Salicide (self-aligned silicide) technology for ultra thin SIMOX MOSFETs

Summary form only given. A study of the TiSi₂-Si material system in ultrathin SIMOX MOSFETs and their electrical characteristics are discussed. Starting materials were separation by implantation of oxygen (SIMOX) wafers formed by oxygen ion implantation under conditions of 180 to 200 keV, 1.8 to 2.2×10¹⁸/cm ², and 1350°C, 30 min. annealing. The CMOS process was performed with the standard gate length of 1 μm and LOCOS isolation. The sputtered Ti film on polysilicon gate electrodes and source/drain regions outside the oxide sidewall spacers was reacted with Si to form TiSi₂ by the two-step rapid thermal annealing (RTA) method. SIMOX films at the end of the process were 65 nm to 125 nm thick, depending on O⁺ doses. XTEM measurements indicated that the TiSi₂-Si interface by silicidation proceeded into the silicon films as the initial thickness of the Ti film was increased, and silicon films were fully silicided down to the underlying SiO₂ surface at Ti film thickness of 45 nm. Accordingly, both n and p source and drain sheet resistances were reduced from a few hundreds ohm/square (without silicide) to about 2 ohm/square. It was also found that some voids existed at the TiSi₂-Si interface just beneath the outside edge of the oxide spacer in the MOSFET structure, and a small portion of TiSi₂ climbed up along the sidewall of the spacer. As a result, both NMOSFETs and PMOSFETs with 45-nm thick Ti film did not operate in the electrically open mode. This indicates that the conditions of the full silicidation for ultrathin SIMOX MOSFETs has to be carefully determined from the view point of Ti and Si composition