Development of decoration and preferential-etching methods for delineation of crystal defects in semiconductor materials

Silicon wafers such as Silicon on Insulator (SOI) and strained silicon on Insulator (sSOI) are the essential and basic materials of advanced microelectronic devices. However, they often show various kinds of crystal defects which impair the function of these devices. The most efficient method to date, for detecting such defects and for determining their density, is to delineate them by etching the wafers with a suitable etching solution and characterise them via light optical microscopy. Etch pits are formed at defect sites which are etched at a faster rate than at the perfect lattice. The standard etching solution used for SOI and sSOI is a dilute version of Secco. As Secco contains carcinogenic and environmentally hazardous chromium (VI), the use of which is or will be restricted by law in many countries, suitable chromium (VI)-free etching solutions like Organic Peracid Etches (OPE), modified Chemical Polishing Etches (CP) like CP4 mod and mixtures with organic oxidizing agents like chloranil (CA) have been developed for the successful delineation of various types of crystal defects. However there are still nanometer-sized defects which are hard to detect or escape detection by this method. Copper decoration is a well known method to magnify these defects. It consists in applying a copper nitrate solution to the back of the SOI or sSOI wafer. On annealing, copper diffuses through the substrate and the BOX (buried oxide) to the SOI/sSOI film and on quenching to room temperature, copper precipitates as copper silicide, SiCu3, foremost at crystal defects where the lattice strain is greater than at perfect lattice sites. These silicides increase the volume in these parts of the crystal lattice and defect magnification occurs. A considerable disadvantage of this method is its tendency for artefact formation, when the copper concentration used is too high, with the copper precipitating at the film surface. The consequence is a higher density of etch pits whereby true defect etch pits cannot be differentiated from those caused by artefacts. The aim of this thesis is to show that the processes of decorating and etching can be combined successfully to delineate all crystal defects in SOI and sSOI. An ideal result would have been to find a copper decoration procedure that decorates all existing crystal defects at a copper concentration that avoids artefact formation.Silizium Wafer wie Silicon on Insulator (SOI) und strained Silicon on Insulator (sSOI) stellen die Basismaterialien für die mikroelektronischen Bauteile dar. Jedoch weisen sie oft verschiedene Arten von Kristalldefekten auf, welche die Funktionalität dieser Bauteile beeinflussen. Die effizienteste und bekannteste Methode, zum Nachweis solcher Kristalldefekte und für die Bestimmung ihrer Defektdichte, ist ihre Sichtbarmachung mittels Ätzen des Wafers mit einer geeigneten Ätzlösung. Die anschließende Charakterisierung erfolgt zunächst mit Hilfe der Lichtmikroskopie. Die Bildung von Ätzfiguren („etch pits“) an Defektstellen wird bedingt durch die schnellere Ätzrate am Defekt im Vergleich zum perfekten Kristallgitter. Die Standardätzlösung für SOI und sSOI ist eine verdünnte Version der Secco Lösung. Da die Secco krebserregendes und umweltschädigendes Chrom (VI) enthält, ist oder wird ihr Einsatz als Ätzlösung in immer mehr Ländern verboten. Geeignete Chrom (VI)-freie Ätzlösungen, wie die Organic Peracid Etches (OPE), modified Chemical Polishing Etches (CP) wie CP4 mod und Lösungen mit organischen oxidierenden Verbindungen wie Chloranil (CA), wurden für die erfolgreiche Sichtbarmachung verschiedener Arten an Kristalldefekten entwickelt. Dennoch gibt es immer noch Kristalldefekt, welche eine Größe im nm-Bereich aufweisen, welche mit den erwähnten Ätzmethoden kaum oder nicht nachgewiesen werden können. Das bekannte Verfahren der Kupferdekoration wird für die Vergrößerung derartige Defekte eingesetzt. Dabei wird eine definierte Menge an Kupfernitrat auf die Rückseite des SOI bzw. sSOI Wafers aufgebracht. Anschließend erfolgt das Tempern im Rohrofen. Dabei diffundiert das Kupfer durch das Substrat und die BOX (buried oxide) in den SOI/sSOI-Film und präzipitiert als Kupfersilizid (Cu3Si) beim Quenschen auf Raumtemperatur hauptsächlich an Kristalldefekten, in denen die Kristallgitterverspannung größer als im perfekten Kristallgitter ist. Diese Silizide dehnen das Volumen am Kristallgitter an der Stelle des Defektes aus, was zur Vergrößerung der Defekte führt. Ein bedenklicher Nachteil dieser Methode ist die Tendenz der Artefaktbildung, wenn die eingesetzte Kupferkonzentration zu hoch ist. Dabei präzipitiert das Kupfer auf der Siliziumoberfläche. Daraus resultiert eine höhere Defektdichte an Ätzfiguren, wodurch echte Ätzfiguren, die ihren Ursprung in Kristalldefekten haben, nicht von den durch Artefakte erhaltenen Ätzfiguren unterschieden werden können. Ziel dieser Dissertation ist es zu zeigen, dass die beiden Prozesse Dekoration und Ätzung miteinander für einen erfolgreichen Nachweis aller Kristalldefekte in SOI und sSOI kombiniert werden können. Ein ideales Ergebnis wäre die Entwicklung einer Dekorationsmethode, in der die Dekoration aller vorliegenden Kristalldefekte bei einer Kupferkonzentration erfolgt, welche keine Artefakte induziert

