Damage And Its Mechanism In Si-based Materials Induced By Light Gas Ion Implantation

High dose light gas ion (such as He, H) implantation into crystalline Si could create bubbles in the bulk as well as surface blisters, exfoliations during subsequent annealing. Such damage has wide potential applications in semiconductor devices. Thus, increasing attention has been paid to the study of bubble growth and their applications in semiconductor materials induced by He or H implantation. In this work, three kinds of Si-based materials were implanted by light gas ions. The formation and thermal evolution of the surface damage as well as micro defects have been studied in detail via various techniques. The possible mechanisms on the damage production have been also discussed. The main research contents and results are as follows:Crystalline Si samples were implanted with 40 or 160 keV He ions at a dose of 5×1016/cm2. Cross-sectional transmission electron microscopy (TEM) and thermal desorption spectroscopy (TDS) have been used to investigate the defect microstructures and He release in implanted and annealed samples. XTEM results show that He ion implantation followed by annealing induces formation of a well-defined defect band, which consists of cavities and dislocation loops. The morphology of the cavity band is closely related to the implant energy of He ions. TDS results reveal that He thermal release occurs in two distinguished temperature regions, which are weak release stage at low annealing temperature (peaked at about 800-900 K) and strong release stage at high annealing temperature (peaked at about 1250 K). Moreover, photoluminescence (PL) have been used to investigate the luminescence properties for some of the implanted and annealed samples. For the annealed samples, PL observations clearly show red and infrared luminescence band.Crystalline Si wafers with a SiO₂ layer of thickness about 220 nm were implanted by 40 or 160 keV He ions at a dose of 5×1016/cm2. XTEM and TDS have been performed to study the effects of the oxide layer on cavity evolution and He desorption upon annealing. Meanwhile, the relationship between the effects of the oxide layer and the implant energy of He ions have also been discussed. XTEM observations show that the presence of the oxide layer can effectively inhibit the thermal growth of cavities, which show strong dependence on the energy of He ions. TDS measurements reveal that the top oxide layer on Si surface could induce the disappearance of the desorption peak at low annealing temperature and occurrence of a new peak at the intermediate annealing temperature.Crystalline Si wafers with a thermally grown Si3N4 layer of thickness about 170 nm were implanted with 40 or 160 keV He ions at a dose of 5×1016/cm2. XTEM and TDS have been used to investigate the cavity growth and thermal release of He atoms in samples after different treatments. XTEM results show that the presence of the top Si3N4 layer can suppress the growth of cavities in Si, which show strong dependence on the energy of He ions. However, the thermal growth of cavities in implanted samples is almost not affected after removal the Si3N4 layer. The TDS results reveal that the top Si3N4 layer can act as an effective barrier to the permeation of He from bubbles to the surface, which gives rise to disappearance of the weak release peak at the low temperature region and occurrence of a new release peak at the intermediate temperature region.Crystalline Si samples were first implanted with 160 keV He ions at a dose of 5×1016/cm2. The samples were then subjected to H implantation at different energies (40, 110 and 160 keV) and at the same dose of 1×1016/cm2. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and XTEM have been used to investigate He and H sequential implantation induced surface phenomena and thermal evolution of micro-defects. For samples that H implants are shallower than He, the He pre-implantation could promote the thermal growth of cavities in H implanted region, resulting in the formation of surface blisters as well as exfoliations at the depth of H projected range. For samples that He and H implants are overlapped, the additional H implantation could significantly promote the thermal growth of He cavities accompanied by the shrinkage of He cavity band, leading to a monolayer of large cavities. Meanwhile, most of the Si surface was exfoliated. However, for samples that H implants are deeper than He, the additional H implantation just introduce a large amount of thick dislocations in both He and H implanted regions. Furthermore, positron annihilation spectroscopy (PAS) and elastic recoil detection analysis (ERDA) have also been made to measure the distribution and evolution of vacancy-like defects and H atoms, respectively. Finally, both the interaction between He, H atoms and vacancy-like defects and the mechanism of damage formation have been discussed.