Fabrication, microstructure

Chakarvarti SK, Vetter J (1991) Morphology of etched pores and microstructures fabricated from nuclear track filters. Nucl Instrum Methods B 62 109-115... 

The trend towards miniaturization in microstructure fabrication has created a demand for improved methods of production. The preceding paper (l) detailed one of the areas of research in this area, development of a deep UV-degradable photo-resist and presented a likely candidate, poly(methyl methacrylate-co-3-oximino-2-butanone methacrylate-co-methacrylonitrile) (P(M-OM-CN)). 

A simplified example will illustrate the process of microstructure fabrication. With reference to Fig. 1, an //-type region has been created by diffusion of a donor impurity into a surface of p-type silicon, forming a p — n junction diode. There is a metal contact to the /(-region, and the contact line is insulated from the p-type surface by a layer of silicon dioxide. The diameter of the diode is on the order of 10 micrometers. 

Many physical phenomena, however, obstruct the formation of the ideal struciiue depicted in Fig. 2. The technical literature is well supplied with papers devoted to each of the steps illustrated in Fig. 2. None is as straightforward as appears at first sight. It is instructive to discuss them further, since much of the essence of microstructure fabrication is revealed by examining them in detail. 

Further, economic factors also constrain the utilization of microstructure fabrication technology. These are die factors diat control the cost of production, such as throughput, the rate at which substrates can be processed by the fabrication tools, capital investment required, and demands on operator time and skill. Electron beam exposure, for example, provides high resolution but uses expensive equipment that works slowly. Naturally, all of the elements of cost must be weighed against the value of (lie product produced. 

It must further be noted that both metallurgy and microstructure fabrication are practical disciplines, they are oriented toward the economic production of structures that have a useful role in commerce and industry. In this respect both are engineering rather than scientific disciplines. On the other hand, their deep probing of phenomena on an atomic scale and under unusual conditions produce new discoveries and lead to new concepts that enhance basic science. 

Fig. 4. SEMs of microstructures fabricated molding. See text for details...

R.J. Jackman, S.T. Brittain, A. Adams, H. Wu, M.G. Prentiss, S. Whitesides, G.M. Whitesides, Three-dimensional metallic microstructures fabricated by soft lithography and microelectrodeposition. Langmuir 15, 826-836, 1999. 

Surface roughness is an important factor in the performance and reliability of devices having microscopic dimensions [136]. It can essentially affect all aspects of silicon technology [168, 169]. To guarantee the performance of electronic devices the microstructures fabricated from silicon are required to be smooth, with roughness much smaller than the dimensions of the structure components [127]. As the device dimension gets smaller the device will be composed of thinner oxides and shallower junctions and the effect of surface roughness will become critical. 

Microstructures fabricated by micro-EC miiiing. (a) Profiied microhoie, (b) microarray square coiumns, and (c) micro-spirai beam [15]. 

Fabrication of 3D Microfiuidic Structures, Fig. 14 SEM images of 3D microstructures fabricated by combination of conventional photolithography and... 

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