Method of forming semiconductor structure having layer with re-entrant profile

A method, comprising:

• forming a sacrificial layer over a semiconductor substrate;
• performing an etching process to form an opening in the sacrificial layer, wherein the etching process comprises a first cycle and a second cycle performed after the first cycle, and each of the first cycle and the second cycle comprises:
• applying a passivation gas and an etchant gas over the sacrificial layer;
• and
• performing an ionized gas bombardment on the sacrificial layer after applying the passivation gas and the etchant gas over the sacrificial layer;
• and
• wherein the etchant gas is applied at a first flow rate in the first cycle and is applied at a second flow rate in the second cycle, and the first flow rate is lower than the second flow rate.

A method, comprising:

• forming a sacrificial layer over a semiconductor substrate;
• performing an etching process to form an opening in the sacrificial layer, wherein the etching process comprises a first cycle and a second cycle performed after the first cycle, and each of the first cycle and the second cycle comprises:
• applying a passivation gas and an etchant gas over the sacrificial layer;
• and
• performing an ionized gas bombardment on the sacrificial layer after applying the passivation gas and the etchant gas over the sacrificial layer;
• and
• wherein the ionized gas bombardment is performed at a first temperature in the first cycle and is performed at a second temperature in the second cycle, and the second temperature is higher than the first temperature.