The second step is the removal of the modified layer, either physically by low energy non-reactive ion bombardment (Plasma Enhanced ALE [PEALE]) or chemically by a reactive species (Thermal ALE). The two steps are separated by an inert gas purge. This purging grants the removal of the chemistry after the first step, preventing further chemical reaction and transporting the chemical products out of the chamber after the second step.
In this study, a PEALE conducted on different tools is used, for gate and contact recess study in a AlGaN/GaN heterostructure to form high electron mobility transistors (HEMT) with reduced ohmic contact resistance and threshold voltages. The results show a reduction of ohmic contact resistance at reduced forming temperatures and a linear dependence of the threshold voltage on gate recess depth. In order to determine the etching rate and roughness, atomic force microscopy (AFM) measurements were performed.
The PEALE module is either integrated into a cluster tool consisting of atomic layer deposition (ALD) and chemical vapor deposition (CVD) or done in a combined ALD/ALE chamber. This opens the possibility of etching and depositing in-situ, reducing contamination and degradation of the substrate material.
By this means, metal insulator semiconductor (MIS)-HEMTS with a recessed gate are studied. The monitoring of the individual processes is achieved by test structures like transfer length method structures (TLM) and metal oxide semiconductor (MOS), which showed the improved electric performance of these devices and may indicate unwanted interface issues, respectively. Additional, pre- and post-treatments could improve the interfaces further. The results will be presented and discussed in terms of ALE process development and optimization.
This work was financially supported within the ALEStar project by the government of the Free-state of Saxony and the European Regional Development Fund under grant no. SAB 100402929.
Sulfur- and Nitrogen- Containing Molybdenum Films with a Thermally Stable Precursor
Authors: Leoncini Andrea , Barik Chandan Kr , Liu Feng Q , Tang Jiecong , Sudijono John , Saly Mark 
Published: February 2024

As devices become more and more complex with each generation, process requirements become more stringent and new materials are necessary. This also translates to the need of new precursors, in particular halide free organometallic precursors with high thermal stability. This combination prevents halide contamination/corrosion of the deposited and neighboring films, and expands the ALD window for processes. However, higher thermal stability should not compromise the reactivity of the precursors in the desired processes.
We designed and successfully synthesized a new halide-free Mo precursor. It was characterized by 1H-, and 13C- NMR spectroscopy, and its molecular structure have been confirmed by x-ray crystallography. We studied its thermal stability, volatility, and chemical properties. Thermogravimetric analysis shows good volatility, with T½ of 230 oC and residual mass below 1%.
Isothermal TGA at 130 °C indicates that the chemical is volatile and deliverable to the reaction chamber. Its thermal stress analysis showed that it is stable at 200 oC for more than 1 day, with ~1% residue mass. Pyrolysis experiments showed little decomposition at 475 °C.
We used this precursor to attempt to deposit MoO, MoN and MoS based materials in mild conditions. ALD with NH3 afforded non uniform films with C contamination, and very low gpc. Similar results were obtained with H2O. On the other hand, films deposited with H2S were of uniform thickness with good gpc and selectivity for W over Si. The S content on the Mo-rich films was dependent on the deposition conditions and values as low as 6% could be obtained.

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(Invited) Small Molecule Inhibitor-Based Approaches for Area-Selective Deposition from First Principles
Authors: Tonner-Zech Ralf 
Published: February 2024

Atomic layer deposition tackles ever new research questions. Area-selective deposition is one of these recent challenges. Several approaches have been developed to achieve selectivity. One of the most promising is using comparatively small molecules to block the non-growth surface while leaving the growth surface uncovered for the ALD process.
This approach requires in-depth knowledge of the surface chemistry of both surfaces involved. In addition, the decomposition pathways of SMI-covered surfaces need to be uncovered to enable stable ALD growth over a maximum number of cycles.
These questions are very challenging for lab-based investigations. We present recent progress in the ab initio description of key questions regarding SMI-based ALD processes. At the example of silanol-based SMIs, surface chemistry for Al2O3 growth on Cu while blocking SiO2 will be discussed and compared to experimental findings.[1] Furthermore, the importance of choosing the appropriate surface model will be highlighted. Especially for the challenging question of SMI-layer decomposition.
[1 J. Yarbrough, F. Pieck, D. Grigjanis, I.-K. Oh, P. Maue, R. Tonner-Zech, S. F. Bent, "Tuning Molecular Inhibitors and Aluminum Precursors for the Area-Selective Atomic Layer Deposition of Al2O3", Chem. Mater. 2022, 34, 4646-4659.
We gratefully acknowledge funding from a Merck KGaA, Darmstadt, Germany 350th Anniversary Research Award. Computations were performed on the CSC Frankfurt, HLR Stuttgart, ZIH Dresden and HPC Regensburg.
Figure 1 General structure (a) of the studied SMIs with different reactive and blocking groups (b). Schematic structures of the calculated condensation reactions of the SMIs with OH groups of the SiO2 surface (c). Color code: Si (blue), O (red), and H (white).

