Patent ID: 7985688

Claim:
In a plasma processing chamber, a method for etching a substrate having thereon a silicon layer, said plasma processing chamber having a bottom electrode, said substrate being disposed on said bottom electrode during said etching, comprising: performing a main etch step; terminating said main etch step when a predefined etch depth into said silicon layer is achieved, said predefined etch depth being at least 70 percent of a thickness of said silicon layer; performing an overetch step, said overetch step including a first process step and a second process step, said first process step being performed using a first bottom power level applied to said bottom electrode, said second process step being performed using a second bottom power level applied to said bottom electrode that is lower than said first bottom power level, wherein said first process step and said second process step are alternately performed a plurality of times; and terminating said overetch step after said silicon layer is etched through.