Hiroshi Tobimatsu

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.

Disconnection of NiSi shared contact and its correction using NH 3 soak treatment in Ti/TiN barrier metallization

During Ti/TiN barrier metallization of a shared contact in SRAM, an NH3 soak treatment selectively deoxidized silicon oxide on NiSi at the gate shoulder, improving the resistance of the contact. This deoxidizing NH3 soak treatment drastically reduced the drawbacks of conventional NH3 plasma treatment: plasma-induced damage of gate oxide and excessive nitridation of Ti/TiN. Although NH3 gas does not kinetically deoxidize silicon oxide, it does selectively deoxidize silicon oxide on the NiSi. We think that this is because the NiSi surface promotes the deoxidization of silicon oxide by NH3.