Methods for high precision plasma etching of substrates

A method for treating a substrate, comprising:

• receiving a substrate on a substrate holder in a plasma process chamber, a patterned overlying layer being formed over the substrate to form a first exposed portion of the substrate;
• treating a first exposed portion of the substrate using a first plasma in the plasma process chamber so as to form a first adsorbed layer in the first exposed portion of the substrate, the first adsorbed layer being formed using a combination of elements from the first plasma and the substrate, the first adsorbed layer extending into the substrate with a first thickness;
• removing the first adsorbed layer selectively from the substrate using a second plasma in the plasma process chamber so that a second exposed portion of the substrate is formed, the second exposed portion of the substrate having sidewalls and a bottom;
• treating the second exposed portion of the substrate using the first plasma so as to form a second adsorbed layer in the second exposed portion of the substrate, the second adsorbed layer being formed using the combination of elements from the first plasma and the substrate, the second adsorbed layer having side portions extending into the sidewalls of the second exposed portion of the substrate with a second thickness, and a bottom portion extending into the bottom of the second exposed portion of the substrate with a third thickness;
• and
• removing, selectively, the second adsorbed layer using the second plasma.