Bottom CD Research Articles

Co-combustion of carbon-rich fraction from coal gasification fine slag and biochar: Gas emission, ash sintering, heavy metals evolutions and environmental risk evaluation

Mixed combustion of carbon-rich fraction (RC) from coal gasification fine slag and corncob char (CC) is an effective way of energy recycling. In this paper, the co-firing performance and kinetics of RC and CC were studied, and gas emission pattern, ash sintering trend and the migration and transformation behavior of heavy metals during combustion were explored. The results showed that the combustion performance was enhanced and the reaction activation energy was reduced during the blends burning. The synergistic effect between co-combustion reactions decreased emissions of gaseous pollutants. With the increasing RC compounding ratio and combustion temperature, the ash sintering tendency weakened. Cr and Ni were mostly enriched in the bottom ash, whereas Cu, Zn, As, Cd, and Pb tended to migrate to fly ash and flue gas. Cu, Zn, As, and Pb were in the form of stable fractions. Temperatures accelerated the chemical forms of Cr, Ni, Cu, Zn, and Cd being transformed into stable fractions. The environmental evaluation index suggested that the potential environmental risks of Cr, Zn, Cd, and As were relatively high. The results of this study provide guidance for the synergistic combustion disposal of double solid waste.

Enabling High Aspect Ratio 3D NAND Scaling through Deposition and Etch Co-Optimization (DECO)

Over the past decade, the demands for 3D NAND flash memory devices have been increased tremendously due to ever growing digital economics in consumer electronics, data centers, IOT, healthcare and automotive industries. The growth is further accelerated during the recent Covid period. The industry was able to keep up the scaling roadmap by stacking more memory cell in vertical direction to realize higher bit density at reducing cost per Gig-bit.Unlike devices scaling via feature size reduction, 3D NAND flash vertical stack scaling puts challenges mostly on film deposition and etch. Among many steps, high aspect ratio (HAR) ONON channel hole formation modules remained the most critical steps. Forming billions of perfect channel holes from top to bottom without distortion and twisting is the grand challenge. Besides individual etch and deposition module optimization, deposition and etch Co-optimization (DECO) could provide new opportunities. In this paper, we will present a summary of the recent progress in the approaches and the benefits of DECO as potential pathways to overcome the HAR ONON patterning. We will discuss the ONON Tier Optimization for profile control to reduce the top bowing and enlarge the bottom CD. We will introduce a sacrificial liner approach to prevent top CD enlargement at deeper etch depth. We will also discuss new mask materials for better etch selectivity and profile control to enable the scaling roadmap.

(Invited) Metallizations for Advanced Interconnects and Challenges for Future Nodes

