C. Sung

Gas cluster ion beam processing of gallium antimonide wafers for surface and sub-surface damage reduction

Abstract In order to bring low-power epitaxy-based gallium antimonide (GaSb) electronics and electro-optics to market, high-quality GaSb substrates with smooth surfaces and no surface damage are required. Here, a novel final polishing technique, gas cluster ion beam (GCIB) processing, is shown to improve the surface finish of chemical–mechanical polished (CMP) 50xa0mm (1xa00xa00) GaSb wafers by etching and smoothing CMP surface atoms through the sub-surface damage. For the first time, a fluorine-based gas cluster ion beam is reported for GCIB surface etching and smoothing of GaSb material. For the selected processing sequence, the surface roughness of a high-quality, 0.70xa0nm RMS GaSb wafer was reduced to 0.18xa0nm RMS without any observed changes in the full-widths at half-maximum (FWHM) of the (4xa00xa00) and (1xa01xa01) X-ray peaks of 14 and 20xa0arcsec, respectively. Results indicate that the GCIB process did not contribute to wafer surface or sub-surface polish damage. In a second case, a GCIB etch removed 200xa0nm of material from a non-optimal CMP (1xa00xa00) GaSb surface and reduced the full-width at half-maximum (1xa01xa01) X-ray peak from 76 to 52xa0arcsec in conjunction with a surface roughness decrease from 0.70 to 0.35xa0nm RMS. The data suggests that GCIB processing appears to be promising as a final GaSb wafer polish with an etch rate compatible for large scale manufacturing.

Structural and Morphological Characterization of Ultrathin Films of an Asymmetric Polydiacetylene

A soluble, asymmetrically substituted polydiacetylene, poly(BPOD), has been reported to form stable monolayers at the air-water interface by the Langmuir-Blodgett (LB) technique [2]. Preformed polydiacetylene has been deposited onto hydrophobic substrates as multilayers to form second order nonlinear optical thin films. Second harmonic generation was found to increase with the number of layers. From previous atomic force microscopy (AFM) studies backbone orientation along the dipping direction with an interchain spacing of about 5 A° was indicated [2].The film morphology and preferential molecular orientation of these LB films are further investigated by transmission electron microscopy (TEM). A specifically tailored sample preparation method for the ultrathin LB films was used. Multilayer films were deposited on hydrophobic collodion covered glass substrates for this purpose. Electron diffraction was employed to study the crystalline organization of mono and multilayers of LB films as well as cast films.

Interface Characterization and Delamination Mechanism of c-BN Film

Cubic boron nitride films were prepared by helicon wave plasma CVD process on (100) Si. The growth and delamination mechanism of c-BN film was investigated with FT-IR spectroscopy and transmission electron microscopy. The film deposited under the intense impact of energetic ions is usually delaminated from the substrate after deposition. It is found that moisture in the air, surface roughness of the film and substrate, as well as severe compressive stresses in the film are the primary contributors to film delamination. An aqueous oxidation was verified by EDXS analysis, which generate local stress by volume expansion at the crack region in the c-BN layer. From the experimental results and ??? observation a model for the delamination mechanism of c-BN film is suggested. Based on the delamination mechanism, several kinds of remedies such as post annealing and post N 2 plasma treatment were carried out for improving the adhesion.

Interfaces in Silicon Carbide Whisker and Carbon Fiber Reinforced Calcium Phosphate Composites

The microstructural and chemical characteristics of silicon carbide whisker/calcium phosphate and carbon fiber/calcium phosphate composites were studied using analytical transmission electron microscopy. The interface at these calcium phosphate-based composites was studied, with particular attention to finding evidence of a chemical reaction at the interface. Structural observations made on these composites explain the fact that their mechanical properties may be strongly affected by the structural properties.

Micromechanical Characterization of Gasb by Microbeam Deflecion and Using Nanoprobe and Finite Element Analysis

The commercial development of low-power electronics and electro-optics based on antimonides demands a better understanding of the mechanical properties of ternary and quaternary thin-film alloys fabricated from the InGaAlAsSbP material system. Of particular importance is the determination of Youngs modulus of these materials. In this paper, a technique for studying the mechanical behavior of these thin films was developed by using microbeam bending and finite element modeling. The technique was successfully applied to investigate the mechanical properties of GaSb. A test structure consisting of an array of gallium antimonide microbeams was fabricated with lengths ranging from 50 to 500 μm long. The microbeams were deflected using a calibrated nanoprobe, thereby generating load-displacement curves. Youngs modulus was then extracted from the data using beam bending theory and a finite element simulation of the structures under load. A total of five microbeams with the same trapezoidal cross-section and lengths of 80, 85, 200, 250 and 500 μm were tested to study the technique applicability and size scaling effects on the mechanical properties. It was observed that the 80 and 85 μm beams exhibited linear elastic behavior and the 200, 250, and 500 μm microbeams exhibited non-linear elastic behavior.

