Study of the step coverage and contact resistance by using two-step TiN barrier and evolve simulation

Device aspect ratios and dimensions at the contact and via levels for old and new technologies are driving PVD/WCVD-based metallization to its full limit at integrated circuits (ICs) fabrication sites (Wilson et al., 1993). Contact and via This work describes the work performed at ST Microelectronics regarding the TiN barrier film properties with respect to process variables. Single-step and dual-step TiN barrier processes were studied for contact and via step coverage profiles used for aluminum and tungsten plug technologies. Electrical contact resistance values were evaluated using single and dual step TiN barrier processes. EVOLVE, a topography simulation program was used to study the step coverages and deposited film profiles for single and dual steps TiN barrier processes. In this work we prove that dual step TiN barrier process is superior to single step TiN barrier process in terms of step coverage, current leakage, film stress and contact resistance values.     

Surface hardness behaviour of Ti-Al-Mo alloys

The microhardness characteristics of various micro-constituents formed in the Ti-Al-Mo alloys have been investigated. Four alloys having compositions, Ti-40Al-2Mo, Ti-42Al-2Mo, Ti-40Al-6Mo and Ti-42Al-6Mo, have been chosen for this purpose. All of these were heat treated at 1300°C and 1400°C for 1 h and water quenched. All the specimens after above heat treatments have displayed load independent Vickers hardness values (VHN) around 300 g of applied load. The average surface hardness characteristic of the alloys is largely found to be dictated by the phases that are present. The microstructural specific VHN values vary between 600 and 750. The indentation behaviour, however, is governed by the morphologies and length scales of microstructures. The most remarkable finding of the present study pertains to the formation of shear bands around the periphery of the indenter for a finer basket weave microstructure in the Ti-40Al-2Mo. The cluster of finely located slip steps was clearly seen. Such a report is lacking in literature in this class of alloys.     

Torsional Surface Waves in Nonhomogeneous Anisotropic Medium under Initial Stress

This paper studies the possibilities of propagation of torsional surface waves in nonhomogeneous anisotropic half-space under compressive initial stress. Two types of variations in nonhomogeneity, mainly hyperbolic and quadratic, have been discussed, and it is observed that in both cases the torsional surface wave will propagate in the media under consideration. The velocities of propagation have been computed and are presented in graphs. The study shows that for hyperbolic variation of nonhomogeneity, the increase of the anisotropic factor, increases the velocity of propagation, always keeping it more than that of shear wave in homogeneous medium. The presence of initial stress increases the velocity of propagation. In the case of quadratic variation it is found that the presence of initial stresses increases the velocity of propagation. The increase of anisotropy decreases the velocity, and the decrease in the nonhomogeneity factor increases the velocity, always keeping the velocity of torsional surface waves less than that of shear wave in the homogeneous medium.     

Elimination of current non-uniformity in carbon nanotube field emitters

Activation of abnormal emitting sites in Carbon Nano Tube (CNT) field emitters and their elimination is reported. CVD grown, patterned CNT was used as cathode for field emission studies. We encountered the problem of current non-uniformity in CNT cathode. This non-uniformity was attributed to abnormally active emitting sites during voltage ramp-up. The sudden increase in current resulted in region of positive slope in F–N curve, which can’t be explained by conventional F–N theory. Also the grown CNTs can be a mixture of metallic and semi conducting nature, which may cause deviation from the conventional F–N theory. We could eliminate abnormally active sites by electric field treatment, thereby increasing current uniformity and stability. The work is underway to understand the deviation in FN curve at high fields.     

Genesis of High Hardness in Hot-Rolled Coils of Cold Reducers’ Grade Steels

A significant quantity of cold-reducible hot-rolled (HR) coils is produced every year. These are basically low-carbon steels; however, the quality of HR coils with respect to cold reducibility had not been entirely satisfactory. The hardness of HR coil was generally higher (≥65 HR_B) than desirable for attaining satisfactory cold reducibility. A systematic study was, therefore, undertaken with the objective to control the hardness to ≤55 HR_B by modifying the existing chemistry, finish rolling temperature (FRT), and the coiling temperature (CT). To find the optimum conditions for lower hardness, trial rolling of slabs of cold reducers’ grade of selected chemistry was conducted under varied conditions. An assessment of hardness across the width and of the microstructure was carried out. The evolution of microstructure in the HR band at different locations from the edge of the strip and the genesis for the resulting hardness profile across the width of the HR coil were examined in detail. The influence of grain size on hardness was also analyzed. The paper outlines the role of finish rolling temperature, coiling temperature, chemistry, and grain size in restricting the hardness to values below 55 HR_B.     

An Artificial Neural Network (ANN) Model for Predicting Instability Regimes in Copper-Aluminum Alloys

Materials workability is one of the important aspects for any process design to achieve quality products. Identifying optimum process parameters like temperature, strain rate, and strain are normally done by trial and error. In recent years, processing maps are used in choosing these parameters for hot working of materials. Identification of these parameters requires certain high-level expertise as well as detailed microstructural evidences. In this study, using the available copper-aluminum alloy data, an Artificial Neural Network (ANN) model has been developed to classify the hot-working process parameters, like temperature, strain rate, flow stress for instability regime, directly from the corrected flow stress data without applying the Dynamic Materials Model (DMM). This model uses four compositions of Cu-Al system, ranging from 0.5% to 6% Aluminum. Details about the ANN architecture, and the training and testing of these models are explained. The results obtained using the ANN model are compared and validated with those obtained from the processing maps using DMM. It is further shown that even with smaller data set the development of an ANN model is possible as long as the data has some pattern in it.     

Biogas scrubbing, compression and storage: perspective and prospectus in Indian context

Biogas is a clean environment friendly fuel. Raw biogas contains about 55–65% methane (CH₄), 30–45% carbon dioxide (CO₂), traces of hydrogen sulfide (H₂S) and fractions of water vapours. Presently, it can be used only at the place where it is produced. There is a great need to make biogas transportable. This can be done by compressing the gas in cylinders which is possible only after removing its CO₂, H₂S and water vapour components. Pilot level trials to compress the biogas have been carried out by a number of earlier investigators working on the subject. This paper reviews the efforts made to improve the quality of biogas by scrubbing CO₂ and the results obtained. There is a lot of potential if biogas could be made viable as a transport vehicle fuel like CNG by compressing it and filling into cylinders after scrubbing and drying. Thus the need emerges for a unified approach for scrubbing, compressing and subsequent storage of biogas for wider applications.