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How pH and hydrogen peroxide (H2O2) in colloidal silica-based slurry affect chemical mechanical planarization of polycrystalline Ge2Sb2Te5 (pc-GST) film has been investigated. The polishing rate of pc-GST film increased when the slurry pH decreased or increased from neutral pH. In addition, pc-GST polishing rate was highly affected by adding H202, resulting in a high pc-GST polishing rate in the entire pH ranging from 2 to 11. However, a noticeable difference in surface roughness of pc-GST film polished was observed between acidic (pH 2) and alkaline (pH 11) regions. Low RMS of roughness as well as a high polishing rate of pc-GST film was obtained in the acidic pH region with lwt% H2O2. In contrast, in the alkaline region a high RMS of roughness of pc-GST film was observed owing to enhanced selective corrosion between Ge, Sb, and Te elements. To investigate the different polishing behavior of pc-GST film between acidic and alkaline pH regions, surface characteristics of pc-GST film dipped in acidic or alkaline media were observed by scanning electron microscopy, X-ray photoelectron microscopy, and potentiodynamic measurement. [ABSTRACT FROM AUTHOR]

As for chemical mechanical polishing (CMP) of polycrystalline Ge2Sb2Te5 (pc-GST), the corrosion-inhibition efficiency and polishing rate of 1-vinyl-2-pyrrolidinone (VP) and polyvinyl pyrrolidone (PVP) with molecular weights of 3.5 k, 25 k, and 1300 k g/mol were estimated. The estimation results show that there is an optimal molecule weight of the corrosion inhibitor (i.e., 3.5 k g/mol) to achieve free of corrosion pits and the lowest surface roughness after polishing test. These results demonstrate that the formation of a uniform polymeric passivation layer arising from a corrosion inhibitor can prevent a direct penetration of the oxidizer H2O2 at the optimum molecule weight of the corrosion inhibitor during the pc-GST CMP. [ABSTRACT FROM AUTHOR]

We investigated the effect of the oxidizer K3Fe(CN)6 on the performance of chemical mechanical planarization (CMP) of tungsten film using the acid slurry. The addition of K3Fe(CN)6 in the acid slurry formed the K2WO4 layer on the tungsten film surface, thereby increasing the polishing rate and decreasing the surface roughness of the tungsten film after CMP, which demonstrated better CMP performance than the oxidizer Fe(NO3)3. Furthermore, the addition of H2O2 in the acid solution including K3Fe(CN)6 enhances the chemical dissolution rate of the K2WO4 layer on the tungsten film surface, considerably increasing the polishing rate and decreasing surface roughness of the tungsten film. [ABSTRACT FROM AUTHOR]

Ruthenium (Ru) chemical mechanical planarization (CMP) with a slurry using sodium periodate (NaIO4) as an oxidizer was carried out as a function of pH. The Ru polishing rate was highest at pH 7 and decreased as the pH decreased or increased. In addition, a similar trend in the corrosion current density as a function of pH was found. Two equivalent circuit models were proposed to explain the electrochemical impedance spectroscopy (EIS) results of Ru in NaIO4 solution as a function of pH. From results of EIS, we found that the Ru film had a lowest charge transfer resistance in a neutral region than that in an acidic or alkaline region. This different charge transfer resistance of the Ru film as a function of pH resulted from the different surface composition of Ru oxide species, which was analyzed with X-ray photoelectron spectroscopy. Finally, we briefly derived a series of reaction equations between Ru and NaIO4 on the basis of the above results and discussion. [ABSTRACT FROM AUTHOR]

We investigated the chemical mechanical planarization (CMP) mechanism of nitrogen-doped polycrystalline Ge2Sb2Te5 (pc-GST) using nitric acid slurry without or with 1.0 wt % hydrogen peroxide (H2O2). Without H2O2, the pc-GST film surface undergoes selective corrosion of Ge and Sb, resulting in pitting corrosion. Otherwise, with H2O2, the pc-GST film surface produces a Ge, Sb, Te oxide layer, thereby introducing a cyclic polishing process such as chemical oxidation, chemical and mechanical polishing, and sequential chemical oxidation. As a result, the polishing rate increased up to ~1000 Å/min and the surface roughness decreased to 0.858 nm. [ABSTRACT FROM AUTHOR]

