bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Scaling of Copper Interconnection As Opposed to Alternative Conductors
Authors: Nogami Takeshi 
Published: December 2020

Cu/low-k interconnection is facing to challenges in its extension per scaling in the 3nm node and beyond where the metal pitch is less than 32 nm. As is listed in Table.1, the difficulties lie in securing (1) Cu gap fill capability in scaled via in the dual damascene process flow due to the limited step coverage of PVD Cu seed layer, (2) Vx-Mx breakdown voltage and TDDB reliability due to scaled spacing and misalignment in lithography, (3) Electromigration reliability when the barrier/liner is scaled, (4) Low line resistance due to decreased Cu volume when the barrier/liner scaling is limited, (5) Low via resistance when the barrier/liner scaling is limited, (6) Selectivity in selective CVD deposition of cobalt capping layer which is required for electromigration reliability and (7) Low interconnect parasitic capacitance when thickness of the plasma-induced damage of the intra-layer low-k dielectric becomes comparable to the inter-metal spacing per scaling.
Because of these difficulties in extension of dual damascene Cu interconnection scheme, various alternative metallization unit processes, materials (conductors and dielectrics) and schemes (alternative to dual damascene) have been investigated. These new processes and materials include both (a) those for extension of Cu technology such as Co_Cu hybrid metallization (i.e., Co for via and Cu for wires) and (b) those for entire replacement of Cu to other conductors. Basically extension of Cu interconnects is the preference in the industry rather than entire replacement to alternative conductors and/or metallization schemes, because entire replacement needs to be accompanied with alignment of all unit processes to the new metal schemes such as CMP and/or RIE of the new conductor, deposition of the conductor, wet cleaning compatible to the conductor, and nucleation/adhesion layer formation for the conductor on dielectrics, in all fine dimensions. In addition, even when fine Cu lines are replaced to alternative conductors such as Co, wide power rails need to stay with Cu for the required low line resistance (i.e., Cu_Co composite metallization).
In this talk, process candidates which have potential to resolve the difficulties listed in Table 1 and enable extension of Cu interconnection scheme are reviewed such as (i) via pre-fill processes with vertical ALD of low-k dielectrics [1], (ii) plasma damage resistant low-k dielectric materials [2], (iii) Fully Aligned Via integration process [3], (iv) PVD-assisted ALD barrier formation [4, 5], (v) through cobalt self-forming barrier process barrier/liner scaling processes without loss in their integrity [1, 6 - 8], (vi) graphene capping material on top of Cu interconnects for electromigration reliability 10]. Then, the talk covers (vii) the composite metallization scheme [11] which is an enabler for the post-Cu alternative conductor metallization.

Figure 1
Laser Debonding of Ultrathin Wafers and Packages: A Technology for the New Generation of Electronic Devices
Authors: Bravin Julian , Burggraf Jurgen , Pichler Mathias , Jung Stefan , Brandl Elisabeth 
Published: December 2020

The continuous shrinkage of the device wafers thickness is driving the current mature debonding technologies to their limits. The challenging form factor demands for memory (≤ 30 µm) or new generations of power devices applications are just two examples for the need of lowering the device thickness.
Slide-off as well as mechanical debonding are methods currently in use in high volume production, but these two technologies are not capable to support the new requirements in terms of thermal and mechanical stability, handling, throughput (affecting the cost of ownership - CoO), and process margin. Therefore, device manufactures are looking for a more versatile, universal debonding technology. State of the art UV laser debonding is a very promising candidate which can help bringing the required process margin and flexibility. By combining laser debonding and thermoset materials with a high thermal budget the process window can be significantly enhanced.
Most of the thermoset materials of interest which are used to form a bond and to embed the device topography cannot be stimulated directly with UV light. In order to enable a debonding process for these materials, an additional layer is commonly deposited on the carrier. The post bond uniformity (quantified typically by the total thickness variation - TTV) of the used bulk layer of thermoset adhesive has to be very well controlled in order to enable a defect free thinning of the device wafer: this becomes crucial particularly when the final device layer has to be thinned down below 10 µm.
Besides the optimization of the bond layer thickness uniformity, suitable carriers for different devices and applications were evaluated. Due to the significant variety of the available glass carriers, a customized temporary bonding process can be developed by selecting the most appropriate adhesive and carrier combinations suitable even for very challenging substrates, like reconstituted wafers.
Reconstituted wafers consist of a number of different layers and materials with different thermal expansion coefficients, which makes the stress management and the handling of such substrates extremely difficult. However, the choice of the suitable carrier enables the processing independent of the chosen integration process flow (RDL first; Chip first). Even a carrier flip flop to enable the processing of the back side of the very thin package is possible and this is enabling the creation of ultra-thin and smart packages.
The scope of the current work was to address the post bond adhesive thickness uniformity as well as the stress management. Experimental results will be presented for the process optimization: figure 1 shows two bow measurement results for two different carrier materials and figure 2 shows an example of post-bonding thermoset adhesive uniformity measurement

