Grain boundary structure in twist-type Si bicrystals made from SOI and dopant activation in SOI by high density of currents.

摘要

A new approach for preparing twist-type Si bicrystals and compliant substrates is reported. Thin Si single crystal films prepared from Silicon-On-Insulator (SOI) can be bonded to each other or to Si substrates. Thousands of Si bicrystals bonded at different twist angles can be obtained in a single preparation process and are ready for transmission electron microscopy (TEM) examination. Plan-view and high resolution cross-sectional TEM images of the Si bicrystalsare presented. Images of screw dislocation networks and Moiré fringes of low-angle twist-type Si boundaries are obtained. This technique facilitates the systematic study of low- and high-angle grain boundary structures of Si. One application of the technique is fabrication of compliant substrates for heteroepitaxial growth of SiGe. 6000 Å Si₇₀Ge₃₀ film was grown by MBE. Cross-sectional TEM images of the film are shown.; Heavily ion-implanted boron-doped and arsenic-doped SOI strips were shown to be activated by applying an electrical current. For these samples, patterned SOI stripes were implanted by 40 KeV BF₂+ or As + at a dosage of 5 × 1015 ions/cm2. Without post-implantation annealing, these implanted SOI strips could be activated by applying a current up to 1 × 106 A/cm2; for example, the resistance decreased from 8.80 to 0.61 KΩ for a 10 μm wide, 50 μm long, and 0.2 μm thick n+ silicon strip. This reduction of resistance was close to that obtained by the conventional post-implantation annealing at 900°C for 30 minutes. To separate the effect of Joule heating from current density activation, the temperature of the SOI strips during the cycle of current stressing was measured by Pt sensors. The result indicates that the temperature rise due to Joule heating was low and could not explain the observed activation. We conclude that implanted dopants in Si could be activated by current stressing. To confirm the electrical activation, the carrier concentration was obtained by Hall measurement.