Vacancy-type defects introduced by mechanical polishing in basic ammonothermal GaN and their annealing behavior were studied using a monoenergetic positron beam. The major vacancy-type defect in the sample was identified as a Ga-vacancy (V-Ga) coupled with hydrogen atoms. After mechanical polishing, high-density dislocations and stacking faults were introduced in the subsurface region (<240 nm). In this region, the vacancy-type defects detected by positron annihilation were divacancies (VGaVN) and their complexes with hydrogen atoms. After ultra-high-pressure annealing at 1400 degrees C, {0001} basal slip bands were the predominant defects observed using a transmission electron microscope. The major vacancy-type defects for the annealed samples were identified as V-Ga coupled with multiple V-N [e.g., V-Ga(V-N)(3)] and their complexes with hydrogen atoms. The observed annealing behavior of vacancies agreed with that estimated using photoluminescence spectroscopy.

Li-doped Mg2Sn thin films are promising p-type thermoelectrics, as Li is among the most effective acceptors, yet their impact on defect chemistry, phase stability, and transport remains poorly understood. Here, low-temperature annealing is shown to passivate Li-induced defects and stabilize electrical transport in epitaxial Mg2-xLixSn (0 <= x <= 0.10) thin films grown by molecular beam epitaxy. X-ray diffraction and electron microscopy reveal that Li incorporation produces Sn-rich precipitates from deviation from the 2 : 1 of Mg : Sn stoichiometry, which are partially dissolved after annealing. Depth-resolved positron annihilation spectroscopy indicates a reduction of Mg-vacancy-type defects at moderate Li content, while Hall measurements show decreased hole concentrations and enhanced mobilities, consistent with reduced ionized-impurity scattering. As-grown films exhibit Seebeck coefficients of 40-70 mu V K-1 at room temperature, which increase to similar to 200-250 mu V K-1 after annealing, accompanied by suppression of cycle-to-cycle drift. The optimized films achieve an exceptional peak power factor of similar to 2.4 x 10-3 W m-1 K-2 at the relatively low temperature of 350 K. Thermal conductivity, measured at room temperature, confirms that defect-engineered films retain strong phonon scattering after annealing, yielding zT approximate to 0.25, surpassing prior p-type Mg2Sn epitaxial thin films. A microfabricated pi-type thermoelectric generator using Li-doped Mg2Sn p-legs delivers higher open-circuit voltage than a Mg2Sn(Ge) benchmark with comparable output power, demonstrating the practical viability of the processed films.

This study explores an unconventional path to resolve this conflict by investigating a non-contact die transfer mechanism that aims to eliminate physical handling risks. Our approach focuses on the constructive interaction between aerodynamic principles and passive self-centering to achieve ultra-clean, stable die placement without the complexities of traditional mechanical pick-and-place. The core of this work lies in evaluating how this "contactless" strategy can push the boundaries of post-bond accuracy to the 100-nm level, while simultaneously addressing the industrial demand for high-throughput (2,200 UPH) and void-free Cu-Cu bonding. By reconsidering the fundamental interaction between the die and the transfer system, this paper presents a scalable solution to the high-yield requirements of next-generation heterogeneous chiplet integration.

Post-growth annealing suppresses defect-driven instability in Li-doped Mg 2 Sn epitaxial thin films, increasing mobility and power factor. Stable p-type transport translates to improved micro-TE device output.

This paper investigates the ring size in silica glass, ranging from two-membered rings (2MR) to eight-membered rings (8MR) and larger, after irradiation with swift heavy ions, using Raman spectroscopy. The most prominent Raman scattering band, known as the R-band, can be divided into three distinct peaks: a central peak at 465 cm-1 and two shoulder peaks at 400 cm-1 and 310 cm-1. Previous studies on silica minerals serve as a helpful reference for identifying these peaks. Based on the available information, the peaks at 465 cm-1, 400 cm-1, and 310 cm-1 in silica glass are attributed to 5MR, 6MR, and 8MR or higher, respectively. Irradiation reduces the proportion of larger ring sizes and increases the proportion of smaller ones. A new peak at 940 cm-1 corresponds to edge-shared 2MR in silica glass. The density of the silica glass surface measures 2.44 +/- 0.01 g/cm3. After chemical etching, three types of etched tracks are observed: parallel etched tracks with diameters of several nanometers and an aspect ratio in the hundreds, etched tracks with different curvature directions, and spherical etched regions. The overlap of these tracks leads to densification, an increase in the ratio of 2MR, 3MR, and 4MR, resulting in a shift in the Raman scattering peak.

