In gate etching, what is the phenomenon called in which the pattern sidewall is undercut laterally near the boundary with the underlying insulator?

Answer: B. Notching

Notching occurs when, after etching reaches the underlying insulator, charge builds up on the insulator surface and deflects ions, undercutting the foot of the pattern. Because it locally changes the gate length, it is countered by suppressing charging, for example with pulsed plasma.