Growth rate modeling for selective tungsten LPCVD

Selective chemical vapor deposition of tungsten plugs on sputtered tungsten was performed in a single-wafer cold-wall reactor using silane (SiH4) and tungsten hexafluoride (WF6). Extensive SEM measurements of film thickness were carried out to study the dependence of growth rates on various process conditions, wafer loading, and via dimensions. The results have been interpreted by numerical calculations based on a simulation model which is also presented. Both continuum fluid dynamics and the ballistic line-of-sight approach are used for transport modeling. The reaction rate is described by an empirical rate expression using coefficients fitted from experimental data. In the range 0.2 < p(SiH4)p(WF6) < 0.75, the reaction order was determined as 1.55 and −0.55 with respect to SiH4 and WF6, respectively. For higher partial pressure ratios the second-order rate dependence on p(SiH4) and the minus first-order dependence on p(WF6) were confirmed.