Patent ID: 7789991

Claim:
An apparatus for forming features in a dielectric layer, wherein the dielectric layer is supported by a substrate and wherein the etch layer is covered by a photoresist mask, comprising: a plasma processing chamber, comprising: a chamber wall forming a plasma processing chamber enclosure; a substrate support for supporting a substrate within the plasma processing chamber enclosure; a pressure regulator for regulating the pressure in the plasma processing chamber enclosure; at least one electrode for providing power to the plasma processing chamber enclosure for sustaining a plasma; a gas inlet for providing gas into the plasma processing chamber enclosure; and a gas outlet for exhausting gas from the plasma processing chamber enclosure; a gas source in fluid connection with the gas inlet, comprising; a lag etchant gas source; and a reverse lag etchant gas source; a controller controllably connected to the gas source and the at least one electrode, comprising: at least one processor; and non-transitory computer readable media comprising computer readable code for performing an etch cycle, comprising: computer readable code for performing a lag etch partially etching features in the silicon oxide based dielectric layer, comprising: computer readable code for providing a lag etchant gas; computer readable code for forming a plasma from the lag etchant gas; and computer readable code for etching the etch layer with the lag etchant gas, so that smaller features are etched slower than wider features; and computer readable code for performing a reverse lag etch further etching the features in the silicon oxide based dielectric layer, comprising: computer readable code for providing a reverse lag etchant gas, which is different from the lag etchant gas and is more polymerizing than the lag etchant gas; computer readable code for forming a plasma from the reverse lag etchant gas; and computer readable code for etching the silicon oxide based dielectric layer with the plasma formed from the reverse lag etchant gas, so that smaller features are etched faster than wider features.