The effect of NH4OH concentration on surface qualities, namely, haze level, roughness, and number of remaining particles after final-touch polishing, of silicon wafers was investigated. This investigation found that the surface qualities of the final touch polished silicon wafers were degraded by the agglomeration of colloidal silica abrasives and a weakly formed passivation layer on the silicon-wafer surface at lower NH4OH concentration and enhanced with increasing NH4OH concentration in alkaline slurry. These results were confirmed by measuring the secondary-abrasive size, zeta potential of the colloidal silica abrasive in the slurry, and X-ray photoelectron spectroscopy on the silicon-wafer surface. [ABSTRACT FROM AUTHOR]

For phase-change memory beyond the 30 nm design rule, chemical mechanical planarization (CMP) performing at a high polishing rate, reasonable selectivity, and no corrosion-induced pits is essential for planarizing nitrogen-doped polycrystalline Ge2Sb2Te5 (OST) deposited on the confined memory cell structure. We develop a new alkaline slurry added with KMnO4 used as an oxidizer. The alkaline slurry added with 0.3 wt % KMnO4 has a polycrystalline OST film polishing rate of 5200 Å/min, a polishing rate selectivity between polycrystalline GST and SiO2 film of 100:1, and no corrosion-induced pit. In addition, poly- crystalline GST film CMP using the alkaline slurry added with KMnO4 is observed to follow a cyclic reaction polishing mechanism. [ABSTRACT FROM AUTHOR]

We have investigated the adsorption density of anionic molecules on a ceria surface and its effect on suppressing defects on the SiO2 films during shallow trench isolation (STI) chemical mechanical planarization (CMP). Intermolecular vacancies in poly(m. ethyl methacrylate) (PMMA) caused by ionic repulsive forces between its carboxyl groups provide adsorption sites on the ceria surface for 3-hydroxypentanedioic acid-3-carboxylic acid (hydrogen citrat), which has a molecular length of 8.39 A. This allows for an increase in adsorption density. The coadsorption of PMMA and hydrogen citrate on the ceria surface leads to an increase in negative charge at the ceria particle-water interface and provides repulsive forces between the ceria particle and the SiO2 surface. Ceria slurry prepared with the coadsorption of PMMA and hydrogen citrate shows a suppression of remaining particles (90.9%) and microscratches (100%) on the Si02 film, resulting from a decrease in the adhesion force of ceria particles on the SiO2 film. This effect was analyzed by force measurement using atomic force microscopy. [ABSTRACT FROM AUTHOR]

Four-level nonvolatile small-molecule 4F2memory cells were developed with a sandwiched device structure consisting of an upper Al electrode, upper small-molecule layer (Alq3, aluminum tris(8-hydroxyquinoline)), Ni nanocrystals surrounded by NiO tunneling barrier, lower small-molecule layer, and bottom Al electrode. In particular, an in situ O2-plasma oxidation process following Ni evaporation was developed to produce uniformly stable 10 nm Ni nanocrystals surrounded by a NiO tunneling barrier embedded in the small-molecule layer. They presented a memory margin (Ion/Ioffratio) of ≈1 × 103, a retention time of more than 105s, an endurance of more than 5 × 102erase-and-program cycles, and multilevel cell (MLC) operation, being a terabit nonvolatile memory-cell. A vertically double-stacked 4F2multilevel nonvolatile memory cell was also developed, showing a memory margin of ≈1 × 103in both the top and bottom memory cells and eight-level cell operation. [ABSTRACT FROM AUTHOR]

