Patent ID: 8871105

Claim:
A method of etching silicon in a plasma processing chamber, said method comprising: operating the plasma processing chamber at a first pressure and a first bias to perform a first vertical etch in the silicon to create a hole having a first depth and a sidewall; operating the plasma processing chamber at a second pressure and a second bias to perform a deposition of a protective layer on the sidewall; operating the plasma processing chamber at a third pressure and a third bias to perform a second vertical etch to deepen the hole to a second depth and to create a second sidewall, the second sidewall including a first trough, a second trough and a peak, the first trough corresponding to the first sidewall, the second trough corresponding to the second sidewall, the peak being disposed between the first trough and the second trough; and operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak, wherein the fourth bias is sufficient to induce ion bombardment to eliminate the peak.