US Patent 9368364 Silicon etch process with tunable selectivity to SiO

A tunable plasma etch process includes generating a plasma in a controlled flow of a source gas including NH3 and NF3 to form a stream of plasma products, controlling a flow of un-activated NH3 that is added to the stream of plasma products to form an etch gas stream; and controlling pressure of the etch gas stream by adjusting at least one of the controlled flow of the source gas and the flow of un-activated NH3 until the pressure is within a tolerance of a desired pressure. An etch rate of at least one of polysilicon and silicon dioxide by the etch gas stream is adjustable by varying a ratio of the controlled flow of the source gas to the flow of un-activated NH3.