PROFILE BROADENING OF HIGH-DOSE GERMANIUM IMPLANTS INTO (100)SILICON AT ELEVATED-TEMPERATURES DUE TO CHANNELING

(100) Silicon wafers were implanted with 120 keV germanium ions at sub strate temperatures up to 600 degrees C. The germanium profile was mon itored together with the crystalline fraction of the implanted silicon by Rutherford backscattering spectroscopy channeling in the [100] dir ection. Extensive profile broadening was seen with elevated temperatur e implants accompanied by a peak shift of 50 nm away from the surface for the highest temperature implant at 600 degrees C. A germanium tail was also seen extending deeper than 300 nm for this implant together with a reduction in the peak germanium concentration of more than 60% when compared with similar implants at room temperature. Radiation enh anced diffusion and enhanced sputtering are ruled out as causes for th e profile broadening. Instead we demonstrate channeling along the [100 ] direction to be the cause of both the observed broadening and the in crease in the peak depth. This was confirmed by eliminating such profi le broadening in a sample implanted at 600 degrees C by tilting the im plant away from major axial and planar channels. Positron annihilation spectroscopy was used to monitor the profile of open volume defects i n the implanted material. Data from this analysis show that a defect c oncentration of greater than 10(16)/cm(3) extends to a depth of approx imate to 1.2 mu m for 1 X 10(14) Ge/cm(2) at room temperature. A highe r concentration of such defects appear deeper for similar implants at 450 degrees C. These deep open volume defects can be eliminated by usi ng tilted implants through an amorphous 0.5 mu m SiO2 mask layer. Thei r formation is consistent with germanium ion channeling during the ini tial stages of room temperature implantation and extensive channeling for elevated temperature implantation. (C) 1998 American Institute of Physics. [S0021-8979(98)10206-2].