Processing major fabrication processes

Interconnect. Three-dimensional structures require interconnections between the various levels. This is achieved by small, high aspect-ratio holes that provide electrical contact. These holes include the contact fills which connect the semiconductor silicon area of the device to the first-level metal, and the via holes which connect the first level metal to the second and subsequent metal levels (see Fig. 13.1). The interconnect presents a major fabrication challenge since these high-aspect holes, which may be as small as 0.25 im across, must be completely filled with a diffusion barrier material (such as CVD titanium nitride) and a conductor metal such as CVD tungsten. The ability to fill the interconnects is a major factor in selecting a thin-film deposition process. 

Polypropylene (PP) is a high-volume, low-cost plastic first commercialized in 1959 and produced by many companies. It is unusual in that it is processed in large quantities by all four major fabrication processes moulding, extrusion, film, and fibre technology. Major engineering plka-tions include pipe and automobile parts. It does not absorb water. 

Polypropylene is the only high-volume thermoplastic that is processable by all major fabrication methods molding, extrusion, film, and fiber. Many new polypropylenes with improved engineering properties have been developed. The most promising are glass-reinforced polypropylene, foamed polypropylene, heat-resistant-polypropylene, and oriented sheeting. 

Much work continues on the development and introduction of "thenno-plastlc silicone rubbers" and a wide variety of both silicone and silicone-organic block copolymers are being evaluated at this time. As with the liquid silicone rubbers the major fabrication advantage being sought is direct processing by injection molding techniques [20]. 

In recent years, there has been an increasing need for high strength steels for use in highly stressed structures, including many critical applications in aerospace and industry. Because welding is the major fabricating process employed in the construction of various... 

Beryllium, beryllium-containing aUoys, and beryUium oxide ceramic in soHd or massive form present no hazard whatsoever (31). SoHd shapes may be safely handled with bare hands (32) however, care must be taken in the fabrication and processing of beryUium products to avoid inhalation of airborne beryUium particulate matter such as dusts, mists, or fumes in excess of the prescribed workplace exposure limits. Inhalation of fine airborne beryUium may cause chronic beryUium disease, a serious lung disease in certain sensitive individuals. However, the vast majority of people, perhaps as many as 99%, do not react to beryUium exposure at any level (33). The biomedical and environmental aspects of beryUium have been summarized (34). 

The major process today is the hand lay-up technique in which resin is stippled and rolled into the glass mat (or cloth) by hand. Moulds are easy to fabricate and large structures my be made at little cost. 

A significant portion of design, fabrication and in-service processes and practices are common to all three of these categories of assemblies. These common issues will be explored first, followed by more detailed examination of the genesis and issues particular to each of the three major categories listed above. 

Another factor is the ease with which various membrane materials can be fabricated into a particular module design.1618 Almost all membranes can be formed into plate-and-frame, spiral-wound and tubular modules, but many membrane materials cannot be fabricated into hollow fine fibres or capillary fibres. Finally, the suitability of the module design for high-pressure operation and the relative magnitude of pressure drops on the feed and permeate sides of the membrane can be important factors.4-11 The types of module generally used in some of the major membrane processes are listed in Table 16.2. 

The functions and property characteristics of a product will be largely determined by the performance requirements and material selected for fabrication. The basic requirement of the process is its capability of handling a suitable material. For example, if a major function requirement is for resistance to creep under high loads, it is probable that a long-fiber RP will be necessary. Thus it would immediately eliminate such processes as blow molding and conventional injection molding. 

A major cost advantage for fabricating products is their usual low processing cost. The most expensive part of the product is the cost of plastic materials. Since the material value in a plastic product is roughly up to one-half (possibly up to 80%) of its overall cost, it becomes important to select a candidate material with extraordinary care particularly on long production runs. Cost to fabricate using most processes and particularly... 

Many of these steps include CVD, and CVD is now a major process in the fabrication of monolithic integrated circuits (IC), custom and semi-custom ASIC s, active discrete devices, transistors, diodes, passive devices and networks, hybrid IC s, opto-elec-tronic devices, energy-conversion devices, and microwave devices. 

CVD is a maj or process in the production of thin films of all three categories of electronic materials semiconductors, conductors, and insulators. In this chapter, the role of CVD in the fabrication of semiconductors is reviewed. The CVD production of insulators, conductors, and diffusion barriers is reviewed in the following chapter. The major semiconductor materials in production or development are silicon, germanium, ni-V and II-VI compounds, silicon carbide, and diamond. 

The geometry of modern semiconductor devices is continuously shrinking and will soon reach the 0.20 im bench mark, with great increase in speed and efficiency. To accomplish this goal requires major advances in materials and fabrication processes. Many obstacles remain and one of the most critical is that of solid-state diffusion and the development of diffusion barriers. OPO]... 

Based on the micro-electronics fabrication process, Micro-Opto-Electro-Mechanical Systems (MOEMS) have not yet been used in astronomical instrumentation, but this technology will provide the key to small, low-cost, light, and scientifically efficient instruments, and allow impressive breakthroughs in tomorrow s observational astronomy. Two major applications of MOEMS are foreseen ... 

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