Supercritical CO₂ Processing for Submicron Imaging of Fluoropolymers

Abstract

To keep pace with the ever-shrinking feature sizes required in the microelectronics industry, suitable developers with high diffusivities, selectivity, and adjustable solvating power are required. Supercritical fluid (SCF) CO2 possesses many of the above unique properties and could serve as an “environmentally responsible” alternative developer to aqueous base. In this study, the high solubility of fluorinated block copolymers in supercritical CO2 and the selectivity of supercritical CO2 to both polarity changes and the molecular structure of the polymer were utilized to develop an environmentally friendly lithographic process. Polymers with acid-cleavable tetrahydropyranyl groups and supercritical CO2 soluble, fluoro-side-chain-containing methacrylate groups were synthesized with varying volume fractions of the components, and their solubilities in supercritical CO2 were characterized. Chemical amplification was used to effect the polarity change leading to the solubility difference in supercritical CO2, and the lithographic performance was evaluated. Important parameters such as sensitivity, contrast, and resolution were investigated, and 0.2 μm features using supercritical CO2 development were demonstrated.

Hydrofluoroethers as Orthogonal Solvents for the Chemical Processing of Organic Electronic Materials

“…This new dimension in solvent orthogonality which is enabled by the use of HFEs offers unique opportunities for the chemical processing of organic electronic materials. One example is in the area of photolithographic processing: One can use a photoresist that is properly fluorinated to be processable in HFEs [15] (similar photoresists have been developed for processing using supercritical CO 2 [16] composed of a tert-butoxycarbonyl (t-Boc) protected resorcinarene [17] and a photoacid generator (PAG) by a lift-off technique (see Fig. 2).…”

High‐Resolution Patterning of Molecular Glasses Using Supercritical Carbon Dioxide

“…Also, due to their persistent nature, fluorinated compounds are coming under increased scrutiny [5] and their use needs to be phased out. Finally, although scCO 2 -soluble polymeric resists based on fluoropolymer platforms have been studied in recent years, [6,7] no features smaller than 100 nm have been demonstrated. Regardless of exposure method, these materials have not shown sufficient contrast for higher resolutions.…”

Positive- and Negative-Tone CVD Polyacrylic Electron-Beam Resists Developable by Supercritical CO2

“…[1][2][3] scCO 2 is envisioned as an "environmentally responsible" solvent and is widely used in the food and pharmaceutical industries. [4] scCO 2 also has unique properties beneficial for the development of dense, high-aspect-ratio, sub-micrometer features: high diffusivity, high density, low viscosity, and the absence of surface tension, which prevents pattern collapse.…”

“…Acrylic fluoropolymers, which contain a lipophilic acrylate backbone and a CO 2 -philic, fluorinated side chain, are soluble in scCO 2 . [16] Copolymers with an irradiation-sensitive hydrocarbon moiety and a second fluorinated segment have been synthesized and investigated using scCO 2 .…”

“…[16] Copolymers with an irradiation-sensitive hydrocarbon moiety and a second fluorinated segment have been synthesized and investigated using scCO 2 . [2,3] Block copolymers with >60 vol.-% fluorocomponent have been developed in scCO 2 at pressures >4000 psi (1 psi = 6.894 × 10 3 Pa) and temperatures >40°C. Negative-tone features of 200 nm and positive-tone features of 400 nm were resolved.…”