Selective Oxide Deposition

FIGURE 12.24 Schematic cross section of a wafer with selective oxide deposition. 

The selective oxide deposition technique has been additionally developed for BEOL planarization of ILD films, where the difference in deposition rates of ozone/TEOS on PECVD oxide and TiN is exploited [38]. 

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FIGURE 12.25 REM image of a wafer after selective oxide deposition. 

Elbel N, Gabric Z, Langheinrich W, Neureither B. A new STI process based on selective oxide deposition. Symposium on VLSI Technology, Digest of Technical Papers June 1998. p 208-209. 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

A second type of siUcon nitride, called stoichiometric siUcon nitride, is deposited at much higher temperatures using CVD or LPCVD in the form of Si N. Stoichiometric siUcon nitride can be used as a mask for the selective oxidation of siUcon. Here the siUcon nitride is patterned over a siUcon substrate, and the exposed siUcon is oxidized. The siUcon nitride oxidizes very slowly compared to the siUcon. 

CVD processing can be used to provide selective deposition on certain areas of a surface. Selective tungsten CVD is used to fill vias or holes selectively through siUcon oxide layers in siUcon-device technology. In this case, the siUcon from the substrate catalyzes the reduction of tungsten hexafluoride, whereas the siUcon oxide does not. Selective CVD deposition can also be accompHshed using lasers or focused electron beams for local heating. 

It was quite recently reported that La can be electrodeposited from chloroaluminate ionic liquids [25]. Whereas only AlLa alloys can be obtained from the pure liquid, the addition of excess LiCl and small quantities of thionyl chloride (SOCI2) to a LaCl3-sat-urated melt allows the deposition of elemental La, but the electrodissolution seems to be somewhat Idnetically hindered. This result could perhaps be interesting for coating purposes, as elemental La can normally only be deposited in high-temperature molten salts, which require much more difficult experimental or technical conditions. Furthermore, La and Ce electrodeposition would be important, as their oxides have interesting catalytic activity as, for instance, oxidation catalysts. A controlled deposition of thin metal layers followed by selective oxidation could perhaps produce cat-alytically active thin layers interesting for fuel cells or waste gas treatment. 

Last but not least, one should check the inertness of the auxiliary electrodes in single-pellet arrangements, both under open and closed circuit conditions and, also, via the closure of the carbon balance, the appearance of coke deposition. This is especially important in systems with a variety of products (e.g. selective oxidations), where the exact value of selectivity towards specific products is of key interest. This in turn points out the importance of the use of a good analytical system and of its careful calibration. 

VOx supported on TiOi showed good catalytic activity in the selective oxidation of H2S to ammonium thiosulfate and elemental sulfur. V0x/Ti02 catalysts prepared by the precipitation-deposition method can achieve higher vanadium dispersions, and higher H2S conversions compared to those prepared by the impregnation method. 

This method is especially valid for the preparation of gold NPs mixed with activated carbon, which are active and stable for the selective oxidation of hydrocarbons and alcohols in water. Over activated carbon gold could not be directly deposited as NPs by using the techniques described above, such as DP and even by GG. Gold colloids with mean diameters from 2.5 to lOnm stabilized by poly vinyl alcohol or poly vinyl p5rrolidone are used. 

On the other hand, if the hole flow in DNA could be artificially controlled to deposit at the desired site in DNA, it may enable site-selective oxidation and strand scission of DNA, which is desirable from a therapeutical standpoint. Furthermore, understanding DNA-mediated hole transfer is expected to lead to an additional application in the development of biosensors and bioelectronic devices [9]. Therefore, the regulation of the transfer rate and direction of the hole generated in DNA is of interest from the perspective of using DNA as a building block for electronic devices. 

Selective Oxidation-Dehydrogenation and Oxygenation of Organic Molecules Spencer, James, T., Chemical Vapor Deposition of Metal-Containing Thin-Film 40 291... 

There are several ways to prepare thin films for use as model catalyst supports.30-31 For the purposes of this review, we will point the reader toward other sources that discuss two of these methods direct oxidation of a parent metal and selective oxidation of one component of a binary alloy. 32 34 The remaining method consists of the deposition and oxidation of a metal on a refractory metal substrate. This method has been used extensively in our group323131 11 and by others33-52-68 and will be the focus of the discussion here. The choice of the metal substrate is important, as lattice mismatch between the film and the substrate will determine the level of crystallinity achieved during film growth. 

M. Haruta, B. S. Uphade, S. Tsubota, and A. Miyamoto, Selective oxidation of propylene over gold deposited on titanium-based oxides, Res. Chem. Intermed. 24(3), 329-336 (1998). 

Q. Zhu, R. M. van Teeffelen, R. A van Santen, and E. J. M. Hensen, Effect of high-temperature treatment on Fe/ZSM-5 prepared by chemical vapor deposition of FeCls 11. Nitrous oxide decomposition, selective oxidation of benzene to phenol, selective reduction of nitrous oxide by MO-butane, J. Catal. 221, 575—583 (2004)... 

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... 

In the selective oxidation of hydrocarbons or in fuel technologies, catalysed carbon deposition from the gas phase can occur, which can lead to catalyst... 

Oxidation of Tetramethylethylene. Tetramethylethylene, TME, was an excellent model olefin since it was rapidly and selectively oxidized in the presence of many transition metal complexes (12). Oxidation of TME in the presence of the group VIII metal complexes [MCI(CO)-(Ph3P)2] (M = Rh, Ir) at 50°C gave two major products 2,3-dimethyl-2,3-epoxybutane, I, and 2,3-dimethyl-3-hydroxy-l-butene, II (Reaction 5). Reaction mixtures were homogeneous with no observable deposits of insoluble materials. Little oxidation occurred under these conditions in the absence of the metal complexes, but low yields of I and II were obtained in the presence of a radical initiator (Table I). Reactions were severely inhibited by hydroquinone. The ruthenium (II) complex, [RuCl2(Ph3P)3]2, also promoted efficient oxidation of TME yielding I... 

A number of other types of processes that can be considered a form of self-assembly at surfaces are just beginning to appear. The selective oxidation of silicon, followed by etching of the silicon dioxide, as a route to silicon nanowires is an example172 the galvanic deposition of platinum on selenium nanostructures, followed by removal of the selenium, to make nanowalls with complex shapes is a second173,174. 

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