The dimensional scaling of the back-end of line (BeOL)interconnects is a significant challenge for the deposition and fill of conductive metals in narrow lines and small vias that are needed to connect the semiconductor devices. Especially at the lower and the smaller interconnect levels, the scaling of the copper (Cu) dual damascene is becoming the limiting factor due to the increase in the resistance-capacitance delay. The increase in RC delay results in a degradation of the chip performance. So, while the scaling in the logic device landscape leads to a continuous improvement of the device performance and an increased transistor density, the Cu wiring in the interconnects systems tend to perform worse when scaling down the dimensions. This paper addresses methodologies to continue the scaling of the BEOL interconnects down to small CD’s like 12nm. For this, process and materials innovation are the key to reduce the interconnect area and its resistance.[1] Examples that will be discussed include Cu hybrid metallization and the use of new conductor materials or integration methodologies like metal patterning.In being the workhorse for building multilevel interconnects, the first desired direction is to push and extend the conventional Cu dual damascene metallization to small dimensions. However, extending Cu is not only challenging from a metal fill point of view, but also from the resistance as well as reliability point of view. The ideal metal that could replace the conventional Cu should have a low electrical resistance in scaled dimensions, have a good thermal conductivity, is resistant against oxidation and possesses a high melting point.[2] This melting is a good measure for the ease of electromigration due to metal diffusion where a high melting point would allow for a reliable operation without the need for a barrier material to prevent it to diffuse. This brings Ru, Mo and W in the picture as interesting material to replace Cu in the vias, and potential later in the lines as well. Figure 1 (left) shows the tabulated via and line resistance predictions for Cu and alternative metals to Cu like Co, Ru, Mo and W (method described elsewhere [3]). The red color coding is used to indicate too high resistance values, where green indicates the desired target resistance. The resistance benefit for the use of Ru, Mo or W compared to Cu is clearly visible in the table. An efficient way to introduce a new alternative metal in the Cu interconnect metallization without being too disruptive is using a selective metal deposition for the vias landing on the exposed bottom metal (Fig.1 middle). After the vias are filled using a selective metal-on-metal deposition with a barrierless metal like Ru or W [4,5], the remainder of the structures can be filled using the conventional Cu metallization scheme. This process is called a Cu hybrid metallization scheme. Filling the vias before the Cu line metallization, improves the process window and yield for the Cu gapfill. Challenges for the selective deposition of metals in vias will be discussed. The XTEM in Figure 1 (right) shows a successful example of the metal prefill in a via hole with bottom CD of 14nm. The via is nicely filled with the metal while the top lines in the dielectric that are not connected to vias do not show any non-selective deposition.Even though the vias are becoming more and more critical in the signal routing on a system-on-chip level, the resistance penalty for the Cu lines is unacceptable at small CDs as can be seen in the table in Fig.1. But eventually, the Cu electromigration will set the limit because at 10nm CD copper lines are not expected to meet electromigration requirements anymore [6]. This is then an inflection point to also replace the lines with alternative metals like Ru, Mo or more exotic conductors like binary metals. For these metals, the challenges in the line fill, processing, and integration will be discussed which may lead to the introduction of the so-called semi-damascene module [7] instead of using the dual damascene methodology.[1] J. Clarke et al, IEEE VLSI 2014, p. 176[2] D. Gall et al, J. Appl. Phys. 2016, 119, p.085101[3] I. Ciofi et al, IEEE transactions on Electron Devices 2017, 64 (5), p.2306 [5] M.H. van der Veen et al, Proc. of the IITC 2021, S7-2 [4] M. van der Veen et al, Proc. of the IITC 2020, p.16 [6] K. Croes et al, IEDM 2018, p 5.3.1[7] Zs. Tőkei et al, IEDM 2020, p 32.2.2 Figure 1

Bottom Drag Coefficient on a Shallow Barrier Reef

AbstractThe present paper reports of a field experiment over a shallow, roughness‐varying barrier reef at Maupiti island, French Polynesia. The depth‐averaged momentum balance is used to estimate the bottom drag coefficient Cd, which varies from 0.01 to 0.3, with dependence on both depth and reef structure. The depth effect on Cd is well predicted by a log dependency, as used in previous laboratory and fields observations. The present results extend the approach to a system with more wave exposure and higher roughness‐to‐depth ratio. Additionally, the statistical relationship between high‐resolution reef topography and hydrodynamical parameters is discussed.

Surface Turbulence Reveals Riverbed Drag Coefficient

AbstractFlow in rivers and the coastal ocean is controlled by the frictional force exerted on the water by riverbed or seabed roughness. The frictional force is typically characterized by a drag coefficient Cd, which is estimated from bulk measurements and often assumed constant. Here, we demonstrate a relationship between bed roughness and water surface turbulence that can be used to make remote estimates of Cd. We observe that regions with larger bed roughness result in greater turbulent kinetic energy (TKE), which is transported upward by river boils to the water surface. We present a relationship between surface TKE and Cd, and validate this relationship by comparing remotely sensed estimates of Cd to those from in situ measurements. Thus, our results provide an approach for estimating bottom roughness and Cd based entirely on remotely sensed data, including their spatial variability, which can improve modeling of river discharge and morphodynamics in data‐poor regions.

The influence of Cd Content Transported by Different Sources on Different Surface and Bottom Layers

