High Aspect Ratio Contact Profile Control and Cryogenic Etch Process

Abstract

High Aspect Ratio (HAR) contact formation is a necessary process in advanced memory technology nodes. A widely used method for HAR contact is cryogenic plasma etch with CxHyFz gases. Such a process faces different technical challenges including contact punch through, contact open and high contact to contact capacitance. In this paper, a model on HAR contact profile control is proposed, in which the mechanisms such as sidewall polymer distribution, polymer sticking possibility, radical chemical etch and ion bombardment are considered. It is demonstrated that a low-bowing-position profile is helpful to avoid the contact bridging issue and yield low contact resistance. Such a profile could be formed by using carbon hard mask induced polymer, which covers the top part of the sidewall, allowing the lower sidewall to form a bowing profile. The amount of the polymer depends on ion energy, ion angle distribution and so on.