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A new fabrication method of SiGe-on-Insulator (SGOI) and Ge-on-Insulator (GOI) structures are presented as well as the application to high-mobility channel CMOS devices. This method, the Ge-condensation technique, consists of epitaxial growth of a SiGe layer with a low Ge fraction on an SOI substrate and successive oxidation at high temperatures, which can be incorporated in conventional CMOS processes. During the oxidation, Ge atoms are pushed out from the oxide layer and condensed in the remaining SiGe layer. The interface between the Si and SiGe layers is disappeared due to the interdiffusion of Si and Ge atoms. Eventually, an SGOI layer with a higher Ge fraction is formed on the buried oxide layer. The Ge fraction in the SGOI layer can be controlled by the oxidation time because total amount of Ge atoms in the SGOI layer is conserved throughout the oxidation process. We found that the lattice relaxation in the SGOI layer also can be controlled through the initial SiGe thickness. P- and n-type strained SOI MOSFETs, which were fabricated on relaxed SGOI substrates formed by this technique, exhibited mobility enhancement of 50% and 80%, respectively. CMOS ring oscillators comprised of the MOSFETs exhibited reduction in propagation delay of 70%-30% compared to a conventional SOI-CMOS device. Ultrathin-body strained SGOI pMOSFETs with high Ge fraction and surface channels were also fabricated by this technique. These devices exhibited hole-mobility enhancement factors up to 2.3. Furthermore, Ge-on-Insulator (GOI) structures with thicknesses less than 10 nm were realized for ultrathin body GOI-CMOS applications by using the Ge-condensation technique. In conclusion, the Ge-condensation technique is a promising technique for fabricating various types of high-mobility channel-on-insulator devices.
An ionized cluster beam (ICB) source was used to deposit Al onto SiO2 substrates. A 60 gtm diameter wire held at the substrate served as a mask. After Al deposition, the wire was removed and the masked area was examined by scanning electron microscopy (SEM) and by scanning Auger microprobe (SAM). The ICB source was operated at 0, 3, and 6 kV acceleration voltages. The substrate was held at 80°, 200°, and 400°C during Al depositions. The Al deposition rate averaged 240 A per min. The chamber pressure during deposition was 2×10-6 Torr. The diffusion distance of Al under the mask edge was determined from the SEM micrographs and SAM line scans. The maximum diffusion distance for all acceleration voltages occured at a substate temperature of 200°C. The maximum diffusion distance at 200°C was 29 μm at 6 kV acceleration voltage. The minimum diffusion distance was 12 μm at 400°C for an acceleration voltage of 6 kV.
Aluminum oxide (A12O3), nitride(A1N) and silicon nitride(SiN) films were prepared at a low substrate temperature of 100°C. Film resistivity was higher than 5x1013 Ω-cm and the breakdown voltage was greater than 3x10° V/cm. The films deposited on sapphire and silicon substrates were very flat, and were chemically and thermally stable. The A1-O, A1-N and Si-N bonds could be formed effectively by using both ionized clusters and reactive gas ions, and transparent and good quality films were obtained. Through these results, the simultaneous use of an ionized cluster beam (ICB) system and a microwave ion source was found to have a high potential for preparing oxide and nitride films at a low substrate temperature.
Polyethylene thin films were deposited by the ionized cluster beam (ICB) method. The dielectric, resistivity, and breakdown field measurements showed that the ICB polyethylene films have excellent properties as an electrical insulator. The characteristics of Au/polyethylene/Si MIS diodes and MISFErs indicated that the ICB method can control the film-substrate interface property. The SIMS and ESCAan alyses showed that the ICB films have pure and stable chemical structure.
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