Blister suppression in the CO+ molecule implanted SOI substrates with ultrathin buried oxides

Abstract

The formation of gettering layers in CO+ ion implanted (COII) n-type (001) silicon wafers with a layer of thermal SiO2 and silicon-on-insulator (SOI) was first demonstrated before and after the processes of direct bonding and thermal cleavage/transfer of Si layers to a silicon substrate. High leakage currents at the negative bias mean that the defects in the BOX and the substrate were not annealed completely after the standart heat treatments. The formation of an intermediate layer (IL) of silicon / carbon / oxide/ SixCyO on Si/SiO2 heteroboundaries during subsequent heat treatments at 600−900 °C, as well as layer-by-layer oxidation/etching at temperatures of 1000−1100 °C, was detected. An increase in the IL layer thickness to ∼3−5 nm correlates with an increase to (5–8) x1012 cm−2 in the density of Di states on the Si/SiO2 heteroboundaries. When transferring a silicon layer, together with a thermal silicon dioxide (SmartCut® method) layer to a Si substrate implanted with CO+ ions, the Di value decreases by more than an order of magnitude to ∼5 × 1010 cm−2, but the mobility of electrons and holes essentially differs from the values in bulk silicon. Based on these results, a model for the formation of negatively charged deep levels and oxygen-, and carbon-containing precipitates in a few micrometer space charge region (SCR) of silicon under the buried oxide (BOX) is proposed.