Ferroelectric Oxide Single-Crystalline Layers by Wafer Bonding and Hydrogen/Helium Implantation
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U11.8.1
Ferroelectric Oxide Single-Crystalline Layers by Wafer Bonding and Hydrogen/Helium Implantation
Ionut Radu, Izabela Szafraniak, Roland Scholz, Marin Alexe, and Ulrich Gösele Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany ABSTRACT Layer splitting by helium and/or hydrogen and wafer bonding was applied for the transfer of thin single-crystalline ferroelectric oxide layers onto different substrates. The optimum conditions for achieving blistering/splitting after post-implantation annealing were experimentally obtained for LiNbO3, LaAlO3, SrTiO3 single crystals and transparent PLZT ceramic. Under certain implantation conditions large area exfoliation instead of blistering occurs after annealing of as-implanted oxides. Small area single-crystal oxide layer transfer was successfully achieved. INTRODUCTION One of the main demands for the integration of functional materials, including ferroelectric oxides, is the availability of high-quality oxide thin layers on technological important substrates. In recent years a major effort has been directed towards integration of oxide materials into semiconductor technology. Epitaxial growth approach lead to singlecrystalline films, but for a large lattice mismatch in the percentage range a high density of threading dislocation can hardly be avoided if a critical thickness has been exceeded. Layer transfer by hydrogen implantation and wafer bonding is one of the promising approaches for non-lattice-matched materials integration allowing fabrication of complex heterostructures, which cannot be obtained by classical thin film deposition methods [1]. This technology, also known as “Smart-Cut®”, “layer splitting”, or “layer exfoliation”, was first introduced by Bruel [2] in 1995 as a highly effective method for the fabrication of high quality silicon-on-insulator (SOI) wafers. Briefly a donor wafer is implanted with helium and/or hydrogen at a certain energy with doses ranging from 1016 up to 1017 cm-2. The as-implanted donor wafer is then bonded to a host wafer and annealed at elevated temperatures, first to increase the bonding energy, and then to achieve splitting. Application of the layer splitting approach for complex oxides is an attractive alternative to fabricate thin single-crystalline oxide films with precise thickness on any substrate at low temperatures [3]. It was previously shown that in order to achieve splitting after a post implantation annealing the wafer temperature during implantation must fall within a window that is specific to each material [4]. For perovskite oxides the temperature window is rather narrow making the layer transfer a relatively difficult process. The present paper shows our latest achievements concerning layer splitting of oxide materials including the optimization of the implantation parameters as well as the annealing conditions for layer splitting. It shows also for the first time the transfer of small area singlecrystal oxide layers with sub-micron thicknesses.
U11.8.2
EXPERIMENTAL In the present
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