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Theoretical Study of Step Coverage and Comparison with Experimental Results from Low Pressure Chemical Vapor Deposition Process of Tungsten Film

As the feature size of trench or via hole decreases below 1 µ m, a void formation caused by nonconformal step coverage leads to serious problems in the reliability of integrated circuits. In this work, the numerical simulation for the microscopic feature scale model was performed to study the step coverage in low pressure chemical vapor deposition processes by using Monte Carlo method and string algorithm. Several mechanisms such as direct deposition, re-emission, and surface diffusion were included in the model. Dependence of step coverage on aspect ratio, sticking coefficient, surface diffusion coefficient, initial trench shape, and various re-emission mechanisms was investigated and discussed in detail. Then comparison was made with experimental results from SiH4-reduced LPCVD of tungsten film for various substrate temperatures and carrier gases. The activation energy of sticking coefficient and deposition rate on the flat surface at the top of the trench were 13.0 and 6.4 kcal/mol, respectively. Sticking coefficient for Ar, H2, and He at 275° C, 0.3 mbar, WF6/SiH4/carrier gas=10/10/200 sccm was 0.04, 0.10, and 0.29, respectively, implying that a low temperature process using Ar carrier gas is preferred for better step coverage.