Precise defect control is crucial for optimizing thermoelectric (TE) materials. However, thin film processes differ from bulk synthesis, necessitating distinct approaches to defect management. This study investigates the impact of varying Mg flux rates in the molecular beam epitaxy (MBE) growth of epitaxial Mg _2 Sn (Ge) thin films, with Mg: Sn (Ge) ratios from 3.9 to 9.1 while maintaining constant Sn and Ge flux rates. Our results indicate that while the films mainly consisted of the Mg _2 Sn phase due to excess Mg compensating evaporation at the growth temperature, the Mg flux rate significantly influenced film growth dynamics. X-ray diffraction analysis showed that higher Mg flux rates increased microstrain and decreased vertical grain sizes, suggesting increased planar defect density. However, the full-width half maximums of rocking curves tend to be reduced at higher flux rates, attributed to enhanced in-plane grain alignment and reduction of point defect density. Positron annihilation experiments revealed lower vacancy-type defects at higher Mg flux rates, aligning with the rocking curve measurements. The higher Mg flux rates enhanced surface migration and promoted larger horizontal grain growth. As these grains coalesce, slight misalignments between them introduce strain within the crystal lattice. To accommodate this strain, planar defects such as stacking faults form, as indicated by the x-ray pole figure measurements. Despite the higher crystal quality and reduction in vacancy-type defects, the total thermal conductivity of the films decreased with increasing Mg flux rates. This suggests that modulating Mg flux rates in MBE-grown Mg _2 Sn thin films, it is possible to achieve enhanced crystalline alignment and controlled formation of beneficial higher-dimensionality defects, which together contribute to the reduction in thermal conductivity and improve the film’s overall TE performance.

While direct placement die-to-wafer (D2W) hybrid bonding is essential for advanced packaging, its performance is often compromised by an extended storage time between surface activation and bonding. However, the underlying chemical degradation mechanisms have not been fully elucidated because of the challenge of correlating macroscopic bond strength with molecular-scale interfacial changes. Here, we introduce a comprehensive analytical approach, combining a novel, highly accurate bonding energy measurement with multi-modal surface spectroscopy. This method reveals that degradation is governed by a dual-factor mechanism: the loss of interfacial water and the depletion of surface silanol groups. The direct correlation between these interfacial changes and the reduction in bonding energy was quantitatively confirmed by thermal desorption and sum-frequency generation spectroscopy. This study provides the first quantitative insight into the degradation kinetics during storage, offering a clear scientific basis for optimizing D2W hybrid bonding processes.

AlGaN quantum wells (QWs) emitting at 265 nm were fabricated on face-to-face annealed sputter-deposited AlN (FFA Sp-AlN) templates with n-AlGaN and different homoepitaxial AlN thicknesses (200-2000 nm) by metalorganic vapor phase epitaxy (MOVPE). Thicker MOVPE-AlN led to higher dislocation densities. The type and concentration of vacancies in n-AlGaN, as well as the photoluminescence efficiencies and time-resolved photoluminescence lifetimes of the QWs were nearly unchanged regardless of the MOVPE-AlN thickness, suggesting nearly identical internal quantum efficiencies. The results prove high-quality AlGaN QW growth with only 200 nm thick MOVPE-AlN, resulting in reduced total thickness of AlN by using FFA Sp-AlN.

The annealing properties of vacancies in HfO2 layers deposited on Si substrates and their role in amorphous-to-crystalline transition were studied with monoenergetic positron beams. HfO2 layers with a thickness of 4-30 nm were fabricated by the atomic layer deposition technique. The major vacancy-type defects in these layers were identified as a Hf vacancy (V-Hf) coupled with multiple oxygen vacancies (V(O)s) and larger vacancy clusters. After annealing at 500 degrees C, the concentration of vacancy clusters started to increase, which was attributed to the agglomeration of intrinsic open spaces in the amorphous phase upon the phase transition from amorphous to monoclinic crystalline phases. The amorphous-crystalline transition started near the interface between the HfO2 layer and bottom electrodes (TiN). After the crystallization, the concentration of vacancy clusters decreased as the annealing temperature increased.

