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Surface Effects in Chemically Amplified Photoresists:

Environmental Stability and Segregation

Erin L. Jablonski1,, Vivek M. Prabhu1, Sharadha Sambasivan1, Daniel A. Fischer2, Eric K. Lin1,

Dario L. Goldfarb3, Marie Angelopoulos3, and Hiroshi Ito4

1Polymers and 2Ceramics Divisions, National Institute of Standards and Technology

Gaithersburg, MD 20899

3IBM T. J. Watson Research Center, Yorktown Heights, NY 10598

4IBM Almaden Research Center, San Jose, CA 95120

It is well known that chemically amplified photoresists are sensitive to certain airborne molecular contaminants, notably amines, during post exposure delay, although the actual cause and specific failure mechanism are unknown. To assess the effect of low concentrations of atmospheric species on the performance of chemically amplified photoresists, an environmentally controlled system has been developed that allows fine tuning of processing conditions coupled with immediate surface and bulk characterization using near edge x-ray absorption fine structure spectroscopy (NEXAFS). In order to quantify component segregation and identify surface phenomena that may be responsible for pattern degradation, the surface and bulk chemistry of model photoresists were analyzed using NEXAFS equipped with in situ processing capabilities for exposure, controlled dosing of a model contaminant gas, and heating. It has been found that the photo-acid generator (PAG) segregates to the surface of the photoresist film; as film thickness becomes progressively thinner and the chemistry of the photoresists changes as more fluorinated components are incorporated, the behavior of this PAG-rich, high fluorine content surface layer may introduce additional/unique sensitivity to airborne contaminants and failure mechanisms compared to previous photoresist materials. This technique is therefore valuable to elucidate the influence of atmospheric contaminants in next generation chemically amplified photoresists, particularly with the move toward new chemistries and thinner films, which have been shown to be more environmentally unstable compared to past materials. In addition, use of photoresist blend formulations at the 157 nm node presents a number of materials issues, including polymer/substrate and polymer/air interfacial (surface energy) effects, blend miscibility, and small molecule diffusion in thin films. NEXAFS has been used to probe the surface and bulk chemistry of these chemically amplified photoresists to determine possible causes of pattern degradation, including polymer component and small molecule diffusion/segregation to the photoresist surface and interactions between components of the photoresist formulation and developer. We find significant segregation of one blend component to the polymer film surface and discuss implications for the performance of thin film blend photoresists.

*Erin L. Jablonski, Division 854, MSEL, Room B312, Building 224, Mail Stop 8541, Telephone (301) 975-4769, Fax (301) 975-3928, email: erin.jablonski@nist.gov, not a Sigma Xi member.
This abstract is in the area of Materials.