GAS ADDITIVES FOR SIDEWALL PASSIVATION DURING HIGH ASPECT RATIO CRYOGENIC ETCH

Methods and apparatus for etching a feature in a substrate are provided. The feature may be etched in dielectric material, which may or may not be provided in a stack of materials. The substrate may be etched using cryogenic temperatures and particular classes of reactants. In various examples, the substrate may be etched at a temperature of about −20° C. or lower, using a mixture of reactants that includes at least one reactant that is an iodine-containing fluorocarbon, an iodine-containing fluoride, a bromine-containing fluorocarbon, a sulfur-containing reactant, or one of another select set of reactants. In various embodiments, the combination of low processing temperature with particular reactants results in very effective bow control.