Preparation and structure of epitaxial CeO2/YSZ/Si buffer layer

Growth of an epitaxial insulating ceramic layer on silicon substrate is a key technology to realize memory devices such as DRAM and FRAM. For these devices, preparation of epitaxial buffer layer between ferroelectric layer and Si substrates is essential to prevent interdiffusion and to form electrically clean interface between ferroelectric layers and Si substrates. This study describes preparation and interface structure of CeO2/YSZ buffer layer on Si(001) substrates. The buffer layer was prepared by either sputtering or pulsed laser deposition (PLD). For sputtering, (Zr+Y) metal film was deposited on SiO2/Si(001) substrate. The metals were reacted with SiO2 layer having a few nm thick on the surface of Si substrate to form epitaxial YSZ thin layer (reactive sputtering). Then additional YSZ thin films and CeO2 films were deposited using YSZ and CeO2 ceramic target, respectively. For PLD, a KrF excimer laser was focussed on the YSZ sintered target and formed a very thin YSZ film on a Si(001). After YSZ layer formation, CeO2 was also deposited on YSZ layer and epitaxial CeO2 layer was prepared. The critical thickness of YSZ layer in order to prepare epitaxial CeO2 layer was only 0.5 nm, which corresponds to only one atomic layer of YSZ. The mechanism of epitaxial layer formation, crystal structure and interface structure were discussed for the buffer layers prepared by both sputtering and PLD.