Diffusion coefficient of B in HfO2

We implanted B ions in a 110-nm-thick HfO₂ layer, subjected the substrates to various thermal processes, and evaluated the diffusion coefficient by comparing experimental and numerical data. We found that the diffusion coefficient of B in HfO₂ is higher than that in SiO₂ by about four orders and almost the same as that in Si. Therefore, the penetration of B through this layer can be expected to be significant, making the use of a cover layer indispensable for p⁺ polycrystalline silicon gate devices.