No description available.

No description available.

No description available.

Czochralski (Cz) silicon wafers are used almost exclusively for the fabrication of VLSI devices. Such silicon contains excess oxygen which precipitates as oxide particles either when the initial ingot is grown or subsequently during the wafer device fabrication. Such oxide particles can produce reduced device performance or failure if they occur within the active device regions. However, they can be used to improve the device performance by a process known as internal oxide gettering. The wafers are given a series of preanneal treatments to produce controlled precipitation in which a surface zone of the wafer to a depth of typically in the range of 10 to 50 μm is denuded of oxide particles, while the remainder of the wafer contains large numbers of well formed particles. The devices are fabricated in the surface denuded zone and harmful contaminating metal impurities are attracted during the heat treatment stages away from the device regions to precipitate at the underlying oxide particles or their associated dislocations. In this way device yields can be significantly increased. Because of the importance of these oxide particles and the oxygen precipitation process for VLSI fabrication, considerable efforts have been made to develop methods to assess the numbers and distributions of such particles within the wafers. The number density range of most interest is 10⁷ to 10¹⁰ cm^-3, and the particle size range is typically 30 to 300 nm. The method that has mostly been used is surface etching followed by optical microscopy to obtain etch pit densities. Transmission electron microscopy is a research method used for obtaining detailed information concerning a small number of individual particles. However, because these methods are destructive, much attention has been given during the last few years to the development of infra-red microscopy methods to directly image the particles within the silicon wafers. Although the particles are smaller than the resolution of these methods, individual particles can nevertheless be imaged. This is because the particles are mostly further apart than the resolution limit, and the sensitivity can be sufficient high that adequate contrast occurs. The contrast arises from scattering or absorption of the light by the particle. Infra-red imaging methods developed include infra-red microscopy (IRM), laser scattering tomography (LST), optical precipitate profiler (OPP) and scanning infra-red microscopy (SIRM), all described more fully in Chapter 2. The SIRM has been developed and used to investigate a variety of semiconductor specimens in the Materials Department, Oxford University, during the last ten years. The SIRM has a good performance and flexibility making it especially suitable as a research instrument. Although all of these infra-red imaging methods have been successful to different degrees in assessing oxide particles in Cz silicon wafers, their performance has at least initially been assessed by comparing the number densities and distributions thus obtained with the corresponding results produced by etch pit studies. Furthermore, no serious attempt has yet been made to develop a rigorous theory of the imaging process and to compare the predictions with the experimental images. One of the main objectives of the present work is to do this or at least to make a significant start to such a project based on the SIRM. The outline of an ideal project which aims at a full understanding of the imaging process and the contrast mechanisms is as follows. The performance of the present Oxford SIRM should be improved and the number of imaging modes increased. The improved performance, i.e. better lateral and depth resolutions and higher sensitivity, would enable smaller particles and higher number densities to be imaged, and hence better quantitative data obtained. The larger number of imaging modes would enable the optimum method to be used to image different types of particle. A rigorous theory should be developed that can describe the imaging process and the contrast mechanisms. First, the illumination system should be studied, and in particular the structure of the focussed probe within the specimen and how the structure changes on focussing deeper into the specimen. Second, the interaction of the light with the specimen should be investigated and especially how light is scattered by individual oxide particles in silicon for the case of the particle size being smaller than the light wavelength. Third, the detection system should be considered. For example, for the reflection confocal SIRM, how the light back scattered by the particles is collected by the probe forming lens and imaged at a pin-hole aperture placed in the front of the detector. Well designed experiments are required to determine the imaging properties of the different modes and comparisons should be made between the experimental and theoretical data. The successful conclusion of such a project would enable SIRM images of the particles to be more fully interpreted and hence more detailed information obtained concerning the particles. Furthermore, the images expected from different types of particle could be more closely predicted, e.g. whether they are detectable or not, and hence materials projects could be better planned at the outset. In this thesis we describe the methods that are presently being used to assess oxide particles in bulk silicon (Chapter 2). We review the literature on scanning optical microscopy covering both visible and infra-red light, present some considerations regarding the design of a high performance and versatile SIRM, and describe the various microscope modes that have been or could be used to image particles in semiconductors with infra-red light (Chapter 3). We give a detailed rigorous theoretical analysis of the energy distributions in the probe for the case when the light is focussed by a high numerical aperture lens from air into silicon (Chapters 4, 5). Numerically computed distributions are obtained to illustrate how the probe changes under different conditions, e.g. different focussing depths (Chapter 6). The relationship between the penetration depth of the probe and the spherical aberration coefficient arising from the silicon specimen is determined (Chapter 7). The classical theory of light scattering is applied to individual spherical silicon dioxide particles embedded in silicon. Numerical results are presented and a contrast mechanism is proposed to describe how the scattered intensity depends on particle size (Chapter 8). A formal solution relevant to the reflection confocal SIRM is given to treat the backward propagation of light using a model which takes into account the polarisation state of the incident light, the spherical aberration introduced by the silicon wafer, the polarisation state of the scattered light and the size of the pin-hole (Chapter 9). Experimental results are obtained for most of the imaging modes described in Chapter 3, specimens being selected so that the wide range of the imaging capabilities of the SIRM is shown, and experimental contrast values are compared with theoretical values (Chapter 10). Finally, overall conclusions are drawn and suggestions are made for completing the work started here (Chapter 11).