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(Invited) Plasma-Enhanced Atomic Layer Etching for Metals and Dielectric Materials
Authors: Chae Heeyeop , Kim Yongjae 
Published: February 2024

The critical dimensions of semiconductor devices are continuously shrinking with 3D device structure and are approaching to nanometer scale. The demand for dimension control in angstrom level is drastically increasing also in etching processes. Atomic layer etching (ALE) processes are being actively studied and developed for various semiconductor, dielectric materials as well as metals. In this talk, various plasma-enhanced ALE (PEALE) processes will be discussed for isotropic and anisotropic patterning of metals and dielectric materials such as molibdenum, ruthenium, cobalt, titanium nitride, tantalum nitride, halfnium oxide, zirconium oxides.[1-7] Typical ALE processes consist of surface modification step and removal step. For the surface modification, various fluorination, chlorination and oxidation schemes are applied through fluorocarbon deposition, halogenation, oxidation with radicals generated plasmas. For the removal or etching step, various schemes were applied including ion-bomardment, heating, ligand volatilization, ligand exchange, and halogenation. The surface characteristics and requirements of plasma-enhanced ALE will be also discussed.
1) K. Koh, Y. Kim, C.-K. Kim, H. Chae, J. Vac. Sci. Technol. A, 36(1), 10B106 (2017)
2) Y. Cho, Y. Kim, S. Kim, H. Chae, J. Vac. Sci. Technol. A, 38(2), 022604 (2020)
3) Y. Kim, S. Lee, Y. Cho, S. Kim, H. Chae, J. Vac. Sci. Technol. A, 38(2), 022606 (2020)
4) D. Shim, J. Kim, Y. Kim, H. Chae, J. Vac. Sci. Technol. B., 40(2) 022208 (2022)
5) Y. Lee, Y. Kim, J. Son, H. Chae, J. Vac. Sci. Technol. A., 40(2) 022602 (2022)
6) J. Kim, D. Shim, Y. Kim, H. Chae, J. Vac. Sci. Technol. A., 40(3) 032603 (2022)
7) Y. Kim, S. Chae, H. Ha, H. Lee, S. Lee, H. Chae, Appl. Surf. Sci. 619, 156751 (2023)
Atomic Layer Deposition of Multi-Component Films Using Precursor Co-Dosing
Authors: Poodt Paul 
Published: February 2024

A growing number of ALD applications require the deposition of ternary or quarternary compounds. Examples include doped films (e.g. ZnO:Al), mixed oxides to tune dielectric properties (e.g. HfZrO), tunable bandgap materials for solar cells (e.g. ZnOS) or opto-electronic materials (e.g. InGaN), and high mobility oxide semiconductors (e.g. InGaZnO). A common method to deposit multicomponent films in ALD is the supercycle approach [1], where sub-cycles of different binary compounds are combined to deposit films where the resulting net composition is determined by the cycle ratio of the individual sub-cycles. A drawback of the supercycle method is that essentially multilayer stacks are deposited instead of true alloys and the film composition varies out-of-plane, potentially impacting film properties.
An alternative method is to use precursor co-dosing, where two or more precursors are simultaneously dosed and co-adsorb during a half-reaction. The resulting film composition is then determined by the ratio of the partial pressures of the individual precursors during the precursor dose. As each ALD cycle deposits a true alloy, it results in excellent out-of-plane compositional uniformity. The co-dosing method has first been reported in the late 1980’s to deposit ternary and quarternary III-V compounds [2] and has been used since for a wide range of materials. In the last decade it has become the method of choice for depositing multicomponent materials with Spatial ALD.
A proper understanding of the relation between film composition and precursor partial pressure during co-dosing is essential for accurate control of the film composition. This is not straightforward, as the surface chemistry of co-dosing can be quite complex, involving competitive adsorption, heterogeneity of reactive sites, exchange reactions and more. We will discuss how the surface chemistry of precursor co-dosing determines the film composition. In analogy to the IUPAC classification of adsorption isotherms for single adsorbents [3], we will introduce a similar classification of adsorption isotherms for multiple absorbing precursors which we will use to review and explain results reported in literature. Finally, we will discuss some interesting new opportunities for co-dosing, such as the deposition of gradient composition films and the use of co-dosing for area-selective deposition.
[1]: A. Mackus et al, Chem. Mater. 31 (2019) 1142
[2]: M. Tischler, S. Bedair, J. Cryst. Growth 77 (1986) 89
[3]: M. Thommes et al, Pure & Appl. Chem. 87 (2015) 87
Multimodal Microscopy Characterisation of 2D Materials
Authors: Flack Angela 
Published: February 2024

