Methods of fabricating a semiconductor IC having a hardened shallow trench isolation (STI)

A method for fabricating a semiconductor IC comprising:

• depositing a layer of silicon nitride overlying a semiconductor substrate;
• applying and patterning a layer of photoresist to form an etch mask having an opening exposing a portion of the layer of silicon nitride;
• etching the portion of the layer of silicon nitride;
• etching a trench extending into the semiconductor substrate underlying the portion of the layer of silicon nitride;
• filling the trench with an oxide material;
• performing a CMP operation to remove the oxide material overlying the layer of silicon nitride;
• deglazing a surface of the oxide material within the trench;
• and
• forming a nitrided oxide layer at the surface of the oxide material by subjecting the surface of the oxide material to a nitrogen-containing plasma, wherein forming the nitrided oxide layer comprises subjecting the surface of the oxide material to a nitrogen plasma comprising NH3 as a reactant, and in at least one cycle to a nitrogen plasma comprising NF3 as a reactant.

A method for fabricating a semiconductor IC in and on a semiconductor substrate comprising:

• etching an isolation trench extending into the surface of a semiconductor substrate;
• substantially filling the trench with an oxide material;
• performing a planarizing operation to remove a portion of the oxide material and to expose a surface of the oxide material in the trench;
• plasma nitriding a portion of the oxide material to form a nitrided oxide layer at the surface, wherein plasma nitriding comprises subjecting the surface of the oxide material to a nitrogen-containing plasma in a plasma reactor, and wherein low frequency power in the plasma reactor is adjusted to control thickness of the nitrided oxide layer.