Removing imperceptible fluoride residue after chemical dry-cleaning to fabricate uniform low-resistance NiSi film

The authors investigated the integrity of the interface between a Ni film and a Si substrate treated by in situ chemical dry-cleaning using ammonium fluorosilicate, or (NH4)2SiF6. In the conventional cleaning scheme, imperceptible fluoride residue at the interface between Ni and Si, even after subliming at 120 °C, was detected by synchrotron x-ray photoelectron spectroscopy. The authors found that the fluoride residue could be removed by additional subliming at 200 °C in a separate chamber following the conventional cleaning scheme (two-step sublimation cleaning). The sheet resistance of nickel monosilicide (NiSi) films fabricated by two-step sublimation cleaning was lower and the NiSi–Si interface was more uniform than for those fabricated by conventional cleaning. This suggests that the fluoride residue triggered the formation of a rough interface between the Ni and Si layers, thus leading to the performance degradation of the NiSi films.