Spatial characterisation of transition metal dichalcogenides (TMDCs) is crucial for understanding their optoelectronic properties and optimising film growth conditions. In this work, we present a multimodal microscopy platform combining conventional widefield, Raman, photoluminescence and second harmonic generation imaging for the characterisation of 2D materials.
The platform was used to characterise CVD grown WSe2 crystals. Raman imaging identified the presence of both monolayer and multilayer WSe2 through a change in the intensity and position of the E12g / A1g phonon modes. Photoluminescence imaging confirmed the presence of monolayer WSe2 with emission at 780 nm and identified two distinct multilayer regions through changes in the photoluminescence wavelength and intensity. Lastly, second harmonic generation imaging under femtosecond laser excitation was used to obtain the relative growth orientation of the three identified domains in the crystal.
Figure 1 highlights Raman imaging of WSe2. (a) Intensity of the E12g / A1g (250 cm-1) Raman band, (b) Peak position of the E12g / A1g (250 cm-1) Raman band, (c) least squares spectral matching revealing three distinct Raman spectral areas, (d) Averaged Raman spectra from areas A, B and C.

Figure 1
3-Terminal Igzo FET Based 2T0C DRAM Combined Bit-Line Structure
Authors: Kim Ji-Hun , Kim Hyeon-Jun , Kim Ki-Jun , Shim Tae-Hun , Hong Jin-Pyo , Park Jea-gun 
Published: February 2024

The IGZO (InGaZnO)-based two-transistor zero-capacitor(2T0C) DRAM has attracted much attention as an alternative memory to overcome the scale-down limit of current 1T1C DRAM due to its low power consumption and monolithic 3D stacking capability. In particular, its low power consumption and the feasibility of low temperature process make it highly implementable for 3D DRAM. For operating the 2T0C DRAM, four metal lines are necessary, i.e., write word line and write bit line (WBL) for operating write transistor (WTR), and read word line and read bit line (RBL) for operating read transistor (RTR).
In this study, we propose a 3-terminal 2T0C DRAM to enhance its memory characteristics, where RBL was combined with WBL, enabling 2T0C memory operation with only three metal lines as shown in Fig. 1(b). In addition, we investigated the dependency of retenetion time of the proposed 2T0C DRAM on channel length. In particular we evaluated the dependency of the sneak current of 2T0C DRAM on off-current of transistor. For the fabrication of 3-terminal IGZO 2T0C DRAM, a top gate IGZO transistor was fabricated using RF sputtering and two transistors were connected by storage node and bit line bridge as shown in Fig. 1(d).The storage node was formed by connecting the gate of RTR to drain of WTR. And source electrodes of both transistors were coupled. To determine the voltage values for memory operation, the transfer curve of each transistor was characterized and the threshold voltages for both RTR and WTR were around 1 V. The write and read voltages were set to 3 and 2 V, respectively. The retention time was measured by performing periodic read operations after writing and measuring the RTR currents. In addition, the retention time of transistors for varying channel length and gate capacitance was characterized. The retention time was defined as the time to be taken for decreasing the currents by 90 %. Furthermore, the disturbance of 2T0C DRAM with 2x2 array structure was investigated. The RTR currents of selected cells were measured depending on the memory state of adjacent cells.
It was found that the retention times of transistors with 10- and 100-um RTR channel lengths were approximately 15 and 30 seconds, respectively. It was observed that the memory state was not changed from “0“ to “1“ by disturbant currents, but, RTR currents of “0“ state cell increased slightly when an adjacent cell was turned on. However, as shown in Fig.1(i) and (j), when off-currents of transistor of 2T0C DRAM decreased from 20 nA to 200 pA, it was confirmed the sneak current of 2T0C decreased. Finally, several technical apporaches how to suppress the disturbant currents will be presented in detail.

Acknowledgement

This research was supported by BrainKorea21 Four.

Figure 1
Mixed Oxide High-K Dielectrics - from Gate Dielectrics to Non-Volatile Memories to SSI-LEDs
Authors: Kuo Yue 
Published: February 2024

Metal oxides were first used as the high-k gate dielectrics in thin film transistors (TFTs). In late 1990s, they were applied to MOSFETs to solve the high leakage current problem in the ultra-thin SiO2 gate dielectric. HfO2 was identified as a viable solution for this application due to its relatively large effective k value and low leakage current. However, HfO2 is subject to crystallization at a relative low temperature of about 600ºC. We introduced the doping method, i.e., by adding a third element to the metal oxide, to solve this problem. The crystallization temperature, the effective k value, the interface state density, and the interface layer thickness of the new film were influenced by the concentration of the added element (1). Eventually, we demonstrated that the 12% Zr doped HfO2, i.e., ZrHfO, had a crystallization temperature higher than 900ºC and many good dielectric properties. The ZrHfO thin film can be sputter deposited.
In this talk, structures, preparation methods, operation principles, and characteristics of the following devices will be discussed and new developments will be addressed.

