We propose a novel technique to form Si/Ge/SiO2 multilayered structures by utilizing ion implantation of oxygen into Si/Ge multilayers. Figure 1 shows the processes used in this technique. First Si/Ge multilayers are formed on a Si substrate and then oxygen ions are implanted into these samples. Since the final stable state of oxygen is SiO2, oxygen atoms implanted into the Ge layers change their bonding partners from Ge to Si atoms if oxygen atoms in the Ge layers are mobile. Figure 2 shows the Auger electron spectroscopy (AES) depth profiles of a sample of Si(30 nm)/Ge(28 nm)/Si(30 nm)/Si-substrate, (a) as-implanted and (b) after annealing in H2 atmosphere at 400 deg followed by additional annealing in Ar at 600deg. The energy and the dose of oxygen implantation in the experiments were 30 keV and 1x10^17 cm-2. In the oxygen depth profile, two peaks are clearly observed near the interfaces between the Ge layer and the upper and lower Si layers. This means that oxygen atoms move to the interfaces during the implantation process. After the annealing, the oxygen profile becomes sharper. At the same time, a shoulder in the Ge profile appears at a depth which corresponds to the deeper oxygen peak. This indicates that Ge atoms are excluded from the Si oxide layer. By using this process, we can fabricate multilevel buried oxide layers in a Si/Ge structure. Since SiO2 forms a large barrier to Si and Ge, new Si-based materials for electronic and optical devices are expected to be made.
Fig. 1: Fabrication process of multilevel buried oxide layers by oxygen-ion-implanted into Si/Ge multilayers..
Fig. 2: AES depth profiles of Si, Ge, and O for a Si/Ge/Si sample: (a) as-implanted, (b) after hydrogen-annealing at 400deg followed by 600deg Ar-annealing.
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