Figure 1
(Invited) Evaluation of 2" Power-Grade GaN Substrates Produced By the Near Equilibrium Ammonothermal (NEAT) Method
Authors: Hashimoto Tadao , Letts Edward , Key Daryl , Jordan Benjamin , Shang Eric , Dudley Michael , Raghothamachar Balaji , Liu Yafei 
Published: December 2020

This paper provides evaluation of 2" GaN substrates produced by the near equilibrium ammonothermal (NEAT) method. Ammonothermal growth is a proven method of producing low-dislocation GaN crystals with practical productivity. [1, 2] By choosing a near-equilibrium growth condition, consistent growth with maintained crystal quality has been achieved. [3] Several tens of bulk GaN crystals were grown simultaneously, yielding many 2" GaN substrates in one growth batch. Figure 1 is an example of bulk GaN crystals after shaping and Figure 2 is an example of 2" GaN wafer.
We have developed an X-ray mapping technique which presents the distribution of full width half maximums (FWHMs) of rocking curves from 002 and 201 diffractions over a 2" wafer. The X-ray mapping revealed superior microstructure quality of NEAT GaN substrates. NEAT GaN substrates typically show an average full width half maximum (FWHM) of the 002 X-ray rocking curve of 30 arcsec or better, as shown in Figure 3.
The X-ray mapping data were compared with other characterization techniques, including X-ray topography. X-ray topography confirmed that a dislocation density of typical NEAT GaN substrate was about 2 x 105 cm-2. Wide area X-ray topography also revealed flatter lattice of a NEAT GaN substrate compared with a GaN substrate fabricated by hydride vapor phase epitaxy (HVPE).
Additionally, recent progress in oxygen reduction yielded NEAT GaN substrates with reduced residual donors, coloration and optical absorption. The oxygen concentration was about 2 x 1018 cm-2. An absorption coefficient of 1.3 cm-1 was obtained at 450 nm.
The usability of NEAT GaN substrates was also confirmed through device fabrication. Multiple collaborators successfully fabricated high-power diodes with breakdown voltage over 1000V.
References
[1] E. Letts, Y. Sun, D. Key, B. Jordan, and T. Hashimoto, J. Cryst. Growth 501 (2018) 13.
[2] R. Dwilinski, R. Doradzinski, J. Garczynski, L. Sierzputowski, R. Kucharski, M. Zajac, M. Rudzinski, R. Kudrawiec, W. Strupinski, and J. Misiewicz, Phys. Stat. Sol. A 208 (2011) 1489.
[3] T. Hashimoto, E.R. Letts, D. Key, and B. Jordan, Jpn. J. Appl. Phys 58 (2019) SC1005. Acknowledgement
This work was supported by U.S. Department of Energy (DOE), Advanced Research Program Agency, Energy (ARPA-E), SWITCHES program (grant number DE-AR0000445), US DOE ARPA-E OPEN 2018 programs (DE-AR0001008 and DE-AR0001008), U.S. DOE, the Office of Energy Efficiency and Renewable Energy (EERE) under the Advanced Manufacturing Office (AMO), Small Business Innovation Research (SBIR) program (grant number DE-SC0013791), US DOE EERE AMO FY18/FY19 Lab Call (grant number DE-LC-000L059), and the Office of Naval Research (grant number N00014-19-1-2069).

Figure 1
Photocurrent Measurements of AlGaN/GaN Hemt Under X-Ray Irradiation
Authors: Miyata Atsuki , Hoshii Takuya , Wakabayashi Hitoshi , Tsutsui Kazuo , Kakushima Kuniyuki 
Published: December 2020

The photocurrent of AlGaN/GaN HEMT under x-ray exposure was measured. A sharp response in the photocurrent was observed with the exposure and the current showed linear relationship with the x-ray tube current. An increase in the photocurrent was measured, especially for high intensity exposure, and a tail in the current was observed after shutting the exposure. The transient response in the photocurrent may have relationship with the deep defects in the epitaxial wafer.

Introduction

Gallium nitride (GaN) HEMTs are widely used in the devices for power and RF applications. Due to the epitaxial growth of the layers on foreign substrates, lots of defects are incorporated in the epitaxial wafer. In this study, we measured the photocurrent of the AlGaN/GaN HEMT under x-ray exposure, and its transient response was observed.

