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Thursday, 29 July 2004

Ordering in Thermally Oxidized Silicon

New evidence is overturning the assumption that the thermal oxide grown on single crystal silicon is completely amorphous. SSRL researchers Anneli Munkholm (now at Lumileds Lighting) and Sean Brennan recently published work in Physical Review Letters showing that there is residual order within the oxide. The thermal oxide film on silicon has been studied extensively for decades because these oxides form the basis of most of the integrated circuits used in modern electronics. The new results have implications for theoretical models of the oxidation process.

The residual order was found in a wide range of oxidation recipes with oxide thicknesses from 6 nanometers (nm) up to 100 nm, on silicon with different surface orientations (Si(001) surfaces with and without miscut, as well as for Si(011) and Si(111) surfaces). The new model depends on the silicon atoms within the oxide becoming disordered while expanding towards the surface due to injection of oxygen atoms into the silicon lattice. The expansion and the disorder are smaller at the interface between the crystal and oxide film than at the surface. The results can be used to determine the density of the oxide as a function of its depth. The amount of residual order varies depending on the oxidation recipe used, suggesting that the residual order can be controlled.

Reference: Phys. Rev. Lett. 93, 036106 (2004)