Cobalt Silicide Formation Characteristics in a Single Wafer Rapid Thermal Furnace (SRTF) System

Thin cobalt silicide formation, including two phase transitions, was studied using a single-wafer rapid thermal furnace (SRTF) system. TiN-capped cobalt films on four types of wafer surfaces (monocrystalline Si, amorphous Si, n⁺ amorphous Si, and p⁺ amorphous Si) were investigated. Cobalt silicide process sensitivity was investigated in nitrogen ambient as a function of process temperature (350~700degC) and wafer surface condition. Process time (wafer residence time in a preheated near-isothermal process chamber) was fixed at 90s for simplicity. The cobalt silicidation showed two characteristic transition regions, one at about 450degC, and the other at between ~500degC and ~630degC, representing the two phase transitions during the silicidation sequence. The first transition temperature was at about 450degC regardless of wafer surface type. However, the second transition temperature was strongly influenced by the type of wafer surface. The authors focus their analysis on sheet resistance (sheet rho) and sheet rho uniformity of TiN-capped 9 nm thick cobalt films. Except for the phase transition regions around 450degC and 500~630degC, the sheet rho uniformity has improved as a result of annealing