Influence of Organic Contamination on Silicon Dioxide Integrity

The influence of organic contamination before oxidation on 8-nm-thick silicon dioxide integrity was studied. Contamination results from the intentional adsorption of dioctyl phthalate (DOP) on silicon wafers. Metal-oxide semiconductor (MOS) capacitors were fabricated on the wafers to measure the electrical characteristics of the oxide. A reduction in the dielectric breakdown field strength of the oxide was found to occur after DOP adsorption of more than 1×1013 mol/cm2. The flat-band voltage shift (ΔV fb) and interface trap charge density (D it) increased with an increase in the amount of DOP below 1×1013 mol/cm2. Positive charges arose from DOP in the oxide during oxidation, which was determined from a negative ΔV fb. Furthermore, with an increase in the DOP level from 1×1013 to 1×1015 mol/cm2, D it hardly increased whereas ΔV fb gradually increased. This suggests that positive charges at the silicon-oxide interface are fixed. It is thought that an increase in the amount of positive charge in the oxide reduces the dielectric breakdown voltage. From infrared (IR) adsorption measurement, we found that even after DOP decomposition due to oxidation, positive charges within DOP remained, and they degrade oxide integrity.