The structural characteristics of nanosized ceria particles were investigated to clarify the relationship between the structural characteristics of abrasives and the problem of residual particles in shallow trench isolation chemical mechanical planarization (STI CMP). The ceria particles were synthesized via a solid-state displacement reaction method, and their crystalline structure was controlled by regulating the oxygen partial pressure at the reaction site on the precursor. In a calcination process with a high oxygen concentration, the synthesized ceria particles had a cubic fluorite structure (CeO2) because of the decarbonation of the cerium precursor at a high oxygen partial pressure. The particles calcined with a low oxygen partial pressure had an included hexagonal structure (Ce2O3). The ceria slurry prepared with the cubic CeO2 yielded a higher removal rate than the slurry prepared with the hexagonal Ce2O3. Furthermore, the ceria slurry with the cubic structured particles had less residual particles on the oxide film than the slurry with the hexagonal structured particles. The resulting residual particles originated because Ce2O3 is easily agglomerated and adsorbed on the wafer surface due to the high surface activity resulting from the oxygen vacancy on the particle surface. [ABSTRACT FROM AUTHOR]

The influence of the molecular weight of poly(acrylic acid) (PAA) on chemical mechanical planarization (CMP) for shallow trench isolation (STI) was investigated. The adsorption behaviors of PAA as a function of molecular weight on deposited plasma-enhanced tetraethylorthosilicate and chemical vapor deposition Si3N4 films were analyzed by the force measurement using atomic force microscopy (AFM). The AFM results revealed that the affinity of PAA with the nitride film is higher than the affinity with the oxide film, and thus a denser adsorption layer on the nitride film is formed with higher molecular weight of PAA, which leads to higher selectivity in STI CMP. Additionally, to determine the correlation between the dispersion stability of the CeO2 resulting from the presence of PAA with different molecular weight and CMP performance, the colloidal properties of the slurry as a function of the molecular weight of PAA were examined. [ABSTRACT FROM AUTHOR]

We investigated the effect of the presence of strained SiGe layer inserted between unstrained Si and buried oxide layer and the Ge concentration in strained SiGe layer on the memory margin of capacitor-less memory-cell. We observed that memory margin of unstrained Si on strained SiGe-on-insulator capacitor-less memory-cells increases with the Ge concentration of the strained SiGe layer and obtained memory margin at the Ge concentration of 19 at% that was 3.2 times larger than that at the silicon-on-insulator capacitor-less memory-cell. This enhancement was due to the potential-barrier lowering increasing exponentially with the Ge concentration resulting from higher hole confinement in spite of the reduction in the saturated drain current. [ABSTRACT FROM AUTHOR]

We proposed a dislocation sink technology for achieving Si1−xGex multi-bridge-channel field-effect-transistor beyond 5 nm transistor design-rule that essentially needs an almost crystalline-defect-free Si1−xGex channel. A generation of a dislocation sink via H+ implantations in a strain-relaxed Si0.7Ge0.3 layer grown on a Si substrate and a following annealing almost annihilate completely misfit and threading dislocations located near the interface between a relaxed Si0.7Ge0.3 layer and a Si substrate. A real-time (continuous heating from room temperature to 600 °C) in situ high-resolution-transmission-electron-microscopy and inverse-fast-Fourier-transform image observation at 1.25 MV acceleration voltage obviously demonstrated the annihilation process between dislocation sinks and remaining misfit and threading dislocations during a thermal annealing, called the [SiI or GeI + VSi or VGe → Si1−xGex] annihilation process, where SiI, GeI, VSi, and VGe are interstitial Si, interstitial Ge, Si vacancy, and Ge vacancy, respectively. In particular, the annihilation process efficiency greatly depended on the dose of H+ implantation and annealing temperature; i.e. a maximum annihilation process efficiency achieved at 5 × 1015 atoms cm−2 and 800 °C. [ABSTRACT FROM AUTHOR]

