Characterization of advanced etching reactors using novel diagnostic tools

Plasma etching equipment used for sub-micron integrated circuit fabrication at present are exclusively based on 13.56 MHz, capacitively coupled, parallel-plate geometry. The underlying mechanisms of plasma processes in these reactors are not well understood and there is even less understanding of how the etch-tool parameters relate to the plasma discharge characteristics which actually determine the etch process. In this thesis, new diagnostic techniques were applied for the characterization and optimization of plasma etching processes in various reactor configurations. Specifically, diode and triode configurations were studied extensively using tuned scanning Langmuir probes. Both radial and axial distributions of plasma density were measured for a range of process parameters. Extensive mapping of plasma region in these reactors have shown that the plasma density distribution is dramatically different for dissociative molecular etching gases as compared to inert gases. Furthermore, the density distribution was found to be strongly dependent on the electronegativity of the process gas. In the triode configuration, the relative phase between the RF voltage waveforms applied to the electrodes was found to determine both the magnitude and distribution of the plasma density. Typically, higher etch-rates and better etch-uniformity were obtained for out-of-phase excitation(180°) as compared with the in-phase excitation(0°) in the triode. The understanding gained by these studies has lead to the development of a novel magnetic multipole based triode reactor configuration. This new reactor configuration can be operated at low pressures and produces high-rate, low damage etching of submicron features with required profile control. In addition, a new plasma etching diagnostic technique based on thermal imaging of wafer was developed. The technique has been found to be useful for in situ real-time monitoring of end-point and uniformity of etching as well as for inferring wafer temperature and heat transfer characteristics. Also, a simple end-point detection technique based on plasma impedance monitoring was developed which eliminates the need for optical access to the wafer/plasma

Efficient methods for enol phosphate synthesis using carbon-centred magnesium bases

Efficient conversion of ketones into kinetic enol phosphates under mild and accessible conditions has been realised using the developed methods with di-tert-butylmagnesium and bismesitylmagnesium. Optimisation of the quench protocol resulted in high yields of enol phosphates from a range of cyclohexanones and aryl methyl ketones, with tolerance of a range of additional functional units

A simple shear deformation theory for nonlocal beams

In this paper, a simple beam theory accounting for shear deformation effects with one unknown is proposed for static bending and free vibration analysis of isotropic nanobeams. The size-dependent behaviour is captured by using the nonlocal differential constitutive relations of Eringen. The governing equation of the present beam theory is obtained by using equilibrium equations of elasticity theory. The present theory has strong similarities with nonlocal Euler–Bernoulli beam theory in terms of the governing equation and boundary conditions. Analytical solutions for static bending and free vibration are derived for nonlocal beams with various types of boundary conditions. Verification studies indicate that the present theory is not only more accurate than Euler–Bernoulli beam theory, but also comparable with Timoshenko beam theory

Numerical study of circular double-skin concrete-filled aluminum tubular stub columns

The sandwiched concrete in a circular double-skin concrete-filled aluminum tubular (DCFAT) column is subjected to the lateral confinement from inner and outer aluminum tubes. The effects of double-skin confinement have not been considered in the existing numerical models for the analysis of DCFAT stub columns. This paper describes a numerical model for the simulation of concentrically compressed circular DCFAT short columns. The numerical model is developed using the fiber element methodology. A new expression for determining the lateral confining pressures on the sandwiched concrete in circular DCFAT stub columns is proposed based on experimental results and incorporated in the computational technique. The stress-strain relations for determining the material performance of aluminum and confined sandwiched concrete are described. The numerical model is validated through comparisons with the experimental results of circular DCFAT stub columns. The numerical predictions correlate well with the tested column results, especially the aluminum stress-strain responses, load-strain responses, and ultimate axial load. A parametric study is performed to ascertain the influences of geometric and material variables on the behavior of DCFAT stub columns. The numerical results reveal that the use of aluminum instead of steel in a composite column could reduce the column weight by about 22.5%. The comparison of experimental results with the ultimate loads obtained by the design approaches specified in AISC 360-16, Eurocode 4, and Liang\u27s design model indicates that the codified methods generally either underestimate or overestimate the strengths of DCFAT columns, and Liang\u27s design model gives accurate predictions

Nonlinear analysis of circular high strength concrete-filled stainless steel tubular slender beam-columns

