Atomic Layer Etch for Vertical Sidewalls in Carbon Patterning

The continuous plasma etching process is segmented into discrete atomic layer etching cycles, where each cycle removes a controlled monolayer thickness. This segmentation allows precise control over etching depth and prevents the cumulative footing effect that occurs in conventional continuous plasma etching, thereby maintaining vertical sidewalls while achieving the desired etching rate.

The etching process employs periodic alternating exposure to oxygen-containing gas (for surface modification) and inert gas with plasma (for etching). This periodic action creates self-limiting reactions that occur in distinct cycles, preventing the isotropic damage and footing issues associated with continuous plasma exposure, while maintaining efficient material removal through repeated cycles.

Before the actual etching occurs, the carbon-containing material surface is preliminarily modified by exposure to oxygen-containing gas without plasma. This preliminary oxidation creates a reactive surface layer that enables controlled, uniform etching in subsequent plasma exposure, preventing pitch walking by ensuring consistent etching rates across different feature dimensions and locations.

The process changes the physical and chemical parameters of the surface through oxygen exposure, transforming the carbon-containing material into a more reactive state. This parameter change enables precise control over etching depth and uniformity, maintaining dimensional precision while achieving high material removal rates through optimized plasma exposure conditions.

The atomic layer etching process maintains continuous useful action by eliminating idle time between cycles. The oxygen exposure and plasma etching steps are tightly coupled with minimal purge time, and the self-limiting nature of each cycle ensures that the next cycle can begin immediately. This continuity maximizes the fraction of time spent on productive etching, offsetting the increased cycle count with efficient cycle execution.

The use of inert gas atmosphere during plasma exposure prevents unwanted side reactions and maintains stable, repeatable etching conditions. This inert environment allows for optimized plasma parameters that increase etching rate within each cycle, reducing the total number of cycles needed while maintaining vertical sidewalls, thereby reducing overall process time.