According to the investigation data of Jiaozhou Bay in 1992, the vertical distribution, horizontal distribution and seasonal variation of Cd in the surface and bottom waters from the center of the bay to the south of the mouth of Jiaozhou Bay are studied, and the seasonal distribution, range of distribution and horizontal distribution trend are determined. The results show that in May, August and October, in the waters from southern mouth to the center of the bay, the Cd content of surface and bottom waters ranged from 0.12-1.19μg/L, in line with the national water quality standards for Class I and Class II seawater, which indicates that water quality was slightly polluted by the Cd content orwas not polluted. The surface levels of Cd vary seasonally from low to high: spring, summer, and fall, the same was true for Cd seasonal variation in bottom waters. In the surface and bottom waters of Jiaozhou Bay from the south of the bay mouth to the center of the bay, in May, August and October, when the Cd content in surface waters was relatively low, and the corresponding bottom layer was relatively low; when the Cd in surface waterswas relatively high, the corresponding bottom layer was relatively high; this shows that the loss of Cd content both from the surface and the bottom was relatively high. In May, August and October, in the waters from the southeast of the bay to the center of the bay, the horizontal distribution of Cd in the surface and the bottom waters have an opposite trend. From May to October, the seasonal variation of Cd content in surface waters in the southeast of the bay was mainly affected by the Cd content transported by main sea currents, while the bottom waters are mainly affected by river-transported Cd content. From May to October, in the central waters of Jiaozhou Bay, the seasonal changes of surface and bottom Cd content are not consistent withthat of Cd content transported by main sea currents. On the temporal scale, in the waters of Jiaozhou Bay from the south of the bay to the center of the bay, in May, August and October, the Cd content in the surface and bottom watersvariateswithin the same range, maintaining the consistency. On the spatial scale, in the waters from the southeast of the bay to the center of the bay, in May, August and October, according to the comparison between the Cd content transported by main sea currents and that transported by rivers, it can be proved that the horizontal distribution of Cd content in the surface waters was opposite to that of in the bottom waters.

Potential CCP Pulsed Plasma Application at Beol AIO Etch Process

Plasma etching has been extensively used for more than 30 years in semiconductor manufacturing industry [1]. Typically, plasma reactor RF power sources have constant average power to excite the plasma in a vacuum chamber. Such mode of operation is termed as continuous-wave (CW) RF mode [2]. As COMS is being scaled down to 28nm node and beyond, CW plasmas etching processes are reaching their limits to satisfy the multiply stringent requirements, such as better uniformity, higher selectivity, less plasma induced damage, tighter critical dimension and profile control. The RF pulsed plasma is one of promising knobs to increase the flexibility of plasma processing by enlarging the range of operating conditions [3-5]. There are two main parameters characterizing the RF pulse: one is the pulsed frequency at which the RF power is turned on and off per second; the other is the pulse duty cycle, which is defined as the ratio between the pulse on time and the total pulse duration. As the multiple-frequency RF powers have been introduced for the better control plasma flux and energy in CCP system, the effect of different RF power pulsing varies, bias only, source only and synchronized pulsed plasmas also shows quite different performances. In this work, self-aligned via (SAV) based all-in-one (AIO) etch processes were performed in one commercial etcher, and the effects of pulsed plasmas on the etch process were analyzed. The different pulsed mode, pulsed duty cycle, pulsed frequency on CCP chamber were tested on the SAV based AIO etching process in BEOL copper interconnect system. We compared the bias only, source only and synchronized pulsed plasma performances, checked the duty cycle effects, which varies from 10% to 90%. The Physical performances were analyzed by CDSEM, SEM, TEM, and TK. Compared with conventional CW plasmas, the performances of AIO etching process could be significantly improved via pulsed plasma, such as more rounding chamfer profile, via bottom CD control, and better SAC process with higher selectivity to metal hard mask. Acknowledgement This work is sponsored by Shanghai Rising-Star Program (B type). REFERENCES [1] S. Banna, A. Agarwal, G. Cunge, M. Darnon, E. Pargon, and O. Joubert. J. Vac. Sci. Technol. A, vol. 30, 2012, pp. 040801. [2] S. Banna, A. Agarwal, K. Tokashiki, H. Cho, S. Rauf, V. Todorow, K. Ramaswamy, K. Collins, P. Stout, J. Y. Lee, J. Yoon, K. Shin, S. J. Choi, H. S. Cho, H. J. Kim, C. H. Lee, and D. Lymberopoulos. IEEE Trans. Plasma Sci., vol. 37, 2009, pp. 1730-1746. [3] R. W. Boswell and D. Henry. Appl. Phys. Lett., vol. 47, 1985, pp. 1095-1097. [4] P. Subramonium and M. J. Kushner. Appl. Phys. Lett., vol. 79, 2001, pp. 2145-2147. [5] A. Rousseau, E. Teboul, N. Lang, M. Hannemann, and J. Ropcke. J. Appl. Phys., vol. 92, 2002, pp. 3463-3471.

Heavy Metal Contents of Fly Ashes from Selected Biomass Samples

In this study, heavy metal levels in selected fly ash samples of various biomass types (municipal solid waste, hazelnut shell, wheat straw, olive husk, walnut shell, almond shell, sunflower shell, and beech wood) were determined. The concentrations of Zn, Pb, Cd, Mn, Cr, Ni, Co, Cu, Sn, Sb, Se, V, Mo, and As metals were determined in the fly ash samples. Chemical analyses of biomass fly ashes showed that they were mainly composed of SiO 2 , CaO, K 2 O, and Al 2 O 3 . The highest heavy metal levels were found in MSW fly ash. The fly ash from beech wood has generally higher As, Cd, Pb, and Hg contents than those of agricultural residues. Compared with bottom ash, Pb and Cd concentrations in fly ash were 10–20 times higher. The fly ash samples from beech wood and hazelnut shell have aerosol particles of more than 30 and 10%, respectively.

