Cleaning chemistries, silicon

Figure 5.2. The clean Si(100)—2 x 1 surface, with rows of silicon dimers lining the surface. The buckling of the dimers is shown in this figure. These dimers play an important role in the chemistry of organic molecules at this surface.

This chapter will focus on organic/silicon interfaces formed via solution phase reactions using hydrogen-terminated crystalline silicon surfaces as a starting point. While some of the surface chemistry issues have been reviewed previously [7,8], more recent developments will be emphasized here. We will not discuss the considerable literature of reactions with porous silicon [8], or studies of molecules reacting with clean silicon surfaces under ultrahigh vacuum (UHV) conditions [9-11] which have been reviewed elsewhere. 

In brush cleaning, an alkaline chemistry such as NH4OH is often used to remove the particles such as particles of silica, alumina, glass, polystyrene latex (PSL), and silicon nitride from various wafers in the first brush. The basic chemistry is used mainly to increase the repulsive charge by the zeta potential between the particle and the substrate. 

Effects of Various Chemistries on Silicon-Wafer Cleaning... 

In the 1970s and 1980s both the clean and H-covered Si surfaces were characterized by diffraction and spectroscopic methods, but only in the last decade have there been reproducible studies of chemical kinetics and dynamics on well-characterized silicon surfaces. Despite the conceptual simplicity of hydrogen as an adsorbate, this system has turned out to be rich and complex, revealing new principles of surface chemistry that are not typical of reactions on metal surfaces. For example, the desorption of hydrogen, in which two adsorbed H atoms recombine to form H2, is approximately first order in H coverage on the Si(lOO) surface. This result is unexpected for an elementary reaction between two atoms, and recombi-native desorption on metals is typically second order. The fact that first-order desorption kinetics has now been observed on a number of covalent surfaces demonstrates its broader significance. 

In-situ emd thin-film growth studies of SiOa on Si have been performed by a number of investigators to study the interface chemistry (21,22,35,36). Hollinger, et al.(35) exposed atomically clean silicon to a pure oxygen ambient at 5 x 10 Ibrr pressiue at 700 C in their analysis chamber. Spectra were excited with Mg K-a x-rays which produce 1154 eV Si 2p electrons with an escape depth of approximately 34 A (32). Both the O Is and Si 2p peaks were followed as a function of exposure and... 

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