Effect of implant energy on silicon defect evolution

Recent studies on the relationship between defect evolution and transient enhanced diffusion (TED) have lead to the discovery that, for sub-amorphous Si+ implants, atoms released by extended defects (i.e. {311}'s)are a primary source of interstitials for TED. In this paper, the effect of implant energy on the interstitials stored in {311} defects is reported. Silicon wafers were implanted with Si+ at fluences of 1x10(14)/cm(2) and 2x10(14)/cm(2) and energies of 30, 50 and 100 keV. Rapid thermal anneals (RTA) and furnace anneals were performed at times ranging from a few minutes to several hours, at temperatures of 700 degrees, 750 degrees and 800 degrees C. Cross-sectional and plan-view TEM was used to obtain microstructural information. The extended defects observed upon annealing consisted of both {311} defects and dislocation loops. It was found that the ratio of the interstitials bound by extended defects and the implant dose was 0.3. Changing the implant energy did not change the total number of interstitials trapped in both types of defects combined. There was a noticeable variation in the type of defect that dominated each implant regime, despite the constant value of the trapped interstitial to dose ratio. For an RTA of 5 min. at 750 degrees C, the ratio of {311} "rod-like" defects to dislocation loops in the 2x10(14)/cm(2) sample unexpectedly increased as the energy increased from 30 to 50 keV. Longer furnace anneals were employed to determine the activation energy of {311} dissolution. Our data suggests a slightly higher activation energy for {311} dissolution of approximately 4.2 eV versus the previously reported 3.6 eV, however, this difference may be within experimental error.