Hydrogen-terminated silicon surface oxidation

The procedure for preparing atomically smooth, hydrogen-terminated silicon surfaces involves a number of steps removal of hydrocarbon contamination, formation of a uniform oxide, oxide removal, etching of the silicon surface, and the formation of the passivation layer. The uniformity of the oxide is important in developing a smooth surface at the Si/Si02 interface. 

On the other hand, the different result was obtained for DFM-AFM lithography. The anodic oxidation does not occur in this lithography because the sufficient current is not injected, which is proved in the lithography using the hydrogen-terminated silicon substrate. That is, SAM is not removed from the substrate surface and a different chemical reaction occurs on the SAM surface. 

FTIR has been used to study the sihcon/electrolyte interface. The formation of porous silicon on n-Si during photoetching in fluoride media can readily be followed since the hydrogen-terminated surface is identified by the Si-H stretch bands centred around 2100 cm (Peter et ah, 1989 Peter et ah, 1990a). Similarly, the transition from a hydrogen-terminated to an oxide-covered surface during electropolishing has been followed by in-situ infrared spectroscopy (da Fonseca et al, 1996 and 1997). 

Fig. 59. Molecular modification of semiconductor silicon surfaces. Removal of the oxide generates a hydrogen-terminated layer that reacts with a range of molecular functional groups including alkenes. 

Values of AEG calculated on the basis of the effective mass model are sensitive to the height of the barrier present at the surface of the confined structures [De4, Xu2]. For the case of oxidized PS, it is obvious that the silicon crystallites are embedded in a wide-gap material. In the case of a hydrogen termination of the crys-... 

Therefore, surface modification strategies for the formation of direct silicon-carbon bonds require, first, a special pre-treatment of the silicon surface to prevent oxidation and, second, an activation of the silicon surface for subsequent reaction with organic moieties. This has been achieved by treatment of the silicon surface with hydrofluoric acid to generate a hydrogen-terminated Si(lll) surface, which can further react with unsaturated co-functionahzed alkenes in the presence of UV irradiation or by thermal activation [27,44,45]. Using this method, carboxylic acid modified silicon substrates have been successfully generated and coupled to thiol modified ONDs via a polylysine/sulfosuccinimidyl 4-(M-maleimidomethyl)-cyclohexane-l-carboxylate couphng (Fig. 12). 

The formation of ultraclean and oxide-free surfaces is important in the fabrication of high-quality electronic devices. In some cases stabilization of the surface is also important for example, the Si(lll) surface is unstable in vacuum and reconstructs to a lower-energy configuration, e.g. Si(lll) 7x7. In the last few years, a variety of experimental techniques have been used to investigate the nature of the interaction between silicon surfaces and HF solutions and, in particular, the structure and properties of the hydrogen-terminated surface. 

In summary, oxide layers on silicon surfaces are chemically dissolved in HF leading to the formation of an atomically rough hydrogen-terminated surface. At (111) surfaces, relatively large domains of ideally terminated Si(lll) H (1x1) can be formed by subsequent immersion in buffered HF of pH 8-9. The smoothening process is controlled by the rate of step recession at the surface. 

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