Bed Drag Coefficient Variability under Wind Waves in a Tidal Estuary

In this paper we report the results of a study of the variation of shear stress and the bottom drag coefficient CD with sea state and currents at a shallow site in San Francisco Bay. We compare shear stresses calculated from turbulent velocity measurements with the model of Styles and Glenn reported in 2000. Although this model was formulated to predict shear stress under ocean swell on the continental shelf, results from our experiments show that it accurately predicts these bottom stress under wind waves in an estuary. Higher up in the water column, the steady wind-driven boundary layer at the free surface overlaps with the steady bottom boundary layer. By calculating the wind stress at the surface and assuming a linear variation of shear between the bed and surface, however, the model can be extended to predict water column shear stresses that agree well with data. Despite the fidelity of the model, an examination of the observed stresses deduced using different wave-turbulence decomposition schemes suggests that wave-turbulence interactions are im- portant, enhancing turbulent shear stresses at wave frequencies.

Model simulations of the Gulf of Maine response to storm forcing

The storm response of the Gulf of Maine/Georges Bank region was investigated using the Dartmouth three‐dimensional, nonlinear, finite element coastal ocean circulation model called QUODDY, with uniform density and quadratic bottom stress. A suite of model hindcast experiments were conducted for the 4–8 February 1987 period that featured a strong nor'easter. The model was forced at the open ocean boundaries by the M2 semidiurnal tidal sea level and in the interior by realistic surface wind stresses and, in some cases, atmospheric pressure. The reference model run, with just tidal and wind stress forcing and a time‐space constant bottom drag coefficient Cd of 0.005, captured 65% of the observed detided, low‐pass filtered or “subtidal” sea level variance of a representative array of coastal and bottom pressure stations in the Gulf. However, there remained large unexplained model/observed sea level differences, particularly during the storm. Model sensitivity testing to a realistic range of constant Cd values did not improve model results significantly. However, results of a model run in which atmospheric pressure forcing, derived through linear interpolations of regional measurements, was added to wind stress forcing captured 82% of the observed subtidal sea level variance.

BED DRAG COEFFICIENT VARIABILITY IN A TIDAL ESTUARY: FIELD MEASUREMENTS AND NUMERICAL MODELING

In this paper, we report the results of a study of the variation of shear stress and the bottom drag coefficient CD with sea state and currents at a shallow site in San Francisco Bay. Via field experiments, we find that themodel of Styles & Glenn, though formulated to predict CD and shear stress under ocean swell on the continental shelf, accurately predicts enhanced drag and mean stress under wind waves in an estuary, albeit only very close tothe bed. Higher up in the water column, the steady wind-driven boundary layer at the free surface overlaps with the steady bottom boundary layer, and this overlap needs to be accounted for to accurately model shear stress.Applying the enhanced CD of Styles & Glenn to the estuarine circulation model TRIM-3D of Gross et al and Inagaki et al, we find that enhanced drag under wind waves rctards the flushing of contaminants and sediment in South San Francisco Bay, and it enhances channel-shoal asymmetry.

Tide-Induced Sediment Resuspension and the Bottom Boundary Layer in an Idealized Estuary with a Muddy Bed

Abstract Sediment transport and bottom boundary layer (BBL) in an idealized estuary with a muddy bed were studied by numerical simulations. The focus was placed on description and prediction of the dynamics of nepheloid layer (a fluid–mud layer) developed in the estuary because of the coupling effect of the seawater and resuspended sediment concentration. The Princeton Ocean Model was coupled to a sediment transport model to conduct the numerical experiments. A semidiurnal tide with a spring–neap cycle was used to force the model at the estuary entrance. A stability function was introduced to the bottom drag coefficient Cd for a slip bottom boundary condition in order to consider the effects of sediment-induced stratification. When the seawater density is not affected by the resuspended sediments, spring tides resuspend sediments to the sea surface near the estuary entrance where the bottom stress is larger than the critical stress value. The sediment distribution in the BBL near the entrance is dominantl...

