| 摘要 |
A multistage etching process is provided for etching through portions of a layer stack during the formation of a control gate in a semiconductor device. The multistage etching process allows for controlled removal of a tungsten silicide layer within the layer stack by reducing the potential for loading, microloading, over-etching, under-etching, etc. In a first stage of the multistage etching process, part of the tungsten silicide layer is selectively etched away using a plasma that exhibits an etching selectivity (ratio of tungsten silicide etch rate to polysilicon etch rate) less than about 1.2. During the second stage of the multistage etching process, the remaining amount and/or residue parts of the tungsten silicide layer is selectively etched away using a plasma that exhibits an etching selectivity (ratio of tungsten silicide etch rate to polysilicon etch rate) greater than about 1.2.
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