Karen A. Graziano

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.

Novel acid-hardening positive photoresist technology

A newly developed positive photoresist technology which produces a crosslinked image is described. This resist has demonstrated high sensitivity and resolution for e-beam and X-ray applications. The resist uses conventional novolak polymers and melamine crosslinking agents with thermal acid generators to achieve acid-catalyzed crosslinking in the unexposed areas of the resist. An amine base is photochemically generated in the exposed areas which inhibits the crosslinking reaction. The exposed area remains soluble in conventional aqueous base developers. Chemistry of the thermal acid generators as well as examples of the photobase generators is discussed. Lithographic results focus on e-beam and X-ray synchrotron applications in which the crosslinked positive image has high contrast and high resolution.

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.

Chemically amplified resists for x-ray and e-beam lithography

The development of both negative and positive resists with high sensitivity and high resolution capability is critical to the production of devices using x-ray exposure technology. This paper describes a class of aqueous developable acid hardened negative and positive resists which produce crosslinked images under x-ray exposure and subsequent processing steps. The resists are chemically amplified for high sensitivity. Linewidths down to 0.1 micron have been printed with a negative resist using e-beam exposure, and 0.4 micron mask-limited featurers have been printed with an x-ray dose of > 60 mJ/cm2. The feasibility of a high resolution positive acid hardened resist has been demonstrated and remains to be optimized.

Study of aging effects in a chemical amplification resist: SAL601‐ER7

The shelf life and film life of the electron beam resist, Microposit SAL601‐ER7 from Shipley, were studied. Solutions and films of this resist were found to exhibit a performance degradation which is a function of the storage time and temperature. Refrigeration significantly improves the stability of the resist. Component studies were used to determine that the shelf life problem is due to an interaction between the novolak resin and melamine crosslinker. Results indicate that considerable stability can be realized by using less reactive crosslinkers in the resist formulation.

Process latitude measurements on chemically amplified resists exposed to synchrotron radiation

Several chemically-amplified resists, positive and negative, have been evaluated for synchrotron x-ray lithography. Some have shown sensitivities as low as 10.1 mJ/cm2. Linewidths of 0.3 micron have been achieved in 1 micron thick single-layer resist with vertical sidewalls and good process latitude, at an x-ray dose of below 50 mJ/cm2. The chemically amplified resists are processed similarly to conventional resists using metal ion free aqueous base developers. Data re presented for resists from Shipley, Rohm and Haas, and Hoechst AG. Lithographic exposures were performed with the University of Wisconsins Aladdin synchrotron, using the ES-1 beamline of the Center for X-ray Lithography.