Dopant etch selectivity control

A method of etching a patterned substrate, the method comprising:

• transferring the patterned substrate into a substrate processing region of a substrate processing chamber wherein the patterned substrate comprises polysilicon, a gate oxide and an active area of single crystal silicon, wherein the polysilicon is above the gate oxide which is above the active area of single crystal silicon;
• flowing a fluorine-containing precursor into a remote plasma region fluidly coupled to the substrate processing region while forming a plasma in the remote plasma region to produce plasma effluents;
• flowing the plasma effluents into the substrate processing region housing the patterned substrate, wherein the plasma effluents flow into the substrate processing region through perforations in an ion suppression element disposed between the remote plasma region and the substrate processing region;
• and
• etching the polysilicon and the active area of single crystal silicon with the plasma effluents, wherein the polysilicon is etched at greater than twice the rate of the active area of single crystal silicon.