Semiconductor fabrication process

Since the late 1970s, electroanalytical array sensors have been constructed by methods similar to the well-established semiconductor fabrication processes, which use... 

To the best of my knowledge, this book is the first one to give a complete overview of the 3-D integration problem. It would provide valuable information for readers from various communities, such as semiconductor fabrication process developers, IC designers, and EDA R D practitioners. The book could also serve as an excellent reference for graduates majoring in microelectronics. 

Semiconductor fabrication processes permit construction of small, sensitive, stress sensors. In fact the levers used in atomic force microscopes are almost ideal for this purpose. The combination of the mechanical properties of silicon nitride and the geometry of the cantilever mean that the lever has a high resonant firequency and a low spring constant [32]. The low spring constant is beneficial for sensor applications because it means that a small applied force can be transduced to a measurable deflection, which lies at the heart of any sensor [33]. When combined with the highly sensitive optical lever AFM detection system, both of these factors mean that this arrangement is a fast and highly sensitive stress sensor. 

In the commercial development of Si devices, diffusion is an important semiconductor fabrication process. This process does not play a major role (except in the case of the sublimation growth of SiC discussed in Chapter 8) in the development of SiC, because the diffusion coefficients for the most part are negligible at temperatures below approximately 1800 °C. As a result of this commercial insignificance, the diffusion process in SiC and its various polytypes has not received a great deal of scientific attention and diffusion data are incomplete. It does, however, appear that the solubility of impurities and their diffusive mobilities in different SiC polytypes are very similar. 

One important area of resist research in recent years is the development of plasma-developable resist systems. The aim of plasma developable resists is to use nonsolvent, all dry development methods to avoid the problems of swelling and consequent resolution limitation associated with conventional resists. Much of the semiconductor fabrication process now utilizes plasma techniques as they are capable of providing high resolution images. An important consideration in this is that the plasma-developable resist images should stand up well to the plasma etching treatments. 

These two factors are significant in determining the signal to noise ratio of the pyroelectric capacitor - multiplexor couple. Among the different materials only the copolymer is directly compatible with the semiconductor fabrication process. The cr olymer also shows a low thermal diffusion and the best merit factor. 

Microfabrication is a process used to generate physical devices onto substrates. These devices are formed by structures with dimensions from millimeter to nanometer range. Figure 3.1 shows a piece of silicon (Si) wafer with devices after the completion of the fabrication. Over the years, microfabrication has advanced significantly from the established semiconductor fabrication processes used for integrated circuits (ICs) to diverse materials and processes such as polymers, liquids, soft lithography, and liquid-based processes. 

Organic impurities are bundled together as total oxidizable carbon (TOC) because of their common effect on the semiconductor fabrication process. Silicon oxidation, uniformity of etching, and gate oxide breakdown voltage of devices can be influenced by TOC. 

Microelectromechanical systems (MEMS) fabrication developed out of the thin-film processes first used for semiconductor fabrication. To understand the unique features of the MEMS fabrieation proeess it is helpful to consider the semiconductor fabrication process. 

The semiconductor fabrication process is cyclic, (a) First, a thin film is deposited on the wafer surface using thin-fihn deposition teeh-niques. (b) A uniform photosensitive polymer (photoresist) is then deposited and (c) exposed to light from a mask that contains the pattern that is desired on the thin film, (d) The photoresist is developed to obtain the desired pattern, (e) The pattern in the photoresist is then transferred to the thin film using an etching technique, and the photoresist is removed. Figure 1.1 shows a cross section of the wafer at each step. This cycle is repeated for each new layer, with some processes requiring as many as 20 to 30 cycles. 

Figure 1.1 The semiconductor fabrication process, (a) Thin-film deposition (yellow), (b) photoresist deposition (blue), (c) photolithography (mask clear and opaque red arrows), (d) photoresist development, and (e) etching to transfer the pattern in the photoresist into the thin film. See color plate section.

The development of nanopores within silicon supports, particularly silicon nitride and silicon oxide, makes use of knowledge derived from electronics and semiconductor fabrication processes. Silicon wafers with thin oxide/nitride films can be readily attained and provide a useful platform for experimentation. Though these materials are not fundamentally nanoporous, techniques have been developed to incorporate nanopores. 

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