The effect of variation of the WF 6 flow rate on the contact resistance in the DCS-based WSi x deposition

Abstract

We analyze the Si/W composition ratio and distributions of phosphorus (P), fluorine (F) and chlorine (Cl) in tungsten silicide thin films as a function of WF 6 flow rate in a dichlorosilane-based deposition process. We investigate the effect of physical properties on the contact resistance between word line and bit line in the DRAM device. In RBS measurements, it is shown that Si/W composition ratio increases from 2.05 to 2.24 after annealing as WF 6 flow rate is decreased. This result was also confirmed by AES analysis. Also, in SIMS analysis, the concentration of phosphorus in the doped poly-Si consisting underlayer after WSi x deposition decreases from 4.75×10 20 to 5.1–5.3×10 19 atoms/cm 3 after annealing and the concentrations of phosphorus in the WSi x thin film increases with the decrease of WF 6 flow rate. But, the concentrations of chlorine does not change noticeably although the concentrations of fluorine tend to decrease as the WF 6 flow rate is decreased. The contact resistance of word line and bit line is found to considerably reduce from 13.6 to 3.0 μΩ-cm 2 as the WF 6 flow rate is decreased.