Methods for forming a round bottom silicon trench recess for semiconductor applications

A method of forming a recess structure in a semiconductor substrate, comprising:

• providing a silicon substrate into a processing chamber, wherein the silicon substrate has a patterned photoresist layer disposed thereon, exposing an active region formed in the silicon substrate, wherein the active region is defined between shallow trench isolations (STI) in the silicon substrate;
• supplying an etching gas mixture in the processing chamber;
• supplying a RF source power to form a plasma from the etching gas mixture;
• and
• performing an anisotropic etching process by applying a RF bias power in the etching gas mixture;
• and
• performing an isotropic etching process by turning off the RF bias power in the etching gas mixture.

A method of forming a recess structure in a semiconductor substrate, comprising:

• (a) providing a silicon substrate into a processing chamber, wherein the silicon substrate has a patterned photoresist layer disposed thereon, exposing an active region formed in the silicon substrate, wherein the active region is defined between shallow trench isolations (STI) in the silicon substrate;
• (b) etching the active region in the silicon substrate with a RF bias power on to form a trench in the active region;
• and
• (c) continuously etching the active region in the silicon substrate with the RF bias off to form a round feature to a bottom of the trench in the active region.