Low temperature selective etching of silicon nitride using microwave plasma

A method for etching silicon nitride selective to silicon oxide, comprising:

• providing a substrate comprising silicon nitride and silicon oxide in a microwave plasma chamber, wherein the microwave plasma chamber comprises:
• a chamber;
• a chamber lid, wherein the chamber lid is a dielectric material;
• a plurality of microwave applicators across a surface of the lid;
• a plurality of power sources, wherein each power source is coupled to one of the plurality of microwave applicators;
• and
• a gas injection path through the lid;
• flowing a first gas into the chamber, wherein the first gas comprises sulfur and fluorine;
• flowing a second gas into the chamber, wherein the second gas is an inert gas, and wherein a ratio of the first gas to the second gas is 0.4 or smaller;
• flowing a third gas into the microwave plasma chamber, wherein the third gas comprises dichloro-silane (DCS), and wherein an amount of DCS is less than an amount of the first gas;
• striking a plasma in the chamber;
• and
• etching the silicon nitride, wherein an etching selectivity of silicon nitride to silicon oxide (silicon nitride:silicon oxide) is 50:1 or greater.

A method of etching a 3D structure, comprising:

• providing the 3D structure in a microwave plasma chamber, wherein the 3D structure comprises:
• a substrate;
• and
• alternating layers of silicon oxide and silicon nitride over the substrate, and wherein the microwave plasma chamber comprises:
• a chamber;
• a chamber lid, wherein the chamber lid is a dielectric material;
• a plurality of microwave applicators across a surface of the lid;
• a plurality of power sources, wherein each power source is coupled to one of the plurality of microwave applicators;
• and
• a gas injection path through the lid;
• flowing a first gas into the chamber, wherein the first gas comprises sulfur and fluorine;
• flowing a second gas into the chamber, wherein the second gas is an inert gas, and wherein a ratio of the first gas to the second gas is 0.4 or smaller;
• flowing a third gas into the microwave plasma chamber, wherein the third gas comprises dichloro-silane (DCS), and wherein an amount of DCS is less than an amount of the first gas;
• striking a plasma in the chamber;
• and
• etching the silicon nitride layers, wherein an etching selectivity of silicon nitride to silicon oxide (silicon nitride:silicon oxide) is 50:1 or greater.