Electron and hole trapping in doped oxides

Doped oxide thin films are quite commonplace in the microelectronics community as insulating layers in Si device technologies. Thus, it is somewhat surprising that very little is known about the electronic structure of defects in these thin film dielectrics. The role of dopants in SiO2 films is of interest to both the commercial and radiation-hardened microelectronics communities when considering issues such as wet clean contamination, plasma processing, x-ray lithography, and source-drain dopant interpenetration into the oxide in sub-micron MOSFET's. An electron paramagnetic resonance, thermally stimulated current, and capacitance-voltage study has been carried out on phosphorus (PSG), boron (BSG), and boron and phosphorus (BPSG) co-doped oxide films on Si. The principal spin-active defects are the phosphorus-oxygen-hole-center (POHC) and the boron-oxygen-hole-center (BOHC), which are unpaired electrons on oxygen atoms with P or B in the near vicinity. The centers are activated by hole capture. The authors find that holes are trapped in the PSG, BSG, and BPSG dielectrics; however, hole trapping is most effective in the PSG and BPSG dielectrics. They find that electrons are trapped to differing extents in the doped films. The BPSG films are the most efficient in trapping electrons; the PSG films are the least efficient. The electrical data can be explained by assuming that the precursor to the BOHC is negatively charged and the precursor to the POHC is electrically neutral. Last, the charge trapping properties of PSG, BSG, and BPSG dielectrics are compared and contrasted with those observed in thermally grown oxides