Microhabitat effects on Cd/Ca and δ13C of benthic foraminifera

Cd/Ca and δ13C were measured on bottom and pore water samples, and samples comprising dead individuals of six species of benthic foraminifera, including Cibicidoides wuellerstorfi, Uvigerina peregrina and Melonis barleeanum, from throughout the sediment mixed layer at three well-characterised sites in the Northeastern Atlantic. ‘Living’ (i.e., Rose Bengal stained) U. peregrina and M. barleeanum from one of the three sites were also analysed. Co-existing living and dead foraminifera of the same species from the same site have similar Cd/Ca and δ13C, and show no significant down core variability. Therefore, comparison of δ13C in foraminifera with bottom water and pore waters was used to estimate average calcification depths within the sediment for each species and thereby determine DCd based on the Cd concentrations at these depths. Pore waters are 2–4 times more enriched in Cd than bottom waters; consequently, DCd values are different from estimates based on bottom water Cd. Results give DCd of ∼1 for all the infaunal species, with no significant water depth dependence. DCd for C. wuellerstorfi based on bottom water Cd are 3.2±1.1 at 3600 m water depth and 3.9±1.3 at 1900 m water depth, being consistent with DCd estimated from culture experiments. The results suggest that the depth dependence of DCd based on bottom water Cd may be partly explained by a pore water influence on the test chemistry for infaunal species.

Last Glacial Maximum paleochemistry and deepwater circulation in the Southern Ocean: Evidence from foraminiferal cadmium

South Atlantic benthic foraminiferal Cd/Ca shows no glacial‐interglacial variation, suggesting that the glacial contribution of North Atlantic Deep Water to the Southern Ocean was not much different than at present. In contrast, Cd/Ca in southeast Indian Ridge cores show lower glacial bottom water Cd, comparable to levels in intermediate depths of the North Atlantic and significantly lower than in the deep South Atlantic. Low glacial Cd/Ca was also recorded in planktonic foraminifera, suggesting a substantial decrease in the nutrient concentration of Subantarctic surface water during the glacial maximum which most likely was caused by increased biological productivity. The Cd data are inconsistent with low glacial benthic foraminiferal δ13C which suggest higher nutrient concentration. We propose that the low Cd/Ca in the Southeast Indian Ridge records reflects a local source of nutrient‐depleted deepwater, formed during the last glacial maximum by open‐ocean convection near the Antarctic Polar Front, downstream of the Kerguelene Plateau. If this source was limited to the southeast Indian basin then its impact on the overall chemistry of glacial Circumpolar Deepwater was rather small. However, if during glaciations open‐ocean convection became the dominant mode of bottom water formation, it might have had a greater impact on CPDW chemistry.

Evidence of a dissolution effect on benthic foraminiferal shell chemistry: δ13C, Cd/Ca, Ba/Ca, and Sr/Ca results from the Ontong Java Plateau

Core‐top benthic foraminifera (Cibicidoides wuellerstorfi) from a depth transect of Soutar box cores from the Ontong‐Java Plateau (1.6–4.4 km) were analyzed for cadmium, barium, and strontium (Cd/Ca, Ba/Ca, and Sr/Ca) and for their stable isotopic composition (δ13C and δ18O). We also measured bottom water δ13C, Cd, and Ba at these sites. Foraminiferal δ13C values remain roughly constant over the entire depth range while bottom water δ13C values increase slightly, such that the δ13C difference between C. wuellerstorfi and bottom water ranges from about +0.2 ‰ in cores above 2.5 km to about −0.2 ‰ in cores below 4 km. This apparent depth dependence has not been previously reported, but this range in Δδ13C values is comparable to the uncertainty in published δ13C calibration studies. We observe strong decreases in foraminiferal Cd/Ca, Ba/Ca, and Sr/Ca ratios (50, 25, and 15 percent, respectively) at water depths greater than about 2.5 km. These decreases are substantially larger than the corresponding changes in bottom water trace element concentrations, and they are not correlated with variations in pore water Cd and Ba concentrations at these sites. Together, the foraminiferal and bottom water Cd/Ca, Ba/Ca, and Sr/Ca data yield decreases in the apparent distribution coefficients for these metals into calcite with increasing water depth, again a pattern which has not been previously reported. These results when combined with the data from published core‐top calibration studies suggest that a preferential loss of Cd, Ba, and Sr occurs during the dissolution of benthic foraminiferal calcite on the sea floor and raise the possibility of a dissolution‐driven decrease in benthic foraminiferal δ13C values.