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

Abstract

Resist layers sensitive to electron-beam (e-beam) exposure and developable in supercritical carbon dioxide (scCO 2 ) can be synthesized by initiated CVD (iCVD), resulting in an all-dry lithographic process. The low energy and low temperatures of the iCVD method permit the retention of the irradiation-sensitive pendent organic functional groups, and the incorporation of the fluorinated acrylates needed for increased solubility in scCO 2 . Negative-tone contrast is realized through crosslinking of the epoxy group of glycidyl methacrylate (GMA) when copolymerized with 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl acrylate (DFHA). The Fineman-Ross equation describes the systematic tuning and random nature of the composition of these iCVD films. Positive-tone contrast with non-swelling 300 nm features was achieved through the anhydride-stabilized chainscission reactions in post-annealed iCVD copolymers of methacrylic acid (MAA) and perfluoroalkyl ethyl methacrylate (PFEMA). The CF 3 end groups in PFEMA contribute to higher scCO 2 solubility than DFHA, allowing development of PFEMA copolymers with lower content of fluorine-containing component at milder condition than DFHA copolymers.

Chemical Vapor Deposition of Conformal, Functional, and Responsive Polymer Films

“…Alternatively, a Type II photoinitiator that creates free‐radical sites on the substrate surface, such as benzophenone, can be used to graft the polymer to the substrate 233, 290. Successful free‐radical polymerization and copolymeriza‐ tion by iCVD has been reported for a wide range of monomers,1 including acrylates,6, 86, 180, 198, 233, 273, 285, 287, 291–294 methacrylates,5, 6, 59, 81, 85, 107, 109, 177, 180, 181, 198, 199, 247, 263, 287–300 styrenics,108, 233, 273, 286, 301, 302 1‐vinyl‐2‐pyrrolidone,188 maleic anhydride,108, 286 and 1,3,5‐trivinyltrimethylcyclotrisiloxane 180, 303–305…”

Vapor Deposition of Fluoropolymer Surfaces

“…Antifouling [54,55], biomaterials [56] Methacrylic acid (MMA) Fuel cells [57] Divinylbenzene (DVB) Photonics [58] Glycidyl methacrylate (GMA) Mechanical properties [59], patterning [60] Hexamethylcyclotrisiloxane (D 3 )…”

“…Furthermore, the cross-linking fixed a high concentration of fluorine groups on the outermost layer of the films showing a surface energy lower than PTFE [59]. In a parallel study, these two monomers, DHFA and PFEMA, were copolymerized with GMA and methacrylic acid (MAA) to develop negative and positive electron beam resists developable by supercritical CO 2 (scCO 2 ) obtaining patterns with features sizes of 300 nm [60].…”

Fluorine‐ and siloxane‐containing polymers for supercritical carbon dioxide lithography

“…Initiated CVD (iCVD) can facilitate reactions under mild processing conditions by thermal decomposition of an initiator and subsequent addition reaction of monomers 13. Using a combination of iCVD and scCO 2 development, negative‐tone patterning was realized by crosslinking the epoxy groups of glycidyl methacrylate when copolymerizing with scCO 2 ‐soluble 2,2,3,3,4,4,5,5,6,6,7,7‐dodecafluoroheptyl acrylate, while positive‐tone patterning with 300 nm resolution was achieved through anhydride‐stabilized chain‐scission reactions in post‐annealed copolymers of methacrylic acid and perfluoroalkylethyl methacrylate 14…”