In the fabrication of cross-point phase-change-memory-cells through atomic-layer-deposition of Ge-doped SbTe (Ge-ST) film followed by chemical-mechanical-polarization (CMP), a remarkable surface tensile stress was generated, originating from the surface stress induced by the pad down force and the surface structure tensile stress in a confined memory-cell structure. It was maximized at the position of the Si3N4-film spacer where the curvature becomes zero. The maximized surface tensile stress produced polishing induced voids via the generation mechanism of the stress corrosion cracking. The generation frequency and nanoscale size of the polishing induced voids rapidly increased at the maximum surface tensile stress during CMP. Then, they slightly decreased and saturated when the surface tensile stress reduced during further CMP. A design of a spacer using a SiO2-film spacer rather a Si3N4-film spacer could prevent the generation of the polishing induced voids, confirming that the generation mechanism of the polishing induced voids is associated with the stress corrosion cracking. [ABSTRACT FROM AUTHOR]

A two-terminal perpendicular spin-transfer torque (p-STT) based neuron with a 100  ×  100 nm device size was fabricated with a p-STT magnetic tunneling junction (MTJ) spin valve. It performed well in the integrate-and-fire event of the input voltage pulse (spike) cycles, which originate from the imperfect structure of the MgO tunneling barrier in a p-STT MTJ spin valve (i.e. a nano-scale poly-grain size distribution of the MgO tunneling barrier). In particular, the integrate-and-fire cycles rapidly increase as the input voltage pulse (spike) amplitude, width, and external assistant perpendicular magnetic field decrease. [ABSTRACT FROM AUTHOR]

We investigated how the nanohole structure on a {111} pyramid textured surface affected the photovoltaic performance of silicon solar cells by varying nanohole depth. During the effective minority carrier recombination lifetime, the surface reflectance decreased with increasing nanohole depth, showing a trade-off relationship. The power conversion efficiency (PCE) of silicon solar cells with the {111} pyramid textured surface peaked at a specific nanohole depth, i.e., 0.43% PCE enhancement (3.32% enhancement relative to a reference cell) was obtained at the nanohole depth of 94.8 nm. [ABSTRACT FROM AUTHOR]

We investigated the Ru spacer-thickness effect on the anti-ferro-magnetic coupling strength (Jex) of a [Co/Pd]n-synthetic-anti-ferro-magnetic layer fabricated with Co2Fe6B2/MgO based perpendicularmagnetic- tunneling-junction spin-valves on 12-in. TiN electrode wafers. Jex peaked at a certain Ru spacer-thickness: specifically, a Jex of 0.78 erg/cm² at 0.6 nm, satisfying the Jex criteria for realizing the mass production of terra-bit-level perpendicular-spin-transfer-torque magnetic-random-accessmemory. Otherwise, Jex rapidly degraded when the Ru spacer-thickness was less than or higher than 0.6 nm. As a result, the allowable Ru thickness variation should be controlled less than 0.12nm to satisfy the Jex criteria. However, the Ru spacer-thickness did not influence the tunneling-magnetoresistance (TMR) and resistance-area (RA) of the perpendicular-magnetic-tunneling-junction (p-MTJ) spin-valves since the Ru spacer in the synthetic-anti-ferro-magnetic layer mainly affects the anti-ferro-magnetic coupling efficiency rather than the crystalline linearity of the Co2Fe6B2 free layer/MgO tunneling barrier/Co2Fe6B2 pinned layer, although Co2Fe6B2/MgO based p-MTJ spin-valves ex-situ annealed at 275 °C achieved a TMR of ~70% at a RA of ~20 Ω μm². [ABSTRACT FROM AUTHOR]

For the double MgO based perpendicular magnetic tunneling junction (p-MTJ) spin-valves with a top Co2Fe6B2 free layer ex situ annealed at 400 °C, the tunneling–magnetoresistance ratio (TMR) strongly depended on the platinum (Pt) seed layer thickness (tPt): it peaked (∼134%) at a specific tPt (3.3 nm). The TMR ratio was initially and slightly increased from 113%–134% by the enhancement of the magnetic moment of the Co2Fe6B2 pinned layer when tPt increased from 2.0–3.3 nm, and then rapidly decreased from 134%–38.6% by the degrading face-centered-cubic crystallinity of the MgO tunneling barrier when tPt increased from 3.3–14.3 nm. [ABSTRACT FROM AUTHOR]