The process development of direct placement (or sequential bonding) in die-level hybrid bonding has not yet reached full maturity. A key distinction between die-level and wafer-level hybrid bonding is the queue time (Q-time) between activation/deionized water (DIW) rinse and bonding. In wafer-towafer (W2W) bonding, the bonding sequence has been done immediately and simultaneously after DIW cleaning within a cluster bonding tool. In contrast, die-to-wafer (D2W) bonding introduces a time lag due to tool-to-tool transfer and individual die handling/bonding, resulting in an extended Q-time. In this study, the Q-time in D2W hybrid bonding has been comprehensively investigated using a novel method for accurately measuring bond strength. During the extended Q-time, water evaporation at the bonding interface occurs, leading to insufficient water retention which is critical for direct bonding. This results in an increased microscopic interface gap, ultimately weakening the bond strength in direct bonding. The extent of water evaporation and the hydrophilicity of the interface were analyzed using water contact angle (WCA), thermal desorption spectroscopy (TDS) and zeta potential measurements, all of which corroborated this phenomenon. These findings provide critical insights into the challenges and optimization strategies for the D2W bonding process, paving the way for an improved D2W stacking methodology.

Roles of Al-vacancy (VAl) complexes on the cathodoluminescence (CL) spectra of Si-doped AlN grown by halide vapor phase epitaxy (HVPE) on a physical-vapor-transported (0001) AlN substrate are described, making a connection with the results of positron annihilation measurements. A combination of HVPE and AlN substrate enabled decreasing deleterious carbon concentration and dislocation density, respectively, thus accentuating the influences of VAl-complexes on the luminescence processes. A low-temperature CL spectrum of unintentionally doped AlN exhibited predominant excitonic emissions at around 6 eV and a marginal deep-state emission band at around 3.7 eV that originates from residual carbon (<1016 cm−3) on nitrogen sites (CN). However, the sample was revealed to contain a considerable amount (∼1017 cm−3) of vacancy clusters, most likely comprising a VAl and nitrogen-vacancies (VN), namely, VAlVN1−2, which act as nonradiative recombination centers that decrease overall CL intensity at elevated temperatures. With increasing Si-doping concentration ([Si]), major vacancy species progressively changed from VAlVN1−2 to VAlON1−2, where ON is oxygen on N sites, which exhibit other deep-state emission bands ranging from 3.2 to 3.5 eV. Further increase in [Si] gave rise to the formation of donor-compensating defects comprising VAl and Si on the second-nearest-neighbor Al sites (SiAl), abbreviated by VAl−SiAln, which exhibit emission shoulders at around 2.9–3.0 eV. When [Si] exceeded 5 × 1018 cm−3, an emission band at around 4.5 eV emerged, which had been ascribed to originate from the nearest-neighbor SiAlCN complexes. Because VAl-complexes, including those containing impurities, are thermally stable, incorporation of vacancies should be blocked at the growth stage.

Selective-area doping of GaN using ion implantation (I/I) followed by ultra-high-pressure annealing (UHPA) under 1-GPa-N2 has emerged as a promising technique for GaN power devices. In this article, the impacts of UHPA on the midgap recombination centers (MGRCs) in undoped, Si-implanted, Mg-implanted, and Mg/N-implanted GaN epitaxial layers are described based on the results of photoluminescence (PL) and time-resolved PL measurements. For undoped GaN, PL lifetimes at 300 K for the near-band-edge emission decreased with increasing the annealing temperature (Ta), indicating higher Ta increased the concentration of MGRCs. In contrast, for I/I-GaN, PL lifetimes or PL intensities at 300 K for the near-band-edge emission increased with increasing Ta, indicating higher Ta decreased the concentration of MGRCs originating from the I/I-induced vacancy-type defects comprising Ga and N vacancies [e.g., (VGaVN)3]. Nevertheless, MGRC concentrations in I/I-GaN after UHPA remained several orders of magnitude higher than in undoped GaN. Additional N-I/I onto Mg-implanted GaN followed by UHPA at Ta = 1480 °C enhanced the activation of a Mg acceptor substituted on a Ga site (MgGa) and decreased the concentration of MGRCs. For Mg- and Mg/N-implanted GaN, the progressive activation of MgGa acceptors with increasing Ta was confirmed. However, the PL lifetimes for Mg- and Mg/N-implanted GaN with Mg concentrations higher than 1 × 1018 cm−3 were limited to shorter than 1 ps. To fabricate reliable p-contacts and electron inversion layers using Mg- or Mg/N-I/I combined with UHPA, it is crucial to eliminate or etch away residual defective layers near the surface, which limits the minority carrier lifetime to below 1 ps.

