Study Of Cavity Formation And Helium Desorption In Crystalline Si Implanted With He Ions

With the development of semiconductor technology, it is very necessary to fabricate semiconductor materials and devices of high quality. Ion implantation as an important tool has been widely used in fabricating semiconductor materials and devices. Previously, ion implantation was mainly adopted in material modification, p-n junction creation, and so on. Recently, it has been found that high dose light gas ion implantation into semiconductor materials can induce cavity formation after subsequent high temperature annealing. Such cavities have many potential applications in the modern Si technology, such as gettering of fast diffusing metallic impurities, control of lifetime for minority charge carries, and etc. Since then the study of cavity formation in Si and its applications have been paid more and more attention.In this work, samples of CZ n-type Si (100) with and without 220 nm SiO2 surface layer were implanted at room temperature with 40 keV He ions at a dose of 5×1016 ions/cm2. Techniques, such as cross-sectional transmission electron microscope (XTEM), thermal desorption spectroscopy (THDS), photoluminescence (PL), have been used to investigate the cavity formation upon annealing, thermal release of He atoms and the luminescence properties related to the induced defects. Meanwhile, the possible effects due to the presence of the surface oxide layer on cavity growth and He desorption were also studied. XTEM results show that, He ion implantation followed by an annealing at 800℃for 1 hour can produce a well-defined damage band in Si with the width of 220 nm, accompanying with the release of He atoms from various defects. The size of cavities in the band distributes in the range of 4-25 nm, with the mean size of about 11 nm. However, the presence of the oxide surface layer can significantly influence the cavity growth in Si., which lead to the shrinkage of the cavity band, The shrinkage effects have been mainly found in the Si region close to the SiO2/Si interface.THDS results reveal that He release from the implanted Si show two release peaks. One is the weak release with the peak temperature of about 900 K, the other is the strong release with the peak temperature of about 1250 K. They are related to the He desorption from the smaller defects and large bubbles, respectively. The presence of the oxide layer could act as an effective barrier to He diffusion at low annealing temperature, and thus gives rise to formation of overpressurized bubbles at the intermediate temperature region. The occurrence of new desorption peak may be attributed to the creation of these overpresurrized bubbles. PL results indicate that He implantation followed by annealing can also result in strong luminescence, which are located at 680 nm and 930 nm, respectively. The PL intensity was found to increase with the annealing temperature. We suggest that these luminescence bands may be resulted from the formation of nanometer Si clusters.