Cyclic Self-Limiting Etching of Organic Polymers

Organic polymer materials play a key role in today’s semiconductor manufacturing industry. They are used to pattern structures and form templates for complex multilayer-patterning schemes. Every patterning process begins with photoresist polymers and often includes underlying hydrocarbon-based mask layers. The pattern defined by the photoresist is transferred to successive underlying layers by exploiting the differences in etch rates between different materials. In this paper, we explore the etching characteristics of the hydrocarbon layers which typically serve as masks for layers beneath them. Due to the shrinkage in feature sizes, the profile of the photoresist polymers needs to be controlled at the atomic level. However, properties such as profile control, etch selectivity, and polymer damage depend on parameters that are often difficult to control, displaying positive and negative effects at the same time. Therefore, the balance required to manage such trade-offs will be increasingly difficult when atomic scale precision is required. Here, we identify a self-limiting process for the etching of organic materials. By using continuous plasma observations and a two-step oxidation–volatilization cyclic etch experiment, we demonstrate the plausible existence of self-limiting atomic layer etching (ALE). Additionally, using first-principles density-functional theory calculations, the atomic mechanisms behind the etching of polymer surfaces in both continuous plasma and cyclic etch processes are described in detail. Our results not only demonstrate ALE in organic polymers but also open pathways for a viable and self-limiting ALE process of organic polymers, a topic of fundamental importance in the modern semiconductor manufacturing industry.