An Islamic Cultural Center for Cornell University

An Islamic Cultural Center for Cornell University in Ithaca, NY Britton Award Winner, Thesis Boar

Evolutionary ecology of hares (Lepus spp.) from northwest Africa: the existence of cryptic species and description of a new species (Lepus saharae sp. nov.)

Objective: We examine the different pressures that lead to the occurrence of new species and thus to their phylogenies. From an evolutionary ecology perspective, we examine the phylogenetic relationships of different lineages, as well as the evolutionary pressures that lead to them and, in some cases, mask them. Organisms and locales: Hares (Lepus spp.) in northwest Africa that are morphologically similar, which, superficially, makes it appear that there is only one species. Methods: We describe different populations of hares in northwest Africa. We describe the morphology of a new species and provide photographs of specimens from across the study area. We analyse five mitochondrial DNA fragments. Results: Mitochondrial DNA analysis revealed the presence of three Lepus species which are different from both Lepus capensis and L. victoriae and which have contiguous, partially overlapping geographical ranges. One of the species, found in the western Sahara (Morocco), is new (Lepus saharae sp. nov.). The other two species (Lepus mediterraneus Wagner, 1841 and Lepus schlumbergeri Remy-St. Loup, 1894) inhabit the northern and central regions of Morocco. The distributions of at least two of the three species extend to countries other than Morocco. Various eco-evolutionary pressures have masked this diversity until now. Certainly, the species have had to adapt to different habitats that include mountains and desert; and isolation of populations by distance, or because of climatic or geographical barriers has led – or at least facilitated – them to appear different. Yet some evolutionary pressures have made them converge morphologically, making it appear that there is only one species

Descripción de España : (obra del siglo XII)

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201

DESIGN, FABRICATION AND HEAT TRANSFER STUDY OF GREEN HOUSE DRYER

ABSTRACT The objective of the present study was to design to fabricate and to test the green house dryer in natural mode. The system is capable of generating a continuous flow of hot air temperature up to 60°C. Experiments were conducted in the premises of SHIATS in Allahabad at latitude of 25°N. Measurement of solar intensity, relative humidity inside and outside the green house dryer, moisture removal rate, air velocity, temperature at different point were recorded. These data were used for determination of the coefficient of convective mass transfer and then for development of the empirical relation of convective mass transfer coefficient with drying time under the open sun and natural mode. It is observed that the convective mass transfer coefficient is lower for drying inside the green house than the open sun drying

Descripción de España

Al tít. precede otro con caracteres árabesTexto en árabe y españolSignaturizad

Parameter Optimization In 3D Printer Recycle Machine

3D printing technology has evolved rapidly to becoming one of the most postulate method in manufacturing process. Commonly, standard manufacturing process which is subtractive that produces a lot of waste opposite to 3D printing technology is way friendly to the environment. The idea of this application additive manufacturing method in 3D printing leads to less or no wasted materials and consumption of plastic materials has significantly increased due to high demand in market. However, the plastic waste products from the 3D printing still undergo significant increase due to the problem in every human-made creation. In order to minimize the negative impact of plastic waste to the environment, a machine of recycle 3D printing has been made and study on parameter optimization on 3D printer recycle machine have been done. The study used Minitab software to analyze the factor of parameter of 3D printing recycle machine. Taguchi method was used to suggest some experiments to be performed and provides an optimal value for each parameter that needs to be optimized in the operation of extruding. Analysis of extruded filament was conducted for every 30cm with minimum of three repetitions. In comparison of the new extruding filament and original filament show that some minor difference of the mechanical properties by using tensile test method. Percentage of error for diameter of filament indicates that 1.77mm diameter with 1.14% as the lowest error while diameter of 1.82mm with 4.00% as the highest error. This shows that 3D printer recycle machine has been optimized with the percentage of error below than 5% and it could be further improved in order to help in minimizing the negative impact of plastic wastes to the environment