Experiments

AlGaN/GaN HEMT on a Si substrate was fabricated by Ohmic contact to the 2DEG with top electrode (Ti/Al/Ni/Au) with thermal treatment[1], followed by mesa isolation by dry etching. Finally, backside contact was formed by Al evaporation. The area of the exposure was 5×5 cm2. A bias voltage of 40 V was applied to the substrate, where the dark current was as low as 0.5 nA. The x-ray source was WKα and tube current was changed from 10 to 150 mA.

Results and discussions

Fig.1 shows the photocurrent response to the x-ray exposure. A sharp response of the photocurrent was obtained when the x-ray is exposed to the devices. A linear relationship with the photocurrent and the tube current was obtained, as shown in fig. 2. However, a gradual increase in the photocurrent was observed, especially at high tube current. Moreover, a tail photocurrent was also observed after shutting the x-ray. The magnitude of the tail current was high with large tube current. The gradual increase and the tail in the photocurrent might be caused by the trapping of photogenerated carriers.[2]

Conclusion

A gradual increase in the photocurrent was observed under high intensity x-ray exposure to the AlGaN/GaN HEMT. Also, a tail current was measured after shutting the exposure. These photocurrent transient responses might have some relationship with the defects in the epitaxial wafer.

References

[1]Z. X. Qin, et al., Appl. Phys. A 78, 729-731 (2004)
[2]Jean-Yves Duboz, et al.
Phys. Lett.
92, 263501 (2008)

Figure 1
(Invited) Interfacial Engineering for High Voltage Performance of Perovskite Photovoltaic Cells
Authors: Miyasaka Tsutomu , Zhanglin Guo , Jena Ajay , Kim Gyu Min , Takei Izuru 
Published: December 2020

Since our first discovery of perovskite solar cell (PSC) in 2009, enormous efforts have been put into different aspects of PSCs and the progress has been incredibly fast on all fronts. The background, on-going R&Ds, and future direction of PSC research have been reported by our group as a comprehensive review.1 Although efficiency level has reached 25%, PSCs face serious challenges of practical stability and durability required for industrialization. Compositional engineering of lead halide perovskites by mixing different cations and anions, using modulator molecules and mixing 2D and 3D structures have improved the stability of perovskites against heat and moisture. However, organic cations in halide perovskites (methylammonium, etc.) and use of diffusible ionic dopants in hole transport materials (HTMs) are responsible for low stability of perovskites at high temperatures (>120oC). In this respect, use of all-inorganic perovskite materials and dopant-free HTMs is highly desired.2 We have conducted the device fabrication in this direction using CsPbI3 and CsPbI2Br as solution-processed perovskite films. The perovskite absorbers were made into junction with dopant-free HTMs to develop thermally stable PSCs.By chemical engineering to improve the quality of interfacial structure at the hetero-junction, all-inorganic and dopant-free PSCs yielded power conversion efficiency up to 15%. Further we could enhance the open-circuit voltage (Voc) of this PSC up to 1.42V, which is the highest Voc ever achieved with a single perovskite cell.3 In preparation of all-inorganic perovskites, a big challenge should also be directed to development of lead-free perovskite materials for environmental safety in practical applications.2

Among extensive applications of PSCs for outdoor and indoor power generation, use of PSCs in space environments is promising because thin perovskite photovoltaic films demonstrate high stability and tolerance against exposure to high energy particle irradiations (proton and electron beams).4 Thin absorbers (<500 nm) avoid accumulation of particles and due to intrinsic defect tolerant nature of perovskites, radiation-induced collision damage is highly suppressed. Our current efforts in making PSCs based on both lead and lead-free perovskites, and future perspectives of perovskite photovoltaics will be presented.
References:

A. K. Jena, A. Kulkarni, and T. Miyasaka, Chem. Rev. 2019, 119, 3036–3103.

T. Miyasaka, A. Kulkarni, G. M. Kim, S. Oez and A. K. Jena, Adv. Energy Mat., 2019, 1902500.

G. Zhanglin, T. Miyasaka, et al. J. Am. Chem. Soc.
2020, 142, 21, 9725–9734.

Y. Miyazawa, M. Ikegami, H.-W. Chen, T. Ohshima, M. Imaizumi, K. Hirose, and T. Miyasaka, iScience
2018, 2, 148-155.
Interlayer Solid-Phase Reaction in Halide Perovskite Thin Films Fabricated Via Alternate Infrared Laser Deposition
Authors: Matsuki Nobuyuki , Iida Yuki , Shimada Takahiro , Abe Yuta , Sato Tomomasa 
Published: December 2020