< 1 nm EOT ZrHfO gate dielectric layers (2),

nanocrystals embedded ZrHfO NVMs in which electrons and holes could be stored separately based on the type of nanocrystal material (3), and

solid state incandescent LEDs (SSI-LEDs) which are formed from the thermal excitation of the simultaneous formation of a large number of nano-resistors during the dielectric breakdown process (4,5,6).

J.-Y. Tewg, Y. Kuo, and J. Lu, Electrochem. Solid-State Letters, 8(1), G27-G29 (2005).

Yan, Y. Kuo, and J. Lu, Electrochem. Solid-State Letts., 10(7), H199-H202 (2007).

Zhang and Y. Kuo, ECS Trans., 66(4), 195-202 (2015).

Y. Kuo and S. Zhang, ECS J. Solid State Sci. Technol., 8(12), Q223-Q225 (2019).

W.-S. Lin and Y. Kuo, ECS J. Solid State Sci. Technol., 10, 126001 (2021).

A. Samuel and Y. Kuo, Solid State Electronics, 204, 108651 (2023).
Fabrication and Electrical Characterization of GaAs/GaN Junctions
Authors: Ishimi Shota , Hirose Makoto , Shimizu Yasuo , Ohno Yutaka , Nagai Yasuyoshi , Liang Jianbo , Shigekawa Naoteru 
Published: February 2024

GaAs/GaN heterojunctions are likely to be an ideal platform for high-frequency/high-output-power electron devices because of excellent electrical properties of GaAs and GaN as well as the similarity in their coefficients of thermal expansion. We have to note, however, that heteroepitaxial growth of GaAs/GaN junctions is quite difficult because of difference in crystal structures (in case of GaAs/wurtzite GaN junctions) and large mismatch in lattice constants (GaAs/zincblende GaN junctions). In this work we fabricate p+-GaAs/n-GaN heterojunctions by bonding GaAs and GaN epi wafers to each other using surface-activated-bonding technologies [1,2], selectively etching off the GaAs substrate used in the epitaxial growth, making ohmic contacts on the exposed surface of GaAs layer, and forming GaAs mesas. Ohmic contacts on the backside of GaN epi wafer are formed before bonding. The junctions are annealed at 400 ℃ in contact formation on GaAs surfaces. The temperature is much lower in comparison with the temperature in a wafer-fusion process of GaAs and GaN (750 ℃), which were reportedly applied for fabricating group-III arsenide/nitride heterojunction bipolar transistors [3]. Observation using cross sectional transmission electron microscope (TEM) of as-bonded and 400-℃ annealed GaAs/GaN interfaces shows that no voids are formed at the GaN/GaAs interfaces by the 400-℃ annealing. We also fabricate n+-GaAs/n-GaN heterojunctions for comparison.
We measure the capacitance-voltage characteristics and current-voltage characteristics for reverse-bias voltages of the p+-GaAs/n-GaN and n+-GaAs/n-GaN junctions and find that the characteristics of the two junctions are close to each other, which suggests that the band profiles of GaN layers in the p+-GaAs/n-GaN and n+-GaAs/n-GaN junctions are almost the same, i.e., the Fermi-level pinning occurs at the GaAs/GaN interfaces. More importantly, the reverse-bias characteristics are measured up to -60 V. The reverse-bias voltage corresponds to an electric field of as high as ~2 MV/cm, which is comparable to the breakdown field of GaN (3-4 MV/cm) [4]. We also excite minority electrons in the p+-GaAs layer using a 488-nm Ar laser and successfully observe the photo current due to the transport of minority electrons across the reverse-biased GaAs/GaN interfaces.
Acknowledgement: TEM samples were fabricated under the Inter-University Cooperative Research in IMR of Tohoku University. Epi wafers used in the work were provided from Sciocs (present Sumitomo Chemical) Co., Ltd.
[1] H. Takagi, et al. Appl. Phys. Lett. 68, 2222 (1996). [2] S. Yamajo, et al., Jpn. J. Appl. Phys. 57, 02BE02 (2018). [3] C. Lian, et al. Appl. Phys. Lett. 91, 063502 (2007). [4] T. Maeda, et al., IEEE Electron Device Lett., 43, 96 (2022).