Cu gettering to nanovoids in SOI materials

In this paper, the gettering of Cu impurities in silicon-on-insulator (SOI) materials is studied. Nanovoids are formed in the substrate of SOI beneath the buried oxide (BOX) by room temperature H⁺ (3.5×i10¹⁶ /cm²) or He⁺ (9×10¹⁶ /cm² ) implantation and subsequent annealing at 700°C. The gettering of different doses of Cu (5×10¹³/cm², 5×10¹⁴ /cm², 5×10¹⁵/cm²), which are introduced in the top Si layer by ion implantation, to the nanovoids are investigated by cross-section transmission electron microscopy (XTEM) and secondary ion mass spectroscopy (SIMS). The results demonstrate that Cu impurities in the top Si layer can diffuse through the buried oxide (BOX) layer of SIMOX and Smart-Cut SOI at temperature above 700°C and be trapped by the nanovoids. Some of Cu impurities can be captured by the intrinsic defects at the BOX interface of SIMOX, but will be released out at high temperatures. The gettering effect of SIMOX intrinsic defects at BOX is much lower than that of the nanovoids. No Cu impurities are trapped at the perfect BOX interfaces of Smart-Cut SOI. After 1000°C annealing, high dose of Cu (3.6×10¹⁵/cm²) was gettered by the nanovoids. The Cu gettering efficiency to the nanovoids increased with the decreasing of Cu doses. When the Cu doses in the top Si layer were lower than 4×10¹⁵/cm², the nanovoids could getter more than 90% of the Cu impurities and reduce the Cu concentration in the top Si layer to less than 4%. The results indicate that nanovoids gettering is a promising method for removing the impurities in SOI materials.