• PDF / 1,918,885 Bytes
• 6 Pages / 417.6 x 639 pts Page_size
• 16 Downloads / 271 Views

DOWNLOAD

REPORT

---

POINT DEFECT SUPERSATURATION AND ENHANCED DIFFUSION IN SPE REGROWN SILICON.*

S. J. PENNYCOOK, J. NARAYAN, AND 0. W. HOLLAND Solid State Division, Oak Ridge National Laboratory,

Oak Ridge,

TN 37831

ABSTRACT Transient, greatly enhanced diffusion has been observed on annealing solid-phase-epitaxial (SPE) grown Si-Sb alloys. This is shown to be due to a high concentration of interstitials being trapped during SPE regrowth. The migration enthalpy, for diffusion of Sb by an interstitialcy mechanism was measured as 1.8 ± 0.2 eV. The interstitials eventually condensed into loops, marking the end of the transient. In a SPE grown Si-Bi alloy a similar transient enhanced diffusion was observed, with an activation energy of 2.0 ± 0.2 eV, but no loops formed.

INTRODUCTION Supersaturated Si alloys have recently been produced using ion implantation followed by new thermal processing techniques, such as furnace or pulsed laser annealing.[1,2] These techniques remove the implantation damage but leave the dopant trapped on substitutional sites to achieve electrically active dopant concentrations greatly exceeding the solubility limit. Such alloys have been characterized by ion channeling for determining the lattice location and concentration of dopant, and by transmission electron microscopy (TEM) to demonstrate the absence of extended defects. However, possible non-equilibrium concentrations of point defects could not be detected by these techniques. Here we demonstrate that alloys produced by solid-phase-epitaxial (SPE) growth contain a high concentration of trapped interstitials which gives rise to transient, greatly enhanced dopant diffusion during subsequent annealing. Si-Sb Alloys 2 1

Samples of (100)Si were implanted with 1 Sb+ (200 keV, integrated dose 2 4.4 x 1015 cm- ) and recrystallized, either by SPE growth (furnace annealing 0 under flowing dry He gas at 550 C for 20 minutes), which will be referred to 2 as sample 1, or by LPE growth (pulsed ruby laser annealing, 1.4 J cmand 15 ns pulse duration). Ion channeling analyses of these alloys are shown in Fig. la and b. we have also used a graded energy implant, SPE regrown at 0 550 C for 30 minutes, to give an approximately uniform concentration of 1.6 at. % down to a depth of about 100 nm as shown in Fig. Ic, which will be referred to as SPE sample 2. All alloys are >99% substitutional and exceed the retrograde maximum solubility of 0.16 at. %. Thin TEM samples were prepared by a chemical thinning procedure and studied in a Philips EM400 electron microscope. Annealing the thin samples at temperatures of 0 0 0 650 -750 C (SPE samples) or 850 -950°C (LPE samples) induced the precipitation of the dopant in excess of the solubility limit. The thin regions of the TEM samples did not contain the layer of residual implantation damage underlying the SPE regrown layer and thus this damage could not affect the precipitation process occurring within the regrown layer. The electrical junction had also been removed from these thin regions. *Research sponsored by the Division of Ma