Supercritical CO2 for Resist Development: Towards an All-Dry Lithography Process

The increased use of organic solvents, halogenated solvents, and water in manufacturing and processing of ICs has led to a need of environmentally responsible and energy efficient processes. Alternatives to the previously mentioned solvents have been researched and one possibility is supercritical carbon dioxide (scCO$_{2})$. It has been well established that by adding a small volume of polar solvents (also called co-solvents) to an scCO$_{2}$ mixture, the solubility of a polar solute in scCO$_{2}$ can dramatically increase. This fact makes scCO$_{2}$ technology extremely attractive as an alternative solvent for lithography. Various resist platforms were tested to demonstrate their ability to be developed in CO$_{2}$. These include copolymers of functionalized methacrylates or phenolics with perfluorooctyl methacrylates, homopolymers of functionalized methacrylates, and novel small molecule resists. Films were either deposited via spin-coating or hot filament chemical vapor deposition (Gleason Group, MIT). Depending on the resist system, features on the order of 100 nm were obtained after development in scCO$_{2}$.