Defects introduced by plasma activation in amorphous SiO2 were probed by a monoenergetic positron beam. Doppler broadening spectra of the annihilation radiation were measured as a function of the incident positron energy for SiO2 deposited from tetraethylorthosilicate using plasma-enhanced chemical vapor deposition on Si substrates. After N-2 plasma activation, electron (and/or positron) trapping centers were primarily introduced in the subsurface region (<= 6 nm). The defect concentration decreased after postplasma processes: deionized water rinsing and additional H2O plasma activation, which was associated with the formation of silanol groups at the surface. However, a certain number of defects existed in the subsurface region, and they were not annealed out at the typical annealing temperature for bonding SiO2 layers (400 degrees C). Because these defects can cause softening of the top surface region and attract water trapped between two wafers or in SiO2, they are considered to contribute to the wafer-bonding process.

Annealing behaviors of vacancy-type defects in Mg and N-implanted GaN were studied by positron annihilation. The major defect species in as-implanted samples was identified as Ga-vacancy (V-Ga)-type defects. For Mg-implanted GaN with sequential N-implantation after annealing above 1000 degrees C, the defect species were vacancy clusters such as (VGaVN)(3). Due to the downward shift of the Fermi level position resulting from a partial activation of Mg, the charge states of defects tended to become positive. For N-implanted GaN, the size of the vacancy cluster started to decrease above 1200 degrees C annealing, which was attributed to recombinations between V(N)s coupled with V(Ga)s and excess N atoms. The impact of sequential N-implantations on vacancies in Mg-implanted GaN was found to be most pronounced when the ratio of the concentration of N to that of Mg was three.

Wafer bonding is a step in processing of state-of-the-art integration architectures in CMOS devices. Sufficiently high bonding strength and low distortion with high alignment accuracy are essential to realize these device structures. A challenge in realizing advanced architectures is reducing the thermal history associated with the bonding process. Although much research has been conducted on wafer bonding methods compatible with the latest semiconductor manufacturing processes, discussions on the interface mechanisms during low temperature annealing have been insufficient. In this study, plasma-activated bonding was carried out using SiCN, which is a major bonding dielectric material. The bonding strength and water remaining at the interface were subsequently evaluated. We found that a SiCN film achieved greater bonding strength after post bond annealing at a low temperature of 250 °C and completely consumed the interfacial water. Analyses of the surface and interface revealed the carbon bonding leads to great bonding interface by low-temperature annealing.

Annealing behaviors of vacancy-type defects in low-dose ion-implanted GaN are studied by positron annihilation. N+, Al+, and Si+ ions are implanted with a dose of 1 x 1012 cm-2. For Al- and Si-implanted GaN after annealing at 1100 degrees C, the depth profiles of the net donor concentration (N D) are close to those for implanted impurities, but N D is 2-3 times higher than Al or Si concentrations. N D of N-implanted GaN is higher than that of an unimplanted sample but is lower than that of the Al- and Si-implanted samples. The origin of donor-like defects introduced by ion implantation is expected to be N-vacancy-related defects. A comparison between depth profiles of vacancy-type defects and N D reveals that Ga-vacancy (VGa)-type defects play a significant role in the annealing behavior of N D. Photoexcitation of VGa-type defects and their electron detrapping phenomena are also studied.

