Methods and apparatus for etching semiconductor structures

A method for etching a substrate, comprising:

• flowing a gas mixture of C3H2F4 and a companion gas into a process chamber, the gas mixture having an oxide to nitride etching selectively of approximately 1:1;
• generating a first RF power pulse of an RF power source connected to an upper electrode above the substrate to form plasma in the process chamber;
• generating a first RF bias power pulse of at least one RF bias power source connected to a lower electrode under the substrate during the first RF power pulse to perform an anisotropic etch, via the plasma, of at least one layer of oxide or nitride on the substrate using a pattern mask, a duration of the first RF bias power pulse being less than a duration the first RF power pulse;
• depositing a passivation layer on the at least one layer of oxide or nitride on the substrate during the first RF power pulse when the first RF bias power pulse is completed;
• and
• evacuating the process chamber when the first RF power pulse is completed.

A non-transitory computer readable medium having instructions stored thereon that, when executed, cause a method of operating a substrate processing system to be performed, the method comprising:

• flowing a gas mixture of C3H2F4 and a companion gas into a process chamber, the gas mixture having an oxide to nitride etching selectively of approximately 1:1;
• generating a first RF power pulse of an RF power source connected to an upper electrode above a substrate to form plasma in the process chamber;
• generating a first RF bias power pulse of at least one RF bias power source connected to a lower electrode under the substrate during the first RF power pulse to perform an anisotropic etch, via the plasma, of at least one layer of oxide or nitride on the substrate using a pattern mask, a duration of the first RF bias power pulse being less than a duration the first RF power pulse;
• depositing a passivation layer on the at least one layer of oxide or nitride on the substrate during the first RF power pulse when the first RF bias power pulse is completed;
• and
• evacuating the process chamber when the first RF power pulse is completed.