Oxides and Nitrides

The most surprising finding in magnetism is that non-magnetic semiconductors such as ZnO and GaN [15], CuO, and Ti02 [16] become ferromagnetic at room temperature and above when they are doped with just a few percent of transition 

Such undercoordination-associated dilute magnetism cannot be understood in terms of the conventional superexchange or double-exchange interactions theory of magnetism in insulators nor can a carrier-mediated ferromagnetic exchange mechanism account for the magnimde of the Curie temperatures, which are well in excess of 400 K (1/30 eV). 

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Calcium hydride is highly ionic and is insoluble in all common inert solvents. It can be handled in dry air at low temperatures without difficulty. When heated to about 500°C, it reacts with air to form both calcium oxide and nitride. Calcium hydride reacts vigorously with water in either Hquid or vapor states at room temperature. The reaction with water provides 1.06 Hters of hydrogen per gram CaH2. 

Gate oxide dielectrics are a cmcial element in the down-scaling of n- and -channel metal-oxide semiconductor field-effect transistors (MOSEETs) in CMOS technology. Ultrathin dielectric films are required, and the 12.0-nm thick layers are expected to shrink to 6.0 nm by the year 2000 (2). Gate dielectrics have been made by growing thermal oxides, whereas development has turned to the use of oxide/nitride/oxide (ONO) sandwich stmctures, or to oxynitrides, SiO N. Oxynitrides are formed by growing thermal oxides in the presence of a nitrogen source such as ammonia or nitrous oxide, N2O. Oxidation and nitridation are also performed in rapid thermal processors (RTP), which reduce the temperature exposure of a substrate. 

Etching. After a resist is patterned on a wafer, the exposed or unwanted substrate is removed by etching processes. Subsequentiy the resist is removed, leaving a desired pattern in a functional layer of the integrated circuit. Etching is performed to pattern a number of materials in the IC fabrication process, including blanket polysiHcon, metal layers, and oxide and nitride layers. The etch process for each material is different, and adapted to the material requirements of the substrate. 

Early work in ellipsometry focused on improving the technique, whereas attention now emphasizes applications to materials analysis. New uses continue to be found however, ellipsometry traditionally has been used to determine film thicknesses (in the rang 1-1000 nm), as well as optical constants. " Common systems are oxide and nitride films on silicon v ers, dielectric films deposited on optical sur ces, and multilayer semiconductor strucmres. 

MOSFETT s, and silicon oxide is deposited. The source/drain positions where electrical contact is to be made to the MOSFETs are defined, using the oxide-removal mask and an etch process. For shallow trench isolation, anisotropic silicon etch, thermal oxidation, oxide fill and chemical mechanical leveling are the processes employed. For shallow source/drains formation, ion implantation techniques are still be used. For raised source/drains (as shown in the above diagram) cobalt silicide is being used instead of Ti/TLN silicides. Cobalt metal is deposited and reacted by a rapid thermal treatment to form the silicide. Capacitors were made in 1997 from various oxides and nitrides. The use of tantalmn pentoxide in 1999 has proven superior. Platinum is used as the plate material. 

Starting MaterlabSi wafer covered with a layer of oxide and nitride... 

Metal halides, oxides, and nitrides Bent s rule for transition metals... 

Main-group elements X such as monovalent F, divalent O, and trivalent N are expected to form families of transition-metal compounds MX (M—F fluorides, M=0 oxides, M=N nitrides) that are analogous to the corresponding p-block compounds. In this section we wish to compare the geometries and NBO descriptors of transition-metal halides, oxides, and nitrides briefly with the isovalent hydrocarbon species (that is, we compare fluorides with hydrides or alkyls, oxides with alkylidenes, and nitrides with alkylidynes). However, these substitutions also bring in other important electronic variations whose effects will now be considered. 

Figure 7.15 (a) Enthalpy of formation of ternary oxides and nitrides from their binary constituent compounds as a function of the ratio of ionic potential [16]. Reprinted with permission from [16] Copyright (1997) American Chemical Society, (b) Gibbs energy of the oxide-sulfide equilibrium for group 1 and 2 metals at 1773 K as a function of the optical basicity of the metal. 

In this section the properties of chemically and thermally oxidized and nitridized PS will be discussed. Wet anodic oxidation of PS is commonly accompanied by luminescence and is therefore discussed in Section 7.4. 

The submitters used lithium (99.9%, Alfa Products) as a ribbon (0.28 mm thick, 25 mm wide). [The checkers used lithium (99.9%, Aldrich Chemical Company, Inc.) as a wire (3.2 mm diam. in mineral oil).] Its surface was cleaned by scraping off the lithium oxide and nitride with an X-Acto knife under mineral oil. The ribbon was then cut into 20-30 mg pieces that were rinsed with pentane before use. 

TABLE 9.1 Various Properties of Metal Oxides and Nitrides... 

TABLE 9.2 Temperatures and Heats of Volatilization of Various Oxide and Nitride Products at Various Pressures3... 

In order to achieve selective oxide and nitride etching, additives to F-source plasmas are chosen to make a F-deficient chemical environment. These include H2, C2H4 and CH4 which are quite efficient F scavengers. The amount of additive necessary remains more an art than a science because oxide and nitride selectivity requires operation in an environment very close to the demarcation between etching and polymerization shown in Figure 10. In fact in some cases (57,59) polymer deposition on Si occurs... 

The use of pre-cut metal is dissuaded since the coating of oxide and nitride on the cutting surface makes dissolution difficult... 

The hydrides, oxides and nitrides of the elements of the first three groups of the periodic system all behave as normal ionic compounds. They all show normal valencies, they crystallize in coordination lattices, do not show any metallic conductivity and, in so far as an estimate can be made of their heats of formation, they agree fairly well with the values to be expected for ionic compounds. 

The structures of the hydrides, oxides and nitrides in this group are rather peculiar, for they can always be described as lattices, as found in pure metals, with the negative ions inserted in the octahedral holes of these structures. In the case of TiN, TiO and, in general, all compounds AB, all octahedral holes are occupied, and the structure is that of the sodium chloride type. There are nitrides of other types, too, e.g. A2N, A3N, etc., in which cases only a part of the octahedral holes are occupied. 

The ligands oxide and nitride, O2- and N3, occupy even more space than do halide ions and have correspondingly lower effective bond length ratios R(02 [L) 0.6 R(02 /X ) 0.8. 

Boron is (1) a yellowish-brown crystalline solid and (2) an amorphous greenish-brown powder. Both forms are unaffected by air at ordinary temperatures but when heated to high temperatures in air form oxide and nitride. Crystalline boron is unattacked by HC1 or HNO3, or by NaOH solution, but with fused NaOH forms sodium borate and hydrogen reacts with magnesium but not with sodium. 

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