Copolymer fraction effect on the acid catalyzed reaction kinetics in model 193 nm photoresists

 

Shuhui Kang

Polymers Division, MSEL

100 Bureau Dr., Stop 8541

Bldg 224, Rm. A327

(301)-975 4602 (Phone)

(301) 975-3928 (Fax)

skang@nist.gov

 

Mentor: Vivek M. Prabhu

Sigma Xi Member:  No

Category:  Materials

 

            Photolithography is the critical process that enables the fabrication of sub-100 nm structures for integrated circuit manufacturing.  The basic imaging material, highly tuned formulations called chemically amplified photoresists, may quickly be approaching fundamental resolution limits due to intrinsic materials and processing physics and chemistry.  Current imaging technology is dependent on nanometer level control of the diffusion-reaction process of a UV sensitive photoacid generator in polymer-based photoresists containing acid-labile protection groups.  Many studies have focused on the physical-chemical properties of the photoacid such as the size and the acidity.  Few have investigated the effect of polymer photoresist polarity on the reaction kinetics.  In addition, the mechanisms regarding the photoacid diffusion-reaction are not consistent and even contrary to each other in various aspects like reaction order and acid loss factor. 

            In this study, we use a model 193 nm photolithography copolymer photoresist system which includes an acid-labile and a non-reactive monomer to investigate the dependence of the acid catalyzed kinetics on the copolymer composition, temperature, and UV exposure dose by Fourier transform infrared spectroscopy.  We find that the reaction rate significantly depends on the non-reactive comonomer content.  The molecular origin of this behavior is traced to the reduced photoacid diffusivity in the polymer matrix through hydrogen bonding with the polar group of the non-reactive comonomer groups.  The same hydrogen bonding also is present between the photoacid and reaction byproduct leading to a trapping effect.  This study clarifies several issues regarding the acid diffusion-reaction kinetics to provide guidelines for future resist design.