Semiconductor manufacturing industry has reduced the size of wafer for enhanced productivity and performance, and Extreme Ultraviolet (EUV) light source is considered as a promising solution for downsizing. A series of EUV lithography procedures contain complex photo-chemical reaction on photoresist, and it causes technical difficulties on constructing theoretical framework which facilitates rigorous investigation of underlying mechanism. Thus, we formulated finite difference method (FDM) model of post exposure bake (PEB) process on positive chemically amplified resist (CAR), and it involved acid diffusion coupled-deprotection reaction. The model is based on Fick’s second law and first-order chemical reaction rate law for diffusion and deprotection, respectively. Two kinetic parameters, diffusion coefficient of acid and rate constant of deprotection, which were obtained by experiment and atomic scale simulation were applied to the model. As a result, we obtained time evolutional protecting ratio of each functional group in resist monomer which can be used to predict resulting polymer morphology after overall chemical reactions. This achievement will be the cornerstone of multiscale modeling which provides fundamental understanding on important factors for EUV performance and rational design of the next-generation photoresist.
For decades, downsizing has been a key issue for high performance and low cost of semiconductor, and extreme ultraviolet lithography is one of the promising candidates to achieve the goal. As a predominant process in extreme ultraviolet lithography on determining resolution and sensitivity, post exposure bake has been mainly studied by experimental groups, but development of its photoresist is at the breaking point because of the lack of unveiled mechanism during the process. Herein, we provide theoretical approach to investigate underlying mechanism on the post exposure bake process in chemically amplified resist, and it covers three important reactions during the process: acid generation by photo-acid generator dissociation, acid diffusion, and deprotection. Density functional theory calculation (quantum mechanical simulation) was conducted to quantitatively predict activation energy and probability of the chemical reactions, and they were applied to molecular dynamics simulation for constructing reliable computational model. Then, overall chemical reactions were simulated in the molecular dynamics unit cell, and final configuration of the photoresist was used to predict the line edge roughness. The presented multiscale model unifies the phenomena of both quantum and atomic scales during the post exposure bake process, and it will be helpful to understand critical factors affecting the performance of the resulting photoresist and design the next-generation material.
Masks used for sub-20 nm half pitch of devices are required to be defect-free as well as to have more
complicate and smaller patterns. For higher resolution for sub-20 nm device, the masks that can provide wider process
windows on wafers are made using new e-beam resists and new mask materials. An introduction of advanced mask
systems needs methodologies to overcome defect challenges that did not occur at previous mask systems. The defects
should be related with chemical and physical properties from negative and positive e-beam resists or/and new type
blanks used for advanced masks such as EUV or optical masks. As a mask pattern size is shrunken, the masks also have
complicate structures and different surface properties from low end mask systems. Defect removal on the masks is
important even at a develop process among mask manufacturing processes. This paper reports that advanced technology
applications on mask develop processes have been performed to remove defects on the masks. First, a new rinse system
has applied into a mask develop process for defect reduction. Second, a new develop process was also performed to
remove defects on masks. The new develop process combined with the new rinse system has reduced more than 50% of
defects including e-beam resist residue defects and other defects. This paper mainly focuses on defects related to
negative and positive resists on masks and their solutions to reduce or/and remove the defects, which are used for sub-20
nm half pitch of devices, in terms of mask develop process.