Embodiments of the present invention generally relate to methods of forming a microcrystalline silicon layer on a substrate in a deposition chamber. In, one embodiment, the method includes flowing a processing gas into a diffuser region between a backing plate and a showerhead of the deposition chamber, flowing the processing gas through a plurality of holes in the showerhead and into a process volume between the showerhead and a substrate support in the deposition chamber, igniting a plasma in the process volume, back-flowing gas ions formed in the plasma through the plurality of holes in the showerhead and into the diffuser region, mixing the gas ions and the processing gas in the diffuser region, re-flowing the gas ions and processing gas through the plurality of holes in the showerhead and into the process volume, and depositing a microcrystalline silicon layer on the substrate.