Method of controlling trench microloading using plasma pulsing

A method for fabricating shallow trench isolation (STI) structures, comprising:

• providing a substrate having a patterned mask layer formed thereon corresponding to a plurality of STI structures to be etched, wherein the plurality of STI structures comprise a plurality of first STI structures disposed in a first region having a first density of first STI structures and a plurality of second STI structures disposed in a second region having a second density of second STI structures, wherein the second density is greater than the first density;
• etching the substrate through the patterned mask layer using a plasma formed from a process gas to form a plurality of STI structure recesses on the substrate;
• and
• pulsing the plasma for at least a portion of etching the substrate by pulsing a biasing power and a source power to control etch depth microloading of individual second STI structures in the second region with respect to each other by pulsing the biasing power and the source power.