New plating bath for electroless copper deposition on sputtered barrier layers

A new copper plating bath for electroless deposition directly on conductive copper-diffusion barrier layers has been developed. This plating bath can be operated at temperatures between 20 and 50°C and has good stability. High temperature processing allows for increased deposition rates and decreased specific resistivity values for the deposited copper films. Electroless Cu films deposited from this bath showed a conformal step coverage in high aspect ratio trenches and, therefore, are promising as seed layers for copper electroplating. The effect of the bath composition, activation procedure and processing temperature on the plating rate and morphology of the deposited copper has been studied and is presented here.     

Room temperature electroless plating copper seed layer process for damascene interlevel metal structures

Described in this paper is the development of a room temperature electroless copper seed layer deposition process on ultra-thin TiN barrier layers. This novel process is compatible with damascene interlevel metal structures for sub-0.18 micron ULSI processes. An optimum copper layer thickness of 50 nm and a deposition rate of 45 nm min⁻¹ was targeted and obtained. Atomic force microscopy (AFM) reveals that the non-uniformity of the seed layer is less than 10% of the film thickness, while four-point probe measurements indicate that the resistivity of the copper seed layer is less than 6 μΩ cm⁻¹. Secondary ion mass spectroscopy (SIMS) reveals that potential metallic contaminants such as sodium, potassium, calcium and magnesium ions do not penetrate the TiN barrier layer. Rutherford back scattering (RBS) indicates that the palladium concentration in the seed layer is approximately 1%, which is low enough to avoid wafer contamination and increased resistivity in the subsequent electroplated copper layer.     

The role of recreational hunting in the recovery and conservation of the wild turkey (Meleagris gallopavo spp.) in North America

The North American wild turkey was historically abundant in its ancestral range prior to European arrival on the continent. The dual factors of unregulated hunting and habitat loss reduced wild turkey populations to a fraction of their former abundance. Hunting organizations pushed for early legislation that paved the way for wild turkey conservation and restoration. First attempts at restoration were often based on release of pen-reared turkeys, and a great deal of time and money was spent on this unsuccessful approach. Advanced capture techniques allowed trap and transfer of wild turkeys to unoccupied habitat and began population restoration. With the aid of the hunter-founded National Wild Turkey Federation in 1986, a sophisticated system of state-to-state transfer was perfected. Aggressive trap and transfer programs over a thirty-year period restored wild turkeys in both the United States and Canada and by the early 2000s their numbers had recovered to near pre-colonial abundance.     

Preparation and composition of mesophyll,epidermis and fibre cell walls from leaves of perennial ryegrass (lolium perenne) and italian ryegrass (lolium multiflorum)

Cells of mesophyll, epidermis and residual fibrous material were obtained from leaves of Italian and perennial ryegrass harvested at different stages of maturity by mechanical disruption of leaf tissue. Mesophyll cells were selectively removed by filtration through 0.045 mm nylon mesh and remaining non-mesophyll cells centrifuged in metrizamide solutions (56–58% wt to vol.) of known density (1.308–1.329 g cm³ at 5°C) to obtain a pure epidermis cell fraction and a residual fibre fraction. Whole mesophyll cells contributed 63–72%, epidermis 12–15% and the fibre fraction 15–24% to the total leaf dry matter. Fibre values were higher in late-cut samples. Cell walls were prepared from mesophyll and epidermis cells by disruption and washing to remove cell contents. Fibre cells were judged free of cell contents and received no further treatment. Examination of cell wall preparations by light and electron microscopy showed that both mesophyll and epidermis preparations were essentially free from contaminating material. Mesophyll cell walls were uniformly thin (200 nm) while those of epidermis ranged from 2000–3000 nm at the outer face, thinning to 300 nm or less at the inner surface. An electron-light layer (cuticle) of approximately 200 nm thickness was present covering the outer face of the epidermis. The fibre fraction largely consisted of sclerenchyma, but contained, in addition, other vascular cells, detached annular rings and heavily silicified leaf hairs. Analysis of cell walls accounted for 85–90% of dry matter. Cellulose was the major component of all cell walls examined (approximately 40% of dry matter) with xylose residues accounting for a further 11% of mesophyll, 13.5–17.5% of epidermis and 21–25% of fibre cell walls. Arabinose was low in fibre cells but was present in much higher proportions in mesophyll and epidermis walls. The ratio of arabinose to xylose was approximately 1:1.5 for mesophyll, 1:2.5 for epidermis and 1:7.0 for the fibre fraction. The molar ratio acetyl to xylose remained fairly constant at 1:4 regardless of the grass, cell type or maturity of the sample. The uronic acid content of epidermis was higher than that in other cell types and showed an increase with increasing maturity of the grass, reaching over 9% in late-cut samples. Total phenolic material represented 2–3% of mesophyll and epidermis cell walls and 6% of fibre walls. Ferulic acid alone was released from the primary cell walls by saponification and p-coumaric and ferulic acids from the secondary-thickened fibre walls. Crude protein values (NX6.25) were high in mesophyll cell wall preparations and low in epidermis and fibre cell walls. Amino acid patterns were similar for both grasses and cell types but hydroxyproline was found in greater amounts in fibre cell walls than in either epidermis or mesophyll.     

Evaluation of Canning Quality Traits in Black Beans (Phaseolus vulgaris L.) by Visible/Near-Infrared Spectroscopy

Black bean (Phaseolus vulgaris L.) processing presents unique challenges because of discoloration, breakage, development of undesirable textures, and off-flavors during canning and storage. These quality issues strongly affect processing standards and consumer acceptance for beans. In this research, visible and near-infrared (Vis/NIR) reflectance data for the spectral region of 400–2,500 nm were acquired from intact dry beans for predicting five canning quality traits, i.e., hydration coefficient (HC), visual appearance (APP) and color (COL), washed drained coefficient (WDC), and texture (TXT), using partial least squares regression (PLSR). A total of 471 bean samples harvested and canned in 2010, 2011, and 2012 were used for analysis. PLSR models based on the Vis/NIR data showed low predictive performance, as measured by correlation coefficient for prediction (R _pred) for APP (R _pred?=?0.275–0.566) and TXT (R _pred?=?0.270–0.681), but better results for predicting HC (R _pred?=?0.517–0.810), WDC (R _pred?=?0.420–0.796), and COL (R _pred?<?0.533–0.758). In comparison, color measurements from a colorimeter on drained canned beans showed consistently good predictions for COL (R _pred?=?0.796–0.907). In spite of the low or relatively poor agreement among the sensory panelists as determined by multirater Kappa analysis (K _free of 0.20 for APP and 0.18 for COL), a linear discriminant model using the Vis/NIR data was able to classify the canned bean samples into two sensory quality categories of “acceptable” and “unacceptable”, based on panelists’ ratings for APP and COL traits of canning beans, with classification accuracies of 72.6 % or higher. While Vis/NIR technique has the potential for assessing bean canning quality from intact dry beans, improvements in sensing and instrumentation are needed in order to meet the application requirements.