By fabricating CoFeB/MgO/CoFeB-based perpendicular-magnetic tunnel junction (p-MTJ) spin-valves stacked with a [Co/Pd]n-SyAF layer based on a TiN bottom electrode on a 12 inch Si wafer (001) substrate, we investigated how the bridging layers of Ta, Ti, and Pt and their thickness variation affected the tunneling magneto-resistance (TMR) ratio of Co2Fe6B2 pinned-layer behavior in magnetic-tunnel-junctions. TMR ratios for Ta, Ti, and Pt bridging layers were observed to be 64.1, 70.2, and 29.5%, respectively. It was confirmed by high resolution transmission electron microscopy (HR-TEM) that this difference resulted from CoFeB/MgO/CoFeB MTJ layers with Ta and Ti bridging layers being textured well with a bcc (100) structure, indicating that Ta and Ti bridging layers bridged SyAF fcc (111) and MTJ bcc (100). On the other hand, the MTJ layer with Pt bridging layer was incorrectly textured, indicating that a Pt bridging layer is unsuitable to bridge SyAF fcc (111) and MTJ bcc (100) due to Pt being diffused into the CoFeB pinned-layer. In addition, perpendicular magnetic anisotropy (PMA) behavior of the CoFeB pinned-layer was found to depend strongly on a bridging layer thickness; higher TMRs of Ta and Ti were observed at the optimal bridging layers’ thickness, which enable the realization of PMAs of the pinned-layer and ferro-coupling of the pinned-layer with the lower-SyAF layer. Among the three bridging materials (Ta, Ti, and Pt), we observed that Ti showed the highest TMR ratio and widest thickness range for a high TMR ratio, indicating that a higher TMR ratio is needed to obtain the best deposition process margin. [ABSTRACT FROM AUTHOR]

We design a Co2Fe6B2/MgO-based p-MTJ spin-valve without a [Co/Pt]n lower synthetic-antiferromagnetic (SyAF) layer to greatly reduce the 12-inch wafer fabrication cost of the p-MTJ spin-valve. This spin-valve achieve a tunneling magnetoresistance (TMR) of 158% and an exchange field (Hex) of 1.4 kOe at an ex situ annealing temperature of >350 °C, which ensures writing error immunity. In particular, the TMR ratio strongly depends on the body-center-cubic capping-layer nanoscale thickness (tbcc), i.e., the TMR ratio peaks at tbcc = 0.6 nm. [ABSTRACT FROM AUTHOR]

The TMR ratio of Co2Fe6B2/MgO-based p-MTJ spin valves stacked with a [Co/Pd]n-SyAF layer decreased rapidly when the ex situ magnetic annealing temperature (Tex) was increased from 275 to 325 °C, and this decrease was associated with degradation of the Co2Fe6B2 pinned layer rather than the Co2Fe6B2 free layer. At a Tex above 325 °C the amorphous Co2Fe6B2 pinned layer was transformed into a face-centered-cubic (fcc) crystalline layer textured from [Co/Pd]n-SyAF, abruptly reducing the Δ1 coherence tunneling of perpendicular-spin-torque electrons between the (100) MgO tunneling barrier and the fcc Co2Fe6B2 pinned layer. [ABSTRACT FROM AUTHOR]

We investigated the impact of tungsten contamination on minority-carrier recombination lifetime, the photodiode dark/photo current and sensitivity of a pinned photodiode, and the sensing margin of a CMOS image sensor (CIS) cell. After an intentional tungsten contamination and followed by driving at 800 °C for 30 min, tungsten contaminant were located from the surface to p- and n-type regions of a photodiode. The tungsten contamination degraded minority-carrier recombination life-time and the dark current and sensitivity of a pinned photodiode; i.e., there was a good correlation between the minority recombination lifetime and the sensitivity of a photodiode. As a result, tungsten contamination directly degraded the sensing margin of a CIS cell photodiode; i.e., it decreased with increasing tungsten contaminant concentration. [ABSTRACT FROM AUTHOR]

