Method and apparatus for high aspect ratio dielectric etch

A method for etching high aspect ratio features in a dielectric layer over a substrate in a plasma processing chamber, comprising:

• placing the substrate in the plasma processing chamber, with an upper electrode and a lower electrode, wherein the substrate is placed over the lower electrode, and wherein the upper electrode is space apart above the lower electrode and the substrate;
• providing an etching gas into the plasma processing chamber;
• forming a plasma in the plasma processing chamber, between the upper electrode and the lower electrode;
• providing a bias to the upper electrode of at least 500 volts to provide secondary electrons with enough energy to pass through a plasma sheath to vias, wherein a positive charge at the bottom of the vias accelerates the secondary electrons to the bottom of the vias;
• providing a pulsed bias of at least 500 volts to the lower electrode for etching the dielectric layer, wherein the providing bias to the upper electrode and providing bias to the lower electrode, comprises switching a bias between the upper electrode and lower electrode, wherein the switch is performed at a frequency between 10 Hz to 100 kHz;
• and
• wherein the forming a plasma in the plasma processing chamber, between the upper electrode and the lower electrode, comprises providing a high frequency RF with a frequency of over 10 MHz to at least one of the upper electrode or lower electrode.