In device fabrication

The apphcation of a high electric field across a thin conjugated polymer film has shown the materials to be electroluminescent (216—218). Until recentiy the development of electroluminescent displays has been confined to the use of inorganic semiconductors and a limited number of small molecule dyes as the emitter materials. Expansion to the broad array of conjugated polymers available gives advantages in control of emission frequency (color) and facihty in device fabrication as a result of the ease of processibiUty of soluble polymers (see Chromogenic materials,electrochromic). 

These model compounds can also be used in device fabrication, since thin films of appropriate thickness can be obtained by sublimation and subsequent deposition onto a substrate in vacuum. Electrical as well as optical properties of such devices have turned out to be strongly dependent on both the molecular packing within the crystallites and the polycrystalline morphology. Understanding and control of this aspect is one of the current scientific challenges. 

On the way to more reliability in device fabrication, Kronholz et al. reported on the reproducible fabrication of protected metal nanoelectrodes on silicon chips with <30nm gap width and their electrochemical characterization [33]. For the fabrication of the chips, an optical lithography step and two electron-beam steps are combined (Figure 18). 

Unlike silicon-based materials where selective reactants are of ultimate importance, and III-V and metallic materials where product volatility dominates etching considerations, selective etching of organic films is driven by incorporating the desired reactivity (or lack of it) into the film itself. In device fabrication all types of materials are present simultaneously and the process engineer must be aware of the important aspects of the chemistry of each material in addition to the gas phase reactions that produce chemically active species. It is hoped that the discussions presented here provide a basis for approaching such a complex chemical system and for critically evaluating studies which appear in the literature. 

The first reactions were carried out at room temperature in devices fabricated from a thiolene resin cured between two glass slides. 2-Hydroxypropyl methacrylate (HPMA) was polymerized by ATRP, and reaction kinetics similar to those obtained in a traditional batch reaction were obtained by adjusting the total flow rate of the fluid through the channel and treating the residence time in the channel as the reaction time (Fig. 21b,c) [102]. 

A poor surface morphology is a major concern in device fabrication and substantial efforts have been made during the last years to resolve this issue. Different concepts have been developed, such as effective encapsulants (primarily AIN) for protection of the SiC surface [8] and annealing in CVD-reactors using Si overpressure [9]. These concepts appear to be quite successful, at least up to 1,700°C, and are reviewed in Section 4.3.1. 

In device fabrication, the location of functional materials is as important as their properties. The integration of solid particles into devices usually requires placing them in specific positions. Hence, the combination of top-down patterning techniques and bottom-up self-assembly is crucial in obtaining (submicron) patterned functional nanostructures on surfaces. 

Microelectronic device fabrication currently relies primarily upon photoresist processing for integrated circuit pattern delineation. Adhesion of polymeric photoresist patterns, especially those of micron and submicron dimensions, to the required fabrication substrates is of paramount importance. Photoresist image adhesion problems encountered in device fabrication have been solved by chemical interfacial treatments. Current new trends in microelectronic adhesion technology will be described and discussed with emphasis upon the chemical nature of the interface involved as determined by ESCA. 

Etching of semiconductors in the dark and under illumination plays an important role in device fabrication. Since mostly Si and GaAs are used in devices, the research on etching processes is concentrated on these materials. Taking GaAs as an example, the dissolution at low pH can be described by [229] ... 

Pig. VB-1 shows the temperature dependence of QEe ,(EL) of a device fabricated from a blend of OCICIO-PPV containing 20% (by weight) Bu-PBD. Lor devices with Bu-PBD, QE , increases with temperature at 85°C QE ,(EL) is twice that obtained at room temperature. The data from an identical device fabricated with pure OClClO-PPV (without Bu-PBD) are shown for comparison QEe, (EL) decreases slightly with temperature for devices made without Bu-PBD. The increase in QE t is unambiguous measurements were taken on more than 10 devices for each Bu-PBD concentration with excellent reproducibility. The increase with temperature is reversible. The increase is a function of the Bu-PBD content the optimum is at approximately 20% Bu-PBD. The increase in QEj, ,(EL) does not result from an increase in QEe (PL) QE fPL) is temperature independent (within experimental error) between room temperature and 85°C in devices fabricated with and without the Bu-PBD. 

Chemical etching is a process for removal of silicon dioxide films through dissolution in solutions. Dissolution of silicon oxides, in the context of this book, is related to the anodic behavior of silicon electrodes. However, the dissolution of anodic oxides is not well studied. In contrast, there is a wealth of information on the dissolution of other types of oxides. Much of this information must also be applicable, at least the qualitative and mechanistic nature, to that of anodic oxides. Also, because oxides of different types are commonly used in device fabrication, compiling the etch rate data of these oxides and those of silicon (presented in Chapter 7) in the same volume would be useful in practice. Additionally, because silica-water interaction, which has been extensively investigated in the geological field, is fundamental to the etching of silicon oxides, some of the results from the investigations on the dissolution of rocks and sands are also included. 

The etch rate of silicon relative to other materials is also important in device fabrications. The data on relative etch rate, which is specific to a specific set of conditions, are widely spread in the literature. For example, the relative etch rate of silicon has been reported for Sii. GC , in NH4OH, boron monophosphide epitaxial layer in HF-HNO3, SiOj in HF solutions, SiOj in KOH, SiOj and nitride in TMAH, ° ° Si02 in different oxides and metallic films, various glasses... 

The etching systems for silicon etching have been extensively investigated since the 1950s when etching began to be used in device fabrication processes, accumulating an enormous amount of technical... 

The etch rate of silicon relative to other materials is also important in device fabrications. The data on the relative etch rate, which is specific to a specific set of conditions, is widespread in the literature. Some examples are Si jGe, in... 

Current microelectronic processing involves working around fundamental constraints imposed by cost and physics. However, working in the presence of constraints is fundamental to chemical engineering improved devices and processes are developed through optimization of all kinds. In other words, the industry must continue to learn how to squeeze most out of what Mother Nature permits. In device fabrication, where rates of transport and physical/chemical transformation govern, chemical engineering principles are needed more than ever. 

Sihcon (100) surfaces play a decisive role in many technologically important device applications. The stiucture of the surface has been widely studied, both experimentally and theoretically [16-18]. The knowledge of the surface provides a good reference for the study of the interactions of the surface and the complex molecules. Thus, in this research, we investigate the issue of attachment of aromatic molecules to the dimerized sihcon (100) surface. This is an importance in device fabrication. In theoretical research, slab models and cluster models have been extensively used to describe Si(lOO) -2x1 surfaces [16-18]. Among these models, the cluster model has been extensively used in theoretical research of the surface since it is simple and amenable to model the fundamental features of the surface. The smallest cluster model for the 2x1-reconstmcted Si(lOO) surface is the one-dimer cluster, which includes two surface... 

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