Fabrication of a shallow trench isolation by plasma oxidation

A method of fabricating an STI, the method comprising:

• providing a silicon substrate;
• sequentially forming a pad oxide layer and a stop layer on the silicon substrate;
• performing a lithography and an etching process to define and pattern a trench pattern in the pad oxide layer and the stop layer;
• performing an RIE process to etch the silicon substrate not covered by the pad oxide layer and the stop layer to form a trench in the silicon substrate, the trench having two <111> oriented silicon sidewalls and one <100> oriented bottom;
• wet etching a portion of the pad oxide layer around the STI edge to expose a portion of the top surface of the silicon substrate located beneath the silicon nitride layer surrounding the periphery of the trench;
• synchronously oxidizing both the two <111> oriented silicon sidewalls and the <100> oriented bottom of the trench and the exposed portion of the top surface of the silicon substrate surrounding the periphery of the trench using a high-density Kr/O2 plasma oxidation process, at both a low temperature and a low pressure to form a liner oxide layer having a first thickness on both the <111> oriented silicon sidewalls and the <100> oriented bottom of the trench, and a thicker oxide layer having a second thickness, greater than the first thickness, on the STI edge;
• and
• filling in the trench with a dielectric layer;
• wherein the oxidation rates on both the <111> oriented silicon sidewalls and the <100> oriented bottom of the trench are the same during the high-density Kr/O2 plasma oxidation process, while the oxidation rate at the STI edge is greater than the oxidation rate on the interior surface of the trench.