Stanley A. Ficner

Development of two new thick-film photoresists

This paper describes the development of two advanced new thick film photoresists. Statistical experimental design was used to investigate the performance characteristics of a select group of novolak resins and diazonaphthoquinone photoactive compounds. After these initial formulation experiments, evaluations of the best candidate were carried out on an Ultratech stepper using current production photoresists as a benchmark. The main evaluation criteria were used as outputs of the designed experiment (resolution, side-wall profile, t-topping, and photosensitivity) and then correlated with resin characteristics and relative photosensitizer concentration. The results of these studies led to the development of two formulations for specific photoresist thicknesses: EXP AZR 9147 photoresist for 5 micrometer and EXP AZR 9262 photoresist of 24 micrometer. These final formulations show improvements in all evaluated performance fields versus the current production benchmarks.

Novel DNQ PACs for high-resolution i-line lithography

The use of i-line lithography for the 16 to 64 Mbit DRAM device generations calls for increased performance of i-line resists. This paper reports on investigations on novel sensitizers for advanced i-line lithography, starting out with a discussion of general design criteria, then discussing methodology and results of a screening phase, and examining in greater detail a small number of selected candidates for which resolution, exposure latitude, and depth-of-focus data were obtained. Finally, a new advanced resist for i-line lithography, AZR 7500, is presented, and its performance is evaluated in terms of the above criteria as well as thermal flow resistance.

Refractive indices in thick photoresist films as a function of bake conditions and film exposure

Prism coupling is applied to thick film DNQ/novolak photoresist materials in the 4.6 to 24 micrometer range. Refractive indices are obtained as a function of softbake temperature and softbake time for exposed and unexposed resists. The results for AZR P4330 RS and AZR EXP 9244 photoresists are compared at a film thickness of 4.6 micrometer. Each photoresist shows an increase in refractive index at 633 nm with softbake temperature and softbake time and a decrease in refractive index with an increase in exposure. The refractive index changes of the films are correlated to the solvent content as determined by radioactive labeling and by gas chromatography. In thicker films, solvent gradients profiles could be obtained by the application of an inverse WKB approximation to the effective indices. The lithographic performance of AZREXP 9244, a new generation thick film photoresist, is examined at various softbake temperatures and softbake times and interpreted in terms solvent content as obtained from the refractive index.

Identification of diazonaphthoquinone esters of polyhydroxybenzophenone compounds

The seven possible 2,1-diazonaphthoquinone-5-sulfonates of 2,3,4- trihydroxybenzophenone have been isolated and characterized by IR, chromatographic and advanced NMR techniques. HPLC procedures for their analysis are given which show counterintuitive effects in the HPLC elution sequence due to the effect of intramolecular H-bonding on the polarity of some esters. A reaction scheme is proposed which qualitatively identifies preferred pathways to the trisester.

Synthesis and lithographic performance of highly branched polymers from hydroxyphenylmethylcarbinols

A new synthesis pathway for 4- and 2-hydroxymethylcarbinol (4- and 2-HPMC) has made a new class of highly branched polymers readily available. The polymers, which are isomers of polyhydroxystyrene, show unexpected dissolution behavior in aqueous bases which differs from the solubility characteristics seen for the linear polymers obtained by free-radical polymerization. This behavior is traced back to the influence of the changing bond types in the co-polymerization series on the kinetic parameters. With respect to lithography, the absorption of the polymers is too high to make them attractive as DUV resist materials. Although their bond structure shows all bond types that also exist in novolaks, the HPMC polymers are found to be more PHS-like than novolak-like in their performance with DNQ sensitizers. However, they are compatible with DNQ/novolak resists, and can be used in resin blends with novolaks without phase separation.

Advanced photoresist for high-throughput i-line stepper applications

The use of i-line photolithography is finding increased importance in generating todays advanced semiconductor devices. The requirements in this area have led to the recent development of wide field i-line steppers whose large field sizes permit higher device throughput. The introductions of these wide field i-line steppers generate additional demands on the photoresist used in the manufacturing process. This paper describes the development of an advanced i-line photoresist for use in high-throughput applications. The requirements of this photoresist are high photospeed of the order of 75 mJ/cm2 to achieve targeted throughput requirements at low lamp power densities, high resolution of approximately 0.80 micrometers at NA equals 0.24 to satisfy device critical dimension requirements, and high resistance to thermal flow to permit further processing stages. The photoresists formulation and processing were optimized to produce the desired performance characteristics. Exposure, focus latitude, photosensitivity, and resistance to thermal flow were determined and correlated with resin dissolution characteristics, relative photosensitizer concentration, softbake and post exposure bake temperatures.

Statistical experimental design on the optimization of high-performance photoresist

The ultimate photolithographic performance of a photoresist is essentially determined by the nature and relative concentration of the chemical components in the formulation and the process conditions selected. To meet the stringent performance requirements demanded by the advanced microlithography technology, each individual constituent of the photoresist process described must be optimized simultaneously. This study presents an effective and time saving approach using experimental design techniques to address the complicated multi-variable of resist formulation and process condition optimization. The responses for the design experiment in terms of lithographic performance were: exposure and focus latitude, photosensitivity and resist pattern thermal flow temperature are correlated with the resin dissolution characteristics, relative photosensitizer concentration, pre- and postexposure bake temperatures and development time.