The effect of changes in poly(acrylic acid) (PAA) conformation on removal of Si3N4 film was investigated. PAA was used as a passivation agent by adsorption on an Si3N4 film in shallow-trench isolation chemical-mechanical planarization (STI CMP). Adsorption behavior of PAA on the Si3N4 film and the conformation transition were determined by adsorption isotherms and force measurements using atomic force microscopy (AFM) as a function of ionic strength. AFM results revealed that, as ionic strength increases, the repulsive force between the negatively charged carboxylate groups along the backbone of PAA is reduced due to counterion screening and to the changes of PAA conformation from a stretched to a coiled configuration. At high ionic strength, the coiled conformation of PAA formed a dense passivation layer on the Si3N4 film, which led to suppression of the removal rate of Si3N4 film from 72 to 61 Å/min in the STI CMP process. [ABSTRACT FROM AUTHOR]

The effects of the molecular weight and concentration of poly(acrylic acid) (PAA) with different primary abrasive sizes in ceria slurry on the nitride film loss, removal rate, film surface roughness, and removal selectivity of SiO2-to-Si3N4 films were investigated by performing chemical mechanical polishing (CMP) experiments using blanket and patterned wafers. In the case of the blanket wafers, we found that for a lower PAA molecular weight, the removal selectivity of SiO2-to-Si3N4 films increased more significantly with increasing PAA concentration in slurry containing a larger primary abrasive size. For the patterned wafers, with a higher PAA molecular weight in the ceria slurry suspension, the erosion of the Si3N4 film was less, but the removed amount was also smaller, and the surface roughness became worse after CMP. These results can be qualitatively explained by the layer of PAA adsorbed on the film surface, in terms of electrostatic interaction and rheological behavior. [ABSTRACT FROM AUTHOR]

The dielectric functions of undoped and P-doped Si1–xGex (SiGe) films with a compressive strain on silicon-on-insulator (SOI) substrates are obtained by using spectroscopic ellipsometry. The respective Kato–Adachi and Tauc–Lorentz models are best fitted to the undoped and P-doped SiGe films to obtain their complex dielectric functions. The undoped SiGe films are characterized by multimodal peaks in the dielectric function, whereas the P-doped SiGe films exhibit only a broad peak. Further, the E0 and E1 critical points (CPs) of the undoped SiGe films are strongly dependent on the Ge concentration, whereas the E2 CPs are independent of concentration. The E0 and E2 CPs in the undoped SiGe films on an SOI substrate are lower than those of SiGe on a bulk-Si substrate owing to the higher strain. For P doping in SiGe, its dose causes non-monotonic variations in Eg and E0. [ABSTRACT FROM AUTHOR]

A perpendicular spin transfer torque (p-STT)-based neuron was developed for a spiking neural network (SNN). It demonstrated the integration behavior of a typical neuron in an SNN; in particular, the integration behavior corresponding to magnetic resistance change gradually increased with the input spike number. This behavior occurred when the spin electron directions between double Co2Fe6B2 free and pinned layers in the p-STT-based neuron were switched from parallel to antiparallel states. In addition, a neuron circuit for integrate-and-fire operation was proposed. Finally, pattern-recognition simulation was performed for a single-layer SNN.

A matrix element for thickness fluctuation (δTSOI) scattering was derived to demonstrate the mobility dependence on Eeff, especially at a low inversion charge concentration, with an ultrathin channel thickness below 7 nm. This case contrasts other research with a lack of such dependence on either thick silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors (MOSFETs) or bulk MOSFETs. Our matrix element implies that the quantized energy fluctuation associated with δTSOI varies with the average distance of electrons from the surface interface. In particular, it implies the effects of the change in transverse potential on the subband energy fluctuation for each subband, which results in a different matrix element for each applied gate bias. By using this matrix element model, the low-field electron mobility was shown to depend not only on TSi but also on Eeff. Furthermore, the results of a simulation of electron mobility degradation as a function of TSi at low Eeff agreed well with previous experimental results. [ABSTRACT FROM AUTHOR]