Channeled ion beam synthesis: a new technique for forming high-quality rare-earth silicides

Abstract

High dose 166Er or 160Gd implantations are used to form rare-earth (RE) silicides in Si. After implanting 0.8−2.0 × 10 17 at./cm 2 with 90 keV into Si(111) substrates kept at ∼ 450 to 530°C, we found that using conventional non-channeled implantation (tilted over 7°), it is impossible to form a continuous RESi 1.7 layer. On the contrary, using channeled implantation, a continuous epitaxial ErSi 1.7 layer with very good crystalline quality can be synthesized; a lowest χ min value of 1.5% for a surface ErSi 1.7 layer is obtained. This different behaviour is explained using a model based on the difference in implantation depth, defect density and sputtering yield between random and channeled implantation, and the results are compared with Monte Carlo simulations. Such a high-quality RESi 1.7/Si system offers a rare opportunity to study the structure, orientation and strain comprehensively using Rutherford backscattering and channeling spectrometry, X-ray diffraction and TEM. We found that the azimuthal orientation of the hexagonal RESi 1.7 layer to the cubic Si substrate is RESi 1.7[0001]/t|Si[111] and RESi 1.7{11 2 0}/t|Si{110}. It is further observed that the ErSi 1.7 epilayer is compre strained and quasi-pseudomorphic. In the case of GdSi 1.7, the most difficult rare-earth silicide to form, and enhanced stabilization of the hexagonal over the orthorhombic phase is observed.