Chemically induced CD shrink techniques based on sidewall erosion

Chemically induced CD shrink techniques based on sidewall erosion rely on chemical reactions that preferentially take place at the sidewalls of already-patterned resist features, leading to their erosion. The hydrophilic overlayer process is a good example of this technique. 

The next sequence calls for the coating of a thin layer of a hydrophiUc polymer from an appropriate solvent on top of the photoresist. The polymeric HOL must have a lower glass transition temperature (7g) than the photoresist polymer it must be able to diffuse into the photoresist polymer on baking and it must be phase compatible with the photoresist polymer. Suitable hydrophilic polymers include, but are not limited to, polymers and copolymers of fluoroalkyl methacrylic acid, fluoroalkyl acrylic acid, etc. Surfactants may be used to improve the wettability of the HOL over the resist polymer layer. 

the hydrophilic polymer/hydrophobic photoresist coating is baked at an appropriate temperature above the 7g of the hydrophilic polymer, but below or at the Tg of the photoresist polymer. Baking will enhance the diffusion of the melted glassy hydrophilic polymer into the photoresist polymer, leading to the 

The last step calls for the development of the HOL polymer/photoresist film stack in an aqueous basic solvent such as 0.26 N tetramethylammonium hydroxide. This will dissolve and wash away the exposed part of the resist, comprising the carboxylic acid moieties. The preferential diffusion of the HOL into the exposed area of the photoresist results in deprotection of the photoresist polymer at the edge of the unexposed features, leading to their dissolution. This is the basis of the CD reduction, improved process window, and exposure latitude, and smoother sidewall and line edge profile of photoresist features processed with HOL relative to the features processed without HOL.  

---