Preparation and Patterning of GaSb Surfaces with Br-IBAE for Antimonide Based Molecular Beam Epitaxy

Bromine Ion Beam Assisted Etching (Br-IBAE) is shown to be useful in removing GaSb wafer chemical mechanical polish (CMP) surface and subsurface damage; creating microstructure patterns in GaSb surfaces through stencil, photoresist, and oxides masks; and stabilizing the as-etched GaSb surface with a thin, easily thermally desorbed oxide layer. Thus, the Br-IBAE technique is well suited as a GaSb surface final-polish technique in overgrowth applications that require “epi-ready” GaSb (100) surfaces for molecular beam epitaxy (MBE) as well as applications such as quantum wires and dots that require high-quality GaSb/AlInGaSb MBE overgrowth over patterned GaSb (100) surfaces.

Interfacial characterization of a SiC fiber-reinforced AlN composite

In this study, an attempt was made to improve the mechanical properties of AlN by the incorporation of SiC (SCS-6) fibers (TEXTRON Specialty Materials, Lowell, MA) in a unidirectional array. The SiC fibers are one of the most important reinforcements for ceramic- and metal-matrix composites due to high tensile strength (3,450 MPs), high tensile modulus (400 GPa), and low density (3.0 g/cc). The SiC fiber (15 vol %)-reinforced AlN composite was fabricated by hot-pressing in vacuum. The microstructure and chemistry of interfacial regions in as-fabricated and crept composite were characterized using analytical transmission electron microscopy, in order to investigate the nature of the reaction between the fiber and matrix during both composite fabrication and creep tests and to understand the reinforcing effects of SiC fiber in the AlN matrix. Interfacial characteristics of the composite play an important role in influencing the mechanical properties of the composite.

Microstructure and chemistry of second phases in MgO- and NiO-codoped alumina by analytical transmission electron microscopy

Small amounts of additives can greatly affect the sintering of ceramic powders. Since the addition of small amounts of MgO (~ 0.25 wt%) to A1203 enables it to sinter close to theoretical density [1], the influence of small amounts of additives on the sintering of A1203 has been widely studied [2-4]. The additives form second phases which profoundly affect the sintering behaviour, i.e. reduce grain boundary mobility and inhibit exaggerated grain growth. MgO inhibits grain growth in fully dense alumina, and the degree of inhibition depends on the purity of the starting powder [5]. Studies have also been conducted concerning the influence of NiO on grain growth in alumina [4]. NiO has been reported to behave similarly to MgO [4, 6]. Sintering in MgOand FeO-codoped alumina has been studied by Zhao and Harmer [7] in order to investigate the role of multiple solid-solution additives in sintering. They observed that MgO inhibits grain growth strongly in very pure powders and FeO promotes grain growth more than densification in alumina. Therefore, FeO was not a favourable additive. In the study reported here, MgO and NiO were used as multiple solid-solution additives. The MgO-NiO system consists of a complete solid solution extending from the higher melting point of MgO to the lower melting point of NiO [8]. The purpose of this study was to investigate the microstructure and chemistry of second phases, segregated particles and crystalline defects in alumina codoped with MgO and NiO using analytical transmission electron microscopy (TEM). As a result, it became possible to infer the location of MgOand NiO-codopants and impurities during the sintering process. Alumina codoped with 0 .15wt% MgO and 0.10 wt % NiO was fabricated by hot pressing at 1480 °C and 27.58 MPa in vacuum. TEM samples were sectioned from the alumina using a low-speed diamond saw and mechanically ground to -300 ~m. Circular discs of 3 mm in diameter were core drilled from the ground sections, mechanically ground to -120/~m, then dimpled to -30/ ira . The samples were ion milled with 5 kV Ar ÷ ions at an incident angle of 12 ° until perforation was achieved. A light carbon film was evaporated on the samples to prevent charging in the electron microscope. The microstructure and chemistry of second phases, segregated particles and crystalline defects in the alumina were investigated by bright field image, convergent beam electron diffraction (CBED),

Second Phases and Impurity Segregations in MgO- and NiO-CO-Doped Alumina

The microstructural and chemical characteristics of the segregated particles, Ni-(Mg)-Al spinel phases, and K-s’’’ alumina precipitates in fine-grained alumina co-doped with 0.15 wt % of MgO and 0.10 wt % of NiO were studied using analytical transmission electron microscopy. The segregated Ni particles and second phases were generally found at triple junctions or on grain boundaries. The K-s’’’ alumina precipitates were found to contain occasionally a high density of stacking faults. These microstructural observations point out the location of the dopants and impurities during the sintering process.