Patent ID: 7166536

Claim:
A method of anisotropic plasma etching a laterally defined structure in a silicon substrate using a process gas, the method comprising the steps of: precipitating at least one passivating material on at least a side wall of the laterally defined structure at least one of prior to the anisotropic plasma etching and during the anisotropic plasma etching; adding at least one fluorine-delivering etching gas to the process gas, the at least one fluorine-delivering etching gas including at least one compound selected from the group consisting of CIF 3 , BrF 3 and IF 5 ; adding NF 3 to the process gas as an additive for consuming the at least one passivating material; and adding a light, easily ionizable gas to the process gas to at least one of improve selectivity, reduce charging effects, increase separation between light ions and heavy ions, and reduce or suppress stray trench fields; wherein a frequency of a substrate voltage is less than about 2 MHz, so that lighter ions can follow a variation of the electrical field more easily due to their lower inertia.