Silicon films, production

For application of protein-immobilized porous materials to sensor fields, use of an electroactive substance as the framework material is important. DeLouise and Miller demonstrated the immobilization of glutathione-S-transferase in electrochemically etched porous silicon films [134], which are attractive materials for the construction of biosensors and may also have utility for the production of immobilized enzyme bioreactors. Not limited to this case, practical applications of nanohybrids from biomolecules and mesoporous materials have been paid much attention. Examples of the application of such hybrids are summarized in a later section of this chapter. 

In the Development stage, detailed product design is carried out. This is the key step for the chemical vapor deposition of thin silicon films. As described in the next section, to obtain uniform thin films rapidly, it is desirable to optimize the design of the plasma-enhanced, chemical-vapor-deposition (PECVD) reactor. 

Figure 11. Mechanism for F-atom reaction with a silicon film leading to the products Sip2 and Sip4.

A molecular beam of XeFj(gas) and a beam of argon ions were directed at the center of a silicon film which had been deposited on a quartz crystal microbalance. The sensitivity of the microbalance was such that the removal of one monolayer of silicon could be detected. In these experiments, the reaction products [e.g., SiF fgas)] were detected using mass spectrometry the surface concentrations were detected using Auger spectroscopy and the rate that material was being removed from the surface was measured with the microbalance. 

Commonly accepted practice restricts the term to plastics that serve engineering purposes and can be processed and reprocessed by injection and extrusion methods. This excludes the so-called specialty plastics, eg, fluorocarbon polymers and infusible film products such as Kapton and Upilex polyimide film, and thermosets including phenolics, epoxies, urea—formaldehydes, and silicones, some of which have been termed engineering plastics by other authors (4) (see Elastomers, synthetic-fluorocarbon elastomers Fluorine compounds, organic-tetrafluoroethylene copolymers with ethylene Phenolic resins Epoxy resins Amino resins and plastics). 

When considering a production reactor, we first assume that the requisite quality film can be made at least one at a time. The challenge then is to develop a reactor that is capable of acceptable wafer throughput with each wafer having film thickness within an acceptable tolerance. For example, we may want a reactor that can process 30 wafers per hour with thickness uniformity on a single wafer, and from wafer to wafer, of 5%. In addition, we may impose other conditions such as permissible number of particles per cm2, or for epi silicon films, the allowable number of defects per cm2. When we speak of wafer throughput, we are concerned with the actual cost per wafer for this process step. 

A typical surface profile is shown on the video display. Vertical resolution of 5 A and horizontal resolution of 400 A is claimed. As long as the deposited film can be etched off the substrate without etching the substrate, this technique can be used for any thin film. Its primary utility is for R D studies, as it is clearly not a production technique. The only film for which it is not suited is an epi silicon film on a single-crystal silicon substrate. A technique for measuring the thickness of these films will be described in the section on Infrared Spectroscopy. 

An early attempt to make a real electrochemical sensor based on a molecularly imprinted methacrylate polymer utilised conductometric measurements on a field-effect capacitor [76]. A thin film of phenylalanine anilide-imprinted MAA-EDMA copolymer was deposited on the surface of semiconducting p-type silicon and covered with a perforated platinum electrode. An AC potential was applied between this electrode and an aluminium electrode on the back side of the semiconductor and the capacitance measured as a function of the potential when the device was exposed to the analyte in ethanol. The print molecule could be distinguished from phenylalanine but not from tyrosine anilide and the results were very variable between devices, which was attributed to difficulties in the film production. The mechanism by which analyte bound to the polymer might influence the capacitance is again rather unclear. 

Fig. 7.3. Schematic drawing of the string ribbon (SR) process. Two strings are pulled through the silicon melt. They define the edges of the silicon film. Currently two strings are pulled in parallel ( Gemini technique), with a new geometry of four strings in line coming into production (so called Quad process)...

