Evaluating the minimum thickness of gate oxide on silicon using first-principles method

The continuing reduction in integrated circuit element size results in contemplating physical structures with dimensions in which an atomistic picture becomes important. So far, an essential element responsible for the ever-shrinking device is the feasibility of reducing the SiO2 gate insulator thickness from one technology generation to another. Using a first-principles pseudopotential approach, we made such an attempt to evaluate the minimum thickness of SiO2 on Si substrate at which a proper barrier height between SiO2 and Si holds. This was done by studying the band offset between SiO2 and Si as a function of SiO2 thickness. The SiO2/Si(100) interface structure is constructed between β-cristobalite SiO2 layer and Si(001). Three superlattices containing two, four and eight layers of SiO2 are considered. Based on the fact that the band offsets reach a saturation value after approximately 7 Å of SiO2 thickness, we estimate that the minimum gate oxide thickness is 7 Å.