It is now widely pursued to investigate the growth mechanism of halide perovskite thin films in detail to elucidate the degradation mechanism and to develop the thin films with superior photovoltaic properties. We have applied infrared laser molecular beam deposition (IRL-MBD), which can control the deposition of halide perovskite at the atomic layer level in ultra-high vacuum condition [1]. In our IRL-MBD process, CH3NH3PbI3 (MAPbI3) layers are formed by alternately depositing CH3NH3I (methylammonium iodide: MAI) and PbI2 layers, and subsequent interlayer solid-phase reaction at room temperature. In this study, we focus on the effect of the layer thickness on the interlayer solid-phase reaction and the properties of the formed MAPbI3 thin films.
A synthetic silica substrate cleaned using organic solvents was introduced into the IRL-MBD chamber via a load lock. After that, PbI2 and MAI molecular beams were alternately irradiated onto the substrate by evaporating MAI and PbI2 sources using an infrared laser beam (wavelength: 808 nm, input power: 2~3 W). The deposition rate of PbI2 was controlled at 0.1 nm/s using a quartz crystal microbalance (QCM) thickness monitor and manual laser power control. The evaporation rate of MAI was manually adjusted so that the pressure in the chamber was kept at 4×10-4 Pa during the irradiation of MAI onto the substrate. Figure 1 shows a schematic layer structure of the samples A, B and C consisting of 1, 5 and 10 pair(s) of [MAI/PbI2] bilayer, respectively. The irradiation time of MAI and the nominal thickness of PbI2 were A: [80 min/300 nm]×1, B: [16 min/60 nm]×5 and C: [8 min/30 nm]×10.
Figure 2 shows the X-ray diffraction (XRD) patterns obtained from the samples. The sample A shows two diffraction peaks corresponding to PbI2(001) and MAPbI3(110), while the samples B and C exhibits only single peak corresponding to MAPbI3(110) in the shown diffraction angle range. Figure 3 shows the schematic structure of the samples inferred from the results described above. In the sample A, PbI2 layer, which is not completely reacted with MAI, remains in the thin film. In contrast, in the samples B and C, only the phase of MAPbI3 is observed, indicating that PbI2 and MAI react completely by the interlayer solid-phase reaction. The results suggest that PbI2 has a critical film thickness that causes a complete interlayer solid-phase reaction with MAI at room temperature between 60 nm and 300 nm. The critical film thickness is likely comparable to the penetration depth of MAI into PbI2 and is supposed to be dependent on the temperature during the interlayer solid-phase reaction.
[1] K. Kawashima, Y. Okamoto, O. Annayev, N. Toyokura, R. Takahashi, M. Lippmaa, K. Itaka, Y. Suzuki, N. Matsuki and H. Koinuma, Sci. and Tech. of Adv. Mater.
18, 307-315 (2017).

Figure 1
Highly Purified Materials for Sn-and Pb-Based Perovskite Solar Cells
Authors: Wakamiya Atsushi 
Published: December 2020

Perovskite solar cells are promising cost-effective next generation printable photovoltaics. These solar cells have attracted the interest of many researchers. Thanks to tremendous effort of the researchers in this field, the power conversion efficiencies (PCEs) have been substantially increased in a short period, which is mainly due to improvements of the fabrication protocols for the perovskite layer as well as the development of new materials for buffer layers.
Our approaches toward efficient lead and lead-free perovskite solar cells are as follows:

Development of highly-purified perovskite precursor materials

Development of solution process fabrication methods for the perovskite layer

Development of organic semiconductors for efficient charge-collection layers

We have synthesized lead-halide and tin halide complexes as purified precursors for perovskite materials, which were later commercialized by TCI and are now widely used in this field as standard precursor materials. We also focus on the intermediates formed during the film-growth and have developed efficient fabrication methods based on the formation mechanism. We have designed and synthesized novel pi-conjugated materials designed to control frontier orbital energy levels, molecular aggregation properties, and the interface with the perovskite layer.
In this talk, our recent progress on tin halide perovskite solar cells as well as lead halide perovskites will be introduced.
Transparent Hole-Transporting Materials Containing Partially Oxygen-Bridged Triphenylamine Skeletons for Efficient Perovskite Solar Cells
Authors: Minh Anh Truong , Murdey Richard , Wakamiya Atsushi 
Published: December 2020