A novel geometry for powder X-ray diffraction (XRD), termed ‘focal construct geometry’ (FCG) is introduced and developed with both non-ideal samples and non-ideal sample conditions. FCG utilises an annular beam that has the unique feature of ‘focusing’ scattering maxima at single loci along a primary axis, hence offering diffraction data of enhanced intensity. This main advantage of FCG can be used within fields in need of rapid material identification, such as security screening in airports. A theoretical comparison between FCG and conventional transmission mode XRD showed that even though FCG suffers from broader diffraction peaks, an alternative approach to FCG data interpretation has the potential to provide narrower scattering maxima than conventional XRD. However, in order to employ this approach, discrimination between converging and diverging FCG scattering maxima is essential. Peak broadening was investigated by altering various aspects of FCG instrumentation components by either pencil beam XRD or FCG, indicating broad diffraction peaks independent of the beam geometry employed. Development of FCG resulted in the successful analysis of non-ideal samples, such as non-crystalline liquid samples, samples exhibiting preferred orientation and samples with large grain size, demonstrating advantages over conventional XRD. Furthermore, ideal samples (in terms of crystallinity, preferred orientation and grain size) were analysed by FCG under non-ideal conditions. This involved randomly orientating a single planar sample with respect to the primary axis, contrary to previous research that present FCG with a single planar sample normal to the primary axis. Sample rotation resulted in FCG scattering maxima with different xyz coordinates depending on the degree, axis and direction of rotation. Moreover, FCG analysis of multiple samples (normal to the primary axis) showed that as with all XRD arrangements, a priori knowledge of the samples’ position along the primary axis is required for effective data analysis. Investigation into the ability of FCG’s annular beam to act as a pre-sample coded aperture demonstrated an alternative method to interpret FCG images by recovering conventional XRD data. Additionally, two novel post-sample encoders (linear wire and Archimedean spiral) were considered. This enabled spatial discrimination of unknown samples along a primary axis and material identification for conventional XRD techniques. Combination of FCG with an absorbing edge post-sample encoder indicated discrimination between converging and diverging FCG scattering maxima. This ability can enable interpretation of single FCG images, as well as depth information of unknown samples within an inspection volume (e.g. airport luggage), hence enabling material identification. / © Cranfield University 2014

This thesis present photoluminescence spectroscopy and X-ray diffraction analyses of four different cadmium zinc telluride samples with different quality and features and similar zinc molar concentration of 10%. Photoluminescence spectroscopy of the samples let us obtain several physical parameters of the samples which are indicators of quality, composition, structure, and impurity levels of the samples. The band gap energy of the samples obtained from the photoluminescence spectra at low temperatures helped us to estimate zinc molar concentration of the samples. Temperature dependence of band gap energy in these samples has been analyzed and exciton-LO phonon interactions in the samples has been analyzed. From temperature dependence of full width at half maximum of the photoluminescence peak several parameters including concentration of impurity centers and inhomogeneity of the samples are determined and compared in order to check the quality of the samples. Thermal quenching of the photoluminescence peak has been analyzed and the processes which are associated with each parameter are determined and discussed. X-ray diffraction analyses of the sample for the location and width of the peaks have been analyzed and several characteristics of the samples including quality, lattice constant and zinc molar concentration of the samples are determined and compared. The parameters that are obtained from these analyses are compared with the ones from the photoluminescence spectra and showed a good agreement between the results of these two non-destructive characterization techniques. / Graduate / 0605 / 0544 / 0794

This thesis present photoluminescence spectroscopy and X-ray diffraction analyses of four different cadmium zinc telluride samples with different quality and features and similar zinc molar concentration of 10%. Photoluminescence spectroscopy of the samples let us obtain several physical parameters of the samples which are indicators of quality, composition, structure, and impurity levels of the samples. The band gap energy of the samples obtained from the photoluminescence spectra at low temperatures helped us to estimate zinc molar concentration of the samples. Temperature dependence of band gap energy in these samples has been analyzed and exciton-LO phonon interactions in the samples has been analyzed. From temperature dependence of full width at half maximum of the photoluminescence peak several parameters including concentration of impurity centers and inhomogeneity of the samples are determined and compared in order to check the quality of the samples. Thermal quenching of the photoluminescence peak has been analyzed and the processes which are associated with each parameter are determined and discussed. X-ray diffraction analyses of the sample for the location and width of the peaks have been analyzed and several characteristics of the samples including quality, lattice constant and zinc molar concentration of the samples are determined and compared. The parameters that are obtained from these analyses are compared with the ones from the photoluminescence spectra and showed a good agreement between the results of these two non-destructive characterization techniques. / Graduate / 0605 / 0544 / 0794

