Thermal oxidation, silicon

Finally, with some precursors, complete removal of contaminants can sometimes be troublesome. Consequently, some authors have chosen to use dioxygen as the reactive gas to avoid carbon contamination [62-64]. Thus, pure platinum films have been obtained on thermally oxidized silicon substrate by decomposition of [Pt(CH3)3(CpCH3)j or [Pt(K -acac)2] in ArjOj mixtures at 623 K. Pt films produced from [Pt(K -acac)2] contained less than lat% carbon, while oxygen contamination was not detectable [64]. Similarly, a significative reduction of carbon incorporation into Ru films was evidenced when oxygen was used as a reactive gas during CVD from [RuCp(CO)2]2 [62]. 

Deal, BE, Standardized Terminology for Oxide Charges Associated with Thermally Oxidized Silicon, J. Electrochem. Soc., 127, 979, 1980. 

In fabrication of the catalysts by laser electrodispersion, thermally oxidized silicon wafers with a thickness of Si02 oxide layer of 1 pm were used as a substrate. A substrate with so thick an oxide layer can be regarded as an insulator. In some cases, wafers of crystalline (1 0 0) Si were used, which had on their surface only a thin (l-2nm) layer of a natural oxide. This layer is tunnel-transparent for electrons, and, therefore, charge exchange between supported nanoparticles and silicon is possible. 

Fig. 15.12. Specific catalytic activity vs. surface density of copper nanoparticles on thermally oxidized silicon in reactions involving chlorohydrocarbons (1) CC14 + C8H16 at 150°C, (2) the same at 130°C and e = 10, (3) isomerization of dichlorobutenes at 110°C, (4) isomerization of dichlorobutenes at 130°C, and (5) CC14 + C10H22 at 130°C.

Fig. 15.14. Comparison of specific catalytic activities of Ni and Cu nanoparticles deposited onto a thermally oxidized silicon by laser electrodispersion (n m 5 x 1012cm-2) with those of catalysts prepared by the method of impregnation and reduction (1% Ni/Si02, 1% Cu/Si02). Reaction of carbon tetrachloride addition to olefins.

FIG. 5 Particle mobility profile (from plate to plate) between two thermally oxidized silicon wafers in I mM NaCI at various locations from the sidewall 0.1 mm ( ). 0.4 mm (O), 0.902 mm ( ). and 2.5 mm (A). Drawn lines correspond to a linear least squares curve tit to the hydrodynamic equations describing fluid flow between the plates. 

B. E. Deal, The current understanding of changes in the thermally oxidized silicon structure, J. Electrochem. Soc. 121, 198c, 1974. 

In addition to the anodized aluminium specimens, commercially available glass plates for microscopic studies and thermally oxidized silicon wafers (20 mm x 20 mm pieces with a hole) were also coated for model experiments. These hydrophilic materials were ultrasonically cleaned in ethanol (analytical grade, 10 min). Thick polymer films on glass plates were formed by solvent evaporation of the polymer solution (10%). The wafers were spin-coated (solution of 1% polymer in 2-butanone, 2000 min 30 s) and heated at 120°C for 1 h. Typical thicknesses of these layers were about 50 nm. 

Fig. 5.2-69 Interface state density in thermally oxidized silicon for two different orientations. Notice the low density around mid-gap [2.95, after [2.48] p. 340]...

Cr-O-Si cermet layers were prepared by RF-sputtering of a Cr 0 Si target (Leybold-Heraeus Co.) with a nominal atomic ratio of 1 1 1, onto thermally oxidized silicon wafers in a Leybold-Heraeus Z 801 load lock system as described in [86]. The thicknesses of the cermet layers were in the range of 100-200 nm. The SiO < layer was deposited in a Balzers-BAK 550 box coater by electron beam evaporation of an SiO. x 1) source material at lO Pa, onto an oxidized Al substrate at 300°C. Typical atomic ratios of Cr 0 Si = (0.8-l) (Ll-1.2) (l) for the cermet and of 0 Si = 1.3 1 for the SiO, layer were measured by RBS for the as-deposited layers, with homogeneous in-depth distributions of the constituents. The samples proved to be completely amorphous in the as-grown state as shown by both XRD and selected arc electron diffraction (SAED). Trace amounts of a CrjSi phase were found only after heat treatment at 600°C. 

Another motivation for searching alternate dielectrics is that silicon oxide also presents several drawbacks in terms of the quality of the insulator-semiconductor interface. Also, the realization of more complex circuits than individual transistors is not possible with thermally oxidized silicon wafers, because in that case the gate electrode cannot be patterned. 

Electrochemical oxidation of (Hg,Cd)Te has several shortcomings. Various reports have indicated a lack of thermal stability of the oxide (2)(10-13). Also, the oxide-semiconductor interface and oxide near the interface has relatively poor interface quality as compared to thermally oxidized silicon (14-18). Anodic oxidation at an elevated temperature has been used in one instance (9), and was reported to have increased stabiiity over room temperature anodic oxides. This idea has not been further explored. 

In our experiments, nanotubes are grown on thermally oxidized silicon wafers by the CVD of xylene (CgHio), and ferrocene (Fe(C5H5)2). Ferrocene is dissolved in xylene at concentrations of 0.01 g/ml, preheated at about 150-180°C, co-evaporated and fed into the CVD chamber, which was pumped down to a... 

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