Transparent organic semiconductors are desirable for organic optoelectronic devices. While electrical performance is often improved by increasing the p-conjugation length, the resulting red-shifted absorption profile typically leads to loss of transparency. Therefore, it is a great challenge to design and develop organic semiconductor materials that possess both high electrical performance and transparency in visible light region. We have previously developed promising transparent hole-transporting materials (HTMs) based on the quasiplanar skeletons of partially oxygen-bridged triphenylamines.
In the present study, we have designed new transparent HTMs by introducing diarylamines into the 7-position of a quasiplanar partially oxygen-bridged triphenylamine. The combination of an oxygen-bridged triphenylamine strong donor and a diarylamine weak donor makes the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) localize on the oxygen-bridged triphenylamine and diarylamine, respectively, leading to minimal orbital overlap between the HOMO and the LUMO, therefore, weak absorption. Three HTMs, namely, HND-Cbz, HND-DTP, and HND-NOMe, were synthesized by connecting a partially oxygen-bridged triphenylamine structure to carbazole, dithieno[3,2-b:2′,3′-d]pyrrole, and bis(4-methoxyphenyl)amine through Buchwald-Hartwig amination with yields of 91%, 70%, and 88%, respectively. All of three materials are amorphous and thermally stable with decomposition temperatures higher than 350 °C. The vacuum-deposited thin films are transparent, with absorption edges from 405 nm to 419 nm. The space-charge limited current (SCLC) hole mobilities of HND-Cbz, HND-DTP, and HND-NOMe are 1.3 x 10-
7, 3.5 x 10-
5 and 1.4 x 10-
4 cm2 V-
1 s-
1, respectively while the HOMO energy levels are –5.34, –5.30 and –5.08 eV. The HOMO levels lie above the corresponding valence band of typical perovskites (e.g. –5.45 eV for MAPbI3 or –5.56 for Cs0.05FA0.15MA0.80PbI2.75Br0.25), making these molecules potentially good candidates for hole-transporting materials in perovskite solar cells. To verify this, perovskite solar cells having the structures ITO/SnO2/Cs0.05FA0.15MA0.80PbI2.75Br0.25/HTM/Au for the solution processed HTM and ITO/SnO2/Cs0.05FA0.15MA0.80PbI2.75Br0.25/HTM/MoO3/Au/MoO3 for the vacuum processed HTM layer, were fabricated. With HND-Cbz, HND-DTP and HND-NOMe as the HTM, the best power conversion efficiency reached 13.7%, 15.0% and 17.2%, respectively.

Figure 1
Compositional Engineering of FA-Based Lead Halide Perovskitesfor Shear Coating Processes
Authors: Kim Hansol , Gu Hyewon , Chung Choong-Heui , Song Chang Eun , Hong Ki-Ha 
Published: December 2020

Recently Organic-inorganic halide perovskite (OIHP) solar cells have become one of the most promising next-generation photovoltaic materials due to their excellent electrical and optical properties. Formamidinium lead triiodide (HC(NH2)2PbI3, FAPbI3) exhibits the narrowest band gap (~1.45 eV) among Pb-based halide perovskites, which is closer to Shockley-Queisser limit than that (~1.55 eV) of Methylammonium Lead Iodide (CH3NH3PbI3, MAPbI3). Therefore, FAPbI3 has been widely adopted for recently developed highly efficient photovoltaic cells.

In addition, FAPbI3 has better stability than MAPbI3, which can be easily decomposed at a high temperature or humid environment. The spin-coating has been widely adopted to make FAPbI3-based solar cells, whereas the large-area coating technologies have not been extensively studied, yet.
This study presents the compositional engineering research on the polymorph control of formamidinium-based lead halide perovskites for the large-area film coating. The polymorph control of FAPbI3 has been one of the most important issues since its first appearance in photovoltaic applications. Non-perovskite structure (δ-FAPbI3) is thermodynamically more stable than the three-dimensional perovskite structure (α-FAPbI3). We adopted the shear coating method to make perovskite layers and controlled the polymorphism through A-site mixing. MA, commonly used A-site molecule, is excluded because MA can be a weak spot at the humid condition. Br mixing is not applied due to the photo-induced phase separation issue.
Our results reveal that double-cation mixing (Cs-FA or Rb-FA) is not enough and triple-cation mixing (Rb-Cs-FA) cannot be avoided to make robust α-FAPbI3 for the shear coating process. We present the ternary phase diagram of (Rb-CS-FA)PbI3 to show the process window based on the XRD analysis of mixed perovskite films. The photovoltaic cell shows 15.8% power conversion efficiency (PCE) at the best compositional mixing point, which is the best PCE for FA-based perovskite solar cells fabricated by shear coating method without MA-Br mixing.