157 nm Resist Materials: A Progress Report.

Abstract

The goal or this work has been to study candidate fluorocarbon materials that might serve as platforms from which to design 157nm resists. A specific goal of the work has been to identify transparent candidate materials that might provide a polymer backbone and acceptable etch resistance. Several model compounds were synthesized and their vacuum UV spectra were measured in the gas phase.Substituted norbornane (bicyclo[2.2.1]heptane) was of significant interest in this regard because we had used this structure successfully in the design systems for 193nm exposure. Surprisingly, 2-monofluoronorbornane is unstable and undergoes spontaneous dehydrohalogenation upon exposure to glass in vacuo. However, 2,2-substitution with fluorine and with other electron withdrawing groups such as trifluoromethyl and even carbonyl groups gives norbornyl derivatives with greatly improved transparency at 157nm. These observations led to the design a variety of novel norbornenes that can be polymerized by metal catalyzed addition polymerization to give etch resistant polymer platforms with greatly improved transparency at 157nm and led to the study of acrylic co-polymers derived from 2-(trifluoromethyl)acrylic acid.

DFT Calculations of Photoabsorption Spectra in the VUV Region for Design of Photoresist Materials for 157 nm Lithography.

“…Crawford et al have reported that a copolymer of tetrafluoroethylene and norbornene shows a low absorbance (1.3 µm-1) at 157 nm for a 1:1 ratio [2]. Significant efforts have been devoted to developing resist materials, such as polymers based on fluorinated methylmethacrylate [3] and alicyclic [4] and styrenic [5] monomers substituted with hexafluoroisopropanol.…”

Novel Fluoropolymers for Use in 157nm Lithography.

“…Thus, the use of NBHFA monomer in preparation of 157 nm polymers by radical initiation has been met with a challenge. Alternatively, transition-metal-initiated addition polymerization can be employed to prepare polynorbornenes and in fact tBOC-protected NBHFA has been polymerized by Willson et al with a Ni initiator [11]. PNBHFA thus prepared has a significantly lower 157 mn absorption (OD=2.2-1.67/µm) than P(NBHFA-SOZ) (3.…”

Modified Acetal Approach to 157nm Resist Design.

“…Sci. Technol., Vol.15, No.4, 2002 fluorination of the polymer backbone [6,7,[9][10][11][12]. Recent spectroscopic studies [13] on the effect of the hexafluoroisopropanol (UFIP) group on the absorbance of polystyrene, for example, have shown that the absorbance of polystyrene is reduced from 6.6µm' to 3.44µm 1 for poly(4-HFIPstyrene).…”