Reactive gas

Gases used in the manufacture of semiconductor materials fall into three principal areas the inert gases, used to shield the manufacturing processes and prevent impurities from entering the source gases, used to supply the molecules and atoms that stay behind and contribute to the final product, and the reactive gases, used to modify the electronic materials without actually contributing atoms or molecules. 

Point-of-Use Purification. For the user of cylinder quantities of reactive specialty gases, there are only a limited number of ways to remove impurities and obtain high purity. Specialized point-of-use purifiers have been developed that purify small streams of many important reactive gases. Whereas these point-of-use purifiers cannot remove all important impurities, they are usually effective for removing the contamination added by the users gas distribution system, mostly air and moisture. 

Finally, the metallisation layer usually requires patterning, which can be done by reactive ion etching (RIE) or back-sputtering. The two processes are similar. In both techniques accelerated ions hit the substrate and forcibly detach atoms or molecules from the surface. RIE uses reactive gases such as chlorine, Cl or trichlorofluoromethane [75-69-4] CCl E. Inert gases such as argon or neon are used in back-sputtering. 

The concentration of indoor pollutants is a function of removal processes such as dilution, filtration, and destruction. Dilution is a function of the air exchange rate and the ambient air quality. Gases and particulate matter may also be removed from indoor air by deposition on surfaces. Filtration systems are part of many ventilahon systems. As air is circulated by the air-conditioning system it passes through a filter which can remove some of the particulate matter. The removal efficiency depends on particle size. In addition, some reactive gases like NOj and SOj are readily adsorbed on interior surfaces of a building or home. 

Coulometry measures the amount of cunent flowing dirough a solution in an electrochemical oxidation or reduction reaction and is capable of measuring at ppm or even ppb levels of reactive gases. Thus a sample of ambient air is drawn through an electrolyte in a cell and the required amount of reactant is generated at the electrode. This technique tends to be non-specific, but selectivity can be enhanced by adjustment of pH and electrolyte composition, and by incorporation of filters to remove interfering species. 

Guidance to Protect POTW Workers from Toxic and Reactive Gases and Vapors, June 1992 812/B-92-001 NSCEP 812/B-92-001 ERIC W115 NTIS PB92-173236. 

Carbon oxohalides are reactive gases or volatile liquids which feature planar molecules of C2t, symmetry they are isoelectronic with BX3 (p. 196) and the bonding is best described in terms of molecular orbitals spanning all 4 atoms rather than in terms of localized orbitals as... 

The nitrosyl halides are reactive gases that feature bent molecules they can be made by direct halogenation of NO with X2, though fluorination of NO with Agp2 has also been used and CINO can be more conveniently made by passing N2O4 over moist KCl ... 

Nitryl fluoride and chloride, XNO2, like their nitrosyl analogues, are reactive gases they feature planar molecules, analogous to the... 

Pollutants have various atmospheric residence times, with reactive gases and large aerosols being rapidly removed from air. In the London air pollution episode of December 1952, the residence time for sulfur dioxide was estimated to be five hours daily emissions of an estimated 2,000 tons of sulfur dioxide were balanced by scavenging by fog droplets, which were rapidly deposited. Most relatively inert gases remain in the atmosphere for extended periods. Sulfur hexafluoride, used extensively in the electric power industiy as an insulator in power breakers because of its inertness, has an estimated atmospheric lifetime of 3,200 years. 

The composition of the atmosphere to which components at high temperature may be exposed varies very widely, and most work on these aspects has accordingly been carried out in clean air. The aggressiveness of air is considerably enhanced by the presence of trace amounts of other reactive gases such as steam, carbon dioxide and sulphur dioxide thus the figures subsequently quoted may in fact be appreciably lower than those encountered in specific atmospheres. The data presented should, however, prove an adequate guide to the order of the effect to be expected. 

Properties of deposits These are usually adherent and coherent. A/, is pure provided that all adverse chemically reactive gases are removed prior to sputtering nitrogen, for example, can form a nitride with copper, and oxygen can form oxides with most metals. 

As mentioned previously, a CVD reaction may occur in the gas phase instead of at the substrate surface if the supersaturation of the reactive gases and the temperature are sufficiently high. This is generally detrimental because gas-phase precipitated particles, in the form of soot, become incorporated in the deposit, causing nonuniformity in the structure, surface roughness, and poor adhesion. In some cases, gas-phase precipitation is used purposely, such as in the production of extremely fine powders (see Ch. 19). 

Neither Ca, Sr nor Ba metal has any structural integrity. The principal application of metallic Ca is as a reducing agent in the preparation of metals, such as Th and Zr. Like Mg, it can be used in the deoxidation and desulfurization of steels. Small quantities are used for alloying with Al and for the removal of Bi from Pb. Neither Sr nor Ba have any significant commercial uses. Barium is used to a limited extent as a getter to remove reactive gases from vacuum tubes. 

Two units in series can be used for highly reactive gases in other reagents... 

The chemically reactive gases ethylene oxide (CH2)20, and formaldehyde (methanal, H.CHO) possess broad-spectrum biocidal activity, and have found application in the... 

Figure 3.11 Schematic diagram of a high-pressure/high-temperature STM design in which only the tip is exposed to reactive gases. The instrument can image a surface, while it is active as a catalyst, under gas flow conditions at pressures up to 5 bar and temperatures up to 500 K. The volume of the cell is 0.5 ml. (Reproduced from Ref. 31).

Type SR-1 compounds include soluble or reactive gases and vapors which are expected to be taken up by the respiratory tract tissues and may deposit in any or all of the regions of the respiratory tract, depending on the dynamics of the airways and properties of the surface mucous and airway tissues, as well as the solubility and reactivity of the compound. 

Type SR-2 compounds include soluble and reactive gases and vapors which are completely retained in the extrathoracic regions of the respiratory tract. SR-2 compounds include sulfur dioxide (S02) and hydrogen fluoride (HF). 

Other Gas Reactions. Several other reactive gases or vapours were examined but found to be unsatisfactory. No ester formation ( 1745 cm"1) was found when oxidatized films were exposed to acetic acid or formic acid vapour. Alcohol/carboxylic acid reactions in the solid state have often been suggested as the source of ester products, but not substantiated (4,5). Gaseous ammonia reacted with carboxylic acid groups to give absorptions at 1550 cm"1 [-C(=0)-0 ] and 1300 cm"1 (NHi +). However, these absorptions were very broad and the method inferior to acid measurement by SF. Although N20 did not react with oxidized polyolefins, the reaction of N02 with oxi-... 

---