Challenges in Today's Photoresist for 32 nm Resolution and Beyond

Friday, May 23, 2008 - 4:00 p.m. to Saturday, May 24, 2008 - 4:55 p.m.

ChEMS Seminar

Featuring Wen-Li Wu, Sc.D.
Fellow, Polymers Division
National Institute of Standards and Technology


Location:  Donald Bren Hall, Room 1500


Abstract:
For the past two decades chemically amplified photoresist has been the workhorse in the lithographic process for semiconductor industry, however, very little work has been directed to measure the chemical composition and its fluctuations along the reaction-diffusion front and the dissolution front.  Such information is definitely needed for one to identify the origin of the resolution and LER limits facing today’s photoresists.  Only afterwards systematic approaches can then be devised to extend the use of chemically amplified photoresists to 32 nm node and beyond.


 Poly(methyladamantyl methacrylate) (PMAdMA) was used as the model material in this work.  We demonstrated the use of neutron reflectivity (NR) as a general method to quantify the evolution of the reaction-diffusion front with a nanometer resolution.  The compositional heterogeneity in terms of the extent of reaction along the buried reaction front was monitored using a combination of FTIR and NR.  Work is in progress to directly measure the spatial distribution of the compositional heterogeneity along the reaction front using off-specular NR.


 Dissolution is the final and the defining step of the feature quality in photoresist patterns; it is also one of the less studied areas in polymer physics.  For photoresists including PMAdMA their dissolution process invokes an ionization step, i.e. they dissolve as polyelectrolytes.  To complicate the matter further a gel layer was observed ahead of the dissolution front in PMAdMA even though its molecular weight was far below that of molecular entanglement.  A combination of NR, FTIR and quartz crystal micro-balance measurement has been applied to measure the swelling, the dissolution kinetics and the counterion distribution within the polyelectrolyte gel.  The results illustrate the complexity and many challenges ahead of us in pushing chemically amplified photoresists to 32 nm node and beyond.


About the Speaker:
Wen-Li Wu, Sc.D., is currently a National Institute of Standards and Technology Fellow in the Materials Science and Engineering Laboratory.  He received his Sc.D. degree from MIT in 1972, and was with the Monsanto Company from 1973 to 1979 before joining NIST.  Among his many honors and awards are:  the Department of Commerce Bronze, Silver, and Gold Medals; Fellow of the American Physical Society in 1992; and Fellow of the Polymer Materials Science and Engineering Division, American Chemical Society, 2007.  


Wu’s primary field of scientific expertise is the development of advanced x-ray/neutron scattering methods and their novel application to the investigation of the structure and properties of polymeric materials in thin films and at interfaces. His contributions to industry include the development of the x-ray and neutron-based characterization of the structure and properties of nanoporous thin films for future interlevel dielectrics, the introduction and demonstration of the viable use of small-angle x-ray scattering for critical dimension metrology for sub-50 nm structures, and an advanced suite of measurement tools to probe the fundamental resolution limits of photoresists for the fabrication of sub-100 nm features.  Wu has published over 167 papers in refereed journals and has been cited over 1800 times.  He has lectured widely, and holds four patents.