Silicon wafer chemistries

Contamination of silicon wafers by heavy metals is a major cause of low yields in the manufacture of electronic devices. Concentrations in the order of 1011 cm-3 [Ha2] are sufficient to affect the device performance, because impurity atoms constitute recombination centers for minority carriers and thereby reduce their lifetime [Scl7]. In addition, precipitates caused by contaminants may affect gate oxide quality. Note that a contamination of 1011 cnT3 corresponds to a pinhead of iron (1 mm3) dissolved in a swimming pool of silicon (850 m3). Such minute contamination levels are far below the detection limit of the standard analytical techniques used in chemistry. The best way to detect such traces of contaminants is to measure the induced change in electronic properties itself, such as the oxide defect density or the minority carrier lifetime, respectively diffusion length. 

The surface chemistry of SAMs of silanes on planar substrates such as oxidized silicon wafers is comparable to the chemistry of silica gel, with the absence of a porous structure [47]. 

The aim of this book is to cover a novel interdisciplinary research area of high current interest, namely microsystems for use in chemistry and the life sciences, with a set of comprehensive reviews. Since 1975, when Steve Terry and his coauthors at Stanford published an account of their gas chromatograph on a silicon wafer, a large number of publications have appeared in the literature. Particularly after 1990 this field started exploding. For an inexperienced scientist it is a difficult task to obtain a good overview of what has happened during the last few years. Even conferences with the best possible coverage of authors would only feature recent research results. 

FIGURE 2.2 Microstructures defined on a <100> silicon wafer for chemical separation. Design I-cross-type separator Design 11-45° type separator [84]. Reprinted with permission from the Royal Society of Chemistry. 

Fig. 10.19. Steps for nanotransfer printing a thin layer of Au on to a silicon wafer using a self-assembled monolayer (SAM) surface chemistry. Plasma oxidizing the surface of the wafer generates OH groups. Solution or vapor phase exposure of the wafer to 3-mercaptopropyltrimethoxysilane yields a SAM with exposed thiol groups. Contacting...

Organic conductive films, e.g. polyaniline or polythiophene, have an interesting potential application due to their easy processability combined with a low weight. A plasma deposition process is even more interesting from a technical point of view, because it is, as opposed to wet chemistry, much more compatible with production processes in vacuum. The sample used was polymerized by Kruse et al. [454] on a silicon wafer over 20 min in a microwave plasma chamber at 2.45 GHz using 2-iodothiophene (at... 

In an early HREELS study of Cr deposition onto polyimide (2b.81. bonding interactions of the Cr atom affecting the carbonyl stretching vibrations were clearly evident. In a further attempt to gain more details on the chemistry developing at the metal-polymer interface, another preliminary set of spectra was recently collected during the metallization of a polyimide film deposited directly onto a silicon wafer (with its native oxide) (Fig. 7). 

For the plasma chemistry illustrated above, the chemistry at the surface of a silicon wafer is given by ... 

Effects of Various Chemistries on Silicon-Wafer Cleaning... 

Multiple PCR chambers have been fabricated on a single microfluidic chip and explored for high throughput PCRs [78-83]. An example of a multichamber micro-PCR device, the micro-DNA amplification and analysis device, (p-DAAD) consisted of 16p-DAADs in parallel with each p-DAAD consisting of four microreactors fabricated on a 4" silicon wafer (see Fig. 4). Multichamber micro-PCR devices [84] have been demonstrated for DNA amplifications of five gene sequences related to E. coli from three different DNA templates and detected by TaqMan chemistry with a limit of detection (LOD) of 0.4 copies of target DNA. 

A good example is the molecule SiO, a cosmic precursor to silicon oxide chemistry as we now know it on earth (22). In more recent times, too, this molecule has assumed considerable significance because of its relevance to oxidation reactions taking place at the surfaces of silicon wafers and to the creation of antireflection coatings on these and other solid-state devices. Unlike its more familiar counterpart carbon monoxide, SiO is normally quick to aggregate and disproportionate [Reaction (5)] at temperatures below 1000°C ... 

Colloids are extremely important to both commerce and life. The Information Age of the late twentieth century nurtured many advancements allowing more detailed investigation of colloidal materials. Lasers and computers, of course, have greatly affected all areas of science. In return, colloids play a major role in the semiconductor industry. Silica-alumina sols polish silicon wafers that go into diode lasers, memory chips, and microprocessors. Everyone takes advantage of colloidal suspensions, especially since the human body contains so many with its cells, proteins, and DNA. As society pushes to make so many things smaller, more functional, and more efficient, colloid science will become increasingly pertinent to technological developments, see also Solution Chemistry. 

Microchip substrate is open to a variety of materials. Silicon wafer is a good material to build up microstructures if fabrication facilities are available. Glass has good chemical and optical properties, and some polymers are cost effective for mass production. The surface treatment of the microchannel is critically important for all materials. This is because of the nonspecific adsorption of the analytes and antibodies to the channel wall that will result in considerable analytical error. It is very important to modify the surface with some blocking reagents or other materials to prevent protein adsorption before experiments. Therefore, we must choose a material of which, surface chemistry is well understood. 

An ideal substrate would be smooth, rigid (i.e. a polished metal), coated with an ultra-thin PDMS layer anchored by a well-understood and controllable chemistry. This has been achieved by taking semi-conductor silicon wafers which have a thin oxidized silica layer which can be treated by a self-assembling silane monolayer, such as vinyl terminated alkyltrichlorosilane. This can then be reacted with SiH-containing PDMS this hydrosilylation reaction is well-understood and the random substitution of such SiH groups along a PDMS chain has been well established by NMR studies. The low hysteresis surface that can be obtained in this manner is illustrated by the data in Table 4. 

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