Roughness measurements of thin SiO2 and poly-Si interfaces using high resolution cross-sectional TEM

Interfaces related to gate oxide in MOSFET with Si(100)/SiO2/poly-Si system have been investigated. Using cross-sectional transmission electron microscopy, we observe the interfacial roughness between the poly-Si/SiO2 and the Si/SiO2 interfaces. Six different kinds of samples with SiO2 thicknesses varying from 1.4 to 50nm are grown by dry oxidation. The interfacial roughnesses of both Si/SiO2 and poly-Si/SiO2 have similar dependence on SiO2 thickness (T-ox) and are observed to be larger in the ultra-thin oxides (T-ox less than or equal to 4.2nm). T-ox is also found to exhibit larger variations for small T-ox although the undulation of poly-Si/SiO2 interfaces agrees, to some extent, with the underlying Si/SiO2 interfaces from place to place for T-ox less than or equal to 2.4nm. These results suggest that the surface control at atomic level will become an extremely critical issue in fabricating MOSEET with ultra-thin gate oxides.