The miniaturization of Si-MOS-FET logic integrated circuits necessitates the precise control of electron and hole densities through high-concentration impurity doping to realize transistors within the 2 nm technology node. Among the various thermal treatment techniques, microwave annealing (MWA) has emerged as a promising method for forming high-concentration active layers, offering advantages such as rapid processing and potential nonthermal effects. However, existing MWA systems suffer from interference and standing-wave effects because of their multimode cavity design, which makes it challenging to understand the underlying mechanisms. This study investigated the fundamental heating mechanisms of MWA, focusing on both the electric and magnetic field contributions. The role of Joule heating was examined, and the presence of nonthermal microwave effects was explored by applying MWA to Si substrates implanted with phosphorus or boron and comparing the results with those of conventional rapid thermal processing. The experimental evaluations included sheet resistance measurements, impurity distribution analysis, and defect assessments using slow-energy positron annihilation spectroscopy. The findings indicate that MWA enables the effective activation of implanted impurities at low temperatures, reduces defect formation, and minimizes impurity diffusion, highlighting its potential as a low-temperature processing technique for fabricating advanced semiconductor devices.

To investigate the carrier recombination processes in GaN crystals grown by the low-pressure acidic ammonothermal (LPAAT) method, the photoluminescence (PL) spectra and PL lifetimes of LPAAT GaN crystals grown on acidic ammonothermal (AAT) GaN seed crystals were correlated with the growth polarity and species/concentration of point defects. The PL spectra of LPAAT GaN grown toward the (0001¯) direction (−c region), which provided the highest growth rate, exhibited a predominant near-band edge (NBE) emission. Neither bandgap narrowing nor Burstein–Moss shifts due to high concentration residual impurities were observed in the NBE emissions, indicating higher purity than the previously reported AAT GaN crystals. In addition, strain-induced energy shift or energy broadening of excitonic emission peaks was not observed, indicating excellent crystal coherency. Because of the reduced concentration of midgap recombination centers, a record-long room-temperature PL lifetime for the NBE emission of ammonothermal GaN (40 ps) was obtained from the −c region. Meanwhile, the PL spectra also exhibited the yellow and blue luminescence bands originating from particular deep-state radiative recombination centers. The major vacancy-type defects acting as midgap recombination centers are identified as vacancy complexes comprising a Ga vacancy (VGa) and a few N vacancies (VN), namely, VGa(VN)n buried by H and/or O, where n is an integer. Further reduction of such defect complexes will allow less compensated stable carrier concentration in the LPAAT GaN crystals.

The annealing properties of open spaces in 90-nm-thick SiO2 deposited from tetraethylorthosilicate (TEOS) using plasma-enhanced chemical vapor deposition (PECVD) were studied with monoenergetic positron beams. From the lifetime of positronium (Ps) and an empirical model assuming a spherical open space, the mean diameter of open spaces was estimated to be 0.45 nm for PECVD-SiO2 before annealing. In the annealing temperature range below 350 °C, the size of the open spaces and their concentration increased as the temperature increased. Because initial water desorption from PECVD-SiO2 occurred in this temperature range, the observed increases in the size and concentration of spaces were attributed to the detrapping of water from such regions. Above 400 °C annealing, Ps formation was suppressed due to carrier traps introduced by the desorption of gas incorporated during TEOS decomposition. The size of the open spaces reached its maximum value (0.61 nm) after 800 °C annealing and started to decrease above 900 °C. After 1000 °C annealing, although the size of the spaces was close to that in thermally grown SiO2, their concentration remained low, which was attributed to residual impurities in the SiO2 network.

Defect formation in epitaxial Mg2Sn1-x Ge x thermoelectric thin films grown via molecular beam epitaxy (MBE) was studied. We examined the defect formations and structures using cross-sectional transmission electron microscopy and positron annihilation spectroscopy. The defect formation tends to be influenced by Ge incorporation into the Mg- 2 Sn matrix phase of epitaxial thin films. Mg vacancies (V (Mg) ) were identified as point defects, primarily concentrated in the film's mid-layer. In films with higher Ge composition, stacking faults were observed. The concentration of vacancy-type point defects decreased as the Ge concentration increased. This implies that the vacancy atoms, which would have otherwise been created by increasing chemical pressure due to the higher Ge content, might have played a role in the formation of stacking faults. The high concentration of vacancy-type defects resulted in the lowest thermal conductivity, demonstrating their significance as effective phonon scattering centers in epitaxial thermoelectric films.