The study of small and intermediate-sized clusters has become an important research field because of the role clusters play in the explanation of the chemical and physical properties of matter on the way from molecules to solids/ Depending on their size, clusters can show reactivity and optical properties very different from those of molecules or solids. The great interest in silicon clusters stems mainly from the importance of silicon in microelectronics, but is also due in part to the photoluminescence properties of silicon clusters, which show some resemblance to the bright photoluminescence of porous silicon. Silicon clusters are mainly produced in silicon-containing plasma as used in chemical vapor deposition processes. In these processes, gas-phase nucleation can lead to amorphous silicon films of poor quality and should be avoided.On the other hand, controlled production of silicon clusters seems very suitable for the fabrication of nanostructured materials with a fine control on their structure, morphological, and functional properties. ... 

Surface bombardment by positive ions (particularly SiH ) plays a critical role in the growth of amorphous silicon films. The silane radicals SiHs and SiH2 have a positive electron affinity therefore, the silane discharge is essentially electronegative and dissociative attachment processes make a significant contribution in the balance of charged particles and production of negative silane ions ... 

Silicone PSA products are used in a number of medical and industrial appKcations, ranging from a variety of PSA tapes and transfer films to automotive bonding. Advantages for the silicone PSA products include resistance to temperature extremes, chemical resistance, conformity to irregular surfaces, and electrical properties. They are also unique to most PSAs in their ability to adhere to difficult low-energy substrates, such as polytetrafluoroethylene and other silicones. 

Be familiar with the design of a representative array of nine chemical products. These products include small hemodialysis devices, solar desalinators, hand warmers, fuel cells to power automobiles, and thin silicon films that coat microelectronic devices. 

About 10 % of the silicone production is used for apparel and technical textiles. In this field silicones are mainly used to functionalize textiles. The characteristic hydrophobicity of silicones was firstly utilised in the mid-1950s. The products used in this period were based on combinations of hydrogen siloxanes and OH-terminated dimethylsiloxane fluids. Catalyzed with metal compounds like tin laurate, these products lead to a crosslinked silicone film on the fiber surface. Compared to the previously used impregnating agents like paraffin waxes or stearylchromium compounds, the silicones provide a much better hydrophobicity and even rubbing fastness and wash resistance are improved dramatically. 

Silicone resin products, water dilutable (M-SFOl) emulsions of silicone resins mineral fillers, inor-ganic/organic pigments, water (dispersing agent), additives (film forming agents < 3%) ... 

Yajima [76] was the first to study the preparation of silicon carbide fibers from carbosilanes. These and other SiC-containing polymers were used to produce SiC powders with a crystallite size as small as several nanometers [77, 78]. The advantage ofthe production route from liquid to solid to produce SiC has also attracted attention for SiC film production in microelectronics or as protection layers. In this way, amorphous, polycrystalline films of high purity produced by the dip-coating of substrates in PCS solutions and subsequent pyrolysis in an inert gas atmosphere, have been prepared [115]. 

Metal salt paraffin dispersions (such as aluminium) are products positively charged due to the trivalent aluminium salt, which produces a counter-polar charge on the fibre surface. Polysiloxanes form a fibre-encircling silicone film with methyl groups perpendicular to the siuface. The hydrophobicity of the finish is affected by the film formation... 

In this review we detail how the color of mesoporous silicon can be tuned, like many other properties (see handbook chapter Tunable Properties of Porous Silicon ). This has been achieved by both control of the physical structure of silicon at the nanoscale and chemical means. The physical color of porous silicon films, membrane flakes, and photonic crystals is much more easily tuned than those of milled microparticle powders. The latter display various shades of brown, rather than the gray of solid silicon, and this has to date been an obstacle for applications in certain high-volume consumer products. 

Other applications of silane include low-temperature chemical vapor deposition of silicon dioxide films by controlled oxidation, chemical vapor deposition of silicon nitride films by controlled reaction with ammonia, and deposition of amorphous silicon films in the production of solar cells and copier drums. 

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