Diffusion in SiO₂

· Diffusion in SiO₂ films is important as it is used as a mask to prevent diffusion of impurity atoms in silicon

· Group III and Group V elements are glass formers in SiO₂ and so lower the melting temperatures of the oxide film.

· As a general rule, over the temperature used in VLSI, diffusivities of B, As, P and Sb are very low when their concentrations are below that which causes the glass to melt.

· Hydrogen, He, OH, Na, O₂ and Ga are fast diffusants in SiO_2.

· SIMS analysis is a powerful tool for diffusion profile measurements. It can measure boron and arsenic concentrations as low as 5X10¹⁵ atoms /cm³, and has a high depth resolution of a few tens of angstroms. Therefore it is an ideal tool for measuring shallow diffusion profiles.