Fundamentals of the Reaction-Diffusion Process in Chemically Amplified Photoresists

 

Author:  Kristopher A. Lavery

Mentors:  Vivek M. Prabhu, Eric K. Lin

 

Polymers Division, MSEL

Building 224, Room A227, MS8541

 

Office: (301) 975-6736

Fax: (301) 975-3928

Email: klavery@nist.gov

 

Sigma Xi member?: No

Category: Materials

                   

 

More demanding requirements are being made of photoresist materials for the fabrication of nanostructures with increasingly small feature critical dimension (CD).  For next generation polymeric photoresists, targeted for use in extreme ultraviolet (EUV) lithography, line width roughness (LWR) control and heightened resist sensitivity are key requirements for success.  The observed LWR and CD values result from many factors in interdependent processing steps.  One of these factors is the deprotection interface formed during the post-exposure bake (PEB) step.  We use model EUV photoresist materials to systematically address the influence of exposure-dose on the resulting surface roughness.  We report the spatial evolution of the deprotection reaction using a bilayer geometry to represent the line-edge as a function of dose for fixed PEB time using neutron reflectivity.  The resulting deprotection profile is also compared with the integrated deprotection level obtained from Fourier transform infrared (FTIR) spectroscopy.  The bilayer consists of an acid feeder layer containing photoacid generator (PAG), whereas the bottom layer is a model EUV photoresist, poly(hydroxystyrene-co-tert-butylacrylate)with perdeuterated t-butyl moieties.  The deuterium labeling allows the deprotection profile to be measured with nanometer resolution.  The evolution of the compositional profile with exposure dose will be discussed, as well as the potential role in limiting the ultimate feature line roughness.