Uniformity control for high selective down-flow plasma etching on silicon oxide

Down-flow plasma etching is mentioned instead of high-density capacitively coupled plasma (CCP) etching to prevent the control gate (CG) against physical damage during the intra-level dielectric (ILD) etch back, which is the process prior to form cobalt silicide word lines. However, owning to lack of ion bombardment, it is hard to achieve good etch uniformity. This paper presents the design of experiments (DOE) in varied the parameters of RF power and the chemistry ratio of NH3/NF3 to achieve the optimal condition on the etch uniformity improvement. As a result, the cobalt silicide gate Rs distribution is improved ca. 150% at dense region and ca. 40% at periphery region, respectively.