Effect of exposure to air on sheet resistance and phase composition of Co silicides annealed at a low temperature of 470 °C

Attention has been attracted to Co silicides due to their superior properties in deep-submicron integrated circuit technology. In this paper, the effect of exposure to air on the properties of Co silicides has been studied. Co films of 20-nm thickness were deposited onto polysilicon layers using Ar sputtering. After deposition, the samples were exposed to air at room temperature for different times, ranging from 0 to 48 h, before a rapid thermal annealing (RTA) at 470 °C. It is found that exposure to air significantly changes the sheet resistance (Rs) and the phase composition of the silicides. The sample exposed to air for 48 h has Rsof∼71 Ω/sq, which is about 10% lower than that for the sample annealed immediately. This is due to the fact that more Co2Si phase and less CoSi phase are formed in the former sample. The mechanism can be attributed to the gases in air (e.g. O2), which contaminate the Co/Si interface and act as a kinetic barrier during the subsequent RTA. It has been demonstrated that gaseous contamination from air strongly influences the CoSix phase transformation.