An experimental investigation into soft-pad grinding of wire-sawn silicon wafers

Silicon is the primary semiconductor material used to fabricate microchips. A series of processes are required to manufacture high-quality silicon wafers. Surface grinding is one of the processes used to flatten wire-sawn wafers. A major issue in grinding of wire-sawn wafers is reduction and elimination of wire-sawing induced waviness. Results of finite element analysis have shown that soft-pad grinding is very effective in reducing the waviness. This paper presents an experimental investigation into soft-pad grinding of wire-sawn silicon wafers. Wire-sawn wafers from a same silicon ingot were used for the study to ensure that these wafers have similar waviness. These wafers were ground using two different soft pads. As a comparison, some wafers were also ground on a rigid chuck. Effectiveness of soft-pad grinding in removing waviness has been clearly demonstrated.     

Fine grinding of silicon wafers: a mathematical model for the chuck shape

Fine grinding of silicon wafers is a patented technology to manufacture super flat semiconductor wafers cost-effectively. Two papers on fine grinding were previously published in this journal, one discussed its uniqueness and special requirements, and the other presented the results of a designed experimental investigation. As a follow up, this paper presents a study aiming at overcoming one of the technical barriers that have hindered the widespread application of this technology, namely, the difficulty and uncertainty in chuck preparation. Although the chuck shape is critically important in fine grinding, there are no standard procedures for its preparation. Furthermore, the information on the relation between the set-up parameters and the resulting chuck shape is not readily available. In this paper, a mathematical model for the chuck shape is first developed. Then the model is used to predict the relations between the chuck shape and the set-up parameters. Finally, the results of the pilot experiments to verify the model are discussed.     

Fine grinding of silicon wafers: a mathematical model for grinding marks

The majority of today’s integrated circuits are constructed on silicon wafers. Fine-grinding process has great potential to improve wafer quality at a low cost. Three papers on fine grinding were previously published in this journal. The first paper discussed its uniqueness and special requirements. The second one presented the results of a designed experimental investigation. The third paper developed a mathematical model for the chuck shape, addressing one of the technical barriers that have hindered the widespread application of this technology: difficulty and uncertainty in chuck preparation. As a follow up, this paper addresses another technical barrier: lack of understanding on grinding marks. A mathematical model to predict the locus of the grinding lines and the distance between two adjacent grinding lines is first developed. With the developed model, the relationships between grinding marks and various process parameters (wheel rotational speed, chuck rotational speed, and wheel diameter) are then discussed. Finally, results of pilot experiments to verify the model are discussed.     

Esophageal atresia and tracheoesophageal fistula: success and failure rates in the United Arab Emirates

Randomized, prospective trials examining the effectiveness of carotid endarterectomy have given distinct information into the mechanisms and prevention of embolic strokes. The North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the Asymptomatic Carotid Atherosclerosis Study (ACAS) have demonstrated the benefits of carotid endarterectomy for patients who meet the precise selection criteria and are treated according to established study protocols. The existing challenge to clinicians lies in the application of trial results to the individual patient.     

Damage Field Ahead of a Tensile Crack in an Elastic-Plastic and Viscoplastic Material

This paper investigates the interaction between a macroscopic crack and microscopic damage in an elastic-plastic and viscoplastic material subjected to tensile in-plane loading. The aim is to predict the fracture conditions by accounting for void accumulation in the vicinity of the crack-tip. A power law relates the stress to the strain of the material. The damage, which invokes the growth and coalescence of microvoids, is confined to a small circular zone surrounding the crack-tip. At the onset of crack extension, the applied stress for small-scale and large-scale yielding solutions is found to be proportional to a₀ ^-1/(n+1), where 2a₀is the initial crack length and n is the strain hardening exponent of the material. For small-scale yielding, the conditions required for fatigue crack growth and steady-state creep are determined. In particular, the variations of the normalized crack length with the number of loading cycles and the time required for failure are shown for various strain hardening exponents, applied loading, and material damage parameters. This revised version was published online in July 2006 with corrections to the Cover Date.     

Efficient initiation of S-phase in yeast requires Cdc40p, a protein involved in pre-mRNA splicing

The S. cerevisiae CDC40 gene was originally identified as a cell-division-specific gene that is essential only at elevated temperatures. Cells carrying mutations in this gene arrest with a large bud and a single nucleus with duplicated DNA content. Cdc40p is also required for spindle establishment or maintenance. Sequence analysis reveals that CDC40 is identical to PRP17, a gene involved in pre-mRNA splicing. In this paper, we show that Cdc40p is required at all temperatures for efficient entry into S-phase and that cell cycle arrest associated with cdc40 mutations is independent of all the known checkpoint mechanisms. Using immunofluorescence, we show that Cdc40p is localized to the nuclear membrane, weakly associated with the nuclear pore. Our results point to a link between cell cycle progression, pre-mRNA splicing, and mRNA export.     

Qualitative vision-based navigation based on sloped funnel lane concept

Intelligent Service Robotics - Funnel lane is a map-less visual navigation technique that tries qualitatively to follow a path that has been recorded before by a camera. Unlike some other methods,...     

A note on the twisting deformation of a non-homogeneous shaft containing a circular crack

A closed form solution is obtained, within the limitations of the theory of elasticity of non-homogeneous solids, for a cylindrical bar containing a penny-shaped crack and subjected to torsional loads only. The material of the solid is assumed to possess a shear modulus which is a power function of the space coordinate normal to the crack plane. The singular stress field arising at the rim of the crack is studied in detail and some physical results which are relevant in the application of the Griffith-Irwin theory of fracture are derived.     

Novel synthetic inhibitors of selectin-mediated cell adhesion: synthesis of 1,6-bis[3-(3-carboxymethylphenyl)-4-(2-alpha-D- mannopyranosyloxy)phenyl]hexane (TBC1269)

Reports of a high-affinity ligand for E-selectin, sialyl di-Lewis(x) (sLe(x)Le(x), 1), motivated us to incorporate modifications to previously reported biphenyl-based inhibitors that would provide additional interactions with the protein. These compounds were assayed for the ability to inhibit the binding of sialyl Lewis(x) (sLe(x), 2) bearing HL-60 cells to E-, P-, and L-selectin fusion proteins. We report that dimeric or trimeric compounds containing multiple components of simple nonoligosaccharide selectin antagonists inhibit sLe(x)-dependent binding with significantly enhanced potency over the monomeric compound. The enhanced potency is consistent with additional binding interactions within a single selectin lectin domain; however, multivalent interaction with multiple lectin domains as a possible alternative cannot be ruled out. Compound 15e (TBC1269) showed optimal in vitro activity from this class of antagonists and is currently under development for use in the treatment of asthma.