Selective etch using material modification and rf pulsing

A method of removing material from a semiconductor substrate, the method comprising:

• modifying a material on a semiconductor substrate having at least two exposed materials on a surface of the semiconductor substrate, wherein the modifying comprises forming a plasma from a precursor with an RF bias power to generate plasma effluents that modify the material;
• forming a low-power plasma within a processing chamber housing the semiconductor substrate, wherein the low-power plasma is a radio-frequency (RF) plasma, and wherein the low-power plasma is formed by a pulsed RF bias power operating at between about 20 W and 50 W at a pulsing frequency between about 500 Hz and about 2,000 Hz at a duty cycle of between about 20% and 50%;
• operating a DC pulsed power on an alternating frequency with the RF bias power pulsing;
• and
• etching one of the at least two exposed materials on the surface of the semiconductor substrate at a selectivity of at least about 20:1 with respect to a second of the at least two exposed materials on the surface of the semiconductor substrate.

A substrate processing chamber comprising:

• a pedestal configured to support a semiconductor substrate;
• an RF bias power electrically coupled with the pedestal and configured to generate a plasma within the processing chamber at a power of between about 20 W and about 50 W, wherein the RF bias power is a pulsing power configured to pulse at a frequency below about 5,000 Hz;
• and
• a DC pulsing power electrically coupled with the substrate processing chamber and configured to produce priming particles for the RF bias plasma.