Concrete-filled stainless steel tubular (CFSST) slender columns are increasingly used in composite structures owing to their distinguished features, such as aesthetic appearance, high corrosion resistance, high durability and ease of maintenance. Currently, however, there is a lack of an accurate and efficient numerical model that can be utilized to determine the performance of circular CFSST slender columns. This paper describes a nonlinear fiber-based model proposed for computing the deflection and axial load-moment strength interaction responses of eccentrically loaded circular high-strength CFSST slender columns. The fiber-based model incorporates the accurate three-stage stress-strain relations of stainless steels, accounting for different strain hardening characteristics in tension and compression. The material and geometric nonlinearities as well as concrete confinement are included in the computational procedures. Existing experimental results on axially loaded CFSST slender columns are utilized to verify the proposed fiber-based model. A parametric study is conducted to examine the performance of high-strength slender CFSST beam-columns with various geometric and material parameters. It is shown that the fiber-based analysis technique developed can accurately capture the experimentally observed performance of circular high-strength CFSST slender columns. The results obtained indicate that increasing the eccentricity ratio, column slenderness ratio and diameter-to-thickness ratio remarkably decreases the initial flexural stiffness and ultimate axial strength of CFSST columns, but considerably increases their displacement ductility. Moreover, an increase in concrete compressive strength increases the flexural stiffness and ultimate axial strength of CFSST columns; however, it decreases their ductility. Furthermore, the ultimate axial strength of CFST slender columns is found to increase by using stainless steel tubes with higher proof stresses

Nonlinear analysis of biaxially loaded rectangular concrete-filled stainless steel tubular slender beam-columns

Rectangular concrete-filled stainless steel tubular (CFSST) beam-columns utilized as supporting members for building frames may experience axial compression and biaxial moments. A numerical simulation considering the local buckling effects for thin-walled rectangular CFSST slender beam-columns has not been performed. This paper reports a stability modeling on the structural characteristics of rectangular CFSST slender beam-columns accounting for different strain-hardening of stainless steel under tension and compression. The influences of local buckling are considered in the simulation utilizing the existing effective width formulations. The developed numerical model simulates the strength interaction and load-deflection behavior of CFSST slender beam-columns. Comparisons of computed results with test data provided by experimental investigations are performed to validate the proposed fiber model. The influences of different geometric and material property on ultimate strengths, ultimate pure moments, concrete contribution ratio, strength interaction and load-deflection responses of CFSST slender beam-columns are examined by utilizing fiber model. A design formula considering strain hardening of stainless steel is derived for calculating the ultimate pure moment of square CFSST beam-columns

Nonlinear analysis of rectangular concrete-filled double steel tubular short columns incorporating local buckling

Rectangular concrete-filled double steel tubular (CFDST) columns with inner circular steel tube possess higher structural performance than conventional concrete-filled steel tubular (CFST) columns. However, the local buckling of the outer steel tube of thin-walled rectangular CFDST columns has not been accounted for in the existing fiber element models and design codes that may overestimate the column ultimate axial strengths. This paper describes a computationally efficient fiber-based modeling technique developed for determining the behavior of concentrically-loaded rectangular CFDST short columns including the local buckling effects of the external steel tube and the confinement offered by the internal circular steel tube. The effective width concept is used to simulate the post-local buckling of the outer steel tube. Comparative studies are undertaken to verify the fiber-based model with the relevant test results. The computational model is then employed to investigate the axial load-strain responses of rectangular CFDST short columns with various key design variables. A design equation is developed for computing the ultimate axial loads of short rectangular CFDST columns and compared with design methods given in several international design codes. It is shown that the fiber-based modeling technique and the proposed design model predict well the structural performance of short CFDST columns

Inelastic analysis of octagonal concrete-filled steel tubular short columns under eccentric loading

Octagonal concrete‐filled steel tubular (OCFST) columns combine the benefits of circular and square concrete‐filled steel tubular (CFST) columns so that they not only possess higher strength and ductility but also provide the ease of connection to composite beams. However, research studies have been very limited on the performance analysis of OCFST short beam‐columns subjected to eccentric loading. In this study, a fiber‐based numerical model is developed for the performance simulation of high‐strength OCFST short beam‐columns under eccentric loading. The simulation model takes into account material nonlinearities and concrete confinement induced by the octagonal steel tube. Computational methods are given that predict the axial load–moment interaction curves and moment–curvature responses of OCFST beam‐columns. The developed fiber model is verified against available test data with good accuracy. The influences of important parameters on the responses of high‐strength OCFST short beam‐columns are studied by means of utilizing the computational model. It is found that the behavior of OCFST beam‐columns is significantly influenced by the diameter‐to‐thickness ratio of the cross‐section, concrete strength, steel yield stress, and axial load ratio. Interaction equations are proposed for expressing the axial load–moment strength envelopes of the cross‐sections of OCFST beam‐columns and validated against numerical results