Leonard Edward Bogan

Deep UV ANR Photoresists For 248 nm Excimer Laser Photolithography

This paper describes the development of deep UV resist materials based on chemically amplified crosslinking systems for use in excimer laser photolithography at the KrF lasing wavelength of 248 nm. This work will describe the use of a transparent resin, polyp-vinyl)phenol, which has excellent plasma etch resistance and demonstrates high resolution (sub half-micron line-space pairs for a 1.0 micron thick film) when used in an Advanced Negative Resist (ANR) formulation, XP-8843. Under 140C post-exposure bake conditions, XP-8843 exhibits fast photospeed (15 mJ/cm2), high contrast (4.1), vertical sidewalls, and good process latitude.

Optimization of the absorbance of novolak resin films at 248 nm

It is generally accepted that a 1 jim thick resist film should have an absorbance of no more than 0.25 absorbance unit at the exposure wavelength to enable formation of high-resolution images with vertical wall profiles. Conventional materials are ill-suited for use with KrF excimer laser exposure as the primary component (ca. 80% w/w) of conventional photoresist formulations is novolak resin with absorbance □ 0.6 a.u.flim at 248 nm. This paper describes the optimization of novolak resin composition to give films with minimal absorbance at 248 nm. The deep-UV (248 nm) absorbance of dilute solutions of substituted phenols has been measured and found to follow a welldefmed and predictable pattern. Use of this information to model the absorbance of novolak resin solutions is complicated by the effects of polymer secondary structure on UV absorbance. The absorbance of novolak homopolymer solutions has been studied in four solvents and found to be dependent on polymer composition, secondary structure, molecular weight, and solvent. In order to observe the effects of composition independent of secondary structure, highly branched novolak oligomers were prepared by condensation of commercially available phenols with 2,4,6-tris(dimethylaminomethyl)phenol (Rohm and Haas DMP3O). The optical densities of films of these structurally uniform oligomers were compared. The most transparent copolymers had optical densities which were essentially the same as that of a m -cresol novolak homopolymer, ca. 0.35 absorbance units/Rm.

Understanding the novolak synthesis reaction

A major objective in the advancement of electronics technology is the miniaturization of integrated circuits. The limiting factor in this miniaturization is and has been imaging technology, or microlithography. Advances in microlithography will come from better optics, which are designed by engineers, and better photoresists, which are designed by chemists.