Silicones mechanical defects

In the early days of silicon device manufacturing the need for surfaces with a low defect density led to the development of CP solutions. Defect etchants were developed at the same time in order to study the crystal quality for different crystal growth processes. The improvement of the growth methods and the introduction of chemo-mechanical polishing methods led to defect-free single crystals with optically flat surfaces of superior electronic properties. This reduced the interest in CP and defect delineation. 

W. Frank. The interplay of solute and self-diffusion—A key for revealing diffusion mechanisms in silicon and germanium. In D. Gupta, H. Jain, and R.W. Siegel, editors, Defect and Diffusion Forum, volume 75, pages 121-148, Brookfield, VT, 1991. Sci-Tech Publications. 

Three questions concerning ultrastabilization remain outstanding. They regard the precise mechanism of A1 removal, the nature of the intermediate defect structure (both are depicted schematically in Fig. 38), and the origin of the silicon needed for framework reconstruction. Gas sorption studies (172) indicate that materials prepared in a manner similar to that for sample 4 in ref. 163 (see above) contain a secondary mesopore system with pore radii in the range IS-19 A, suggesting that tetrahedral sites are reconstituted with silicon that, contrary to earlier speculations, does not come only from the surface or from amorphous parts of the sample, but also from its bulk, which may involve the elimination of the entire sodalite cages. 

Theoretical studies of diffusion aim to predict the distribution profile of an exposed substrate given the known process parameters of concentration, temperature, crystal orientation, dopant properties, etc. On an atomic level, diffusion of a dopant in a silicon crystal is caused by the movement of the introduced element that is allowed by the available vacancies or defects in the crystal. Both host atoms and impurity atoms can enter vacancies. Movement of a host atom from one lattice site to a vacancy is called self-diffusion. The same movement by a dopant is called impurity diffusion. If an atom does not form a covalent bond with silicon, the atom can occupy in interstitial site and then subsequently displace a lattice-site atom. This latter movement is believed to be the dominant mechanism for diffusion of the common dopant atoms, P, B, As, and Sb (26). 

Point Defect Generation During Phosphorus Diffusion. At Concentrations above the Solid Solubility Limit. The mechanism for the diffusion of phosphorus in silicon is still a subject of interest. Hu et al. (46) reviewed the models of phosphorus diffusion in silicon and proposed a dual va-cancy-interstitialcy mechanism. This mechanism was previously applied by Hu (38) to explain oxidation-enhanced diffusion. Harris and Antoniadis (47) studied silicon self-interstitial supersaturation during phosphorus diffusion and observed an enhanced diffusion of the arsenic buried layer under the phosphorus diffusion layer and a retarded diffusion of the antimony buried layer. From these results they concluded that during the diffusion of predeposited phosphorus, the concentration of silicon self-interstitials was enhanced and the vacancy concentration was reduced. They ruled out the possibility that the increase in the concentration of silicon self-interstitials was due to the oxidation of silicon, which was concurrent with the phosphorus predeposition process. 

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