1The Reactive Ion Etching of Au on GaAs Substrates in a High Density Plasma Etch Reactor

The etching of Au using photoresist masks and hard masks on GaAs substrates was investigated using a dual frequency high density plasma etch reactor. The advantages of plasma etch techniques over current methods for Au metalization include the ability to simplify the metallization process flow with respect to resist lift-off schemes, and the ability to cleanly remove etched material without sidewall redeposition, as is seen in ion milling. Several different etch chemistries, along with other experimental factors, were considered in this study. Specifically, the etching of Au on GaAs substrates using combinations of Hydrogen Bromide (HBr), Chlorine (Cl2), and Argon (Ar) was evaluated by observing the etch rates, etch selectivities and the etch profiles obtained with these mixtures. HBr/Ar chemistry combinations were found to have a significant influence on the etch profile of Au, primarily by generating heavy sidewall polymers. The Cl2/Ar chemistry was found to generate less sidewall polymer during Au etching. The introduction of Cl2 increases the etch rate of Au and reduces sidewall veil deposition. The Au etch rate and profile were further impacted by the level of RF power applied to the reactor. The best process results obtained to date include etch profiles exceeding 75 ° with no sidewall redeposition