METHOD OF ACHIEVING TOP ROUNDING AND UNIFORM ETCH DEPTHS WHILE ETCHING SHALLOW TRENCH ISOLATION FEATURES

摘要

A method of etching a trench in a silicon layer is disclosed. The silicon layer is disposed below a hard mask layer having a plurality of patterned openings. The etching takes place in a plasma processing chamber. The method includes flowing a first etchant source gas into the plasma processing chamber, forming a first plasma from the first etchant source gas and etching through a first portion of the silicon layer with the first plasma at a first etch rate. The first etch rate being sufficiently slow to form an effective top-rounded attribute in a portion of the trench. The method further includes flowing a second etchant source gas into the plasma processing chamber, forming a second plasma from the second etchant source gas and etching through a second portion of the silicon layer with the second plasma, wherein the etching with the second plasma extends the trench into the silicon layer without unduly damaging the top rounded attribute.