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This thesis covers three topics related to the field of crystal engineering. Three different approaches to improving the understanding of hydrogen bonding are covered; analysis of a family of related molecules, investigations of specific functional groups and a systematic, data-driven study of intramolecular hydrogen bonding patterns. Chapters 2 to 4 and chapter 11 cover the background theory to the different methods used to obtain the data discussed in the remainder of the thesis. X-ray and neutron diffraction techniques are discussed, along with sections describing the Cambridge Structural Database, which was used as a data source throughout this work, and a brief section on intermolecular forces. Crystal structure analyses of seventeen gem-alkynol molecules are given in chapters 5 to 10. The gem-alkynol functionality is particularly interesting for a study of intermolecular interactions as it is a combination of both a strong and weak hydrogen bonding group. The group of molecules was investigated with the aim of locating robust supramolecular motifs. The group is subdivided into sections containing molecules with similar structures and their packing patterns are discussed. The second experimental section, chapters 12 and 13, comprises statistical studies into the function of the azido and cyano functional groups as hydrogen bond acceptors. The technique used was to use the Cambridge Structural Database as a data source for the main analysis, then complement the results with simple theoretical calculations. The remaining chapter, 14, describes a systematic analysis of intermolecular hydrogen bonded motifs. A data-driven approach was designed which allows direct comparison of motifs by means of a probability ordered list.

About a hundred samples of y-manganese dioxide covering three materials coded SBP- A, Faradiser M and R2 have been reduced chemically by insertion of H through controlled additions of hydrazine hydrate solutions at about 1 °C. The H-inserted samples and the starting materials were subjected to chemical analysis for oxidation state, X-ray diffraction (XRD) for structure study and Fourier Transform Infrared (FTIR) spectroscopy to gain information on OH bonding. Additional techniques including FTIR spectroscopy at low temperature (~ -180 °C), electrode potential measurement and scanning electron microscopy (SEM) have also been applied. The intergrowth structure of the starting materials consisted of ramsdellite intercepted with pyrolusite layers, known as de Wolff faults, and quantified by the fraction of pyrolusite layers Pr. An additional structural parameter for these materials was the amount of micro twinning (Tw) across the 021/061 ramsdellite planes. This parameter, introduced by Pannetier, is given in percent. Values of (Pr , Tw) have been given as (0.41 , 17) for SBP-A, (0.70,10) for Faradiser M and (0.41, ~100) for R2. Upon H-insertion, the structure of the starting materials expanded homogeneously in a direction and to an extent which depended on the Pr and Tw parameters. Faradiser M, with high Pr and very low Tw, expanded homogeneously in the direction of the b lattice dimension up to an insertion level of 0.69 of s in MnOn/Hs. Above this level, the initial structure changed suddenly into the structure of the final product: the insertion then proceeded homogeneously in the new phase. The main changes were an expansion of the octahedra and a rotation leading to hinged tunnels. This is the first time that the existence of two solid solutions in the MnO2/H system has been noted. With SBP-A, the amount of microtwinning restricted the homogeneous expansion of SBP-A to s = 0.28, which occurred predominantly in the a direction. Further insertion broke the twinning boundary and formed a demicrotwinned phase of composition MnOn Ho.68 in which the tunnels were also hinged. Thereafter H-insertion proceeded heterogeneously from 0.28 to 0.68 in s. Above s = 0.68, the structure developed homogeneously towards that of the fully H-inserted product. The extensive microtwinning in R2 allowed for a homogeneous expansion, thought to be isotropic to maintain the microtwinned structure, up to s = 0.39. Higher insertion levels led to the expansion to proceed heterogeneously to a composition of MnOn Ho.63. Above s = 0.63, a new phase, the final product, was formed with fully demicrotwinned structure and fully hinged tunnels. R-insertion into y-manganese dioxide has never been reported to occur in three stages previously. The FTIR study at room temperature has shown absence of OH bond vibrations at insertion levels prior to the hinging of the tunnels, in contrast to their presence after the structure has rotated and the tunnels had hinged. This is seen as a strong indication of H mobility in the initial structure. The hinging is necessary for OH bonding as it brings the 02 and 01 oxygens closer allowing the proton to bond both covalently and by H-bonding. At low temperature, initially mobile hydrogen could be trapped and OR bonds formed only in H-inserted R2. This was linked to 061-microtwinning. The absence of OH bonds at low temperature in SBP-A and Faradiser M led to the conclusion that these materials have no 061 micro twinning faults. The absence of OH bonds at low temperature in the starting materials, particularly in R2, strongly questions the postulated OH groups in the structure of y-MnO2, according to the cation vacancy model. Electrode potential data supported the above conclusions in terms of the stages of the H-insertion. The battery activity of the materials seemed to be related to the extent at which the materials kept the initial structure with non-hinged tunnels. Comparison with previous works on the same materials suggested that the differences could be accounted for by the kinetics of the H-insertion. While protons in this work were released spontaneously on the surface of the MnO x , their diffusion into the bulk was slow due to the low temperature. In the compared literature, the reverse applies.