Silicon oxide surface as a substrate of polymer thin films

We have measured the thickness of the oxide layer of Si wafers as a function of annealing temperature following treatment with either a modified Shiraki method (hydrophilic) or HF etching (hydrophobic). The results show that in both cases there exists a well-defined oxide layer, approximately 20 Angstrom thick, which forms within at least 20 min of the processing. The density of this layer is initially 35% of the usual silicon oxides. The density of this layer gradually increases, approaching that of the pure oxides as the substrates are annealed from room temperature to 180 degreesC. These results were interpreted in terms of a complexed layer of water. These results are consistent, with dynamic secondary ion mass spectrometry, which shows that the amount of oxygen at the Si interface decreases with increasing temperature. The activation energies, obtained 31.6 and 19.3 kJ/mol for the hydrophilic and hydrophobic surfaces, are consistent with the evaporation energy of water. The effect of the adsorbed water was also evident on the diffusion coefficient of PS from the Si interface. The diffusion coefficient (D*) was expressed as D* = D-WLF(T) exp(-DeltaE(s)/kT) where D-WLF. is the usual WLF temperature dependence diffusion coefficient, and the additional activation energy measured was DeltaE(s) similar to 6.7 kJ/mol per contact. The energy corresponds to the interaction energy between styrene monomers and mostly the adsorbed water layer.