Influence of material and process parameters in the dry-development of positive-tone, polyaldehyde photoresist
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Influence of material and process parameters in the drydevelopment of positive-tone, polyaldehyde photoresist Anthony Engler, Cassidy Tobin, Chi Kin Lo, Paul A. Kohla) School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0100, USA a)Address all correspondence to this author. e-mail: [email protected] Received: 9 April 2020; accepted: 20 August 2020
Poly(phthalaldehyde) (pPHA) and copolymers with aliphatic aldehydes were investigated as dry-develop, positive-tone photoresist. Exposure of the films loaded with a photoacid generator to 248 nm radiation creates an acid that depolymerizes the polymer into volatile monomers, allowing the development of features by vaporization rather than solution-based processes. By controlling the acid content, the vaporization rate of the reaction products, and the degree of liquid formation of the decomposed polymer, control of spatial resolution and the quality of polyaldehyde dry-develop photoresist was achieved. Heat, vacuum, and forced convection were evaluated as development techniques in determining the resist sensitivity, contrast, and resolution. Forced convection of heated nitrogen was the most controllable development method for pPHA films. Five-micron lines and spaces were printed. Poly(aldehyde) copolymer resins had slightly lower spatial resolution but were able to be developed faster due to higher vapor pressure of the depolymerized monomers. Cold photo-exposures and development were used to prevent detrimental liquid formation of the decomposed copolymers. In addition to exploring new dry-development methods that have not been tested before, these findings offer insights into designing better material systems and optimizing processes for dry-develop photoresists.
Introduction New patterning processes and materials for integrated circuits, microfluidics, and photonic structures have generated increasing interest, especially in regard to rapidly reducing the amount of consumable materials used. Photolithography uses electromagnetic radiation to transfer a latent image from a reticle into a photosensitive polymer mixture, photoresist [1, 2, 3]. Photoresist mixtures consist of an inert polymeric resin with photoactive compounds (PACs) capable of undergoing a photo-induced solubility switch in a developer, so that a portion of the resin can be selectively removed to produce a surface relief feature. Contrast, spatial resolution and line-edge roughness are important metrics for the developed patterns. Traditionally, developing the latent image occurs through dissolution in an aqueous or organic solvent, with added costs from safe handling and disposal of solvents and waste. An alternative to solvent-based photoresist development uses only post-exposure soft-baking to dry develop the latent image through vaporization of the exposed image in the case of positive-tone, dry-develop resist. Dry-development methods
require fewer processing steps and chemicals because the liquid develop step is eliminated. Dry-develop photoresist
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